Friction, wear, and lubrication of hydrogels as synthetic articular cartilage

In recent years, synthetic hydrogels have been studied not only as possible replacements for articular cartilage but as platforms for growing cartilag e in a damaged joint. In the present study, the tribological behavior of sy nthesized poly(2-hydroxyethyl)methacrylate (polyHEMA) hydrogels was investi gated in a four-factor, two-level designed experiment using a device develo ped for biotribology research. The contact geometry consisted of a 6-mm dia meter stainless steel ball on flat polyHEMA disks. The variables in the des igned experiment were (a) applied load, (b) lubrication, (c) hydrogel cross link density, and (d) degree of hydrogel hydration. Linear oscillating slid ing contact tests were conducted for 30 min for each test. The results show ed several significant main effects and first-order interactions. Increasin g the applied load from 6 to 20 N increased average hydrogel wear by 125%. Increased crosslink; density reduced wear by over 60%. And increased hydrat ion resulted in an increase of 130% in wear. The coefficient of friction ra nged from a low value of 0.02 to a high of 1.7 while linear wear varied by a factor of over 60. Interactions between (a) hydration and lubrication and (b) hydration and crosslinking on wear were highly significant. The single most important finding from this study was that, as expected, there was no correlation between friction - which is commonly reported in the literatur e on hydrogels - and wear. Most of the data fell into two groups, namely lo w wear/low friction and high wear/low friction. These results may be useful in the tribological design of hydrogels for both low wear and low friction . (C) 2000 Elsevier Science S.A. All rights reserved.