Encapsulation of Proteins into CaCO3 by Phase Transition from Vaterite to Calcite

Phase transition from vaterite to calcite is a general behavior of CaCO 3 materials. The interfacial reaction method using water-in-oil-in-water (W/O/W) emulsion we reported before is an effective method to produce hollow CaCO 3 particles (microcapsules) with vaterite crystalline structure. These vaterite CaCO 3 microcapsules underwent the phase transition to calcite in various aqueous solutions. When some proteins were mixed in the solution used for the phase transition, their encapsulations were achieved satisfactorily at room temperature regardless of their molecular weight. Insulin, lysozyme, bovine serum albumin, and chicken IgY were successfully encapsulated into the phase transition CaCO 3 particles, while the encapsulation of lysozyme was unsuccessful by the interfacial reaction method. Protein included in the phase transition CaCO 3 particle was not discharged by simple water washing but by the dissolution of the CaCO 3 matrix in an acid solution, being advantageous to a responsive protein delivery technology. The recycle uses of the insulin solution used for the encapsulation improved the utilization efficiency of insulin. It was ascertained that the phase transition of vaterite CaCO 3 microcapsule to calcite is a simple, general, and convenient method to encapsulate proteins into CaCO 3 small particles under very mild conditions.