Enhanced Interfacial Adhesion and Osseointegration of Anodic TiO 2 Nanotube Arrays on Ultra-Fine-Grained Titanium and Underlying Mechanisms

The poor adhesion of anodic TiO2 nanotubes (TNTs) arrays on Ti substrates adversely affects applications in many fields especially biomedical engineering. Herein, we describe an efficient strategy to improve the adhesion strength of TNTs by performing grain refinement in the underlying Ti substrate via high-pressure torsion processing, as a larger number of grain boundaries can provide more interfacial mechanical anchorage. This process also improves the biocompatibility and osseointegration of TNTs by increasing the surface elastic modulus. The TNTs in length of 0.4 μm have significantly larger adhesion strength than the 2.0 μm long ones because the shorter TNTs experience less interfacial internal stress. However, post-anodization annealing reduces the F concentration in TNTs and adhesion strength due to the formation of interfacial cavities during crystallization. The interfacial structure of TNTs/Ti system and the mechanism of adhesion failures are further investigated and discussed.