Functionalization of Ti-Nb-Hf-Zr Alloy Surface with a Protein-Based Polymer

Surface modification enables the creation of bioactive implants without modifying the bulk material properties. In this study a treatment that permits to modify the surface of the low elastic modulus and superelastic Ti-25Nb-16Hf-1Zr (wt%) alloy has been developed  in order to improve its bioactivity. Bioactivity in this study includes adhesion, proliferation and differentiation of osteoblasts cell type. The Ti-Nb-Hf-Zr alloy with 95% reduction in thickness has a low elastic modulus (46 GPa), similar to that of cortical human bone, which suggests that the alloy is a good candidate for being used as bone-implant coupling.

The alloy could be used in for example a hip prosthesis or a dental implant. For this reason, it is necessary for it to promote a high cell adhesion and cell differentiation to enhance osteointegration and bone remodelling. This work aims to improve the bioactivity of the alloy by means of a surface modification treatment which is divided in three steps: plasma cleaning, surface silanization and immobilization of H-RGD₆ elastin-like polymer. The functionalized surfaces have been characterized by X-ray photoelectron spectroscopy (XPS), zeta potential and contact angle. Cell culture and inmunofluorescence microscopy images have demonstrate that surface modification has improved adhesion of osteoblasts cell type.

With the polymer H-RGD₆ elastin-like polymer, which contains RGD sequences, the cell adhesion has been improved. On the other hand, we have not observed significant differences in the proliferation tests between the functionalized samples and the untreated ones. Moreover, the calcium deposition (mineralization) after 14 days of culture has been increased in the functionalized samples.