Coacervate-mediated synthesis of porous calcium carbonate microcapsules
Microspheres of calcium carbonate loaded with active agents are synthesized by a bio-inspired mineralization approach. Polyacrilic acid (PAA) is used as the additive to modify mineralization, stabilize amorphous calcium carbonate (ACC) and allow the formation of coacervate droplets. These coacervates are submicron-sized droplets that phase-separate from the aqueous solution due to electrostatic interaction between calcium ions and the negatively charged polyelectrolyte. The size and porosity of the droplets are tailored by controlling the polyelectrolyte concentration and the time scale of the complexation reaction. Incorporation of active agents within the coacervate droplets is achieved by dispersing the respective molecules in the aqueous solution prior to phase separation. In order to stop the complexation and to stabilize the loaded-droplets, counter ions are added to the solution (e.g. sodium carbonate) which leads to mineralization of the complex. Since the reactions take place under aqueous conditions, at mild pH and at room temperature, the process presents effective way to synthesize functional porous minerals as well as biocompatible drug-loaded ACC microcapsules.