Preparation of cationic biodegradable dextran microspheres loaded with BSA and study on the mechanism of protein loading

Aim: The aim of this study was to investigate the feasibility of cationic biodegradable dextran microspheres loaded with bovine serum albumin (BSA) posterior to gel formation (postloading). Method: Positively charged microspheres were prepared by polymerization of hydroxylethyl methacrylate-derivatized dextran (dex-HEMA) and dimethyl aminoethyl methacrylate (DMAEMA) in an aqueous two-phase system and net positive surface charge increased with increasing amounts of DMAEMA. Loading efficiency of dextran microspheres for BSA was analyzed through fluorescence microscopy and measured. The BSA release from the cationic dextran microspheres in vitro was investigated. Results: BSA could penetrate into cationic dextran microspheres, but neutral dextran microspheres could not. Protein-loading efficiency (98.1-100%) by postloading was higher compared with by preloading (60.2-75.9%), when the incubated protein concentration was below 1.5 mg/ml. Even though BSA is incorporated in the hydrogel network based on electrostatic interaction, a controlled release can be achieved by varying the initial network density of the microspheres. Conclusion: These findings suggest that it is a feasible method to prepare dextran microspheres with high surface-charge density to efficiently adsorb oppositely charged protein based on electrostatic interactions.