Zaki M, Aljinaidi A, Hamed M
Department of Production Engineering and Mechanical Design, Faculty of Engineering, Mansoura University, Egypt.
Biomed Mater Eng. 2003;13(3):205-21.
In recent years, there is an increasing utilization and demand to use magnetic fields in bioengineering applications due to its beneficial effects. Although in the last decade more attention has been given by tribologists to the electromagnetic processes taking place between sliding surfaces, which influence the tribological behaviors, but no attention has been concern with the sliding surfaces of the artificial implant joints. Therefore, the present work aims to elucidate the tribological behavior of an artificial joint implant under the effect of magnetic fields. Experimental investigation was carried out on a specially designed and constructed hip simulator on which the variations in the coefficients of friction and wear rates of the sliding surfaces were evaluated under the influence of a medium strength magnetic field suitable to apply in the human body. A realistic Ti-alloy implanted stem was used with an inserted head made from surgical grade stainless steel. This head was allowed to rub against UHMWPE sockets. The utilized type of prosthesis was "The JRI Modular Muller Standard-Total Hip Design". The performed experimental tests were conducted under both dry and lubricated sliding conditions using physiological saline solution. The designed simulator allows the coefficients of friction and the wear rates to be evaluated under realistic physiological loading and motion cycles encountered during normal walking of the human body. Comparative results are presented between the artificial joint performance in the presence and absence of the applied magnetic field. The experimental results have indicated that the presence of a medium strength magnetic field of 270 Gauss strength between rubbing surfaces resulted in high beneficial reductions in friction and wear rate of UHMWPE sliding on stainless steel either under dry or saline lubricating conditions. Therefore recommendation was forward to subject artificial implants made of stainless steel/UHMWPE combination of material to such medium strength magnetic field in animal clinical trials aiming to prolong the implant life. Scanning investigation of rubbing surfaces has revealed that the transfer of polymer to the counterface plays a dominant role in dictating the frictional and wear behaviors under dry sliding condition. Smooth molecular profile of the polymer-transferred leads to progressive reductions in friction and wear while the lumpy polymer transfer, formed at the beginning of sliding, increases both friction coefficient and wear. Two action mechanisms dominate the sliding process; adhesive and abrasive mechanisms. The presence of saline lubricant retards the formation of the beneficial polymer transfer thus leading to faster abrasion of the polymeric counterface which explains the relatively rapid and progressive increases in friction and wear.
近年来，由于磁场的有益作用，其在生物工程应用中的利用率和需求不断增加。尽管在过去十年中，摩擦学家对滑动表面之间发生的电磁过程给予了更多关注，这些过程会影响摩擦学行为，但人工植入关节的滑动表面却未受到关注。因此，本研究旨在阐明人工关节植入物在磁场作用下的摩擦学行为。在专门设计和构建的髋关节模拟器上进行了实验研究，在适合人体应用的中等强度磁场影响下，评估滑动表面的摩擦系数和磨损率的变化。使用了一个逼真的钛合金植入柄，其插入的头部由外科级不锈钢制成。该头部与超高分子量聚乙烯（UHMWPE）髋臼杯进行摩擦。所使用的假体类型为“JRI模块化穆勒标准全髋关节设计”。进行的实验测试在干燥和润滑滑动条件下使用生理盐水溶液进行。所设计的模拟器能够在人体正常行走时遇到的实际生理载荷和运动周期下评估摩擦系数和磨损率。给出了施加磁场和未施加磁场时人工关节性能的对比结果。实验结果表明，在摩擦表面之间存在强度为270高斯的中等强度磁场时，无论是在干燥还是盐水润滑条件下，超高分子量聚乙烯在不锈钢上滑动时，摩擦和磨损率都有显著的有益降低。因此，建议在动物临床试验中，将由不锈钢/超高分子量聚乙烯材料组合制成的人工植入物置于这种中等强度磁场中，以延长植入物寿命。对摩擦表面的扫描研究表明，在干滑动条件下，聚合物向对偶面的转移在决定摩擦和磨损行为方面起主导作用。聚合物转移形成的光滑分子轮廓导致摩擦和磨损逐渐降低，而在滑动开始时形成的块状聚合物转移则会增加摩擦系数和磨损。两种作用机制主导着滑动过程，即粘着机制和磨料机制。盐水润滑剂的存在阻碍了有益聚合物转移的形成，从而导致聚合物对偶面更快磨损，这解释了摩擦和磨损相对快速且逐渐增加的原因。
