Could Ti6Al4V be alternative as a bearing surface articulated with polymer in artificial cervical disc?

- Ball-on-socket rather than ball-on-plat contact was adopted in this study.
- The ball-on-socket structure was designed to simulate a cervical prosthesis.
- The wear simulation has been tested for 10 million cycles based on ISO standard.
- Three kinds of pairs including CPE/TC4, XPE/TC4 and PEEK/TC4 were contrasted.

In order to study the feasibility for Ti6Al4V (TC4) used as a bearing surface in artificial cervical disc, the wear behaviors of polymer-on-Ti6Al4V pairs were assessed in vitro for 10 million cycles (MC) using a wear simulator. The material of polymer ball included conventional ultra-high molecular weight polyethylene (CPE), cross-linking UHMWPE (XPE) and poly ether ether ketone (PEEK). The artificial cervical disc was simplified and designed as a ball-on-socket model with the material configuration of CPE/TC4, XPE/TC4 and PEEK/TC4, respectively. The wear severity, location and damage type on the articulating surfaces were analyzed by SEM. The results indicated that the CPE and PEEK components revealed severe wear and surface damage with a mix failure mechanism of abrasive wear, ploughed grooves and fatigue cracks. For the polymer balls, the edge zone revealed more severe wear characterized by wear grooves and fatigue cracks as well as squeezing traces than the central zone characterized by linear and arc-shaped sliding scratches. In addition, there was a special damage type characterized by severe arc-shaped wear grooves in the edge zone of the polymer ball. However, TC4 component only indicated scratches after wear testing. The average wear rates were 0.83 ± 0.23 mg/MC, 0.15 ± 0.08 mg/MC and 1.28 ± 0.32 mg/MC for CPE/TC4, XPE/TC4 and PEEK/TC4 pair, respectively. Hence, XPE/TC4 pair was the most wear resistant. Considering the biotribological behavior in totality, TC4 may be alternative as a bearing surface articulated with polymer in artificial cervical disc.