Whiteness, Cytocompatibility, and Antibacterial Activity of Carbonate Apatite Granules Containing Zinc Oxide for Bone Regeneration

Bone infections challenge orthopedic treatments, requiring artificial bone materials that combine antibacterial and osteogenic activities. Most inorganic antibacterial agents often compromise the aesthetic quality; it is necessary to impart antibacterial activities to artificial bone materials without compromising their aesthetic appearance. In this study, we focused on zinc oxide (ZnO) as an antibacterial agent, and ZnO-containing carbonate apatite (CAp) granules were fabricated from precursors composed of calcium carbonate (CaCO3) and ZnO via a pH-controlled dissolution–precipitation. The compositional conversion from CaCO3 to apatite in a sodium hydrogen phosphate (Na2HPO4) solution at pH 8.9 was terminated by the formation of zinc phosphate (Zn3(PO4)2·2H2O), whereas complete conversion was achieved in the solution at pH 7.0 without the formation of Zn3(PO4)2·2H2O. The whiteness values of ZnO-containing CAp granules prepared at pH 7.0 were comparable to those of pure CAp granules, indicating that ZnO incorporation did not affect the visual appearance. Furthermore, the ZnO-containing CAp granules exhibited significant antibacterial activity against methicillin-resistant Staphylococcus aureus while maintaining satisfactory cytocompatibility with osteoblast-like cells. These findings demonstrate that ZnO-containing CAp granules possess balanced aesthetic, antibacterial, and biological properties, suggesting their potential as promising artificial bone materials for orthopedic and implant applications where infection control and cytocompatibility are both required.