Abstract
Synovial fluid plays an important role in lubricating synovial joints. Its main constituents are hyaluronic acid (HA) and γ–globulin, acting as boundary lubricants for articular cartilage. The aim of the study was to demonstrate the concentration-dependent effect of HA and γ–globulin on the boundary-lubricating ability of human osteoarthritis (OA) cartilage. Normal, early and advance stage articular cartilage samples were obtained from human femoral heads and in presence of either HA or γ–globulin, cartilage frictional coefficient (µ) was measured by atomic force microscopy (AFM). In advanced stage OA, the cartilage superficial layer was observed to be completely removed and the damaged cartilage surface showed a higher µ value (∼0.409) than the normal cartilage surface (∼0.119) in PBS. Adsorbed HA and γ–globulin molecules significantly improved the frictional behavior of advanced OA cartilage, while they were ineffective for normal and early OA cartilage. In advanced-stage OA, the concentration-dependent frictional response of articular cartilage was observed with γ–globulin, but not with HA. Our result suggested that HA and γ–globulin may play a significant role in improving frictional behavior of advanced OA cartilage. During early-stage OA, though HA and γ–globulin had no effect on improving frictional behavior of cartilage, however, they might contribute to disease modifying effects of synovial fluid as observed in clinical settings.
Highlights
Osteoarthritis (OA) is a common disease of synovial joints, characterized by the degeneration of articular cartilage that involves changes in cartilage structures and compositions [1]
Prior to analysis of frictional behavioral studies, site-specific surface irregularities of samples were determined by histological staining
Safranin O staining is known to bind glycosaminoglycan of articular cartilage
Summary
Osteoarthritis (OA) is a common disease of synovial joints, characterized by the degeneration of articular cartilage that involves changes in cartilage structures and compositions [1]. Solid–fluid biphasic structure of cartilage is known to contribute toward lubricating diarthrodial joints through interstitial fluid pressurization [3]. With lubrication by synovial fluid (SF), the m of cartilage2on2cartilage, cartilage2on2glass and cartilage2on2metal bearings are approximately ,0.01–0.1 [4, 5], ,0.05–0.1 [6, 7], and ,0.2–0.5 [8, 9], respectively, depending on load bearing conditions (i.e., loading duration and magnitude). The cartilage m is initially very small and reaches a steady-state equilibrium value due to the timedependent decrease in cartilage interstitial pressurization [14]. Observed differences in the cartilage m, under the same loading conditions, are mostly caused by variation in assessment time until it reaches an equilibrium steady-state value
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