Changes in morphology of in situ forming PLGA implant prepared by different polymer molecular weight and its effect on release behavior.

The effects of polymer molecular weight on drug release behavior would be more complicated from in situ forming implants (ISFIs) that change gradually from liquid to semi-solid or solid after injection. To investigate this phenomenon, three commercially available D,L-lactic acid-co-glycolic acid (PLGA) polymers with molecular weights of 12, 34, and 48 kDa were used to prepare ISFIs containing leuprolide acetate (LA) as a model peptide. The influence of polymer molecular weight on the membrane formation, morphology, and also on their in vitro drug release behavior over a period of 28 days was investigated. Results showed that the amount of drug released over the first 24 h (36% +/- 0.34%) (burst release), for formulation prepared with polymer RG 503H (medium molecular weight, M(w) 34 kDa), was significantly higher than others (p < 0.05). Surface and cross-section morphology of ISFI prepared with medium molecular weight polymer to cellular and spongy-like structure which was in good agreement with the release behavior of LA from it.