Fabrication of Hybrid Capsules via CaCO₃ Crystallization on Degradable Coacervate Droplets

Organic-inorganic CaCO₃ capsules were prepared by crystallization of CaCO₃ on Pickering emulsion prepared using coacervate droplets made from thermoresponsive and degradable poly(2-methylene-1,3-dioxepane- co-2-hydroxyethyl acrylate) (poly(MDO- co-HEA)) in sole aqueous medium. The diameters of CaCO₃-based Pickering emulsion could be controlled by varying several parameters: diameter of CaCO₃ powders, initial polymer concentration, and copolymer composition. The CaCO₃ Pickering emulsion was able to load low-molecular-weight hydrophobic substances at temperatures above the lower critical solution temperature (LCST) due to formation of polymer-concentrated phases, i.e., coacervate droplets. The diameter of CaCO₃ capsules prepared by crystallization also depended on the diameter of the CaCO₃ Pickering emulsion. The CaCO₃ shell was composed of calcite-type crystals, the most stable polymorph among known CaCO₃ crystals. The facially prepared CaCO₃ capsules are valuable for use in functional biomaterials, such as drug delivery carriers and cell culture scaffolds for noninvasive bone-regenerative medicine.