Calcium carbonate nanoparticles (CaCO3 NPs) show promising osteogenic potential due to their ability to release calcium ions and modulate pH. However, their limited bioactivity, potential cytotoxicity, variable degradation rates, poor mechanical properties, and lack of inherent osteoinductivity present significant challenges. In this study, we hypothesized that decorating CaCO3 NPs with another active material, zinc peroxide (ZnO2), can address some of these challenges and enhance the effectiveness of CaCO3 NPs in the treatment of bone cancer and bone regeneration. For this purpose, CaCO3 NPs with the vaterite polymorph were synthesized and decorated with ZnO2 NPs. These nanostructures were thoroughly characterized and thin films with varying layers were fabricated. The CaCO3/ZnO2 films showed greater initial adhesion of osteosarcoma cells (Saos-2 cells) than the CaCO3 films. While CaCO3 NPs promoted cellular proliferation over time, the CaCO3/ZnO2 nanocomposites (NCs) reduced the proliferation of osteosarcoma cells and triggered apoptosis. Analyses of osteogenic markers, including alkaline phosphatase activity, mineralization, and the expression of Runx-2 and osteocalcin, strongly indicated that CaCO3/ZnO2 NCs possess even greater osteogenic potential than CaCO3 NPs alone. The dual effects of CaCO3/ZnO2 on osteosarcoma cells, promoting both osteogenesis and apoptosis, may be attributed to the self-production of H2O2 and O2, along with the controlled release of calcium and zinc ions. Given their osteogenic potential and significant antibacterial activity against Staphylococcus aureus and Escherichia coli, CaCO3/ZnO2 NCs are promising candidates for treating bone tumors and regeneration of bone defects.

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