Co-Doped (Na+, Mg2+, Zn2+, Fe3+)-Carbonated Hydroxyapatites and Composites with MIIFe2O4: Synthesis, Mechanic, Magnetic, and Antibacterial Properties for Medical Application

Co-doped (Na⁺, Mg²⁺, Zn²⁺, Fe³⁺, CO₃^2-)-calcium phosphates and their composites with 10 or 25 wt% of (Mg/Zn)Fe₂O₄ were synthesized via a one-step method from aqueous solutions and heated to 600°C. X-ray powder diffraction (XRD) analysis confirmed the formation of single-phase modified hydroxyapatites and biphasic calcium phosphate composites with a ferrite phase. The composite based on modified biphasic calcium phosphate with 10 wt% of ZnFe₂O₄ exhibited a higher hardness (HV = 3.28 GPa) than the corresponding co-doped (Na⁺, Mg²⁺, Zn²⁺, Fe³⁺)-hydroxyapatite (HV = 2.49 GPa) and a composite of modified biphasic calcium phosphate with 25 wt% ZnFe₂O₄ (HV = 2.91 GPa). The magnetic properties, studied by the Faraday method, showed that the composite with 25 wt% MgFe₂O₄ possessed a significantly higher magnetic susceptibility (345.9) than its ZnFe₂O₄ counterpart (77.8). Furthermore, an increase in the β-Ca₃(PO₄)₂-based phase in the 25 wt% M^IIFe₂O₄ composites was found to enhance the material's activity toward partial dissolution, a key factor in bone engineering. The antibacterial evaluation against Staphylococcus aureus and Pseudomonas aeruginosa demonstrated the functional potential of co-doped (Na⁺, Mg²⁺, Zn²⁺, Fe³⁺, CO₃^2-)-hydroxyapatites and composites based on modified biphasic calcium phosphates with 25 wt% M^IIFe₂O₄. These results contribute to the development of safe materials with tailored magnetic, mechanical, and biomedical properties.