Synthesis of Mesoporous Calcium Phosphate Microspheres by Chemical Transformation Process: Their Stability and Encapsulation of Carboxymethyl Chitosan

We report on the transformation of calcium carbonate microparticles (CCMs) to calcium phosphate microparticles (CPMs) with modulated morphologies and phases. In this additive-free transformation process, the use of templates or surfactants was circumvented, thereby eliminating potential contamination of the final products. The hydroxycarbonate apatite (HCAP) microspheres in high yield were more stable than CaCO3 microspheres in aqueous solution and had higher specific surface areas, which suggested that they had higher loading capability than their CaCO3 counterpart. In addition, the products had good biocompatibility because they were free from extraneous surfactants or stabilizers and, hence, did not require further purification. In order to examine the loading efficiency of these microspheres, carboxymethyl chitosan (CMC) and doxorubicin, which were both excellent biomedical materials, were taken as model high molecular weight and low molecular weight probes, respectively, to investigate the encapsulation capacity of CPMs. The CPMs showed high encapsulation efficiency for both molecules, with an impressive 40% loading efficiency of the adsorbed CMC biomacromolecules in the porous microparticles.