DEGRADABILITY AND ANTIGEN-RELEASE CHARACTERISTICS OF POLYESTER MICROSPHERES PREPARED FROM POLYMER BLENDS

Biodegradable microspheres were prepared to function as a depot system for the controlled release of a model protein antigen bovine serum al bumin (BSA). As an approach to achieve its controlled release, microsp heres were fabricated blending a high-molecular-weight poly-d,l-lactid e-co-glycolide (M(w) = 61,000) with a low-molecular-weight poly-d,l-la ctic acid (M(w) = 2000, PLA2000). The effects of PLA2000 on microspher e degradability and release characteristics of BSA from microspheres w ere investigated. On the basis of the pH change in microsphere suspens ions and water uptake of microspheres, the kinetics of microsphere deg radation was derived to describe the rate of formation of hydrogen ion s due to hydrolysis of ester linkages of polymers. It substantiated th at PLA2000-containing microspheres were subject to controlled degradat ion that was necessary to achieve continuous release profiles of the a ntigen. Immunization of rabbits by subcutaneous injection of BSA-conta ining microspheres enhanced the antigenicity of BSA, and significantly increased the duration of humoral immune responses. (C) 1995 John Wil ey & Sons, Inc.