Storing Period Effects on Wear Properties in Uhmwpe Inserts for Artificial Joints

INTRODUCTION Artificial joints have been increasingly used in treatment of physically disabled people who have severely damaged joints. In artificial joint, ultra high molecular weight polyethylene (UHMWPE) has been usually employed as a buffer because of its very low friction coefficient, high wear resistance, high impact strength, and biocompatibility. [1]. When artificial joints were replaced, a number of best-fit sized inserts based on x-ray inspection would be chosen for the patients. Usually, more than 70 inserts would be prepared for the arthroplasties. Finally, one of them would be chosen, then rest of them would wait for the next arthroplasties as shelf-stored. If the shelf-stored inserts can be used, the manufacturing cost will reduce to a great extent. However, the shelfstoring period effects on wear properties in UHMWPE insert have not been investigated yet. Then, storing period effects on wear properties in UHMWPE inserts were determined using a pinon-disk wear testing machine. EXPERIMENT PIN-ON-DISK WEAR TEST A pin-on-disk wear testing machine (JT-TOHSI INC., Japan) was used to investigate the tribological behavior of the UHMWPE disks against Co-Cr-Mo pins with distilled water as a lubricant. A contact stress 10Mpa, a constant sliding velocity of 196.5mm/sec (150rpm) and test durations up to 999999 revolutions (78.8km) were chosen. The friction force f was measured with a load cell. The weight difference between before and after the tests was measured as a wear volume. Wear factor was employed to compare each data. TABLE 1 shows wear test conditions.