Microstructure and drug-release studies of sirolimus-containing poly(lactide-co-glycolide) films

Sirolimus-containing poly(lactide-co-glycolide) (PLGA) films were prepared by solution casting and removing the residual solvent, 1,4-dioxane, by liquid and supercritical carbon dioxide (CO(2) ) extraction. The effect of lactide:glycolide ratio, stereochemistry of PLGA, and extraction condition (i.e., temperature and pressure) on the polymer and drug morphologies was studied using wide-angle X-ray scattering and differential scanning calorimetry. The polymer and drug crystallinity increased after liquid and supercritical CO(2) extraction, and the level of drug crystallinity within the film depended on the extraction conditions. Generally, higher levels of drug crystallinity were observed in the films with amorphous polymer matrices, and the drug crystallinity increased with temperature and pressure of the extraction conditions. In vitro drug elution from these films was studied using a USP 4 apparatus. Polymer crystallinity was found to be the determining factor for drug release, whereby films with higher polymer crystallinity eluted less drug compared to films with amorphous polymer matrices.