Bioactivity enhancement of cerium-containing titanium oxide nanotubes. Relationship between surface reactivity and nanostructuring process

The present study is focused on the development of a novel surface by electrochemical modification of titanium substrates (Ti) to enhance bone-bonding ability. A Ce-containing conversion coating was formed on Titanium oxide nanotubes (Ti_TiO2NT) (Ti_TiO2NT_CeOx) in an innovative and straightforward approach by anodic deposition. Both Ti_TiO2NT and Ti_TiO2NT_CeOx materials depict a regular and highly ordered nanotubular morphology with open tops cavities. At a molecular level, cerium ions form a stable link with titanium through a Ti–O–Ce bridging bond in a partially ordered crystal lattice of anatase, inducing a strong passivation effect. Finally, bone-bonding ability of the modified surfaces was evaluated with a bioactivity test, revealing that cerium species induce calcium phosphate precipitation with more efficiency than bare Ti and even Ti_TiO2NT surfaces. The cerium doping strongly affects the electrochemical behavior of Ti_TiO2NT_CeOx surfaces, enhancing the metal passivity. These results prove that nanoscale tailoring of Ti surface by anodic electrodeposition using cerium (i.e., 2.5 wt%) is a suitable method to retain the geometry of the original NTs and provide a reproducible, stable, nanotubular, highly ordered, bioactive and corrosion resistant material, appropriate for applications in regenerative medicine.