Assessment of a beta-metastable titanium alloy for orthopedic use: Corrosion in biomimetic synovial fluid and biocompatibility

This study investigates the potential of a metastable β-titanium alloy for use in orthopedic prostheses through electrochemical, fluorescence, surface characterization, cell viability, and cytotoxicity analyses. Its performance is compared with conventional materials, commercially pure titanium (cpTi), and Ti6Al4V. Increasing demand for orthopedic implants highlights limitations of current alloys, particularly Ti6Al4V, which may release cytotoxic Al and V ions and induce stress shielding due to high stiffness. In contrast, Ti20Zr3Mo3Sn, a metastable β-titanium alloy, was designed without cytotoxic β-stabilizing elements and engineered to exhibit a low elastic modulus (55 GPa), thereby mitigating stress shielding. Electrochemical analyses were performed in phosphate-buffered saline (PBS) and an original Biomimetic Synovial Fluid (BSF) to closely simulate the physiological environment. The Ti20Zr3Mo3Sn alloy demonstrated corrosion resistance and electrochemical properties comparable to those of gold-standard references. In PBS, passive current densities of 35.7, 32.9, and 41.6 × 10 4 mA/cm 2 were measured for cpTi, Ti6Al4V, and Ti20r3Mo3Sn, respectively, at 1V vs OCP. X-ray photoelectron spectroscopy revealed a passive film mainly composed of titanium oxides (∼75%), with contributions from Zr and Sn. In BSF, it was shown that Ti20Zr3Mo3Sn and Ti6Al4V, unlike cpTi, caused the fluidization (decreased rigidity) of lipid membranes. Nonetheless, comprehensive biocompatibility assessments, including viability and cytotoxicity tests with MC3T3-E1 osteoblastic cells and chondrocytes, showed that Ti20Zr3Mo3Sn exhibits properties statistically similar to those of conventional alloys. Both cell types maintained high viability, low cytotoxicity (less than 0.3%), and preserved their capacity for matrix mineralization. These results underscore that Ti20Zr3Mo3Sn is a potential candidate for next-generation load-bearing orthopedic applications.