Wear mechanism and wear particles characterization of Zr-2.5Nb, ZTA, and CoCrMo articulating with UHMWPE in multidirectional motion

In traditional metal-on-polyethylene (MoP) implants, especially cobalt chrome molybdenum-ultra high molecular polyethylene (CoCrMo-UHMWPE) pairing, wear primarily occurs in the PE component. The wear particles from PE are considered a major cause of implant loosening and artificial joint failure. The development of oxidized zirconium-2.5 % niobium (Zr-2.5Nb) and zirconia-toughened alumina (ZTA) has shown promise in reducing wear and osteolysis risks. However, comparative studies on the wear mechanisms and wear particle characteristics of Zr-2.5Nb-UHMWPE, ZTA-UHMWPE, and CoCrMo-UHMWPE remain limited. In this study, Zr-2.5Nb, ZTA, and CoCrMo were selected and paired with UHMWPE as pairing materials. The wear mechanism was studied from the aspects of wear behavior and wear particle characterization at different contact pressures from 2 MPa to 4 MPa under multidirectional motion. The UHMWPE wear loss from Zr-2.5Nb-UHMWPE was 48 %, 27 %, and 18 % lower than that of CoCrMo-UHMWPE bearings at 2, 3, and 4 MPa. The results showed that there was no significant difference in the wear loss of UHMWPE from Zr-2.5Nb-UHMWPE and ZTA-UHMWPE at 2 MPa, but 34.5 % higher than that of ZTA-UHMWPE at 4 MPa. Zr-2.5Nb-UHMWPE exhibited a similar wear performance to ZTA-UHMWPE with no visible scratches on the surface of Zr-2.5Nb and ZTA, while multidirectional scratches appeared on the surface of CoCrMo. Moreover, the UHMWPE wear particles were consistent in size range and morphology, but different in quantity and size distribution at all loading conditions. The number of UHMWPE wear particles produced by the Zr-2.5Nb-UHMWPE pairing was 44 %–60 % lower than that of the CoCrMo-UHMWPE at 2, 3, and 4 MPa. However, the UHMWPE wear particles produced by Zr-2.5Nb-UHMWPE and ZTA-UHMWPE were very similar, which were 153 and 157 at 4 MPa, respectively. With increasing load, size distribution results revealed that the proportion of large-sized wear particles gradually increased for the three pairings. Notably, the UHMWPE wear particle from the Zr-2.5Nb-UHMWPE pairing exhibited the largest average particle size. Shape distribution analysis further indicated that the UHMWPE wear particle generated by the Zr-2.5Nb-UHMWPE pairing was predominantly fibrous in morphology, whereas that from the CoCrMo-UHMWPE pairing displayed the highest proportion of round and oval shapes. Based on the analysis of wear morphology and wear particle characteristics, the results showed that the wear mainly occurred in UHMWPE. Plastic deformation was the main cause of wear particle formation, and the wear mechanisms were adhesive wear and abrasive wear. This study compared the tribological behaviors of three typical pairings, providing a valuable understanding of artificial hip joint materials, which will contribute to optimizing orthopedic implant materials.