The influence of UV irradiation on the biological properties of MAO-formed ZrO2

Zirconium and its alloys are thought to be ideal materials for dental and orthopedic implants. However, the surface of native zirconium is bio-inert. It has been reported that micro-arc oxidation (MAO) is a convenient and effective method to improving the biocompatibility and bioactivity of the zirconium surface, and ultraviolet (UV) irradiation can improve the bioactivity of the MAO-formed ZrO2 without altering its surface morphology, grain size and phase component. The aim of the present study was to evaluate the influence of UV irradiation on the biocompatibility and bioactivity of MAO-formed ZrO2. Two types of samples were established. Those formed by MAO were labeled as MAO ZrO2 samples, while those that underwent UV irradiation after MAO treatment were labeled as MAO-UV ZrO2 samples. In the in vitro study, osteoblasts were seeded on the surfaces of the MAO and MAO-UV samples and were then studied by inverted phase contrast microscopy, scanning electron microscope (SEM) and MTT (3-(4.5-dimethyl-2-thiazolyl)-2.5-diphenayl-2H-tetrazolium bromide) testing. While in the in vivo study, the samples were implanted into calvarias of New Zealand white rabbits and were then evaluated by histology and shear strength analysis. The results indicated that the MAO-UV surfaces showed better biocompatibility, faster new bone formation and firmer bonds with bone than the MAO surfaces. Therefore, UV irradiation may be an optimal second-stage treatment that can improve the properties of MAO-formed ZrO2.