Articular cartilage lubrication

Hydropolymer gel has been considered as a possible candidate for an artificial articular cartilage in artificial joints because it exhibits very low friction when it is in contact with a solid. The origin of such low friction is considered to be associated with the water absorbed in the gel [83-86], some of which is squeezed out from the gel under the load and serves as a lubricant layer between the gel and solid surface, resulting in hydrodynamic lubrication [87, 88]. Although the structural information about the interfacial water is important to understand the role of water for the low frictional properties of hydrogel in contact with a solid and the molecular structure of lubricants other than water at solid/solid interfaces have been investigated theoretically [89-91] and experimentally [92-98], no experimental investigations on water structure at gel/solid interfaces have been carried out due to the lack of an effective experimental technique. 

Freeman, M.E. Furey, M.J. Love, B.J. Hampton, J.M. Friction, wear, and lubrication of hydrogels as synthetic articular cartilage. Wear 2000, 241, 129-135. 

It should be emphasized that the lower frictional coefficient of DN-L gel can be observed under a pressure range of W -lO Pa, which is close to the pressure exerted on articular cartilage in synovial joints. The results demonstrate that the linear polyelectrolyte chains are still effective in maintaining lubrication, even under an extremely high normal pressure. 

Wear and Lubrication In-Vitro Study. Polyurethane surface layers with viscoelastic properties similar to natural articular cartilage has been proposed for use with hemiarthroplasty, a single component joint replacement in which the implant is intended to bear against a natural cartilage surface. Medley and... 

Conclusions. Results from the biocompatibility studies in rabbit supratellar bursa, measurement of hydrophilic properties, lubrication and wear in-vitro studies, determination of viscoelastic properties, measurement of damping coefficient and impact test, total elbow joint replacement design and in-vivo percutaneous implant experiment, all indicate that this series of polyurethanes is an excellent candidate biomaterial for the prosthetic replacement of articular cartilage, artificial joint prostheses and percutaneous implantable devices. 

It has already been shown and discussed — at least in in vitro tests with articular cartilage — that compounds which reduce friction do not necessarily reduce wear the latter was suggested as being more important [10]. It maybe helpful first of all to emphasize once again that friction and wear are different phenomena. Furthermore, certain constituents of synovial fluid (e.g., Swann s Lubricating Glycoprotein) may act to reduce friction in synovial joints while other constituents (e.g., Swann s protein complex or hyaluronic acid) may act to reduce cartilage wear. 

The general comment made here is that the use of synovial fluids — whether derived from human or animal sources and whether healthy or abnormal — is important in in vitro studies of synovial joint lubrication. The documented behavior of synovial fluid in producing low friction and wear with articular cartilage sets a reference standard and demonstrates that useful information can indeed come from in vitro tests. 

An unusually large number of theories and studies of joint lubrication have been proposed over the years. All of the theories focus on friction, none address wear, many do not involve experimental studies with cartilage, and very few consider the complexity and detailed biochemistry of the synovial-fluid articular-cartilage system. 

It is suggested that these results could change significantly the way mechanisms of synovial joint lubrication are examined. Effects of biochemistry of the system on wear of articular cartilage are likely to be important such effects may not be related to physical/rheological models of joint lubrication. 

Swanson, S.A.V. Friction, Wear and Lubrication. In Adult Articular Cartilage, M.A.R. Preeman, Ed., Pitman Medical Publishing Co., Ltd., Tunbridge Wells, Kent, England, 2nd ed., 1979, pp. 415-460. 

Schroeder, M.O. Biotribology Articular Cartilage Friction, Wear, and Lubrication, M.S. thesis, Mechanical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA, July 1995. 

Williams, 111, RE, Powell, G.L., and LaBerge, M. Sliding friction analysis of phosphatidylcholine as a boundary lubricant for articular cartilage, Proc. I.Mech.E. 207,41-166,1993. 

The lubrication of articular cartilage remains a subject of continuing debate and no one lubrication mechanism can be clearly identified. Both... 

The general features of synovial joints are shown In Figure 1. The bearing material Is articular cartilage bonded to subchondral bone and the lubricant is synovial fluid. 

It is known from recent investigations (2, 3, 4) that the transient elastohydrodynamic film formation and supplemental lubrication mechanism such as micro-elastohydrodynamic lubrication, weeping, blphasic, boosted or boundary lubrication are capable of providing sufficient protection to the articular cartilages in natural joints. On the contrary, there is just a little information on the actual lubricating film formation in total replacement joints. 

Professor T Murakami (Kyushu University, Japan). Your application of mlcro-elastohydrodynamic lubrication theory to natural synovial joints provides strong support for fluid film lubrication In natural joints under walking condition. (1) Could you show some data on the effective film parameter which Is defined as the ratio of minimum film thickness to effective roughness after deformation (2) Have you Investigated the Influence of highly concentrated gel formed on articular cartilages in the concave area on the effective film parameter under thin film conditions ... 

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