Preparation and characterization of polylactic acid microspheres containing water-soluble dyes using a novel w/o/w emulsion solvent evaporation method.

Polylactic acid (PLA) microspheres containing soluble dyes as water-soluble model compounds were prepared using the water-in-oil-in-water (w/o/w) emulsion solvent evaporation method. Addition of electrolytes such as NaCl or CaCl2 into the external aqueous phase significantly improved brilliant blue (BB) entrapment efficiency compared to the case of no additives. NaCl was the most effective for obtaining high entrapment efficiency (80-90% of theoretical BB content). The average diameter of the obtained microspheres was in the region of 10-20 microns in all cases. PLA microspheres containing 5 and 10% (w/w) BB exhibited the so-called burst release. The release rate decreased with decrease in the internal aqueous droplet volume in the preparation process. In particular, with PLA microspheres containing 5% (w/w) BB, those prepared with the smallest internal droplet volume (63 microliter), the initial burst release was reduced significantly, and 50% (w/w) of the loaded BB remained in the microspheres for 7 days.