Biomimetic deposition of Fe3O4-incorporated hydroxyapatite coatings on Ti-35Nb-7Zr-5Ta alloy with enhanced electrical response

Bioactive and electrically responsive coatings are promising approaches for improving the functionality of next-generation orthopedic and dental implants. In this study, biomimetic calcium phosphate and calcium phosphate/magnetite (Fe 3 O 4 ) composite coatings were deposited on Ti-35Nb-7Zr-5Ta alloy processed by high-pressure torsion (HPT) using a supersaturated simulated body fluid (SBF 5x) route. The influence of Fe 3 O 4 incorporation on the coatings' morphological, compositional, structural, and electrical properties was systematically investigated. Scanning electron microscopy revealed porous apatite-like coatings covering the alloy surface, while EDS analyses showed a progressive increase in the Ca/P ratio from 0.91 to 1.58 with increasing Fe 3 O 4 content. X-ray diffraction, Raman spectroscopy, and FTIR analyses consistently indicated the formation of calcium-deficient hydroxyapatite (CDHA)-like phases and their evolution toward a more ordered structure in the presence of magnetite. The addition of Fe3O4 also modified the coating morphology and roughness, with the highest roughness reaching 6.60 μm. Electrical characterization demonstrated a substantial enhancement in charge transport after Fe 3 O 4 incorporation. The effective resistance decreased from 2.52 × 10 6 Ω for the undoped coating to approximately (2.19–2.51) × 10 4 Ω for the Fe-containing coatings, corresponding to a reduction of nearly two orders of magnitude. Impedance spectroscopy revealed a transition from predominantly capacitive behavior to a resistive–capacitive response, indicating the formation of electrically active pathways associated with magnetite-containing regions within the composite coating. The combined microstructural, compositional, and electrical results demonstrate that Fe 3 O 4 influences the growth and maturation of biomimetically deposited calcium phosphate coatings while significantly enhancing their electrical responsiveness. These findings highlight the potential of CDHA/ Fe 3 O 4 composite coatings on low-modulus TNZT-HPT substrates as multifunctional surfaces for electrically responsive biomedical implant applications.