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Encyclopedia of tribology


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  • 1. 1 SpringerReference C.B.E., F.R.S., F.R.Eng., F.R.S.E. Prof. Duncan Dowson Introduction to Biotribology 11 Jul 2012 17:24 © Springer-Verlag Berlin Heidelberg 2012 Introduction to Biotribology Biotribology has been one of the most active topics in the broad field of during the past 40 years. The range oftribology subjects covered in the contributions on biotribology in the Encyclopedia on Tribology clearly demonstrate this point. The term was introduced in 1966 (Department of Education and Science ), while aspects of the subjecttribology 1966 dedicated to biological situations were defined as shortly afterwards (Dowson ).biotribology 1970 Although the variety of topics now embraced within the topic of biotribology has grown enormously over the past 40 years, it is intriguing to recognize basic similarities between the mechanisms of lubrication, friction, and wear adopted by different tissues engaged in different functions. Most interfaces in biological systems operate in a mixed lubrication regime, as do many engineering systems, with the ability to accommodate boundary, fluid film, or a mixed lubrication regime to meet functional needs. Many of the basic mechanisms of boundary and fluid film lubrication are operative at different sites. The importance of in vitro experiments to reveal basic biotribological performance characteristics is widely recognized. At the same time, it is now recognized that good simulation of the in vivo situation is essential if laboratory observations are to be representative of in vivo performance. Good simulation is essential in design studies and the preclinical evaluation and screening of implanted products. In the history of biotribology, is a relatively new but widely adopted procedure in many studies.mathematical modeling The use of modern surface analysis equipment together with experimental and modeling approaches to problems in this field is particularly powerful. This is indeed an exciting subject, embracing many disciplines. There is still much to engage the skills of future biotribologists! Attachment and Release This contribution on adhesion in the animal world (Zhendong Dai; “Adhesion in Animal World”) gives an account of the various ways in which small animals to solid surfaces. Basic systems, developed to provide adequate attachmentadhere forces under both dry and wet conditions, include claws, adhesive pads, , and capillary forces.van der Waals forces Natural Synovial Joints The clear similarity between natural and certain plain bearings in engineering naturally resulted in jointsynovial joints tribology attracting much attention in early biotribological studies. The natural joint is widely recognized as a remarkable, dynamically loaded bearing, notably for its longevity, low wear, and low friction. These impressive performance characteristics are attributable to design, the unique properties of the bearing material, and the adoption of a welllubricant suited to a wide range of boundary, fluid film, and mixed lubrication conditions. The two essential components of natural synovial joints are the bearing material (articular cartilage) and the lubricant . The structure and(synovial fluid) constituents of cartilage are presented from an anatomical perspective by (Muehleman and Thorp; “Tribological Design of Animal Joints – An Anatomical Perspective”), while (Fisher; “Articular Cartilage as a Bearing Material, an Engineering Perspective”) addresses the topic from an engineering point of view. Many investigations of the impressive lubrication characteristics of synovial joints were reported in the last and present centuries. Initially, the main objective was to ascertain whether boundary of fluid-film lubrication prevailed in these highly taxed natural bearings. The basic features of hydrodynamic and in engineering situations wereboundary lubrication established about a century ago, and initial approaches to an understanding of synovial joint attempted totribology classify natural joints under one or another of these headings. Views became polarized as a single, dominant mode of lubrication was sought, but in due course it became evident that, as in the majority of engineering bearings, several different mechanisms were called upon. Many studies demonstrated transition from boundary to fluid film lubrication, through a mixed lubrication regime, and back again, within one complete cycle of bearing operation. Well-established concepts of boundary and fluid film lubrication (entraining and squeeze-film) were examined in relation to joint articulations. A number of alternative mechanisms emerged in an exciting period in the mid-1960s. These included “boosted lubrication,” in which the concentration of hyaluronic acid in surface pools on approaching cartilage surfaces generated more viscous and effective lubrication (Maroudas ; Walker et al. ) and the fascinating concept of1967 1968
  • 2. 2 SpringerReference C.B.E., F.R.S., F.R.Eng., F.R.S.E. Prof. Duncan Dowson Introduction to Biotribology 11 Jul 2012 17:24 © Springer-Verlag Berlin Heidelberg 2012 “weeping lubrication,” where applied loads were deemed to pressurize the cartilage and result in of interstitialexudation fluid from the cartilage structure (McCutchen ). In due course, indications of the principal boundary lubrication1967 constituents of synovial fluid (lubricin) emerged (Radin et al. ; Swann ).1970 1978 It was demonstrated (Dowson ) that hydrodynamic lubrication alone could not account for the surface separation of1967 opposing cartilage surfaces and the very low friction recorded for synovial joints. A more optimistic view emerged when elastohydrodynamic (EHL) action was considered. The remarkable potential of micro-elastohydrodynamic action, in which surface roughnesses generate small pressure perturbations capable of significantly squashing elastically the very asperities that generate them. The phenomenon found application in some rubber and polymeric seals and bearings in engineering and then cartilage in (Dowson and Jin ).synovial joints 1986 Synovial joints appear to draw upon several different lubrication mechanisms, depending upon the demands of joint function. Murakami et al. ( , ) described this all-embracing lubrication system as “adaptive multi-mode1990 1998 lubrication.” The basic features of three mechanisms – biphasic, elastohydrodynamic, and brush – are outlined by (Ateshian; “Biphasic Lubrication”); (Jin; “Elastohydrodynamic Lubrication of Natural Synovial Joints”) and (Klein; “Brush and Hydration Lubrication”). It is interesting to note that all have been studied for long periods of time; biphasic for at least 30 years (Mow et al. ), elastohydrodynamic in excess of half a century (Dowson ), and brush, a form of1980 1967 boundary lubrication, since the 1920s (Hardy and Doubleday ). It also appears that all may contribute to the1922 lubrication of other tissues in the body. Surface analysis equipment has played a major role in the development of understanding of essential tribological mechanisms in biology, and this has been matched by impressive developments of computers and computational simulation. (Jin; “Computational Simulation in Biotribology”) addresses the latter topic, in relation to biotribology. Low Elastic Modulus (“Soft”) Tissue Tribology Considerable attention is now given to the tribological characteristics of low biological tissues. Exampleselastic modulus include the , tendons and ligaments, , fat pads, blood flow in narrow capillaries, skin, hair,synovial membrane menisci lungs: heart, intestines, eyes and eyelids, and articular cartilage. Studies of soft tissue lubrication have developed over many years, but there has been a considerable surge of activity in recent times. Lungs, hearts, and intestines change shape and size and against the body wall. about theirrub Speculation tribology commenced some 90 years ago. (Loring and Butler; “Pleural Lubrication and Friction in the Chest”) address recent work on pleural lubrication. The competing concepts of boundary and fluid film lubrication are assessed. The elastic properties of pleural tissue and the rheological characteristics of the pleural liquid are reviewed, and the operating conditions of varying velocity and load noted. While most theoretical and experimental studies generally support the view that the pleural fluid is present in a continuous layer, suggesting fluid-film lubrication, evidence of a friction force independent of velocity is consistent with . There is growing support for the view that elastohydrodynamic lubricationboundary lubrication and particularly micro-elastohydrodynamic lubrication are significant in pleural lubrication. Blood consists of a suspension of 40–45% red blood cells, or erythrocytes, in plasma. A quite remarkable feature of the flow of erythrocytes in capillaries is that their unstressed diameters are often larger than the of the passagesbores through which they pass. Furthermore, there is an endothelial layer lining the capillaries that has a thickness of about 1 μm. A review of the understanding of flow of erythrocytes in small blood vessels by (Secomb; “Tribological Phenomena in Blood Vessels”) confirms the quite remarkable micro-EHL action in capillaries having inside diameters up to about 8 μm. The characteristic EHL film shapes are clearly evident and analysis predicts flow-dependent values of apparent viscosity in small bore tubes in close accord with experimental findings. The load-bearing role of intact menisci in the knee has been recognized for almost 40 years. A very substantial proportion of the force transmitted through the knee can be carried by the menisci (Seedhom et al. ; Shrive ), often1974 1974 regarded as structures. The twin roles of load transmission and gliding over cartilage to distributevestigial lubricant provide another aspect of soft tissue biotribology. Cooke et al. ( ) reported evidence of fluid-film lubrication in1976 laboratory friction tests on synovial membrane. More recently, the friction experienced by fat pads has been studied (Theobald et al. ) with the authors suggesting that a fluid-film mode of lubrication might prevail under some2007 conditions. (Theobald; “Lubricating Properties of the Fat Pad”) outlines the background to the lubrication properties of these significant soft tissues. A most important aspect of biotribology at the level is presented by (Dunn and Sawyer; “Lubrication of Livingmicron Cells”) in their account of the lubrication of living cells. Measurement of the friction characteristics of epithelial cells, which
  • 3. 3 SpringerReference C.B.E., F.R.S., F.R.Eng., F.R.S.E. Prof. Duncan Dowson Introduction to Biotribology 11 Jul 2012 17:24 © Springer-Verlag Berlin Heidelberg 2012 interface with other tissues and fluids, calls for miniature, sensitive, and accurate friction testing equipment. Forces and pressures generally range from zero to 1,000 μN and 5,000 kPa, respectively, with recorded friction coefficients of about 0.03. Hard Tissue Tribology Many studies of have been recorded in the literature and four entries are included under this heading in thisoral tribology encyclopedia. Early investigations upon teeth and factors affecting the wear of teeth, particularlyfocused attention enamel, which is the hardest tissue in the body. In recent times the tribological characteristics of tongue and palate have attracted increased attention under the heading of soft tissue .tribology The wider subject of oral tribology embracing teeth, tongue, palate, saliva, and is reviewedthe temporomandibular joint by (Jing Zheng and Zhong-Rong Zhou; “Oral Tribology”). (Heintze; “The Tribology of Dental Materials”) has outlined the structure of teeth and the wear behavior of the natural material, enamel, and artificial restorative materials such as resins. Tooth cleaning processes have a very long history. The process is described and roles of both toothpaste and brush outlined by (Lewis and Ashcroft; “Tribology of Teeth Cleaning”). Current knowledge of the lubrication of teeth and the mouth by saliva is considered by (Stokes; “Saliva Lubrication”). Attention is drawn to the and viscoelastic properties of saliva and the ability of its proteinaceous content tonon-Newtonian form protective acquired . The general structures of mobile and adsorbed salivary films are described, with thepellicle latter forming a proteinaceous biofilm. Such films protect oral surfaces from wear and damage, such as abrasion by foreign bodies and other teeth. There are some 300 proteins in saliva and 130 in the acquired enamel pellicle (Dawes ).2008 A summary of important tribological characteristics of oral tribology are presented. The formation of a pellicle film produced about a 90% reduction in wear when brushing enamel (Joiner et al. ). Experiments have shown that the2008 coefficients of friction of oral tissue, including teeth, range from about 0.004 to 0.45, depending upon load, sliding speed, and substrates. It has been noted that the inner monolayer of proteins is about 4 nm thick, while the overall adsorbed layer reaches thicknesses of about (20–30 nm) (Cardenas et al. ). Clear evidence from with whole2007 laboratory tests mouth saliva shows both boundary and mixed lubrication characteristics with coefficients of friction in the range 0.02–0.2. For softer substrates, there was also evidence of a transition from mixed to fluid-film (isoviscous EHL) lubrication conditions, corresponding to a at the heel of the Stribeck curve of about 0.004.coefficient of friction Tribology in Everyday Activities Each day most of us experience, or observe others experiencing, the use of facial tissues; the wearing of contact lenses; unfortunate as we move around; or processing and eating various foodstuffs. The selections on these four topicsslipping in the encyclopedia illustrate encounters with tribology in everyday life. The primary use of facial tissues is to remove and contain nasal discharge. The main tribological characteristics are friction and wear of the skin to which tissues are applied (Zwick and Tate; “Facial Tissue”). Most facial tissues are made from mixtures of soft- and hardwood fibers. Their friction with skin can reach almost 0.7 when dry and againstrubbing hard counterfaces. Against the value is closer to 0.4. Treatments have been developed to control friction,facial tissue stick–slip, and the wear of skin. Contact lenses have become major vision aids, particularly in recent decades, since they first emerged in 1886. The early lenses were made of glass, followed by acrylic and then the softer hydrogel materials. The early contact lenses lacked adequate oxygen permeability, but current hydrogel constructs greatly reduce this problem and are more comfortable. Medley and Ngai (“Biotribology of Contact Lenses”) review experimental measurements of friction (see Ngai et al. ).2005 The early results indicated a mixed lubrication regime. Modeling approaches to both the pre- and post-lens interfaces have been recorded (Rennie et al. ). The estimated central film thicknesses were generally in excess of the2005 equivalent roughness of the lens and eyelid, suggesting that elastohydrodynamic action played an important role in the lubrication process. Lipid and protein deposition is observed on the lenses and this may affect the formation of elastohydrodynamic films and the comfort of contact lenses. Producing food involves many aspects of , as does its oral processing. (Suk Meng Goh; “Tribology of Foods”)tribology addresses these issues and outlines the equipment and procedures used to measure friction in both situations. There is considerable interest in the possible link between texture, friction, rheology, and human perception of foodstuffs, such as
  • 4. 4 SpringerReference C.B.E., F.R.S., F.R.Eng., F.R.S.E. Prof. Duncan Dowson Introduction to Biotribology 11 Jul 2012 17:24 © Springer-Verlag Berlin Heidelberg 2012 creaminess and astringency (Luengo et al. ; de Wijk and Prinz ; Engelen et al. ).1997 2005 2005 Friction, and its variation, between shoes and the floor influences the propensity of pedestrians to slip and fall. This further illustration of tribology in everyday activities is discussed by (Clarke, Lewis and Carré; Tribology in see “Footwear-Surface Interactions in Pedestrian Slips”). The variation of tangential and normal foot to ground reactions and their ratio throughout a walking cycle are key parameters in assessing the likelihood of slipping. These parameters are influenced by design, material selection, ground surfaces, and conditions as well as individual gait characteristics. The tribologyshoe of foot-to-ground interactions has played a major role in modern footwear development. Osteoarthritis While are remarkable bearings, joint degeneration and osteoarthritis (OA) is becoming a major problem assynovial joints life expectancy advances. The spine, hip, and knee are particularly vulnerable. A wide-ranging review of the structure and biomechanics of synovial joints and their constituent parts, which should be read in conjunction with the three entries by Ateshian, Fisher, and Zhang, is presented by (Chubinskaya and Wimmer; “Wear of Natural Joints – Osteoarthritis”). Emphasis is placed upon the point that OA is not simply wear of the articulating cartilage layers but a degenerative affecting the whole joint.disease Simulation While simple tribometers can be used to study the roles of and articular cartilage in determining thesynovial fluid tribological characteristics of natural and total replacement synovial joints in vivo, interpretation of the findings is often difficult. Fundamental studies are therefore often carried out in vitro on increasingly sophisticated joint simulators. Preclinical assessment is also undertaken on simulators. The scientific fundamentals underlying these developments are outlined by (Wimmer and Laurent; “Simulation of Physiological Conditions – An Overview”). It is increasingly clear that the full physiological conditions need to be replicated as fully as possible if meaningful indications of in vivo performance are to be achieved. Synthetic Synovial Fluid and Articular Cartilage Since OA is usually associated with increased stiffness, of the synovial fluid (Cooke et al. ), andreduced viscosity 1978 wear of the articular cartilage, the possibilities of replacing the and/or the bearing material readily suggestlubricant themselves as potential treatments. Synovial fluid is a remarkable, complex, and effective lubricant for synovial joints, and in the 1970s, attention was focused upon the therapeutic use of substitute fluids. This field of activity is still expanding and outlined by (Jian-Hua Zhang). Hyaluron has been injected into degenerate joints as an artificial lubricant, while glucosamine has been used to promote cartilage repairs (Jian-Hua Zhang; “Artificial Synovial Fluid”). Cartilage replacement is another possibility for the treatment of some joint disorders. Freeman ( ) edited a1973 comprehensive text on cartilage structure and properties. The development of synthetic cartilage for the repair of degenerate synovial joints, or in total joint replacement, has been outlined by (Murakami; “Tribology of Cartilage Replacement”). Materials such as ultra-high-molecular-weight polyethylene, , , and hydrogelspolyurethane silicone rubber have been investigated. Some hydrogels held 85–90% water to simulate the properties of articularpoly(vinyl alcohol) PVA cartilage (see Muehleman and Thorp; “ ”; and Ateshian;Tribological Design of Natural Joints – An Anatomical Perspective “Biphasic Lubrication”). Most of the synthetic cartilage materials exhibited low friction in simulators ( et al. ;Auger 1993 Scholes et al. ).2006 Hip Joint Replacements Discussion of total joint replacement dominates the entries in this encyclopedia. Total hip joint replacement has been described as the major development in in the past century. Several entries are devoted to propertiesorthopedic surgery of the dominant bearing material, , , modeling of fluid-film lubrication, a laboratory study ofUHMWPE contact mechanics , wear modeling, and metal-on-metal implants.boundary lubrication Impressive and encouraging advances have been reported in replacement hip joint design, manufacture, and surgery
  • 5. 5 SpringerReference C.B.E., F.R.S., F.R.Eng., F.R.S.E. Prof. Duncan Dowson Introduction to Biotribology 11 Jul 2012 17:24 © Springer-Verlag Berlin Heidelberg 2012 during the past half century. The names of McKee ( ) (metal-on-metal) and (Charnley ) (metal-on-polymer) were1967 1979 intimately linked to progress early in the second half of the 20th century. Initial use of the polymer for acetabularPTFE cups provided low friction, but very high wear rates restricted the implant life to about 3 years. UHMWPE provided much lower wear and extended survival times, but at the expense of higher friction. In due course an acceptable percentage of UHMWPE hip implants survived for about 10–15 years. At that stage many patients experienced wear debris–initiated . This restricted survival times, but lifetimes of about 25–30 years are sometimes reported. Improved clinicalosteolysis performance has indeed brought much relief to a large number of patients. Two entries address the performance of UHMWPE in hip joint replacements. (Wang and Dumbleton; “Ultra-High-Molecular-Weight Polyethylene (UHMWPE) as a Bearing Material in Hip Joint Replacements”) outline the developments that have contributed to the domination of UHMWPE as a hip replacement material for half a century. While other material pairs have found favor in recent years, the possibility of reducing polymer oxidation and thus extending the life of UHMWPE implants is also attracting attention, as outlined by (Shirong Ge and Qingliang Wang; “Modified UHMWPE for the Hip Joint – Particle Filled and Reinforced”). An outline of the potential of current contact mechanics analysis for hip joints constructed from various material combinations is presented by (Ling Wang; “Contact Mechanics Studies between the Articulating Surfaces of Artificial Hip Joints”). Examples of the maximum contact pressures for smooth surfaces are given for metal-on-UHMWPE, metal-on-metal, and metal-on-ceramic hip replacements. Approaches to the modeling of elastohydrodynamic conditions in hip replacements have enhanced understanding of the extent to which fluid-film lubrication contributes to surface separation, viscous friction, and the wear process. Although it is now widely recognized that some modern hip replacements operate in all three of the major lubrication regimes, the powerful effect of elastohydrodynamic action has to be incorporated into a full analysis of implant performance (Qingen Meng; “Lubrication Modeling of Artificial Joints”). The enormity of the task and some limitations of current capabilities are outlined. Boundary lubrication is often encountered in hip replacements, and this topic is reviewed by (Cann; “Boundary Lubrication Mechanisms in Artificial Joints”). Several surface-active molecules are present in and phospholipids andsynovial fluid proteins are thought to play a major role in surface protection and boundary lubrication in joint replacements. Hills used his knowledge of surfactants to investigate, over many years, the role of phospholipids in thesurface active boundary of biological tissues, including articular cartilage (Hills and Butler ; Hills ). In recent years attentionlubrication 1984 2000 has turned to the constituents of synovial fluid responsible for boundary lubrication in hip joint replacements (Wimmer et al. ).2003 When lubricating films, both fluid-film and boundary, are penetrated by roughness peaks on opposing surfaces, or when wear debris is present, mechanical wear can take place. Observations suggest that both adhesive and actionsabrasive occur, and most programs are concerned with quantification of the combined actions. The complex process ofsimulator wear modeling is addressed by (Feng Liu; “Wear Modeling of Artificial Hip Joints”). The assumptions made are stated and the predictions compared with the measured weight losses in both metal-on-polymer and metal-on-metal hip joint replacements. In an extensive review of the materials adopted in metal-on-metal hip joints (Fischer and Williams; “Self-Mating Metal Articulations in the Hip Joint”), careful consideration is given to the similarity between most in vivo and in vitro results. Total replacement hip joints present a deceptively simple appearance. Yet details of material selection, manufacturing, design, loading, motion, activity, properties, and the nature of interactions between , surface layerslubricant bulk materials of proportions, and wear debris in very thin, time-dependent films make the in vivo situation difficult tonanometer simulate. Such joints are tribologically remarkable, but potential problems associated with biological response to very fine wear debris and ion release call for careful consideration. Fretting wear is a well-known phenomenon in engineering systems. There are many interfaces in hip joint replacements where this may present problems, such as the stem-bone boundary, the neck at the head-stem junction, thetaper cup-backing and cup-bone junctions, and the active tribological cup-head interface. The fundamental background to ion release and tribo-corrosion is considered by (Yu Yan; “Fretting and Tribo-corrosive Testing”). A basic equation is presented to represent the contributions to total material degradation of the mechanical wear in the absence of corrosion, corrosion and the effects of wear on corrosion, and corrosion on wear.synergistic The importance of in vitro testing of joint replacements, to develop improved materials and designs and to offer preclinical evaluation, is emphasized by (Saverio; “Testing of Artificial Hip Joints”). The basic procedures involve mechanical testing of materials, , and in vitro simulator testing. The review considers general issues, but concentratesmathematical modeling
  • 6. 6 SpringerReference C.B.E., F.R.S., F.R.Eng., F.R.S.E. Prof. Duncan Dowson Introduction to Biotribology 11 Jul 2012 17:24 © Springer-Verlag Berlin Heidelberg 2012 on the hip joint. Artificial joints must receive the CE mark and approval before they can be marketed in Europe or theFDA USA, respectively. Details are provided of the various International Standards for metals, polyethylene, and(ISO) ceramics, together with outlines of procedures for and wear testing, and with particle characterization. Theendurance growing importance of is also emphasized.numerical modeling The contribution by (Lappalainen; “Hemiarthroplasty”) is also mentioned here since the procedure most frequently refers to the hip. It does, however, find application in some knee, shoulder, and finger procedures. Metals are the traditional materials of hemiarthroplasties, but normal motion and loading can lead to excessive cartilage wear. Attention is drawn to current interest in alternative materials such as pyrolitic carbon coatings and .polyurethane It is worth noting that during the past quarter of a century or so, engineering solutions to joint replacement problems have used material pairs of ever-increasing hardness, such as metal-on-metal, metal-on-ceramic, and ceramic-on-ceramic. All these material pairs are quite different from those adopted by nature. Low modulus implants, or cushion bearings, are being developed and evaluated as replacements for degenerate joints, while synthetic cartilage may be used for cartilage lesions, particularly in the knee. It remains to be seen whether the use of appropriate scaffolds and stem cells will provide more robust structures for the repair and replacement of degenerate cartilage. Knee Joint Replacements The number of knee joint replacements now exceeds that of hip joints in a number of countries. This reflects progress in understanding the complex motion and loading in the knee, together with innovative design and manufacture. Four entries relate directly to the knee, covering lubrication, wear, modeling, and testing. The femoral and tibial components are usually made of metal and polyethylene. An outline of elastohydrodynamic lubrication analysis for the knee is presented by (Chengtao Wang; “Lubrication in Knee Prosthesis”). Since the predicted minimum film thicknesses are considerably smaller than the composite surface roughness, it is concluded that fluid film lubrication cannot ensure surface separation throughout the cycle. Joint design must take account of this finding, with wear taking centre stage. Conceptual development of knee replacements, particularly in relation to wear, are described by (Wright-Walker and LaBerge; “Wear in Knee Prostheses – Differences Compared with the Hip”). The influence of materials and innovative design changes upon wear and prosthesis survival rates are outlined. Attempts to combat excessive polyethylene wear on the tibial component of this complex joint, in order to minimize the incidence of and hence extend the life ofosteolysis replacement knees, are reviewed. Most total knee revision operations occur after 10–20 years. Many of the design innovations have resulted from wear reduction concepts, such as mobile rather than fixed bearings and symmetric and asymmetric designs. A notable finding is that the average wear particle size of about 1 μm is roughly twice that encountered in the hip. Wear between tibial trays and polyethylene tibial represents a unique feature of some totalinserts replacement knee joints. Sometimes the is also replaced and this presents an additional wear interface in totalpatella replacement knees. Progress in modeling the wear in total replacement hip joints is described by (Willing; “Wear Modeling in Artificial Knee Joints”). This article, alongside that by Feng Liu for hips, illustrates the growing contribution of to totalnumerical modeling joint replacement technology. There is still much empiricism in wear modeling, related to the adoption of the simple relationship for volumetric wear based upon the experimental findings for the wear of metals under unlubricated conditions by (Archard and Hirst ). The situation in joint replacements is complicated by the well-known phenomena1956 of in polymers, in the surface layers, and the influence of . Modelingstrain hardening molecular orientation lubricants nevertheless has great appeal, both in relation to engineering science and the duration and cost of studies.simulator When taken together both procedures provide considerable insight into tribological performance of joint replacements. Brief mention is made by (Jun Jie Wu; Testing of Artificial Knee Joints) of the between simulator andconcordance numerical modeling results of the essential characteristics of knee joint performance in vitro. Simulators have developed gradually over the past 30 or 40 years, with demonstrable limitations, or inadequacies, at any stage being eliminated or reduced in subsequent designs. An outline of knee joint simulator specifications and the International Standards now available is provided. Ankle Joint Replacements
  • 7. 7 SpringerReference C.B.E., F.R.S., F.R.Eng., F.R.S.E. Prof. Duncan Dowson Introduction to Biotribology 11 Jul 2012 17:24 © Springer-Verlag Berlin Heidelberg 2012 The third major load-carrying joint in the lower limb is the ankle. This joint presents more of a nominal line contact geometry than the nominal evident in knees and hips. Early clinical experience of ankle replacement waspoint contacts much less encouraging than for the hip and knee, as explained by (Brockett, Fleming, Jennings, Jin and Fisher; “Tribology of Ankle Joints”). Ankle arthritis is nevertheless a disturbing and troublesome condition for many subjects and particularly for people engaged in strenuous sports and occupations. Current forms of metal-on-polymer ankle joint replacements now reflect developments in the knee, with both fixed and mobile structures being available. Implant at 10 years has been reported to be about 90%. The authors state that the wear performance of totalsurvivorship replacement ankle joints is now attracting increasing clinical interest. Upper Limb Joints The lubrication and wear of joints in the upper limb, shoulder, finger, and elbow, are reviewed by (Shepherd; “Tribology of Shoulder, Elbow and Finger Joints”). In all cases it is concluded that, if micro-elastohydrodynamic action is neglected, prevails between the near universal metal-on-polymer components of these joints. The major reasonboundary lubrication for this is the relatively high roughness of the polymeric surface, compared with the thickness of the lubricating film. A useful summary of the operating conditions in each joint is provided, together with published wear rates. There are relatively few simulators available for satisfactory testing of , other than the hip and the knee. Asynovial joints critical review of the reasons for this, even though many subjects suffer from degeneration in their smaller joints, is presented by (Joyce; “Testing of Other Joints”). Many of the joints considered, such as the shoulder, elbow, wrist, and finger, relate to the upper limb and should be read in association with the previous article (Shepherd). However, ankle joints, the main subject of the contribution from (Brockett et al.), are also mentioned. Much of Joyce’s review focuses upon the lack of realistic simulators for joints other than the hip and the knee. While this is understandable at this stage in the development of satisfactory replacements for the extensively afflicted main load bearing joints, it does reinforce the case for adequate testing. This will enhance understanding of the tribologicalsimulator performance of implants, and also enable comparisons to be made of the performance of different designs of prostheses as a procedure. None of this can be achieved unless the natural conditions under which the jointpreclinical testing functions are adequately simulated in the laboratory. Spinal Discs Prostheses for degenerate or damaged spines present a particular challenge to both the tribologist and the surgeon. Fusion of the spine may be recommended in some cases, but the use of implants to restore function is also considered. The material pairs for replacement discs have followed developments reported for other sites. Metal-on-polyethylene was followed by harder combinations such as metal-on-metal and ceramic-on-ceramic. Bio-mechanical and bio-tribological investigations of the loads, motions, lubrication, and wear of replacement discs have increased in recent times, as outlined by (Kaddick; “Testing of Artificial Discs”). In vivo loads and motions reported by several investigators are presented, together with typical contact areas, penetration, and wear rates. The development of test procedures in this developing field is noted. Failure//Retrieval Analysis Failure analysis is a well-established and valuable procedure in engineering. Many studies of worn or fractured components have resulted in product improvement and enhanced reliability. It is particularly useful in orthopedics, as outlined by (Cheng-Kung Cheng; “Retrieval Analysis”). Most of the contribution is related to knee joints, but the lessons are general and can be widely applied. The formal procedure is outlined and a number of interesting case studies are presented. As experience of implant performance increases, retrieval analysis is likely to become ever more important. Prosthetic Sockets The mechanics of interfaces between external prostheses and their sockets plays a major role in determining the comfort of amputees. It is estimated that there are more than three million amputees in the world and improving comfort and effectiveness is a major issue. Friction helps to support body weight and stability and is thus helpful, but if excessive it can
  • 8. 8 SpringerReference C.B.E., F.R.S., F.R.Eng., F.R.S.E. Prof. Duncan Dowson Introduction to Biotribology 11 Jul 2012 17:24 © Springer-Verlag Berlin Heidelberg 2012 also promote skin breakdown and pain. These issues are considered by (Winson Lee, Aaron Leung and Ming Zhang; “Contact Pressure at the Limb/Prosthesis Interface”). References J.F. Archard, W. Hirst, The wear of metals under unlubricated conditions. Proc. R. Soc. London, Ser. A ,236 397–410 (1956) D.D. Auger, D. Dowson, J. Fisher, Friction and lubrication in cushion form bearings for artificial hip joints. Proc. Inst. Mech. Eng (Part 3H), 25–33 (1993)207 M. Cardenas, U. Elofsson, L. Lindh, Salivary mucin MUC5B could be an important component of in vitro pellicles of human saliva: An in situ ellipsometry and atomic force microscopy study. Biomacromolecules , 1149–11568 (2007) J. Charnley, (Springer, Berlin/Heidelberg, 1979), p. 376Low friction arthroplasty of the hip; theory and practice A.F. Cooke, D. Dowson, V. Wright, Lubrication of synovial membrane. Ann. Rheum. Dis. , 56–59 (1976)35 A.F. Cooke, D. Dowson, V. Wright, The rheology of synovial fluid and some potential synthetic lubricants for degenerate synovial joints’. Eng. Med. (2), 66–72 (1978)7 C. Dawes, Salivary flow patterns and the health of hard and soft oral tissues. J. Am. Dent. Assoc. , 18S–24S139 (2008) R.A. de Wijk, J.F. Prinz, The role of friction in perceived oral texture. Food qual. prefer. , 121–129 (2005)16 Department of Education and Science, Lubrication (Tribology) Education and Research. A Report on the Present (Department of Education and Science, HMSO, London, 1966)Position and Industry’s Needs D. Dowson, Modes of lubrication in human joints, in lubrication and wear in living and artificial human joints. Proc. Inst. Mech. Eng. (Part 3J), 45–54 (1967)181 D. Dowson, Whither tribology. Proc. Inst. Mech. Eng. (3L), 181–185 (1969, 1970)184 D. Dowson, Z.M. Jin, Micro-elastohydrodynamic lubrication of synovial joints. Proc. Inst. Mech. Eng., Eng. Med. , 63–65 (1986)15 L. Engelen, R.A. de Wijk, A. van der Bilt, J.F. Prinz, A.M. Janssen, F. Bosman, Relating particles and texture perception. Physiol. Behav. , 111–117 (2005)86 M.A.R. Freeman (ed.), (Sir Isaac Pitman and Sons, London, 1973), pp. 1–341Adult Articular Cartilage W.B. Hardy, I. Doubleday, Boundary lubrication-the paraffin series. Proc. R. Soc., A , 550–574 (1922)100 B.A. Hills, Boundary lubrication in vivo. Proc. Inst. Mech. Eng., Part H, J. Eng. Med. (H1), 83–94 (2000)214 B.A. Hills, B.D. Butler, Surfactants identified in synovial fluid and their ability to act as boundary lubricants. Ann. Rheum. Dis. , 641–648 (1984)43 A. Joiner, A. Schwarz, C.J. Philpotts, T.F. Cox, K. Huber, M. Hannig, The protective nature of pellicle towards toothpaste abrasion on enamel and dentine. J. Dent. , 360–368 (2008)36 G. Luengo, M. Tsuchiya, M. Heuberger, J. Israelachvili, Thin film rheology and tribology of chocolate. J. Food Sci. (4), 767–772 (1997)62 A. Maroudas, Hyaluronic acid films, in lubrication and wear in living and artificial human joints. Proc. Inst. Mech. Eng. (Part 3J), 122–124 (1967)181 C.W. McCutchen, Physiological lubrication, in lubrication and wear in living and artificial human joints. Proc. Inst. Mech. Eng. (Part 3J), 55–62 (1967)181 G.K. McKee, Developments in total hip joint replacement, in lubrication and wear in living and artificial human joints. Proc. Inst. Mech. Eng. (Part 3J), 85–89 (1967)181 V.C. Mow, S.C. Kuei, W.M. Lai, C.G. Armstrong, Biphasic creep and stress relaxation of articular cartilage in compression: theory and experiments. J. Biomech. Eng. , 73–84 (1980)102 T. Murakami, The lubrication in natural synovial joints and joint prostheses. JSME Int. J., Ser. 111 , 465–47433 (1990) T. Murakami, H. Higaki, Y. Sawae, N. Ohtsuki, S. Moriyama, Y. Nakanishi, Adaptive multimode lubrication in natural synovial joints and artificial joints. Proc. Inst. Mech. Eng., Eng. Med. (Part H), 23–35 (1998)212 V. Ngai, J.B. Medley, L. Jones, J. Forrest, J. Teichroeb, Friction of contact lenses; silicone versus conventional hydrogels. Tribol. Interface Ser. , 371–379 (2005). Elsevier48 E.L. Radin, D.A. Swann, P.A. Weisser, Separation of a hyaluronate-free lubricating fraction from synovial fluid.
  • 9. 9 SpringerReference C.B.E., F.R.S., F.R.Eng., F.R.S.E. Prof. Duncan Dowson Introduction to Biotribology 11 Jul 2012 17:24 © Springer-Verlag Berlin Heidelberg 2012 Nature , 377–378 (1970)228 A.C. Rennie, P.L. Dickrell, W.G. Sawyere, Friction coefficient of soft contact lenses: measurement and modeling. Tribol. Lett. (4), 499–504 (2005)18 S.C. Scholes, I.C. Burgess, H.R. Marsden, A. Unsworth, E. Jones, N. Smith, Compliant layer acetabular cups: friction testing of a range of materials and design for a new generation of prosthesis that mimics the natural joint. Proc. Inst. Mech. Eng., Eng. Med. (5 Part H), 383–596 (2006)220 B.B. Seedhom, D. Dowson, V. Wright, The load-bearing function of the menisci: a preliminary study, in The Knee , (1973), ed. by O.S. Ingwersenm, B. van Linge, T.J.G. van Rens, G.E. Rösingh,Joint: Proc. Int. Congr. Rotterdam B.E.E.M.J. Veraart, D. le Vay (Excerpta Medica/Elsevier, Amsterdam/New York, 1974) N. Shrive, The weight-bearing role of the menisci of the knee. J. Bone Jt. Surg. , 381 (1974)56B D.A. Swann, Macromolecules of synovial fluid, in , ed. by L. Sokoloff, vol. 1The Joints and Synovial Fluid (Academic, New York, 1978), pp. 407–435 P. Theobald, C. Byrne, S.F. Oldfield, D. Dowson, M. Benjamin, C. Dent, N. Pugh, L.D.M. Nokes, Lubrication regime of the contact between fat and bone in bovine tissue. Proc. Inst. Mech. Eng., Eng. Med. (Part H),221 351–356 (2007) P.S. Walker, D. Dowson, M.D. Longfield, V. Wright, ‘Boosted lubrication’ in synovial joints by fluid entrapment and enrichment. Ann. Rhuem. Dis. (6), 512–520 (1968)27 M.A. Wimmer, C. Sprecher, R. Hauert, G. Täger, A. Fischer, Tribochemical reaction on metal-on-metal hip joint bearings. A comparison between in-vitro and in-vivo results, WEAR, , 1007–1014, (2003)255 Introduction to Biotribology C.B.E., F.R.S., F.R.Eng., F.R.S.E. Prof. Duncan Dowson School of Mechanical Engineering, The University of Leeds, Leeds, United Kingdom DOI: 10.1007/SpringerReference_332907 URL: Part of: Encyclopedia of Tribology Editors: Prof. Q. Jane Wang and Prof. Yip Wah Chung PDF created on: July, 11, 2012 17:24 © Springer-Verlag Berlin Heidelberg 2012