Microencapsulation by Coacervation of Poly(lactide-co-glycolide). III. Characterization of the Final Microspheres

This paper deals with protein microencapsulation by coacervation of poly(lactide-co-glycolide) solutions in CH2Cl2 induced by the addition of silicone oils of various viscosities. This coating technique proceeds along three steps: phase separation of the coating polyester, adsorption of the coacervate droplets around the protein phase, and hardening of microparticules. Size distribution, surface morphology and internal porosity of the final microspheres clearly depend on the main characteristics of the coacervate, particularly the viscosity, in a direct connection with the CH2Cl2 content. Indeed, the whole porosity (which may be as high as 80%), average pore size and broadness of pore size distribution decrease as the coacervate is more viscous. Hardening of the coacervate droplets is thus so fast that the organic solvent is entrapped within the polymer matrix and predetermines the internal porosity. Finally, size distribution of microspheres is bimodal in a clear relation with the coacervate viscosity. A less viscous coacervate favours smaller microspheres (within the 7-90 µm range), contaminated with a minor population of microparticles below 4 µm.