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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 emulsion solvent evaporation/extraction technique. The influence of the formulation parameters on the in vitro release profiles of BSA was assessed. The results showed that both the encapsulation efficiency and the protein 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 polymer, are explained by ionic and physical interactions between the protein and the wall polymer. In addition, contact angle measurements revealed the absence of protein at the surface of the microspheres and showed that the burst effect, measured with the highest molecular weight polymer, could not be explained by desorption of the protein from the surface but rather by the diffusion of the protein from regions bordering the microsphere surface. |
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