Double emulsion microencapsulation of proteins as model antigens using polylactide polymers: Effect of emulsifier on the microsphere characteristics and release kinetics

Polylactide and polylactide-co-glycolide microspheres containing a model protein, bovine serum albumin, were prepared by a double-emulsion, solvent evaporation process. Using scanning electron microscopy, the surface characteristics of the particles were examined together with the particle size distribution. Particles were approximately 1 μm in diameter with a narrow size range. The zeta potential and hydrophobicity of the surfaces were also investigated as was the crystallinity of the polymer and the microspheres, using differential scanning calorimetry. Drug encapsulation efficiency was highest (>90%) at theoretical loadings of 10% w/w. The surfactants used during preparation of the microspheres influenced the surface properties and loading of the particles as well as the release behaviour of the protein. Keeping all other variables constant, particles were manufactured using polyvinyl alcohol or polyvinylpyrrolidone during formation of the primary emulsion phase. Those formulated with polyvinylpyrrolidone resulted in significantly higher loadings (15.2% w/w vs. 11.3% w/w at 25% w/w theoretical loading) and also exhibited a marked reduction in the 'burst' release of protein (12% vs. 35%), thereby significantly extending the protein release period with 30% released in one week.