Foy J R, Williams P F, Powell G L, Ishihara K, Nakabayashi N, LaBerge M
Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg 24061, USA.
Proc Inst Mech Eng H. 1999;213(1):5-18. doi: 10.1243/0954411991534762.
Hemiarthroplasty may benefit from materials which produce lower friction and improved boundary lubrication protection during start-up conditions. The purpose of this study was to evaluate the effect of phospholipidic boundary lubrication in both rigid and compliant hemiarthroplasty. An in vitro model was designed to dissociate the relative contribution of implant material compliance and the presence of phospholipid to the overall friction of a hemiarthroplasty contact using bovine articular cartilage. Normal bovine articular cartilage was articulated against four flat materials using reciprocating motion: (a) borosilicate glass: (b) borosilicate glass coated with dipalmitoylphosphatidylcholine (DPPC); (c) polyurethane (PU) elastomer (Tecoflex SG93A, a medical-grade aliphatic thermoplastic PU, Thermedics Incorporated. Woburn, Massachusetts); and (d) surface-coated PU (Tecoflex SG93A substrate coated with lipid-attracting copolymer poly[methacryloyloxyethyl phosphorylcholine (MPC)-co-butyl methacrylate (BMA)]. Tests were conducted in physiologically simulated tribological conditions for a non-conformal point contact. Friction and lubrication analysis was performed using both static and kinetic coefficients of friction mu measured for each group as a function of time for a sliding distance of up to 60 m. Results showed that the inclusion of supplemental phospholipid, DPPC, on a rigid substrate significantly decreased mu in comparison with the control (cartilage-glass). Additionally, removal of phospholipid components from the articular cartilage surface produced a significantly greater start-up mu in comparison with normal cartilage at the test onset. The use of a material with a lower modulus resulted in lower mu for the entire duration of the test. Polyurethane elastomer coated with the lipid-attracting copolymer, poly(MPC-co-BMA), resulted in the lowest frictional response. As seen in this study, the improvement of low-modulus hemiarthroplasty may involve the optimization of chemical modification and incorporation of lipid-attracting MPC copolymers onto compliant materials. However, further tests are warranted to determine whether lipid-attracting MPC copolymers perform as well during long-time, in vivo wear studies.
半关节成形术可能会受益于在启动条件下能产生较低摩擦力并改善边界润滑保护的材料。本研究的目的是评估磷脂边界润滑在刚性和顺应性半关节成形术中的作用。设计了一个体外模型，以利用牛关节软骨分离植入材料顺应性和磷脂的存在对半关节成形术接触总体摩擦力的相对贡献。使用往复运动使正常牛关节软骨与四种平面材料进行关节活动：(a)硼硅酸盐玻璃；(b)涂有二棕榈酰磷脂酰胆碱(DPPC)的硼硅酸盐玻璃；(c)聚氨酯(PU)弹性体（Tecoflex SG93A，一种医用级脂肪族热塑性聚氨酯，Thermedics Incorporated，马萨诸塞州沃本）；以及(d)表面涂层PU（涂有吸引脂质共聚物聚[甲基丙烯酰氧基乙基磷酰胆碱(MPC)-共-甲基丙烯酸丁酯(BMA)]的Tecoflex SG93A基材）。在生理模拟的摩擦学条件下对非共形点接触进行测试。使用每组测量的静摩擦系数和动摩擦系数μ作为时间的函数，对长达60米的滑动距离进行摩擦和润滑分析。结果表明，与对照组（软骨-玻璃）相比，在刚性基材上添加补充磷脂DPPC可显著降低μ。此外，与测试开始时的正常软骨相比，从关节软骨表面去除磷脂成分会产生明显更大的启动μ。使用较低模量的材料在整个测试过程中导致较低的μ。涂有吸引脂质共聚物聚(MPC-共-BMA)的聚氨酯弹性体产生了最低的摩擦响应。如本研究所示，低模量半关节成形术的改进可能涉及化学改性的优化以及将吸引脂质的MPC共聚物结合到顺应性材料上。然而，需要进一步测试以确定吸引脂质的MPC共聚物在长期体内磨损研究中是否也能表现良好。
