Tribological Materials on Titanium Alloy (Ti6Al4V) for Orthopedic Applications

Total hip replacement (THR) surgeries have been common in United States and the safety of implants is one of focuses in research. Metal-on-metal (MoM) design was once the most used in THR but its degradation products can cause several adverse reactions to patients, leading to several recalls of commercial products. Inspired from “tribolayer” (Dr. Wimmer et al., 2000), carbide-derived carbon (CDC) is proposed to be a potential modification on MoM to relieve the tribocorrosive effect. The CDC cannot be directly applied on a metallic substrate, on which there must be a carbide precursor first. Thus, the carburization process for the metal substrate is also necessary to be developed in the current study. The main objectives can simply differentiate into three parts: synthesis and characterization, corrosion and tribocorrosion testing and biocompatibility examination. During the development of carburization on titanium alloy, another material, titanium oxycarbide with graphene in structure, was found, which might be another candidate to reduce the tribocorrosion damage on MoM. Therefore, oxycarbide and the CDC were compared for their corrosion and tribocorrosion properties with the control group, untreated Ti6Al4V alloy. Even though ordinary corrosion resistance did not increase due to the treatments, both groups exhibited better tribocorrosion resistance than the control group. Especially, the CDC presented the lowest OCP potential drops, the least induced currents, the lowest friction coefficient and the lowest material loss. Even 100,000 cycle experiments did not entirely wear off CDC’s protection, as verified with Raman spectroscopy. Finally, both materials were examined for their cytotoxicity with the cell proliferation and direct observation by confocal images, demonstrating that they remained biocompatible after treatments. Moreover, confocal images of oxycarbide specimens seemed to show osteoblast-like cells functioning on the surface. With the further examinations, data from mineralization and gene expression clearly indicated the oxycarbide improve the osseointegration on Ti6Al4V alloy. In summary, the two proposed materials showed no cytotoxicity after the treatments. The CDC increased the tribocorrosion resistance and oxycarbide enhanced the osseointegration on titanium substrate. Although both materials might provide beneficial modifications to the current implants, more research is still necessary to fully characterize their potential.