Facile control of hydroxyapatite particle morphology by utilization of calcium carbonate templates at room temperature

Hydroxyapatite (HAp, Ca-10(PO4)(6)(OH)(2)) particles are widely used in orthopedic applications due to their chemical resemblance to the inorganic component of bone tissue. Since physical and chemical properties of HAp particles influence bone regeneration, various synthesis techniques were developed to precisely control the particle properties. However, most of these techniques required high reaction temperatures, which limited the spectrum of obtained HAp particle morphologies. In this study, ellipsoidal, bowknot-like and spherical calcium carbonate (CaCO3) particles were utilized as solid templates to control the morphology of HAp particles (core@ shell, CaCO3@HAp) under ambient conditions. Since CaCO3 templates had different properties, i.e. morphology, polymorph and surface area, they induced HAp formation with different efficacies, where ellipsoidal vaterite and spherical calcite particles exhibited higher CaCO3-to-HAp conversion compared to bowknot-like aragonite particles. In vitro experiments showed that proliferation of human bone cells (hFOB) was higher upon their interaction with ellipsoidal and spherical CaCO3@HAp particles compared to bowknot-like CaCO3@HAp particles. These findings highlighted CaCO3 particles as promising hard templates to control the morphology of CaCO3@HAp particles under ambient conditions for orthopedic applications.