The aim of this study was to assess the performance of a biodegradable dermal substrate in deep dermal skin defects. The substrate consisted of a synthetic biodegradable matrix called Polyactive, which is an elastomeric poly (ether)/ poly (ester) block copolymer. This matrix was manufactured either as a porous substrate, with gradually changing pore size (BISKIN-M), or as a bilayer consisting of a porous underlayer with a fully dense surface layer (BISKIN). Cell-free matrices and matrices seeded with autologous or allogeneic porcine fibroblasts were applied to full-thickness skin wounds in Yucatan miniature pigs. Biopsies were taken at different time intervals up to 24-months post-transplantation. Although all BISKIN substrates showed little or no adherence to the wound bed, the adherence of the BISKIN-M substrates to the underlying wound was achieved within minutes after application. Therefore, only BISKIN-M Polyactive substrates were further evaluated. Wound contraction was inhibited by both cell-free and fibroblast-populated substrates. All substrates showed extensive neovascular and fibrous tissue ingrowth within 2-weeks post-transplantation. Furthermore, during this time period, matrix degradation was observed, starting with the fragmentation of the polymers into particles, which were phagocytized by macrophages. These processes occurred actively up to 3 months and ceased thereafter. Cell-free substrates degraded faster, and also, the collagen deposition was lower as compared with cell-seeded substrates. The tissue surrounding the remnants of the Polyactive substrates after 24-months post-transplantation consisted of a mature connective tissue. The newly formed collagen had the same distribution pattern as observed in normal native dermis. We conclude therefore that treatment of full-thickness skin defects with fibroblast-populated BISKIN-M Polyactive substrates leads to satisfactory dermal regeneration.

A fully differentiated epithelium mimicking the features of native epidermis was obtained in vitro by culturing human or porcine epidermal keratinocytes on polyester filter substrate at the air-liquid interface. In addition, after 2 weeks of culture, hemidesmosome-like structures were formed along the basal area of the plasma membrane of the basal cells at the cell-filter interface. When grafted onto full-thickness skin wounds in pigs, the take of cell sheets detached from the filter with dispase was significantly higher (about 70%) in comparison to mechanically detached keratinocytes (about 15%). With dispase-treated keratinocytes alone, basement membrane formation took place within 7 days postgrafting as judged from the presence of a lamina lucida and positive staining for type IV collagen. Also, numerous hemidesmosomes and anchoring fibrils were observed at the basal cell-"neodermis" interface. The fully differentiated epidermis, generated by culturing keratinocytes at the air-liquid interface and detached from the substrate by dispase-treatment, is less fragile and easier to handle than epidermal autografts obtained by conventional culturing methods. Detachment by a short dispase-treatment appeared in our hands the only method for successful and complete epithelial regeneration in full-thickness wounds.