Enhancement of the capability of hydroxyapatite formation on Zr with anodic ZrO2 nanotubular arrays via an effective dipping pretreatment

Abstract

Hydroxyapatite (HA) depositions on metallic biomedical implants are widely applied to generate bioactive surfaces in simulated biological environments. Highly ordered anodic ZrO₂ nanotubes have attracted increasing interest for biomedical applications. However, previous reports showed that at least 14-28 days were required to obtain HA coating on ZrO₂ nanotubular arrays under biomimetic condition, thus capability to grow HA coating on ZrO ₂nanotubular at room temperature needs to be enhanced. In the present work, we demonstrate that ZrO₂ nanotubular arrays are suitable for an effective dipping treatment to induce more rapid HA coating. A series of ZrO₂ nanotubular arrays having different dimensions were fabricated in fluoride containing electrolyte. Then, we used a dipping treatment for biomimetic formation of an adhesive HA coating on the nanotubular arrays. The coatings formed rapidly using this procedure under biomimetic conditions and did not require a high-temperature annealing process. The as-formed ZrO₂ nanotubular arrays were treated using several dip-and-dry steps, through which the nanotubular arrays were filled and covered with calcium phosphate (CaP) nucleation sites. The specimens readily grew HA once immersed in the simulated biological fluid after 2 days immersion. The carbonated HA coating had several micron thickness after 8 days of immersion while only a thin layer of CaP were observed on annealed ZrO₂ nanotubes immersed in the same solution for the same duration. Tensile testing showed that bonding strength between HA coating and substrate was 21.6 ± 1.6 MPa. This treatment dramatically improves efficiency for promoting HA formation on anodic ZrO₂ nanotubes at room temperature.