Abstract

The use of titanium alloys as materials in orthopedic implants is due to their combined physical and mechanical properties, namely immunity to corrosion, biocompatibility, high strength to weight ratio, low modulus of elasticity, and the capacity to join with bone tissue (osseointegration). In addition, previous studies have shown that the native titanium oxide layer formed enhances the biocompatibility of this material, although the thickness, adherence, and surface area available of this native film has been demonstrated to be poor.  Therefore, the objective of this study is to design a surface treatment that will oxidize and coat a novel titanium alloy known as gamma-titanium aluminide (γ-TiAl) with a bioactive coating of hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂, that will promote bone regeneration and will accelerate the healing process, thus reducing the frequency of hip implant readjustment surgery. Plasma electrolytic oxidation (PEO) was chosen for this purpose because it is cost-effective, can be used on complex geometries, and produces thin films with high tribological, corrosion, and thermal barrier performance. All of these properties are necessary in order to uphold the cyclic loading applied on the implant and the acidic physiological conditions that are present during the healing process. Previous studies have shown promising results on a commercially used titanium alloy, Ti-6Al-4V, which will be used to compare the results obtained for γ-TiAl. During this study the arrangement and optimization of the equipment used for PEO was achieved. In addition, preliminary tests were performed in order to determine the oxidizing process conditions for each γ-TiAl and Ti-6Al-4V substrates by identifying the parameters needed to reach the dielectric constant of both samples. Later on, the substrates will be coated using PEO plus the addition of a calcium and phosphate ion electrolyte in order to incorporate the adequate Ca/P ratio found in bone tissue into the titanium matrix. Then, the morphology, porosity, and corrosion resistance of the hydroxyapatite coating will be evaluated in SBF with the use of Electrochemical Impedance Spectroscopy (EIS), which will model the electrochemical cell as an electric circuit, providing quantitative data about the coating’s condition.