Mechanical, antibacterial and cytotoxic characteristics of nanolayered TiNb–Zr–Ta and nitrogen-doped TiNb–Zr–Ta coatings

Abstract

Titanium and titanium alloy materials are often made as medical implants. Surface properties of titanium medical implants play decisive roles for antibacterial and biological response and tissue biocompatibility. In this study, cathode arc evaporation (CAE) technology was used to deposit TiNb–Zr–Ta and nitrogen-doped TiNb–Zr–Ta coatings with nanostructures on the Ti–6Al–4V dental abutment screws. The deposited coatings were then oxidized at high temperature to produce different oxides on the surface of the coatings. The mechanical properties, antibacterial properties and biocompatibilities of the coatings were analyzed. The effect of coatings on the abutment screw loosening and removal torque between the abutment screw and the pure titanium implant fixture was studied by removal torque measurement. In addition, Staphylococcus aureus (S. aureus) was used for evaluating the antibacterial properties of coatings, and mouse fibroblasts (L929) were used for ISO 10993-5 cytotoxicity analyses to determine whether it had good biocompatibility.Nanolayered structures and multiphases of polycrystalline TiNb–Zr–Ta were obtained by co-deposition of Ta, Zr and TiNb. When small content of N was introduced, the TiNb–Zr–Ta(N) showed a polycrystalline TiNb–Zr–Ta where N atoms entered the metallic lattice at interstitial sites. After oxidation, oxide phases of Ta2O5, TiO2, Nb2O5 and ZrO2 were formed on the surface of TiNb–Zr–Ta and TiNb–Zr–Ta(N). Ta2O5 was obtained on the surface of the coating prior to other oxides such as TiO2, Nb2O5 and ZrO2. The deposited TiNb–Zr–Ta and TiNb–Zr–Ta(N) coatings had high contact angle and exhibited a hydrophobic feature, while the annealed TiNb–Zr–Ta–O and TiNb–Zr–Ta(N)–O showed hydrophilicity. The deposited TiNb–Zr–Ta had similar hardness and Young's modulus values to that of the uncoated Ti–6Al–4V. When N was doped, the TiNb–Zr–Ta(N) had the highest hardness and Young's modulus. The hardness of the annealed TiNb–Zr–Ta(N) coating only decreased slightly due to the small oxide layer of ∼140 nm. Compared with the uncoated Ti–6Al–4V, TiNb–Zr–Ta serial coatings deposited on abutment screws had higher removal torques, which prevented the abutment screw of dental implant from loosening after long-term use. The biocompatibility of TiNb–Zr–Ta serial coatings was similar to that of the uncoated Ti–6Al–4V. In addition, the oxidized TiNb–Zr–Ta and TiNb–Zr–Ta(N) coatings had excellent antibacterial properties. It is speculated that the resulting Ta2O5 of both coatings may inhibit bacterial growth and improve the antibacterial effect. Based on the above advantages, the TiNb–Zr–Ta serial coatings are expected to have the potential to be applied to biomedical implants.