Hydrogel Microcapsules with Dynamic pH-Responsive Properties from Methacrylic Anhydride

Dynamic microcapsules are a highly sought-after class of encapsulant for advanced delivery applications with dynamically tunable release profiles, as actively manipulatable microreactors, or as selective microtraps for molecular separation and purification. Such dynamic microcapsules can only be realized with a nondestructive trigger-response mechanism that changes the permeability of the shell membrane reversibly, as found in hydrogels. However, the direct synthesis of a trigger-responsive hydrogel membrane around a water drop without the use of sacrificial templates remains elusive due to the incompatibility of the synthesis chemistry with aqueous emulsion processing. Here, we report on a facile approach to fabricate reversibly responsive hydrogel microcapsules utilizing reactive anhydride chemistry. Cross-linked and hydrophobic poly(methacrylic anhydride) microcapsules are obtained from microfluidic double emulsion drop templating that enables direct encapsulation of hydrophilic, water-suspended cargo within the aqueous core. Hydrolysis in aqueous environment yields microcapsules with a poly(acid) hydrogel shell that exhibit high mechanical and chemical stability for repeated cycling between its swollen and nonswollen states without rupture or fatigue. The permeability of the microcapsules is strongly dependent on the degree of swelling and hence can be actively and dynamically modified, enabling repeated capture, trap, and release of aqueous cargo over numerous cycles.