Biocompatibility of a biodegradable matrix used as a skin substitute: an in vivo evaluation

Synthetic biodegradable polymeric matrices, with a dense top layer and porous under-layer, made of a (poly)ether/(poly)ester (PEO:PBT) copolymer called Polyactive, and also of poly-L-lactide (PLLA), are under investigation as part of a cell-seeded skin substitute for third-degree, large-scale skin defects. The biocompatibility of subcutaneously implanted matrices representing large body surface areas, were studied at 2, 4, 13, 26, and 52 weeks in rats. To investigate local or systemic effects, the weight development of the complete animal and of their hearts, kidneys, lungs, livers, and spleens, as well as the macroscopic and histologic appearance of the implants and organs, were monitored. Early inflammatory response was associated with surgical implantation trauma. All matrices showed neovascular and fibrous tissue ingrowth into the porous underlayer within 2-4 weeks after implantation. Copolymeric and PLLA matrices increasingly fragmented and liquified. After 1 year, small polymeric fragments embedded in fibrous, vascularized tissue could be retrieved at the implantation site. No systemic effects of the implants on the organs or on the animal as a whole were observed. These results and earlier studies on (skin) cell substrate properties and physicochemical characteristics of the matrices indicate the suitability of the matrices as part of a cell-seeded skin substitute.