Biointerfacial Multilayered Au-n-HAP/Polycaprolactone/Graphene Oxide Ti-Bone Implant: Electrochemical Stability, Interfacial Passivation Dynamics for Long-Term Corrosion Mitigation, and Accelerated Osteogenesis

Developing multifunctional biomaterials requires balancing mechanical strength and biological activity, leading to the exploration of multilayer coatings and interfacial properties to improve clinical effectiveness. The main goal is to develop Au-n-HAP/polycaprolactone (PCL)/graphene oxide (GO) multilayer coatings on titanium to enhance corrosion resistance. For the multilayer coating, the optimal concentrations of PCL (1%, 3%, and 5%) and the dip time intervals (60, 90, 120, and 150 s) were determined. XPS clarified chemical states, showing Au peaks (83.7 and 87.5 eV) and a C 1 s profile with oxygenated GO and PCL species. FESEM verified the formation of the Au-n-HAP layer and interface bonding of PCL/GO on the titanium metal. The 3%, 120 s sample showed better performance, with a Vickers hardness of 325 HV100, a higher corrosion potential Ecorr of +395.12 mV versus saturated calomel electrode, and a lower corrosion current density Icorr of +95.57 μA/cm2. The Au-n-HAP/PCL/GO multilayer coating approach improved long-term electrochemical stability up to 28 days in Ringer’s solution and its protection efficiency (η) of 87%. Biological studies show enhanced MC3T3-E1 cell viability, apatite growth, hemocompatibility, and antibacterial activity against Staphylococcus aureus and Escherichia coli, making this architecture a promising option for long-term orthopedic implants.