1. School of Materials and Physics, China University of Mining and Technology, Xuzhou 221116, China; 2. School of Chemical Engineering, China University of Mining and Technology, Xuzhou 221116, China
Abstract：[Objective] The artificial joint is lubricated using synovial fluid, and variations in the synovial fluid components considerably affect the tribological behavior of the sliding pair of the artificial joint. [Methods] Herein, the “soft-soft” joint pair materials composed of polyether-ether-ketone (PEEK) and highly crosslinked polyethylene (XLPE) are studied based on the composite synovial fluid content following artificial joint replacement. The friction and wear behaviors of the PEEK-XLPE “soft-soft” joint pair materials lubricated via different composite synovial fluids, including albumin (Alb), γ-globulin (γ-Glo), hyaluronic acid (HA), and phospholipids (PLs), are studied. The mechanisms behind the effect of the composite synovial fluid composition and content on the friction and wear of “soft-soft” joint pair materials and wear mechanism of “soft-soft” joint pair materials under different composite synovial fluid are elucidated. [Results] The results showed that the four primary components of the composite synovial fluid had a substantial influence on the friction and wear properties of the artificial joint materials, with the γ-Glo content markedly affecting the friction coefficient. When the γ-Glo content increased from 5.83 mg/mL to 8.75 mg/mL and total protein content increased from 15 mg/mL Alb+3.75 mg/mL γ-Glo to 35 mg/mL Alb+8.75 γ-Glo, the friction coefficient increased by 29.4% and 28.7%, while the wear rate increased by 24.6% and 166.0%, respectively. Moreover, excessively high γ-Glo or total protein content in the composite synovial fluid caused poor protein adhesion between friction surfaces. The wear of “soft-soft” joint pair materials was aggravated when “soft-soft” joint pair materials were used. The changes in the PLs and HA contents of the composite synovial fluid had little influence on the tribological properties of these “soft-soft” joint pair materials, but their effects on wear properties were significant. When the PLs content increased from 0.15 mg/mL to 0.45 mg/mL, the friction coefficient changed little, but the wear rate decreased by 29.5%. Additionally, the wear rate increased by 22.0% when the HA content increased from 0.1 mg/mL to 1.5 mg/mL. This indicated that increasing PLs content improved the wear performance of “soft-soft” joint pair materials because PLs molecules contain hydrophobic fatty acids, which could serve as effective lubricants. Further, the thickness of the Alb film increased with the PLs, but that of γ-Glo film exhibited hardly any changes. However, the existence of PLs rendered the γ-Glo layer uniform and stable, thereby reducing wear. Moreover, PLs got adsorbed to the surface of other molecules or polymerized with other molecules, and “soft-soft” joint pair materials slid between lipid bilayers to reduce friction. However, the adsorption of the Alb improved when HA and PLs were added to the protein mixture, inhibiting the adsorption of the γ-Glo (the volume of γ-Glo is much larger than that of Alb); thus, the inhibition of the γ-Glo adsorption by HA caused the aggravation of wear. [Conclusions] The results show that a change in the content of each component considerably affects the friction and wear characteristics of the PEEK-XLPE joint pair materials. This study provides a theoretical foundation for investigating composite synovial fluid and improving the lubrication performance of artificial joints. Moreover, it is essential to prolong the service life of artificial joints. Furthermore, under the simulated physiological environment (temperature and pH) in vitro, based on the test load, waveform, and displacement in implants for surgery—wear of total hip-joint prostheses—part 2: methods of measurement (YY/T 0651—2020), the influence of composite synovial fluid on the biotribological behavior of the PEEK-XLPE joint pair materials will be explored in the future using a hip joint wear tester, which is expected to lay a foundation for the clinical use of PEEK-XLPE joint pair materials.
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2024, Vol. 64 
