Polymer erosion in PLGA microparticles produced by phase separation method.

This article deals with polymer erosion in biodegradable microparticles produced using the phase separation method. Poly(lactic-co-glycolic acid) copolymers with different compositions and molecular weights were employed. The microparticles were stored in phosphate buffer for 6 months. The molecular weight of the polymers was determined by size exclusion chromatography, and the weight loss was monitored gravimetrically. No weight loss was measured in the first weeks, although the molecular weight decreased significantly already from the start. After a certain storage period which was found to be specific for the type of polymer, the weight of the microparticles decreased rapidly. The start of this weight loss occurred when the molecular weight of the polymer in the degrading microparticles reached a threshold of approximately 15,000. This critical molecular weight was found to be identical for all investigated polymers, i.e. it was independent of the initial molecular weight of the polymer and of the lactic-glycolic ratio.