Nanomechanics of biocompatible TiO₂ nanotubes by Interfacial Force Microscopy (IFM)

Titanium dioxide (TiO₂) coatings exhibit desirable properties as biocompatible coatings. In this paper we report on mechanical properties and deformation behavior of (TiO₂) nanotubes grown on pure titanium substrates through anodic oxidation. Characterization of the as-processed coatings was conducted using scanning electron microscopy (SEM). Nanoindentation, using Interfacial Force Microscopy (IFM), was employed to probe the Young's modulus of the nanotubes. Using the IFM technique, the modulus of the nanotube coating may be measured with minimal contribution from the underlying Ti substrate. The modulus of the (TiO₂) nanotube coating was estimated at 4-8 GPa. This technique was also used to study the inelastic deformation behavior of the nanotubes. (TiO₂) nanotubes were found to inelastically deform by "tube crushing" in the immediate vicinity of indenter tip, increasing the local density. This increase in local density caused an increase in the Young's modulus from roughly 4 GPa to 30 GPa in the first 30 nm of indentation. Densification and the resulting increase in elastic modulus are related to the total work of inelastic deformation, irrespective of the loading history.