Morphology of polyanhydride microsphere delivery systems.

Scanning electron microscopy (SEM) was used to elucidate the mechanism of polymer degradation and drug release in polyanhydride microspheres. Three different fabrication methods--solvent removal, solvent evaporation, and hot melt microencapsulation--were used to prepare polyanhydride microspheres containing a variety of drugs. The morphology of these microspheres releasing drug in vitro and in vivo was studied by SEM and compared with degradation and release data measured by conventional methods. Microspheres prepared by the three techniques were shown to have distinctive morphological characteristics induced by the nature of the fabrication method. In addition, SEM analysis could be used to explain the drug release profiles and polymer degradation behavior seen in vitro as well as the in vivo effects of insulin-loaded microspheres on diabetic rats. This study has shown SEM to be an important and powerful tool for analyzing the effects of microsphere fabrication method on drug release.