Peptide containing microspheres from low molecular weight and hydrophilic poly(d,l-lactide-co-glycolide)

Biodegradable poly(d,l-lactide-co-glycolide) (PLGA) polymers of molecular weight lower than 30 000 Da and free terminal carboxylic acid end groups were evaluated for incorporation of a peptide. These low molecular weight hydrophilic polymers require characterization for carboxylic acid content and fraction of water soluble polymer, both of which significantly affected the structure and peptide incorporation. The polymers from different suppliers have different properties due to their methods of synthesis. The glass transition temperature increased with increase in the molecular weight, where as the carboxylic acid content and the bulk density of the microspheres decreased with an increase in the molecular weight. The particle size of the microspheres increased with molecular weight. The total yield of microspheres decreased with an increase in the water soluble fraction of the polymer, The 75:25 lactide/glycolide polymers showed a decrease in peptide incorporation with molecular weight but the 50:50 did not. The peptide not incorporated into the microsphere was extracted by the aqueous continuous phase during the microsphere preparation. Microspheres with higher molecular weight show lower initial peptide release. The peptide incorporation in low molecular weight polymers can be controlled by modification in the microsphere preparation process. The results suggest that peptide microspheres can be prepared from low molecular weight hydrophilic lactide/glycolide polymers.