A novel environmentally friendly thermochemical process for Ti64 alloy surface modification for biomedical implants

Abstract

This study develops an environmentally friendly novel thermochemical surface modification process of Ti64 alloy by utilizing citric acid and hydrogen peroxide to improve the mechanical properties, biocompatibility, and bioactivity for biomedical applications. The novel process was developed thermochemically, followed by simulated mineralization in Hanks Balanced Salt Solution (HBSS). The study investigates the effects of thermochemicals on surface characteristics by evaluating the influence of eco-friendly chemicals on modifying surfaces and finding the optimal pH value. The findings demonstrated that the modification effectively enhanced the Ti64 alloy mechanical properties with a significant increase in average microhardness by approximately 71 % and a reduction in wear rate by approximately 64.29 %, compared to untreated Ti64 alloy. The surface modification with pH (5,7, and 9) revealed absorptive properties as evidenced by a contact angle below 90°, indicating a hydrophilic surface, enhancing cells' attachment to biomaterials. After soaking Ti64 alloy in HBSS, a uniform coating layer of around 20.5 μm formed, leading to increased bioactivity, as evidenced by a Ca/P ratio of 1.67, comparable to hydroxyapatite in human bone. The hemolysis ratio of 0.027 % at pH 7 indicates little red blood cell (RBC) lysis, indicating increased biocompatibility. The corrosion rate was enhanced with pH (5,7, and 9) approximately (1.975 × 10⁻², 1.078 × 10⁻², and 1.615 × 10⁻²) mm/year, respectively. These findings indicate that the novel process with neutral pH (7) is optimal for surface modification as it is the most effective in enhancing the biocompatibility and bioactivity of the Ti64 alloy, making it suitable for biomedical implants.