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Abstract
The in vitro degradation behaviour of a wide range of poly(D,L-lactic-co-glycolic
acid) (PLGA) has been examined in terms of degree of degradation and morphological
change during an incubation period of up to 53 d. Gel permeation chromatography and
differential scanning calorimetry were employed to characterize their degradation
profiles. It was found that amorphous PLGA exhibited a transient multiple crystallization
behaviour of D- or L-lactic acid oligomers during degradation. This indicated that
the hydrolytic scission of ester bonds tends to primarily target the linkage between
glycolic acid and D- or L-lactic acid or glycolic acid. In addition, two distinctive
glass transition temperatures appeared when these crystallization phenomena occurred,
suggesting the transient presence of fast and slowly eroding polymer domains within
microspheres during the degradation. This study supports the heterogeneous bulk degradation
for PLGA microspheres which has been proposed recently for a large specimen.