Effect of ECAP on Physicochemical and Biological Properties of TiO2 Nanotubes Anodized on Commercially Pure Titanium

Despite many advantages of titanium, such as proper mechanical properties, biocompatibility and corrosion resistance, it has two main weaknesses; low tensile strength compared to other metallic biomaterials, and inadequate osseointegration owing to its bioinert spontaneous surface oxide layer. Grain refinement using Equal Channel Angular Pressing (ECAP) has been preferred as a desirable method to enhance low tensile strength. In addition, osseointegration could be improved by electrochemical oxidation (anodization), resulting in titania nanotubes formation on titanium surface. The latter has been extensively studied on commercially pure titanium (CP-Ti), and the formed nanotubes have been well characterized. However, a thorough observation on anodic nanotubes of ECAP-processed coarse-grained pure titanium (CG-Ti) is missing. In this research, we aimed to investigate the surface characteristics and cytotoxicity of anodic TiO2 nanotubes on ECAP-processed CP-Ti substrate compared to that of CG-Ti. The results generally showed superior use of nanotubes anodized on ECAP-ed CP-Ti substrates over that of coarse-grained ones. We acquired ultrafine-grained titanium (UFG-Ti) by ECAP, and synthesized anodic nanotube arrays on both UFG-Ti and CG-Ti at different times and voltages. We compared the resulted nanotubes' morphologies, physicochemical and biological properties, in which cell culture on anodic TiO2 nanotubes of ECAP-ed CP-Ti has been performed for the first time by this research. FESEM results showed relatively lower diameter and longer nanotubes for UFG-Ti samples rather than CG-Ti ones. Nanotubes of both substrates were amorphous, and CG-Ti nanotubes were more hydrophilic than UFG-Ti nanotubes. Enhanced cell viability and proliferation were achieved on ECAP-ed CP-Ti anodic TiO2 nanotubes. Graphic Abstract

Automated summary

The study aimed to compare the surface characteristics and cytotoxicity of anodic TiO2 nanotubes on ECAP-processed CP-Ti and CG-Ti substrates, showing superior application of anodic nanotubes on ECAP-ed CP-Ti. UFG-Ti samples had smaller diameter and longer nanotubes compared to CG-Ti, with CG-Ti nanotubes being more hydrophilic. Enhanced cell viability and proliferation were achieved on ECAP-ed CP-Ti anodic TiO2 nanotubes.