1.D.130. The Permeable Temperature-sensitive Microcapsule (PTMC) Family
Microcapsules with molecule-selective permeation can serve as microreactors, capsule-type sensors, drug and cell carriers, and artificial cells. To accomplish molecular size- and charge-selective permeation, regular size of pores and surface charges can be formed in a membranes (Kim et al. 2019). "Smart" microcapsules have been designed that provide molecular polarity- and temperature-dependent permeability. With capillary microfluidic devices, water-in-oil-in-water (W/O/W) double-emulsion drops are prepared, which serve as templates to produce microcapsules. The oil shell is composed of two monomers and dodecanol, which turns to a polymeric framework whose continuous voids are filled with dodecanol upon photopolymerization. One of the monomers provides mechanical stability of the framework, whereas the other serves as a compatibilizer between growing polymer and dodecanol, preventing macrophase separation. Above the melting point of dodecanol, molecules that are soluble in the molten dodecanol are selectively allowed to diffuse across the shell, where the rate of transmembrane transport is strongly influenced by a partition coefficient. The rate is drastically lowered for temperatures below the melting point. This molecular polarity- and temperature-dependent permeability renders the microcapsules potentially useful as drug carriers for triggered release and contamination-free microreactors and microsensors (Kim et al. 2019).