Effects of solvent evaporation rate on the properties of protein-loaded PLLA and PDLLA microspheres fabricated by emulsion-solvent evaporation process

This paper investigated the effects of the rate of solvent removal by varying the ambient pressure at a fixed temperature on the morphology, particle size, encapsulation efficiency and release pattern of albumin-loaded PLLA and PDLLA microspheres, prepared by the W/O/W emulsion-solvent evaporation process. For PLLA microspheres prepared either with a fast rate of solvent evaporation (FRSE) or a normal rate of solvent evaporation (NRSE) process, the difference in morphology was minor. In contrast, the different processes did affect the morphology of PDLLA microspheres. Large (surface) pores were observed for PDLLA microspheres fabricated with a FRSE process, while a smooth surface was seen in those with a NRSE process. With the FRSE process, both PLLA and PDLLA microspheres showed smaller particle sizes and lower albumin encapsulation efficiencies than those prepared in the NRSE process. PLLA microspheres prepared with the NRSE process had higher drug encapsulation efficiencies than PDLLA ones, but this was not the case for the FRSE process. An initial burst release of albumin was observed for both PLLA and PDLLA microspheres prepared with the NRSE process, while a lesser burst release was seen for those prepared with the FRSE process. In subsequent stages of drug release, PLLA microspheres prepared with the two different processes showed differences, but this was not the case for PDLLA ones.