In vitro degradation and release characteristics of biodegradable implants containing trypsin inhibitor

The use of a biodegradable implant system that provides a steady, controlled release of drugs or bioactive factors can be an attractive delivery vehicle of substances that can enhance repair processes in the musculoskeletal system. The present in vitro study examined the degradative characteristics and release kinetics of a 50 to 50 polylactic acid/polyglycolic acid implant, used as a carrier of trypsin inhibitor, during a 10-week period. Morphological and scanning electron microscopic examinations demonstrated that the implant degraded in a gradual, extended fashion such that by 10 weeks the implant was completely dissolved. It also was shown that the protein was released from the implant in a sigmoidal fashion with increased release between 3 and 7 weeks. More than 95% of the trypsin inhibitor originally incorporated in the implants was released during the 10-week test period. To describe further the degradation process of the implant, temporal changes in its molecular weight and surface axial strain were determined also. It was shown that in the initial 4 weeks, there was a marked decrease in molecular weight of the implants. Axial strain decreased and then increased over time, suggesting an initial period of stiffening followed by a period of degradative softening.