Abstract
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.