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 po lymers in the microencapsulation technique based on the w(1)/o/w(2) do uble emulsion-evaporation method. Stability of the primary emulsion is of critical importance and clearly predetermines the internal morphol ogy 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 inte ract with the coating polymer and possibly with the surfactant, the st abilization 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 result s in the formation of a solid film at the w(1)/o interface and in a hi gh emulsion stability. Addition of a surfactant, such as poloxamer 188 , in the oil phase has a deleterious effect on both the emulsion stabi lity and the internal structure of the microspheres. Use of a dye trac er in the internal aqueous phase was not useful in probing the double emulsion stability and the encapsulation efficiency, because of specif ic interactions between the dye (indigocarmine) and the coating polyes ter. (C) 1995 Academic Press, Inc.