Particle size and loading efficiency of poly(D,L-lactic-co-glycolic acid) multiphase microspheres containing water soluble substances prepared by thehydrous and anhydrous solvent evaporation methods

PLGA multiphase microspheres were prepared by the multiple emulsion solvent evaporation method using acetonitrile as the polymer solvent and mineral o il as the evaporation medium. The preparation process was further developed in the present study to reduce the particle size and to increase the loadi ng capacity of brilliant blue, bovine serum albumin (BSA) and tumour necros is factor-alpha (TNF-cr) which were used as water soluble model drug substa nces. Sorbitan sesqui-oleate (SO-15EX), present at the 1% w/w level in the evaporation medium, prevented agglomeration of the microspheres containing a solid-in-oil (S/O) suspension as the core phase. This S/O suspension core provided significantly higher loading efficiency of the proteins to the W/ O emulsion core. The W/O emulsion system resulted in agglomeration of the p rotein-loaded microspheres and the loading efficiency decreased significant ly. When brilliant blue was included as the model compound, the loading eff iciencies were not influenced by the core type. Heavy mineral oil was emplo yed to stabilize the dispersed unhardened microspheres rather than light mi neral oil that was reported previously. This anhydrous emulsion system empl oying the S/O suspension core and containing a dispersion of TNF-cr enabled the encapsulation of this protein without loss of activity. It was conclud ed that the anhydrous emulsion system is a suitable approach to prepare mul tiple microspheres as an alternative to the W/O emulsion system, especially when solvent sensitive proteins are incorporated into the microspheres.