Protein release profiles and morphology of biodegradable microcapsules containing an oily core

The protein release profiles and the morphology of poly(D,L-lactide-co-glycolide) (PLG) and poly(epsilon-caprolactone) (PCL) microcapsules were investigated. The microcapsules were prepared by the (oil(1)-in-oil2)-in-water emulsion solvent evaporation method using bovine serum albumin (BSA) as a model protein. The internal and external morphologies of the microcapsules were examined using a light microscope, scanning electron microscope and a laser scanning confocal microscope. A Coulter counter was used to determine particle size and particle size distribution. Protein quantitation and molecular integrity were performed by the bicinchoninic acid protein assay micro-method and SDS-PAGE, respectively. Microcapsules with a polymeric wall surrounding an oily core containing the protein were formed. The encapsulation efficiency (39-96%) for PLG and (13-90%) for PCL increased with polymer molecular weight and particle volume mean diameter (Vmd). Vmd ranged from 87-128 to 42-157 microm for PLG and PCL, respectively. The protein release profile for PLG microcapsules was either continuous or irregularly pulsatile depending on particle morphology and was completed after cavity breakdown. However, that of PCL microcapsules was essentially irregularly pulsatile and was completed after a longer period of time without cavity breakdown but with significant swelling. There was no detectable cleavage of the protein during 6 months storage of PLG and PCL microcapsules at 4 degrees C. Furthermore, insignificant degradation of protein occurred during in vitro release from PCL microcapsules. In contrast, significant degradation occurred in PLG microcapsules. This approach to microencapsulation of a protein may be promising for the controlled delivery of protein vaccines, and the oil core may enhance the immunogenicity of some weak subunit vaccine candidates.