Biomineralization-inspired fabrication of chitosan/calcium carbonates core-shell type composite microparticles as a drug carrier

Chitosan/calcium carbonate core-shell type composite microparticles were fabricated via a biomineralization-inspired process with chitosan particles as starting materials. The obtained composite particles were spherical, and the diameter of the composite particles was larger than that of the chitosan particles. XRD measurement indicated that the shell of the composite particle had a crystalline structure. The shell fabrication process was carried out with polyacrylic acid (PAA) or polyglutamic acid (PGlu) as binder molecules between calcium carbonate and chitosan. The crystal form of the shell fabricated with PAA was calcite, which is the most stable form of calcium carbonate crystal. On the other hand, the shell fabricated with PGlu was composed mainly with vaterite crystal, which is not a stable form. Types of the binder molecules influenced the crystal structure of the calcium carbonate shell. Drug release behavior of the model drug-introduced core-shell particles was evaluated in various pH conditions. It was revealed that the inorganic shell suppressed drug release and that the crystal form of the calcium carbonate shell affected suppression of drug release. The core-shell particles prepared in this study was an environmentally friendly hybrid product consisting of inorganic and organic materials and could be used as a novel drug-carrying microcapsule.