In Situ Tantalum Doping of Titanium Dioxide Nanotubes via Electrochemical Method for Enhanced Mechanical and Biological Properties

Titanium dioxide nanotubes (TNTs) have favorable biocompatibility and nanoscale morphologies, and they have been extensively explored for titanium implant surface modifications. However, they are limited by their mechanical strength and weak interfacial adhesion between the nanotube layer and the titanium substrate. This restricts their clinical applications. In this study, a two-step electrochemical anodization method is developed to achieve in situ tantalum (Ta) doping into TNT arrays to enhance their mechanical performance without altering their nanotubular structure. The surface morphology, element and crystal phase composition, surface roughness, wettability, and mechanical properties of the Ta-doped TNTs were then thoroughly characterized. Scanning electron microscopy revealed that the Ta doping did not change the nanotube architecture. In addition, X-ray diffraction confirmed anatase TiO2 formation in all the samples. X-ray photoelectron spectroscopy demonstrated that Ta5+ doping significantly reduced oxygen vacancies, and this was a concentration-dependent effect. Nanoindentation and scratch tests showed that the hardness, the Young’s modulus of the nanotube layer, and the adhesion strength between the nanotubes and the titanium substrate were markedly improved compared to those of the undoped TNTs. These mechanical enhancements may be attributed to lattice densification due to Ta doping. In vitro cell assays further demonstrated that the Ta-TNTs promoted rat bone marrow mesenchymal stem cell adhesion, proliferation, and osteogenic differentiation. This was evidenced by increased alkaline phosphatase activity, enhanced mineralization, and upregulated gene expression levels. The results suggest that the Ta-doped TNTs offer a pathway for the development of mechanically robust and bioactive implant surfaces for dental and orthopedic applications.