POLYLACTIDE MICROPARTICLES PREPARED BY DOUBLE EMULSION-EVAPORATION .2. EFFECT OF THE POLY(LACTIDE-CO-GLYCOLIDE) COMPOSITION ON THE STABILITY OF THE PRIMARY AND SECONDARY EMULSIONS

Polylactide and copolymers with glycolide have been used as coating polymers in the microencapsulation technique based on the w(1)/o/w(2) double emulsion-evaporation method. Stability of the primary emulsion is of critical importance and clearly predetermines the internal morphology of the microspheres, in agreement with the very fast hardening of the oil phase (CH2Cl2) as soon as the primary emulsion is dispersed in water. When the peptide or protein to be encapsulated is able to interact with the coating polymer and possibly with the surfactant, the stabilization mechanism of the primary emulsion is very complex. It has been shown that the interaction of BSA (bovine serum albumin) with the polyester is as strong as the glycolide content is high, which results in the formation of a solid film at the w(1)/o interface and in a high emulsion stability. Addition of a surfactant, such as poloxamer 188, in the oil phase has a deleterious effect on both the emulsion stability and the internal structure of the microspheres. Use of a dye tracer in the internal aqueous phase was not useful in probing the double emulsion stability and the encapsulation efficiency, because of specific interactions between the dye (indigocarmine) and the coating polyester. (C) 1995 Academic Press, Inc.