Effect of Sliding Velocity on UHMWPE and VEXLPE Friction Against CoCr in Multidirectional, Serum Lubricated Conditions

The recently introduced four-station friction RandomPOD device was utilized in multidirectional, circular translation pin-on-disk (CTPOD) tests. The effect of sliding velocity on friction with orthopaedic bearing materials was studied. The tests included UHMWPE and VEXLPE pins against polished CoCr disks in serum lubrication at 37 °C. In the constant velocity tests, the sliding velocities used were from 5 to 50 mm/s at intervals of 5 mm/s. The test length with each velocity was 24 h. In the constant acceleration tests, the velocity steadily increased from 0 to 50 mm/s in 24 h. In all tests, the sample size was 4. No strong effect of velocity on friction was observed. This indicated a boundary lubrication mechanism. With sliding velocities above 10 mm/s, VEXLPE showed significantly lower friction than UHMWPE. The finding was in agreement with earlier dynamic RandomPOD tests. Clinically, the use of VEXLPE may result in lower frictional heating.