BOVINE SERUM-ALBUMIN RELEASE FROM POLY(ALPHA-HYDROXY ACID) MICROSPHERES - EFFECTS OF POLYMER MOLECULAR-WEIGHT AND SURFACE-PROPERTIES

Two commercially available PLGA polymers (lactic acid/glycolic acid 50 :50, with respective molecular weights of 87 and 15 kDa) were used to prepare microspheres containing a model protein, bovine serum albumin (BSA), following a process based on the (water-in-oil)-in-water emulsi on solvent evaporation/extraction technique. The influence of the form ulation parameters on the in vitro release profiles of BSA was assesse d. The results showed that both the encapsulation efficiency and the p rotein release rate were closely dependent on the molecular weight of the coating polymer. The increase of the encapsulation efficiency, and the quasi-absence of burst effect with the low molecular weight polym er, are explained by ionic and physical interactions between the prote in and the wall polymer. In addition, contact angle measurements revea led the absence of protein at the surface of the microspheres and show ed that the burst effect, measured with the highest molecular weight p olymer, could not be explained by desorption of the protein from the s urface but rather by the diffusion of the protein from regions borderi ng the microsphere surface.