INFLUENCE OF FORMULATION VARIABLES ON THE IN-VITRO RELEASE OF ALBUMINFROM BIODEGRADABLE MICROPARTICULATE SYSTEMS

Poly(D,L-lactide-co-glycolide) microspheres containing BSA were prepar ed by a modified solvent evaporation method using a double emulsion. T hese microspheres were characterized for size, morphology, surface ads orbed protein, encapsulation efficiency and release kinetics. The infl uence of two formulation variables (the procedure to obtain the first emulsion and the lyophilization of the microspheres once obtained) on the physical characteristics and release behaviour of the microspheres was also investigated. Sonicated microspheres were smooth and spheric al, with a mean particle size of 20 mu m and an encapsulation efficien cy of 81%. When the first emulsion was prepared by vortex mixing the p articles were irregular and porous, with a mean size of 31 mu m and a lower encapsulation efficiency (56%). The sonication allows a more hom ogeneous emulsion as well as a lower percentage of albumin adsorbed on the surface. The in vitro release profile was described as a biexpone ntial process with an initial burst effect due to the release of the p rotein adsorbed on the microsphere surface and a second sustained rele ase phase due to protein diffusion through the channels or pores forme d in the polymer coat. The release of BSA was dependent on the prepara tion method. The greatest burst release was found for microspheres for mulated using the vortex mixer, 58% of the encapsulated protein was re leased during the first 24 h, whereas sonicated microspheres released 32.2%. This burst effect could be reduced by lyophilizing the microsph eres following their preparation. The amount of protein released decre ased to 28.3% and 51.6% in sonicated and non-sonicated microspheres re spectively, when they were lyophilized.