IN-VITRO PREDEGRADATION AT ELEVATED-TEMPERATURES OF POLY(LACTIDE)

In this study in vitro predegradation at elevated temperatures, used t o obtain an increased degradation rate, was investigated. The in vitro degradation was followed by mass loss, molecular weight loss and chan ges in thermal properties. Two biodegradable polymers, the homopolymer PLLA and a copolymer PLA96 (96% L4 %D lactide), were hydrolytically d egraded at 90 degrees C in a phosphate buffered solution. Both polymer s, PLLA and PLA96, showed an initial linear degradation rate, but with longer implantation periods the degradation rate decreased and total degradation was best described as an asymptotic. Mass loss of the copo lymer PLA96 was twice that of PLLA. The chemical analysis of the in vi tro predegraded polymers coincided for both the decrease in molecular weight and the thermal properties with physiologically degraded poly(l actide). The results of this study show that although the degradation temperature is well above the glass transition temperature and not com parable to physiological temperatures, there seems to be good correlat ion between the in vitro degraded material and physiologically degrade d material. In vitro predegradation enables investigation of the entir e degradation process of a polymer in a short-term study. Moreover, in vitro predegradation allows direct comparison of the degradation rate of various polymers.