The effect of solvent removal conditions on performance and release property of protein-loaded microparticles

This study was designed to investigate the influence of solvent removal conditions on the performance and release properties of protein-loaded poly(epsilon-caprolactone) microparticles. The microparticles were prepared by the coacervation method in three different conditions. The effects of vacuum pressure, fabrication temperature and evaporation time on the crystallinity, surface morphology, particle size as well as the yield of microparticles, encapsulation efficiency of BSA and in vitro release property were investigated. There was no significant difference in the size of microparticles prepared by varying the vacuum pressure and temperature. Similar results were obtained for the production yield of microparticles and the loading efficiency of protein in these microparticles. However, accelerating the evaporation rate of solvent significantly reduced the crystallinity of polymer from 54.13 +/- 2.67% down to 44.64 +/- 2.17% (p < 0.05). The release of protein from the resulting microparticles was rapid, within 6 h, after which BSA was continuously and slowly released for up to 7 days. The protein release rate and polymer crystallinity possessed a good correlation (r = -0.951). This result indicated that the higher the crystallinity, the slower the release rate. In other words, change in vacuum pressure and temperature reduced the crystallinity of polymer, which was feasible for protein to release from amorphous domain in microparticles.