Hydrothermal growth mechanism of controllable hydrophilic titanate nanostructures on medical niti shape memory alloy

Different titanate nanostructures were deposited on the surface of NiTi by a hydrothermal process using 5-20 M NaOH at 90-150 °C for 6-72 h. SEM and XRD analyses revealed that different structures such as nanoflakes, nanorods, nanograins, nanofibers, microwhiskers, etc., were formed. As the processing time was increased, the nanoflakes evolve into nanofibers or microwhiskers. Compared with pristine NiTi, the new surfaces displayed different degrees of hydrophilicity. A formation mechanism adopting the growth unit model of anion coordination-polyhedra is proposed. The general formation of titanate nanostructures can be visualized as a sequence of nucleation, formation, and combination of the growth units. The excellent controllability of this process with precise accuracy offers incredible potential in the surface modification of NiTi biomedical materials for medical applications. © ASM International.