Survival of cultured allogeneic keratinocytes transplanted to deep dermal bed assessed with probe specific for Y chromosome

Dried human-cultured epidermis accelerates wound healing in a porcine partial-thickness skin defect model

Introduction

Autologous cultured epidermis (CE) is an effective approach for overcoming the deficiency of donor sites to treat extensive burns. However, the production of autologous CE takes 3-4 weeks, which prevents its use during the life-threatening period of severe burns. In contrast, allogeneic CE can be prepared in advance and used as a wound dressing, releasing several growth factors stimulating the activity of recipient cells at the application site. Dried CE is prepared by drying CEs under controlled temperature and humidity conditions until all the water is completely removed and no viable cells are present. Dried CE accelerates wound healing in a murine skin defect model and is potentially a new therapeutic strategy. However, the dried CE safety and efficacy have not yet been studied in large animal models. Therefore, we studied the safety and efficacy of human-dried CE in wound healing using a miniature swine model.

Methods

Human CE was manufactured using Green's method from donor keratinocytes. Three types of CEs (Fresh, Cryopreserved, and Dried) were prepared, and the ability of each CE to promote keratinocyte proliferation was confirmed in vitro. Extracts of the three CEs were added to keratinocytes seeded in 12-well plates, and cell proliferation was evaluated using the WST-8 assay for 7 days. Next, we prepared a partial-thickness skin defect on the back of a miniature swine and applied three types of human CE to evaluate wound healing promotion. On days 4 and 7, the specimens were harvested for hematoxylin-eosin, AZAN, and anti-CD31 staining to assess epithelialization, granulation tissue, and capillary formation.

Results

The conditioned medium containing dried CE extract significantly enhanced keratinocyte proliferation compared to the control group (P < 0.05). In vivo experiments revealed that human-dried CE significantly accelerated epithelialization at day 7 to the same extent as fresh CE, compared to the control group (P < 0.05). The three CE groups similarly affected granulation formation and neovascularization.

Conclusions

Dried CE accelerated epithelialization in a porcine partial-thickness skin defect model, suggesting that it may be an effective burn treatment alternative. A clinical study with a long-term follow-up is needed to assess the applicability of CEs in clinics.

The use of human-derived feeder layers for the cultivation of transplantable human epidermal cell sheet to repair second degree burn wounds

BACKGROUND AND OBJECTIVES

Human epidermal cell sheet (human-ECS) is a feasible treatment option for wound injury. Traditionally, researchers often use murine 3T3 fibroblast cells as feeder layer to support human epidermal cell sheet grafts, thus increase risk to deliver animal-borne infection. To overcome the potential risks involved with xenotransplantation, we develop human foreskin fibroblast cell as feeder layer culture system and investigate the effects of human-ECS on second-degree burn wound healing in mini-pig in order to develop more effective and safer therapies to enhance wound healing in human.

MATERIALS AND METHODS

Human epidermal keratinocytes and fibroblasts were isolated from foreskin tissue and were co-cultured to manufacture human-ECS. The cell morphology was monitored with phase-contrast microscopy, the stem cell markers were assessed by flow cytometry, and by colony-forming efficiency (CFE) assay. The structure of human-ECS was observed by hematoxylin and eosin staining. Expression of cytokines in human-ECS was confirmed by enzyme-linked immunosorbent assay. Second-degree burn wounds were created on the dorsal of miniature pig to evaluate the effect of oil gauze, oil gauze combined with commercial epidermal growth factor (EGF) cream, and oil gauze combined with human-ECS. Wound healing rate, histological examination, and Masson staining were measured to observe the wound repair efficacy. Real-time PCR and Western blot were utilized to detect the expression level of EGF and interleukin 6 (IL-6).

RESULTS

Stratified human-ECS with 6-7 layers of epidermal cells was successfully cultivated with human-derived feeder cells, in which epidermal cell highly expressed CD49f and CFE was 3% ± 0.45%. Application of human-ECS induced a higher wound healing rate than commerical EGF cream and oil gauze control. The expression of EGF in human-ECS group was higher than those in the other groups; however, the expression of IL-6 was significantly decreased at day 14 by human-ECS treatment group.

CONCLUSIONS

Human-derived feeder cells are suitable for cultivation of human-ECS, avoiding pathogen transmission. Human-ECS could enhance second-degree burn wound healing, and its promoting effect involved secreting a variety of cytokines to regulate tissue reparative process.

Bi-layered living cellular construct resulted in greater healing in an alloxan-induced diabetic porcine model

Tissue-engineered skin constructs, including bi-layered living cellular constructs (BLCC) used in the treatment of chronic wounds, are structurally/functionally complex. While some work has been performed to understand their mechanisms, the totality of how BLCC may function in wound healing remains unknown. To this end, we have developed a delayed wound healing model to test BLCC cellular and molecular mechanisms of action. Diabetes was chemically-induced using alloxan in Yucatan miniature pigs, and full-thickness wounds were generated on their dorsum. These wounds were either allowed to heal by secondary intention alone (control) or treated with a single or multiple treatments of a porcine autologous BLCC. Results indicated a single treatment with porcine BLCC resulted in statistically significant wound healing at day 17, while four treatments resulted in statistically significant healing on days 10, 13, and 17 compared to control. Statistically accelerated wound closure was driven by re-epithelialisation rather than contraction or granulation. This porcine diabetic model and the use of a porcine BLCC allowed evaluation of healing responses in vivo without the complications typically seen with either xenogenic responses of human/animal systems or the use of immune compromised animals, expanding the knowledge base around how BLCC may impact chronic wounds.

Stem and Somatic Cell Monotherapy for the Treatment of Diabetic Foot Ulcers: Review of Clinical Studies and Mechanisms of Action

Diabetic foot ulcer (DFU) is one of the most severe complications of diabetes mellitus, often resulting in a limb amputation. A cell-based therapy is a highly promising approach for an effective DFU treatment. However, there is no consensus regarding the most effective cell type for DFU treatment. Various cell types contribute to chronic wound healing via different mechanisms. For example, application of keratinocytes can stimulate migration of native keratinocytes from the wound edge, while mesenchymal stem cells can correct limb ischemia. To assess the effectiveness of a certain cell type, it should be administered as a monotherapy without other substances and procedures that have additional therapeutic effects. In the present review, we described therapeutic effects of various cells and provided an overview of clinical studies in which stem and somatic cell-based therapy was administered as a monotherapy. Topical application of somatic cells contributes to DFU healing only, while injection of mesenchymal stem cells and mononuclear cells can break a pathophysiological chain leading from insufficient blood supply to DFU development. At the same time, the systemic use of mesenchymal stem cells carries greater risks. Undoubtedly, cell therapy is a potent tool for the treatment of DFU. However, it is vital to conduct further high-quality clinical research to determine the most effective cell type, dosage and way of administration for DFU treatment. Ischemia, neuropathy and neuro-ischemia are underlying factors of diabetic foot ulcer. Stem and somatic cells monotherapy can improve chronic wound healing via different mechanisms.

Dried human cultured epidermis accelerates wound healing in diabetic mouse skin defect wounds

Cryopreserved allogeneic cultured epidermis (CE) is used for treating second-degree burn wounds and diabetic foot ulcers; however, the need for cryopreservation limits its use. We have previously reported that CE accelerates wound healing irrespective of its viability and hypothesized that dehydrated CEs lacking living cells may act as an effective wound dressing. We prepared dried CE and investigated its morphological and physical properties and wound-healing effects and compared them with those of cryopreserved CE. Hematoxylin-eosin staining, immunostaining for basement membrane, and electron microscopy revealed that the morphologies of dried CE and cryopreserved CE were comparable and that the membrane structure was not damaged. The breaking strength, modulus of elasticity, and water permeability of dried CE were comparable with those of the cryopreserved CE. Furthermore, the levels of various active cytokines and chemokines in dried CE were comparable with those in cryopreserved CE. Dried CE applied to skin defect in diabetic mice significantly reduced the wound area and increased the new epithelium length 4 and 7 days after implantation, similar to that observed for cryopreserved CE. Consequently, dried CE had similar morphological and physical properties and wound-healing effects compared with those of cryopreserved CE and can be a physiological and versatile wound-dressing.

Epidermolysis Bullosa: A Review of the Tissue-Engineered Skin Substitutes Used to Treat Wounds

Skin wound healing is a crucial process for regenerating healthy skin and avoiding the undesired consequences associated with open skin wounds. For epidermolysis bullosa (EB), a debilitating group of fragile skin disorders currently without a cure, skin blistering can often be severe and heal poorly, increasing susceptibility to life-threatening complications. To prevent these, investigational therapies have been exploring the use of tissue-engineered skin substitutes (TESSs) aimed at replacing damaged skin and promoting long-term wound closure. These products have either been developed in house or commercially sourced and are composed of allogeneic or autologous human skin cells, often with some form of bioscaffolding. They can be broadly classified based on their cellular composition: keratinocytes (epidermal substitutes), fibroblasts (dermal substitutes) or a combination of both (composite substitutes). Encouraging long-term wound healing has been achieved with epidermal substitutes. However, these substitutes have not demonstrated the same efficacy for all patients, which may be due to the molecular heterogeneity observed between EB subtypes. Autologous composite TESSs, which more closely resemble native human skin, are therefore being investigated and may hold promise for treating an extended range of patients. Additionally, future TESSs for EB are focused on using gene-corrected patient skin cells, which have already demonstrated remarkable long-term wound healing capabilities. In this review, we provide an overview of the different TESSs that have been investigated in clinical studies to treat patients with EB, as well as their long-term wound healing results. Where available, we describe the methods used to develop these products to inform future efforts in this field.

Ex vivo gene modification therapy for genetic skin diseases-recent advances in gene modification technologies and delivery

Genetic skin diseases, also known as genodermatoses, are inherited disorders affecting skin and constitute a large and heterogeneous group of diseases. While genodermatoses are rare with the prevalence rate of less than 1 in 50,000 - 200,000, they frequently occur at birth or early in life and are generally chronic, severe, and could be life-threatening. The quality of life of patients and their families are severely compromised by the negative psychosocial impact of disease, physical manifestations, and the lack or loss of autonomy. Currently, there are no curative treatments for these conditions. Ex vivo gene modification therapy that involves modification or correction of mutant genes in patients' cells in vitro and then transplanted back to patients to restore functional gene expression has being developed for genodermatoses. In this review, the ex vivo gene modification therapy strategies for genodermatoses are reviewed, focusing on current advances in gene modification and correction in patients' cells and delivery of genetically modified cells to patients with discussions on gene therapy trials which have been performed in this area.

Human cultured epidermis accelerates wound healing regardless of its viability in a diabetic mouse model

Allogeneic cultured epidermis (allo-CE) is a cultured keratinocyte sheet manufactured from donor cells and promotes wound healing when used in deep dermal burns, donor sites, and chronic ulcers and serves as a wound dressing. Allo-CE is usually cryopreserved to be ready to use. However, the cryopreservation procedure will damage the cell viability, and the influence of Allo-CE, according to its viability or wound healing process, has not been evaluated sufficiently. In this study, we aimed to prove the influence of keratinocyte viability contained in allo-CEs on wound healing. We prepared CEs with Green’s method using keratinocytes obtained from a polydactyly patient and then prepared four kinds of CEs with different cell viabilities [fresh, cryopreserved, frozen, and FT (freeze and thaw)]. The cell viabilities of fresh, cryopreserved, frozen, and FT CEs were 95.7%, 59.9%, 16.7%, and 0.0%, respectively. The four CEs had homogeneous characteristics, except for small gaps found in the FT sheet by transmission electron microscopy observation. The four CEs were applied on the full-thickness skin defect of diabetic mice (BKS.Cg-Dock 7^m +/+ Lepr^db/Jcl), and the wound area and neoepithelium length were evaluated on days 4, 7, and 14. As a result, FT CEs without viable cells similarly promoted epithelialization on days 4 and 7 (p<0.05) and accelerated wound closure on day 7 (p<0.01) as fresh CEs compared with the control group. In conclusion, the promoting effect of allo-CE on wound healing does not depend on cell viability. Lyophilized CEs may be a suitable wound dressing with a long storage period at room temperature.

Cultured Human Epidermis Combined With Meshed Skin Autografts Accelerates Epithelialization and Granulation Tissue Formation in a Rat Model

INTRODUCTION

As the take rate of cultured epidermal autografts in burn wound treatment is variable, widely expanded meshed auto skin grafts are often used in combination with cultured epidermal autograft to increase the take rate and achieve definitive wound coverage. However, a long time (3-4 weeks) required to prepare a cultured epidermis sheet is a disadvantage. Allogeneic cultured epidermis can be prepared in advance and cryopreserved to be used in combination with auto meshed skin grafts for treating third-degree burns. Nevertheless, the human cultured epidermis (hCE) has not been proved to accelerate wound healing after meshed skin grafting. Here, we investigated the effect of hCE on wound healing in a rat model of meshed skin grafting.

MATERIALS AND METHODS

Human cultured epidermis was prepared from human neonatal foreskin and assessed by the release of growth factors into the culture medium using enzyme-linked immunosorbent assay. Skin wounds were inflicted on male F344 rats and treated by the application of widely meshed (6:1 ratio) autogenous skin grafts with or without hCE (n = 8 rats per group). Wound area, neoepithelium length, granulation tissue formation, and neovascularization were evaluated on day 7 postgrafting.

RESULTS

Human cultured epidermis secreted IL-1α, Basic fibroblast growth factor, platelet-derived growth factor-AA, TGF-α, TGF-β1, and vascular endothelial growth factor in vitro. In rats, hCE accelerated wound closure (P = 0.003), neoepithelium growth (P = 0.019), and granulation tissue formation (P = 0.043), and increased the number of capillaries (P = 0.0003) and gross neovascularization area (P = 0.008) compared with the control group.

CONCLUSIONS

The application of hCE with meshed grafts promoted wound closure, possibly via secretion of growth factors critical for cell proliferation and migration, suggesting that hCE can enhance the healing effect of widely expanded skin autografts.

Epidermal Stem Cells in Skin Wound Healing

Significance: Skin serves as a protective barrier for mammals. Epidermal stem cells are responsible for maintaining skin homeostasis. When cutaneous injuries occur, skin homeostasis and integrity are damaged, leading to dire consequences such as acute, chronic, or infected wounds. Skin wound healing is an intrinsic self-saving chain reaction, which is crucial to facilitating the replacement of damaged or lost tissue. Recent Advances: An immense amount of research has uncovered the underlying mechanisms behind the complex and highly regulated wound healing process. In this review, we will dissect the biological process of adult skin wound healing and emphasize the importance of epidermal stem cells during the wound healing. Critical Issues: We will comprehensively discuss the current clinical practices used on patients with cutaneous wounds, including both traditional skin grafting procedures and advanced grafting techniques with cultured skin stem cells. The majority of these leading techniques still retain some deficiencies during clinical use. Moreover, the regeneration of skin appendages after severe injuries remains a challenge in treatment. Future Directions: Understanding epidermal stem cells and their essential functions during skin wound healing are fundamental components behind the development of clinical treatment on patients with cutaneous wounds. It is important to improve the current standard of care and to develop novel techniques improving patient outcomes and long-term rehabilitation, which should be the goals of future endeavors in the field of skin wound healing.

Cryopreserved cultured epithelial allografts for pediatric deep partial dermal burns: Early wound closure and suppression of scarring

BACKGROUND

In deep partial thickness dermal burns (DDB) where greater than 50% of the dermis is lost, severe pain, scarring and contractures occur. Therefore, skin grafting may be required. In children, scar contracture occurs because scarred skin does not stretch with growth creating the need for additional scar-releasing or skin-grafting surgeries. In order to resolve this problem, we used cryopreserved cultured epithelial allograft (cryopreserved allo-CEG), which can be grafted shortly after sustaining a wound. We reevaluated the promotion of early wound closure of burns and suppression of scarring by this treatment.

METHODS

Cryopreserved allo-CEGs were used to treat 50 cases of pediatric DDB from 1992 to 2000. These cases were reviewed with regard to the time until epithelialization, take percentage, and pain level. Also, in order to examine why cryopreserved allo-CEG promotes healing of burns and suppresses scarring, growth factors and cytokines in the cryopreserved allo-CEG were measured. Cryopreserved allo-CEG sheets were solubilized and concentrations of TGF-α, TGF-β1, IL-1α, IL-1β, PDGF-AA, VEGF, KGF, IL-6, b-FGF, as well as metalloprotease-1 (MMP-1) and HGF, which are noted to have scarring suppression effects, were measured before grafting.

RESULTS

Grafting of cryopreserved allo-CEGs in 50 cases of childhood DDB resulted in early epithelialization (9.32 ± 3.63 days on the average) and an almost 100% take rate. Also, pain relief (pain reduction or elimination, reduced need for anesthetics) was seen in all cases. Although 15-23 years have now elapsed, adverse events have not been observed. Cryopreserved allo-CEG contains IL-1α, IL-1β, PDGF-AA, TGF-α, TGF-β1, VEGF, and IL-6 have wound healing effects. The concentration of IL-1α was higher than the concentrations of other components, and this was followed by TGF-α, TGF-β1, b-FGF and VEGF. Although the concentration of MMP-1, which has a scarring suppression effect, was high, HGF was not detected.

CONCLUSION

Cryopreserved allo-CEG contains growth factors that promote wound healing and factors that suppress scarring. Three effects, namely (1) early wound closure, (2) scarring suppression, and (3) pain relief were seen with grafts of cryopreserved allo-CEG in cases of childhood DDB. These observations show that cryopreserved allo-CEG is clinically useful and effective for the treatment of childhood DDB.

Survival of Allogeneic Self-Assembled Cultured Skin

BACKGROUND

Deficiency of autologous skin for reconstruction of severe wounds is a major problem in plastic surgery. Autologous substitutes can provide additional coverage, but due to the duration of production, treatment is significantly delayed. The allogeneic approach offers a potential of having an off-the-shelf solution for the immediate application.

METHODS

In this study, we assess the engraftment and immunogenicity of allogeneic bilayered bioengineered skin prepared by a self-assembly method. Bioengineered skin has the potential immunological advantage of lacking passenger leukocytes including antigen-presenting cells. The skin constructs were transplanted across major histocompatibility complex (MHC) barriers in a porcine animal model. Animals received a second grafting of the same skin construct 7 weeks after the first set of grafts together with MHC-matched constructs to assess for clinical sensitization.

RESULTS

All alloconstructs successfully engrafted with histologic evidence of neovascularization by day 4. Complete cellular rejection and tissue loss occurred by day 8 for most grafts. After the second application, accelerated rejection (<4 days) took place with the development of swine MHC-specific cytotoxic alloantibody.

CONCLUSIONS

These data demonstrate preclinically that self-assembled allogeneic constructs engraft and reject similar to allogeneic skin despite the absence of professional donor antigen-presenting cells.

Skin and skin substitutes in burn management

Early burn excision has reduced the mortality from major burns. This practice presents the problem of wound coverage after excision, since the availability of autologous donor sites is limited in very large burns. This article reviews the methods available for covering burn wounds. Methods of expanding autologous skin are discussed as well as techniques using allogeneic tissue and xenograft. Newer synthetic skin substitutes have become an important advance and are also described. Cultured skin replacements are also discussed along with their shortfalls. The treatment of a patient with major burns may require the use of many different skin substitutes, as none is entirely satisfactory on its own.

Epidermal healing in burns: autologous keratinocyte transplantation as a standard procedure: update and perspective

Background:

Treatment of burned patients is a tricky clinical problem not only because of the extent of the physiologic abnormalities but also because of the limited area of normal skin available.

Methods:

Literature indexed in the National Center (PubMed) has been reviewed using combinations of key words (burns, children, skin graft, tissue engineering, and keratinocyte grafts). Articles investigating the association between burns and graft therapeutic modalities have been considered. Further literature has been obtained by analysis of references listed in reviewed articles.

Results:

Severe burns are conventionally treated with split-thickness skin autografts. However, there are usually not enough skin donor sites. For years, the question of how covering the wound surface became one of the major challenges in clinical research area and several procedures were proposed. The microskin graft is one of the oldest methods to cover extensive burns. This technique of skin expansion is efficient, but results remain inconsistent. An alternative is to graft cultured human epidermal keratinocytes. However, because of several complications and labor-intensive process of preparing grafts, the initial optimism for cultured epithelial autograft has gradually declined. In an effort to solve these drawbacks, isolated epithelial cells from selecting donor site were introduced in skin transplantation.

Conclusions:

Cell suspensions transplanted directly to the wound is an attractive process, removing the need for attachment to a membrane before transfer and avoiding one potential source of inefficiency. Choosing an optimal donor site containing cells with high proliferative capacity is essential for graft success in burns.

Wound-healing potential of Cultured Epidermal Sheets is unaltered after lyophilization: a preclinical study in comparison to cryopreserved CES

Lyophilized Cultured Epidermal Sheets (L-CES) have been reported to be as effective as the cryopreserved CES (F-CES) in treating skin ulcers. However, unlike F-CES, no preclinical study assessing wound-healing effects has been conducted for L-CES. The present study was set out to investigate the microstructure, cytokine profile, and wound-healing effects of L-CES in comparison to those of F-CES. Keratinocytes were cultured to prepare CES, followed by cryopreservation at −70°C and lyophilization. Under microscopic observation, intact cells with apparent intracellular junctions were observed in L-CES. The L-CES, like fresh CES, consisted of three to four well-maintained epidermal layers, as shown by the expression of keratins, involucrin, and p63. There were no differences in the epidermal layer or protein expression between L-CES and F-CES, and both CES were comparable to fresh CES. TGF-α, EGF, VEGF, IL-1α, and MMPs were detected in L-CES at levels similar to those in F-CES. In a mouse study, wounds treated with L-CES or F-CES completely healed at least 4 days faster than untreated wounds. CES-treated wounds completely healed by day 10, while the untreated wounds did not heal by day 14. Masson's trichrome staining showed that collagen deposition in the CES-treated wounds was highly increased in the dermis of the wound center compared to that in the control wounds. Thus, this study demonstrates that L-CES is as clinically effective as F-CES for wound treatment.

Clinical Evaluation of NIKS-Based Bioengineered Skin Substitute Tissue in Complex Skin Defects: Phase I/IIa Clinical Trial Results

BACKGROUND

Complex skin defects, such as burns and acute cutaneous trauma, are life-threatening injuries, often requiring temporary allograft placement to maintain fluid homeostasis and prevent infection until permanent wound closure is possible.

THE PROBLEM

The current standard of care for the management of full-thickness wounds that are unable to be closed in a single surgical stage is temporary coverage with cadaver allograft until an acceptable wound bed has been established. This approach has limitations including limited availability of human cadaver skin, the risk of disease transmission from cadaveric grafts, and inconsistent cadaver allograft quality.

BASIC/CLINICAL SCIENCE

Near-diploid neonatal human keratinocyte cell line (NIKS)-based human skin tissue is a full-thickness, living human skin substitute composed of a dermal analog containing normal human dermal fibroblasts and a fully-stratified, biologically and metabolically active epidermis generated from NIKS keratinocytes, a consistent and unlimited source of pathogen-free human epidermal progenitor cells.

CLINICAL CARE RELEVANCE

NIKS-based human skin tissue is a living bioengineered skin substitute (BSS) intended to provide immediate wound coverage and promote wound healing through sustained expression by living cells of wound healing factors.

CONCLUSION

A phase I/IIa clinical trial found that NIKS-based BSS was well tolerated and comparable to cadaver allograft in the ability to prepare full-thickness complex skin defects prior to autografting. There were no deaths and no adverse events (AE) associated with this BSS. Exposure of the study subjects to the skin substitute tissue did not elicit detectable immune responses. Notably, this tissue remained viable and adherent in the wound bed for at least 7 days.

Progress and opportunities for tissue-engineered skin

Tissue-engineered skin is now a reality. For patients with extensive full-thickness burns, laboratory expansion of skin cells to achieve barrier function can make the difference between life and death, and it was this acute need that drove the initiation of tissue engineering in the 1980s. A much larger group of patients have ulcers resistant to conventional healing, and treatments using cultured skin cells have been devised to restart the wound-healing process. In the laboratory, the use of tissue-engineered skin provides insight into the behaviour of skin cells in healthy skin and in diseases such as vitiligo, melanoma, psoriasis and blistering disorders.

Evaluation of ApligrafR persistence and basement membrane restoration in donor site wounds: a pilot study

Apligraf is a bilayered tissue-engineered product consisting of a bovine collagen matrix with neonatal fibroblasts, overlaid by a stratified epithelium containing living keratinocytes. The United States Food and Drug Administration has approved its use for venous leg ulcers and neuropathic diabetic foot ulcers. Apligraf provides a dermal matrix and produces cytokines similar to the human skin. However, its mechanism of action and ultimate fate in host wounds are unclear. The aim of this study was to evaluate the persistence of Apligraf fibroblasts and keratinocytes in human acute partial-thickness wounds (split-thickness donor sites) treated with Apligraf. In an open-label, within-patient, three-centered, controlled pilot study, 10 patients were treated with Apligraf, Apligraf dermis only (without epidermis), and a polyurethane film for donor site wounds of the same size, depth, and anatomical location. Apligraf DNA persistence was the primary outcome measure. Basement membrane components, cosmetic outcome, time to wound healing, and safety parameters were secondary outcome measures. One week after the initial treatment, reverse transcription polymerase chain reaction analysis found that two Apligraf and two Apligraf dermis-only-treated sites had Apligraf DNA present. Four weeks posttreatment, only one Apligraf and one Apligraf dermis-only sites showed the presence of Apligraf DNA. There was no difference between the three treatment modalities in establishing basement membrane in donor site wounds. No differences in other secondary outcomes were found. Apligraf DNA persisted in a minority of patients at 4 weeks in acute partial-thickness wounds. Apligraf's success in speeding healing of acute wounds appears to be related to factors other than the persistence of donor DNA or effect on basement membrane restoration.

Clinical Approach to Wounds: D??bridement and Wound Bed Preparation Including the Use of Dressings and Wound-Healing Adjuvants

This is a clinical review of current techniques in wound bed preparation found to be effective in assisting the wound-healing process. The process begins with the identification of a correct diagnosis of the wound's etiology and continues with optimizing the patient's medical condition, including blood flow to the wound site. Débridement as the basis of most wound-healing strategies is then emphasized. Various débridement techniques, including surgery, topical agents, and biosurgery, are thoroughly discussed and illustrated. Wound dressings, including the use of negative pressure wound therapy, are then reviewed. To properly determine the timing of advance therapeutic intervention, the wound-healing progress needs to be monitored carefully with weekly measurements. A reduction in wound area of 10 to 15 percent per week represents normal healing and does not mandate a change in the current wound-healing strategy. However, if this level of wound area reduction is not met consistently on a weekly basis, then alternative healing interventions should be considered. There is a growing body of evidence that can provide guidance on the appropriate use of such adjuvants in the problem wound. Several adjuvants are discussed, including growth factor, bioengineered tissues, and hyperbaric medicine.

The role of hyaluronic acid in wound healing: assessment of clinical evidence

Hyaluronic acid (hyaluronan), a naturally occurring polymer within the skin, has been extensively studied since its discovery in 1934. It has been used in a wide range of medical fields as diverse as orthopedics and cosmetic surgery, but it is in tissue engineering that it has been primarily advanced for treatment. The breakdown products of this large macromolecule have a range of properties that lend it specifically to this setting and also to the field of wound healing. It is non-antigenic and may be manufactured in a number of forms, ranging from gels to sheets of solid material through to lightly woven meshes. Epidermal engraftment is superior to most of the available biotechnologies and, as such, the material shows great promise in both animal and clinical studies of tissue engineering. Ongoing work centers around the ability of the molecule to enhance angiogenesis and the conversion of chronic wounds into acute wounds.

Viability and Function of Autologous and Allogeneic Fibroblasts Seeded in Dermal Substitutes after Implantation

BACKGROUND

Fibroblast-seeded collagen sponges have been used for the treatment of skin defects and skin ulcers. However, the viability of the fibroblasts after implantation is still unknown. The objective of this study was to investigate the viability and distribution of autologous and allogeneic fibroblasts after implantation and to clarify which type is more effective for wound healing.

MATERIALS AND METHODS

Skin samples of Hartley guinea pigs were retrieved and autologous fibroblasts were isolated and cultured. Fibroblasts isolated from the skin of a Strain2 guinea pig were used as allogeneic fibroblasts. Three full-thickness wounds were created on the backs of guinea pigs and an acellular collagen sponge, a collagen sponge seeded with autologous fibroblasts, and a collagen sponge seeded with allogeneic fibroblasts were transplanted. Before implantation, fibroblasts were labeled with PKH26. The guinea pigs were sacrificed 1, 2, and 3 weeks after implantation. The epithelization and contraction of the wounds were assessed, and the viability and distribution of the seeded fibroblasts were observed in cross sections.

RESULTS

Three weeks after implantation, the PKH26-labeled autologous and allogeneic fibroblasts remained viable. In the wounds covered with the autologous fibroblast-seeded collagen sponge, the epithelization was fastest, and the percent wound contraction was smallest. In contrast, in the wounds covered with allogeneic fibroblasts, the epithelization was slowest and the percent contraction was largest.

CONCLUSION

The allogeneic fibroblasts seeded in the collagen sponge survived and remained viable on the grafted area, but did not accelerate wound healing.

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.

Cryopreserved and lyophilized cultured epidermal allografts in the treatment of leg ulcers: a pilot study

BACKGROUND

In the conservative therapy of venous leg ulcers modern types of dressings are used most frequently. In the past 20 years 'active wound dressings' - cultured epidermal keratinocytes as autografts and allografts - were also introduced in the management of leg ulcers.

METHODS

The aim of our study was to compare the effect of cryopreserved and lyophilized cultured epidermal allografts in the treatment of venous leg ulcers. Evaluation of the therapy was documented as photodocumentation, planimetry, healing time and evaluation of pain relief over a 3-month period after application. Fifty patients with venous leg ulcers were selected. Twenty-five patients (group I) were treated with cryopreserved keratinocytes and 25 (group II) with lyophilized keratinocytes.

RESULTS

The final evaluation 3 months after the application of allografts showed 84% of healed ulcers in group I and 80% in group II. The number of healed ulcers and the healing rate both showed no statistically significant differences. The size of the ulcer was reduced by half during the first week in both groups. The size differences during the first week are statistically significant in both groups and they are comparable (P < 0.001). The intensity of the pain was statistically significantly reduced during the first week after application in both groups (P < 0.001).

CONCLUSIONS

The cryopreserved and lyophilized cultured allografts are comparable in healing rate, course of healing and relief of pain, and also in planimetric changes during the healing of venous leg ulcers. Lyophilized allografts are more convenient for routine use than cryopreserved allografts as they can be stored at room temperature. These results could give rise to the more frequent use of lyophilized allografts in slow-healing venous leg ulcers.

Plastic Surgery

The range of casualties treated by the Defence Medical Services in the recent Gulf conflict has reaffirmed the important role of plastic surgery within the military. This review seeks to highlight some areas of recent innovation and improvement within the realms of plastic surgery generally, of which some, such as the introduction of Flammacerium and the availability of skin substitutes, have direct military relevance.

Bilayered bioengineered skin substitute (Apligraf): a review of its use in the treatment of venous leg ulcers and diabetic foot ulcers

The bilayered bioengineered skin substitute (BBSS) [Apligraf] is used for the treatment of venous leg ulcers and diabetic foot ulcers. It has an epidermal layer formed from human keratinocytes and a dermal layer composed of human fibroblasts in a bovine type I collagen matrix. BBSS does not contain any antigen-presenting cells such as Langerhans cells, dermal dendritic cells, endothelial cells or leucocytes. In clinical trials, there was no evidence of clinical rejection and immunological tests indicated no humoral or cellular response to the keratinocytes or fibroblasts of BBSS. Further clinical trials are required to identify the exact mechanism of action of BBSS in chronic wounds. BBSS plus compression therapy was well tolerated and was superior in efficacy to compression therapy alone in a multicentre, randomised trial in patients with venous leg ulcers. At 6 months' follow-up, complete wound healing occurred in 63 versus 49% of patients and the median time to wound closure was 61 versus 181 days. In a subgroup of patients with hard-to-heal ulcers (>1 year's duration), wound healing was achieved in significantly more patients (47 vs 19%) and the median time to wound healing was significantly shorter (181 days vs not attained). In a multicentre, randomised trial, BBSS was well tolerated and effective in patients with full-thickness neuropathic diabetic foot ulcers. Ulcer healing occurred in significantly more patients (56 vs 38%) and the median time to wound healing was shorter (65 vs 90 days) with BBSS than with saline-moistened gauze at 12 weeks' follow-up. Patients in both groups also received standard diabetic foot care. The cost effectiveness of BBSS in patients with chronic ulcers has yet to be examined in well designed, prospective clinical trials. However, according to a modelled analysis incorporating data from a multicentre randomised trial, BBSS was cost effective in patients with hard-to-heal venous leg ulcers. The average annual medical cost of managing patients with ulcers of >1 year's duration was estimated to be 20,041 US dollars per patient treated with BBSS plus compression therapy and 27,493 US dollars per patient treated with compression therapy alone (1996 costs).

CONCLUSIONS

Clinical trials have shown that BBSS in conjunction with standard compression therapy was effective and well tolerated in patients with venous leg ulcers, especially patients with ulcers of >6 months' duration or that extended to the subcutaneous tissue. In addition, BBSS in conjunction with standard diabetic foot care was effective and well tolerated in patients with full-thickness neuropathic diabetic foot ulcers. BBSS represents a useful adjuvant to standard ulcer therapy in patients with venous leg ulcers or full-thickness neuropathic diabetic foot ulcers that do not respond to conventional ulcer therapy.

Modulating diseased skin with tissue engineering: actinic purpura treated with Apligraf

BACKGROUND

Actinic purpura (AP) is an important medical issue and quality of life issue in the elderly. Current treatment of AP is limited to prevention of cutaneous aging.

OBJECTIVE

To assess the utility of tissue engineered skin (Apligraf, Organogenesis, Canton, MA) as a tissue modulator in diseased skin and as treatment for AP.

METHODS

A thin partial-thickness section of AP was removed from the forearm of an elderly gentleman and replaced with fenestrated Apligraf. Healing, durability and cosmetic outcome were assessed.

RESULTS

Apligraf-treated skin healed rapidly with good clinical "take." Lack of new skin tears and resultant erosions or ulcer formation suggests improved durability of the Apligraf-treated area occurred.

CONCLUSION

These results suggest that tissue engineered skin modulates aged dermal tissue to behave in a more sturdy fashion. Furthermore, in selected cases Apligraf may represent a treatment option for AP.

Evaluation of tissue-engineered skin (human skin substitute) and secondary intention healing in the treatment of full thickness wounds after Mohs micrographic or excisional surgery

BACKGROUND

Human Skin Substitute (Apligraf, Organogenesis, Inc., Canton, MA) is a bi-layered tissue-engineered living biological dressing developed from neonatal foreskin. It consists of a bovine collagen matrix containing human fibroblasts with an overlying sheet of stratified human epithelium containing living human keratinocytes. Human Skin Substitute (HSS) appears to be immunologically inert, and has shown usefulness in the treatment of chronic and acute wounds.

OBJECTIVE

Primary objectives were to evaluate the safety and efficacy of HSS in the treatment of full-thickness wounds in a prospective case series. Secondary objectives were to determine the rate of complete wound reepithelialization, incidence of complete wound healing, pain at wound site, overall cosmetic outcome, and patient satisfaction.

METHODS

Fourteen patients were enrolled in the study, of which 12 were evaluable. HSS was applied in a blinded fashion to 6 of the patients immediately following Mohs or excisional surgery for skin cancer. The remaining 6 patients were allowed to heal by secondary intention. Both groups were evaluated at weekly appointments until complete reepithelialization occurred. During each evaluation, wound quality was assessed through the Vancouver Burn Scar Assessment Scale by the investigator and an independent blinded dermatologist. The investigator, blinded observer, and patient further evaluated the cosmetic outcome of the wound through the use of a Visual Analog Scale over a 6-month period.

RESULTS

HSS patients and secondary intention patients were equivalent in comorbid factors such as pain, erythema, edema, exudate, infection, or hematoma between the groups. The incidence of complete wound healing at 6 months was 100% for both groups. Both groups also appeared to heal at similar rates, as defined by the complete reepithelialization of the wound. HSS patients ultimately resulted in more pliable and less vascular wounds as defined by the Vancouver Burn Scar Assessment Scale. Patient satisfaction with cosmetic outcome in both groups was positive at 6 months.

CONCLUSIONS

HSS appears to be a safe, well-tolerated biological dressing with equivalent comorbid factors to secondary intention healing. HSS, however, seems to produce a more pliable and less vascular scar than those developed through healing by secondary intention. HSS also appears to produce more satisfactory cosmetic results when compared to secondary intention healing.

Wounding of bioengineered skin: cellular and molecular aspects after injury

Skin substitutes are increasingly being used in the treatment of difficult to heal wounds but their mechanisms of action are largely unknown. In this study, using histology, immunostaining, flow cytometry, enzyme-linked immunosorbent assay, and reverse transcription polymerase chain reaction, we determined the response to injury of a human bilayered skin substitute. Meshing or scalpel fenestration of the construct was found to stimulate keratinocyte migration and to decrease proliferation. By 24 h, flow cytometry of the keratinocyte component showed that meshing was associated with a 33% decrease in the number of cells in S phase (p < 0.01). An approximately 2-fold decrease in staining for Ki67, a proliferation marker, was observed with meshing of human bilayered skin substitute. The process of reepithelialization was apparent by 12 h, however, the wounded human bilayered skin substitute was healed by day 3, and a stratum corneum and fully stratified epithelium were re-established by day 4. Reverse transcription polymerase chain reaction analysis and enzyme-linked immunosorbent assays showed that the expression of acute proinflammatory cytokines (interleukins 1alpha, 6, and 8, tumor necrosis factor alpha) peaked by 12-24 h postinjury. The levels of mRNA of certain growth factors (transforming growth factor beta1, vascular endothelial growth factor, insulin-like growth factor 2) but not others (platelet-derived growth factors A and B, keratinocyte growth factor, fibroblast growth factors 1 and 7, transforming growth factor beta3) increased by 12 h and peaked by 1-3 d after injury, returning to normal by day 6. Immunostaining for tumor necrosis factor alpha and transforming growth factor beta1 paralleled these findings by reverse transcription polymerase chain reaction. We conclude that human bilayered skin substitute, as a prototypic bilayered skin substitute, is a truly dynamic living tissue, capable of responding to physical injury in a staged and specific pattern of cell migration, reepithelialization, and cytokine expression.

Allogeneic fibroblasts in dermal substitutes induce inflammation and scar formation

In the present study, we compared the use of autologous versus allogeneic fibroblasts in dermal skin substitutes in a porcine wound model. The allogeneic fibroblast populations were isolated from female and a male pig (allo-1, - 2 and - 3) and the controls, autologous fibroblasts, from female graft-recipient pigs (control). The histocompatibility of the three donor pigs with the recipient pigs was determined with a mixed lymphocyte reaction. In two pigs, full-thickness wounds were treated with the fibroblast-seeded dermal substitutes (n = 5 per animal) and immediately overgrafted with meshed split-skin autografts. After 6 weeks, wound contraction was measured by planimetry and scar formation was scored. At 2, 4, and 6 weeks biopsies were taken and evaluated for the presence of inflammatory reactions, myofibroblasts, and scar formation. The mixed lymphocyte reaction of both recipient pigs showed the highest responses on peripheral blood mononuclear cells of the allo-3 donor pig, and was low or negative for allo-1 and allo-2. In all "allogeneic" wounds, more inflammatory cells were observed over time along with inflammatory foci consisting of a mix of lymphocytes and granulomatous cells. After 4 weeks, myofibroblasts were absent in the control wounds, whereas in "allogeneic" wounds, myofibroblasts colocalized with inflammation foci. The final scar tissue of the "allogeneic" wounds showed granulating areas with thin, immature collagen bundles. In contrast, the control wounds showed a dermal tissue with mature collagen bundles organized randomly like in normal skin. The wounds treated with allo-3 fibroblasts showed in both pigs a significant increase in scar formation and wound contraction when compared with control wounds. In conclusion, for optimal restoration of dermal skin function with minimal scar formation, skin substitutes containing autologous fibroblasts are preferred over skin substitutes with allogeneic fibroblasts.

A guide to biological skin substitutes

The role of artificial skin substitutes in burn surgery and the treatment of chronic wounds is constantly evolving. New products are regularly being produced and approved for clinical use. Studies on existing products clarify their efficacy and effectiveness in different clinical scenarios. This review is aimed at busy clinicians in order to bring them up to date with the latest developments in the field of artificial skin substitutes. It examines the components, structure, performance and comparative costs of the main commercial skin substitutes, and reviews briefly technologies under development that have not yet become widely available.

Intrabody-mediated phenotypic knockout of major histocompatibility complex class I expression in human and monkey cell lines and in primary human keratinocytes

Cultured keratinocyte allografts from unrelated donors can be readily grown as sheets in large-scale cell culture and have been used as an immediate skin cover for severely burned patients. Despite the absence of passenger leukocytes and the unlimited amount of material that can be obtained for permanent skin coverage, the allografts are susceptible to rejection. Since MHC class I (MHCI) antigens serve as targets for allograft rejection, we investigated whether 'phenotypic knockout' of human MHCI could be achieved through expression of an ER-directed anti-human MHCI single-chain intrabody (sFvhMHCI) that is directed against a monomorphic, conformational epitope, expressed across species lines, on the MHCI heavy chain. Co-immunoprecipitation of both MHCI heavy chain and beta2-microglobulin occurred in transfected monkey COS-1 cells, while Jurkat T cells stably expressing the ER-directed sFvhMHCI intrabody showed that complete phenotypic knockout of MHCI cell surface expression could be achieved. Infection of several human cell lines of divergent tissue sources and different HLA haplotypes resulted in marked down-regulation of MHCI expression, even under conditions where inflammatory cytokines (eg gamma-IFN) which up-regulate MHCI expression were used. Finally, when adenovirus encoding the anti-human MHCI intrabody was used to transduce primary human keratinocytes, a marked reduction of surface MHCI expression was observed. These in vitro studies set the groundwork for in vivo studies to determine if intrabody-mediated knockout of MHCI can impair alloantigen expression and prolong the survival of keratinocyte allografts.

Adjuncts to preparing wounds for closure: hyperbaric oxygen, growth factors, skin substitutes, negative pressure wound therapy (vacuum-assisted closure)

Achieving closure in a chronic wound requires provision of adequate oxygen delivery to the tissue, adequate protein and other nutritional factors, a moist environment, an appropriate inflammatory milieu, dèbridement, and correction of contributing medical diagnoses. In some patients, these conditions are achieved easily, whereas in others, greater effort is required. Adjunctive treatments, including HBO2, growth factors, skin substitutes, and negative-pressure wound therapy (e.g., V.A.C.) can provide the proper conditions for healing in appropriately selected patients.

Cryopreserved cultured epidermal allografts achieved early closure of wounds and reduced scar formation in deep partial-thickness burn wounds (DDB) and split-thickness skin donor sites of pediatric patients

Burn treatment in children is associated with several difficulties, e.g. available skin replacement is small, donor area could expand, and subsequent hypertrophic scar and contracture could become larger along with their physical growth. In order to have better clinical results, the authors prepared cryopreserved cultured epidermal allografts from excess epidermal cells of other patients, and applied the epidermal allografts to 55 children, i.e. 43 cases of deep partial-thickness burn wounds (DDB) due to scald burn and 12 cases with split-thickness skin donor sites. In the 43 DDB patients, epithelialization was confirmed 9.1+/-3.6 days (mean+/-S.D.) after treatment. In 10 of the 43 patients, epithelialization was comparable between the area which received the epidermal allografts (grafted area) and the area which did not receive the epidermal allografts but was covered with usual wound dressing (non-grafted area). As a result, epithelialization day was 7.9+/-1.7 in grafted areas and 20.5+/-2.3 in non-grafted areas. In the 12 patients with split-thickness skin donor sites, epithelialization was confirmed 6.3+/-0.9 days after treatment. Epithelialization of the grafted and non-grafted areas was comparable in 8 of the 12 patients, and it was 6.5+/-1.1 days and 14.1+/-1.6 days, respectively. In these 10 DDB patients and 8 split-thickness skin donor site patients, redness and scar formation were also milder in the grafted area. The 55 patients have been followed up for 1-8 years (mean, 4.75 years), and scar formation was suppressed in both DDB and split-thickness skin donor sites. These findings showed that cryopreserved cultured epidermal allografts achieve early closure of the wounds and good functional outcomes.

Skin grafting

No longer an option of last resort, skin grafting has become a technique that is routinely and sometimes preferentially considered as skin replacement for burns, chronic ulcers, and skin defects after cutaneous surgical procedures. When selected as the best alternative for wound closure, autologous skin grafts are commonly considered the gold standard. Availability of autologous grafts is a major obstacle, however, and the search for a manufactured skin replacement has continued. In cases in which autologous grafts cannot be performed, skin substitutes have become an attractive alternative.

Frozen human epidermal allogeneic cultures promote rapid healing of facial dermabrasion wounds

BACKGROUND

Clinical studies have shown that cultured human epidermal allogenic sheets promote faster reepithelization of skin donor sites and deep partial-thickness wounds.

OBJECTIVE

We describe the results of a controlled, clinical study of facial dermabrasion sites treated with a single application of frozen cultured human allogenic epidermal sheets that were thawed for 5-10 minutes at room temperature before application.

METHODS

Ten patients with scars from acne or of other etiology underwent facial dermabrasion. One side of the face was treated with the frozen and thawed cultures, the other side was treated with standard dry dressing.

RESULTS

The epidermal cultures promoted faster reepithelization of the wounds, with complete reepithelization in an average time of 4.6 days, whereas controls healed in an average of 7. 9 days. The reduction in healing time was 42% (P = 4.82 x 10(-7)). Pain was reduced in sites treated with the thawed cultures.

CONCLUSION

Epidermal allogenic cultures, preserved by freezing, promoted significantly faster reepithelization and reduced pain intensity of dermabraded facial wounds, suggesting that they could be used routinely to improve the recovery from dermabrasion.

Frozen allogeneic human epidermal cultured sheets for the cure of complicated leg ulcers

BACKGROUND

Skin ulcers due to venous stasis or diabetes are common among the elderly and are difficult to treat. Repeated applications of cell-based products have been reported to result in cure or improvement of leg ulcers of small size in a fraction of patients.

OBJECTIVE

To examine the effects of frozen human allogeneic epidermal cultures for the treatment of acute and chronic ulcers.

METHODS

We treated a series of 10 consecutive patients with leg ulcers of different etiology and duration with frozen human allogeneic epidermal cultures stored frozen and thawed for 5-10 minutes at room temperature before application. Three patients had ulcers with exposed Achilles or extensor tendon. The ulcers treated were as large as 160 cm2 in area and of up to 20-years' duration. After preliminary preparation of the wounds by debridement to remove necrotic tissue and application of silver sulfadiazine to control infection, thawed cultures were applied biweekly from 2 to 15 times depending on the size and complexity of the ulcer.

RESULTS

All ulcers healed, including those with tendon exposure. After the first few applications, granulation tissue formed in the ulcer bed and on exposed tendons, and epidermal healing took place through proliferation and migration of cells from the margins of the wound. The time required for complete healing ranged from 1 to 31 weeks after the first application.

CONCLUSION

The use of frozen human allogeneic epidermal cultures is a safe and effective treatment for venous or diabetic ulcers, even those with tendon exposure. It seems possible that any leg ulcer will be amenable to successful treatment by this method.

Acute excisional wounds treated with a tissue-engineered skin (Apligraf)

BACKGROUND

Tissue-engineered products are usually composed of living cells and their supporting matrices that have been grown in vitro, using a combination of engineering and life sciences principles. Apligraf is a bilayered product composed of neonatal-derived dermal fibroblasts and keratinocytes, and Type I bovine collagen.

OBJECTIVE

To evaluate in a prospective, multicentered open study, the effects of tissue therapy with a tissue-engineered skin (Apligraf) with partial or full-thickness excisional wounds.

METHODS

One hundred and seven patients participated in this study. The tissue-engineered skin was applied once, immediately after excisional surgery, usually for skin cancer, and patients were followed for up to one year.

RESULTS

The safety results were impressive, with no clinical or laboratory evidence of rejection. Clinically, graft persistence was good to excellent in 77 of 105 (73.3%) of patients at one week, falling to 56.6% and 53.6% at two weeks and one month respectively.

CONCLUSION

To date, this is the largest experience with a tissue-engineered skin product in acute wounds, and this study suggests that tissue therapy may be safe and useful.