The Biotribological Behaviour of an Artificial Cervical Disc Model with Ball-on-Socket Contact Type Under Different Material Configurations

The artificial cervical disc was simplified and designed as a ball-on-socket model with the material configuration of polymer-on-Ti6Al4V (TC4). The material of polymer ball included ultra-high molecular weight polyethylene and poly(ether ether ketone) (PEEK). In order to improve the wear resistance of TC4, a W-DLC composite coating was also prepared on TC4 socket by physical vapour deposition method. Hence, there were three kinds of pairs including PE/TC4, PE/W-DLC and PEEK/W-DLC. The long-term wear behaviours of these three material configurations were assessed in vitro using a wear simulator under 10 million cycles (MC) testing intervals. The articulating surfaces of ball and socket were characterized by light microscopy and scanning electron microscopy, respectively. The results indicated that polymer component suffered severe damage characterized by scratches, fatigue cracks and arc-shaped wear grooves on the edge zone of ball. Metal component only revealed thin scratches. Compared with polymer component, the wear rate can be omitted for metal component. The dominant wear mechanism was abrasion wear for metal component while the dominant failure mechanism was a mix of ploughing, fatigue and plastic deformation for polymer component. W-DLC coating protected TC4 from being scratched. However, it also brought many coating wear debris and intensified the wear of polymer component. The most wear-resistant material configuration was PE/TC4 with a total wear rate of about 0.81 mg/MC among the three pairs. Titanium was alternative as a bearing surface in cervical implant.