The use of cultured epithelial autograft in the treatment of major burn wounds: eleven years of clinical experience

Cultured epithelial autografts for coverage of large burn wounds in eighty-eight patients: the Indiana University experience

Since 1990, the authors have used a new technique for coverage of large burns, which begins with early tangential excision and coverage with cadaver allograft (A), followed by placement of cultured epithelial autograft (CEA) onto an allodermis base (CEA/A). They present their 18-year experience (1990-present) using CEA in 88 patients (20 children and 68 adults) with age range of 6 months to 73 years. A review of prospectively collected data was conducted on adult and pediatric patients grafted with CEA at the Indiana University Medical Center for definitive wound coverage (TBSA 28-98%). These patients were followed up for 3 to 90 months. Complications, take rates, and outpatient follow-ups were noted. The mean final take rate of CEA/A was 72.7%, and the overall patient survival rate was 91% (80 of 88 patients). Complications were classified as early and late, they included: (early) blistering and shearing (31%), pruritus and itching (4.7%), (late) CEA loss (2 patients, 2.3%), and wound contractures (66%). Contracture releases were performed on 32 patients (36%); of which, 18 were children (56%). Cultured keratinocytes provide an excellent alternative or adjunct to conventional split-thickness skin grafting in treating large burn wounds. A dedicated team of physicians, nurses, and therapists well rehearsed in CEA care are vital for success in keratinocyte grafting. The final graft take of 72.7% with a 91% overall survival rate gives much optimism for continuing to use CEA in critically burned patients.

Expression of keratinocyte growth factor and its receptor in rat tracheal cartilage: possible involvement in wound healing of the damaged cartilage

Keratinocyte growth factor (KGF) is involved in the development and regeneration of a variety of tissues. To clarify the role of KGF in cartilage wound healing, we examined the expression of KGF and its receptor (KGFR) immunohistochemically in the wound healing area of rat tracheal cartilage, and the direct effect of recombinant KGF on the proliferation and differentiation of primary cultures of rat chondrocytes. KGF was found in the cytoplasm of both chondrocytes and perichondrial cells. On the other hand, KGFR was detected only in the plasma membrane of chondrocytes. Although the expression of KGF was similar in the cartilage and perichondrial area before and after injury, KGFR expression was induced after injury and limited to proliferating chondrocytes. The staining pattern of KGF and KGFR was same in the mature and the immature rat tracheal cartilage. Moreover, in vitro experiments using primary cultured chondrocytes revealed that KGF at 200 ng/ml significantly increased the number of chondrocytes (~1.5-fold), and significantly reduced acid mucopolysaccharide production. These results indicate that KGF stimulates chondrocyte proliferation, suggesting that KGF could therapeutically modulate the wound healing process in the tracheal cartilage.

MMP- and TIMP-secretion by human cutaneous keratinocytes and fibroblasts--impact of coculture and hydration

Epithelial-mesenchymal interactions are important in wound healing and scarring, but are difficult to study in vitro. We have previously reported on an in vitro keratinocyte-fibroblast coculture system exploring these interactions and found that coculture modifies the levels of cytokines they secrete. The same coculture model was used to study changes in MMP- and TIMP-activity. We hypothesised that the previously shown decrease of collagen is partly due to increased MMPs. Adult human cutaneous keratinocytes and fibroblasts were cocultured under serum-free conditions. Keratinocytes were either kept at the air-liquid interface or hydrated. The conditioned medium was submitted to a multiplex sandwich enzyme-linked immunosorbent assay including gelatinases, collagenases, stromelysins, and tissue inhibitors of metalloproteinases. Collagen content was determined by western blot. Zymography depicted the gelatinases in conditioned media. For confirmation of the coculture results fibroblasts were treated with conditioned media from keratinocyte monocultures as well. MMP-1, MMP-9, and MMP-10 were mainly secreted by keratinocytes, whereas MMP-2, TIMP-1 and -2 by fibroblasts. MMP-13 was secreted by both cell types at comparable levels. Collagenases, gelatinases, MMP-3, and TIMPs increased significantly in cocultures compared to monocultures. Hydration of keratinocytes revealed a significant increase of MMP-3 and MMP-2, and a decrease of TIMP-2. Paracrine interactions between keratinocytes and fibroblasts modify strongly MMPs and TIMPs, whereas hydration of keratinocytes had a smaller impact in this context. The observed changes may be in part responsible for reduced collagen in coculture-conditioned media. The present coculture experiments reemphasise the role of epidermis in controlling scarring.

Swine pericardium as dermal substrate for human keratinocyte culture

BACKGROUND

Synthetic skin analogues or living allogeneic or autologous cells are used as dressings for the care of skin wounds, as well as temporary or permanent substitutes for damaged epithelia.

OBJECTIVES

To evaluate if keratinocyte growth on a swine pericardium substrate mimics the natural epithelial layers compared with cultures on allogeneic dermis, which is accepted as having appropriate physical and chemical properties for growth and differentiation.

METHODS

Keratinocytes were cultured on a swine pericardium substrate and allogeneic dermis, either submerged or at the air-liquid interface. At 7, 14 and 21 days postseeding the cultures were evaluated by light microscopy after both haematoxylin and eosin staining and immunohistochemistry.

RESULTS

Cell-substrate interactions led to growth, stratification and differentiation of cells, with the definition of epithelial layers. The submerged system showed a continuous growth rise on both composites, but this was more prominent with the swine pericardium substrate. An increase in the number of layers at the air-liquid interface with the dermis composites, in contrast to the submerged cultures, occurred only from days 7 to 14. The pattern of keratinocyte growth on swine pericardium substrate was much better in the submerged than in the air-liquid interface cultures.

CONCLUSIONS

The results indicate that swine pericardium is a better substrate than allogeneic dermis for keratinocyte cultures in submerged but not in air-liquid interface cultures. Swine pericardium as a substrate opens one more possibility for skin restoration after trauma or burns.

Tissue engineering of skin

The engineering of skin substitutes and their application on human patients has become a reality. However, cell biologists, biochemists, technical engineers, and surgeons are still struggling with the generation of complex skin substitutes that can readily be transplanted in large quantities, possibly in only one surgical intervention and without significant scarring. Constructing a dermo-epidermal substitute that rapidly vascularizes, optimally supports a stratifying epidermal graft on a biodegradable matrix, and that can be conveniently handled by the surgeon, is now the ambitious goal. After all, this goal has to be reached coping with strict safety requirements and the harsh rules of the economic market.

A review of tissue-engineered skin bioconstructs available for skin reconstruction

Situations where normal autografts cannot be used to replace damaged skin often lead to a greater risk of mortality, prolonged hospital stay and increased expenditure for the National Health Service. There is a substantial need for tissue-engineered skin bioconstructs and research is active in this field. Significant progress has been made over the years in the development and clinical use of bioengineered components of the various skin layers. Off-the-shelf availability of such constructs, or production of sufficient quantities of biological materials to aid rapid wound closure, are often the only means to help patients with major skin loss. The aim of this review is to describe those materials already commercially available for clinical use as well as to give a short insight to those under development. It seeks to provide skin scientists/tissue engineers with the information required to not only develop in vitro models of skin, but to move closer to achieving the ultimate goal of an off-the-shelf, complete full-thickness skin replacement.

Evaluation of a novel biodegradable polymer for the generation of a dermal matrix

Dermal skin substitutes can be used to overcome the immediate problem of donor site shortage in the treatment of major skin loss conditions, such as burn injury. In this study, the biocompatibility, safety, and potential of three variants of NovoSorb (a family of novel biodegradable polyurethanes) as dermal scaffolds were determined in a series of in vitro and in vivo systems. All three polymers exhibited minimal cytotoxic effects on human skin cells, allowing keratinocytes, dermal fibroblasts, and microvascular endothelial cells to grow normally in coculture. Subcutaneous implantation of the polymers in rats demonstrated no systemic toxic effects of the materials or their degradation products. The anticipated local foreign body reaction compared favorably with commercially available medical sutures. Assessment of a three-dimensional polymer matrix followed. The success of sequential culturing of dermal fibroblasts and keratinocytes within the matrix indicated that the generation of a cultured skin substitute is achievable. The polymeric matrix also provided a scaffold for the guided formation of a cultured microvasculature. When engrafted onto a surgically created full-thickness sheep wound, the noncellular matrix integrated, healed with an epidermis supported by a basement membrane, and was capable of withstanding wound contraction. The resistance to contraction compared favorably with a commercially available collagen-based dermal matrix (Integra). These results suggest that the NovoSorb matrix could form the basis of an elegant two-stage burn treatment strategy, with an initial noncellular biodegradable temporizing matrix to stabilize the wound bed followed by the application of cultured skin substitute.

Use of a novel porcine collagen paste as a dermal substitute in full-thickness wounds

A commercially available porcine collagen sheet material has been found previously to be useful as an implant for reconstructive surgery. However, its use as a dermal substitute has been hindered by slow cell penetration and vascularization. A novel paste formulation of this material was investigated for its potential role as a dermal substitute in full-thickness wounds. A porcine punch biopsy model was initially used to assess the integration of a wide range of material formulations. Selected formulations were then assessed further in a larger wound-chamber model. Paste formulations were compared with those of sheet and another commercially available dermal regeneration template. The porcine collagen paste became integrated into full-thickness wounds without rejection and without excessive inflammation. It was detected in wounds up to day 27 postimplantation. Porcine collagen paste was readily infiltrated by host cells by day 2 and supported migrating keratinocytes on its surface. Staining for endothelial cells indicated neovasculature formation as early as day 4 and functional newly formed microvessels were noted at day 7. This was comparable with neovascularization of an alternative and clinically proven dermal regeneration template and was significantly superior to the sheet material formulation at the same time points. Our findings suggest that porcine collagen paste may be suitable as an alternative to current dermal substitutes in full-thickness wounds.

Enhancement of keratinocyte performance in the production of tissue-engineered skin using a low-calcium medium

The success of laboratory-expanded autologous keratinocytes for the treatment of severe burn injuries is often compromised by their lack of dermal remnants and failure to establish a secure dermo-epidermal junction on the wound bed. We have developed a tissue-engineered skin substitute for in vivo use, based on a sterilized donor human dermis seeded with autologous keratinocytes and fibroblasts. However, culture rates are currently too slow for clinical use in acute burns. Our aim in this study was to increase the rate of production of tissue-engineered skin. Two approaches were explored: one using a commercial low-calcium media and the other supplementing well-established media for keratinocyte culture with the calcium-chelating agent ethylene glutamine tetra-acetic acid (EGTA). Using commercial low-calcium media for both the initial cell culture and subsequent culture of tissue-engineered skin did not produce tissue suitable for clinical use. However, it was possible to enhance the initial proliferation of keratinocytes and to increase their horizontal migration in tissue-engineered skin by supplementing established culture medium with 0.04 mM EGTA without sacrificing epidermal attachment and differentiation. Enhancement of keratinocyte migration with EGTA was also maximal in the absence of fibroblasts or basement membrane.

[Innovative wound therapy and skin substitutes for burns]

The success of modern burn therapy is based mainly on special burn intensive care, topical treatment, early eschar excision, and wound closure by immediate skin grafting or skin substitutes. This paper describes the current state of wound care and skin substitutes in burn therapy.