Preparation of poly(l-lactide) microspheres of different crystalline morphology and effect of crystalline morphology on drug release rate

Abstract The physicochemical properties of progesterone-loaded poly(l-lactide) microspheres prepared by the solvent evaporation method were studied, focusing on the crystallinity of the polymer matrices. The solvent evaporation process was found to govern the physical characteristics of microspheres. Solvent removal at atmospheric pressure yielded microspheres of crystalline polymer matrices, while faster solvent removal under a reduced pressure gave microspheres of amorphous polymer matrices. The crystallinity of the polymer matrices was closely correlated with the morphology and physical properties of microspheres, and affected the drug release rate. The microspheres of crystalline polymer matrices had rough surfaces with large surface areas, and exhibited a rapid drug release. In contrast, the microspheres of amorphous polymer matrices had smooth surfaces with smaller surface areas, and provided a slower drug release. The results of X-ray powder diffraction, differential scanning calorimetry and Fourier-transform infra-red spectroscopy suggested that progesterone formed a molecular dispersion in the amorphous polymer matrices.