Double-Emulsion-Templated Anisotropic Microcapsules for pH-Triggered Release

Biocompatible microcapsules with a function of pH-triggered release are promising for the site-specific release of bio-actives in the human body. In this work, smart microcapsules with three distinct configurations of membranes are produced to control the rate of pH-triggered release. The microcapsules are prepared with a template of water-in-oil-in-water double-emulsion drops. The oil shells of drops contain two polymers dissolved in an organic solvent: one is a biodegradable polymer selected from poly(lactic acid), poly(lactic-co-glycolic acid), and polycaprolactone, and the other is a pH-responsive cationic polymer. Upon the depletion of organic solvent, two polymers confined in the shell undergo phase separation and double-emulsion drops transform to microcapsules with the solid membrane. Three different configurations of the membranes - spherical, snowman-like, and eyeball-like structures - are exclusively produced according to the selection of biodegradable polymers. Although all the microcapsules release hydrophilic encapsulant loaded in the core when they are subjected to a weakly acidic condition, the release kinetics strongly depends on the configuration of the membrane. Larger surface coverage and thinner membrane of pH-responsive domains result in faster release.