Systematic Study of (MoTa)xNbTiZr Medium- and High-Entropy Alloys for Biomedical Implants- In Vivo Biocompatibility Examinations

Abstract In this study, the application of medium- and high-entropy (MoTa)xNbTiZr alloys in biomedical implants was systematically analyzed. The alloy with the best combination of mechanical properties was selected and characterized for in vitro and in vivo response for the first time to examine its biomedical properties. A logarithmic increase in the hardness and the yield strength was observed as a function of the Mo and Ta content. Alloys with up to 0.4 mole fraction of Mo and Ta showed a plastic strain of more than 30 % under compression. The nanoindentation results showed that the addition of Mo and Ta increased the elastic modulus of the system linearly. It was surmised that the addition of Ta and Mo above a critical concentration (mole fraction = 0.4) was unfavorable from a biomedical perspective as it increased the brittleness and elastic modulus and decreased the ductility of the system. Therefore, the (MoTa)0.2NbTiZr alloy is a potential structural material for biomedical implants because of its excellent strength and ductility. The developed alloy was investigated for its corrosion properties and compared with commercial biomedical alloys. Furthermore, the biocompatibility of the alloy was examined using an in vivo examination. The alloy was implanted in the skeletal muscles of mice for four weeks and the histology of the surrounding tissue was studied. The alloy exhibited strong passive behavior in a phosphate buffer solution and non-toxic soft tissue response.