Simulated Coating Interface of (Au-<i>n</i>-HAP-TiO₂) Ti-Metal Bone Implants: Improved Coating Thickness and Long-Term Corrosion Resistance by the Electrophoretic Deposition Method

Recent investigations into novel biomaterials have revealed a necessary trade-off between mechanical and biological properties. This understanding has driven the exploration of various dopant elements to optimize the material performance for biomedical applications. The prime objective of this work is to develop gold-decorated nanohydroxyapatite coatings (Au-<i>n</i>-HAP) on titanium (Ti) via electrophoretic deposition (EPD) owing to their ability to enhance the corrosion resistance and biocompatibility of Ti. The crystalline nature of Au-<i>n</i>-HAP was evidenced by XRD, and the presence of phosphate groups was further confirmed by FTIR and Raman. The XPS survey spectrum confirms the presence of Au as distinct peaks at 83.7 and 87.5 eV with expected binding energy values. FE-SEM analysis indicates the formation of TiO₂-Au-<i>n</i>-HAP interfacial bonding at the titanium-coating interface. The corrosion resistance of <i>n</i>-HAP and Au-<i>n</i>-HAP composite coatings on titanium was assessed in Ringer's solution using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS). The sample coated at 80 V showed the best performance, with a maximum Vickers microhardness of 280 HV100 and excellent corrosion stability, as evidenced by a corrosion potential (<i>E</i>_corr) of -141.49 mV vs SCE and a low corrosion current density (<i>I</i>_corr) of 155.12 μA/cm². Furthermore, a COMSOL Multiphysics 6.1 model accurately predicted a coating thickness of 19 μm, which closely matched the experimental (20 μm) and FE-SEM cross-sectional (21 μm) measurements. Overall, the findings showed that the Au-<i>n</i>-HAP composite-coated Ti provided better corrosion resistance in Ringer's solution than both <i>n</i>-HAP-coated and bare Ti during both short- and long-term immersion (up to 28 days). The Au-<i>n</i>-HAP composite-coated Ti displayed enhanced in vitro cytocompatibility of MC3T3-E1 preosteoblastic cell lines up to 150 μg/mL and better antibacterial activity against <i>S. aureus</i> and <i>E. coli</i> besides being hemocompatible. In terms of its higher corrosion resistance, lower toxicity, and superior biocompatibility, the Au-<i>n</i>-HAP composite-coated Ti can be explored as an implant material for orthopedic applications.