IN-VITRO AND IN-VIVO DEGRADATION OF DOUBLE-WALLED POLYMER MICROSPHERES

By exploiting the phenomenon of phase separation, double-walled micros pheres consisting of a core of one polymer surrounded by a coating of a second polymer were formed using a modified process of solvent evapo ration. This paper discusses the characterization and in vitro and in vivo degradation of these microspheres made of two biodegradable polym ers with poly(lactic acid) (PLA) as the external layer and poly(1,3-bi s(p-carboxyphenoxypropane)-co-(sebacic anhydride)) 20:80 (P(CPP:SA)20: 80) as the inner core. The microspheres degraded in vitro were analyze d by Fourier-transform infrared (FTIR) spectroscopy, gel permeation ch romatography (GPC), differential scanning calorimetry (DSC), and optic al and scanning electron microscopy (SEM). The same methods were used to characterize the microspheres used in the in vivo study before intr amuscular implantation. The tissue containing the microspheres was exp lanted and studied histologically by optical microscopy and SEM. The m icrospheres from both studies showed the same patterns of degradation, albeit at slightly different rates. The polyanhydride was hydrolyzed into oligomers first, with the PLA degrading more slowly, decreasing i n molecular weight and increasing in fragility over the course of the study. The main difference between the two studies was that in vitro t he inner core of degrading polyanhydride was trapped by the outer laye r of PLA, even as long as 187 days while after only 72 days in vivo th e polyanhydride had disappeared.