The parameters influencing the morphology of poly(ɛ-caprolactone) microspheres and the resulting release of encapsulated drugs

Polymer microparticles used for drug encapsulation and delivery have various surface morphologies depending on the type of formulation ingredients and parameters of the manufacture process. This works aims at investigating the critical parameters governing the morphology of microparticles and to underline the influence of their surface state on the drug release. The classical fabrication process by the “emulsion-solvent evaporation” is addressed using poly(ɛ-caprolactone) as the polymer and methylene chloride as the volatile organic solvent. The typical surfactants poly(vinyl alcohol) and polysorbate 80 have been considered. Scanning electron microscopy observations showed the various surface morphologies mainly depending on the stirring rate, the viscosity of the oil phase and by the presence of inappropriate surfactants. Because of arrested coalescence during solvent evaporation, the evaporation of the organic solvent causing particles hardening is the most important parameter that controls the morphology. Indeed, slow evaporation allows partial coalescence of the soft particles swollen by the organic solvent, whereas the particles morphology is frozen rapidly upon fast evaporation, thus preventing damaged surface states. Moreover, an effective stabilizing system for the primary emulsion is also a determining factor to control the final morphology. The morphology of the particles has a definite influence on the drug delivery of cholecalciferol. The surface morphology should be taken into consideration in the design of polymer microparticles because it allows a control over the drug release kinetics.