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Anthony Unsworth - One of the best experts on this subject based on the ideXlab platform.
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Does surface wettability influence the friction and wear of large-diameter CoCrMo alloy hip resurfacings?
Proceedings of the Institution of Mechanical Engineers. Part H Journal of engineering in medicine, 2013Co-Authors: Sarah Curran, S C Scholes, Tom Hoskin, Sarah Williams, Amy Kinbrum, Anthony UnsworthAbstract:The role of surface tension in the Lubrication of metal-on-metal (CoCrMo alloy) hip resurfacings has been investigated to try to explain why all metal joints fail to be lubricated with simple water-based lubricants (sodium carboxymethyl cellulose), which have similar rheology to synovial Fluid, but are lubricated with the same Fluid with the addition of a proportion of bovine serum. As part of this study, surfactants, in the form of detergents, when added to carboxymethyl cellulose, have been shown to produce a predominantly Fluid-Film Lubrication mechanism with friction even lower than the biological lubricant containing serum. Friction factors were reduced by 80% when a detergent was added to the lubricant. It is considered that the failure of the water-based Fluids to generate Fluid-Film Lubrication is due to the fact that ‘boundary slip’ takes place where the Fluid does not fully attach to the bounding solid surfaces as assumed in Reynolds’ equation, thereby drawing in less lubricant than predicted fr...
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In Pursuit of Fluid Film Lubrication
2012Co-Authors: Anthony UnsworthAbstract:Investigation of how natural joints functioned seemed closely dependent on the Lubrication mechanisms involved. This was equally relevant to artificial joints where, if Fluid-Film Lubrication could be generated, the rubbing surfaces would be completely separated by the liquid Film which would have the advantage of reducing friction, since this depends only on the shearing of the lubricant Film, and reducing wear since the two surfaces would not be touching. In 1969 when I first entered this research area, hip joints were mainly small diameter ( Ceramic-on-ceramic was different. This could be polished very smoothly and was hydrophilic so it could draw the water based lubricants (synovial Fluid), into the contact region, which in turn generated Fluid-Films. This meant that with alumina-on alumina, wear was not a problem-but fracture was in some circumstances. As more was learned about Lubrication, large diameter CoCrMo hip resurfacing devices became possible. Whilst small diameter metal-on-metal hip joints were unable to generate Fluid-Film Lubrication, larger diameter hips could, provided the lubricant contained serum (similar to synovial Fluid). This was interesting since water based lubricants of similar rheology to synovial Fluid (carboxy methyl cellulose, CMC) could not produce Fluid-Films (Figure 1) even though theory suggested that they should. Thus it was assumed that the proteins present in the natural lubricant were important, but the reason was unknown. Returning to the original assumptions of Osborne Reynolds in deriving the theory of hydrodynamic Lubrication, we see that in order to draw Fluid into the contact area, the Fluid adjacent to the solid boundary was assumed to be travelling at the same speed as the boundary itself. To do this the lubricant must ‘wet’ the surface or attach to it- but what if the surfaces are hydrophobic? The speed of drawing the Fluid into the contact will be lower than the surface speed and so less Fluid will be drawn in and the pressure generated will be lower than predicted by theory. So a simple experiment was tried using a large diameter CoCrMo alloy hip resurfacing device where a water-based lubricant (CMC) first had bovine serum added, then a simple detergent to reduce the surface tension. Figure 1 shows clearly that the Lubrication improves markedly with the detergent – even more so than the bovine serum. This suggests that the wettability of the surfaces is important. Another approach to enhancing Fluid-Film Lubrication stems from the concept of elasto-hydrodynamic theory. Here, lower modulus, more compliant surfaces, produce thicker Fluid-Films for similar entraining velocities and applied loads. Thus we developed compliant hip and knee joints using hydrophilic poly carbonate urethane (PCU) acetabulae against metals or ceramics. These produced phenomenally low coefficients of friction (circa 0.001) and in the knee, wear rates of only 0.06 mm 3 /million cycles (two orders of magnitude lower than metal on UHMWPE). Another interesting biomaterial is carbon-fibre reinforced poly-ether-ether-ketone (CFR-PEEK). Very long term hip simulator wear experiments (25 million cycles), showed wear rates which were lower than cross-linked polyethylene (circa 1.5 mm 3 /million cycles), yet friction was very high (µ=0.2–0.3). Clearly this was not Fluid-Film Lubrication but improvements are being investigated.
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Polyurethane unicondylar knee prostheses: Simulator wear tests and Lubrication studies
Physics in Medicine and Biology, 2007Co-Authors: S C Scholes, Anthony Unsworth, E. JonesAbstract:Many materials are used as artificial joint bearing surfaces; these include conventional stainless steel or CoCrMo-on-ultra-high molecular weight polyethylene (UHMWPE), CoCrMo on itself and alumina-on-alumina. However, these joints have a limited lifespan resulting in failure of the prosthesis and the need for revision surgery. A number of materials have been introduced recently in an attempt to overcome these problems. Polycarbonate urethane (PU) is a compliant material that can be used as an artificial joint bearing surface which has been developed to mimic the natural synovial joint more accurately by promoting Fluid Film Lubrication. Tribological tests were performed on CoCrMo-on-PU unicondylar knee prostheses to assess their performance in vitro. The wear produced by these components was considerably lower than that found for conventional joints. They also exhibited low friction and operated close to full-Fluid Film Lubrication with viscosities of lubricant similar to those found in patients with arthritis. These tests gave encouraging results for the tribological performance of this material couple for use as an alternative bearing combination.
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Design aspects of compliant, soft layer bearings for an experimental hip prosthesis
Proceedings of the Institution of Mechanical Engineers. Part H Journal of engineering in medicine, 2005Co-Authors: S C Scholes, Anthony Unsworth, E. Jones, I C Burgess, N SmithAbstract:Currently, an artificial hip joint can be expected to last, on average, in excess of 15 years with failure due, in the majority of cases, to late aseptic loosening of the acetabular component. A realistic alternative to the problem of wear in conventional joints is the introduction of bearing surfaces that exhibit low wear and operate in the full Fluid-Film Lubrication regime. Contact analyses and friction tests were performed on compliant layer joints (metal-on-polyurethane) and the design of a prototype ovine arthroplasty model was investigated. When optimized, these components have been shown to achieve full Fluid-Film Lubrication.
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A frictional study of total hip joint replacements.
Physics in Medicine and Biology, 2000Co-Authors: S C Scholes, Anthony Unsworth, A A J GoldsmithAbstract:Polymeric wear debris produced by articulation of the femoral head against the ultra-high-molecular-weight polyethylene socket of a total hip replacement has been implicated as the main cause of osteolysis and subsequent failure of these implants. Potential solutions to this problem are to employ hard bearing surface combinations such as metal-on-metal or ceramic-on-ceramic prostheses. The aim of this study was to investigate the difference in Lubrication modes and friction of a range of material combinations using synthetic and biological Fluids as the lubricants. The experimental results were compared with theoretical predictions of Film thicknesses and Lubrication modes. A strong correlation was observed between experiment and theory when employing carboxy methyl cellulose (CMC) Fluids as the lubricant. Under these conditions the ceramic-on-ceramic joints showed full Fluid Film Lubrication while the metal-on-metal, metal-on-plastic, diamond-like carbon-coated stainless steel (DLC)-on-plastic and ceramic-on-plastic prostheses operated under a mixed Lubrication regime. With bovine serum as the lubricant in the all ceramic joints, however, the full Fluid Film Lubrication was inhibited due to adsorbed proteins. In the metal-on-metal joints this adsorbed protein layer acted to reduce the friction while in the ceramic coupling the friction was increased. The use of bovine serum as the lubricant also significantly increased the friction in both the metal-on-plastic and ceramic-on-plastic joints. The friction produced by the DLC-on-plastic joints depended on the quality of the coating. Those joints with a less consistent coating and therefore a higher surface roughness gave significantly higher friction than the smoother, more consistently coated heads.
S C Scholes - One of the best experts on this subject based on the ideXlab platform.
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Does surface wettability influence the friction and wear of large-diameter CoCrMo alloy hip resurfacings?
Proceedings of the Institution of Mechanical Engineers. Part H Journal of engineering in medicine, 2013Co-Authors: Sarah Curran, S C Scholes, Tom Hoskin, Sarah Williams, Amy Kinbrum, Anthony UnsworthAbstract:The role of surface tension in the Lubrication of metal-on-metal (CoCrMo alloy) hip resurfacings has been investigated to try to explain why all metal joints fail to be lubricated with simple water-based lubricants (sodium carboxymethyl cellulose), which have similar rheology to synovial Fluid, but are lubricated with the same Fluid with the addition of a proportion of bovine serum. As part of this study, surfactants, in the form of detergents, when added to carboxymethyl cellulose, have been shown to produce a predominantly Fluid-Film Lubrication mechanism with friction even lower than the biological lubricant containing serum. Friction factors were reduced by 80% when a detergent was added to the lubricant. It is considered that the failure of the water-based Fluids to generate Fluid-Film Lubrication is due to the fact that ‘boundary slip’ takes place where the Fluid does not fully attach to the bounding solid surfaces as assumed in Reynolds’ equation, thereby drawing in less lubricant than predicted fr...
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Polyurethane unicondylar knee prostheses: Simulator wear tests and Lubrication studies
Physics in Medicine and Biology, 2007Co-Authors: S C Scholes, Anthony Unsworth, E. JonesAbstract:Many materials are used as artificial joint bearing surfaces; these include conventional stainless steel or CoCrMo-on-ultra-high molecular weight polyethylene (UHMWPE), CoCrMo on itself and alumina-on-alumina. However, these joints have a limited lifespan resulting in failure of the prosthesis and the need for revision surgery. A number of materials have been introduced recently in an attempt to overcome these problems. Polycarbonate urethane (PU) is a compliant material that can be used as an artificial joint bearing surface which has been developed to mimic the natural synovial joint more accurately by promoting Fluid Film Lubrication. Tribological tests were performed on CoCrMo-on-PU unicondylar knee prostheses to assess their performance in vitro. The wear produced by these components was considerably lower than that found for conventional joints. They also exhibited low friction and operated close to full-Fluid Film Lubrication with viscosities of lubricant similar to those found in patients with arthritis. These tests gave encouraging results for the tribological performance of this material couple for use as an alternative bearing combination.
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Design aspects of compliant, soft layer bearings for an experimental hip prosthesis
Proceedings of the Institution of Mechanical Engineers. Part H Journal of engineering in medicine, 2005Co-Authors: S C Scholes, Anthony Unsworth, E. Jones, I C Burgess, N SmithAbstract:Currently, an artificial hip joint can be expected to last, on average, in excess of 15 years with failure due, in the majority of cases, to late aseptic loosening of the acetabular component. A realistic alternative to the problem of wear in conventional joints is the introduction of bearing surfaces that exhibit low wear and operate in the full Fluid-Film Lubrication regime. Contact analyses and friction tests were performed on compliant layer joints (metal-on-polyurethane) and the design of a prototype ovine arthroplasty model was investigated. When optimized, these components have been shown to achieve full Fluid-Film Lubrication.
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A frictional study of total hip joint replacements.
Physics in Medicine and Biology, 2000Co-Authors: S C Scholes, Anthony Unsworth, A A J GoldsmithAbstract:Polymeric wear debris produced by articulation of the femoral head against the ultra-high-molecular-weight polyethylene socket of a total hip replacement has been implicated as the main cause of osteolysis and subsequent failure of these implants. Potential solutions to this problem are to employ hard bearing surface combinations such as metal-on-metal or ceramic-on-ceramic prostheses. The aim of this study was to investigate the difference in Lubrication modes and friction of a range of material combinations using synthetic and biological Fluids as the lubricants. The experimental results were compared with theoretical predictions of Film thicknesses and Lubrication modes. A strong correlation was observed between experiment and theory when employing carboxy methyl cellulose (CMC) Fluids as the lubricant. Under these conditions the ceramic-on-ceramic joints showed full Fluid Film Lubrication while the metal-on-metal, metal-on-plastic, diamond-like carbon-coated stainless steel (DLC)-on-plastic and ceramic-on-plastic prostheses operated under a mixed Lubrication regime. With bovine serum as the lubricant in the all ceramic joints, however, the full Fluid Film Lubrication was inhibited due to adsorbed proteins. In the metal-on-metal joints this adsorbed protein layer acted to reduce the friction while in the ceramic coupling the friction was increased. The use of bovine serum as the lubricant also significantly increased the friction in both the metal-on-plastic and ceramic-on-plastic joints. The friction produced by the DLC-on-plastic joints depended on the quality of the coating. Those joints with a less consistent coating and therefore a higher surface roughness gave significantly higher friction than the smoother, more consistently coated heads.
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The Effects of Material Combination and Lubricant on the Friction of Total Hip Prostheses
Wear, 2000Co-Authors: S C Scholes, Anthony Unsworth, R.m. Hall, R. ScottAbstract:Polymeric wear debris produced by articulation of the femoral head against the ultra-high-molecular-weight polyethylene (UHMWPE) socket of a total hip replacement has been implicated as the main cause of osteolysis and subsequent failure of these implants. Potential solutions to this problem are to employ hard-bearing surface combinations such as metal-on-metal or ceramic-on-ceramic prostheses. The aim of this study was to investigate the difference in Lubrication modes and friction of a range of material combinations using synthetic and biological Fluids as the lubricants. The experimental results were compared with theoretical predictions of Film thicknesses and Lubrication modes. A strong correlation was observed between experiment and theory when employing carboxy methyl cellulose Fluids as the lubricant. Under these conditions, the ceramic-on-ceramic joints showed full Fluid Film Lubrication while the metal-on-metal and metal-on-plastic prostheses operated under a mixed Lubrication regime. With bovine serum as the lubricant in the all ceramic joint however, the full Fluid Film Lubrication was inhibited due to adsorbed proteins. In the metal-on-metal joints, this adsorbed protein layer acted to reduce the friction while in the ceramic coupling the friction was increased. The use of bovine serum as the lubricant also significantly increased the friction in the metal-on-plastic joint. Therefore, the simple calculations using non-biological lubricants should not be relied upon in the design of orthopaedic bearing surfaces.
E. Jones - One of the best experts on this subject based on the ideXlab platform.
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Compliant layer knee bearings: Part I: Friction and Lubrication
Wear, 2010Co-Authors: M. Flannery, E. Jones, S. Flanagan, Colin BirkinshawAbstract:Abstract Compliant layer technology, in which a soft polymer mimics the performance of natural cartilage, potentially represents a resolution to the wear and associated longevity coupled with conventional metal-on-plastic joints. In this two-part study, the friction and wear of compliant layer polyurethane (PU) tibial inserts articulating against metal femoral components were investigated as part of a preliminary in vitro screening. In Part I the friction and Lubrication regimes were evaluated both experimentally using Stribeck analysis and theoretically using the theory of Hamrock and Dowson to investigate the joints ability to operate within a Fluid Film Lubrication regime. Using aqueous carboxymethyl cellulose (CMC) Fluids as the lubricant the joints were shown to operate with low friction and specifically, in some individual joints, with friction factors equivalent to ceramic-on-ceramic bearings as observed in hip bearings. Protein containing lubricants caused an increase in friction relative to the CMC solutions and it is proposed that this results from the shearing of interfacial protein layers adsorbed onto the articulating surfaces. Overall, the friction and Lubrication results demonstrated the ability of compliant layer joints to operate with Fluid Film Lubrication and consequential lower frictional torque during the walking cycle. In Part II of this study the wear performance of this articulation system will be investigated.
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Polyurethane unicondylar knee prostheses: Simulator wear tests and Lubrication studies
Physics in Medicine and Biology, 2007Co-Authors: S C Scholes, Anthony Unsworth, E. JonesAbstract:Many materials are used as artificial joint bearing surfaces; these include conventional stainless steel or CoCrMo-on-ultra-high molecular weight polyethylene (UHMWPE), CoCrMo on itself and alumina-on-alumina. However, these joints have a limited lifespan resulting in failure of the prosthesis and the need for revision surgery. A number of materials have been introduced recently in an attempt to overcome these problems. Polycarbonate urethane (PU) is a compliant material that can be used as an artificial joint bearing surface which has been developed to mimic the natural synovial joint more accurately by promoting Fluid Film Lubrication. Tribological tests were performed on CoCrMo-on-PU unicondylar knee prostheses to assess their performance in vitro. The wear produced by these components was considerably lower than that found for conventional joints. They also exhibited low friction and operated close to full-Fluid Film Lubrication with viscosities of lubricant similar to those found in patients with arthritis. These tests gave encouraging results for the tribological performance of this material couple for use as an alternative bearing combination.
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Design aspects of compliant, soft layer bearings for an experimental hip prosthesis
Proceedings of the Institution of Mechanical Engineers. Part H Journal of engineering in medicine, 2005Co-Authors: S C Scholes, Anthony Unsworth, E. Jones, I C Burgess, N SmithAbstract:Currently, an artificial hip joint can be expected to last, on average, in excess of 15 years with failure due, in the majority of cases, to late aseptic loosening of the acetabular component. A realistic alternative to the problem of wear in conventional joints is the introduction of bearing surfaces that exhibit low wear and operate in the full Fluid-Film Lubrication regime. Contact analyses and friction tests were performed on compliant layer joints (metal-on-polyurethane) and the design of a prototype ovine arthroplasty model was investigated. When optimized, these components have been shown to achieve full Fluid-Film Lubrication.
C M Taylor - One of the best experts on this subject based on the ideXlab platform.
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Fluid Film Lubrication in Automobile Valve Trains
Proceedings of the Institution of Mechanical Engineers Part J: Journal of Engineering Tribology, 1994Co-Authors: C M TaylorAbstract:It is nearly twenty years since the so-called energy crisis of the 1970s. This stimulated an increased awareness of the scarcity of natural resources and the necessity for their efficient and effective use. During the intervening period there has also been a mounting pressure from the ‘green’ lobby to recognize the fragility of the environment. The automobile is a significant factor world-wide with regard to both these aspects because of fuel consumption and exhaust considerations. These developments have led to intensive studies of the lubricated machine elements which are vital to the functioning of the internal combustion engine—the piston assembly, the bearings and the valve train. This paper will focus upon the valve train and in particular the Fluid Film Lubrication of its most significant part, the cam and follower. The important role of lubricant additives, the formation of reaction Films, boundary Lubrication, contaminants and wear and failure mechanisms will not be addressed. In part the paper w...
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Fluid Film Lubrication in the internal combustion engine
Journal of Physics D: Applied Physics, 1992Co-Authors: C M TaylorAbstract:The interdisciplinary nature of the subject of tribology has been frequently emphasized during the last quarter of a century. An interested observer might reasonably question, however, the strength of the link between Fluid-Film Lubrication at the one end of the tribological spectrum and dry wear/surface phenomena at the other. The foundations of fundamental understanding of the former area were laid over one hundred years ago whilst one suspects that with regard to the latter fields current knowledge represents but the tip of the iceberg. In recent years there has been wide review of Fluid-Film Lubrication and of those who gave the topic substance. A repetition would serve no particular purpose. Rather it is proposed to consider the subject in the context of the thin lubricating Films to be found in the internal combustion engine which powers our motor vehicles. This engine can be described as a device to generate lubricant Films of the order of a micrometre in thickness. A consideration of the current understanding of the tribological machine elements involved from the perspective of Fluid-Film Lubrication is revealing, both with regard to the development of this subject area and its growing links to other tribological disciplines reflecting surface-contact phenomena.
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Fluid-Film Lubrication in the internal combustion engine : an invited review
Journal of Physics D, 1992Co-Authors: C M TaylorAbstract:The interdisciplinary nature of the subject of tribology has been frequently emphasized during the last quarter of a century. An interested observer might reasonably question, however, the strength of the link between Fluid-Film Lubrication at the one end of the tribological spectrum and dry wear/surface phenomena at the other. The foundations of fundamental understanding of the former area were laid over one hundred years ago whilst one suspects that with regard to the latter fields current knowledge represents but the tip of the iceberg
Duncan Dowson - One of the best experts on this subject based on the ideXlab platform.
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Fluid Film Lubrication in artificial hip joints
Tribology Series, 2003Co-Authors: Z.m. Jin, J.b. Medley, Duncan DowsonAbstract:The importance of Fluid-Film Lubrication mechanisms experienced in hip implants is reviewed. For the different types of hip implants currently used in clinical practice, including conventional/cross-linked polyethylene-on-metal/ceramic, metal-on-metal and ceramic-on-ceramic bearing couples, a detailed review is presented of theoretical Fluid-Film Lubrication analyses along with friction measurements and wear studies, both having a strong emphasis on the Fluid-Film mechanisms involved. Future studies and improvements of hip implants from a Fluid-Film Lubrication point of view are discussed.
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The relationship between steady-state wear rate and theoretical Film thickness in metalon-metal total replacement hip joints
Tribology Series, 2003Co-Authors: Duncan DowsonAbstract:Metal-on-Metal total replacement hip joints are thought to operate primarily in the boundary, or mixed Lubrication regimes, but recent studies [1] have suggested that Fluid-Film Lubrication alleviates the severity of contact and hence wear under some conditions. It is shown that the iso-viscous/elastic mode of Fluid-Film Lubrication applies in such implants. Measurements of steady-state wear rates for different prostheses, in different simulators and under different operating conditions reported from independent tests in laboratories in the U.K., Canada and the U.S.A. are analysed and related to the theoretical elasto-hydrodynamic Film thickness. The results exhibit reasonable consistency, even though the test conditions were quite different. A transition from boundary Lubrication through mixed Lubrication, representing a change in wear rate of some two orders of magnitude, is evident in the wear results as the Film thickness increases. At Film thicknesses beyond about (15 nm–20 nm) the wear rate varies little as the Film thickness increases over a large range. It is shown that very low wear rates of (0.05 mm 3 to 0.10 mm 3 )/10 6 cycles are achievable beyond this Film thickness range through careful tribological design. It would take 9–18 years to generate one pin-head of metallic wear under these conditions.
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Analysis of Fluid Film Lubrication in artificial hip joint replacements with surfaces of high elastic modulus
Proceedings of the Institution of Mechanical Engineers. Part H Journal of engineering in medicine, 1997Co-Authors: Z.m. Jin, Duncan Dowson, John FisherAbstract:AbstractLubrication mechanisms and contact mechanics have been analysed for total hip joint replacements made from hard bearing surfaces such as metal-on-metal and ceramic-on-ceramic. A similar analysis for ultra-high molecular weight polyethylene (UHMWPE) against a hard bearing surface has also been carried out and used as a reference. The most important factor influencing the predicted lubricating Film thickness has been found to be the radial clearance between the ball and the socket. Full Fluid Film Lubrication may be achieved in these hard/hard bearings provided that the surface finish of the bearing surface and the radial clearance are chosen correctly and maintained. Furthermore, there is a close relation between the predicted contact half width and the predicted lubricating Film thickness. Therefore, it is important to analyse the contact mechanics in artificial hip joint replacements. Practical considerations of manufacturing these bearing surfaces have also been discussed.
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Elastohydrodynamic and micro-elastohydrodynamic Lubrication
Wear, 1995Co-Authors: Duncan DowsonAbstract:Abstract Elastohydrodynamic Lubrication is the dominant mode of Lubrication in many critical, highly stressed machine elements such as gears, rolling bearings, cams and followers. It also governs the effective operation of many highly deformable or ‘soft’ bearing systems such as elastomeric bearings, seals and synovial joints. The major developments in the understanding of this exciting mode of Fluid Film Lubrication during the latter half of the twentieth century is reviewed and attention is drawn to continuing topics of investigation.
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Fluid Film Lubrication in natural hip joints
Tribology Series, 1993Co-Authors: Z.m. Jin, Duncan Dowson, John FisherAbstract:The Film thickness in the normal human hip joint has been predicted under steady-state entraining motion, pure dynamic squeeze-Film motion and the transient condition involving both the entraining and squeeze-Film motions. The simplified method adopted to predict the Film thickness has been compared with the full numerical method under both steady-state entraining and transient conditions for the normal human ankle joint and good agreement has been found. The transient Film thickness predicted for the hip joint is almost constant throughout one walking cycle due to the combined effect of entraining during the swing phase, generating a sufficiently large lubricant Film and squeeze-Film action preserving this lubricant Film during the stance phase. However, the lubricant Film thickness predicted is only of the order of 1.5 (μm) and thus it seems clear that micro-elastohydrodynamic action also plays as important a part in the Lubrication of hip joints as it was found in a previous study to have in the ankle joint.