Giant biocompatible and biodegradable PEG–PMCL vesicles and microcapsules by solvent evaporation from double emulsion droplets

Abstract

We report the formation of giant vesicles and microcapsules having diameters of the order of 250 μm obtained using the biocompatible and biodegradable amphiphilic block copolymer poly(ethylene glycol)- b-poly(γ-methyl ε-caprolactone). Using the solvent evaporation method with monodisperse water–oil–water double emulsion droplets, we found either preferentially giant vesicles or preferentially spherical microcapsules with thicker walls compared to the vesicle membrane. The morphology depends on the volume of the evaporating oil shell of the double emulsion droplets for a given concentration of the block copolymer. Accordingly, by using a microfluidic flow focusing device to form the double emulsion, it is possible to direct whether vesicles or microcapsules are preferentially formed, simply by adjusting the volume of the oil shell through the volumetric flow rates of the device. During the evaporation of the organic solvents from the oil shells, rough surface morphologies of the double emulsion droplets were observed as intermediate stages in their transformation to either vesicles or microcapsules. These intermediate stages are most likely related to a dewetting of the evaporating oil phase from the surface of the inner droplet, resulting in a spot-like dewetting pattern, or a phase separation of the oil phase into polymer-rich and polymer-poor domains.