Binary Zn–Ti alloys for orthopedic applications: Corrosion and degradation behaviors, friction and wear performance, and cytotoxicity

Abstract

Zinc (Zn) and its biocompatible and biodegradable alloys have substantial potential for use in orthopedic implants. Nevertheless, pure Zn with a hexagonal close-packed crystal structure has only two independent slip systems, therefore exhibiting extremely low elongation and yield strength in its as-cast condition, which restricts its clinical applications. In this study, as-cast Zn–xTi (titanium) (x = 0.05, 0.10, 0.20, and 0.30 wt.%) binary alloys were hot-rolled and their microstructures, mechanical properties, wear resistance, and cytocompatibility were comprehensively investigated for orthopedic implant applications. The microstructures of both as-cast and hot-rolled Zn–xTi alloys consisted of an α-Zn matrix phase and a TiZn16 phase, while Zn–0.2Ti and Zn–0.3Ti exhibited a finer α-Zn phase due to the grain-refining effect of Ti. The hot-rolled Zn–0.2Ti alloy exhibited the highest yield strength (144.5 MPa), ultimate strength (218.7 MPa), and elongation (54.2%) among all the Zn–xTi alloys. The corrosion resistance of Zn–xTi alloys in Hanks’ solution decreased with increasing addition of Ti, and the hot-rolled Zn–0.3Ti alloy exhibited the highest corrosion rates of 432 μm/y as measured by electrochemical testing and 57.9 μm/y as measured by immersion testing. The as-cast Zn–xTi alloys showed lower wear losses than their hot-rolled counterparts. The extracts of hot-rolled Zn–xTi alloys at concentrations of ≤ 25% showed no cytotoxicity to MG-63 osteosarcoma cells and the extracts of Zn–xTi alloys exhibited enhanced cytocompatibility with increasing Ti content.