Simultaneously improving wear resistance and mechanical performance of ultrahigh molecular weight polyethylene via cross-linking and structural manipulation

Abstract

Radiation cross-linking and re-melting extensively used to decrease the wear of ultrahigh molecular weight polyethylene (UHMWPE) deteriorated the mechanical performance undesirably. This study aimed at simultaneously enhancing wear resistance and mechanical performance of UHMWPE bearings by cross-linking of the UHMPWE before melt processing followed by structural manipulation. Wear rate decreased substantially from 12.1 ± 1.1 mg/MC for compression molded UHMWPE (CM-UHMWPE) to 1.5 ± 0.7 mg/MC for melt injection molded cross-linked UHMWPE (MP-xUHMWPE). Owing to imposing a controllable shear flow, large amounts of self-reinforced oriented lamellae were formed. Mechanical properties were thus remarkably improved, which compensated for the loss of mechanical performance caused by cross-linking. Especially, yield strength and ultimate tensile strength increased significantly by 98.3% and 51.0%, climbing to 41.6 ± 1.4 and 62.8 ± 1.3 MPa, respectively. Interestingly, melt processing recombined the residual free radicals in MP-xUHMWPE induced by radiation cross-linking effectively, generating a notably lower oxidation level (0.7 ± 0.1) of MP-xUHMWPE compared to xUHMWPE without any thermal treatment (4.7 ± 0.4) after accelerated aging. Our work opens a radical avenue to fabricate high-performance UHMWPE bearings, enabling its use under high stress, particularly for younger and more active patients.