MICROENCAPSULATION BY COACERVATION OF POLY(LACTIDE-CO-GLYCOLIDE) .3. CHARACTERIZATION OF THE FINAL MICROSPHERES

This paper deals with protein microencapsulation by coacervation of po ly(lactide-co-glycolide) solutions in CH2Cl2 induced by the addition o f silicone oils of various viscosities. This coating technique proceed s along three steps: phase separation of the coating polyester, adsorp tion of the coacervate droplets around the protein phase, and hardenin g of microparticles. Size distribution, surface morphology and interna l porosity of the final microspheres clearly depend on the main charac teristics of the coacervate, particularly the viscosity, in a direct c onnection with the CH2Cl2 content. Indeed, the whole porosity (which m ay be as high as 80%), average pore size and broadness of pore size di stribution decrease as the coacervate is more viscous. Hardening of th e coacervate droplets is thus so fast that the organic solvent is entr apped within the polymer matrix and predetermines the internal porosit y. Finally, size distribution of microspheres is bimodal in a clear re lation with the coacervate viscosity. A less viscous coacervate favour s smaller microspheres (within the 7-90 mum range), contaminated with a minor population of microparticles below 4 mum.