Surface modification by pre-adsorption of proteins and polypeptides on Ti substrate with controlled hydrophilicity to improve biocompatibility

Abstract

The water contact angle (WCA) value of the Ti substrate surfaces was successfully controlled to high hydrophilicity (≤ 20 deg.) by the treatment of UV light irradiation, atmospheric plasma or hydrothermal treatment, and stored in different environments to control the variation in WCA over time. Proteins with various molecular mass were used to investigate the protein adsorption on the Ti substrate controlled WCA. ATR-FTIR was employed to quantify the protein adsorption amount. It was found that all proteins had relatively higher adsorption amount on superhydrophilic surface. The adsorption amount of proteins was similar under the same WCA value. PEGs, as organic molecules without peptide bonds, was unable to be adsorbed on Ti with WCA < 60 deg., while can be adsorbed only on the hydrophobic surfaces with WCA > 90 deg. In particular, we have carried out in vivo tests upon the protein pre-adsorbed Ti specimens. The in vivo tests indicated that the Ti substrate which pre-adsorbed proteins with high molecular mass had much higher osteoconductivity than that without protein adsorption. On the other hand, the PEGs adsorbed substrates showed no effect on osteoconductivity enhancement. This was due to its lack of peptide bonds. It was considered that implants adsorbed polypeptides can greatly enhance the osseointegration, regardless the mass and type of molecules. In general, the adsorption of protein and polypeptide containing amino acid is an effective way to improve osseointegration, before implantation into body environment. It provides crucial guidance to the biocompatibility improvement of the metallic bone implant materials.