Biological activity of titania coating prepared with zirconium oxychloride and titania on zirconia surface

Abstract

Zirconia is recognized as a promising dental implant material because of its good biocompatibility, sufficient mechanical strength, minimal ion release and aesthetic effects similar to natural teeth. However, the limitations of inert surface of zirconia affect the long-term efficacy of zirconia implants. To enhance the osseointegration of zirconia implants, titania (TiO₂) coating is prepared on the zirconia surface by immersion in a mixed zirconium oxychloride (ZrOCl₂) and TiO₂ suspension in a water bath. The surface and longitudinal section morphology are observed by scanning electron microscopy (SEM). The chemical composition is evaluated through energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The roughness and hydrophilicity of zirconia surface are also examined. A three-point bending test is conducted on the samples to explore the effect of this surface treatment on the mechanical strength of zirconia. Vickers hardness measurements are performed to evaluate the gradient change of the longitudinal section of the zirconia substrate. The MC3T3-E1 cells are seeded on zirconia discs, and a LIVE/DEAD double-staining test is conducted to detect the cytotoxicity of the TiO₂ coating. The cell morphology is studied through fluorescence microscope. The degrees of cell proliferation, mineralization and alkaline phosphatase (ALP) activity are calculated and compared. Detection of the mRNA expression of osteogenic differentiation-related markers is performed by RT-PCR. A TiO₂ coating is generated on the zirconia surface and significantly improves the surface roughness and hydrophilicity while not adversely affecting the mechanical strength of zirconia. The hardness of the zirconia substrate shows a gradient change. The TiO₂ coating can promote proliferation, spreading and osteogenic differentiation of MC3T3-E1 cells. These findings suggest that modifying the surface of zirconia with a TiO₂ coating may have a favourable osteogenic effect.

Keywords: Bioactivity; Gradient hardness; Osteogenesis; TiO(2); Zirconia.