Electrochemical Surface Characterization of a Femtosecond Laser Treated and Anodized Ti and Ti6Al4V Alloy for Bone and Dental Implants

Abstract

Pure Titanium (Titanium grade 2) and Ti6Al4V (Titanium grade 5) alloys are commonly used biocompatible materials for medical bone implants and dental protheses. As some implants have to be removed after a certain amount of time after the implantation, the osteo repellent surface is one of the most important property for the removable bone implants such as bone screws and plates. On contrary, for the dental protheses the property of the most importance is osseointegration. Femtosecond laser treatment causes ablation and produces LIPSS (“laser induced periodic surface structures”) which can consist of cones on macro scale and ripples on nano scale which showed structures and roughness similar to that of a bone. Therefore, surface modifications by electrochemical anodization and femtosecond laser could be seen as promising methods for improving both osteo-repellence and osteointegration properties of the bone implants and dental protheses. The aim of this work is electrochemical and surface characterization of the anodized Titanium and Ti6Al4V alloy treated by the femtosecond laser. Firstly, Titanium and Ti6Al4V samples were anodized potentiostaticaly up to 100V in 25% phosphoric acid solution for 120s. Following the potentiostatic anodization, samples were structured with femtosecond laser to produce micro cones and nano ripples on top of the cones. As a final step, laser treated spots were potentiodynamicaly anodized using a SDCM (Scanning Droplet Cell Microscopy) setup. Influence of different potentials, scan rates and electrolytes were studied and optimized, consequently. Morphology and topography were examined by the means of SEM (Scanning Electron Microscopy) and AFM (Atomic Force Microscopy), while crystallography was determined by the XRD (X-Ray Diffraction). Furthermore, the composition of the oxide layer was determined by the XPS (X-ray photoelectron spectroscopy). Oxide forming factor (kox), a relative permittivity εr, and ECSA (Electrochemical surface area) were obtained from the cyclic voltammograms (CV) and electrochemical impedance spectroscopy (EIS) experimental data. Electrochemical impedance spectroscopy data was modeled and compared between not preanodized, preanodized and anodized and not anodized after femtosecond laser structuring. Finally, bioassessment with osteoblast was done to examine the growth of the osteoblast cells on the modified surface structures. Value of the oxide forming factor (kox) for the pure Titanium and Titanium grade 5 were successfully calculated and compared with a Scanning Electron Microscopy. Calculated values of the relative permittivity εr are in agreement with the literature values. Finally, obtained results indicate that anodized and subsequently femtosecond laser treated samples could be used as medical bone and dental implants.