Multifunctional “gum metal” Titanium-Based Alloy: Its Long-Term Electrochemical Behavior and Macrophage Response
Résumé
We obtained the multifunctional Ti-23Nb-0.7Ta-2Zr-1.2O alloy by the melting process with good mechanical properties, good bone tissue compatibility, superior anticorrosive resistance and negligible toxicity. In this paper we characterize this biomaterial by using both electrochemical (cyclic voltammetry and linear polarization, electrochemical impedance spectroscopy – EIS), microscopic (scanning electron microscopy – SEM) and spectroscopic (X-ray photoelectron spectroscopy – XPS) methods and macrophage-based culture studies. We analyzed its long-term behavior regarding corrosion rates, variations of the open circuit potentials and corresponding open circuit potential gradients, namely its possible susceptibility to the local corrosion, the over time evolution of the physical processes at the interface between this alloy and simulated biofluid (Ringer solution of different pH values) and also, the in time surface modifications. The alloy native passive film consists from very protective TiO2, Nb2O5, ZrO2 oxides and tantalum suboxides; it has a thickness of about 6.5 nm ± 1 nm, is more compact and thicker than that on Ti surface and is able to confer a better protection to the substrate. Long-term behavior indicated more protective passive films, higher resistance to corrosion; these passive films became more resistant in time due to new depositions from the solutions which thickened the initial passive films. SEM micrographs confirmed these new depositions having some pores. EDS elemental analysis attested the presence of calcium and phosphorous elements on the alloy surface. In vitro studies with RAW 264.7 macrophages performed in terms of cell survival and proliferation, morphology and pro-inflammatory mediator secretion demonstrated that the gum alloy does not sustain a persistent inflammatory response.