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Dermal substitutes can be used to improve the wound healing of deep burns when placed underneath expanded, thin autologous skin grafts. Such dermal matrix material can be derived from xenogeneic or human tissue. Antigenic structures, such as cells and hairs must be removed to avoid adverse inflammatory response after implantation. In this study, a cost-effective method using low concentrations of NaOH for the de-cellularization of human donor skin preserved in 85% glycerol is described. The donor skin was incubated into NaOH for different time periods; 2, 4, 6 or 8 weeks. These dermal matrix prototypes were analyzed using standard histology techniques. Functional tests were performed in a rat subcutaneous implant model and in a porcine transplantation model; the prototypes were placed in full thickness excision wounds covered with autologous skin grafts.An incubation period of 6 weeks was most optimal, longer periods caused damage to the collagen fibers. Elastin fibers were well preserved. All prototypes showed intact biocompatibility in the rat model by the presence of ingrowing blood vessels and fibroblasts at 4 weeks after implantation. An inflammatory response was observed in the prototypes that were treated for only 2 or 4 weeks with NaOH. The prototypes treated with 6 or 8 weeks NaOH were capable to reduce wound contraction in the porcine model. In neo-dermis of these wounds, elastin fibers derived from the prototype could be observed at 8 weeks after operation, surrounded by more random orientated collagen fibers. Thus, using this effective low cost method, a dermal matrix can be obtained from human donor skin. Further clinical studies will be performed to test this material for dermal substitution in deep (burn) wounds.

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Collagenous dermal templates can prevent scarring and wound contraction in the healing of full-thickness defects. In a porcine wound model, full-thickness wounds were substituted by reconstituted and native collagen sponges in combination with autologous split-skin mesh grafts and covered with a semipermeable wound membrane. Native collagen sponges were also linked with either hyaluronic acid, elastin, or fibronectin. Reconstituted collagen matrixes, composed of cross-linked small collagen fibrils, disintegrated within a week and did not contribute to dermal regeneration, whereas native collagen matrixes, composed of intact collagen fibers, disintegrated within 2 weeks and did contribute to dermal regeneration. Addition of extracellular matrix proteins retarded the disintegration to 4 weeks. However, fibronectin-treated matrixes caused aberrant epithelization. When hyaluronic acid was added, matrixes were invaded by more fibroblasts and myofibroblasts. This process correlated with fibrosis and wound contraction. In contrast, the native collagen/elastin matrix reduced the amount of fibroblasts and myofibroblasts. This latter matrix resulted in optimal dermal regeneration and little wound contraction.

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Positive results of tubulization in peripheral nerve reconstruction have been established in animals by many investigators. Clinically, tubulization by means of a venous tubulus is accepted as a reliable technique, but histological results are not known and functional analysis is limited. The aim of this investigation was to study the histological effect of venous tubuli in peripheral nerve reconstruction. In 20 rabbits the saphenous nerves were transected and anastomosed. In ten rabbits (series 1) a venous tubulus was placed around the nerve suture. In another ten rabbits (series 2) a venous tubulus was sutured over a 3 mm nerve gap. Conventional suturing was done in ten contralateral saphenous nerves (series 3, controls). Epineurial stitching was performed. The healing was studied after 3 months and after that histological analysis was performed by means of monoclonal antibody staining. The results of our experiments show that covering a nerve anastomosis with a venous tubulus did not enhance healing in comparison to the conventional end-to-end anastomosis, but in contrast evoked extensive fibrous tissue, thereby hampering regeneration of axons.

Photodynamic therapy with topically applied 5-aminolevulinic acid is used successfully for superficial skin lesions. The results for thicker, nodular lesions are less favorable. The method of aminolevulinic acid administration, the concentrations of aminolevulinic acid, and the irradiation schemes used so far have not been investigated thoroughly. As aminolevulinic acid photodynamic therapy has high potential for the increasing problem of skin cancer, we investigated both visually and histopathologically the photodynamic-therapy-induced skin damage after intracutaneous administration of aminolevulinic acid in normal porcine skin. We also investigated the kinetics of the aminolevulinic-acid-induced photosensitizer protoporphyrin IX fluorescence after irradiation in relation to fluence and irradiance. Finally we investigated the effect on photodynamic-therapy-induced damage of a fractionated irradiation. This study demonstrates that intracutaneous administration of aminolevulinic acid leads to higher fluorescence levels and thus to formation of higher protoporphyrin IX concentrations than topical application of aminolevulinic acid cream. The peak level of protoporphyrin IX after intracutaneous administration of aminolevulinic acid is reached earlier than after topical administration. The comeback of fluorescence, indicating re-synthesis of protoporphyrin IX after irradiation, is inhibited with increasing fluence. Photodynamic-therapy-induced damage increases with increasing fluence, but is independent of the irradiance. Finally, the photodynamic-therapy-induced skin damage seems to be greater after fractionated irradiations with two equal light fractions of 15 J per cm2 separated by a dark interval of 2 h.