DEGRADATIVE BEHAVIOR OF POLYMERIC MATRICES IN (SUB)DERMAL AND MUSCLE-TISSUE OF THE RAT - A QUANTITATIVE STUDY

Bilayered matrices, made of synthetic degradable polymers, are develop ed for use as a dermal regeneration template in large surface area ful l-thickness skin defects. The porous underlayer is designed to allow i ngrowth of dermal components and the dense top layer will serve as a s ubstrate for keratinocytes. Considering the importance of the degradat ion kinetics of tissue regeneration templates, quantification of matri x degradation up to 1 yr post-implantation, and histological and ultra structural examination of the implants was performed. In this study a moderate foreign body reaction was observed at both the intramuscular and subcutaneous implantation sites, including the presence of mono- a nd multinucleated phagocytes. Poly(L-lactic acid) underlayers tended t o elicit a stronger cellular infiltrate than co-polymeric ones. In the course of the implantation periods this inflammatory response subside d and neovascular ingrowth and the formation of fibrous tissue in the pores was observed. Matrix degradation was demonstrated, starting with the fragmentation of the constituent polymers into increasingly small er particles. During the implantation period, fragments showed progres sive surface erosion. Poly(L-lactic acid) fragments had a more rounded off appearance as compared to co-polymeric ones. Implant surface area had decreased to less than 20%, 1 yr postimplantation. At both implan tation sites and with all matrices, polymer particles were observed in side phagocytic cells. Degradation kinetics were similar with the diff erent matrices. Implants fragmented more rapidly at the subcutaneous i mplantation site as compared to the intramuscular one. Although the da ta suggest biomaterial degradation, remnants of matrices could still b e retrieved 1 yr postimplantation.