PLA-microparticles formulated by means a thermoreversible gel able to modify protein encapsulation and release without being co-encapsulated

The aim of this work was to develop a novel strategy for the formulation of biodegradable PLA microspheres as delivery systems for proteins or peptides. The strategy is based on the exploitation of the gel-sol transition of the thermoreversible Pluronic F127 gel. The gel allows the formation of the particles without be co-entrapped in the matrix. The microspheres prepared using the novel technique (TG-Ms, or thermoreversible gel-method microspheres) were characterized in vitro (as concerns the size, the morphology, the protein encapsulation, the release and the protein distribution in the polymer matrix), in comparison with microspheres prepared using the classical double emulsion/solvent evaporation method (w/o/w-Ms). Two types of bovine serum albumin (BSA), with different water solubility, were used as model proteins. TG-Ms exhibited small size (7-50 m) and high protein content (8.6%, w/w) regardless of the BSA water solubility, in contrast with w/o/w-Ms, which revealed a size range of 100-130 mu m and a protein content related to the BSA water solubility. TG-Ms, in spite of their smaller size respect of the w/o/w-Ms, displayed a reduced initial burst effect and a higher rate in the second release phase that resulted in a quasi-constant profile. The release behavior of the TG-Ms may be attributable to both the localization of the protein in the particle core, as shown by the confocal laser scanning microscopy analysis on labeled-BSA loaded microspheres, and the few pores in the matrix, as shown by the scanning electron microscopy. A working hypothesis about the mechanism of the particle formation was also discussed. (c) 2006 Elsevier B.V. All. rights reserved