Weight losses and molecular weight changes correlated with the evolution of hydroxyacids in simulated in vivo degradation of homo- and copolymers of PLA and PGA

Abstract

Homo- and copolymers of poly(lactide)s (PLA) and poly(glycolide)s (PGA) were hydrolysed at 37 and 60 °C for periods up to 80 days. We propose that the hydrolyses of PLA100 (100% L-lactide), PLA37.5GA25 (75% D,L-lactide and 25% glycolide) and PLA25GA50 (50% D,L-lactide and 50% glycolide) in buffer solutions at 37 and 60 °C proceed in three stages. During the first stage the molecular weights decrease rapidly with little weight loss. In stage two, the decrease in molecular weight slows down and severe weight loss starts in parallel with which monomer formation is initiated. During the final third stage, when total weight loss is observed, about 50% of the polymer is converted to monomer. The hydrolyses of the soluble oligomers continues until all are transferred to lactic acid and glycolic acid.