Characterization of "neo-dermis" formation beneath cultured human epidermal autografts transplanted on muscle fascia

Epidermal grafting for wound healing: a review on the harvesting systems, the ultrastructure of the graft and the mechanism of wound healing

Epidermal grafting for wound healing involves the transfer of the epidermis from a healthy location to cover a wound. The structural difference of the epidermal graft in comparison to the split-thickness skin graft and full-thickness skin graft contributes to the mechanism of effect. While skin grafting is an epidermal transfer, little is known about the precise mechanism of wound healing by epidermal graft. This paper aims to explore the evolution of the epidermal graft harvesting system over the last five decades, the structural advantages of epidermal graft for wound healing and the current hypotheses on the mechanism of wound healing by epidermal graft. Three mechanisms are proposed: keratinocyte activation, growth factor secretion and reepithelialisation from the wound edge. We evaluate and explain how these processes work and integrate to promote wound healing based on the current in vivo and in vitro evidence. We also review the ongoing clinical trials evaluating the efficacy of epidermal graft for wound healing. The epidermal graft is a promising alternative to the more invasive conventional surgical techniques as it is simple, less expensive and reduces the surgical burden for patients in need of wound coverage.

Cutaneous Tissue Engineering and Lower Extremity Wounds (Part 1)

Tissue-engineered skin is a novel therapeutic with which difficult-to-heal lower extremity wounds may be treated. Such skins are products of cutaneous tissue engineering that provide an alternative for autologous or allogeneic tissue transplantation, thereby avoiding problems associated with donor site availability, the risk of infection, and scarring. Recently developed tissue-engineered skin equivalents have shown to be superior in certain ways to compression therapy for refractory venous ulcers and acute wounds. These biologic products behave similarly to autografts.

Outcome of Burns Treated With Autologous Cultured Proliferating Epidermal Cells: A Prospective Randomized Multicenter Intrapatient Comparative Trial

Standard treatment for large burns is transplantation with meshed split skin autografts (SSGs). A disadvantage of this treatment is that healing is accompanied by scar formation. Application of autologous epidermal cells (keratinocytes and melanocytes) may be a suitable therapeutic alternative, since this may enhance wound closure and improve scar quality. A prospective, multicenter randomized clinical trial was performed in 40 adult patients with acute full thickness burns. On two comparable wound areas, conventional treatment with SSGs was compared to an experimental treatment consisting of SSGs in combination with cultured autologous epidermal cells (ECs) seeded in a collagen carrier. The primary outcome measure was wound closure after 5-7 days. Secondary outcomes were safety aspects and scar quality measured by graft take, scar score (POSAS), skin colorimeter (DermaSpectrometer) and elasticity (Cutometer). Wound epithelialization after 5-7 days was significantly better for the experimental treatment (71%) compared to the standard treatment (67%) (p = 0.034, Wilcoxon), whereas the take rates of the grafts were similar. No related adverse events were recorded. Scar quality was evaluated at 3 (n = 33) and 12 (n = 28) months. The POSAS of the observer after 3 and 12 months and of the patient after 12 months were significantly better for the experimental area. Improvements between 12% and 23% (p ≤ 0.010, Wilcoxon) were detected for redness, pigmentation, thickness, relief, and pliability. Melanin index at 3 and 12 months and erythema index at 12 months were closer to normal skin for the experimental treatment than for conventional treatment (p ≤ 0.025 paired samples t-test). Skin elasticity showed significantly higher elasticity (p = 0.030) in the experimental area at 3 months follow-up. We showed a safe application and significant improvements of wound healing and scar quality in burn patients after treatment with ECs versus SSGs only. The relevance of cultured autologous cells in treatment of extensive burns is supported by our current findings.

Clinical application of cultured epithelial autografts on acellular dermal matrices in the treatment of extended burn injuries

Achieving permanent replacement of skin in extensive full-thickness and deep partial-thickness burn injuries and chronic wounds remains one of the fundamental surgical problems. Presently, split-thickness skin grafts are still considered the best material for surgical repair of an excised burn wound. However, in burns that affect greater than 50% of total body surface area, the patient has insufficient areas of unaffected skin from which split-thickness skin grafts can be harvested. The use of cultured epithelial (or epidermal) autografts (CEAs) has achieved satisfactory results. But the take rate of CEAs is poor in full-thickness bed or in chronically infected area. Providing temporary cover with allograft skin, or a more permanent allodermis, may increase clinical take. This review aims to (1) describe the use of CEAs in the regeneration of the epidermis, (2) introduce the application of the acellular dermal matrices (ADMs) in the clinics, and (3) enhance understanding of the CEAs applied with ADM as an appropriate strategy to treat the extended burn injuries. The current evidence regarding the cultured epithelial cell or keratinocyte autograft and dermal grafts applied in the treatment of burn injuries was investigated with an extensive electronic and manual search (MEDLINE and EMBASE). The included literature (N=136 publications) was critically evaluated focusing on the efficacy and safety of this technique in improving the healing of the deep dermal and full-thickness burn injuries. This review concluded that the use of ADM with CEAs is becoming increasingly routine, particularly as a life-saving tool after acute thermal trauma.

Survival of Apligraf in acute human wounds

Apligraf consists of bovine collagen dermis seeded with allogeneic male fibroblasts and keratinocytes. It is been shown to promote healing, but the length of persistence and pathological features have not been characterized previously in acute wounds. Forty-eight deep dermal wounds were created and Apligraf, a split-skin graft (SSG), or a dressing was applied. Biopsies of wounds were taken for immunohistochemical analysis and polymerase chain reaction was performed to detect the Y chromosome from Apligraf cells in 14 female wounds. Male allogeneic DNA was detected in wounds for the first 4 weeks. All subsequent time points were negative apart from one biopsy at 6 weeks. The wounds took 4-9 weeks to heal, with the Apligraf exhibiting no features of engraftment. This was in contrast to the rapid healing seen in the SSG control group. Histology revealed a more intense cellular infiltrate, but less vascularization below Apligraf compared with controls. Evidence of an epidermal-mesenchymal interaction was observed. This is the first article to elucidate the survival of Apligraf allogeneic cells in acute wounds in immunocompetent human subjects for up to 6 weeks and demonstrates that in the management of acute surgical wounds, Apligraf has a role only as a temporary biological dressing.

Upside-down transfer of porcine keratinocytes from a porous, synthetic dressing to experimental full-thickness wounds

Currently, the use of cultured epithelial autografts as an alternative to split-thickness skin autografts for coverage of full-thickness wounds is limited due to fragility of the sheet and variability in the outcome of healing. This could be circumvented by the transfer of proliferating keratinocytes, instead of differentiated sheets, to the wound bed and the "in vivo" regeneration of epidermis. The aim of this study was to achieve re-epithelialization on experimental full-thickness wounds in the pig using a porous, synthetic carrier seeded with proliferating keratinocytes. Porcine keratinocytes were isolated by enzymatic digestion and cultured in Optimem basal medium with mitogens. In a full-thickness wound model, carriers with different seeding densities were transplanted upside down onto the wound bed. Keratinocytes were labeled using a fluorescent red membrane marker, PKH-26 GL. Transfer of keratinocytes and re-epithelialization were recorded macroscopically and histologically. On day 4 after transplantation, transfer of fluorescently labeled keratinocytes was shown by their presence in the granulation tissue. An immature epidermis, as well as epithelial cords and islands, formed as early as day 8. At day 12 a stratified epidermis and wound closure were established and epithelial cysts were formed by differentiation of epithelial islands. Wounds treated with seeding densities as low as 50,000 cells/cm(2) showed wound closure within 12 days, whereas wounds treated with 10,000 cells/cm(2) or the nonseeded (acellular) carriers did not show complete re-epithelialization before day 17 after treatment. This study showed that porcine keratinocytes, transplanted "upside down" in experimental full-thickness wounds using a synthetic carrier, continued to proliferate and started to differentiate, enabling the formation of a new epidermis in a time frame of 12 days.

[Cultured epidermis for the treatment of severe burns. A 2-year study (18 patients)]

AIM OF THE STUDY

For fifteen years, Edouard Herriot Burn Center has been using cultured epidermis provided by an hospital Laboratory. This means of production results in great freedom for their application compared with the centers who have to buy the cultured epidermis. In order to evaluate our clinical results, a two-year study has been performed.

MATERIAL AND METHODS

Eighteen patients suffering acute burns were concerned. The average burned area was 68% of the total body surface (range 49 to 88). The average age was 31.6 years, ranging from 1 to 58, including two children. Even autologous or allogenic epidermis was used. In our series cultured epidermis was grafted according four different strategies. It was the preparation of the wound bed by skin allografts, the association of widely meshed auto-graft with cultured epidermis, the stimulation of the healing of extensive deep second degree burns with allogenic epidermis, and the coverage of skin auto-graft donor sites.

RESULTS

Two patients died. For the survivors, the average hospital stay was 60 days (range 22 to 90), and on average 70 days over 70% TBSA burns. Cultured epidermis allowed the definitive coverage of 17% of the total body surface of the patients. This study supports the importance of a careful preparation of the patient for the engraftment of cultured epidermis.

CONCLUSION

In our opinion, in spite of the difficulties of handling of cultured epidermis, they represent a precious means of coverage for the rapid and definitive healing of extensive burns over 70% TBSA.

Extracellular matrix and keratinocyte migration

We are just beginning to understand some of the cellular mechanisms involved in human keratinocyte migration on extracellular matrix. Extracellular matrix components have differing effects on keratinocyte motility. Signalling through integrin receptors and secretion of collagenase are both components of this process. An understanding of the effect of extracellular matrix on keratinocyte migration has direct relevance to the problem of wound re-epithelialization and will assist in the development of therapeutic efforts to enhance wound healing artificially.

In vitro characterization of an artificial dermal scaffold

The treatment of extensive burn injuries has been enhanced by the development of artificial skin substitutes. Integra Artificial Skin, an acellular collagen-glycosaminoglycan (C-GAG) dermal equivalent requires a two-stage grafting procedure. However, preseeding the C-GAG dermal equivalent with cultured fibroblasts and keratinocytes, with the aim of performing a single-stage grafting procedure, may be beneficial in terms of replacing the requirement for traditional split-skin grafts. In this comparative in vitro study, the interactions of cultured human dermal fibroblasts and epidermal keratinocytes in Integra Artificial Skin in comparison to cadaver deepidermalized dermis (DED) was investigated. An increase in cell proliferation and migration in the C-GAG dermal equivalent was observed over time. Cocultures of fibroblasts and keratinocytes on both dermal equivalents showed positive expression of proliferation, differentiation, and extracellular matrix (ECM) protein markers. Organization of keratinocytes in the epidermal layers of DED composites were better compared to the C-GAG composites. Deposition of ECM proteins was enhanced in the presence of keratinocytes in both dermal equivalents. Results demonstrate that in vitro the C-GAG dermal equivalent is biocompatible for cell attachment, migration, proliferation, and differentiation. Preseeding Integra Artificial Skin with cultured autologous fibroblasts and keratinocytes for in vivo application, as a single-stage grafting procedure, warrants testing. A better clinical outcome may be achieved as shown by our in vitro results of the coculture composites.

Basement membrane formation during wound healing is dependent on epidermal transplants

The purpose of the study was to compare directly the effect of healing and the formation of the basement membrane during wound healing from two autologous primary keratinocyte cultures in the liquid environment in full-thickness wounds in pigs. Wounds were either transplanted with cultured epidermal autografts (n = 26) or autologous keratinocyte suspensions (n = 24) or treated with saline alone (n = 40) and covered with a chamber. All wounds transplanted with cultured epidermal autografts and keratinocyte cell suspensions had positive "take" after transplantation. Healing times were significantly shorter for wounds treated with either cultured epidermal autografts or keratinocyte suspensions (p = 0.0001) compared with saline-treated wounds but were not different from each other (p = 0.1835). There were no differences in cytokeratin and laminin expression; however, staining with monoclonal antibody against collagen type VII showed a lower signal for cultured epidermal autografts only on days 8 and 16 compared with keratinocyte suspensions. Electron microscope evaluation showed a higher incidence of anchoring fibrils and a more mature dermal-epidermal junction in wounds treated with keratinocyte cell suspensions at day 8. These findings may be due to the single, noncontact-inhibited cells and the early formation of an in vivo neodermis to the wet wound environment. These data suggest that wounds transplanted with autologous keratinocyte suspensions in a wet environment may be an alternative method in the treatment of wounds.

Spontaneous cell sorting of fibroblasts and keratinocytes creates an organotypic human skin equivalent

We show that an inherent ability of two distinct cell types, keratinocytes and fibroblasts, can be relied upon to accurately reconstitute full-thickness human skin including the dermal-epidermal junction by a cell-sorting mechanism. A cell slurry containing both cell types added to silicone chambers implanted on the backs of severe combined immunodeficient mice sorts out to reconstitute a clearly defined dermis and stratified epidermis within 2 wk, forming a cell-sorted skin equivalent. Immunostaining of the cell-sorted skin equivalent with human cell markers showed patterns similar to those of normal full-thickness skin. We compared the cell-sorted skin equivalent model with a composite skin model also made on severe combined immunodeficient mice. The composite grafts were constructed from partially differentiated keratinocyte sheets placed on top of a dermal equivalent constructed of devitalized dermis. Electron microscopy revealed that both models formed ample numbers of normal appearing hemidesmosomes. The cell-sorted skin equivalent model, however, had greater numbers of keratin intermediate filaments within the basal keratinocytes that connected to hemidesmosomes, and on the dermal side both collagen filaments and anchoring fibril connections to the lamina densa were more numerous compared with the composite model. Our results may provide some insight into why, in clinical applications for treating burns and other wounds, composite grafts may exhibit surface instability and blistering for up to a year following grafting, and suggest the possible usefulness of the cell-sorted skin equivalent in future grafting applications.

Novel living skin replacement biotherapy approach for wounded skin tissues

A novel living skin replacement (LSR) biotherapy concept, addressing the challenging problems related to tissue regeneration and wound healing, is presented for the treatment of skin burns, traumatic injuries and ulcerations. LSR combines elements of cell therapy along with those of tissue engineering to allow for the regeneration of wounded skin. It takes advantage of biodegradable microspheres onto which donor skin epidermal and dermal cells can be attached and expanded in vitro for subsequent direct application down to the deepest recesses of the wound bed. The key element of the biotherapy is the ability of the skin cells to migrate freely from the microspheres into the wound for regeneration of the tissues. The large surface to volume ratio of the microspheres allows for the delivery of appropriate cell numbers while minimizing the amount of biomaterial to be resorbed. This novel approach presents a number of advantages over existing therapies including facilitated cell manipulations, ease of storage and transportation, rapid clinical intervention due to the elimination of any surgical suturing or stapling, and a more natural three-dimensional tissue remodeling and anatomical compliance. Preliminary in vitro and in vivo evidence of the LSR functionality and its potential benefits is presented.

Tissue engineering of skin

The skin plays a crucial role in protecting the integrity of the body's internal milieu. The loss of this largest organ is incompatible with sustained life. In reconstructive surgery or burn management, substitution of the skin is often necessary. In addition to traditional approaches such as split- or full-thickness skin grafts, tissue flaps and free-tissue transfers, skin bioengineering in vitro or in vivo has been developing over the past decades. It applies the principles and methods of both engineering and life sciences toward the development of substitutes to restore and maintain skin structure and function. Currently, these methods are valuable alternatives or complements to other techniques in reconstructive surgery. This review article deals with the evolution and current approaches to the development of in vitro and in vivo epidermis and dermis.

Transplantation of cultured mucosal epithelium: an experimental study

We investigated morphological changes after transplantation of cultured mucosal epithelium using a modified Barrandon's method (1988). Serially cultivated human mucosal epithelium was transplanted onto the reverse side of rectangular dorsal skin flaps in hairless mice. The morphological changes in the epithelium were studied using paraffin sections. The modified Barrandon's method used in this study has advantages such as minimum external trauma and less chance of infection. The cultured epithelium was taken within 1 week and gradually increased its epithelial thickness. Keratinized epithelium arises after 3 weeks. At 4 weeks after grafting, the grafted epithelium comprised 7-10 cell layers. The structure of transplanted tissue, in conjunction with surrounding connective tissues, showed dermis-like features at day 7 after transplantation. From these results, it was confirmed that cultured mucosal epithelium could be successfully transplanted and its morphology was similar to that of normal mucosal tissue.

Genetically modified human epidermis overexpressing PDGF-A directs the development of a cellular and vascular connective tissue stroma when transplanted to athymic mice--implications for the use of genetically modified keratinocytes to modulate dermal regeneration

We investigated the hypothesis that keratinocyte-produced platelet-derived growth factor-AA (PDGF-AA) is involved in epidermal-dermal interactions and that PDGF-AA is an important mediator of the temporal and spatial events of tissue repair. Retroviral-mediated gene transfer was used to introduce the gene encoding human PDGF-A into cultures of human diploid keratinocytes. Genetic modification boosted the endogenous in vitro level of PDGF-AA secretion by over 300 fold. When PDGF-secreting cells were transplanted as epithelial sheets to athymic mice, modified keratinocytes underwent terminal differentiation and generated a stratified epithelium comparable to unmodified cells. Seven days after grafting the newly synthesized connective tissue layer subjacent to the PDGF-A-modified grafts was significantly thicker, was rich in mononuclear cells and fibroblasts, and had increased numbers of blood vessels when compared to control grafts of unmodified cells. These results suggest that PDGF-AA secreted by the epidermis is an important mediator of epithelial-mesenchymal interactions and helps to promote growth and vascularization of the underlying dermal tissue. Further, these data demonstrate the feasibility of using genetically modified cells to modulate tissue regeneration.

Cultured epithelial autograft: five years of clinical experience with twenty-eight patients

Cultured epithelial autograft (CEA) has been used as an adjunct in burn wound coverage at the Vancouver Hospital and Health Sciences Centre since 1988, and has been available to all patients admitted with significant burn injuries. During the 5-year period from 1988 to 1992 inclusive, 28 patients treated with CEA survived long enough for assessment. The mean age was 35.3 years with a mean total body surface area burn of 52.2% and a mean total full thickness injury of 42.4%. CEA was applied to wounds covering between 2% and 35% body surface area (BSA; mean 10.4%) after excision to fat or fascia. Most wounds had interim homograft coverage. Preservation of homograft dermis was attempted in three patients at the time of removal without effect. The mean CEA "take" was 26.9% of the grafted area. Eight patients had 50% or greater take and were discharged with between 1 and 19% BSA covered with CEA. Thirteen patients had no take on wounds between 2 and 16% BSA. Overall mortality in burn patients treated at the Vancouver Hospital and Health Sciences Centre from 1988 to 1992 was not significantly different from 1983 to 1987 with the populations being similar in terms of total BSA burns, age, inhalation injury, and homograft availability. When compared to a matched control population from the preceding 5 years, when CEA was not available, there was no significant difference in duration of hospital stay or number of autograft harvests. However, approximately one more debridement without autograft harvest per CEA patient occurred. Timing and depth of wound excision, interim coverage, type of dressing, and wound microbiology were not found to influence good versus poor take. The anterior trunk and thighs were the best recipient sites. Subjective differences between CEA and meshed autograft were noted. The results show that after 5 years of use, CEA engraftment continues to be unpredictable and inconsistent, and hence, it should be used as only a biologic dressing and experimental adjunct to conventional burn wound coverage with split thickness autograft.

Transplantation of keratinocytes in the treatment of wounds

BACKGROUND

Keratinocyte grafting can be used to treat acute traumatic and chronic non-healing wounds. The keratinocyte sheets are fragile and clinical "take" is difficult to assess, especially as activated keratinocytes secrete many growth factors, which have effects on wound healing apart from take. We have developed animal models of grafting that allow us to examine factors influencing autologous keratinocyte graft take. Results show clearly that pretreatment of the wound bed with viable dermis greatly increases the take of keratinocyte grafts.

DATA SOURCES

International literature.

CONCLUSIONS

As a greater understanding of the complex interactions of cell and matrix evolve, so will potential therapeutic maneuvers, not just in the field of cultured keratinocyte grafts, but clearly in that of benign tumors, for example, keloids, and that of oncology. There is now overwhelming evidence of the requirement for a dermal substitute for cultured keratinocyte autografts, and the sheet complexity of the situation demands that this should approximate live human dermis as closely as possible. The stumbling blocks relate to avoiding the risks of viral transmission, tissue matching of host and donor, providing early epithelial cover, and improving delivery systems for fragile keratinocyte grafts.

Culturing skin in vitro for wound therapy

Current tissue-culture techniques enable keratinocytes from a small piece of skin to be grown into sheets of epithelium, or cultured keratinocyte grafts, that are suitable for treating wounds. Serial subculture enables rapid expansion of a cell population, such that grafts of a total area equivalent to that of the surface of an adult can be obtained from an initial skin biopsy of approximately 2 cm2 in under one month. In this article, the methods currently used for culturing keratinocytes, the search for a fully functional replacement for the dermal elements of skin, and the prospects for clinical development of these technologies in the near future are discussed.

Gene transfer into cultured human epidermis and its transplantation onto immunodeficient mice: an experimental model for somatic gene therapy

To try epidermis as a target for somatic gene therapy we studied transfected primary human keratinocytes grown in culture and grafted onto athymic mice. We have developed a novel technique for grafting cultured epidermal sheets onto mice. First, the graft is placed on the dorsal muscle fascia underneath the mouse skin using the latter as a bandage. Secondly, the mouse skin above the graft is removed, which exposes the grafted skin to open air and thus stimulates terminal differentiation. A novel method for the discrimination between murine and human epidermal cells is also presented, employing in situ hybridization with human Alu repeated DNA sequences. During monolayer culture the keratinocytes were lipofected with the gene for human growth hormone in an Epstein-Barr virus-based expression vector. The cells were allowed to develop a multilayered tissue for 5 d, secreting human growth hormone into the medium at a daily rate of at least 50 ng/cm2 of tissue. The transfected tissues were then grafted onto mice. We detected human growth hormone at levels of up to 2.6 ng/ml in mouse serum for 4 d, but later no human growth hormone could be found, although the transplants survived for months. To investigate the fate of the transfected cells in the transplanted tissue, we labeled them with the beta-galactosidase reporter gene. The cells staining positive for X-gal were found exclusively in the most superficial differentiated layers at 7 d after transplantation. This may be the main reason why no human growth hormone is found in the mouse circulation at this time.

Direct comparison of a cultured composite skin substitute containing human keratinocytes and fibroblasts to an epidermal sheet graft containing human keratinocytes on athymic mice

This study compares two techniques for making cultured skin substitutes: a composite graft made of human fibroblasts and keratinocytes on a collagen-glycosaminoglycan membrane (CG) and a cultured epidermal cell sheet graft (CEG), without a dermal component. The "take" and quality of these cultured skin substitutes were evaluated by placing them on full-thickness, excised wounds of athymic mice. These cultured skin substitutes were placed onto 2-X-2-cm wounds created on athymic mice. Mice were sacrificed at days 10, 20, and 42 with histologic sections obtained for light, electron, immunofluorescent, and immunohistochemical microscopy. "Take" was determined separately by a direct immunofluorescent stain for human leukocyte ABC antigens. There were ten mice of each graft type with at least two animals sacrificed at each time point. Results showed positive "take" for all animals. Grossly, there was little difference between the two graft types, with the CEG having occasional blister formation. By light microscopy, the CEG had a dissociation of dermis from epidermis until day 42, which was never apparent with the CG. By day 42, the CG had increased dermoepidermal interdigitations similar to rete ridges, with a mature epithelium. Neither of these findings were seen with the CEG. Immunofluorescent and immunohistochemical microscopy for type IV collagen and laminin, as well as electron microscopy, showed similar retardation of basement membrane formation with the CEG. Using this model, the composite graft had significant advantages over the epidermal sheet graft in the closure of full-thickness wounds.

Restoration of basement membrane structure in pigs following keratinocyte autografting

The attachment of grafts of keratinocyte sheets is mediated in part by the presence and organisation of basement membrane components. The reappearance of basement membrane following keratinocyte autografting was examined in pigs. These studies showed that there was rapid expression of anchoring fibrils and hemidesmosomes, which reached normal numbers at 10 days. However, the length of hemidesmosomes did not reach normal size during the period of study. Weakness of attachment of keratinocyte autografted epidermis was found to lie between the basement membrane and the granulation tissue. This suggests that reported clinical problems with keratinocyte graft attachment may be mediated not only by delay in maturation of the basement membrane but also by its poor integration with collagen of the wound bed.

Treatment of burns with skin substitutes

More than 2 million persons sustain thermal injuries in the United States annually (Monafo and Crabtree, 1985) and more than 10,000 burn victims die (Collini and Kealey, 1989). The principal factors affecting mortality are the total area burned and the area of third degree (full thickness) burns (Tompkins et al., 1985) with wound sepsis being the leading cause of mortality. Early aggressive excision and immediate covering of the wounds improve survival (Herndon and Parks, 1986). Various biological and synthetic substrates have been employed to replace the injured skin. Most of these provide a permeability barrier which substitutes for the epidermal function of the lost skin. An ideal skin replacement should also provide a substitute for dermis, which provides both support and stability for the epidermal replacement and prevents wound contraction. The dermal and epidermal replacement should be firmly integrated by a complete basement membrane zone (BMZ).

New grafts for old? A review of alternatives to autologous skin

Immediate resurfacing of skin defects is a challenging prospect, especially in patients with extensive full-thickness burns. Currently, split-thickness autografts offer the best form of wound coverage, but limited donor sites and their associated morbidity have prompted the search for alternatives. The application of allogeneic skin is restricted by availability and the risk of transmission of infection, whilst synthetic skin substitutes are simply expensive dressings. The problems of limited expansion may be overcome by culturing keratinocytes in vitro. Unlike autologous cells, allogeneic keratinocytes are available immediately, although they survive for less than a week when applied to full-thickness skin defects. Moreover, the absence of a dermal component in these grafts predisposes to instability and contracture. A cross-linked collagen and glycosaminoglycan dermal substitute, covered with thin split-skin grafts or cultured autologous keratinocytes, shows promise in burns patients. An alternative is a collagen matrix populated by allogeneic fibroblasts and overlaid with cultured autologous or allogeneic keratinocytes. The clinical application of cultured grafts remains imperfect but offers the prospect of immediate coverage and massive expansion.

In vivo optimization of a living dermal substitute employing cultured human fibroblasts on a biodegradable polyglycolic acid or polyglactin mesh

The design of a skin-substitute must address the need for a dermal component, as this mesenchymally-derived tissue is important in maintaining the integrity and function of skin. An in vivo study was undertaken to assess the use of two biodegradable meshes, polyglycolic acid and polyglactin-910, as carriers for cultured human fibroblasts in a living dermal replacement. The consistent vascularization and epithelialization of these grafts placed on athymic mice showed that this has potential in re-creating the dermis in a skin-substitute.