Abstract
Abstract The extremely low friction and minimal wear in natural synovial joints appear to be established by effective lubrication mechanisms based on appropriate combination of articular cartilage and synovial fluid. The complex structure of cartilage composed of collagen and proteoglycan with high water content contributes to high load-carrying capacity as biphasic materials and the various constituents of synovial fluid play important roles in various lubrication mechanisms. However, the detailed differences in functions of the intact and damaged cartilage tissues, and the interaction or synergistic action of synovia constituents with articular cartilage have not yet been clarified. In this study, to examine the roles of synovia constituents and the importance of cartilage surface conditions, the changes in friction were observed in the reciprocating tests of intact and damaged articular cartilage specimens against glass plate lubricated with lubricants containing phospholipid, protein and/or hyaluronic acid as main constituents in synovial fluid. The effectiveness of lubricant constituents and the influence of cartilage surface conditions on friction are discussed. In addition, the protectiveness by synovia constituents for intact articular cartilage surfaces is evaluated.
Highlights
In various biotribological systems, it is widely known that the healthy synovial joints maintain superior load-carrying capacity and lubricating properties with extremely low friction and minimal wear even in heavily loaded hip, knee and ankle joints
The synovial joints are prominent natural bearings different in geometric congruity depending on joint positions/ movements and are in general covered with soft layers of biphasic articular cartilage lubricated with synovial fluid containing appropriate lubricating constituents
At reloading-restarting after 5 min unloading at 36 m sliding, the restarting friction is remarkably reduced from the previous high level at interruption, but it is slightly higher than the initial friction, as reported by Murakami et al [26, 27]. This friction reduction was considered to be brought by the recovery of both the hydration and some deformation of articular cartilage, in which the hydration lubrication and biphasic lubrication becomes partly effective accompanied with adsorbed film formation initial adsorbed film may have been partly removed
Summary
It is widely known that the healthy synovial joints maintain superior load-carrying capacity and lubricating properties with extremely low friction and minimal wear even in heavily loaded hip, knee and ankle joints. The synovial joints are prominent natural bearings different in geometric congruity depending on joint positions/ movements and are in general covered with soft layers of biphasic articular cartilage lubricated with synovial fluid containing appropriate lubricating constituents. The superior lubricating performance of natural synovial joints is likely to be actualized not by a single lubrication mode but by the synergistic combination of various modes from fluid film lubrication to boundary lubrication [1, 2]. During normal walking, fluid film lubrication mechanisms such as soft-EHL and/or micro-EHL play major roles to maintain low friction and minimize wear. In thin film conditions such as at slow motion or at movement after standing for a long time, it is expected that adsorbed films [9,10,11,12], surface gel films [13], hydration lubrication [14] and polymeric brush-like layers [15, 16] contribute to keep friction low and protect rubbing surfaces
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
