The effect of initial polymer morphology on the degradation and drug release from polyglycolide

Polyglycolide is a degradable polyester which has been proposed for use as a matrix for controlled drug release. This paper assesses the effects of the initial morphology of the polymer on its behaviour during hydrolytic degradation. The initial morphology does not have a dramatic effect on the progress of degradation, the levels of crystallinity attained during the early stages of degradation being independent of the initial morphology. A sudden increase in both the mass loss and water uptake of the samples occurs after 10 days regardless of the initial morphology, and this is attributed to the formation of a porous surface layer, which occurs when the polymer matrix reaches a critical molecular weight. However, the initial morphology does affect the release profiles of a model drug, theophylline, from the matrices. Samples with a higher initial crystallinity release more drug at earlier stages of the degradation. This is probably due to a partitioning of drug molecules to the surfaces and an increase in the concentration of drug in the amorphous phase.