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Case Studies: Substitute Decision Making

An 86-year-old female patient admitted to hospital due to an increasing inability to cope at home and recent fall in which she suffered a broken hip. She has previously been diagnosed with COPD, hypertension and increasing cognitive deficits.  While in recovery in hospital, an abdominal mass has been found (malignancy suspected but not confirmed), she has had a decrease in her ability to care for herself, difficulty swallowing with increasing aspiration risk, early stages of renal failure and an exacerbation of her cognitive issues.  The patient does not have a formal Advance Directive nor has she assigned a Power of Attorney.  She has three daughters and one son who is a cardiologist and lives out of the province.  The daughters have demanded that the patient be a full code, requested that transfer be made to ICU with a PEG tube placed and dialysis started should it be required.  The son phoned you over the weekend and stated that given his mothers age and complex medical situation he expects that she would be provided symptom management and comfort care but that no aggressive measures should be undertaken to interfere with the natural decline and progression of his mother’s diseases.  He has requested regular updates regarding her status and any interventions or treatments proposed.

What are some of the ethical issues in this case?

• Does ‘increasing cognitive defects’ = lack of capacity?
• Are any ethical principles in conflict? Autonomy? Beneficence? Nonmaleficence?
• Can an SDM demand treatment?
• Who is responsible for proposing a plan of care?

Mr. Parker is an 88-year-old resident of your LTC home with end-stage Alzheimer’s. He is wheelchair bound and spends most of his days sleeping in his wheelchair near a window facing the garden. He needs to be spoon fed but has recently started to refuse to eat. Mr. Parker has three children, one of whom is very involved in the care of her father. The team approaches the daughter about her father refusing to eat, and feels that his refusal is legitimate. Thus, they propose changing the plan of care to palliation. The daughter absolutely refuses, claiming that “you cannot kill my father, I want everything done to keep him living!”

• Do we know whether the resident is capable to make his own health care decisions?
• Are there any known wishes from Mr. Parker? What would he want? What are his values?
• Is his daughter the substitute decision-maker? Can she, in this role, demand treatment and expect that you comply?

Mrs. Beaudoin, who is 97 years old, was admitted to your LTC facility 6 years ago. Shortly after becoming a resident, she suffered a cardiac arrest and was found to be unresponsive by the staff; CPR was initiated for a total of 20 minutes prior to return of spontaneous circulation. She has an advanced directive stating that she agrees to “transfer to an acute care facility”, but other options, such as CPR and intubation, were not explicitly addressed in this document.  She has no formal Power of Attorney.

Initially, Mrs. Beaudoin had lived at your facility watching TV for most of the day. She was wheelchair bound and required assistance with most activities of daily living (ADLs).  Her husband lives at your facility with her and is quite frail with moderate dementia.  Beaudoin is frequently visited by her large extended family, which comprises 4 children and 5 grandchildren.  She is known to have cancer throughout much of her body, moderate dementia, a very bad heart, and type-2 diabetes.

After her cardiac arrest and a short stay in the Hospital ICU, Mrs. Beaudoin is brought back to your facility able to breathe on her own, but with a moderate -severe brain injury caused by lack of oxygen after her cardiac arrest; this has left her unable to communicate in any meaningful way with others. She is receiving thickened fluids as her source of nutrition and hydration, but is only able to consume about half of the calories that would be needed to keep her at her current weight. Unfortunately her health begins to decline further shortly after returning.

The team decides to hold a family conference with the resident’s children, and proposes a plan of treatment that would focus on comfort care only, excluding CPR if needed again. The patient’s eldest daughter does not agree and states that her mother is “a fighter” and wanted to live to be 100 years old so that she could receive a letter from the Queen.  The daughter asks that her mother be transferred back to the acute care hospital to receive the care of “experts” and so that she could be seen by a surgeon for surgery and chemotherapy for her cancer.

The treating physician discusses the case with the intensivist on call at the hospital over the telephone. The intensivist agrees that the prognosis is extremely poor and likely the resident would not benefit from further invasive treatment. The intensivist at TOH holds a family conference with the family and team at the LTC home over the telephone.  He identifies himself as an expert in the field.  The older daughter, reiterates their requests to the intensivist.

• Who is the appropriate substitute decision-maker (SDM) in this case?
• If there is more than one SDM, what should you do if they disagree?
• Because we know Mrs. Beaudoin’s desire to live to be 100, must we ensure that “everything is done” in an attempt to prolong her life?

Mrs. Potter is a 93-year-old resident of your long-term care home who once traveled the world as a culinary expert, sharing her love of food with many. She now has end-stage Alzheimer’s. In the last year it has worsened to the point that she is no longer capable of making her own medical decisions, and she has begun to experience difficulty swallowing solid foods. Three months ago a daughter of Mrs. Potter, her Power of Attorney, consented to have her mother be provided a pureed diet in order to reduce the risk of choking. At present time, however, this daughter believes that the pureed diet is affecting the quality of her mother’s life (even though Mrs. Potter has not expressed this herself). After being completely informed of the risks and benefits, she requests that her mother be given solid foods. The staff feel uncomfortable with the daughter’s request due to the real possibility that Mrs. Potter will choke on solid foods, and are unsure of what to do.

• Does a resident have the right to live at risk?
• Does a substitute decision-maker (SDM) have the right to consent to their loved one living at risk? Does it matter if this is what their loved one would have wanted?
• What mechanisms can be implemented to address the potential moral distress of staff?

Mrs. Green, a 75-year-old patient with renal failure, currently on dialysis, who also has COPD, moderate dementia, diabetes and a new diagnosis of stage one breast cancer. There is also a past history of depression according to the family. She has been admitted to your ICU after falling down her stairs at home and is in critical condition with multiple fractures to her hip, ribs, wrists and neck. Mrs. Green does not have the capacity to make her own medical decisions and has recently started to refuse eating. Upon discussion with GI Specialists, the team agrees that the patient is not an appropriate candidate for a PEG (feeding) tube. The patient’s daughter, who is her POA, insists that the you proceed with the placement of the PEG, stating that if the tube is not placed she will contact her lawyer and proceed with legal action against the physician and hospital.

• Do we know the patient’s wishes, or values?
• Will the fact that the team feels the patient is not medically appropriate (considering risks, benefits, and likelihood of success) for a PEG tube be the deciding factor? That is, can the daughter demand the PEG tube and expect that the team provides it?

Wilson, a 51 y.o. male patient, is admitted to the Intensive Care Unit in critical condition after a motor vehicle accident. He presented unconscious and is therefore unable to make his own medical decisions. The family of this patient provided a detailed formal advance directive which indicated that in the event of a traumatic injury such as this one, where the outcome is uncertain, the patient would consent to aggressive medical intervention in an attempt to stabilize and determine the severity of his injury. Life-sustaining interventions were therefore pursued.

After a myriad of test and a set of neurologic assessments were performed, it was determined that an anoxic brain injury occurred and it was not clear whether the patient would ever regain consciousness. The team needed some time to clearly establish a diagnosis, and the family members were kept informed of any progress that was made.

Several weeks passed as the patient stabilized, and the health care team was finally confident that the patient had met the criteria for being in a Persistent Vegetative State, a diagnosis that was presented to the family. According to the advance directive, if the patient were ever in a situation where their continued existence would be in such a state, he would want all life-sustaining intervention withdrawn, and be allowed to die. The family (spouse is no longer in the picture, 18 y.o. daughter, 20 y.o daughter, and 14 y.o. son) are presented with this formal diagnosis of PVS and are willing to continue to assume the responsibility of SDMs. The 14 y.o. son is adamant that his father is a ‘fighter’ and demands the team continue to ‘do everything possible’, and provide the most aggressive care they can. The 18 y.o. daughter agrees with the son, but the 20 y.o. daughter wants to respect her father’s wishes and refuse further life-sustaining measures.

• Who is(are) the designated SDM(s)?
• Who do we listen to when they disagree?
• Can the SDM(s) consent to a decision that would mean the death of the patient?

A 75-year-old healthy male was working on the roof of his house when he slipped and fell 10 ft. to the ground. He was knocked unconscious. When the paramedics arrived he was awake but confused. His vital signs were stable (e.g., Glasgow Coma Scale [GCS] score of 14). He was immobilized with a C-collar and backboard and taken to the ED. Shortly after arrival in the ED he became more confused, then sleepy. His GCS score decreased from 14 to 10. The attending emergency physician was concerned that perhaps the patient had a significant head injury and was in the process of arranging for a CT scan when the patient’s wife arrived. The patient’s condition continued to deteriorate, to a GCS score of 8. The emergency physician prepared to intubate him, but when she discussed this with the patient’s wife, the wife became upset and stated that her husband had a “living will,” which specifies that, if he became critically ill, he would not want any resuscitative interventions, including intubation.

*From: Pauls, M. et al. (2002). Ethics in the Trenches: preparing for ethical challenges in the emergency department. CJEM, 4:1, Pg. 45.

• Was the patient adequately informed when they declared their wishes? Did they put these wishes into a particular context? That is, were they intended for reversible, or irreversible illness?
• Is the patient’s wife required to make a decision in the best interests of the patient? Who decides what is ‘best’?

A 90 year old female, Mrs. Ruth, from home with her daughter, is admitted to hospital after sustaining a hip fracture. She has a history of chronic obstructive pulmonary disease on home oxygen and moderate to severe aortic stenosis.  (Obstruction of blood flow through part of the heart) She undergoes urgent hemiarthroplasty (hip surgery) with an uneventful operative course.

The patient and her family are of Jewish background. The patient’s daughter is her primary caregiver and has financial power-of-attorney, but it is not known whether she has formal power of attorney for personal care.  Concerns have been raised to the ICU team about the possibility of elder abuse in the home by the patient’s daughter.

Unfortunately, on postoperative day 4, the patient develops delirium with respiratory failure secondary to hospital acquired pneumonia and pulmonary edema. (Fluid in the lungs) Her goals of care were not assessed pre-operatively.  She is admitted to the ICU for non-invasive positive pressure ventilation for 48 hours, and then deteriorates and is intubated. After 48 hours of ventilation, it was determined that due to the severity of her underlying cardio-pulmonary status (COPD and aortic stenosis), ventilator weaning would be difficult and further ventilation would be futile.

The patient’s daughter is insistent on continuing all forms of life support, including mechanical ventilation and even extracorporeal membranous oxygenation (does the work of the lungs) if indicated. However, the Mrs Ruth’s delirium clears within the next 24 hours of intubation, and she is now competent, although still mechanically ventilated. She communicated to the ICU team that she preferred 1-way extubation (removal of the ventilator) and comfort care.  This was communicated in writing to the ICU team, and was consistent over time with other care providers.  The patient went as far to demand the extubation over the next hour, which was felt to be reasonable by the ICU team.

The patient’s daughter was informed of this decision, and stated that she could not come to the hospital for 2 hours, and in the meantime, that the patient must remain intubated.

At this point, the ICU team concurred with the patient’s wishes, and extubated her before her daughter was able to come to the hospital.

The daughter was angry at the team’s decision, and requested that the patient be re-intubated if she deteriorated. When the daughter arrived at the hospital, the patient and daughter were able to converse, and the patient then agreed to re-intubation if she deteriorated.

• Who should make decisions in this situation? Should the ICU team have extubated the patient?
• Do religious beliefs constitute a justification for demanding treatment when it is not indicated?
• Does the change in the patient’s decision mean that she lacked the capacity to make the decision in the first place, or that she was not well informed?

A 30-year-old female who is 37 weeks pregnant is admitted under a “Form 3” to inpatient psychiatry for acute psychosis, severe substance abuse, and uttering death threats about her unborn child. (A Form 3 allows the patient to be held for up to two weeks.) After being re-assessed by Psychiatry, progress notes indicate that the patient is “legally competent”. Some of the nursing staff have voiced that they disagree and that she is not always capable of making informed consent decisions related to herself and/or her fetus.

Several days into her admission, the patient begins to experience mild contractions. The staff have many questions: What is the birthing plan? Can patient consent to one? How will patient rights be protected? How will the OB GYN and Nursing Staff be protected? How will the baby be protected?

OBGYN states she wants patient to consent to caesarian section (C/S), as it is felt this is safest for the patient, the unborn baby, and the staff involved.

At a visit on day 4 of admission, Social Work feels that the patient now wants to protect her unborn baby from harm. In addition, they believe that it would be a great time to have an open conversation about plan of care with the patient. The OBGYN and SW visited the patient to ensure she was able to understand, and the OBGYN determined at this time that the patient was capable to provide consent. The patient decided to sign for caesarian section, if necessary.

At this point, the team and patient made the decision to investigate who the substitute decision-maker would be, should the patient again lose capacity. Joint decision makers were found, in the patient’s parents, who were listed as next of kin. They were asked to jointly make/ agree upon a plan of care for both their daughter and their unborn grandchild. The patient remained on inpatient psychiatry unit until the baby was born two weeks later, by caesarian section.

• Should the substitute decision-makers (SDMs) have been present earlier in this admission? Who was providing consent for the patient, when incapable, when the SDMs were not involved?
• What rights does the fetus have under the law?
• While the patient agreed to C/S in advance, what happens if she changes her mind in the moment?

73-year-old female admitted to hospital with aspiration pneumonia and sepsis.  Past medical history of multiple CVA’s, PEG tube feeding, multiple pressure ulcers.  Patient able to open eyes but not able to follow any commands or respond verbally.  Patient came to hospital from home with her wife.  On admission, the wife was adamant that the patient be a full code. Wife seemed to be unclear regarding patient’s current medical/functional condition, and the health care team felt that due to unrealistic expectations of the wife, the patient was suffering.  The team was struggling with the goals of care that were demanded. Goals of care were only changed when a new physician took over the care of the patient, and was willing to intervene.

• Must the physician/health care team acquiesce to all demands by a substitute decision-maker? What were the reasons she provided for wanting “full code”?
• What would the patient want in this case if she could tell the team? What would it mean to support her wishes?
• What reasons were given by the first physician to not make the patient full code? And from the second physician for agreeing to full code?

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• Review Article
• Open access
• Published: 17 June 2021

Cellular human tissue-engineered skin substitutes investigated for deep and difficult to heal injuries

• Álvaro Sierra-Sánchez   ORCID: orcid.org/0000-0003-4511-408X 1 , 2   na1 ,
• Kevin H. Kim 3 , 4   na1 ,
• Gonzalo Blasco-Morente 4 &
• Salvador Arias-Santiago 1 , 2 , 4 , 5  

npj Regenerative Medicine volume  6 , Article number:  35 ( 2021 ) Cite this article

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• Tissue engineering
• Translational research

Wound healing is an important function of skin; however, after significant skin injury (burns) or in certain dermatological pathologies (chronic wounds), this important process can be deregulated or lost, resulting in severe complications. To avoid these, studies have focused on developing tissue-engineered skin substitutes (TESSs), which attempt to replace and regenerate the damaged skin. Autologous cultured epithelial substitutes (CESs) constituted of keratinocytes, allogeneic cultured dermal substitutes (CDSs) composed of biomaterials and fibroblasts and autologous composite skin substitutes (CSSs) comprised of biomaterials, keratinocytes and fibroblasts, have been the most studied clinical TESSs, reporting positive results for different pathological conditions. However, researchers’ purpose is to develop TESSs that resemble in a better way the human skin and its wound healing process. For this reason, they have also evaluated at preclinical level the incorporation of other human cell types such as melanocytes, Merkel and Langerhans cells, skin stem cells (SSCs), induced pluripotent stem cells (iPSCs) or mesenchymal stem cells (MSCs). Among these, MSCs have been also reported in clinical studies with hopeful results. Future perspectives in the field of human-TESSs are focused on improving in vivo animal models, incorporating immune cells, designing specific niches inside the biomaterials to increase stem cell potential and developing three-dimensional bioprinting strategies, with the final purpose of increasing patient’s health care. In this review we summarize the use of different human cell populations for preclinical and clinical TESSs under research, remarking their strengths and limitations and discuss the future perspectives, which could be useful for wound healing purposes.

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Skin wound healing.

Skin is a vital organ with multitude of functions, one of which is to serve as a barrier to protect against external agents that can cause serious harm. Its relevance becomes apparent with extensive loss of skin due to deep injuries or burns, which affect many parts of human body (limbs, back, and trunk). Delayed intervention can lead to chronic wounds generation or fluid and electrolyte imbalance, poor thermal regulation and sepsis that can ultimately cause death 1 .

To avoid these undesired outcomes, a complex but well-orchestrated process divided in four overlapping phases (hemostasis, inflammation, proliferation, and remodeling) called wound healing (Fig. 1 ), plays a crucial role after a cutaneous injury, restoring function and appearance of damaged skin with minimal scarring 2 .

Hemostasis: activation of fibrin is responsible of clot formation and bleeding is stopped. Inflammation: damaged cells are phagocyted and factors are released to provoke cell migration and proliferation. Proliferation: cells such as dermal fibroblasts, MSCs and SSCs (mesenchymal and skin stem cells) achieve wound’s site and form a provisional extracellular matrix. Remodeling: collagen fibers are realigned, and residues are removed. Created with BioRender.com.

This process requires the involvement and coordination of many cell types and signaling pathways 3 . Firstly, vasoconstriction is achieved due to endothelin and factors released by injured cells, such as epinephrine and catecholamines, and moreover, platelets produce platelet-derived growth factor (PDGF), which activates mesenchymal cells from smooth muscles in the vessel walls causing contraction 3 , 4 . To conclude hemostasis, platelets, through G protein-coupled receptor, bind to thrombogenic subendothelial matrix 5 , activating integrins (αIIbβ3 or α2β1) and glycoproteins (Ib-IX-V and VI), which increase the attachment to fibrinogen, fibronectin and von Willebrand factor and between platelets (platelets plugs) 6 , 7 . Finally, platelets within the plug releases many growth factors (PDGF, transforming growth factor β-TGF-β-, or epidermal growth factor -EGF-), required for the next stages and moreover, provide a surface for assembly and activation of coagulation complexes lead by Factor X, and where, after Factor XIII crosslinks fibrin, thrombus is formed serving as provisional wound matrix 3 , 8 .

In inflammatory phase, transcription-independent pathways (Ca 2+ waves, reactive oxygen species gradients, and pyrogenic molecules) and damaged associated factors such as H 2 O 2 are responsible of inflammatory cells recruitment, activating keratinocytes regeneration and promoting new vessel formation 3 , 9 . In particular, neutrophils secrete antimicrobial agents and phagocyte bacteria and cell debris, meanwhile, macrophages have a microbicidal and pro-inflammatory effect at the beginning, but then, develop an anti-inflammatory role, which accelerate wound healing through the formation of new vessel (Tie2+) and the release of vascular endothelial growth factor (VEGF) 3 , 10 . Moreover, they participate in proliferation phase; inducing the transition of dermal fibroblasts into myofibroblasts and depositing collagen and other extracellular matrix (ECM) components, and also in re-epithelization and remodeling; releasing proteases and phagocytizing excessive cells and matrix no required 3 , 8 , 10 . Mast cells are also important for wound contraction because synthesized enzymes chymase and tryptase, as well as histamines and VEGF, which stimulates keratinocyte proliferation and re-epithelialization and enhances fibroblast proliferation and collagen synthesis 3 , 11 .

Proliferation phase is also triggered by many different cell types 12 . The most important are endothelial cells, which are responsible of angiogenesis in response to factors such as VEGF, PDGF, TGF-β, and fibroblast growth factor (FGF). This is regulated by Notch pathways through VEGF-A produced by subcutaneous adipose stromal cells 3 , 13 . In addition, fibroblasts synthesize ECM and express genes that are responsible of its proliferation and migration, and myofibroblasts, transient cells derived from local fibroblasts and others cells such as mesenchymal stem cells and epithelial cells, also deposit ECM and exhibit contractile characteristics; processes that are fundamental for wound healing 3 .

Finally, regeneration of the dermis is favorable due to their fibrous nature, allowing for migration and proliferation of macrophages and fibroblasts necessary for remodeling and promoting connective tissue formation 3 , 10 . In the case of epidermal layer, re-epithelialization is a complicated process where keratinocytes located in the wound edge loss their adhesions and express integrins, which leads to increased Erk-MAPK signaling and inflammatory cytokine synthesis, causing hyperproliferation of keratinocytes and immune cell activation 3 , 14 . In addition, human skin stem cells (hSSCs) migrate from their niches in order to replace the lost keratinocytes 8 , 12 , 15 and also express higher levels of integrins (α2β1, α3β1, α6β4), that binds collagen or laiminin 3 , and release growth factors, which participate in generation of epithelial cells like keratinocytes, promoting re-epithelization of injured skin 12 , 16 , 17 , 18 .

On balance, wound healing is a coordinated and complex process where many factors such as, inflammatory skin diseases, deep injuries, large sized or chronic wounds can provoke a deregulation due to an altered immune response and the lack of local adult skin cells and hSSCs available for migration, which causes problems to achieve a correct homeostatic restoration 15 , 19 , 20 .

When these critical cells are lacking due to deep and difficult to heal wounds, human mesenchymal stem cells (hMSCs) can also contribute to re-epithelization 21 by stimulating collagen production and reducing fibrosis and scar formation by releasing many growth factors such as EGF or basic fibroblast growth factor (bFGF) 12 .

Hence, much of the efforts have been dedicated to understanding the mechanisms of wound healing and to develop clinically viable therapies based on tissue engineering, to help patients restore function of damaged skin.

Tissue engineering and material science of skin

Tissue engineering (TE) is an interesting and growing multidisciplinary field that involves several biomedical areas such as cell biology, material science, engineering or medicine. It appears as a necessity to solve the lack of organ donors or another efficient substitute for the organ required. For this reason, TE tries to manufacture artificial organs and tissues under controlled conditions to be transplanted in vivo in those cases where own patient’s regenerative or reparative capacities are not achieved 22 .

Study of TE strategies requires to evaluate many aspects such as cell sources, cell nature, material science, incorporation or not of growth factors and disease models required (injuries and animals). Regarding cell biology, selection of an appropriate cell type will depend on the target tissue but the main challenge for clinical use will be to select among allogeneic (stem cells included) or autologous source due to the advantages and disadvantages associated to each one 22 , 23 , 24 . The other important aspect in TE is material science; first approaches were based on the use of synthetic biomaterials that provided structural support and replaced organs but without functionality 23 . However, research of ECM has provoked the development of new biomaterials capable of resembling biological and mechanical aspects such as three-dimensional (3D) structures (scaffolds), which enable nutrient’s transport and vascularization 22 , 23 , 24 . Considering their nature, biomaterials could be synthetic, naturally derived or acellular tissue matrices and they must be biocompatible, biodegradable and bioresorbable to be replaced by native tissue without rejection 23 .

In the case of skin, a tissue-engineered skin substitute (TESS) is any safe product, constituted of human cells and bio-scaffolds, capable of replacing damaged human skin and resembling its structural and functional characteristics such as flexibility, protective barrier or transepidermal water loss 25 , 26 .

In most TESSs, the cellular component is composed of human adult keratinocytes and fibroblasts as part of epidermal and dermal layers, respectively 20 . However, due to the many advantageous properties 8 , 27 of human stem cells (hSCs) and the specific role of hSSCs and hMSCs in restoring homeostatic conditions 12 , 15 , new approaches in the field of skin engineering are focusing on the incorporation of these cell types to TESSs 21 (Table 1 ).

Several biomaterials such as collagen 28 , chitosan 29 , elastin 30 , or hyaluronic acid 31 , 32 have been used for manufacturing TESSs. On balance, they differ in their internal structure: porous, fibrous, hydrogel, or ECM nature, which provide advantageous and drawbacks depending on therapeutic purposes 33 .

In this review, we analyze the different cell types, human adult skin cells but also human stem cells, used to develop research models of TESSs, at preclinical or clinical environment, for the treatment of deep and difficult to heal wounds.

Human adult skin cells in TESSs

Human skin is composed of several cell types distributed in the different layers of skin: epidermis, dermis and hypodermis. Epidermis is mainly composed of keratinocytes, but also melanocytes, Langerhans cells and Merkel cells are present. Dermis is primarily constituted by fibroblasts and extracellular matrix, meanwhile, hypodermis is mainly comprised of adipose tissue cells.

Most of the non-commercial substitutes studied are constituted by epidermal, dermal or both layers, where keratinocytes and fibroblasts are the most used cell types; however, some researchers explored the use of the other epithelial cell types with the purpose of fabricating TESSs that better resemble native skin (Fig. 2 ).

After a deep, severe or chronic injury where, normal phases of healing are not possible, fabrication of TESSs from cells of a human skin biopsy is the most usual advanced therapy. Keratinocytes, fibroblasts and the rest of epithelial cells are isolated, expanded and used in combination with a biological matrix to produce sheets of cultured epithelial substitutes (CESs), cultured dermal substitutes (CDSs) and composite skin substitutes (CSSs), which are engrafted to promote and facilitate cell activation and the release of growth factors necessary to achieve reparation, regeneration and homeostasis of skin. Created with BioRender.com.

Human keratinocytes for preclinical TESSs

Keratinocytes were the first skin cell type isolated and explored 34 , and for this reason the former models of TESSs were based on these cells only. Development of cultured epithelial substitutes (CESs) for burn patients has been one of the main objectives, which has led to many extensively studied commercial devices 35 , 36 .

In recent years, the number of studies evaluating the use of human keratinocytes-only TESSs have been limited. Some authors have used these CESs to compare different culture techniques 37 or dermal matrices (ECM derived from fibroblasts) 38 . The necessity of including dermal components to support in vivo proliferation and preservation of keratinocytes was early demonstrated in athymic mice by Rennekampff et al. 39 where human keratinocytes transplanted with an acellular dermal matrix onto full-thickness skin defects, developed a fully differentiated epidermis and persisted in all animals grafted (vs. 63.6% of those animals without a dermal component).

In 2019, Horch et al. 40 studied in vivo the use of keratinocyte monolayers in hyaluronic acid membranes demonstrating that when keratinocytes were directly implanted towards the full-thickness wound bed of athymic mice, formation of a multilayered and differentiating epidermis was faster (14 days) than conventional technique (>21 days).

Human keratinocytes for clinical TESSs

Owing to the important role of epidermis as a protective barrier, CESs with keratinocytes were the first TESSs explored in patients (Table 2 ). Since 1981, many clinical studies have analyzed the role of CESs in skin regeneration 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , mainly for the treatment of burns (14 of 16 studies), although treatment of surgical wounds was also reported.

Regarding to culture and manufacturing process of CESs, in most of former studies reviewed (in chronological order), keratinocytes were expanded and isolated by enzymatic detachment from culture flasks and directly engrafted onto patients 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 50 , 52 , 54 . In these cases, results differed depending on: parameters analyzed, endpoint of follow-up or pretreatment strategy, but, in general, studies that only applied this type of CES reported worse results in terms of graft take, due probably to the effect of digestive enzymes on epidermal cells.

For this reason, some authors concluded that their use could be interested as temporary biological dressing 54 or combined with meshed split-thickness skin grafting 42 , 43 , 48 . In other cases, the previous engraftment of artificial 52 or allogeneic split-thickness skin grafts 43 , 46 improved the take of these conventional CESs and accelerate wound healing 52 due to the increase of capillarity density 43 .

However, due to the risk associated with these strategies, researches started to investigate the fabrication of more complex CESs where epithelial cells and biomaterials were cultured in vitro before engraftment 49 , 51 , 53 , 55 , 56 . Two studies evaluated the use of fibrin and in both cases take of grafts was higher, improving the relation cost-efficiency 49 and demonstrating that fibrin facilitated the formation of dermo-epidermal junction because ECM proteins secreted by autologous keratinocytes were retained 51 .

Sheridan et al. 53 and Pajardi et al. 55 developed CESs based on acellular dermis or membranes, respectively. In the first case 53 , vascularization after 14 days was higher in the case of autografts (98 ± 1% vs. 45.7 ± 14.2%), however, results of Vancouver Scar Scores (VSSs) after 12 months demonstrated that no differences existed between autologous CESs (1.2 ± 0.7) and autografts (1.0 ± 0.4). In the second case 55 , at the end of the follow‐up, a reduction of 91.5% of wound dimensions was achieved with allogeneic CESs.

Other biomaterials used were collagen and elastin 56 but, in this case, autologous CESs were engrafted before gold standard treatment (autografts) was applied. Results revealed that the combination of CESs and autografts increased epithelization against those cases where only autografts were applied (71% vs. 67%), and after 12 months of follow-up, Patient and Observer Scar Assessment Scale (POSAS) reported better results when CESs were grafted (14.2 ± 7.2 vs. 18.4 ± 10.2). This was the only randomized controlled clinical trial reviewed (NCT00832156) 56 .

Interestingly, one of the studies demonstrated the importance of using an appropriate skin autograft or source. Yamaguchi et al. 52 compared three different treatments for palmoplantar wounds: (i) CESs with autologous epidermal cells from palmoplantar sites, (ii) no-palmoplantar skin grafts, and (iii) palmoplantar skin grafts. No expression of keratin 9 was observed in the case of no-palmoplantar skin grafts and after 1 year, wound size was higher (26.77 ± 6.72 cm 2 ) than in those patients treated with CESs (12.27 ± 4.14 cm 2 ) and palmoplantar skin grafts (4.24 ± 0.68 cm 2 ).

On balance, studies using CESs have evolved from the first reported, including new culture techniques and strategies, however, it does not seem to be the best alternative when deep wounds or difficult to heal wounds needs to be treated. To date, a total of 259 patients (29.1 ± 17.2 years old), the majority of them with burn injuries (88.0% of the cases), with a mean of 57.4 ± 20.0% total body surface area (TBSA) affected, have been treated using this strategy, and the percentage of successful engraftment was 60.5 ± 35.0% without adverse events except in one case, where more reconstructive procedures were required for functional problems 50 (Table 2 ).

Human fibroblasts for preclinical TESSs

Development of human cultured dermal substitutes (CDSs) is essential to achieve a proper integration of the engraftment and successful wound healing. Mineo et al. 31 developed a dermal substitute composed of hyaluronic acid, collagen and human dermal fibroblasts. They demonstrated in vitro, increased amount of VEGF and hepatocyte growth factor (HGF), which effectively created a vascularized wound bed for autologous skin grafting in Sprague Dawley rats with deep dermal burns.

Other studies explored the role of extracellular matrix of human fibroblasts to support the growth of these cells and develop more natural substitutes 57 , 58 for full-thickness wounds, demonstrating in vitro and in vivo, on Sprague Dawley rats, that they have notable effects on wound healing, facilitating fibroblast infiltration, collagen bundle production, and elastic fiber and blood vessel formation 58 .

Mohd Hilmi et al. 29 evaluated a chitosan sponge matrix seeded with human dermal fibroblasts, engrafted onto full-thicknesses wounds excised on the irradiated skin of Sprague Dawley rats. Wounds treated with chitosan CDS showed the most re-epithelialization level (33.2 ± 2.8%) and scar size of wounds were significantly decreased compared with control group where duoderm CGF was applied (0.13 ± 0.02 cm vs. 0.45 ± 0.11 cm).

Finally, the addition of other cell types such as endothelial cells could be useful to increase the regeneration potential of CDSs. One study fabricated a TESS based on endogenous matrix produced by human dermal fibroblasts and cultured with human fibroblasts and endothelial cells, which were capable of forming capillary-like-structures effectively anastomosed with host vessels in vivo 59 .

Human fibroblasts for clinical TESSs

With the advancement of culture techniques and ability to isolate dermal fibroblasts, clinical studies have evaluated the use of CDSs for the treatment of chronic skin ulcers (7 of 10 studies), surgical wounds and burns (Table 3 ) 55 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 . Important findings from these studies highlight the release of cytokines or growth factors, which activates many pathways for skin regeneration 60 , 63 .

In most of the cases, CDSs were fabricated using allogeneic fibroblasts 55 , 60 , 61 , 62 , 63 , 64 , 65 , 68 . Cells were cultured over different scaffolds and placed cell‐seeded side down onto the wound surface.

Regarding to the type of clinical studies reviewed, three were considered as clinical trials 66 , 67 , 68 , one was an observational study 55 and remaining were classified as case reports 60 , 61 , 62 , 63 , 64 , 65 .

Among these, three studies compared different therapies 63 , 66 , 68 . Yamada et al. 63 evaluated the use of allogeneic fresh or cryopreserved fibroblasts cultured on a bilayer sponge composed of hyaluronic acid and collagen for the treatment of deep surgical wounds, demonstrating that cryopreserved cells were capable of releasing cytokines and promoting re-epithelialization at the same level as fresh cells. You et al. 66 reported better results in terms of complete ulcer healing when compared the use of hyaluronic acid-based autologous CDSs (84%) and non-adherent foam dressings (34%). Finally, Momeni et al. 68 studied the use of amniotic membranes alone or combined with allogeneic fibroblasts and compared the results with a control therapy (Vaseline gauze). Results revealed that wound closure of surgical wounds was higher when amniotic membranes were used (alone— 95.5%—, with fibroblasts—94%—vs. control—59%—) and re-epithelialization was faster (alone—11.3 ± 2.9 days—, with fibroblasts—10.1 ± 2.4 days—vs. control —14.8 ± 1.6 days—).

Interestingly, a combination of hyaluronic acid and collagen was the preferred matrix for the manufacture of CDSs 60 , 61 , 62 , 63 , 64 , 65 . Different wounds were treated using these allogeneic CDSs (burns 60 , surgical wounds 63 , and ulcers 61 , 62 , 64 , 65 ), but similar results indicated that their application would be interested as biological wound dressing to produce granulation tissue and secrete VEGF, bFGF, and ECM proteins useful for mesh-auto skin grafts.

Finally, Morimoto et al. 67 used an artificial dermis and autologous fibroblasts for the treatment of diabetic ulcers demonstrating an important wound size reduction after 21 days (from 7.1 ± 4.9 cm 2 to 3.4 ± 2.3 cm 2 ). In contrast, Pajardi et al. 55 used hyaluronan as dermal matrix for the treatment of chronic ulcers reporting a wound size reduction of 73%.

One-hundred five patients (63 males and 42 females), older than those treated with CESs (58.4 ± 14.7 years old), were treated with CDSs. Small injuries (87.6% of cases were chronic skin ulcers) were evaluated and successful engraftment was achieved in 79.5 ± 20.0% of the cases. Adverse events were only observed in five cases, related to local infections (Table 3 ).

Combination of human keratinocytes and fibroblasts for preclinical TESSs

In recent years, the combination of human keratinocytes and fibroblasts in TESSs, called composite skin substitutes (CSSs) has been explored.

CSSs resemble normal skin by containing an epidermal layer of autologous or allogeneic keratinocytes and a dermal layer of fibroblasts incorporated into a stromal scaffold. They not only provide structural dermo-epidermal support, but also deliver growth factors (EGF, PDGF, VEGF) and extracellular matrix that increase the rates of recovery and healing 69 , 70 .

For these reasons, many studies have looked different strategies to explore potential benefits of CSSs. A composite TESS manufactured with fibrin-hyaluronic acid biomaterial has been recently evaluated in vivo in immunodeficient mice with excisional wounds and compared with another fibrin-agarose CSS and secondary wound healing dressings, demonstrating favorable outcomes, similar to autografts in terms of clinical (POSAS scale results: eight for CSS vs. six for autografts), homeostasis (transepidermal water loss: 6.42 ± 0.75 g/h/m 2 for CSS vs. 6.91 ± 1.28 g/h/m 2 for autografts) and histological restoration, after eight weeks of engraftment 32 .

Similarly, Tissue Biology Research Unit of Zurich developed human CSSs based on type I collagen hydrogels, demonstrating, in vitro and in vivo in full-thickness skin defects of athymic rats, that these TESSs homogeneously developed a well-stratified epidermis over the entire surface of the grafts and displayed a well-defined basal cell layer where keratin 19/keratin 15-double-positive keratinocytes are essential in growing skin 71 , 72 .

Supp et al. 73 manufactured composite TESSs based on collagen-glycosaminoglycan for studying recessive dystrophic epidermolysis bullosa (RDEB) on immunodeficient mice and demonstrated that formation of structurally normal anchoring fibrils appears to require expression of type VII collagen in both skin layers. Bacakova et al. 74 also developed collagen-based CSSs by utilizing a nanofibrous poly- l -lactide and observed cell migration and proliferation after 14 days of in vitro culture.

Interestingly, Centre de recherche en organogénèse expérimentale de l’Université Laval/LOEX developed a self-assembly approach, which allows for the production of a scaffold-free cell-based CSS 75 , 76 . Briefly, the dermal layer is composed of stacked fibroblast sheets and keratinocytes are seeded onto the tissue, forming a stratified and cornified epidermis. Auger and Germain’s group have optimized this protocol and studied this model in vitro and in vivo (athymic mice with full-thickness skin injuries), demonstrating timely production of CSSs that could improve clinical availability for the effective wound coverage of patients 77 , 78 , 79 , 80 .

In addition, these types of TESSs have been used as a research tool to investigate other pathological conditions and learn more about the role of these treatments in wound healing. For instance, bin Busra et al. 81 demonstrated in vivo in mice, that fibrin-based CSSs enhanced healing of irradiated wounds after radiotherapy, with higher expression of TGF-β1, PDGF and VEGF than monolayer substitutes.

The vascularization of CSSs has also been studied by incorporating human endothelial cells 82 , 83 , 84 , 85 , with reports showing improvement of graft survival and the formation of vascular networks, which physically resemble normal wound healing process.

Combination of human keratinocytes and fibroblasts for clinical TESSs

Clinical benefits of CESs and CDSs have been observed in many patients; however, the most studied TESSs have been CSSs composed of human keratinocytes and fibroblasts that have been used for the treatment of several dermatological pathologies since 1989 (Table 4 ) 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 .

Most of the studies evaluated the use of CSSs for the treatment of burns, however, experimental designs differed from cell populations used (autologous [19] 86 , 87 , 88 , 89 , 91 , 92 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 vs. allogeneic [2] 90 , 93 ), biomaterials selected, randomization or not, comparison or not with other treatments or pretreatment required.

In those cases where different treatments were compared, engraftment of autografts was the gold standard treatment used as reference for each patient 88 , 90 , 92 , 93 , 95 , 101 , 102 , 104 , 105 , 106 . In one of the cases where allogeneic cells were used, CSSs did not take and the engraftment of more autografts was required 93 . Rest of comparative studies, reported positive results for CSSs in terms of percentage of TBSA closed ([20.5 ± 2.5% for CSSs vs. 52.1 ± 2% for autografts 95 ], [29.9 ± 3.3% for CSSs vs. 47.0 ± 2% for autografts 104 ] after 28 days in both cases), time of healing (7.4 ± 0.9 days for CSSs vs. 7.9 ± 1.5 days for autografts 90 ), appearance (scars were less raised than autografts 88 ), percentage of wound area closed (95.4% for CSSs vs. 99% for autografts after 28 days 92 ), manipulation (easy in comparison with CESs 102 ), protein expression (keratin 19 and type IV collagen 105 ) or percentage of epithelialization (63.5 ± 35% after 21 days of engraftment 106 ).

Remaining studies indicated the beneficial role of using CSSs alone 89 , 96 , 98 , 99 , 100 , 103 or combined with autografts 86 , 87 , 91 , 94 , 97 , 101 for the treatment of deep and difficult to heal injuries, evaluating different parameters such as graft take, histological appearance of new skin and cosmetic and functional outcomes.

Interestingly, some researches remarked the importance, as in the case of CESs, of a pretreatment with auto-dermis or allo-dermis to increase clinical benefits of CSSs 86 , 91 , 94 , 98 , 106 .

Regarding to the biomaterials used for the fabrication of the scaffolds, different types of collagen 87 , 90 , 93 , 95 , 101 , 106 or combined with glycosaminoglycan 86 , 88 , 89 , 91 , 92 , 104 were the preferred sources, although different formulations of plasma/fibrin were also reported 94 , 96 , 98 , 102 , 103 . Finally, hyaluronic acid 97 or acellular dermal matrices derived from human fibroblasts 99 , 100 , 105 were evaluated too.

To date, a total of 241 patients (25.6 ± 14.9 years old) with severe burns (81.7% of the cases), surgical wounds or skin ulcers with a mean of 69.2 ± 11.1% of TBSA affected have benefited from CSSs with a mean percentage of successful engraftment of 80.2 ± 26.3% (0%-100%) with slight adverse events such as local inflammation or increased incidence of exudates (Table 4 ). Interestingly, eleven of twenty one studies included children and five studying children exclusively 91 , 92 , 102 , 104 , 106 .

Human melanocytes for preclinical TESSs

In order to develop a TESS that most resemble natural skin, the incoporation of other cell types present in epidermal layer, such as melanocytes, has been evaluated in preclinical stages.

Liu et al. 107 were one of the first groups to develop a TESSs composed of human fibroblasts, melanocytes and keratinocyes in a type I collagen gel. In vitro and in vivo results revealed proper integration, morphology and successful repair of skin defects in athymic mice and black skins were observed by 6 weeks after grafting.

Biedermann et al. 108 , 109 also developed a pigmented skin composite based on collagen, which was transplanted onto full-thickness skin wounds in rats. After 3 weeks, blood vessels, but no nerve fibers or lymphatic vessels were observed 108 . However, peripheral host nerve fibers were found 15 weeks after transplantation 109 . The same group studied the inflammatory response of these pigmented substitutes, which revealed that granulocytes infiltrate the entire graft at 1 week post-transplantation, while monocyte/macrophage recruitment was observed at 3–12 weeks 110 .

Boyce’s laboratory also evaluated the use of human melanocytes in collagen-based TESSs. They analyzed in vitro and in vivo (athymic mice) the incorporation of different densities of cryopreserved and recovered human melanocytes in a human CSS. Melanocytes were localized into the dermal–epidermal junction of skin substitutes and were capable of restoring cutaneous pigmentation and ultraviolet photoprotection after full‐thickness skin loss conditions 111 , which was corroborated by Goyer et al. 112 , regardless of whether light or dark pigmentation phototype melanocytes were used 113 .

Human Langerhans and Merkel cells for preclinical TESSs

Langerhans cells are a specialized population of dendritic cells that are found in the stratum spinosum of epidermis of the skin. They help to drive protective immune responses following infection of the skin 114 . Merkel cells constitute a unique population of postmitotic cells scattered along the dermo-epidermal junction. These cells have synaptic contacts with somatosensory afferents and play a crucial role in sensory discernment 115 . The number of studies evaluating the use of these cell types for TESSs is limited.

Isolation of Langerhans cells (LCs) is a complicated process. For this reason, only two studies have reported the use of in vitro-derived LCs from monocytes 116 or an acute myeloid leukemia cell line, MUTZ-3 117 , for fabrication of collagen-based TESSs. In both cases, substitutes were composed of human fibroblasts, keratinocytes, and derived LCs. After 11–14 days of in vitro culture, histological evaluation featured a fully stratified epidermis with all the characteristic epidermal strata. Langerin-positive cells were detected suprabasally within the epidermis indicating that keratinocytes provide environmental conditions for long-time maintenance of derived LCs.

Other related studies have reported the presence of Langerhans cells (CD1a+ and human leukocyte antigen—HLA+) in vitro or in vivo in TESSs when epithelial cells were incorporated 118 , 119 , 120 , 121 . This indicates that isolation of keratinocytes, are likely to contain a small proportion of cells that are LCs.

In the case of Merkel cells, only Hahn et al. 122 have reported on immunodeficient mice, the presence of host nerve cells and Merkel cells (keratin 20+ − K20+ – and HLA+) from grafted human keratinocytes and fibroblasts in a collagen-glycosaminoglycan scaffold, suggesting that fine touch sensation may be restored after TESS’s engraftment.

Human stem cells (hSSCs) in TESSs

Human stem cells such as hSSCs, induced pluripotent stem cells (hiPSCs) and hMSCs have been investigated for therapeutic use to enhance wound healing 21 , 27 , 123 . This has led to the fabrication of more complex models of TESSs (Fig. 3 ), which could stimulate more rapid and complete healing; furthermore, drive expression of additional phenotypes to correct anatomic deficiencies through activation of biological signaling pathways 27 .

Different sources of hSCs could be (i) differentiated in vitro to the main cutaneous lineages and then, uses to fabricate artificial skin; (ii) embedded directly into dermal scaffolds and engrafted to achieve an in vivo differentiation; or (iii) combined with human keratinocytes and fibroblasts to benefit from their own angiogenic and immunomodulatory properties. hSSCs human skin stem cell, hiPSCs human-induced pluripotent stem cells, hMSCs human mesenchymal stem cells. Created with BioRender.com.

Human skin stem cells (hSSCs) for preclinical TESSs

The skin is an attractive source of stem cells because of their abundant supply, easy accessibility, ease of harvesting, and possibly providing immune-privileged cells 124 . hSSCs, characterized by their quiescence state (CD71 - , EGF-R low ) and their strong adhesion capacity (high expression of integrin markers) 125 , have been isolated from different parts of skin such as dermal papilla or hair follicles, among others 12 , 124 , 126 , 127 . In particular, dermal papilla stem cells (DPSCs), also called dermal hMSCs, have similar characteristics and differentiation capacity as hMSCs from other tissues 127 , and for this reason they are the hSSCs most studied for skin regeneration and wound repair.

Jeremias et al. 128 integrated skin-derived hMSCs with different dermal substitutes (Integra ® and Pelnac TM ) and showed that both were able to support the maintenance and growth of skin-derived hMSCs. Salerno et al. 129 also evaluated the use of these cells in dermo-epidermal skin substitutes constituted of dermal membranes of chitosan, polycaprolactone and a polymeric blend and, after 14 days of in vitro culture, were capable of observing fibronectin deposits, as a result of dermal differentiation.

Relationship between human DPSCs and hair follicle stem cells (FSCs) has been studied in TESSs by constructing a composite based on a porcine acellular matrix with DPSCs and FSCs in the dermal and epidermal layers, respectively. This composite, when grafted in nude mice with full-thickness skin wounds, resulted in successful integration (less contraction), vascularization (higher expression of VEGF), and the presence of DPSCs-induced formation of hair buds (hair‐specific keratin 6—K6hf+) 130 .

Another study developed by Higgins et al. 131 compared human dermal fibroblasts, DPSCs and FSCs within a collagen scaffold. In vitro and in vivo experiments on nude mice revealed that both, DPSCs and FSCs, can replace interfollicular fibroblasts in skin constructs. Regarding basement membrane formation, DPSCs were found to be superior to fibroblasts with an increased type IV collagen and VEGF expression, coinciding with a formation of a more robust and uniform basal lamina.

Apart from FSCs being used in combination with DPSCs, where a correct stratification, differentiation and well-ordered epithelia was observed 130 , Mohd Hilmi et al. 132 reported that a chitosan-TESS composed of fibroblasts and FSCs serving as the epidermal component, was capable of restoring rat skin after radiation exposure by an increasing collagen bundle deposition.

The role of dermal hMSCs and other types of hSSCs in wound healing has been compared with human adipose tissue-derived MSCs (hAT-MSCs) 133 , 134 . Michalak‑Micka et al. 133 fabricated different collagen-based TESSs constituted of human keratinocytes as epidermal layer and stromal cells from different sources. These substitutes were evaluated in vivo in an immune-incompetent rat model and results revealed that all types of transplants exhibited a multilayered stratified epidermis with a thick stratum corneum. However, an enhanced expression of tropoelastin (a soluble precursor of elastic fibers) were only observed in skin grafts containing hAT-MSCs and dermal hMSCs, which correlated with in vivo results of Zomer et al. 134 , demonstrating their potential to accelerate wound healing.

Human-induced pluripotent stem cells (hiPSCs) for preclinical TESSs

Human-induced pluripotent stem cells (hiPSCs) are stem cells generated from individual somatic cells by exogenous expression of several transcription factors to initiate the reprogramming process 135 . In skin regeneration and for TESSs, hiPSCs have been successfully obtained from fibroblasts 136 , 137 , 138 or cord blood mononuclear cells (CBMCs) 139 , and differentiated into fibroblasts and keratinocytes 136 , 137 , 138 , 139 .

Itoh et al. 136 described one of the first models of skin substitute using hiPSCs for the treatment of RDEB. They differentiated embryoid bodies generated from hiPSCs into fibroblasts and keratinocytes and showed that the hiPSCs-derived fibroblasts were capable of producing and secreting mature type VII collagen in addition to expressing other collagen types (I, III, and IV). Moreover, they fabricated and engrafted in mice a TESS constituted of collagen I matrix and these hiPSCs-derived fibroblasts, demonstrating their capacity to support functional and terminal differentiation of human keratinocytes by the expression of K1 and loricrin. In all, they were able to fabricate a complete hiPSCs-derived skin composite, histologically like normal human skin.

The same group was also able to differentiate hiPSCs into melanocytes 137 and demonstrate that hiPSCs-derived keratinocytes, which expressed K1 and K14, were capable of internalizing melanosomes, essential to generate a functional epidermal-melanin unit.

To support these results, Petrova et al. 138 focused on hiPSCs-derived keratinocyte differentiation and developed a physiological purification method, which resulted in higher yield isolation of a cell population similar to normal human keratinocytes expressing K14 and p63. After their characterization, these derived cells were used in an in vitro TESS model demonstrating their capacity to form the same structure as the human epidermis and also, develop endoplasmic reticulum Ca 2+ store, essential for normal keratinocyte signaling and differentiation.

To improve the survival of skin grafts and avoid immune rejection, CBMCs have emerged as a potential cell source for regenerative medicine and hiPSCs. One advantage of CBMCs as a source is the mandatory HLA typing during the CBMC banking process, making available valuable HLA-matched research materials that can be obtained easily 139 . Kim et al. 139 successfully differentiated hiPSCs from CBMCs into fibroblasts and keratinocytes. These cells were used to produce 3D skin organoids, and after being implanted onto surgical excisions in mice, they resembled skin structure with a similar expression of CD73 and CD105 as primary fibroblasts; and involucrin and loricrin (epidermal differentiation markers) were upregulated.

In addition to fibroblasts and keratinocytes, hiPSCs have been differentiated into other cell types such as melanocytes 137 , sensory neurons and Schwann cells 140 . They have been generated in vitro and successfully incorporated into TESSs with the purpose of fabricating more complex, functional and complete skin substitutes, although exhaustive in vivo analysis is still required.

Human mesenchymal stem cells (hMSCs) for preclinical TESSs

Mesenchymal stem cells are non-hematopoietic multipotent adult progenitor cells that are found in various tissues, including bone marrow, adipose tissue, and umbilical cord. They can be easily harvested and expanded from the different tissues of adult donors, avoiding any potential ethical issues associated with using embryonic stem cells or with genetic manipulations when using hiPSCs. Moreover, their hypo-immunogenic property allows its immediate use as prepared allogeneic cells without significant host reaction 141 , 142 , 143 , 144 , although recent studies have indicated that the immune compatibility between donor and recipient is also important because hMSCs are immune evasive rather than immune privileged 145 , 146 , 147 . Their anti-inflammatory capacity 148 can also be useful in dampening the inflammatory milieu of chronic non-healing wounds and aid in the healing process.

Another beneficial feature of hMSCs is their plasticity to differentiate into both mesenchymal and non-mesenchymal lineages such as ectodermal keratinocyte-like cells (KLCs) 149 , endothelial cells, and different skin appendages, which is being investigated for skin tissue engineering and wound healing therapies 149 , 150 .

Moreover, the addition of hMSCs to current skin substitute models can potentially promote angiogenesis by the recipient’s endogenous cells via paracrine signaling with VEGF 151 .

Human bone marrow-derived MSCs (hBM-MSCs)

hBM-MSCs have been the most studied and the major source of hMSCs. In the skin, hBM-MSCs’ regenerative potential and their ability to differentiate into non-mesenchymal lineages including endothelial cells, keratinocyte-like cells, and skin appendages 152 , have been demonstrated to be useful for wound healing.

He et al. 153 studied the use of hBM-MSCs and their capacity to differentiate in vitro and in vivo into epidermal and dermal cells. Better differentiation was observed in the case of dermal cells, in vitro. They fabricated TESSs composed of hBM-MSCs in a collagen membrane and implanted them into surgical skin wounds generated on the back of mice. After 21 days, wounds were completely healed and a differentiated epidermis and dermis were observed, demonstrating that hBM-MSCs could differentiate in the inducing microenvironment in vivo.

Ojeh et al. 154 used hBM-MSCs as dermal component in a CSS model composed of de‐epidermalized dermis with human keratinocytes and compared it with a traditional CSS composed of human fibroblasts and keratinocytes. In vitro results showed that a hBM-MSC model could generate a hyperproliferative epidermis that was well‐differentiated.

hBM-MSCs have also been analyzed as the epidermal layer in fibrin-TESSs with a dermal layer composed of human fibroblasts 152 . This study compared MSCs from different human sources: bone marrow, umbilical cord Wharton’s jelly (hWJ-MSCs) and adipose tissue (hAT-MSCs). In all cases, an epithelial-like layer was formed after the first week of culture, although after four weeks, more stratified epidermis was observed in the case of hBM-MSCs and hWJ-MSCs. Moreover, after in vivo grafting in nude mice with surgical wounds, mesenchymal cell populations, mainly for hAT-MSCs substitutes, induced the generation of up to ten epithelial-like layers after 15 and 30 days, expressing keratin 5, proteoglycans and collagen fibers, but without expression of HLA markers.

Human umbilical cord Wharton’s jelly-derived MSCs (hWJ-MSCs)

Perinatal stem cells such as hWJ-MSCs have been shown to have excellent proliferation and differentiation capabilities to be applied in regenerative medicine 155 .

Garzón et al. 156 studied these cells in vitro and in vivo by using a bioactive 3D heterotypical model comprised of primary cell cultures of hWJ-MSCs and fibroblasts from oral mucosa or skin in a fibrin-agarose-based matrix as stroma substitute. Their results showed that hWJ-MSCs were unable to fully differentiate into epithelial cells in vitro. However, after in vivo grafting onto immunodeficient, athymic mice, they showed expression of epithelial differentiation and functional markers, and stratification into typical epithelial layers.

Ertl et al. 157 compared hWJ-MSCs with two different human term placenta-derived mesenchymal stem cells (hP-MSCs) in an in vivo full-thickness wound model in mice. All TESSs fabricated with Matriderm ® +MSCs induced a faster healing and a higher number of blood vessels in the wound when compared to controls (49 ± 6% of wound reduction for TESSs vs. 22 ± 7% of wound reduction for controls). In another study, Shi et al. 158 employed hWJ-MSCs with skin microparticles in a murine excisional wound repair model to show multi-direction differentiation into newly formed skin and its appendages such as sebaceous glands, hair follicles and sweat glands.

Interestingly, some authors have explored the use of these silk fibroin-based TESSs combined with an injection of hWJ-MSCs at the edge of the wounds in mice. Results of this treatment indicated that collagen dermis organization was more similar to that typically observed in the normal skin of mice and diminished both innate and adaptative immune infiltrates 159 .

Human adipose tissue-derived MSCs (hAT-MSCs)

hAT-MSCs are an attractive source for hMSCs-based construction of TESSs for their ease of harvesting and expansion in culture and versatile differentiation potential into non-mesenchymal lineages such as ectodermal KLCs 149 , 160 , 161 . Moreover, compared to MSCs from other sources such as the bone marrow, the procurement of hAT-MSCs is associated with lower morbidity and higher yield of cells 155 .

hAT-MSCs for TESSs have been used, in most of the cases, as a dermal component, alone or combined with other cell types. Some in vitro studies evaluated the role of hAT-MSCs as dermal support for human keratinocytes, showing after 7 days of culture, increased collagen IV expression in the epidermal-dermal junction 162 and enhanced proliferation of human keratinocytes 163 . These results were corroborated with an in vivo study in a third degree burn model generated in rats where the treatment with TESSs composed of hAT-MSCs and human keratinocytes on a human amniotic membrane reported faster wound regeneration and less inflammatory cell infiltration than control groups 164 . These TESSs have been also analyzed in murine models of full-thickness defects, demonstrating their capacity to enhance wound healing rates 165 promoting angiogenesis and re-epithelization 166 , 167 .

Furthermore, favorable outcomes have also been observed when hAT-MSCs were combined with other cells to constitute the dermal matrix. TESSs composed of hAT-MSCs co-cultured with human endothelial cells in the dermal layer and human keratinocytes in the epidermal were capable of forming capillary structures in vitro 168 .

Interestingly, pigmented TESSs fabricated with hAT-MSCs and human fibroblasts in the dermal layer were less dark than those manufactured with fibroblasts only, which indicated that cytokines released by hAT-MSCs maintained melanocytes in an immature state where melanin synthesis was decreased 169 .

Another method of delivering hAT-MSCs is using adipose-derived stromal vascular fraction (SVF), which not only contains MSCs, but also endothelial cells and pericytes that are key contributors to vasculature formation. Klar et al. 170 , 171 developed a novel pre-vascularized composite skin substitute model by seeding adipose-derived SVF into a 3D fibrin hydrogel, allowing for the formation of vascular networks in the graft prior to transplantation. In this rat full-thickness wound model, there was more efficient engraftment of the transplanted skin substitute due to rapid anastomoses of the graft capillary plexus with the recipient’s vasculature, epidermal regeneration with stratification, and remodeling of the dermis with low graft contraction.

Human mesenchymal stem cells (hMSCs) for clinical TESSs

Although most of the recent preclinical studies report the use of hAT-MSCs as the main stem cell for TESSs, the number of clinical studies is still limited. Only a small amount of published research has evaluated the use of hMSCs in TESSs as a therapeutic strategy for wound healing (Table 5 ).

Most of the studies reviewed were case reports 172 , 173 , 174 , 175 . Some researchers reported the use of hMSCs-based TESSs combined with autograft treatment 174 , 175 and in other cases, a comparison between biomaterials with or without hMSCs was evaluated 173 , 174 , 176 , 177 .

Regarding tissue of origin, three studies evaluated the use of autologous hBM-MSCs 172 , 173 , 174 . Vojtassák et al. 172 showed enhanced wound healing in one patient with chronic diabetic and venous ulcers using a composite graft fabricated with autologous skin fibroblasts on a collagen and hyaluronan membrane in combination with autologous hBM-MSCs injected and placed on the wounds. After 29 days of treatment, an increased vascularization of dermis was observed due to the differentiation potential of hMSCs into endothelial progenitor cells, which produced VEGF and bFGF.

Yoshikawa et al. 173 studied a MSCs-based treatment of 20 patients with different pathologies whose acellular dermis grafting had previously failed. They combined cultured autologous hBM-MSCs with a collagen sponge, which resulted in a significant improvement of wounds in 18 of 20 patients. Some wounds were treated with collagen membrane only and subcutaneous formation was not observed, in contrast to the rest of wounds treated with hMSCs, where infiltration of inflammatory cells was notable and CD34+ cells (derived from bone marrow) formed vascular endothelia.

Xu et al. 174 applied a composite graft comprised of autologous hBM-MSCs embedded in decellularized allogeneic dermal matrix overlaid with autologous split-thickness skin graft for the treatment of hypertrophic scars resulting from burn injuries. Results demonstrated a better outcome with reduced contraction as compared to areas treated with split-thickness skin-graft alone.

hAT-MSCs were used in three studies 175 , 176 , 177 : Arkoulis et al. 175 and Stessuk et al. 177 combined autologous hAT-MSCs with different dermal matrices (collagen-glycosaminoglycan and plasma, respectively) to treat eight patients with burn injuries or chronic ulcers. In the first case 175 , authors did not recommend the use of this technique routinely because autograft treatment was required, but it could be useful to use it when dealing with highly complex burns patients with contractures affecting cosmetically or functionally challenging areas. Stessuk et al. 177 reported a total re-epithelialization in 5 of 9 chronic ulcers and a healing rate of 74.6 ± 32.6% after 9 days of treatment. Interestingly, one wound treated with plasma membrane without cells required a re-treatment.

Last study that used hAT-MSCs was a phase II randomized clinical trial (NCT02619877) 176 where allogeneic hMSCs embedded on a hydrogel were compared with a control group (Mepitel ® ), for the treatment of chronic ulcers. Results revealed that no obvious clinical rejection existed after 12 weeks (higher anti-HLA antibodies expression in 27% of the patients). Regarding to effectiveness, Kaplan–Meier median time to complete wound healing was 28.5 days for treatment group and 63.0 days for control group.

Finally, one study evaluated the use of allogeneic hWJ-MSCs in combination with amniotic membranes for the treatment of chronic ulcers 178 . After 9 days, wound size declined from 70.96 mm 2 to 3.07 mm 2 and wound healing rate was of 96.7%. Moreover, patients reported decreased pain after 1 month of clinical follow up.

Overall, a total of 57 patients (54.4 ± 19 years old) with different pathologies such as burns, diabetic wounds or skin ulcers were treated with hMSCs. Burn patients had 50–60% of TBSA affected and overall successful engraftment of TESSs was 90.2 ± 16.3% without adverse events. Interestingly, five of the seven studies investigated used autologous cells (Table 5 ).

Future approach: human immune cells in TESSs

As previously described, participation of immune cells, such as neutrophils, macrophages or mast cells, in wound healing of skin is essential due their dual role as pro-inflammatory cells in first stages, and as anti-inflammatory effectors when safety is ensured 3 .

These cells are capable of phagocyte cell debris, synthetize or release several cytokines, which promotes angiogenesis and wound healing (VEGF), activate keratinocyte’s proliferation, and re-epithelialization or induce fibroblasts transition into myofibroblasts to increase ECM and collagen deposition 3 , 10 . Moreover, recent studies have indicated that immune cells are members of stem cells niches, developing a proactive role in regulating stem cells when tissues are damaged 10 , 179 , 180 .

Macrophages and Foxp3+ CD4+ regulatory T (Treg) cells seems to be the most important immune cell populations involved in this context 10 , 179 , 180 . Macrophages are capable of sensing the metabolic environment 181 and therefore, modulating stem cells function 179 , meanwhile, Treg cells infiltrated in wounds express the epidermal growth factor receptor (EGF-R), which is related with an improvement of wound healing 180 .

In wound healing of skin when regenerative phases are triggered, macrophages around the follicle die off and release factors such as WNT7b and WNT10a, which promote the activation of FSCs 182 . Moreover, these macrophages physically contact with epithelial stem cells, secreting pro-proliferative and epithelial remodeling factors such as IL-10 and PDGF-β 183 , apart from TGF-β1, which induces fibroblast proliferation and their differentiation into myofibroblasts 184 .

In the case of Treg cells, they are predominantly localized around hair follicles in contact to FSCs. Their role in skin regeneration could be interested for lesions, which affect epidermal appendages such as hair follicles 179 , 180 . Several researches have studied the link between Treg cells and hair follicles biology, demonstrating that in alopecia areata patients the number of Foxp3+ Treg cells is reduced in comparison with healthy controls 185 . In addition, stimulation of Treg proliferation with IL-2 administration demonstrated successful hair regeneration in 80% of patients 186 , which is due to the expression of the Notch ligand Jagged‐1 (Jag1), required to promote hair follicle cycling by enhancing the activation and differentiation of FSCs 180 .

For all of this, incorporation of human immune cells in TESSs, alone or combined with other cell populations might be interesting to increase regeneration potential and develop more complex models of artificial skin, which included epidermal appendages such as hair follicles. However, no preclinical research has been published yet in this field, which is essential to ensure their wound healing’s safety and effectiveness.

Allogeneic cells: a real strategy for clinical TESSs?

In addition to determining the cell composition of TESSs, for clinical purpose, the selection between allogeneic or autologous cells is a critical decision. While the use of allogeneic cells ensures quicker availability, graft survival is usually short-term (4–8 weeks) 187 . The use of autologous source avoids any possible host rejection and permits a more permanent TESS for full-thickness burns and chronic wounds 95 . The downside of autologous cells is the longer period (~4 weeks) required to produce a sufficiently sized graft.

Interestingly, many of the TESSs developed for clinical use (Tables 2 – 5 ) were constituted of autologous cells, mainly for CESs, CSSs or hMSC-based TESSs, with only five studies reporting the use of allogeneic cells 55 , 90 , 93 , 176 , 178 . However, in the case of CDSs, the use of allogeneic fibroblasts was preferred against autologous fibroblasts 66 , 67 , which could be explained by their use as temporary dressing to prepare the wound´s bed for future therapies or the small size of wounds treated, when a short-term biological recovery dictates the long-term outcomes 147 (Table 3 ).

In the case of adult skin cells, the use of autologous populations for TESSs seems to be clear, to avoid rapid rejection. However, when allogeneic hMSCs are selected, there is a controversy because their immunogenicity have been proven 188 , but no acute adverse events have been reported when were applied as therapy in several pathologies 146 .

To avoid this concern, immunosuppression treatment could be effective for the use of allogeneic cells in many clinical conditions, however, this poses a risk for long-term therapies where other pathologies could be developed due to a continuous suppression of immune system and moreover, in the case of skin or TESS transplants, is either less or/not effective 189 .

On balance, although immune rejection of allogeneic hMSCs occurs more slowly than other cell types 145 , 188 , they are immune evasive rather than immune privileged and for this reason, it could be interesting to use haplo-identical hMSCs 145 , 147 to increase the potential benefits of allogeneic TESSs when autologous approach is not possible.

Main biomaterials for clinical TESSs

Many different biomaterials have been investigated for the development of TESSs; from xenogeneic scaffolds such as porcine acellular matrix 130 , natural polymers like silk fibroin 159 , agarose 32 , 156 or chitosan 29 , 129 , 132 to substances that resemble in better way the native dermal components of skin: collagen 56 , 60 , 61 , 62 , 63 , 64 , 65 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 95 , 101 , 104 , 106 , plasma/fibrin 49 , 51 , 94 , 96 , 98 , 102 , 103 , hyaluronic acid 60 , 61 , 62 , 63 , 64 , 65 , 97 , elastin 56 , amniotic membrane 68 , 178 or extracellular matrix derived from fibroblasts 39 , 99 , 100 , 105 .

For clinical purposes, the main biomaterials used have been collagen alone or combined with glycosaminoglycan, hyaluronic acid, plasma/fibrin, amniotic membranes and acellular dermal matrices (Table 6 ).

Collagen is the most abundant of animal proteins, localized in soft and hard connective tissues where its fibrils, with high tensile strength and stability via cross-linking, comprise the majority of ECM and form a highly organized, 3D scaffold that surrounds the cells. Moreover, it is a dynamic and flexible biomaterial (used as sponge, gel or membrane) with high biocompatibility and intrinsic biodegradability ideal for biomedical applications 190 . Glycosaminoglycan is a negatively charged polysaccharide and one of the most prevalent crosslinks of collagen, that affects their mechanical properties and fibril formation 191 . The main aspect to consider the incorporation into TESSs is the presence of negatively charged carboxyl and sulfate groups that are responsible of maintaining water in tissues 192 , and therefore, skin barrier.

Hyaluronic acid is also an important component of human skin 193 , 194 and its use for TESSs is recommended. It is easy to handle, their biosafety has been corroborated by its use as injectable dermal fillers 195 , and its effectiveness have been demonstrated for skin restoration in terms of hydration and transepidermal water loss 196 , mainly when the water regulation and neoangiogenic boost are relevant issues 197 . Moreover, biodegraded hyaluronic acid, enhances angiogenic pathways and the migration and proliferation of cells 198 .

In the case of plasma/fibrin-based matrices, their use for TESSs have reported positive results due to the presence of many natural components responsible of coagulation and involved in the first stages of wound healing. It has been demonstrated that enhances cell proliferation (keratinocytes mainly), due to the presence of basement membrane proteins such as laminin, collagen or Perlecan 199 .

Finally, amniotic membrane and acellular dermal matrix are the less common biomaterials used for TESSs, however, they also provide structural support and secrete important proteins or factors required for wound healing. Amniotic membrane has high tensile strength due to a structure comprised of an epithelial monolayer, a thick basement membrane and avascular stroma. In addition, it releases several growth factors for angiogenesis, downregulates TGF-β expression, promotes fibroblast differentiation and keratinocytes proliferation, and reduces levels of pain and discomfort experienced by the patients 200 . The use of acellular dermal matrix derived from fibroblast is an interested strategy because the use of natural ECM shares many properties with native human skin and minimizes the host response after transplantation 78 , but specific formation is required to carry out it successfully.

Notwithstanding the tremendous advances in skin tissue engineering, we have yet to construct a complete TESS. Current substitutes are mainly composed of human keratinocytes and fibroblasts, but still lack some of the functional components such as nerves, adnexal structures and pigmentary cells that make up the native skin, and the esthetic and functional outcome is less than ideal.

Moreover, to develop an ideal TESS that could be applied at clinical level, the use of appropriate wound and animal preclinical models is essential. In this review, most of the in vivo studies evaluated excisional or burn wounds in mice or rats. The use of these animals together with other small mammals such as rabbit or guinea pig is due to their cost and easy to handle, however, their anatomical and physiological skin properties and wound healing process differ from the humans (for example, thin epidermis and dermis and heal primarily through wound contraction instead of re-epithelialization) 201 .

After analyzing their properties, many authors suggested that the use of pigs should be the preferred animal model 201 , 202 , 203 , 204 . Among similarities reported, epidermis and dermis of human and pig skin are comprised of four and two layers, respectively, without significant differences of thickness, and dermo‐epidermal junction has an undulating appearance 204 . In terms of functionality, permeability is also similar 204 . However, the use of this model is expensive and more difficult due to their size and for this reason the number of studies with human TESSs is limited 205 or own pig derived cells are used 206 , 207 .

Considering the types of wounds analyzed, burns or full-thickness skin injuries are the most studied models at preclinical level but also in a clinical environment. Application of commercial biological substitutes have been extensively reviewed 208 and analyzed 209 and even the use of cell therapies have reported positive results 210 . However, the development of TESSs constituted of different cell types and biomaterials seems to be essential to increase skin wound healing potential.

Apart from the use of stem cells, even from burned and debrided skin 205 , future perspectives in the field of TESSs for wound healing are focused on the development of more similar models of artificial skin where 3D bioprinting 211 , designing stem cell niches 212 or incorporation of immune cells 10 , 179 , 180 will play an important role.

To date, the positive clinical results obtained with autologous and allogeneic TESSs based on human adult skin cells and hMSCs, regarding successful engraftment (60–90% in most of the studies), safety (slight adverse events in some cases), re-epithelialization and wound healing rates, are promising. However, if we improve current techniques such as the selection of an appropriate animal model and biomaterial or application of 3D bioprinting and expand the toolset with innovative strategies based on ever expanding understanding of skin healing and regeneration (immune cells or stem cell niches), the fabrication of a more functional and physiological TESS, which is clinically beneficial and esthetically acceptable to our patients, is not beyond reach.

Data availability

No datasets were generated or analyzed during the current study.

Naves, L. B., Dhand, C., Almeida, L., Rajamani, L. & Ramakrishna, S. In vitro skin models and tissue engineering protocols for skin graft applications. Essays Biochem. 60 , 357–369 (2016).

Article   PubMed   Google Scholar  

Reinke, J. M. & Sorg, H. Wound repair and regeneration. Eur. Surg. Res. 49 , 35–43 (2012).

Article   CAS   PubMed   Google Scholar  

Rodrigues, M., Kosaric, N., Bonham, C. A. & Gurtner, G. C. Wound healing: a cellular perspective. Physiol. Rev. 99 , 665–706 (2019).

Berk, B. C., Alexander, R. W., Brock, T. A., Gimbrone Jr., M. A. & Webb, R. C. Vasoconstriction: a new activity for platelet-derived growth factor. Science (80-.). 232 , 87–90 (1986).

Article   CAS   Google Scholar  

Pradhan, S., Khatlani, T., Nairn, A. C. & Vijayan, K. V. The heterotrimeric G protein G1 interacts with the catalytic subunit of protein phosphatase 1 and modulates G protein–coupled receptor signaling in platelets. J. Biol. Chem. 292 , 13133–13142 (2017).

Article   CAS   PubMed   PubMed Central   Google Scholar  

Wagner, C. et al. Analysis of GPIIb/IIIa receptor number by quantification of 7E3 binding to human platelets. Blood 88 , 907–914 (1996).

Santoro, S. A. Identification of a 160,000 dalton platelet membrane protein that mediates the initial divalent cation-dependent adhesion of platelets to collagen. Cell 46 , 913–920 (1986).

Bielefeld, K. A., Amini-Nik, S. & Alman, B. A. Cutaneous wound healing: recruiting developmental pathways for regeneration. Cell. Mol. Life Sci. 70 , 2059–2081 (2013).

Van Der Vliet, A. & Janssen-Heininger, Y. M. W. Hydrogen peroxide as a damage signal in tissue injury and inflammation: murderer, mediator, or messenger? J. Cell. Biochem. 115 , 427–435 (2014).

Article   PubMed   PubMed Central   CAS   Google Scholar  

Brazil, J. C., Quiros, M., Nusrat, A. & Parkos, C. A. Innate immune cell–epithelial crosstalk during wound repair. J. Clin. Investig. 129 , 2983–2993 (2019).

Article   PubMed   PubMed Central   Google Scholar  

Dvorak, A. M. Mast cell-derived mediators of enhanced microvascular permeability, vascular permeability factor/vascular endothelial growth factor, histamine, and serotonin, cause leakage of macromolecules through a new endothelial cell permeability organelle, the vesiculo-vacuolar organelle. Chem. Immunol. Allergy 85 , 185–204 (2005).

Stone li, R. et al. Advancements in regenerative strategies through the continuum of burn care. Front. Pharmacol. 9 , 672 (2018).

Liu, Z.-J. et al. Regulation of Notch1 and Dll4 by vascular endothelial growth factor in arterial endothelial cells: implications for modulating arteriogenesis and angiogenesis. Mol. Cell. Biol. 23 , 14–25 (2003).

Hobbs, R. M., Silva-Vargas, V., Groves, R. & Watt, F. M. Expression of activated MEK1 in differentiating epidermal cells is sufficient to generate hyperproliferative and inflammatory skin lesions. J. Invest. Dermatol. 123 , 503–515 (2004).

Pastar, I. et al. Epithelialization in wound healing: a comprehensive review. Adv. Wound Care 3 , 445–464 (2014).

Article   Google Scholar  

Watt, F. M., Celso, C., Lo & Silva-Vargas, V. Epidermal stem cells: an update. Curr. Opin. Genet. Dev. 16 , 518–524 (2006).

Fuchs, E. Skin stem cells: rising to the surface. J. Cell Biol. 180 , 273–284 (2008).

Ito, M. et al. Stem cells in the hair follicle bulge contribute to wound repair but not to homeostasis of the epidermis. Nat. Med. 11 , 1351–1354 (2005).

Gurtner, G. C., Werner, S., Barrandon, Y. & Longaker, M. T. Wound repair and regeneration. Nature 453 , 314–321 (2008).

Vig, K. et al. Advances in skin regeneration using tissue engineering. Int. J. Mol. Sci . 18 , 789 (2017).

Sierra-Sánchez, Á., Montero-Vilchez, T., Quiñones-Vico, M. I., Sanchez-Diaz, M. & Arias-Santiago, S. Current advanced therapies based on human mesenchymal stem cells for skin diseases. Front. Cell Dev. Biol. 9 , 643125 (2021).

Sharma, P., Kumar, P., Sharma, R., Bhatt, V. D. & Dhot, P. S. Tissue engineering; current status & futuristic scope. J. Med. life 12 , 225–229 (2019).

Olson, J. L., Atala, A. & Yoo, J. J. Tissue engineering: current strategies and future directions. Chonnam Med. J. 47 , 1 (2011).

Ikada, Y. Challenges in tissue engineering. J. R. Soc. Interface 3 , 589–601 (2006).

Sheridan, R. L. & Tompkins, R. G. Skin substitutes in burns. Burns 25 , 97–103 (1999).

Davison-Kotler, E., Sharma, V., Kang, N. V. & García-Gareta, E. A universal classification system of skin substitutes inspired by factorial design. Tissue Eng. Part B Rev. 24 , 279–288 (2018).

Boyce, S. T. & Lalley, A. L. Tissue engineering of skin and regenerative medicine for wound care. Burn. Trauma 6 , 4 (2018).

Dong, C., Lv, Y., Dong, C. & Lv, Y. Application of collagen scaffold in tissue engineering: recent advances and new perspectives. Polymers (Basel). 8 , 42 (2016).

Article   PubMed Central   CAS   Google Scholar  

Mohd Hilmi, A. B., Halim, A. S., Jaafar, H., Asiah, A. B. & Hassan, A. Chitosan dermal substitute and Chitosan skin substitute contribute to accelerated full-thickness wound healing in irradiated rats. Biomed. Res. Int . 2013 , 795458 (2013).

Rodríguez-Cabello, J. C., González de Torre, I., Ibañez-Fonseca, A. & Alonso, M. Bioactive scaffolds based on elastin-like materials for wound healing. Adv. Drug Deliv. Rev. 129 , 118–133 (2018).

Article   PubMed   CAS   Google Scholar  

Mineo, A., Suzuki, R. & Kuroyanagi, Y. Development of an artificial dermis composed of hyaluronic acid and collagen. J. Biomater. Sci. Polym. Ed. 24 , 726–740 (2013).

Sierra-Sánchez, Á. et al. Hyaluronic acid biomaterial for human tissue-engineered skin substitutes: Preclinical comparative in vivo study of wound healing. J. Eur. Acad. Dermatol. Venereol. 34 , 2414–2427 (2020).

Chaudhari, A. A. et al. Future prospects for scaffolding methods and biomaterials in skin tissue engineering: a review. Int. J. Mol. Sci. 17 , 1974 (2016).

Rheinwald, J. G. & Green, H. Serial cultivation of strains of human epidemal keratinocytes: the formation of keratinizing colonies from single cells. Cell 6 , 344 (1975).

Google Scholar  

Chocarro-Wrona, C., López-Ruiz, E., Perán, M., Gálvez-Martín, P. & Marchal, J. A. Therapeutic strategies for skin regeneration based on biomedical substitutes. J. Eur. Acad. Dermatol. Venereol. 33 , 484–496 (2019).

Dill, V. & Mörgelin, M. Biological dermal templates with native collagen scaffolds provide guiding ridges for invading cells and may promote structured dermal wound healing. Int. Wound J . 13314 https://doi.org/10.1111/iwj.13314 (2020).

Kalyanaraman, B. & Boyce, S. T. Wound healing on athymic mice with engineered skin substitutes fabricated with keratinocytes harvested from an automated bioreactor. J. Surg. Res. 152 , 296–302 (2009).

Ghetti, M. et al. Subpopulations of dermal skin fibroblasts secrete distinct extracellular matrix: implications for using skin substitutes in the clinic. Br. J. Dermatol. 179 , 381–393 (2018).

CAS   PubMed   PubMed Central   Google Scholar  

Rennekampff, H. O., Kiessig, V., Griffey, S., Greenleaf, G. & Hansbrough, J. F. Acellular human dermis promotes cultured keratinocyte engraftment. J. Burn Care Rehabil. 18 , 535–544 (1997).

Horch, R. E. et al. Keratinocyte monolayers on hyaluronic acid membranes as ‘upside-down’ grafts reconstitute full-thickness wounds. Med. Sci. Monit. 25 , 6702–6710 (2019).

O’Connor, N. E., Mulliken, J. B., Banks-Schlegel, S., Kehinde, O. & Green, H. Grafting of burns with cultured epithelium prepared from autologous epidermal cells. Lancet 317 , 75–78 (1981).

Teepe, R. G. C. et al. The use of cultured autologous epidermis in the treatment of extensive burn wounds. J. Trauma 30 , 269–275 (1990).

Blight, A., Mountford, E. M., Cheshire, I. M., Clancy, J. M. P. & Levick, P. L. Treatment of full skin thickness burn injury using cultured epithelial grafts. Burns 17 , 495–498 (1991).

Donati, L., Magliacani, G., Bormioli, M., Signorini, M. & Baruffaldi Preis, F. W. Clinical experiences with keratinocyte grafts. Burns 18 , S19–S26 (1992).

Rue, L. W., Cioffi, W. G., McManus, W. F. & Pruitt, B. A. Wound closure and outcome in extensively burned patients treated with cultured autologous keratinocytes. J. Trauma 34 , 662–668 (1993).

Hickerson, W. L., Compton, C., Fletchall, S. & Smith, L. R. Cultured epidermal autografts and allodermis combination for permanent burn wound coverage. Burns 20 , S52–S55 (1994).

Williamson, J. S., Snelling, C. F., Clugston, P., Macdonald, I. B. & Germann, E. Cultured epithelial autograft: five years of clinical experience with twenty-eight patients. J. Trauma 39 , 309–319 (1995).

Paddle-Ledinek, J. E., Cruickshank, D. G. & Masterton, J. P. Skin replacement by cultured keratinocyte grafts: an Australian experience. Burns 23 , 204–211 (1997).

Pellegrini, G. et al. The control of epidermal stem cells (holoclones) in the treatment of massive full-thickness burns with autologous keratinocytes cultured on fibrin. Transplantation 68 , 868–879 (1999).

Barret, J. P., Wolf, S. E., Desai, M. H. & Herndon, D. N. Cost-efficacy of cultured epidermal autografts in massive pediatric burns. Ann. Surg. 231 , 869–876 (2000).

Ronfard, V., Rives, J. M., Neveux, Y., Carsin, H. & Barrandon, Y. Long-term regeneration of human epidermis on third degree burns transplanted with autologous cultured epithelium grown on a fibrin matrix. Transplantation 70 , 1588–1598 (2000).

Yamaguchi, Y. et al. Epithelial-mesenchymal interactions in wounds: treatment of palmoplantar wounds by nonpalmoplantar pure epidermal sheet grafts. Arch. Dermatol. 137 , 621–628 (2001).

CAS   PubMed   Google Scholar  

Sheridan, R. L. et al. Initial experience with a composite autologous skin substitute. Burns 27 , 421–424 (2001).

Elliott, M. & Vandervord, J. Initial experience with cultured epithelial autografts in massively burnt patients. ANZ J. Surg. 72 , 893–895 (2002).

Pajardi, G. et al. Skin substitutes based on allogenic fibroblasts or keratinocytes for chronic wounds not responding to conventional therapy: a retrospective observational study. Int. Wound J. 13 , 44–52 (2016).

Gardien, K. L. M. et al. Outcome of burns treated with autologous cultured proliferating epidermal cells: a prospective randomized multicenter intrapatient comparative trial. Cell Transplant. 25 , 437–448 (2016).

Łabuś, W. et al. Atomic force microscopy in the production of a biovital skin graft based on human acellular dermal matrix produced in-house and in vitro cultured human fibroblasts. J. Biomed. Mater. Res. Part B Appl. Biomater. 106 , 726–733 (2018).

Jang, H. J., Kim, Y. M., Yoo, B. Y. & Seo, Y. K. Wound-healing effects of human dermal components with gelatin dressing. J. Biomater. Appl. 32 , 716–724 (2018).

Mazio, C. et al. Pre-vascularized dermis model for fast and functional anastomosis with host vasculature. Biomaterials 192 , 159–170 (2019).

Kashiwa, N. et al. Treatment of full-thickness skin defect with concomitant grafting of 6-fold extended mesh auto-skin and allogeneic cultured dermal substitute. Artif. Organs 28 , 444–450 (2004).

Hasegawa, T. et al. An allogeneic cultured dermal substitute suitable for treating intractable skin ulcers and large skin defects prior to autologous skin grafting: three case reports. J. Dermatol. 32 , 715–720 (2005).

Yonezawa, M. et al. Clinical study with allogeneic cultured dermal substitutes for chronic leg ulcers. Int. J. Dermatol. 46 , 36–42 (2007).

Yamada, N., Uchinuma, E., Matsumoto, Y. & Kuroyanagi, Y. Comparative evaluation of re-epithelialization promoted by fresh or cryopreserved cultured dermal substitute. J. Artif. Organs 11 , 221–224 (2008).

Yamada, N., Uchinuma, E. & Kuroyanagi, Y. Clinical trial of allogeneic cultured dermal substitutes for intractable skin ulcers. J. Artif. Organs 15 , 193–199 (2012).

Taniguchi, T., Amoh, Y., Tanabe, K., Katsuoka, K. & Kuroyanagi, Y. Treatment of intractable skin ulcers caused by vascular insufficiency with allogeneic cultured dermal substitute: a report of eight cases. J. Artif. Organs 15 , 77–82 (2012).

You, H. J., Han, S. K. & Rhie, J. W. Randomised controlled clinical trial for autologous fibroblast-hyaluronic acid complex in treating diabetic foot ulcers. J. Wound Care 23 , 521–530 (2014).

Morimoto, N. et al. An exploratory clinical study on the safety and efficacy of an autologous fibroblast-seeded artificial skin cultured with animal product-free medium in patients with diabetic foot ulcers. Int. Wound J. 11 , 183–189 (2014).

Momeni, M. et al. A randomized, double-blind, phase I clinical trial of fetal cell-based skin substitutes on healing of donor sites in burn patients. Burns 45 , 914–922 (2019).

Sun, B. K., Siprashvili, Z. & Khavari, P. A. Advances in skin grafting and treatment of cutaneous wounds. Science 346 , 941–945 (2014).

Bell, E., Ehrlich, H. P., Buttle, D. J. & Nakatsuji, T. Living tissue formed in vitro and accepted as skin-equivalent tissue of full thickness. Science 211 , 1052–1054 (1981).

Pontiggia, L. et al. Markers to evaluate the quality and self-renewing potential of engineered human skin substitutes in vitro and after transplantation. J. Invest. Dermatol. 129 , 480–490 (2009).

Hartmann-Fritsch, F. et al. Collagen hydrogels strengthened by biodegradable meshes are a basis for dermo-epidermal skin grafts intended to reconstitute human skin in a one-step surgical intervention. J. Tissue Eng. Regen. Med. 10 , 81–91 (2016).

Supp, D. M. et al. Collagen VII expression is required in both keratinocytes and fibroblasts for anchoring fibril formation in bilayer engineered skin substitutes. Cell Transplant. 28 , 1242–1256 (2019).

Bacakova, M. et al. A two-layer skin construct consisting of a collagen hydrogel reinforced by a fibrin-coated polylactide nanofibrous membrane. Int. J. Nanomed. 14 , 5033–5050 (2019).

L’Heureux, N. et al. A human tissue-engineered vascular media: a new model for pharmacological studies of contractile responses. FASEB J. 15 , 515–524 (2001).

Michel, M. et al. Characterization of a new tissue-engineered human skin equivalent with hair. In Vitro Cell. Dev. Biol. Anim. 35 , 318–326 (1999).

Beaudoin Cloutier, C. et al. Production of a bilayered self-assembled skin substitute using a tissue-engineered acellular dermal matrix. Tissue Eng. -Part C. Methods 21 , 1297–1305 (2015).

Larouche, D. et al. Improved methods to produce tissue-engineered skin substitutes suitable for the permanent closure of full-thickness skin injuries. Biores. Open Access 5 , 320–329 (2016).

Beaudoin Cloutier, C. et al. In vivo evaluation and imaging of a bilayered self-assembled skin substitute using a decellularized dermal matrix grafted on mice. Tissue Eng. 23 , 313–322 (2017).

Cantin-Warren, L. et al. Specialized living wound dressing based on the self-assembly approach of tissue engineering. J. Funct. Biomater . 9 , 53 (2018).

bin Mh Busra, M. F., Chowdhury, S. R., bin Ismail, F., bin Saim, A. & Idrus, R. H. Tissue-engineered skin substitute enhances wound healing after radiation therapy. Adv. Ski. Wound Care 29 , 120–129 (2016).

Klar, A. S., Biedermann, T., Simmen-Meuli, C., Reichmann, E. & Meuli, M. Comparison of in vivo immune responses following transplantation of vascularized and non-vascularized human dermo-epidermal skin substitutes. Pediatr. Surg. Int. 33 , 377–382 (2017).

Asano, Y., Shimoda, H., Okano, D., Matsusaki, M. & Akashi, M. Transplantation of three-dimensional artificial human vascular tissues fabricated using an extracellular matrix nanofilm-based cell-accumulation technique. J. Tissue Eng. Regen. Med. 11 , 1303–1307 (2017).

Dai, N. T. et al. Development of a novel pre-vascularized three-dimensional skin substitute using blood plasma gel. Cell Transplant. 27 , 1535–1547 (2018).

Miyazaki, H. et al. A novel strategy to engineer pre-vascularized 3-dimensional skin substitutes to achieve efficient, functional engraftment. Sci. Rep. 9 , 7797 (2019).

Hansbrough, J. F., Boyce, S. T., Cooper, M. L. & Foreman, T. J. Burn wound closure with cultured autologous keratinocytes and fibroblasts attached to a collagen-glycosaminoglycan substrate. JAMA J. Am. Med. Assoc. 262 , 2125–2130 (1989).

Kuroyanagi, Y. et al. A cultured skin substitute composed of fibroblasts and keratinocytes with a collagen matrix: preliminary results of clinical trials. Ann. Plast. Surg. 31 , 340–351 (1993).

Boyce, S. T. et al. Comparative assessment of cultured skin substitutes and native skin autograft for treatment of full-thickness burns. Ann. Surg. 222 , 743–752 (1995).

Dana Harriger, M., Warden, G. D., Greenhalgh, D. G., Kagan, R. J. & Boyce, S. T. Pigmentation and microanatomy of skin regenerated from composite grafts of cultured cells and biopolymers applied to full-thickness burn wounds. Transplantation 59 , 702–707 (1995).

Muhart, M., McFalls, S., Kirsner, R., Kerdel, F. & Eaglstein, W. H. Bioengineered skin [2]. Lancet 350 , 1142 (1997).

Boyce, S. T., Kagan, R. J., Meyer, N. A., Yakuboff, K. P. & Warden, G. D. Cultured skin substitutes combined with integra artificial skin to replace native skin autograft and allograft for the closure of excised full- thickness burns. J. Burn Care Rehabilit. 20 , 453–461 (1999).

Boyce, S. T. et al. Cultured skin substitutes reduce donor skin harvesting for closure of excised, full-thickness burns. Ann. Surg. 235 , 269–279 (2002).

Nanchahal, J., Dover, R. & Otto, W. R. Allogeneic skin substitutes applied to burns patients. Burns 28 , 254–257 (2002).

Llames, S. G. et al. Human plasma as a dermal scaffold for the generation of a completely autologous bioengineered skin. Transplantation 77 , 350–355 (2004).

Boyce, S. T. et al. Cultured skin substitutes reduce requirements for harvesting of skin autograft for closure of excised, full-thickness burns. J. Trauma 60 , 821–829 (2006).

PubMed   Google Scholar  

Llames, S. et al. Clinical results of an autologous engineered skin. Cell Tissue Bank. 7 , 47–53 (2006).

Scuderi, N., Anniboletti, T., Carlesimo, B. & Onesti, M. G. Clinical application of autologous three-cellular cultured skin substitutes based on esterified hyaluronic acid scaffold: our experience. In Vivo (Brooklyn). 23 , 991–1003 (2009).

Gómez, C. et al. Use of an autologous bioengineered composite skin in extensive burns: Clinical and functional outcomes. A multicentric study. Burns 37 , 580–589 (2011).

Boa, O. et al. Prospective study on the treatment of lower-extremity chronic venous and mixed ulcers using tissue-engineered skin substitute made by the self-assembly approach. Adv. Ski. Wound Care 26 , 400–409 (2013).

Takami, Y., Yamaguchi, R., Ono, S. & Hyakusoku, H. Clinical application and histological properties of autologous tissue-engineered skin equivalents using an acellular dermal matrix. J. Nippon Med. Sch. 81 , 356–366 (2014).

Golinski, P. et al. Development and characterization of an engraftable tissue-cultured skin autograft: alternative treatment for severe electrical injuries? Cells Tissues Organs 200 , 227–239 (2015).

Kljenak, A. et al. Fibrin gel as a scaffold for skin substitute–production and clinical experience. Acta Clin. Croat. 55 , 279–289 (2016).

Fernández-González, A. et al. Clinical, histological and homeostasis evaluation of an autologous tissue bio-engineered skin substitute in a patient with 70% of total body surface area (TBSA) burn. Cytotherapy 19 , S233 (2017).

Boyce, S. T. et al. Randomized, paired-site comparison of autologous engineered skin substitutes and split-thickness skin graft for closure of extensive, full-thickness burns. J. Burn Care Res. 38 , 61–70 (2017).

Germain, L. et al. Autologous bilayered self-assembled skin substitutes (SASSs) as permanent grafts: a case series of 14 severely burned patients indicating clinical effectiveness. Eur. Cells Mater. 36 , 128–141 (2018).

Meuli, M. et al. A cultured autologous dermo-epidermal skin substitute for full-thickness skin defects: a phase I, open, prospective clinical trial in children. Plast. Reconstr. Surg. 144 , 188–198 (2019).

Liu, Y. et al. Reconstruction of a tissue-engineered skin containing melanocytes. Cell Biol. Int. 31 , 985–990 (2007).

Biedermann, T. et al. Tissue-engineered dermo-epidermal skin analogs exhibit de novo formation of a near natural neurovascular link 10 weeks after transplantation. Pediatr. Surg. Int. 30 , 165–172 (2014).

Biedermann, T., Klar, A. S., Böttcher-Haberzeth, S., Reichmann, E. & Meuli, M. Myelinated and unmyelinated nerve fibers reinnervate tissue-engineered dermo-epidermal human skin analogs in an in vivo model. Pediatr. Surg. Int. 32 , 1183–1191 (2016).

Klar, A. S. et al. Differential expression of granulocyte, macrophage, and hypoxia markers during early and late wound healing stages following transplantation of tissue-engineered skin substitutes of human origin. Pediatr. Surg. Int. 30 , 1257–1264 (2014).

Boyce, S. T. et al. Restoration of cutaneous pigmentation by transplantation to mice of isogeneic human melanocytes in dermal-epidermal engineered skin substitutes. Pigment Cell Melanoma Res. 30 , 531–540 (2017).

Goyer, B. et al. Impact of ultraviolet radiation on dermal and epidermal DNA damage in a human pigmented bilayered skin substitute. J. Tissue Eng. Regen. Med. 13 , 2300–2311 (2019).

Supp, D. M. et al. Light or dark pigmentation of engineered skin substitutes containing melanocytes protects against ultraviolet light-induced DNA damage in vivo. J. Burn Care Res . https://doi.org/10.1093/JBCR/IRAA029 (2020).

Deckers, J., Hammad, H. & Hoste, E. Langerhans cells: sensing the environment in health and disease. Front. Immunol. 9 , 93 (2018).

Abraham, J. & Mathew, S. Merkel cells: a collective review of current concepts. Int. J. Appl. basic Med. Res. 9 , 9–13 (2019).

Bechetoille, N. et al. Effects of solar ultraviolet radiation on engineered human skin equivalent containing both langerhans cells and dermal dendritic cells. Tissue Eng. 13 , 2667–2679 (2007).

Laubach, V. et al. Integration of Langerhans-like cells into a human skin equivalent. Arch. Dermatol. Res. 303 , 135–139 (2011).

Fransson, J., Heffler, L. C., Linder, M. T. & Scheynius, A. Culture of human epidermal Langerhans cells in a skin equivalent. Br. J. Dermatol. 139 , 598–604 (1998).

Régnier, M., Patwardhan, A., Scheynius, A. & Schmidt, R. Reconstructed human epidermis composed of keratinocytes, melanocytes and Langerhans cells. Med. Biol. Eng. Comput. 36 , 821–824 (1998).

Hafemann, B. et al. Use of a collagen/elastin-membrane for the tissue engineering of dermis. Burns 25 , 373–384 (1999).

Centanni, J. M. et al. Stratagraft skin substitute is well-tolerated and is not acutely immunogenic in patients with traumatic wounds: Results from a prospective, randomized, controlled dose escalation trial. Ann. Surg. 253 , 672–683 (2011).

Hahn, J. M. et al. Identification of Merkel cells associated with neurons in engineered skin substitutes after grafting to full thickness wounds. PLoS ONE 14 , e0213325 (2019).

Ojeh, N., Pastar, I., Tomic-Canic, M. & Stojadinovic, O. Stem cells in skin regeneration, wound healing, and their clinical applications. Int. J. Mol. Sci. 16 , 16 (2015).

Shi, C., Zhu, Y., Su, Y. & Cheng, T. Stem cells and their applications in skin-cell therapy. Trends Biotechnol. 24 , 48–52 (2006).

Martin, M. T., Vulin, A. & Hendry, J. H. Human epidermal stem cells: role in adverse skin reactions and carcinogenesis from radiation. Mutat. Res. -Rev. Mutat. Res. 770 , 349–368 (2016).

Potten, C. S. & Booth, C. Keratinocyte stem cells: a commentary. J. Invest. Dermatol. 119 , 888–899 (2002).

Sellheyer, K. & Krahl, D. Skin mesenchymal stem cells: prospects for clinical dermatology. J. Am. Acad. Dermatol. 63 , 859–865 (2010).

Jeremias, T. et al. Dermal substitutes support the growth of human skin-derived mesenchymal stromal cells: potential tool for skin regeneration. PLoS ONE 9 , e89542 (2014).

Salerno, S. et al. Dermal-epidermal membrane systems by using human keratinocytes and mesenchymal stem cells isolated from dermis. Mater. Sci. Eng. C. 71 , 943–953 (2017).

Leirós, G. J. et al. Dermal papilla cells improve the wound healing process and generate hair bud-like structures in grafted skin substitutes using hair follicle stem cells. Stem Cells Transl. Med. 3 , 1209–1219 (2014).

Higgins, C. A. et al. Multifaceted role of hair follicle dermal cells in bioengineered skins. Br. J. Dermatol. 176 , 1259–1269 (2017).

Mohd Hilmi, A. B., Hassan, A. & Halim, A. S. A bilayer engineered skin substitute for wound repair in an irradiation-impeded healing model on rat. Adv. Wound Care 4 , 312–320 (2015).

Michalak-Micka, K. et al. Impact of human mesenchymal cells of different body site origins on the maturation of dermo-epidermal skin substitutes. Pediatr. Surg. Int. 35 , 121–127 (2019).

Zomer, H. D., Jeremias, T., da, S., Ratner, B. & Trentin, A. G. Mesenchymal stromal cells from dermal and adipose tissues induce macrophage polarization to a pro-repair phenotype and improve skin wound healing. Cytotherapy https://doi.org/10.1016/j.jcyt.2020.02.003 (2020).

Takahashi, K. et al. Induction of pluripotent stem cells from adult human fibroblasts by defined factors. Cell 131 , 861–872 (2007).

Itoh, M. et al. Generation of 3D skin equivalents fully reconstituted from human induced pluripotent stem cells (iPSCs). PLoS ONE 8 , e77673 (2013).

Gledhill, K. et al. Melanin transfer in human 3D skin equivalents generated exclusively from induced pluripotent stem cells. PLoS ONE 10 , e0136713 (2015).

Petrova, A. et al. 3D in vitro model of a functional epidermal permeability barrier from human embryonic stem cells and induced pluripotent stem cells. Stem Cell Rep. 2 , 675–689 (2014).

Kim, Y. et al. Establishment of a complex skin structure via layered co-culture of keratinocytes and fibroblasts derived from induced pluripotent stem cells. Stem Cell Res. Ther. 9 , 217 (2018).

Muller, Q. et al. Development of an innervated tissue-engineered skin with human sensory neurons and Schwann cells differentiated from iPS cells. Acta Biomater. 82 , 93–101 (2018).

Lin, Y. & Hogan, W. J. Clinical application of mesenchymal stem cells in the treatment and prevention of graft-versus-host disease. Adv. Hematol. 2011 , 1–17 (2011).

Liang, J. et al. Allogenic mesenchymal stem cells transplantation in refractory systemic lupus erythematosus: a pilot clinical study. Ann. Rheum. Dis. 69 , 1423–1429 (2010).

Koppula, P. R., Chelluri, L. K., Polisetti, N. & Vemuganti, G. K. Histocompatibility testing of cultivated human bone marrow stromal cells–A promising step towards pre-clinical screening for allogeneic stem cell therapy. Cell. Immunol. 259 , 61–65 (2009).

Squillaro, T., Peluso, G. & Galderisi, U. Clinical trials with mesenchymal stem cells: an update. Cell Transplant. 25 , 829–848 (2016).

Ankrum, J. A., Ong, J. F. & Karp, J. M. Mesenchymal stem cells: immune evasive, not immune privileged. Nat. Biotechnol. 32 , 252–260 (2014).

Lohan, P., Treacy, O., Griffin, M. D., Ritter, T. & Ryan, A. E. Anti-donor immune responses elicited by allogeneic mesenchymal stem cells and their extracellular vesicles: are we still learning? Front. Immunol . 8 , 1626 (2017).

Galipeau, J. & Sensébé, L. Mesenchymal stromal cells: clinical challenges and therapeutic opportunities. Cell Stem Cell 22 , 824–833 (2018).

Di Nicola, M. et al. Human bone marrow stromal cells suppress T-lymphocyte proliferation induced by cellular or nonspecific mitogenic stimuli. Blood 99 , 3838–3843 (2002).

Seo, B. F., Kim, K. J., Kim, M. K. & Rhie, J. W. The effects of human keratinocyte coculture on human adipose-derived stem cells. Int. Wound J. 13 , 630–635 (2016).

Zuk, P. A. et al. Human adipose tissue is a source of multipotent stem cells. Mol. Biol. Cell 13 , 4279–4295 (2002).

Ghannam, S. et al. Mesenchymal stem cells inhibit human Th17 cell differentiation and function and induce a T regulatory cell phenotype. J. Immunol. 185 , 302–312 (2010).

Martin-Piedra, M. et al. Effective use of mesenchymal stem cells in human skin substitutes generated by tissue engineering. Eur. Cells Mater. 37 , 233–249 (2019).

He, L. J. et al. Full-thickness tissue engineered skin constructed with autogenic bone marrow mesenchymal stem cells. Sci. China, Ser. C. Life Sci. 50 , 429–437 (2007).

Ojeh, N. O. & Navsaria, H. A. An in vitro skin model to study the effect of mesenchymal stem cells in wound healing and epidermal regeneration. J. Biomed. Mater. Res. 102 , 2785–2792 (2014).

Kalaszczynska, I. & Ferdyn, K. Wharton’s jelly derived mesenchymal stem cells: future of regenerative medicine? Recent findings and clinical significance. Biomed. Res. Int. 2015 , 430847 (2015).

Garzón, I. et al. Wharton’s jelly stem cells: a novel cell source for oral mucosa and skin epithelia regeneration. Stem Cells Transl. Med. 2 , 625–632 (2013).

Ertl, J. et al. Comparative study of regenerative effects of mesenchymal stem cells derived from placental amnion, chorion and umbilical cord on dermal wounds. Placenta 65 , 37–46 (2018).

Shi, S., Jia, S., Liu, J. & Chen, G. Accelerated regeneration of skin injury by co-transplantation of mesenchymal stem cells from Wharton’s jelly of the human umbilical cord mixed with microparticles. Cell Biochem. Biophys. 71 , 951–956 (2015).

Millán-Rivero, J. E. et al. Silk fibroin scaffolds seeded with Wharton’s jelly mesenchymal stem cells enhance re-epithelialization and reduce formation of scar tissue after cutaneous wound healing. Stem Cell Res. Ther . 10 , 126 (2019).

Chavez-Munoz, C. et al. Transdifferentiation of adipose-derived stem cells into keratinocyte-like cells: engineering a stratified epidermis. PLoS ONE 8 , e80587 (2013).

Ebrahimian, T. G. et al. Cell therapy based on adipose tissue-derived stromal cells promotes physiological and pathological wound healing. Arterioscler. Thromb. Vasc. Biol. 29 , 503–510 (2009).

Paganelli, A. et al. In vitro engineering of a skin substitute based on adipose-derived stem cells. Cells Tissues Organs 207 , 46–57 (2019).

Moriyama, M. et al. Adipose-derived stromal/stem cells improve epidermal homeostasis. Sci. Rep. 9 , 18371 (2019).

Motamed, S. et al. Cell-based skin substitutes accelerate regeneration of extensive burn wounds in rats. Am. J. Surg. 214 , 762–769 (2017).

Zhang, A.-J., Jiang, T., Li, Q., Jin, P.-S. & Tan, Q. Experimental research on ADSCs-NCSS in wound repair. Exp. Ther. Med. 16 , 4429–4436 (2018).

Mendez, J. J. et al. Mesenchymal stromal cells form vascular tubes when placed in fibrin sealant and accelerate wound healing in vivo. Biomaterials 40 , 61–71 (2015).

Huang, S.-P. et al. Adipose-derived stem cells seeded on acellular dermal matrix grafts enhance wound healing in a murine model of a full-thickness defect. Ann. Plast. Surg. 69 , 656–662 (2012).

Sánchez-Muñoz, I. et al. The use of adipose mesenchymal stem cells and human umbilical vascular endothelial cells on a fibrin matrix for endothelialized skin substitute. Tissue Eng. 21 , 214–223 (2015).

Klar, A. S. et al. Human adipose mesenchymal cells inhibit melanocyte differentiation and the pigmentation of human skin via increased expression of TGF-β1. J. Invest. Dermatol. 137 , 2560–2569 (2017).

Klar, A. S. et al. Tissue-engineered dermo-epidermal skin grafts prevascularized with adipose-derived cells. Biomaterials 35 , 5065–5078 (2014).

Klar, A. S. et al. Characterization of vasculogenic potential of human adipose-derived endothelial cells in a three-dimensional vascularized skin substitute. Pediatr. Surg. Int. 32 , 17–27 (2016).

Vojtassák, J. et al. Autologous biograft and mesenchymal stem cells in treatment of the diabetic foot. Neuro Endocrinol. Lett. 27 , 134–137 (2006).

Yoshikawa, T. et al. Wound therapy by marrow mesenchymal cell transplantation. Plast. Reconstr. Surg. 121 , 860–877 (2008).

Xu, Y., Huang, S., Fu, X. & Fu, X. Autologous transplantation of bone marrow-derived mesenchymal stem cells: a promising therapeutic strategy for prevention of skin-graft contraction. Clin. Exp. Dermatol. 37 , 497–500 (2012).

Arkoulis, N., Watson, S. & Weiler-Mithoff, E. Stem cell enriched dermal substitutes for the treatment of late burn contractures in patients with major burns. Burns 44 , 724–726 (2018).

Moon, K. C. et al. Potential of allogeneic adipose-derived stem cell–hydrogel complex for treating diabetic foot ulcers. Diabetes 68 , 837–846 (2019).

Stessuk, T. et al. A topical cell therapy approach for diabetic chronic ulcers: effects of mesenchymal stromal cells associated with platelet-rich plasma. J. Cosmet. Dermatol. https://doi.org/10.1111/jocd.13321 (2020).

Hashemi, S. S. et al. The healing effect of Wharton’s jelly stem cells seeded on biological scaffold in chronic skin ulcers: a randomized clinical trial. J. Cosmet. Dermatol. 18 , 1961–1967 (2019).

Naik, S., Larsen, S. B., Cowley, C. J. & Fuchs, E. Two to tango: dialog between immunity and stem cells in health and disease. Cell 175 , 908–920 (2018).

Ali, N. & Rosenblum, M. D. Regulatory T cells in skin. Immunology 152 , 372–381 (2017).

O’Neill, L. A. J., Kishton, R. J. & Rathmell, J. A guide to immunometabolism for immunologists. Nat. Rev. Immunol. 16 , 553–565 (2016).

Castellana, D., Paus, R. & Perez-Moreno, M. Macrophages contribute to the cyclic activation of adult hair follicle stem cells. PLoS Biol. 12 , e1002002 (2014).

Shook, B., Xiao, E., Kumamoto, Y., Iwasaki, A. & Horsley, V. CD301b+ macrophages are essential for effective skin wound healing. J. Invest. Dermatol. 136 , 1885–1891 (2016).

Liu, Y. et al. TGF-β1 promotes scar fibroblasts proliferation and transdifferentiation via up-regulating MicroRNA-21. Sci. Rep . 6 , 32231 (2016).

Han, Y. M. et al. Imbalance of T-helper 17 and regulatory T cells in patients with alopecia areata. J. Dermatol. 42 , 981–988 (2015).

Castela, E. et al. Effects of low-dose recombinant interleukin 2 to promote T-regulatory cells in alopecia areata. JAMA Dermatol. 150 , 748–751 (2014).

Phillips, T. J. et al. The longevity of a bilayered skin substitute after application to venous ulcers. Arch. Dermatol. 138 , 1079–1081 (2002).

Zangi, L. et al. Direct imaging of immune rejection and memory induction by allogeneic mesenchymal stromal cells. Stem Cells 27 , 2865–2874 (2009).

Dixit, S. et al. Immunological challenges associated with artificial skin grafts: Available solutions and stem cells in future design of synthetic skin. J. Biol. Eng. 11 , 49 (2017).

Chattopadhyay, S. & Raines, R. T. Review collagen-based biomaterials for wound healing. Biopolymers 101 , 821–833 (2014).

Bi, Y., Patra, P. & Faezipour, M. Structure of collagen-glycosaminoglycan matrix and the influence to its integrity and stability. in 2014 36th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBC 2014. Vol. 2014, 3949–3952 (Institute of Electrical and Electronics Engineers Inc., 2014).

Lee, D. H., Oh, J. H. & Chung, J. H. Glycosaminoglycan and proteoglycan in skin aging. J. Dermatological Sci. 83 , 174–181 (2016).

Fallacara, A., Manfredini, S., Durini, E. & Vertuani, S. Hyaluronic acid fillers in soft tissue regeneration. Facial Plast. Surg. 33 , 087–096 (2017).

Yang, J.-A. et al. Transdermal delivery of hyaluronic acid–Human growth hormone conjugate. Biomaterials 33 , 5947–5954 (2012).

Greene, J. J. & Sidle, D. M. The hyaluronic acid fillers. Facial Plast. Surg. Clin. North Am. 23 , 423–432 (2015).

Nicoletti, G. et al. Long-term in vivo assessment of bioengineered skin substitutes: a clinical study. J. Tissue Eng. Regen. Med. 9 , 460–468 (2015).

Nicoletti, G. et al. Versatile use of dermal substitutes: a retrospective survey of 127 consecutive cases. Indian J. Plast. Surg. 51 , 46–53 (2018).

Chen, W. Y. & Abatangelo, G. Functions of hyaluronan in wound repair. Wound Repair Regen. 7 , 79–89 (1999).

Alexaline, M. M. et al. Influence of fibrin matrices and their released factors on epidermal substitute phenotype and engraftment. J. Tissue Eng. Regen. Med. 13 , 1362–1374 (2019).

Lo, V. & Pope, E. Amniotic membrane use in dermatology. Int. J. Dermatol. 48 , 935–940 (2009).

Sullivan, T. P., Eaglstein, W. H., Davis, S. C. & Mertz, P. The pig as a model for human wound healing. Wound Repair Regen. 9 , 66–76 (2001).

Debeer, S. et al. Comparative histology and immunohistochemistry of porcine versus human skin. Eur. J. Dermatol. 23 , 456–466 (2013).

Stricker-Krongrad, A., Shoemake, C. R. & Bouchard, G. F. The miniature swine as a model in experimental and translational medicine. Toxicol. Pathol. 44 , 612–623 (2016).

Khiao In, M. et al. Histological and functional comparisons of four anatomical regions of porcine skin with human abdominal skin. Anat. Histol. Embryol. 48 , 207–217 (2019).

Amini-Nik, S. et al. Stem cells derived from burned skin-The future of burn care. EBioMedicine 37 , 509–520 (2018).

Dearman, B. L., Stefani, K., Li, A. & Greenwood, J. E. Take of a polymer-based autologous cultured composite skin on an integrated temporizing dermal matrix: proof of concept. J. Burn Care Res. 34 , 151–160 (2013).

Fleischmann, T., Nicholls, F., Lipiski, M., Arras, M. & Cesarovic, N. in Methods in Molecular Biology. Vol. 1993, 251–259 (Humana Press Inc., 2019).

Pham, C., Greenwood, J., Cleland, H., Woodruff, P. & Maddern, G. Bioengineered skin substitutes for the management of burns: a systematic review. Burns 33 , 946–957 (2007).

Greenwood, J. E. The evolution of acute burn care - retiring the split skin graft. Ann. R. Coll. Surg. Engl. 99 , 432–438 (2017).

Back, C., Dearman, B., Li, A., Neild, T. & Greenwood, J. E. Noncultured keratinocyte/melanocyte cosuspension: Effect on reepithelialization and repigmentation-A randomized, placebo-controlled study. J. Burn Care Res. 30 , 408–416 (2009).

Ishack, S. & Lipner, S. R. A review of 3-dimensional skin bioprinting techniques: applications, approaches, and trends. Dermatol. Surg. 46 , 1500–1505 (2020).

Donnelly, H., Salmeron-Sanchez, M. & Dalby, M. J. Designing stem cell niches for differentiation and self-renewal. J. R. Soc. Interface 15 , 20180388 (2018).

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Acknowledgements

This study has been funded by Instituto de Salud Carlos III through the project PI13–02576 (co-funded by European Regional Development Fund “A way to make Europe”) and Regional Government of Andalusia (SAS PI-0458–2016 and salud-2016–73581-tra). The work of Álvaro Sierra-Sánchez was supported by a predoctoral fellowship (BOE 05/01/2018) funded by Instituto de Salud Carlos III (co-funded by European Social Fund “Investing in your future”) with the dossier number FI18/00269. This study is part of his doctoral research in the Biomedicine’s program of University of Granada.

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Cell Production and Tissue Engineering Unit, Virgen de las Nieves University Hospital, Andalusian Network of Design and Translation of Advanced Therapies, Granada, Spain

Álvaro Sierra-Sánchez & Salvador Arias-Santiago

Biosanitary Institute of Granada (ibs.GRANADA), Granada, Spain

Department of Dermatology, University of Arkansas for Medical Sciences, Little Rock, AR, USA

Kevin H. Kim

Department of Dermatology, Virgen de las Nieves University Hospital, Granada University, Granada, Spain

Kevin H. Kim, Gonzalo Blasco-Morente & Salvador Arias-Santiago

Department of Dermatology, Faculty of Medicine, University of Granada, Granada, Spain

Salvador Arias-Santiago

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Á.S.-S. and K.H.K. reviewed bibliography and wrote the manuscript, G.B.-M. and S.A.-S. reviewed bibliography and revised the manuscript. Á.S.-S. and K.H.K. are co-first authors of this manuscript.

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Sierra-Sánchez, Á., Kim, K.H., Blasco-Morente, G. et al. Cellular human tissue-engineered skin substitutes investigated for deep and difficult to heal injuries. npj Regen Med 6 , 35 (2021). https://doi.org/10.1038/s41536-021-00144-0

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Published : 17 June 2021

DOI : https://doi.org/10.1038/s41536-021-00144-0

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Vivian is an 80-year-old resident of the Sapphire Peaks Residential Aged Care home. She is generally well. While boarding the shuttle bus to do her weekly shopping, Vivian missed her footing and fell backwards, hitting her head on the pavement. She rapidly became unresponsive and was rushed to the closest Emergency Department.

Vivian is unconscious and does not have capacity to make decisions about medical treatment. The medical team discuss Vivian’s treatment options with her children Amy (aged 47) and James (aged 45), their father Ed (Vivian’s ex-husband who she hasn’t seen since they divorced 15 years ago, and who is visiting with Amy from interstate), and Vivian’s sister Rachel, who has a close relationship with Vivian. Amy and James are also close to their mother and visit her often.

The neurosurgical specialist team advise that due to her severe head injury, Vivian requires urgent surgery to relieve intercranial pressure caused by the bleeding around her brain. The surgery is needed for Vivian to survive, but it is an invasive procedure, and given her age and the extent of the trauma there is a risk that she may not survive the anaesthesia or operation.

Vivian does not have an Advance Care Directive, or a guardian or attorney, so a substitute decision-maker’s consent is needed to proceed with the surgery. Amy recalls a recent conversation with her mother, following a friend’s death, where she told Amy that she would not want to have any major operations or medical treatment at this stage of her life, and would not want to be kept alive if she were dying. Ed remembers Vivian having similar conversations with him when they were married. Amy and James want to respect their mother’s wishes and although devastated, they decide not to consent to the operation. Rachel is horrified and cannot bear the thought of Vivian dying if there is a chance she might survive. She begs Amy and James to reconsider.

Points for reflection

• Who is Vivian's legally recognised substitute decision-maker?
• What happens if there is a disagreement among Vivian’s family members about her treatment?
• Can Vivian’s substitute decision-maker/s refuse consent to the operation?
• What factors should Vivian’s substitute decision-maker/s consider when making the decision?
• Does the clinical team have to follow the decision?

1. Who is Vivian’s legally recognised substitute decision-maker?

As Vivian does not have an Advance Care Directive, or appointed guardian or attorney, the laws in all States and Territories set out a hierarchy of ‘default’ substitute decision-makers (known as a person responsible, Statutory Health Attorney, medical treatment decision-maker, health care decision maker, or health attorney, depending on the State or Territory). The appropriate decision-maker is usually someone who has a close and continuing relationship with the person e.g. the person’s spouse or another family member.

As Vivian is divorced from Ed and they do not have a close and continuing relationship, he is no longer her spouse and cannot be her decision-maker. Applying the law in each State and Territory, Vivian’s decision-makers are as follows:

• In Queensland, South Australia, Tasmania, the Australian Capital Territory and New South Wales , Vivian’s relatives who have a close and continuing relationship with her can make the decision. Therefore, Amy, James and Rachel can be her decision-makers.
• In the Australian Capital Territory , the health professional may ask the decision-maker they believe is best able to represent the person’s views to give consent.
• In Victoria , Vivian’s adult children who have a close and continuing relationship with her (Amy and James) are higher on the list of decision-makers than an adult sibling (Rachel). Where there are two or more adult children, the eldest can make the decision, in this case, Amy .
• In Western Australia , Vivian’s nearest relative who maintains a close relationship with her is her decision-maker. In the order of priority among relatives, a person’s children (Amy and James) are higher in the list than a sibling (Rachel). Therefore, Amy and James can be Vivian’s decision-makers.
• In the Northern Territory,  Amy and James are higher in the hierarchy of decision-makers than Rachel. They are therefore Vivian’s decision-makers.

2. What happens if there is a disagreement among Vivian’s family members about her treatment?

When disputes arise, it is rare for the guardianship and other legal systems to become involved, and for cases to be decided by courts or tribunals. Most conflicts are managed within the treating hospital or health service using internal dispute resolution policies or procedures. These seek to facilitate open communication and achieve consensus among decision-makers through processes such as clinical reviews, obtaining an independent second medical opinion, family or case conferences, and mediation. Legal advice may also be sought from the health service’s legal team.

In some States and Territories, guardianship and medical treatment legislation sets out how disagreements can be resolved. This may involve referring the disagreement for dispute resolution (e.g. through the Public Advocate or Public Guardian in some jurisdictions), and, as a last resort, applying to tribunals or courts to make the decision.

In this case, Rachel disagrees with Amy and James and wants Vivian to have the surgery. In practice the hospital would most likely hold a family meeting to attempt to reach consensus among them.

3. Can Vivian’s substitute decision-maker/s refuse consent to the operation?

A substitute decision-maker can make most medical treatment decisions for a person who no longer has capacity, including decisions about whether life-sustaining treatment should be provided, withheld or withdrawn.

In all States and Territories,  Vivian’s decision-maker/s can refuse consent to the operation.

This area of law can be complex, especially in relation to stopping life-sustaining treatment once it has started.

4. What factors should Vivian’s substitute decision-maker/s consider when making the decision?

When making the treatment decision, Vivian’s substitute decision-maker/s should consider:

• what decision Vivian would have made if she had capacity; and
• whether treatment would be in Vivian’s interests, after considering the potential risks, burdens and benefits of the treatment.

The laws in each State and Territory also set out principles to guide substitute decision-makers e.g. decision-making principles, health care principles.

The principles in most jurisdictions require substitute decision-makers to consider the person’s:

• views, preferences and wishes (if known);
• interests and welfare; and
• treatment options, risks and alternatives.

Here, Vivian’s decision-maker/s should consider Vivian’s previous statements about her treatment preferences e.g. that she does not want any major operations or medical treatment, and does not want to be kept alive if she is dying. The risks of the surgery (e.g. death); other available treatment options (here, there are none); the benefits of future treatment (she may survive) and the burdens (including what her prognosis would be if she does survive); and other decision-making principles should also be considered.

5. Does the clinical team have to follow the decision?

Generally a substitute decision-maker’s decision should be followed, even if refusing treatment will result in a person’s death. If the clinical team undertakes the surgery without first obtaining consent from a substitute decision-maker, they could be liable under criminal or civil law or be subject to disciplinary action.

If a clinical team is concerned about the decision a substitute decision-maker makes (e.g. they believe it is not in the person’s best interests), they may seek advice from the hospital or health service’s legal team, or a medical defence insurer. In some State and Territories, the Public Guardian or Public Advocate’s office may be able to provide information or assistance.

Final legal observations

Vivian’s legally recognised substitute decision-makers (which vary depending on which State or Territory Vivian is in) must decide whether or not to consent to the operation. In doing so they must take into consideration the factors discussed in reflection point 4. If there is disagreement among Vivian’s decision-maker/s, a meeting could be held between the family and clinical team to reach consensus. In this scenario the clinical team should follow the substitute decision-maker’s/s’ decision about Vivian’s treatment, unless they have concerns about the decision, in which case legal advice should be sought.

Page updated 21 August 2024

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Case Studies on Safer Alternatives for Solvent Degreasing Applications

• Trichloroethylene (TCE)
• Methyl chloroform (TCA)
• Dichloromethane (DCM, methylene chloride)

You may download a PDF version of this page below.

The transition to sustainable manufacturing is best accomplished by using pollution prevention (P2) approaches. This paper summarizes a number of case studies that highlight the P2 approach of switching to aqueous and less toxic metal cleaners to reduce health risks and manufacturing costs. EPA compiled these case studies as a supplement to Pollution Prevention (P2) Spotlight: Reducing Trichloroethylene (TCE) Waste in the Fabricated Metals Sector (pdf) (180.2 KB)

What are cleaning solvents and how are they used?

Cleaning solvents are used to remove oil, grease, solder flux, and other contaminants. Facilities that produce metal products often use solvents and other chemicals as degreasers to clean metal parts in preparation for further finishing operations, like painting or welding.

Trends in the reduced use of TCE reported by the fabricated metals sector to EPA’s Toxic Release Inventory (TRI) database:

• Quantity of TCE releases to air decreased from 3 million lbs in 2001 to 0.6 million lbs. in 2012.
• The number of fabricated metal facilities reporting TCE decreased to 44 from 141, suggesting many facilities have eliminated TCE use entirely or reduced its use below the 10,000 pound reporting threshold.

Trichloroethylene (TCE) : used as a solvent for metal degreasing, as well as a refrigerant and in dry cleaning fluid. TCE is a volatile organic compound (VOC) that poses a human health hazard to the central nervous system, kidney, liver, immune system, reproductive system, and to the developing fetus. TCE is also characterized by U.S. Environmental Protection Agency (EPA) as carcinogenic to humans by all routes of exposure (i.e., by inhalation, ingestion, and dermal exposure). Learn more about TCE .

Methyl chloroform (TCA) : used as a solvent and in some consumer products. Exposure to TCA can result in mild motor impairment (e.g., increased reaction time), lightheadedness, impaired balance, and lack of muscle control in acutely exposed humans. Cardiac arrhythmia and respiratory arrest may result from the depression of the central nervous system.

Dichloromethane (DCM, methylene chloride) : used as a solvent in paint strippers, a process solvent in the manufacture of pharmaceuticals and film coatings, a propellant in aerosols, and a solvent for metal cleaning and finishing in electronics manufacturing. Effects of short-term (acute) exposures to workers and consumers, including bystanders, can result in harm to the central nervous system, or neurotoxicity. Effects of longer periods of exposure (chronic) for workers includes liver toxicity, liver cancer, and lung cancer. Learn more about DCM (pdf) .

Case Studies:

1. Schick (formerly American Safety Razor) in Verona, Virginia, manufactures a variety of blades and tools from steel stock. TCE was used as a cleaning solvent in both liquid and vapor cleaning/degreasing operations at a newly acquired facility. Schick's prior experience with TCE as a potential environmental contaminant, combined with increasing costs associated with its distillation and waste disposal and higher regulatory risk, made TCE elimination a priority.

Schick installed aqueous “wash boxes” on production lines to replace TCE-based cleaning processes, and also used an alcohol-based vapor degreaser as an effective substitute. TCE use has been completely eliminated at this plant. In addition to risk reduction, these P2 measures have resulted in an estimated cost reduction of $250,000 a year from reduced energy, material and hazardous waste disposal costs.

Learn more: www.epa.gov/p2/pollution-prevention-accomplishments-schick-manufacturing-verona-virginia

2. Lightolier in Fall River, Massachusetts, fabricates aluminum reflectors for lighting product lines. The facility was using large amounts of TCE and acids annually. Only 10 percent of the used TCE was captured for recycling. In addition, the company became aware of hidden costs such as liability, worker safety, and opportunities for increased productivity.

Lightolier found that 10 percent of one employee’s time was spent monitoring the TCE degreasers and manifesting the used TCE sent to a recycler, a week’s worth of labor was dedicated to Emergency Planning and Community Right-to-Know Act (EPCRA) reporting for TCE, and 40 percent was spent on Right-to-Know training strictly for TCE.

Furthermore, Lightolier’s degreasing systems were old and required increasing maintenance. The company replaced the TCE degreasers with an aqueous degreaser and a powder coat degreaser. In addition, switching from pure petroleum lubricants to water-soluble coolants would eliminate the generation of oily parts in the first place.

Since removing the degreasers and making other improvements such as installing still-rinse tanks, implementing countercurrent rinsing, and increasing the drip time to reduce acid discharges, the company has eliminated approximately 1.25 million lbs of TCE and saved an estimated $170,000. Volatile organic compound (VOC) emissions have dropped 90 percent from 125,000 to 12,000 lbs per year, also significantly reducing air compliance costs.

3. V.H. Blackinton & Co., Inc in North Attleboro, MA, is a large manufacturing operation -- blanking, stamping, punching and machining raw stock prior to cleaning, enameling, brazing, polishing, plating and refinishing -- of metal plated items. The facility had used ozone-depleting Freon, as well as TCE and other VOCs and ammonia but was able to eliminate them.

Blackinton eliminated the use of Freon by replacing the existing finished work dryer with one that uses a deionized water rinse and hot air. The TCE cleaning operations were replaced with an aqueous cleaning system. Approximately 45 gallons of water-based cleaner is used annually, achieved by carefully monitoring the bath chemistry and ultra-filtering the cleaner weekly for reuse. In addition, a small in-tank filter, an oil skimmer, and conversion to compatible water-based pressing and stamping oils, made the new aqueous cleaning system more efficient.

More recently, new brazing furnaces with belts twice as wide as those in the old furnaces were installed, doubling the process capacity. The new furnaces use a 25 percent hydrogen and 75 percent nitrogen mix, eliminating over 20,000 lbs a year of disassociated anhydrous ammonia used in the old furnaces. The cost of the new system and quality of the finished product is the same or better. A close looped cooling water system that reuses water for the furnaces conserves 5000 gallons per day and additional water conservation activities eliminate the use of more than 25,000 gallons per day.

4. Danfoss Chatleff LLC in Buda, Texas, manufactures refrigeration and air conditioning components, and had been using a TCE-based degreaser to remove machine oil from metal parts. The facility replaced TCE with an aqueous degreaser/parts washer and evaporator eliminating 9,900 lbs of hazardous waste per year and saving the facility $36,000/year. The new cleaning process requires less operator time, estimated to be worth $25,000/year. By eliminating the use of TCE, Danfoss also significantly reduced future environmental risk/liability associated with the shipping, storage, and use of a hazardous chemical. (Danfoss also estimates saving approximately $10,000 per year in disposal costs and $1,000 in training and reporting costs.)

5. Perkins Products Inc. in Chicago, Illinois, was using mineral spirits for parts cleaning to remove straight cutting oil from metal work pieces in the milling department. The company replaced these solvents with aqueous detergents. The detergent was found to be safer for employees, better for the environment, less expensive and compatible with current production process. A total of 1,600 gallons of solvent were eliminated, 10,400 lbs of VOCs were avoided, and $500 saved per year, with only a one-year return on investment period.

Learn more: www.istc.illinois.edu/UserFiles/Servers/Server_427403/File/TN15-116.pdf (pdf)

6. Marathon in Ashland, Minnesota, had been using a terpene-based cleaner and petroleum distillate for external cleaning of large equipment. The terpene solvent was suspected to be impairing the biological processes of the refinery’s wastewater treatment plant. During testing, two aqueous cleaners were applied as a foam that adhered to vertical surfaces for several minutes -- enough time for the cleaner to work -- then rinsed off with hot water. The refinery staff using one of the foaming agents described the result as "requiring less chemical, less time and less water, while providing better results" compared to the terpene-based cleaner.

Learn more: www.mntap.umn.edu/industries/facility/machine/resources/marathon/

7. Lockheed Martin Defense Systems in Pittsfield, Minnesota, used 125 tons each year of 1,1,1- trichloroethane (trichlor, 1,1,1-TCA, methyl chloroform) and chloroflourocarbon-113 (CFC-113, Freon) in 39 vapor degreasers to clean precision products, emitting 70 tons of these chemicals each year into the air.

The company evaluated alternative cleaners for economic and technical feasibility and potential worker health and safety impact. Ultimately, seven aqueous systems and two semi-aqueous systems replaced 36 of the 39 degreasers and reduced facility solvent use to less than 2 tons per year, and air emissions to less than 1 ton per year. Cost savings included: $497,000 in solvent procurement; $17,500 in waste disposal and $65,000 in permitting and record keeping. The company incorporated a “closed loop” aqueous cleaning system in the transmission assembly and repair process. The system included a variety of substrates (steel, stainless steel, aluminum, cast iron, and bronze) and contaminants (plastic and oil, grease, wax and metal, plastic or rubber shavings) requiring removal. This process reduced consumption of 2,000,000 gallons of water per year and saved $3,450 in water and sewer costs.

8. Dayton Rogers metal stamping facility in Minneapolis, Minnesota, was using TCA as a vapor degreaser to remove forming lubricant oil from parts prior to dry-sander deburring. The solvent was eliminated by upgrading its deburring operation to deburr and clean parts simultaneously. The company modified the vibratory tumbling machines to increase throughput, added a wet sander and switched to a water-based lubricant so that removing the forming lubricants would be easier in the water-based deburring system. This resulted in saving $26,575 per year and a payback period for the equipment of approximately three months. This approach would be suitable in stamping and machining operation where deburring is done, but precision cleaning is not necessary.

Learn more: www.mntap.umn.edu/industries/facility/machine/pretreat/

9. Rosemount Aerospace Inc. in Burnsville, Minnesota, used TCA during sensor cleaning at a large manufacturer of aircraft data instrumentation. After sensor assembly, the TCA comes in contact with silicone oil during testing to remove the oil before a soldering process. Aqueous cleaners tested on the sensors removed light oils and fingerprints at least as well as the existing vapor degreasing system and eliminated worker exposure to TCA.

Learn more: www.mntap.umn.edu/industries/facility/machine/resources/aqueous/

10. APS Materials Inc., a small metal finishing company in Dayton, Ohio, used TCA and methanol in its degreasing operation to clean orthopedic implants such as those used for metal knee and hip replacements. A dilute limonene solution was tested as replacement cleaner. This dilute terpene-based cleaner adequately cleaned metal parts without adversely affecting the performance of the plasma-arc coating application. The replacement cleaner resulted in a cost savings of $4,800 per year and a payback period of 4.5 months. Elimination of the disposal problems associated with methanol and TCA, coupled with the maintenance of plasma-arc coating quality, makes the use of terpene-based cleaners attractive to other plasma spray coating processes as well as other metal cleaning/coating operations.

Learn more: citeseerx.ist.psu.edu/pdf/fde6e9ef6360a57c05edb79c7560d2199e67c693

According to an EPA analysis of TRI data, in 2013 (pdf) (219.81 KB) 61 out of 280 facilities reporting the use of DCM in the U.S. reported newly implemented source reduction activities. Two examples include:

• An organic chemical manufacturer that previously used DCM to clean equipment when changing from one process to another, switched to a less hazardous cleaning solution of water and limonene; and,
• An optical instrument manufacturer started using aqueous cleaning solutions instead of DCM.

11. Roberts Automatic Products, a third generation family-owned precision production machining company in Chanhassen, Minnesota specializes in precise and complex computer numeric control (CNC) machining and screw machine parts. Roberts used DCM as a degreasing solvent to clean its parts and reported to TRI as much as 40,000 pounds a year of DCM wastes that were released or treated by the plant.

Roberts purchased the Serec closed-loop vacuum degreasing unit in 2011 and put it into service in 2012. Roberts reduced its DCM waste to 13,636 pounds from more than 44,000 pounds the previous year. The facility is no longer required to file TRI reports for DCM and has eliminated DCM as a source of toxic waste and a hazardous air pollutant.

• Safer Alternatives for Solvent Degreasing Applications (pdf) (416.09 KB, September 2016)
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Apple Five Forces Analysis & Recommendations (Porter’s Model)

This Five Forces analysis gives insights into the external factors influencing Apple’s success. Michael E. Porter’s Five Forces analysis framework is a strategic management tool for evaluating the five forces affecting the business organization: customers, suppliers, substitutes, new entrants, and competitors. This Five Forces analysis of Apple Inc. sheds light on what the company does to ensure industry leadership. Despite the negative effects of external factors in the competitive landscape of the computer software and hardware, consumer electronics, and online services markets, Apple’s mission statement and vision statement are fulfilled through relevant business goals and strategies. Based on this Five Forces analysis, the company addresses competitive forces and external factors through effective leaders, such as Tim Cook. This Five Forces analysis indicates external factors that Apple’s strategic efforts must focus on to keep its leadership in the industry.

Based on the Five Forces analysis model, external factors in Apple’s industry environment point to competitive rivalry or intensity of competition, and the bargaining power of buyers or customers as the primary forces for consideration in the company’s strategic planning. Nonetheless, all five forces influence the company’s business situation, together with the effects of other external factors, such as the industry and market trends identified in the PESTLE/PESTEL analysis of Apple Inc .

Summary: Five Forces Analysis of Apple Inc.

Apple’s generic competitive strategy and intensive growth strategies are partly based on competitive forces in the external business environment. These forces limit or reduce the firm’s market share, revenues, profitability, and business development potential. This Five Forces analysis points to the following strengths or intensities of competitive forces in Apple’s industry environment:

• Competitive rivalry or competition: Strong force
• Bargaining power of buyers or customers: Strong force
• Bargaining power of suppliers: Weak force
• Threat of substitutes or substitution: Weak force
• Threat of new entrants or new entry: Moderate force

Recommendations. Considering the results of this Five Forces analysis, Apple must focus its attention on competitive rivalry and the bargaining power of buyers. This external analysis supports the company’s current position of continuous innovation. Innovation and the business competitive advantages shown in the SWOT analysis of Apple address the five forces in the external environment, although much of the company’s effort is for strengthening its position against competitors and for attracting customers to its products. An applicable course of action is to intensify research and development for innovation to develop novel products that complement iPhones, iPads, and other current products. Apple can also improve its support and resources for software or app developers, to strengthen the company’s ecosystem of hardware, software, and online services against the competitive challenges identified in this Five Forces analysis.

Competitive Rivalry or Competition with Apple (Strong Force)

Apple faces the strong force of competitive rivalry or competition. This component of Porter’s Five Forces analysis model determines the intensity of the influence that competitors have on each other. In Apple’s case, this influence is based on the following external factors:

• High aggressiveness of technology firms (strong force)
• Low differentiation of many products (strong force)
• Low switching cost (strong force)

Competitors’ aggressiveness in innovation and marketing imposes a strong force in the information technology industry environment. In the market for consumer electronics, software, and Internet services, Apple competes with Google (Alphabet) , Microsoft , Samsung, and Sony . In the video-streaming market, Netflix , Disney , Amazon , and Facebook (Meta) compete with Apple TV Plus. This Five Forces analysis also considers other technology firms, such as IBM and Intel , which influence Apple’s competitive environment. Moreover, in terms of product differentiation, products in the market are generally similar in fulfilling specific purposes. For example, many popular apps are available for Android and iOS devices, and cloud storage services from different companies are similar and available to users on different platforms. In this Five Forces analysis of Apple, such a condition creates a strong force by making it easy for customers to switch to other sellers or providers. On the other hand, the low switching cost means that it is easy for customers to switch from Apple to other brands, based on price, function, accessibility, network externalities, and related concerns. The combination of these external factors in this part of the Five Forces analysis leads to tough competitive rivalry that is among the most significant considerations in Apple’s strategic management.

Bargaining Power of Customers/Buyers (Strong Force)

The bargaining power of buyers is strong in affecting Apple’s business. This component of Porter’s Five Forces analysis model determines how buyers’ purchase decisions and related preferences and perceptions impact businesses. In Apple’s case, buyers’ strong power is based on the following external factors:

• Small size of individual buyers (weak force)
• High availability of information to buyers (strong force)

It is easy for customers to change brands, thereby making them powerful in compelling Apple to ensure customer satisfaction. On the other hand, each buyer’s purchase is small compared to the company’s total revenues. In this Five Forces analysis of Apple, such a condition makes customers weak at the individual level. However, the availability of detailed comparative information about competing products’ features empowers buyers to shift from one provider to another. This external factor enables buyers to exert a strong force in the industry, although promotional strategies and tactics in Apple’s marketing mix (4P) can communicate tailored information to persuade customers to buy the company’s products. Thus, this part of the Five Forces analysis shows that Apple must include the bargaining power of buyers or customers as one of the most significant strategic variables in the business.

Bargaining Power of Apple’s Suppliers (Weak Force)

Apple Inc. experiences the weak force or bargaining power of suppliers. This component of the Five Forces analysis model indicates the influence of suppliers in imposing their demands on the company and its competitors. In Apple’s case, suppliers have a weak bargaining power based on the following external factors:

• Moderate to high number of suppliers (weak force)
• Moderate to high overall supply (weak force)
• Large size of some equipment and component manufacturers (strong force)
• High ratio of firm concentration to supplier concentration (weak force)

The global size of its supply chain allows Apple Inc. to access many suppliers around the world. In Porter’s Five Forces analysis context, the resulting high number of suppliers is an external factor that presents only a weak to moderate force against the company. Also, the moderate to high overall supply of inputs, such as semiconductors, makes individual suppliers weak in imposing their demands on Apple. However, some large suppliers, such as OEMs and producers of chips, significantly influence the industry. Nonetheless, in this Five Forces analysis case, the high ratio of firm concentration to supplier concentration limits suppliers’ power and influence in the industry. This external factor reflects the presence of a small number of big companies, like Apple and Samsung, in contrast to a larger number of medium-sized and large suppliers. Thus, this part of the Five Forces analysis shows that the bargaining power of suppliers is a minor issue in developing Apple’s operations management strategies for supply chain management, value chain effectiveness, innovation, and industry leadership.

Threat of Substitutes or Substitution (Weak Force)

The competitive threat of substitution is weak in affecting Apple’s computing technology, consumer electronics, and online services business. This component of the Five Forces analysis framework determines the strength of substitute products in attracting customers. In Apple’s case, substitutes exert a weak force based on the following external factors:

• Moderate to high availability of substitutes (moderate force)
• Low performance of substitutes (weak force)
• Low buyer propensity to substitute (weak force)

Some substitutes for Apple products are readily available in the market. For example, instead of using iPhones, people can use digital cameras to take pictures, and landline telephones to make calls. In this Five Forces analysis of Apple, such an external factor exerts a moderate force in the industry environment. However, these substitutes have low performance because they have limited features. Many customers would rather use Apple products based on convenience and advanced functions. This condition weakens the force of substitution in impacting the company’s business in this Five Forces analysis context. Also, buyers have a low propensity to substitute. For instance, customers would rather use smartphones than go through the hassle of buying and maintaining a digital camera, an analog phone, and other devices. This part of the Five Forces analysis shows that Apple does not need to prioritize the threat of substitution in management decisions for business processes, like marketing, market positioning, and product design and development.

Threat of New Entrants or New Entry against Apple (Moderate Force)

Apple Inc. experiences the moderate force or threat of new entrants. This component of Porter’s Five Forces analysis model indicates the possibility and effect of new competitors entering the market. In Apple’s case, new entrants exert a moderate force based on the following external factors:

• High capital requirements (weak force)
• High cost of brand development (weak force)
• High capacity of some potential new entrants (strong force)

Establishing a business to compete with Apple Inc. requires high capitalization. Also, it is extremely costly to develop a strong brand to compete with large companies, like Apple. These external factors make new entrants weak in this Five Forces analysis case of the IT business. However, there are large firms with the financial capacity to enter the market. For example, Google has already done so through its consumer electronics. Samsung also used to be a new entrant. These examples show that there are large companies that have the potential to directly compete with Apple Inc. in multiple markets. Thus, the overall threat of new entry is moderate. This part of the Five Forces analysis shows that Apple must maintain its competitive advantages through innovation and marketing to remain strong against new entrants’ moderate competitive force.

• Apple empowers small businesses to grow and serve their customers .
• Apple Inc. – Form 10-K .
• Apple introduces global developer resource for labs, sessions, and workshops .
• Apple scores record 13 Academy Award nominations .
• Jahan, S. A., & Sazu, M. H. (2023). Role of IoTs and analytics in efficient sustainable manufacturing of consumer electronics. International Journal of Computing Sciences Research, 7 , 1337-1350.
• Sforcina, K. (2023). Digitalizing Sustainability: The Five Forces of Digital Transformation . Taylor & Francis.
• U.S. Department of Commerce – International Trade Administration – Software and Information Technology Industry .
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The Impact of Generic Substitution on Health and Economic Outcomes: A Systematic Review

Institute of Public Health, Medical Decision Making and Health Technology Assessment, Department of Public Health and Health Technology Assessment, UMIT, University for Health Sciences, Medical Informatics and Technology, Eduard Wallnoefer Center 1, 6060 Hall i.T., Austria

Division of Public Health, Decision Modelling, Health Technology Assessment and Health Economics, ONCOTYROL, Center for Personalized Cancer Medicine Innsbruck, Karl Kapferer Strasse 5, 6020 Innsbruck, Austria

Dresden Medical School “Carl Gustav Carus”, Dresden University of Technology, Fetscherstraße 74, 01307 Dresden, Germany

Department of Pharmacotherapy, University of Utah, 30 S 2000 E, Rm 4410, Salt Lake City, Utah 84112 USA

M. Mitrovic

Center for Health Decision Science, Department of Health Policy and Management, Harvard School of Public Health, 677 Huntington Avenue, Boston, MA 02115 USA

Institute for Technology Assessment, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, 101 Merrimac St., 10th FL, Boston, MA 02114 USA

Generic drugs are considered therapeutically equivalent to their original counterparts and lower in acquisition costs. However, the overall impact of generic substitution (GS) on global clinical and economic outcomes has not been conclusively evaluated.

To test whether (1) generics and original products yield the same health outcomes, and (2) generic therapies save economic resources versus original therapies.

We performed a systematic literature review in Medline, Embase, and the Cochrane Database of Systematic Reviews to identify original studies that examine clinical or economic outcomes of GS. After standardized data extraction, reported outcomes were categorized as supporting or rejecting the hypotheses. Each reported outcome was assessed and accounted for supporting and opposing GS. One publication could provide multiple outcome comparisons.

We included 40 studies across ten therapeutic areas. Fourteen studies examined patients on de novo therapy; 24 studies investigated maintenance drug therapy, and two studies considered both settings. Overall, 119 outcome comparisons were examined. Of 97 clinical outcome comparisons, 67 % reported no significant difference between generic drugs and their off-patent counterparts. Of 22 economic comparisons, 64 % suggested that GS increased costs. Consequently, hypothesis (1) was supported but hypothesis (2) was not. We found no major differences among studies that investigated clinical outcomes with de novo or maintenance therapy.

The review suggests that clinical effects are similar after GS. However, economic savings are not guaranteed. More systematic research comparing clinical and economic outcomes with or without GS is needed to inform policy on the use of generic substitution.

Key Points for Decision Makers

Introduction

Governments and other healthcare payers are increasingly challenged by rising healthcare expenditures and constrained resources. In countries from the Organization for Economic Co-operation and Development, pharmaceutical expenditures account on average for about 1.5 % of the gross domestic product [ 1 , 2 ]. Generic substitution (GS) is a commonly employed method for reducing pharmaceutical costs by substituting patented original drugs through generic counterparts with lower acquisition costs [ 3 ].

With the passage of the Drug Price Competition and Patent Term Restoration Act (Hatch-Waxman Act) in the USA in 1984, the market entry for generic drugs was streamlined through an abbreviated approval process requiring only a demonstration of bioequivalence for generic approval [ 4 ]. Although policies on GS vary from country to country, the policies usually allow the authority to substitute a cheaper generic equivalent for an off-patent original product to a physician (prescribing by international non-proprietary nomenclature) and/or a pharmacist (dispensing of the product preferred by the policy maker or payer).

Such policies are supported by a myriad of studies on GS; most of them were published between the late 1970s and the 1990s when generic substitution was a new and challenging issue [ 5 , 6 ]. Nevertheless, there is still a lack of appropriate studies involving putatively similar generics—with questionable differences of similarity—which might partly explain the observable variance in clinical responses and side effects. There are several reasons why GS may not be appropriate which are not related to bioequivalence issues [ 7 – 9 ]. For example, inappropriateness is determined by excipient characteristics, but it may also depend on disease entities and clinical conditions, for example, whether a generic drug is applied for de novo or for maintenance therapy.

In order to be considered generic, a drug needs to match the original product in dosage, safety, strength, administration form, quality, performance and intended use. Under these conditions, generics are generally considered to have an equivalent clinical effect when substituted for the original name product [ 10 , 11 ].

When two generic products are each at the far opposite range of bioequivalence they are equivalent to a brand but not to each other. This results in either over- or under-dosing. Patient confusion and/or nurse confusion in drug intake leads to decreased adherence. Decreased quality of excipients and manufacturing quality can impact drug release and intended action. Any of these scenarios can lead to unintended adverse events that can cost more than the savings in drug costs.

Although bioequivalent generic drugs exist for many original products, it remains controversial whether bioequivalence reflects clinical equivalence. The safety of substituting narrow therapeutic index drugs (NTI), for instance, has been the topic of much debate. Since the therapeutic window of these drugs is relatively small, they can “exhibit limited or erratic absorption, formulation-dependent bioavailability and intra-patient pharmacokinetic variability that requires blood-level monitoring” [ 12 ]. Such differences in clinical outcomes can also affect the intended economic savings. If, for instance, rates for adverse events were higher in patients switching to generic drugs, overall expenses may be higher than expected or may even exceed the amount spent previously for the original drug.

Considering the variety of drugs and drug types, literature pertaining to clinical and economic outcomes of GS may be more robust in some therapeutic areas or treatment stages than others. However, to date, we are not aware of any research that has attempted to summarize the entire body of evidence on the impact of GS across multiple therapeutic areas including clinical and economic outcomes.

Therefore, the aim of this study was to evaluate whether (1) original medications and their corresponding generic equivalents yield the same health outcomes and (2) whether generic therapies save economic resources in contrast to original therapies when evaluating health outcomes and economic outcomes. A systematic review of the published literature was conducted for patients starting a new therapy (de novo) and patients on maintenance therapy.

Literature Search

A systematic literature search was performed in the following electronic databases: Medline using the PubMed interface, the Cochrane Database of Systematic Reviews, and Embase. A comprehensive search syntax (see “ Appendix ”) that included the terms “generic substitution”, “drug substitution”, “drug switching”, “adverse event”, “drug safety”, “risk benefit ratio”, “cost containment”, “health economic”, “adherence”, “compliance”, “persistence” and “medication adherence” was run through PubMed and the Cochrane Database of Systematic Reviews in September 2012. A subsequent literature search was performed in November 2012 using a less distinct syntax with the term “generic substitution” for titles and abstracts in Medline, Cochrane Database of Systematic Reviews and Embase. All searches were limited to the publication years from 2000 to 2012. In addition, cited references of the included studies were searched manually.

Literature Selection

We selected only full publications of original research studies that focused on GS, examined clinical or economic outcomes and included either a separate or pre-post comparator group. Exclusion criteria were: (a) publication language was neither English nor German, (b) study design implied no original research, (c) study endpoints did not include clinical or economic outcomes, (d) study intervention was not limited to generic switching but comprised broader options such as therapeutic interchange. Additionally, studies were excluded that exclusively assessed stakeholder opinions, satisfaction or knowledge of GS. Likewise, budget impact analyses, which projected cost or market consequences due to generic product entry to the marketplace, were excluded. Both selection and data extraction were realized by two independent scientists, who were supplemented by a third scientist or discussion in cases of disagreement.

Data Extraction

We developed a standardized assessment form, containing the following domains: citation, funding source/conflict of interest, research question/objective, specific drug, NTI drug (yes/no), drug class, reference comparator, results, outcome types, adherence measures, conclusions, study type and limitations reported by the authors. For clinical outcomes, we extracted reported endpoints on dose adjustment, additional medication, adherence, adverse events, healthcare utilization, surrogate outcome parameters, and others. For economic outcomes, we extracted reported endpoints on drug costs of the investigated drug as well as additional drugs, outpatient and inpatient healthcare utilization costs, co-payments and healthcare costs in general.

De novo and maintenance therapy regimens were defined as whether or not patients had received the investigated active ingredient before study commencement. Consequently, patients who were initiated on a chronic treatment were classified as receiving de novo therapy.

Data Synthesis

We condensed the study data on each outcome by classifying them as either supporting or opposing each of the two hypotheses. According to the definition of generic drugs, clinical outcomes were categorized as supporting the first hypothesis if no statistically significant difference was found between original and generic drug therapy or in case clinical outcomes yielded statistically significant better outcomes, e.g., lower adverse events or higher adherence rates, than original drugs. The second hypothesis was considered supported if the therapy costs under GS were significantly reduced. Finally, each outcome comparison was counted as supporting or not supporting and the percentage of supporting evidence of the total number of comparisons was derived for each hypothesis.

As studies often examined several outcome measures, the sum of outcome comparisons differs from the number of studies included. Therefore, we distinguished between terminology of “studies” and “outcome comparisons”.

Systematic Literature Search and Study Characteristics

After removing duplicates, the systematic literature search yielded 3,386 citations. After title and abstract screening, 202 publications remained in the database. By means of full text examination, 162 studies were excluded, most of them ( n  = 68) for formal criteria, that is, the publication type turned out to be a comment, editorial, letter to the editor or an extended abstract. Forty-three studies were excluded because they did not focus on economic, clinical, and/or humanistic outcomes. Thirty-five publications were excluded due to study type (review, case-studies, hypothetical cost-saving analyses). Ten studies were excluded because they focused on therapeutic interchange rather than generic substitution, and six articles were excluded because instead of GS the main interventions were policy changes or price adjustment measures. In the end, 40 studies (publications [ 20 – 59 ] in the reference list) matched the selection criteria and were included in the review (Fig.  1 ).

PRISMA statement. The flow diagram depicts the flow of information through the different phases (identification–screening–eligibility—included) of the systematic review. It maps out the number of records in each phase and shows how many studies have been included or excluded, respectively

Included studies were performed in 16 countries from three continents (20 studies from North America, eight studies from Europe and 12 studies from Asia). While 80 % of the studies investigated clinical outcomes only, 7.5 % investigated economic outcomes only and 12.5 % examined both clinical and economic outcomes. The studies covered ten therapeutic classes, four of which included NTI drugs (13 studies on NTI drugs of 40 included studies = 32 %).

The selected studies were largely heterogeneous regarding therapeutic categories, types of therapy (i.e., chronic/ maintenance therapy vs. new/de novo therapy), study design, switching sequences (e.g., parallel patient groups vs. cross-over designs), settings, funding and others. (Tables  1 , ​ ,2) 2 ) Study designs included randomized controlled trials (17.5 %), prospective cohort studies (10 %) and retrospective cohort studies (60 %). Additionally, there was one decision model, one non-randomized controlled trial (2.5 % respectively) and three studies with study designs that remained unclear (7.5 %). The time frame of the studies ranged from eight weeks for interventional studies to 93 months in observational studies. Similarly, population size ranged from eight patients to 221,881 patients (Table  1 ).

Table 1

Overview of studies included in the review

D de novo therapy, M maintenance therapy, D   +   M both, C clinical, E economic, C   +   E clinical and economic, AED antiepileptic drug

a Patient number in the health economic decision model

Table 2

Study characteristics

We identified 14 studies with a study population receiving de novo therapy and 24 studies on maintenance therapy. Two studies examined both de novo and maintenance therapy under generic substitution. Study characteristics grouped by de novo or maintenance therapy remained heterogeneous. However, studies on economic outcomes seemed to examine maintenance therapy more often (seven of eight economic outcomes comparison studies) than de novo therapy (one of eight studies). In addition, GS of NTI drugs was examined more often in maintenance therapy (10 of 12 NTI studies), than in de novo therapy (2 of 12 NTI studies). Accordingly, maintenance therapy studies covered more sensitive therapeutic categories than studies on de novo therapy. While studies on maintenance therapy included mostly antiepileptic drugs (AEDs), anticoagulants, antipsychotic drugs and immunosuppressive drugs, studies on de novo therapy included mainly antihypercholesterolaemic drugs or osteoporosis medication and others.

Clinical Outcomes

Clinical outcomes were examined by 37 of 40 studies that led to 97 comparisons of clinical outcomes. These studies covered all ten therapeutic classes as described above and investigated about 26 different drugs. Table  3 displays an overview of our findings sorted by de novo and maintenance therapy.

Table 3

Clinical outcome comparisons (study references in square brackets)

Of the investigated clinical outcome comparisons in de novo therapy, 76 % found generic drugs to produce similar clinical outcomes when compared with the original reference drugs (25 of 33 clinical outcome comparisons). Likewise, 64 % of the examined clinical outcome comparisons demonstrated equal effectiveness with GS (38 of 59 clinical outcome comparisons) in maintenance therapy patients. Of the studies that included both therapy types (treatment stages), 40 % reported similar clinical outcomes with generic substitution.

All in all, 67 % of the clinical outcome comparisons included in this analysis revealed no difference between original and generic drug therapy effectiveness with generic therapy, and therefore, supported our first hypothesis.

Economic Outcomes

Regarding economic outcomes, we extracted reported data on drug costs for the investigated drug and/or potential co-medication, as well as costs on healthcare utilization (inpatient and outpatient) and co-payments.

Of the 40 included studies, three examined economic outcomes only whereas another five studies examined both economic and clinical outcomes. These eight studies led to 22 outcome comparisons. The most frequent study design underlying the economic analyses was retrospective database analysis (five of eight economic studies). Another study projected actual economic observations from a Canadian retrospective open cohort study to a US setting using mathematical approaches, while another study determined the relapse incidence at which switching to a generic drug was cost-neutral through a simple decision analytical model. Only one prospective cohort study was found within this economic context.

These eight studies examined economic outcomes of GS in epilepsy patients treated with AEDs (37.5 %), organ transplant recipients treated with immunosuppressives (37.5 %), atypical neuroleptics (12.5 %) and anticoagulants in patients with continuous use of warfarin (12.5 %).

Seven of eight economic studies (87.5 %) found drug acquisition costs of the investigated medication to be lower for generic drugs (Table  4 ). Five studies identified drug costs for additional medication during generic drug use. In four of them (80 %) the supplementary medication costs exceeded the cost savings obtained from lower costs for the investigated medication due to GS. Total costs for inpatient and outpatient healthcare utilization (e.g., physician visits, hospitalization visits, etc.) were always lower with use of original products. Only costs that arose during the study periods ranging from 180 days to 5 years were included.

Table 4

Economic outcome comparisons (study references in square brackets)

In the consolidated evaluation of economic outcome comparisons, 64 % indicated that staying with an original product incurs lower costs than GS. One of these studies examined economic outcomes for de novo therapy, in this case immunosuppressives after organ transplantation, and found total costs to be lower with originator therapy. In the group of maintenance therapy, 55 % of the economic comparisons opposed our second hypothesis.

Seven of eight economic studies calculated the total healthcare costs according to their reported economic outcomes. Contrary to our finding from counting whether or not outcome comparisons supported our second hypothesis, half of these studies found that GS leads to lower costs.

Our findings suggest that 67 % of the evidence reported clinical similarity of GS as compared to original drug therapy, whereas 64 % of the comparisons of economic outcomes suggest costs to be lower when using original drugs. Accordingly, our first hypothesis was supported and our second hypothesis was rejected.

When stratifying the groups by de novo and maintenance therapy, we found a slight difference among studies on clinical outcomes: 76 % of clinical comparisons found similar effects for generics in de novo therapy and 64 % of clinical comparisons found similar effects in generics in maintenance therapy. Likewise, all economic comparisons in patients receiving de novo therapy (one study) versus 56 % in maintenance therapy (seven studies) revealed lower cost with originator therapy. None of the economic outcome comparisons revealed similar costs. However, the low number of studies in each group limits the generalizability of these results.

The majority of economic studies are related to sensitive therapeutic categories and maintenance therapy. Data on economic consequences of generic drug substitution in less sensitive therapeutic categories such as antihypercholesterolemics or osteoporosis were missing or did not meet our inclusion criteria. Thus, our review may suffer from publication bias and the economic conclusions are only relevant to these sensitive therapeutic areas. In the absence of evidence, no conclusions on economic advantages of one policy (e.g., generic substitution) over the other (e.g., originator therapy) can be drawn for less sensitive therapeutic areas. Moreover, with only one economic study analysing the economic impact of generic substitution for de novo therapy, the result must not be generalized. Hence, more evidence is needed to examine the economic impact of generic substitution in a real-life therapy situation, where chronic generic therapy may involve multiple substitution and thus multiple switching. Total healthcare costs were calculated in seven of eight studies. Half of these found cost reductions to be realized with generic drugs, whereas the other half found costs to be lower with the original drug. In contrast, our dichotomous classification supporting or opposing GS resulted in a stronger preference for originator drugs (lower healthcare cost in general).

The high heterogeneity among the cost types reported in the economic studies is also important to note, even among those which claimed to take the payer perspective. If only drug costs of the investigated drug and concomitant medication were examined, findings were likely to show cost reductions after GS. However, if dose adjustments, co-medication or healthcare utilization were considered depending on the rates of adverse events, GS no longer realized cost reductions. Instead, economic outcomes became more preferable in original drugs. It may be speculated that such results depend on additional factors such as therapeutic area, patient age or education level, number of medications or general healthcare context.

These considerations also apply to our analysis on clinical outcomes. If we focus on patient-relevant outcomes such as additional medication, adherence and adverse events only, disregarding surrogate outcomes or others, 67 % (12 out of 18 clinical outcome parameters for these three dimensions) of the categorized data on clinical outcomes remain in favour of our hypothesis of similar clinical effects. Evidence on all clinical outcomes did support the first hypothesis more often in de novo therapy (76 % of the relevant 33 clinical outcome comparisons) than in maintenance therapy (64 % of the relevant 59 clinical outcome comparisons).

This review has multiple limitations which should be considered when interpreting the results. We used a dichotomous classification of evidence, whether studies reported a statistically significant difference between generic and original drugs or not. We used this simplifying approach as the broad topic of this review resulted in a very heterogeneous pool of studies which impaired comparability and information had to be condensed in order to be able to provide a meaningful summary on the topic. Moreover, studies were not critically appraised regarding methodological aspects in a formal manner. For example, a comparison of therapy with one generic drug versus therapy with the originator drug in an 8-week randomized clinical study may answer a different question to a 2-year observational study in a real-life setting including multiple switching under a generic substitution policy. Among the included studies, three compared original drugs with their generic counterpart as well as drugs of different active ingredients [ 13 – 15 ]. Of these only the data comparing generics with the original reference drug were included. Additionally, our analysis did not include substitution between biological originator drugs and biosimilars. Finally, we took a semi-quantitative approach to summarize the evidence. Rather than pooling results in a formal meta-analysis, we simply counted outcome comparisons in favour of or against the compared strategies, and therefore did not weigh studies by sample size or precision. We also ignored dependency between multiple comparisons within one study and did not perform formal statistical tests or uncertainty analysis. Therefore, our analyses are merely exploratory, and should be interpreted with appropriate caution.

Of the included studies, 22 displayed a direct financial interest in their investigated drugs. In 55 % of these studies, the potential interest was linked to the original product, in 31 % of the studies this was linked to a generic and three studies (14 %) could not be specified, for instance due to a variety of author honoraria from several industry partners. Among those with a link to an original product, ten of twelve studies (83 %) found original drugs to generate preferable outcomes (clinical or economic), and of the studies with a link to a generic product, six of seven studies (86 %) found generics to be the dominant drug. Therefore, detection bias should be further explored in subsequent analyses.

We found economic outcomes to be more favourable in original drugs than in generics, which is in accordance with Duh et al. [ 16 ] who detected higher than expected healthcare costs in generic AEDs and revealed that GS may even increase healthcare costs. The included studies of this review mainly suggested further underpinnings of their specific findings, or extensions of the covered methodology such as reporting of additional outcomes, broader or different populations or different medications. Considering the variety of original research that we identified with our systematic literature search, few systematic reviews or meta-analyses have been published focusing only on specific aspects of GS, mainly within sensitive therapeutic classes [ 16 – 19 ]. Kesselheim et al. [ 18 ], for instance, investigated the impact of generic AEDs on clinical outcomes, namely seizure control, and hypothesized superiority of original products. Although the meta-analysis showed “no difference in the odds of uncontrolled seizure for patients on generic medications compared with patients on original-name medications”, observational studies found health services utilization to be slightly increased after GS. The authors attributed this insight to a detection bias caused by “concern from patients or physicians about the effectiveness of generic AEDs”. Similarly, economic outcomes of AEDs were assessed by Duh et al. [ 16 ] who found generic AEDs to cause higher healthcare costs than their original counterparts in both stable and unstable epilepsy patients. Multiple-generic substitution increased this effect even more.[ The findings of these two reviews apply to our results in regard to both clinical and economic outcomes. Desmarais et al. [ 17 ] investigated the clinical equivalence of original and generic psychotropic medications such as anticonvulsants and mood stabilizers. Besides raising compliance issues, generics caused clinical deterioration, adverse effects and changes in pharmacokinetics while leading to lower than expected cost savings. The authors therefore suggested generic switching of psychotropic medication to be advised only on an individual basis while simultaneously monitoring the switch [ 17 ].

Another systematic review by Kesselheim et al. [ 18 ] focused on clinical evidence in cardiovascular disease while also examining related opinions of editorialists. The analyses did not reveal superiority of either drug type, but found a considerable amount of editorials opposing generic drugs. While these reviews addressed mostly sensitive therapeutic categories, most of them found generics to result in similar clinical effects. In accordance with our findings, these reviews found economic consequences to be higher in periods of generic use compared to periods of original use. Altogether, these reviews revealed reservations and concerns in treatment routines of generics.

Based on our findings, we are able to observe suggested trends based on a significantly heterogeneous review. Future work will look to validate these trends with more robust methods as demonstrated in other more homogenous clinical and economic reviews.

We detected a need for more systematic reviews that determine the impact of GS on clinical and economic outcomes while differentiating between therapeutic classes since substitution may be more sensitive in some areas than others due to their pharmaceutical characteristics. Moreover, patient groups should be subdivided into patients receiving a new and those receiving a maintenance therapy as generics may have different effects for those who start a new treatment than for those who are already stable on a treatment. This is especially true for sensitive therapeutic classes not only with a narrow therapeutic window (e.g., AEDs), but also others such as drugs used in schizophrenia.

Despite mainly similar clinical effects, our analyses suggest that original to generic drug substitution may not reduce costs, particularly in sensitive therapeutic areas such as with AEDs or immunosuppressive drugs. Evidence on clinical outcomes was slightly more distinct in studies with patients on maintenance therapy than in treatment-naïve patients. As we found only one economic study in patients receiving de novo therapy, a comparison with the remaining seven studies with maintenance therapy patients seems unreasonable. Since evidence is heterogeneous and in this context influenced by several other influencing factors, further research is needed in GS. Studies should ideally be based on real world evidence to determine the true comparative effectiveness of GS. Preference should be given to interventional approaches which randomize patients to generic and brand arms, control for co-morbidities, disease severity, maintenance versus de novo therapy, etc. We therefore recommend that research in GS focuses on systematic approaches in therapeutic areas in order to analyse outcomes and uncertainty.

Acknowledgments and funding

This study was in part funded by Abbott (Allschwil, Switzerland). We would like to thank Anke-Peggy Holtorf and Zoltán Kaló for their scientific input.

Author contributions

• Holger Gothe developed the concept, reviewed and interpreted the literature, and wrote the review. He updated and amended the manuscript in order to meet the reviewer’s suggestions. He is the guarantor for the overall content.
• Imke Schall did conceptual work, extracted and interpreted the literature, and wrote the review.
• Kim Saverno did conceptual work, extracted and interpreted the literature, and wrote the review.
• Martina Mitrovic extracted and interpreted the literature.
• Agnes Luzak extracted and interpreted the literature.
• Diana Brixner designed the concept, reviewed the data, interpreted the results and wrote the review.
• Uwe Siebert supervised the conceptual work, as well as the accomplishment of the review and the preparation of the manuscript. He is the corresponding author of the paper.

Conflict of interest declarations

The Institute of Public Health, Medical Decision Making and Health Technology Assessment, at UMIT received funding from Abbott, a manufacturer of branded generics, for the study at hand. Holger Gothe, Imke Schall, Kim Saverno, Martina Mitrovic, and Agnes Luzak were staff members at UMIT during the accomplishment of the review, Uwe Siebert is Department Director at UMIT. Diana Brixner has been funded by Abbott to travel to meetings to present data relevant to this publication.

Appendix: search strategy

Detailed search syntax for medline via pubmed and the cochrane database of systematic reviews.

Publications cited in the article

Publications included in the review.

Substitute Goods Research Paper

• To find inspiration for your paper and overcome writer’s block
• As a source of information (ensure proper referencing)
• As a template for you assignment

Substitute Goods; Pens and Pencils

Substitute goods can be defined as those goods that customers views as alternative. They can also be seen as those goods that give consumers similar benefits. In other words, these goods satisfy the same needs. In most cases, the buyer takes several things into consideration before making their final decisions on the choice of the goods to buy more so in the case of substitute goods.

In this case, pens and pencils can be considered as substitute goods. This is because they yield same benefits to the consumer. For instance, both pen and pencil are used for writing. They can be used interchangeably. Consumers may either decide to write using pen or using a pencil. Therefore, pens and pencils are perfect substitutes. This is because they are both used exactly for the same purpose, which is writing.

Impacts on supply of pens of a technological breakthrough which reduces the cost of producing pens

Substitute goods usually offer a high level of competition in the market. This is because buyers can easily substitute them any time. This aspect creates competition between these products.

In this case, if a technological breakthrough reduces the cost of producing pens, then the minimum price levels which pen producers can offer in the market will fall accordingly. This will lead to a fall in prices of pens. However, the prices of pencils will remain constant.

The quantity of a product supplied in the market is directly proportional to the prices of the product in the market (Forgang and Einolf 171). In other words, the higher the prices, the higher the quantities of a specific product that producers will be willing to provide in the market.

In this case, technological advancement has led to reduction in the cost of production of pens. This implies that the producer will be willing to supply a larger quantity of pens at the prevailing price levels. Therefore, the quantity of pens supplies in the market is more likely going to increase.

As a result of reduction in the production cost of pens, producers may decide to lower the prices. As a result, pens will become cheaper compared to pencils. Since the two commodities are substitutes, some buyers will shift from using pencils to pens.

However, this statement is based on the assumption that the consumers are behaving rationally. A rational consumer will tend to choose an alternative that maximizes their benefits and minimizes their costs.

A technological breakthrough in pen manufacturing will cause the supply function of the pens to shift outwards. The quantity of pens supplied will increase significantly. This is as a result of increase in the quantity demanded as a result of a fall in prices.

Impacts on the price of pens and the quantity demanded for both pens and pencils after a technological breakthrough which reduces the cost of producing pens

Since substitute goods can be used interchangeably, they exert competitive pressure in case the prices or the quality of one of these products changes. In this case, a technological development has led to a significant reduction in the prices of pens. As a result, the quantity of pens demanded will increase.

From the graph above, it is clear that the quantity demanded is inversely proportional to the prices. In other words, the higher the prices, the lower the quantity of a product demanded and vice versa. From the graph above, the original price of pen was p1.

After a technological breakthrough, the production of pens falls significantly. As a result, the prices of pens fall from p1 to p2. At price p1, the buyers are willing to buy Q1 of pens. At price level p2, the buyers are willing to buy Q2 of pens. Therefore, it is clear that the quantity of pens demanded will increase significantly after a fall in prices.

On the other hand, the quantity of pencils demanded will fall significantly. Since pens and pencils are substitutes and that they serve the same purpose to the consumer, most of the buyers will turn to buy pens because they will be cheaper.

The substitute goods usually have positive cross elasticity of demand. This implies that an increase in price of one of these goods leads to an increase in prices of the other good. Consequently, the quantity of pencils demanded will fall significantly.

From the graph above, a decrease in the prices of pens will cause the demand curve for pencils to shift in. This leads to a reduction in the quantity of pencils demanded significantly.

How managers for pen-makers and pencil-makers should decide given the above answers

From the above discussion, it is clear that the technological breakthrough in production of pens will favour pen manufacturers while it will present a big threat to the pencil manufacturers.

This is because the quantity demanded of pencils will tend to fall as more people shifts from using pencils to pens which are now cheaper than before. Therefore, there is a need for the managers of pen-makers and pencil-makers to take appropriate actions in order to retain and improve their performance respectively.

For the pencil-makers manager, it is advisable to take appropriate actions which can reverse the trends of demand for pencils arising from a fall in prices of pens. One of the actions that the managers can consider is differentiation. Differentiations play a significant role in increasing the sales of substitute goods which tends to compete in the same market (Piana par 6).

According to Forgang Einolf, differentiation will also help the pencil makers from reducing prices to unprofitable levels (170). Since pens and pencils do not have exact identical features, it will be easier to differentiate the two products.

This can be through improvement in the quality and also introducing a wide variety of pencils. As a result, buyers will tend to buy the product to enjoy the unique features which are not present in the other substitutes. As a result, the demand for pencils will increase.

On the other hand, the managers for pen-makers need to apply appropriate measures in order to maximize their profits. Since the level of demand for the pens has increased, the managers should take necessary measures to increase their production in order to satisfy the increase in demand.

This will help in reducing shortages of peens in the markets. This may require expansion in their production capacities in order to satisfy this demand.

Works Cited

Forgang, William and Einolf, Karl. Management Economics: An Accelerated Approach . New York: M.E. Sharpe, 2007.

Piana, Valentino. “ Substitute Goods .” Economics Web Institute , 2005. Web.

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Culturally Responsive Professional Development Through Conceptual Change; A Case Study of Substitute Teachers in Urban School Districts

Frank J. Feola , Cleveland State University

Date of Award

Degree type.

Dissertation

Education and Human Services

First Advisor

Carl, James

Subject Headings

Substitute teachers -- Ohio -- Case studies, Teachers -- In-service training -- Ohio -- Case studies, Multicultural education -- Ohio -- Case studies, Autodidactic cultural diversity development, Autoethnography, Case study, Conceptual change model, Culturally responsive teaching, Culture, Narrative inquiry, Policy, Qualitative research, Substitute teachers, Urban schools

The purposes of this research were to analyze the influence of participants' experiences on their culturally responsive pedagogical development and consider the policy implications for higher education, schools and school districts, and the state. Four substitute teachers from three urban school districts participated in a professional development experience--autodidactic cultural diversity development--to learn about culturally responsive pedagogy and implement it in their classrooms. Participants' upbringing, collegiate experiences, substitute teaching experiences, and the professional development influenced their development as culturally responsive educators. This research may also be used to inform policy discussions regarding the value and applicability of the substitute teaching experience for preservice teachers and cultural diversity professional development for substitute teachers. Autodidactic cultural diversity development is comprised of the culturally responsive pedagogical taxonomy (Feola's taxonomy) and literature-integrated, autoethnographic reflection. The taxonomy includes nine facets for learning the attitudes and skills of culturally responsive pedagogy. Participants read nine excerpts from the culturally responsive teaching literature, which illustrated aspects of the taxonomy, over 15 weeks and used an autoethnographic reflection form to analyze eight substitute teaching experiences. The structured reflection promoted the integration of the literature and their teaching experiences. Case study and narrative inquiry methodologies informed data collection and analysis. Utilizing data from two focus groups, two individual interviews, and eight written reflections, participants' culturally responsive pedagogical development was analyzed through a conceptual framework of the conceptual change model. NVIVO, a qualitative research analysis software, was used to facilitate data analysis. Each participant's case highlights her or his development and the aspects of this experience that promoted the

Recommended Citation

Feola, Frank J., "Culturally Responsive Professional Development Through Conceptual Change; A Case Study of Substitute Teachers in Urban School Districts" (2009). ETD Archive . 97. https://engagedscholarship.csuohio.edu/etdarchive/97

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