Effect of counterface roughness on the wear of conventional and crosslinked ultrahigh molecular weight polyethylene studied with a multi-directional motion pin-on-disk device

The effect of counterface roughness on the wear of conventional gamma -ster ilized, and electron-beam-crosslinked ultrahigh molecular weight polyethyle ne was studied with a circularly translating pin-on-disk device. The counte rfaces, CoCr disks, were either polished, or roughened so that they represe nted the type of roughening and the range of surface roughness values (R-a = 0.014-0.24 mum) observed in explanted femoral heads of total hip prosthes es. The lubricant was diluted calf serum, and the test length 3 million cyc les. A total of 24 tests were done. With both types of polyethylene, there was a strong correlation between R-a, and wear factor k. The power equation s were k = 5.87 x 10(-5)(R-a)(0.91) for conventional polyethylene (R-2 = 0. 94), and k = 7.87 x 10(-5)(R-a)(2.49) for crosslinked polyethylene (R-2 = 0 .82). Crosslinking improved wear resistance significantly. The wear of cros slinked polyethylene against the roughest counterfaces was lower than the w ear of conventional polyethylene against the polished counterfaces. Against rough counterfaces, the wear of crosslinked polyethylene was an order of m agnitude lower than that of conventional polyethylene. On the crosslinked p olyethylene pins that were tested against polished counterfaces, remains of original machining marks were still visible after the test. The average si ze of wear particles produced by both types of polyethylene against rough c ounterfaces was similar, 0.4 mum, whereas that produced by conventional and crosslinked polyethylene against polished counterfaces was significantly s maller, 0.2 and 0.1 mum, respectively. (C) 2001 John Wiley & Sons, Inc.