The effect of TCPL devices on tissue-implant interface analysis using adult sheep as a model

Inflammatory response and the subsequent fibrous capsule formation are often used as a screening method to determine biocompatibility of an implanted material. In this study, porous implants of tricalcium phosphate-lysine (TCPL) delivery devices were implanted subcutaneously in adult rams. The fibrous capsule surrounding the implant was studied histochemically to determine the resorbability rate of the device. Fibrous capsular tissues were carefully dissected away from the capsule noting the tissue closest to the implanted material. Evaluation of the sections (5um, H&E) collected from various areas of the implants (n = 127) revealed that: vascularity, macrophages, multinucleated giant cells and plasma cells at the TCPL implant-interface were evident after the first month. Persistence of these cell types and progressive angiogenesis in subsequent months was apparent in all tissues collected from experimental animals. The formation of distinct cell layers was remarkable at the six and twelve month phases. After the first month, macrophages were the predominant cell type at the interface and as the tissue progressed away from the implant the presence of fibroblast and plasma cells were observed. The layer of tissue furthest from the implant mostly consisted of structured collagen fibers with minimal number of microvasculature. The presence of inflammatory cells at the interface sites in all phases was further evidenced by immunohistochemical analysis (IL-1 and IL-6). The inflammatory cells seen at the interface along with the formation of a structured fibrous tissue resembles a normal repair process and supports our previous observations regarding the biocompatibility and biodegradability of TCPL delivery device.