Degradation of poly(ester) microspheres.

Biodegradable polymeric microspheres have been prepared by spray drying, precipitation, rotary evaporation and press grinding methods. Erosion of microspheres of poly(lactide), poly(3-hydroxybutyrate), copolymers of lactide and glycolide, and copolymers of 3-hydroxybutyrate and 3-hydroxyvalerate at 85 degrees C and 37 degrees C have been studied using ion chromatography, nuclear magnetic resonance, residual mass measurements, viscometry and gel permeation chromatography. Such studies demonstrated that these polyester matrices degraded via (1) random chain scission and (2) release of soluble monomeric and oligomeric products. Protein release from microspheres prepared by these methods indicated that most of the protein is released before the polymer matrix loses weight.