Enhanced bioactivity of self-organized ZrO 2 nanotube layer by annealing and UV irradiation

Abstract

Superhydrophilic ZrO 2 nanotube layer was prepared by anodic oxidation of commercial pure Zr in aqueous solutions containing 1 M (NH 4) 2SO 4 and 0.15 M NH 4F. The effect of annealing and ultraviolet (UV) irradiation treatment on the microstructure, water contact angle and bioactivity of the ZrO 2 nanotube layer was investigated. The as-anodized nanotube layer consists of cubic and amorphous ZrO 2, no apatite crystals are deposited on its surface even after immersion in simulated body fluids (SBF) for 30 days, exhibiting weak apatite-inducing ability. After annealing at 450 °C for 3 h, the nanotube layer is composed of cubic and monoclinic ZrO 2, and its apatite-forming ability is significantly enhanced because of its lattice structure matching that of apatite, apatite can be induced after immersion in SBF for 15 days. UV irradiation of the ZrO 2 nanotube layers does not alter their surface morphologies and phase components, however, can improve the bioactivity only when the ZrO 2 nanotube layer is well crystallized. The enhanced bioactivity by UV irradiation is thought to result from the abundant basic Zr OH groups on the crystallized ZrO 2 nanotube layer. Annealing and UV irradiation treatment do not alter the superhydrophilic nature of the ZrO 2 nanotubes.