CANINE BONE RESPONSE TO TYROSINE-DERIVED POLYCARBONATES AND POLY(L-LACTIC ACID)

Tyrosine-derived polycarbonates are a new class of degradable polymers developed for orthopedic applications. In this study the long-term (4 8 week) in vivo degradation kinetics and host bone response to poly(DT E carbonate) and poly(DTH carbonate) were investigated using a canine bone chamber model. Poly(L-lactic acid) (PLA) served as a control mate rial. Two chambers of each test material were retrieved at 6-, 12-, 24 -, and 48-week time points. Tyrosine-derived polycarbonates were found to exhibit degradation kinetics comparable to PLA. Each test material lost approximately 50% of its initial molecular weight (M(omega)) ove r the 48-week test period. Poly(DTE carbonate) and poly(DTH carbonate) test chambers were characterized by sustained bone ingrowth throughou t the 48 weeks. In contrast, bone ingrowth into the PLA chambers peake d at 24 weeks and dropped by half at the 48-week time point. A fibrous tissue layer was found surrounding the PLA implants at all time point s. This fibrous tissue layer was notably absent at the interface betwe en bone and the tyrosine-derived polycarbonates. Histologic sections r evealed intimate contact between bone and tyrosine-derived polycarbona tes. From a degradation-biocompatibility perspective, the tyrosine-der ived polycarbonates appear to be comparable, if not superior, to PLA i n this canine bone chamber model. (C) 1996 John Wiley & Sons, Inc.