Observations on stability and contraction of composite skin grafts: xenodermis or allodermis with an isograft overlay

Cytotoxicity testing of scaffolds potentially suitable for the preparation of three-dimensional skin substitutes

The preparation and study of three-dimensional functional skin substitutes has been the focus of intense research for several decades. Dermal substitutes are now commonly used in medical practice for a variety of applications. Here, we assess the toxicity of seven selected acellular dermal matrix materials to establish their potential for use in future three-dimensional skin substitute studies. The cytotoxicity of acellular dermis (of Allo- and Xenograft origin) prepared in our lab and biomaterials based on collagen and hyaluronic acid (Coladerm H and Coladerm H-L) were compared to that seen in three commercially available products (Xe-Derma, AlloDerm and Xeno-Impl). Murine fibroblasts NIH-3T3 and human dermal fibroblasts were used in cytotoxicity tests, with any resultant cytotoxic effects caused by the seven tested dermal scaffolds visualised using an inverted microscope system and confirmed in parallel using colorimetric MTT cell proliferation assays. While most of the dermal substitutes did not demonstrate a cytotoxic effect on our two cell types, Xeno and Xeno-Impl scaffolds clearly did. The cytotoxic effect of acellular Xeno dermal matrix could essentially be removed through a regime of multiple washes, but we were unable to remove the cytotoxic effect of Xeno-Impl. Thus, Xeno-Impl alone has been excluded from our future work on preparation of 3D skin substitutes.

Keratinocytes in the treatment of severe burn injury: an update

Burns are among the most life-threatening physical injuries, in which fast wound closure is crucial. The surgical burn care has evolved considerably throughout the past decennia resulting in a shift of therapeutic goals. Therapies aiming to provide coverage of the burn have been replaced by treatments that have both functional as aesthetic outcomes. The standard in treating severe burns is still early excision followed by skin grafting. The use of cultured keratinocytes to cover extensive burn wounds appeared very promising at first, but the technique still has several limitations of which the long time to culture, the major costs, the risk of infection and the need for an adequate dermal layer limit clinical application. The introduction of dermal substitutes, composite grafts, tissue engineering based on stem cell application have been advocated. The aim of this review is to assess the use of cultured keratinocytes in terms of technical aspects, clinical application, limitations and future perspectives. Cultured keratinocytes are expected to keep playing a role in wound healing, especially in the field of chronic wounds. In severe burns, despite its limitations, keratinocytes can be beneficial if implemented as one of the elements in a broader wound management.

A Comparison of Human and Porcine Acellularized Dermis: Interactions with Human Fibroblasts In Vitro

BACKGROUND

Dermal substitutes derived from xenograft materials require elaborate processing at a considerable cost. Acellularized porcine dermis is a readily available material associated with minimal immunogenicity. The objective of this study was to evaluate acellularized pig dermis as a scaffold for human fibroblasts.

METHODS

In vitro methods were used to evaluate fibroblast adherence, proliferation, and migration on pig acellularized dermal matrix. Acellular human dermis was used as a control.

RESULTS

Pig acellularized dermal matrix was found to be inferior to human acellularized dermal matrix as a scaffold for human fibroblasts. Significantly more samples of human acellularized dermal matrix (83 percent, n = 24; p < 0.05) demonstrated fibroblast infiltration below the cell-seeded surface than pig acellularized dermal matrix (31 percent, n = 49). Significantly more (p < 0.05) fibroblasts infiltrated below the surface of human acellularized dermal matrix (mean, 1072 +/- 80 cells per section; n = 16 samples) than pig acellularized dermal matrix (mean, 301 +/- 48 cells per section; n = 16 samples). Fibroblasts migrated significantly less (p < 0.05) distance from the cell-seeded pig acellularized dermal matrix surface than in the human acellularized dermal matrix (78.8 percent versus 38.3 percent cells within 150 mum from the surface, respectively; n = 5). Fibroblasts proliferated more rapidly (p < 0.05) on pig acellularized dermal matrix (n = 9) than on the human acellularized dermal matrix (7.4-fold increase in cell number versus 1.8-fold increase, respectively; n = 9 for human acellularized dermal matrix). There was no difference between the two materials with respect to fibroblast adherence (8120 versus 7436 average adherent cells per section, for pig and human acellularized dermal matrix, respectively; n = 20 in each group; p > 0.05).

CONCLUSION

Preliminary findings suggest that substantial differences may exist between human fibroblast behavior in cell-matrix interactions of porcine and human acellularized dermis.

Evaluation of a porcine origin acellular dermal matrix and small intestinal submucosa as dermal replacements in preventing secondary skin graft contraction

The degree to which a split thickness skin graft (STSG) contracts after application to its recipient bed is related in part to the proportion of the dermis harvested from the donor site. Harvesting thicker skin grafts may produce better cosmetic results in the recipient bed but result in increased donor site morbidity. The combination of an autologous ultra thin split thickness graft with an underlying non-autologous dermal component may reduce secondary skin graft contraction without further increasing donor site morbidity. This study was aimed at assessing the suitability of two porcine derived biomaterials (Permacol and small intestinal submucosa, SIS) for use in combination with skin grafts in a Sprague-Dawley rat model. Full thickness wounds (1 cm(2)) were created in Sprague-Dawley rats and grafted with skin in combination with Permacol or SIS either as a one-stage operation or following a 2-week-period of vascularisation of these dermal matrices before a second stage operation to cover with skin. Skin graft viability and wound area were assessed at weekly intervals until 4 weeks after graft application. Both Permacol and SIS were able to support an overlying skin graft but had no beneficial effect on skin graft contraction in this model compared to skin grafts alone.

Time Related Histopathologic Changes of Acellularized Xenogenic Pulmonary Valved Conduits

A biologically engineered xenogenic heart valve based on the concept of acellularization offers promise as a means of overcoming the limitations of current prosthetic valves. We evaluated the process of repopulation by recipient cells on an acellularized xenograft treated with a saline (NaCl)-sodium dodecyl sulfate (SDS) solution. Porcine pulmonary valved conduits acellularized with NaCl-SDS solution were implanted in the right ventricular outflow tract of goats under cardiopulmonary bypass. The goats were sacrificed at 1 week and at 1, 3, 6, and 12 months after implantation. Echocardiographic evaluations of the valves were performed before sacrifice. Visual inspections and histopathologic examinations of the explanted xenogenic valved conduits were performed. Immunohistochemical staining was used to identify the composition of the recellularized cells. Fibroblasts and myofibroblasts were stained by vimentin and smooth muscle actin, and endothelial cells were stained by factor VII related antigen and CD31. Echocardiographic examinations of implanted acellularized xenogenic pulmonary valves revealed satisfactory function except for mild regurgitation and stenosis. On gross examination, all leaflets were well preserved, and no calcification was observed. Microscopic analysis of the acellularized leaflets showed progressive cellular ingrowth over time. The recellularization started from the leaflet base and progressed toward the free margin. Microthrombi were detected on unrecellularized portions. Inflammatory response was detected in the early phase, although it gradually subsided. At 6 months after implantation, cellular ingrowth by fibroblasts, myofibroblasts, and endothelial cells progressed up to 50% of the leaflet's height and progressively increased to 70% after 12 months. Extracellular matrices were regenerated by repopulating cells on the recellularized portion. This study suggests that acellularized xenogenic porcine valved conduits are biocompatible heart valve prostheses that are repopulated with autologous cells and extracellular matrices over a reasonable span of time and preserve the functional integrity without degeneration or calcification of leaflets.

Tissue-engineered heart valve leaflets: an effective method of obtaining acellularized valve xenografts

To determine the most effective method of producing the acellularized xenograft heart valve leaflets, we compared pathological findings of the xenograft heart valve leaflets produced by three methods; freeze-thawing, Triton and NaCl-SDS treatment and further analyzed the pattern of endothelial cells seeded onto them.

MATERIALS AND METHODS

Two pigs were sacrificed and three pulmonary valve leaflets were harvested from each animal. They were immediately stored in a tissue preservation solution and assigned in one of the three preparation methods for acellularization. Endothelial cells from the jugular vein of a goat were isolated and seeded onto the acellularized xenograft heart valve leaflets. Light and Electron microscopic analyses were performed.

RESULT AND CONCLUSION

H & E stain showed that cells were almost absent in the leaflet treated with NaCl-SDS, while cells were partly present in the leaflets treated, one with Triton and the other Freeze-thawing. Transmission microscopic analyses showed cell-free matrix with well preserved collagen architecture under the seeded endothelial cells in the leaflets treated with NaCl-SDS. In conclusion, the valve leaflets treated with NaCl-SDS among three representative methods of acellularization of tissues (freeze-thawing, Triton X-100, and NaCl-SDS) showed the better results than the others in terms of the efficacy of decellularization and response to endothelial cell seeding.

Integra as a dermal replacement in a meshed composite skin graft in a rat model: a one-step operative procedure

BACKGROUND

Current use of Integra, the collagen-based dermal analogue, requires a two-step grafting procedure to achieve wound closure with an "ultrathin" autograft.

METHODS

A one-step operative procedure of meshed composite skin graft (MCSG) using Integra as a dermal template for a meshed split thickness autograft was developed in rats. The silicon layer of Integra was removed, the resulting dermal analogue was meshed (1:1.5), expanded, and placed on excised full thickness wound and covered with a meshed (1:1.5 or 1:6) split thickness autograft. Grafted wounds were dressed with BioBrane, Vaseline gauze, silver-impregnated nylon, or silver-nylon and direct current (SNDC). At scheduled intervals up to 3 months postgrafting, wounds were examined for epithelialization, collagen deposition and fibrosis, hair growth, and contraction. The results of wound closure and healing following the one-step procedure were compared with the outcome of the two-step grafting procedure where application of meshed Integra (step one) was followed in 14 days by removal of the silicon layer and application of the meshed autograft (step two).

RESULTS

The one-step procedure applied to meshed autograft/Integra (1:1.5/1:1.5) composite graft accelerated wound closure by 6-19 days when compared with the two-step procedure. At 3 months postgrafting, the contraction of the healed wound dressed with SNDC, BioBrane, or Vaseline gauze was reduced by 13-16% following the one-step procedure compared with the two-step procedure (p < 0.05). The one-step procedure allowed the expansion of the autograft layer to 1:6 while achieving wound healing results similar to grafting with 1:1.5 meshed autograft layer using the two-step grafting procedure.

CONCLUSION

Single-step application of meshed, thin, split thickness autograft over meshed Integra-derived dermal substitute allows more rapid wound closure with less contraction and more efficient use of graft donor skin than can be obtained with the commonly used two-step grafting procedure.

Use of porcine acellular dermal matrix as a dermal substitute in rats

OBJECTIVE

To examine porcine acellular dermal matrix (ADM) as a xenogenic dermal substitute in a rat model.

SUMMARY BACKGROUND DATA

Acellular dermal matrix has been used in the treatment of full-thickness skin injuries as an allogenic dermal substitute providing a stable wound base in human and animal studies.

METHODS

Xenogenic and allogenic ADMs were produced by treating porcine or rat skin with Dispase and Triton X-100. Full-thickness skin defects (225 mm2) were created on the dorsum of rats (n = 29), porcine or rat ADMs were implanted in them, and these were overlain with ultrathin split-thickness skin grafts (STSGs). In two adjacent wounds, 0.005- or 0.017-inch-thick autografts were implanted. In other experiments, the antimicrobial agent used during ADM processing (azide or a mixture of antibiotics) and the orientation of the implanted ADM (papillary or reticular side of ADM facing the STSG) were studied. Grafts were evaluated grossly and histologically for 30 days after surgery.

RESULTS

Significant wound contraction was seen at 14, 20, and 30 days after surgery in wounds receiving xenogenic ADM, allogenic ADM, and thin STSGs. Contraction of wounds containing xenogenic ADM was significantly greater than that of wounds containing allogenic ADM at 30 days after surgery. Graft take was poor in wounds containing xenogenic ADM and moderately good in those containing allogenic ADM. Wound healing was not significantly affected by the antimicrobial agent used during ADM preparation or by the ADM orientation.

CONCLUSION

Dispase-Triton-treated allogenic ADM was useful as a dermal substitute in full-thickness skin defects, but healing with xenogenic ADM was poor.

Long-term outcome of xenogenic dermal matrix implantation in immunocompetent rats

BACKGROUND

Acellular dermal matrix (ADM) has been used successfully in the treatment of full-thickness skin injuries as an allogenic dermal substitute. To assess the efficacy of xenogenic ADM in such wounds, we examined the long-term wound healing and immunological responses to porcine ADM in a rat model.

MATERIALS AND METHODS

Xenogenic and allogenic ADMs were produced by treating porcine (fresh or cryopreserved) or rat skin with dispase and Triton X-100. Full-thickness skin defects on the rat dorsum were implanted with porcine or rat ADMs and overlaid with split-thickness skin grafts (STSGs). Wounds were evaluated grossly and immunologically at 1, 6, and 12 months after surgery.

RESULTS

Extensive wound contraction was seen in wounds implanted with porcine ADM, but healing was significantly (P < 0.01) better in the rat ADM or STSG groups at 6 and 12 months postsurgery. Sera obtained from porcine ADM-implanted rats reacted strongly with porcine ADM and specifically with the papillary dermis and basal lamina. One month postsurgery, extensive inflammation but few intact mast cells were seen in wounds implanted with porcine ADM and significant (P < 0.02) levels of residual porcine ADM were detectable immunologically. Little inflammation was evident in the STSG or rat ADM groups at any time. Significant lymphocyte proliferation (P < 0.05) occurred in the 6- and 12-month groups in response to porcine, but not rat, ADM.

CONCLUSIONS

In wounds implanted with xenogenic ADM, a short-lived acute inflammatory response, long-lasting humoral and cell-mediated immune responses, and generally poor wound healing were observed.

Characterization of acellular dermal matrices (ADMs) prepared by two different methods

The efficacy of acellular dermal matrix (ADM) in the treatment of full-thickness skin injuries as a dermal substitute depends on its low antigenicity, capacity for rapid vascularization, and stability as a dermal template. These properties will be determined largely by the final composition of the ADM. We have treated human skin with either Dispase followed by Triton X-100 detergent or NaCl followed by SDS detergent, cryosectioned the resulting ADMs, and then characterized them immunohistochemically. Staining for cell-associated antigens (HLA-ABC, HLA-DR, vimentin, desmin, talin), extracellular matrix components (chondroitin sulfate, fibronectin, laminin, vitronectin, hyaluronic acid), elastin, and collagen type VII was dramatically reduced or absent from ADMs prepared by both methods. However, significant amounts of elastin, keratan sulfate, laminin, and collagen types III and IV were still observed in both ADMs. Both methods of ADM preparation resulted in extensive extraction of both cellular and extracellular components of the skin but retention of the basic dermal architecture. In general, ADM prepared by the NaCl-SDS method retained larger amounts of each antigen than did that prepared by the Dispase-Triton method. This was most evident for laminin and type VII collagen but larger amounts of type IV collagen, fibronectin, desmin, elastin, and HLA-DR were also evident in the NaCl-SDS ADM.

Optimized mesh expansion of composite skin grafts in rats treated with direct current

BACKGROUND

The purpose of this study was to determine the optimum autoepidermal and allodermal expansion ratio of each component of a meshed composite skin graft (MCSG) that would lead to successful healing.

METHODS

Male Sprague-Dawley rats were used as hosts of the MCSG and donors of autologous tissue. Male ACI rats were used as donors of allodermis. MCSGs with open meshed area (autoepidermal/allodermal) of 9:1/1.5:1, 9:1/3:1, 9:1/6:1, or 6:1/6:1 were applied to full-thickness skin defects and treated with a silver nylon dressing (SN) or SN with direct current (DC). Wound size, hair regrowth, and thickness of dermal layer were evaluated at 3 months.

RESULTS

MCSGs of 9:1/1.5:1, 9:1/3:1, and 6:1/6:1 mesh ratios healed completely within 3 months with no difference in wound size between SN dressing groups or DC-treated groups. Application of DC reduced MCSG contraction and stimulated regrowth of hair.

CONCLUSION

Fresh autoepidermis can be expanded 6:1 on a 6:1 allodermis or 9:1 on a 3:1 allodermis and achieve successful wound healing.

Dispase/detergent treated dermal matrix as a dermal substitute

A method for preparing acellular allogeneic dermal matrix (ADM) and its effectiveness as a dermal substitute are described. Treatment of rat skin with Dispase followed by Triton X-100 completely removed cellular components from the dermis. Subcutaneously implanted ADM evoked no immunological reaction and 20 weeks after implantation, the size of the implanted ADM was reduced to about 60 per cent of its original area. ADM became completely vascularized within 2 weeks after implantation into full thickness skin defects in the rat and inhibited extensive wound contracture. A second layer of ADM placed onto the implanted ADM served as an excellent dressing, providing mechanical protection and permitting vascularization of the underlying implant. Onlay skin autografts placed onto vascularized allogeneic ADM showed good survival when the skin was grafted more than 1 week after ADM implantation. Dispase/detergent treated ADM derived from animal or human skin may be useful in full thickness skin defects providing a vascularized bed for subsequent epidermal coverage.