Hydrogel Microcapsules with Dynamic pH-Responsive
Properties from Methacrylic Anhydride
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Abstract
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