Fabrication of the Silicate Containing CaTiO₃ Film with Hydrophilic and Smooth Surface on Titanium to Improve Osteoconductivity

Abstract

It has been reported that hydrophilicity and hydrophobicity of implants influenced the bioactivity. However, it is hard to maintain the hydrophilicity in case of being stored in air. So it is critical to find a way to maintain implants’ hydrophilicity. In general, silicate has been known to contribute the hydrophilicity. In this study, the silicate containing CaTiO₃ films have been prepared on Ti substrates by two-step treatment for biomaterial applications. The hydrophilicity, osteoconductivity and protein adsorption of treated specimens have been investigated. The 1st step treatment for Ti is to form TiO₂ as precursors, either by anodizing in sulfuric acid solution at 298 K, liquid phase oxidation in nitric acid solution with hydrogen peroxide at 353 K, or thermal oxidation at 673 K in air. Hydrothermal treatment in silicate containing alkaline solution is the 2nd step to convert TiO₂ to silicate containing CaTiO₃ films. The SEM, XRD, XPS, WCA (water contact angle) investigations and protein adsorption measurements have been carried out to characterize the surface properties. This surface maintained 10 deg. in WCA after 7 d exposure in air, while the specimen without silicate has WCA of more than 40 deg. The osteoconductivity is evaluated based on the contact ratio of formed hard tissue on the implanted specimens after 14 d implantation in rats’ tibia at in vivo test. The as-prepared film not only has exhibited smooth and superhydrophilic surface, but also has achieved high osteoconductivity and great protein adsorption capacity.

Fig. 1 Change in water contact angle of Ti with storage time in air (gray circle as-polished Ti) after anodizing in (a) 0.1 M Na₂SiO₃, (b) 1 M Na₂SiO₃, and (c) 0.1 M NaOH solutions. Internal profiles are XPS results for (a) and (c).