Influence of shaking and surfactants on the release of bsa from plga microspheres

The aim of the present work was to study the release of a model protein, bovine serum albumin (BSA) encapsulated within biodegradable poly (D,L-lactide-co-glycolide) (PLGA) microspheres prepared by a modified solvent evaporation method using a double emulsion. These microspheres were characterized for size, morphology, surface adsorbed protein, encapsulation efficiency and release kinetics. Two types of in vitro assays were developed to evaluate the influence of shaking and the addition of surfactants on the release profile of encapsulated protein. Scanning electron microscopy (SEM) observation showed spherical and smooth surface particles, with a mean particle size of 20 microm and an encapsulation efficiency of 81%. Surface associated protein was about 25%. The in vitro release profile showed a biphasic pattern described by means of a biexponential equation. There was an initial burst effect due to the release of the protein adsorbed on the microsphere surface and a sustained release phase due to protein diffusion through the channels or pores formed in the polymer coat. The release obtained profiles in static and dynamic assays showed statistically significant differences in the amount of the released protein, whereas the release rate was not affected. The burst effect was 28.30+/-1.63% and 35.20+/-1.50% of the total encapsulated protein for the static and dynamic assays respectively. The addition of surfactants (SDS) to the release medium increased the rate and the amount of drug released. In both assays the value of the slow release rate constant, beta, was 0.029+/-0.002 days(-1) when the surfactant was added, and 0.017+/-0.0014 days(-1) in the samples without surfactant. It is believed that the surfactant leads to an increase in the microsphere surface polarity which allows channel and pore formation inside the polymer through which the protein diffuses easily.