DEGRADATION AND CALCIFICATION OF A PEO/PBT COPOLYMER SERIES

In this study the influence of polyethylene oxide content (70, 60, 55, 40 and 30%) on degradation and calcification of dense polyethylene oxide (PEO)/polybutyleneterephthalate (PET) copolymer cylinders was evaluated at subcutaneous sites in goats. Histologically, the 30/70 and 40/60 PEO/PBT implants revealed no signs of calcification and of degradation, although slight surface alterations were evident after 1 year. In contrast, peripheral fragmentation and intermediate calcification were observed for 55/45 and 60/40 PEO/PBT specimens. After subsidence of the inflammatory reaction to the surgical intervention, the tissue reaction to these four PEO/PBT proportions was characterized by a fibrous capsule, although macrophages were frequently seen bordering 55/45 and 60/40 fragments. More extensive degradation and calcification were encountered for 70/30 PEO/PBT samples. Peripheral crack formation occurred from 4 weeks on and at 12 weeks, surface fragmentation was observed for th is material. Fragments were usually surrounded by macrophages and, in addition, phagocytes with a foamy appearance were found. Fragmentation and phagocytotic activity increased during the course of the experiment. Using confocal Raman microspectroscopy, it was demonstrated that phagocytes contained 70/30 PEO/PBT fragments in their cytoplasm, as intracellular fragments were chemically composed of PEO and PET. Systemic effects of the fragmentation were not observed in axial lymph nodes. It can be concluded from the data obtained in this model that a PEO/PBT copolymer series was well tolerated. This study showed that PEO content in PEO/PBT copolymers is directly related to degradation and calcification of these materials and that the extent of these parameters may vary under different experimental conditions. The application of confocal Raman microspectroscopy enables analysis of the chemical composition of intracellular fragments and may therefore be a valuable instrument in the prediction of long-term implant performances.