Effects of hydrothermal treatment time on the release kinetics of Ni ²⁺ and Zn ²⁺ , corrosion behavior and biological properties of Zn-supported Ni-Ti-O nanopores coatings

Bone implant materials with excellent corrosion resistance, antibacterial property, and controlled ion release kinetics are crucial for their clinical application. In this study, Zn-supported Ni-Ti-O nanopores (NPs) coating was prepared on the surface of nickel-titanium (NiTi) implants by anodization and hydrothermal treatment (HT), the effects of HT time on coatings structure, antibacterial property, corrosion resistance, Ni²⁺ and Zn²⁺ release behavior and biocompatibility were studied. The results indicate that with the extension of HT time, the coating thickness increases, while the diameters of the NPs decrease. After 3 h of HT, the average diameter of the NPs is 42.52 nm, which is about 1/2 of that after anodization (86.63 nm). Furthermore, our experimental results show that with the extension of HT time, the corrosion resistance is improved, and the corrosion current density of the sample NP-30-Zn-3h is 3.214 × 10^-8 A⋅cm^-2, which is one order of magnitude lower than that of the NiTi substrate (7.529 × 10^-7 A⋅cm^-2). In addition, Zn-supported Ni-Ti-O NPs coatings exhibit excellent antibacterial property and biocompatibility, especially the sample NP-30-Zn-3h. Interestingly, with the extension of HT time, the release of Ni²⁺ and Zn²⁺ is inhibited, and Zn²⁺ concentration released from the sample NP-30-Zn-3h is about 3.65 mg/L at days 7 and 14, which is close to the reported osteoblast-stimulating concentration of 3.53 mg/L.