Title: Nanostructured surface modification of coarse-grained and ultrafine grained Ti-13Nb-13Zr alloy for biomedical application

Abstract

I n the last decade electrochemical methods, that enable surface modification are extensively used in the production of implants, among others electrochemical anodization (anodic oxidation) which enables the obtainment of a nanostructured oxide layer on the surface of metallic biomaterial composed of nanotubes. The advantage of this surface treatment is the ability to obtain adequate surface modulus of elasticity, hardness, corrosion resistance and biocompatibility. Ultrafine-grained (UFG) Ti-13Nb-13Zr (TNZ) alloy, obtained by high pressure torsion (HPT) (pressure 4.1 GPa, 5 rotations), was subjected together with coarse-grained (CG) alloy to surface modification, using the electrochemical anodization at a voltage of 25V in 1M H3PO4+0.5wt.% during 90 minutes. Characterization of the morphology of nanostructured surfaces was done using scanning electron microscopy (SEM), while the topography and surface roughness of the materials were determined using atomic force microscopy (AFM). Corrosion resistance was examined using the potentiodynamic method in artificial saliva and Ringer's solution at a temperature of 37º C with a pH of 5.5. Examination of the surface modulus of elasticity and hardness was performed using the nanoindentation test. Cytotoxicity of tested materials and cell culture viability were assessed using the tetrazolium salt colorimetric test (MTT test) with mouse (L-929) and human lung (MRC-5) fibroblasts in a liquid medium. Morphology and adhesion of cells on the surface were analyzed using SEM. Surface nanostructure modification has led to the formation of an oxide layer on the surface of all tested materials. The obtained results indicate the influence of the HPT process on the homogeneity of the nanostructured oxide layer. Also, electrochemical anodization led to an increase in surface roughness. An electrochemical test has shown increase of corrosion resistance in a solution of artificial saliva after surface nanostructure modification. On the other hand, recorded was a decrease in corrosion stability obtained in Ringer's solution. Characterization of the materials surface using nanoindentation showed a decrease in the values of modulus of elasticity and hardness, for materials with a nanostructured oxide layer, which are close to the values of bone tissue in the human body. The result of the MTT test showed that CG and UFG TNZ alloys before and after surface nanostructure modification were not cytotoxic. The obtained results showed that the materials before and after the surface nanostructure modification were adequate in their biocompatibility for use in implantology.