The Influence of Probe Curvature on Articular Cartilage Friction Measurements

Abstract

Abstract The potential lubrication mechanisms for articular cartilage remain as complex as the material itself. Many studies have examined systematically the effects of sliding velocity on the frictional response of cartilage but a systematic analysis of contact area remains largely uncharted. Here we explore this potential effect three ways: a constant force experiment, a constant pressure experiment, and a non-constant pressure and force experiment. Hard, impermeable spheres are used as probes and with sizes varied between 1.6 mm and 25.4 mm allowing a sweep of physiologically relevant pressures. The aim is to effectively isolate the influence of the probe curvature on the friction measurements. Articular cartilage samples were collected from horses at necropsy from the left and right distal, medial aspect of the radius. Each test was run for five minutes at a reciprocated sliding speed of 1 mm/s. Two lubrication regimes are observed during testing, an area-dependent regime at lower areas and an area-independent regime at higher areas. Therefore measurements made using different probe sizes will most likely result in different measurements of the friction behavior and great care should be given when comparing these results.