Thermo-Responsive Microcapsules with Tunable Molecular Permeability for Controlled Encapsulation and Release

Microcapsules with regulated transmembrane transport are of great importance for various applications. The membranes with a tunable cut-off threshold of permeation provide advanced functionality. Here, thermo-responsive microcapsules are designed, whose hydrogel membrane shows a tunable cut-off threshold of permeation with temperature. To produce the microcapsules, water-in-oil-in-water (W/O/W) double-emulsion droplets are microfluidically produced, whose oil shell contains oil-soluble hydrogel precursor of poly(N, N-diethylacrylamide) copolymerized with benzophenone (PDEAM-BP). The PDEAM hydrogels, crosslinked by BP, show volume-phase transition around 34 °C, which makes the microcapsules with the PDEAM hydrogel membrane thermo-responsive. The microcapsules show temperature-dependent changes in radius and membrane thickness. More importantly, the cut-off threshold of permeation can be reversibly adjusted by temperature control as the degree of swelling decreases with temperature. This enables the molecule-selective encapsulation and the controlled release of the encapsulants in a programmed manner by adjusting the temperature. The microcapsules can be rendered to be photo-responsive by encapsulating photothermal polydopamine nanoparticles during the microfluidic operation, which allows the control of the degree of swelling with near-infrared (NIR) irradiation. The thermo- and photo-responsive microcapsules with a tunable cut-off threshold are appealing as a new platform for drug carriers, microreactors, and microsensors.