Histological evaluation of biodegradable and non-degradable membranes placed transcutaneously in rats

The aim of this study was to assess histologically the response to membrane materials that might be used for guided tissue regeneration procedures, using a transcutaneous model on the dorsal surface of the rat. The materials included expanded polytetrafluoroethylene (PTFE) membrane (Gore-Tex), PTFE Millipore filter, biodegradable polylactic acid (PLA) and polyhydroxybutyrate/polyhydroxyvalerate copolymer membranes. 70 implants were placed in 10 rats under general anaesthesia. At 2 weeks after the operative procedure, the specimens were assessed histologically for the composition of the tissue surrounding the material, the types of cell in the infiltrate and the degree of absorption particularly in the superficial tissues. PTFE was associated with greater epithelial downgrowth and a mainly polymorphonuclear infiltrate. PLA showed a high incidence of absorption, with a mainly monocytic infiltrate. Considerable variation was found between these extremes. It was concluded that the healing responses associated with the membranes were complex and varied, and further work is required to establish the factors which govern the variation in the healing response. The findings are of relevance to regenerative procedures which rely on the guiding influence of artificial membranes on the healing tissues. The PLA material was well tolerated and was gradually absorbed. Further research may enable this material to form the basis of a one stage guided tissue regeneration procedure.