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Friction and wear behavior of ultrahigh molecular weight polyethylene on Co-Cr and titanium alloys in dry and lubricated environments
Abstract
Dry oscillatory sliding tests were performed with ultrahigh molecular weight polyethylene (UHMWPE) sliding against cast cobalt chrome, heat-treated Co-Cr, and titanium alloys. It was determined that the average value of steady state wear rate of UHMWPE against titanium was significantly greater than that against Co-Cr, but the friction coefficients against the two metals were not significantly different. In addition, results revealed that the value of steady state wear rate of polyethylene against as-cast Co-Cr was less than that against heat-treated Co-Cr. Wear rates in distilled water were significantly higher than those in dry conditions, while the friction coefficients were significantly lower. Scanning electron micrographs revealed that a transfer film of UHMWPE formed on the surface of the metal in both dry and wet conditions, although the appearance of the film was different in each case. The differences observed in the transfer film may have been responsible for the differences in tribological behavior of the UHMWPE.
... Tetreault and Kennedy reported that PE wear when slid against titanium alloy and Co-Cr alloy under water-lubricated conditions was higher than that under dry conditions. They also reported that breakage of the PE chains under water-lubricated conditions occurred more easily than under dry conditions [8]. Buchanan et al. reported that titanium oxide particles formed by disruption of the surface oxide film on titanium alloy became embedded in the PE and abraded the titanium alloy sliding surface in aqueous solutions [9]. ...
... The abrasive wear resistance of the titanium alloy was improved by surface modification such as ion-implantation, thermal oxidation, oxygen diffusion and diamond-like carbon (DLC) coating [6,[10][11][12]. Under dry sliding, PE is sometimes transferred to the mating metal surface, and sometimes not, and the form of the transferred PE was sometimes a film and sometimes an isolated deposit [2,5,6,8,13]. The formation of a PE transfer film on the mating metal surface was hindered by water [2,8,13]. ...
... Under dry sliding, PE is sometimes transferred to the mating metal surface, and sometimes not, and the form of the transferred PE was sometimes a film and sometimes an isolated deposit [2,5,6,8,13]. The formation of a PE transfer film on the mating metal surface was hindered by water [2,8,13]. ...
Sliding tests with a polyethylene (PE) pin against aluminum (Al) and titanium (Ti) disks were conducted under dry conditions, in n-undecane and in ethanol using a unidirectional pin-on-disk machine to evaluate lubrication compatibility. Compared to the dry condition, n-undecane lubrication reduced friction of both the PE pin/Al disk pair and PE pin/Ti disk pair and increased the wear of the tested materials other than PE pin slid against Ti disk. Ethanol lubrication reduced friction and wear of the PE pin/Ti disk pair but increased those of the PE pin/Al disk pair. In all environments tested, the wear of the PE pin/Ti disk pair was lower than that of PE pin/Al disk pair. Profile measurements of the wear tracks on the disks, microstructural observation and chemical analysis of the worn surfaces were performed. The results suggest that the tribological behavior was influenced by the abrasive wear resistance of the metal, the permeability of the solvent into PE, chemical reactivity of the solvent and the thermal conductivity of the metal.
... The effects of lubricants were studied using dry test conditions, water, and diluted bovine serum lubrication [4,[51][52][53]. The trend today is to use similar lubricants for POD-bearing material testing as would be for the corresponding full (e.g., hip and knee) implant simulator tests. ...
... Consequently, researchers began examining articulating surfaces and comparing them to those from retrieved implants in order to evaluate whether the wear mechanisms were similar [4,55]. Surface evaluations revealed that dry lubrication resulted in melting of the surface, which caused delamination and polyethylene transfer [51][52][53] and led to very high wear rates when the product of pressure and velocity limit of the material was exceeded [51,56,57]. Although water lubrication also displayed polyethylene transfer [4,22,53], which was not clinically relevant, serum lubrication produced scratches on otherwise burnished surfaces similar to those of retrieved implants [4,14,35,57]. ...
... Surface evaluations revealed that dry lubrication resulted in melting of the surface, which caused delamination and polyethylene transfer [51][52][53] and led to very high wear rates when the product of pressure and velocity limit of the material was exceeded [51,56,57]. Although water lubrication also displayed polyethylene transfer [4,22,53], which was not clinically relevant, serum lubrication produced scratches on otherwise burnished surfaces similar to those of retrieved implants [4,14,35,57]. Serum or other protein containing lubrication emerged as the requirement in laboratory tests to facilitate wear mechanisms similar to those in vivo [4,14,35,[57][58][59][60]. ...
Screening of candidate materials by simple and affordable testing machines has been part of the development of orthopedic bearings since the 1970s. The promising candidates would then be tested in a joint simulator and in vivo testing of the most promising materials would follow. However, there is uncertainty about the capability of pin-on-disk (POD) testers to realistically simulate clinically relevant wear mechanisms with repeatability across different laboratories. We describe the factors, conditions, and potential pitfalls involved in the setup of POD testing for wear assessment of UHMWPE and provide a quick review and critique of the international standard testing methodologies of POD testing relevant to UHMWPE.
... Earlier wear testers relied on Archard's law that wear rate of UHMWPE depended on load and sliding distance only (Archard, 1953). Unidirectional disk-on-plate (Galante and Rostoker, 1973), unidirectional pin-on-disk (Barbour et al., 1999;Brown et al., 1976;Cooper et al., 1993;Dowson and Harding, 1982;Klapperich et al., 1999;Seedhom et al., 1973;Tetreault and Kennedy, 1989), bi-directional thrust-washer , reciprocating pin-on-disk or pin-onplate (Cooper et al., 1993;Deng and Shalaby, 1997;McKellop et al., 1978;Wang et al., 1997) and unidirectional sphere-ondisk (Rose et al., 1982) were early designs in accordance with the theory. ...
... Early studies attempted to compare wear rates obtained in the laboratories with clinical wear rates (Dumbleton, 1978) of 0.13 mm/year for Charnley prostheses in an attempt to validate testing conditions . While the effects of lubricants were studied using dry, water and serum lubrication (Dowson and Harding, 1982;Dumbleton and Shen, 1976;McKellop et al., 1978;Tetreault and Kennedy, 1989), there was no consensus regarding the wear measurement technique (Brown et al., 1976;Dowson and Harding, 1982;Seedhom et al., 1973). Measurements were either based on changes in polyethylene weight or height. ...
... Consequently, researchers began examining articulating surfaces and comparing them to those from retrieved implants in order to evaluate whether the wear mechanisms were similar (Brown et al., 1976;McKellop et al., 1978). Surface evaluations revealed that dry lubrication resulted in melting of the surface, which caused delamination and polyethylene transfer (Dowson and Harding, 1982;Dumbleton and Shen, 1976;Tetreault and Kennedy, 1989) and led to the high wear rates when the product of pressure and velocity limit of the material was exceeded (Dumbleton and Shen, 1976;Rose et al., 1982;Shen and Dumbleton, 1974). While water lubrication also displayed polyethylene transfer (Cooper et al., 1993;McKellop et al., 1978;Tetreault and Kennedy, 1989), which was not clinically relevant, serum lubrication produced scratches on otherwise burnished surfaces similar to those of retrieved implants (McKellop et al., 1978;Rose et al., 1982;Walker et al., 1996;Wright et al., 1982). ...
The introduction of numerous formulations of Ultra-high molecular weight polyethylene (UHMWPE), which is widely used as a bearing material in orthopedic implants, necessitated screening of bearing couples to identify promising iterations for expensive joint simulations. Pin-on-disk (POD) testers capable of multidirectional sliding can correctly rank formulations of UHMWPE with respect to their predictive in vivo wear behavior. However, there are still uncertainties regarding POD test parameters for facilitating clinically relevant wear mechanisms of UHMWPE. Studies on the development of POD testing were briefly summarized. We systematically reviewed wear rate data of UHMWPE generated by POD testers. To determine if POD testing was capable of correctly ranking bearings and if test parameters outlined in ASTM F732 enabled differentiation between wear behavior of various formulations, mean wear rates of non-irradiated, conventional (25-50kGy) and highly crosslinked (≥90kGy) UHMWPE were grouped and compared. The mean wear rates of non-irradiated, conventional and highly crosslinked UHMWPEs were 7.03, 5.39 and 0.67mm(3)/MC. Based on studies that complied with the guidelines of ASTM F732, the mean wear rates of non-irradiated, conventional and highly crosslinked UHMWPEs were 0.32, 0.21 and 0.04mm(3)/km, respectively. In both sets of results, the mean wear rate of highly crosslinked UHMPWE was smaller than both conventional and non-irradiated UHMWPEs (p<0.05). Thus, POD testers can compare highly crosslinked and conventional UHMWPEs despite different test parameters. Narrowing the allowable range for standardized test parameters could improve sensitivity of multi-axial testers in correctly ranking materials.
... How to reduce the degree of UHMWPE wear in human body is the most important issue in increasing the survive life of the artificial arthroplasty. Laboratory wear test apparatus of artificial hip arthroplastic materials include four types [3,[6][7][8][9][10][11]: pin-on-plate, pin-on-disc, hip simulator, and ring-on-disc. Since the survive life of the arthroplasty depended on the wear rate. ...
... Therefore, the evaluating factors should include: wear mechanism, friction coefficient, wear factor, UHMWPE debris and transfer film. A review of literature shows the wear factors are between 10 −7 to 10 −8 mm 3 N −1 m −1 [3,[6][7][8][12][13][14][15] adopted in these literatures include ZrO 2 , Al 2 O 3 , Co-Cr-Mo alloy, or stainless steel. The apparatus used in previous papers was either pin-on-disc or pin-on-plate. ...
... The frictional behaviors of UHMWPE on Al 2 O 3 alloy were similar to that on TZP, but the friction coefficients are different. Fig. 3 shows the friction coefficient (which refers to the stable friction coefficient hereafter in this paper) of the above materials with various surface roughness and some relative references [7,8,13,14,19]. It appears that when the ring reciprocally slide on smoother contact surface (R a < 0.04 m), the friction coefficient of Al 2 O 3 was lowest (µ = 0.033 ± 0.003). ...
A study on the wear behavior of an ultra high molecular weight polyethylene (UHMWPE) sliding on the discs made of two types of ceramics was conducted by a ring-on-disc reciprocal wear test. The properties including friction coefficient, wear factor, debris, and transfer film of UHMWPE were evaluated and correspondent to the variables in the wear tests. Those variables included type of disc materials (zirconia and alumina), lubricants, types of contact face of UHMWPE rings, and surface roughness of discs. The results indicated that the friction coefficient and wear factor were closely controlled by the roughness of the disc. The wear mechanisms of UHMWPE sliding on zirconia could be categorized by two types of surfaces differentiated by a critical roughness (Ra) of 0.10 μm. The effects of debris and transfer film (i.e. third body effect) were investigated. By reducing the initial roughness of UHMWPE, pre-coating a transfer film onto the disc, and using saline as a lubricant can slightly reduce the friction coefficient, and improve the wear factor of the UHMWPE on ZrO2 disc.
... Component geometries were for a Triathlon CR implant (Stryker Corporation, Kalamazoo, MI, USA) which includes a femoral component, a tibial tray, and an ultra-high molecular weight polyethylene (UHMWPE) insert. All components behaved as rigid bodies with contact between the femoral component and UHMWPE insert defined with a coefficient of friction of µ = 0.04 [20,21]. Contact is determined by the virtual simulator by evaluating whether penetration exists between two surfaces (e.g., femoral component and UHMWPE insert) in the inferior-superior (IS) direction. ...
... With no other forces acting on the knee, the medial side will be tighter in both the healthy and the TKA knee due to medial side ligaments exerting higher forces than their lateral counterparts [19,20]. For this reason, the change in compressive ligament forces due to component malrotation had a more noticeable effect on the medial compartment of the knee. ...
Component alignment accuracy during total knee arthroplasty (TKA) has been improving through the adoption of image-based navigation and robotic surgical systems. The biomechanical implications of resulting component alignment error, however, should be better characterized to better understand how sensitive surgical outcomes are to alignment error. Thus, means for analyzing the relationships between alignment, joint kinematics, and ligament mechanics for candidate prosthesis component design are necessary. We used a digital twin of a commercially available joint motion simulator to evaluate the effects of femoral component rotational alignment. As anticipated, the model showed that an externally rotated femoral component results in a knee which is more varus in flexion, with lower medial collateral ligament tension compared to a TKA knee with a neutrally aligned femoral implant. With the simulation yielding logical results for this relatively simple test scenario, we can have more confidence in the accuracy of its predictions for more complicated scenarios.
... PE -Ti6Al4V [33] 0.22 ...
Purpose
The aim of this study was to evaluate the abrasive wear of the sliding screw-rod joint used in growth guidance system (GGS) stabilizers, allowing the translation of the screw along the rod during the spinal growth process in a standard and modified system.
Methods
The study used single kinematic screw-rod pairs made of titanium alloy Ti6Al4V. Mechanical tests (cyclic loads) simulated the stabilizer's operation under conditions similar to actual use. A microscopic evaluation was conducted, analyzing abrasive wear based on measured abrasion areas. Numerical simulations were performed for the standard joint system and for a structural change (an additional insert to increase contact area between the rod and sliding screw cap).
Results
The study evaluated the abrasive wear of the mating elements of the stabilizer. Mechanical tests showed an increase in the force observed (11.74±2.52 N) with the increasing number of load cycles. Microscopic evaluation showed abrasion of the caps and rods in two areas (upper and lower). Numerical simulations indicated the highest stresses in the standard system were on the mating elements, i.e., the rod and the cap (15.6 MPa). In the modified joint, stress distribution differed, concentrating on the surface of the insert and the rod, with maximum values of 6.0 MPa (PE insert) and 12.4 MPa (PEEK insert).
Conclusions
Comparing the stress distributions obtained in the numerical simulations and the abrasive wear effects produced in the mechanical tests, a similar mechanism was observed (the destruction of the top layer of the mating elements of the stabilizer).
... Five cof were examined with two dry sliding situations (cof = 0.2 and cof = 0.25), two lubricated sliding (cof = 0.05 and cof = 0.1) and a frictionless sliding. The cof data were taken from [11], [12] and [13]. biomaterials, whereas influences implants have a multi directional sliding. ...
Coefficient of friction (cof) is an important variable when dealing with con-tact between mechanical parts. It depends on various tribological variables and the value can be determined only by experiments. Cof correlates with the wear of material and this is a severe problem in biomedical engineering. This research numerically studied the effects of cof between talar and bear-ing in the total ankle replacement (TAR) implants. The aim is to evaluate the contact situations affected by cof. The TAR models consist of cobalt chrome (CoCr) alloy and ultra high molecular weight polyethylene (UHMWPE) bio-materials. Five cof values of the dry, lubricated and frictionless TAR me-chanical contacts under ankle gait load were examined. The models use a fixed 1 mm element size for UHMWPE bearing component and four element sizes for the talar component, range from 1 mm to 0.4 mm. Results show that, 1) higher cof induces higher contact pressure, 2) contact stress is not af-fected by cof, 3) proper talar element size is 0.4 mm and 4) frictionless model can be used for the TAR contact mechanic computation. Frictionless model calculates equal contact stress and lower contact pressures with an error of 2.68 % compared to the smooth model.
... The material used in this study consists of 3 types of materials, as shown in Table 1. The assumptions used in this simulation are: 1. Contact of the Titanium implant model with UHMWPE has a coefficient of friction of 0.2 [13] 2. The contact screw is considered bonded to compensate for the absence of the initial tightening force [10] 3. Contact between the ilium bone and the sacrum implant is assumed to be without friction; as compensation, the iliac screw in contact with the ilium bone and sacrum implant is considered bonded. ...
This study focused on the design of specific prostheses in the case of patients affected by Chordoma of the lumbar 4, lumbar 5, sacrum, and coccyx. A chordoma is a group of malignant and rare cancers, commonly found in the spine or skull bones. As a treatment method, if cancer has not spread beyond the bone, the infected bone’s removal procedure is replaced with an artificial bone (prosthesis). The design method is carried out using a CT Scan of patient data, which is processed into a 3D model with Materialise Mimics software, 3D model engineering is done using Solidworks software and finite element analysis with ANSYS. The design process is carried out with several kinds of design variations, including the bone-implant model with a solid and shell model which is divided into several components, the use of iliac screw lateral connector, modification of iliac screw locking head, and modification of iliac screw locking head with cross connector. From the results of the calculation analysis and simulation, the best concept chosen based on the lowest dominant Peak von Mises Stress value in the iliac screw section is designs using the Iliac Screw Locking Head with Shell Model Lattice Structure.
... Premièrement, la prothèse de cheville induit un mouvement entre des composants métalliques et un insert en polyéthylène. Seules quelques études ont examiné les processus de « tribocorrosion » à l'interface entre un métal et un polymère [448][449][450]. L'utilisation d'un pion inerte au lieu du polymère induit de profonds changements dans la nature et la forme des particules d'usure et le mécanisme d'usure simulé pour ces prothèses articulaires. ...
La durabilité à long terme des prothèses articulaires repose sur leur résistance vis-à-vis de la corrosion et leur comportement à l'usure. Quels que soient les matériaux utilisés, des produits de dégradation (ions métalliques et débris d’usure) se forment, du fait de la corrosivité des fluides corporels et de la biomécanique des articulations. Généralement, ces produits sont associés aux complications post-opératoires et en conséquence, leurs effets constituent des préoccupations cliniques critiques. A cet égard, la tribocorrosion est une considération sérieuse dans la performance des prothèses articulaires. Ce travail vise à contribuer à l'amélioration de la compréhension des mécanismes de dégradation d’un alliage de CoCrMo, utilisé en tant que prothèse articulaire, en appréhendant le couplage de charges mécaniques et l’activité cellulaire. Cette thèse a été entreprise selon une approche itérative, qui débute par l’étude du comportement électrochimique du milieu physiologique simulé, propice à la culture cellulaire (le RPMI-1640). L’alliage métallique et les cellules ont successivement été ajoutés au système d’étude. Les essais ont révélé que l'oxydation du CoCrMo est accélérée en présence d'espèces carbonées et de composés organiques, et que les cellules interviennent sur la libération d’ions métalliques. Un dispositif de biotribocorrosion a été développé dans le but d’évaluer l’influence des produits de dégradation sur le métabolisme cellulaire. Cette étude multidisciplinaire exhaustive a combiné des techniques expérimentales d’électrochimie, de biologie et de tribologie, afin de souligner l'importance de la chimie de surface du biomatériau sur sa résistance à la tribocorrosion et son caractère cytotoxique. Finalement, une méthodologie expérimentale a été proposée dans ce travail, en vue de mieux comprendre l’interaction entre les fluides physiologiques simulés et les biomatériaux.
... Therefore, the use of a hard material as counter-body to simulate wear of metal-onpolyethylene bearings is not appropriated. Only a few studies have focused on real tribocorrosion processes between a metal and polymer [37][38][39]. In addition, wear particles are not always generated from simulated friction, however commercially available nanoparticles and microparticles are also used to assess the cytotoxicity of wear particles from orthopaedic implants and prostheses. ...
... The lubricant itself could cool down the temperature of the experiment environment. Tetreault and Kennedy [94] revealed that dry tests would produce a different wear mechanism compared to that under wet simulation. They explained that high temperature would exist between contact surfaces if no lubricant was used, and this could result in the delamination and material transfer. ...
Development of artificial joints is a great progress for joint replacement operations of human being, but the short longevity of prostheses has concerned both industries and researchers since the advent of modern implants. Thus, continuous improvements have been made alongside the clinical applications. The methodologies to inspect the potential properties of new designs have also seen many advances. The test machines have evolved from easy pin-on-disk configuration to the modern joint simulator. Besides, various wear traces provided by testing machines are investigated greatly, and multi-directional files are recommended as motion profiles for in vitro testing. The typical testing parameters, like sliding speed or loading profile, are discussed in this article, and their working mechanisms are described in detail. Meanwhile, the calf or bovine serum has been regarded as the gold standard for testing lubricant, and the future trend of fluid will be focused on investigating the effects of lubricant composites on the tribological properties. Hard particles and proteins are discussed as well, and their effects on the wear mechanisms are the focus. Finally, various approaches to measure the wear rate, wear factor and the thickness of lubricant film are presented, and suggestions are given for the development in future.
... u x and u y are the velocity magnitude in the x-and y-directions, respectively, and ω z is the angular velocity about the z-direction. Fig. 1 (a) shows a configuration in which the pin is stationary and loaded onto a disc that performs a reciprocating motion along the xdirection with velocity u x [20][21][22][23][24][25][26][27][28][29][30]. Conversely, Fig. 1 (b) depicts a pin that performs a reciprocating motion along the x-direction with velocity u x while loaded onto a stationary disc [31]. ...
Pin-on-disc (PoD) experiments are widely used to quantify and rank wear of different material couples for prosthetic hip implant bearings. However, polyethylene wear results obtained from different PoD experiments are sometimes difficult to compare, which potentially leaves information inaccessible. We use machine learning methods to implement several data-driven models, and subsequently validate them by quantifying the prediction error with respect to published experimental data. A data-driven model can supplement results from PoD wear experiments, and enables predicting polyethylene wear of new PoD experiments based on its operating parameters. It also reveals the relative contribution of individual PoD operating parameters to the resulting polyethylene wear, thus informing design of experiments, and potentially reducing the need for time consuming PoD wear measurements.
... 28,29 For example, many studies have been published on the wear and friction of UHMWPE against stainless steel, cobalt chrome, and titanium alloys, with results used to select materials for THR. [30][31][32] They were also used to evaluate UHMWPE wear and friction against ceramic materials which outperformed CoCr, 33 as well as COC 34,35 and MOM interactions. 36 Such testing neither takes into account the geometry nor other full THR system characteristics which may in the end be the most dominant factors for both wear and the friction of a hip replacement in vivo. ...
We propose and have evaluated a method to measure hip friction during wear testing on a popular multi-station hip simulator. A 6-degree-of-freedom load cell underneath the specimen sensed forces and torques during implant wear testing of simulated walking. This included internal–external and adduction–abduction rotations which are often neglected during friction testing on pendulum-type machines. Robust mathematical analysis and data processing provided friction estimates in three simultaneous orthogonal rotations, over extended multi-million cycle wear tests. We tested various bearing couples including metal-on-plastic, ceramic-on-plastic, and metal-on-metal material couples. In one test series, new and intentionally scratched CoCrMo 40-mm-diameter femoral heads were tested against conventional ultrahigh-molecular-weight polyethylene, highly cross-linked, and highly cross-linked with vitamin E versions. The scratching significantly increased friction and doubled the wear of all groups. Before scratching, friction levels for the aforementioned plastic groups were 0.056 ± 0.0060, 0.062 ± 0.0080, and 0.070 ± 0.0045, respectively, but after scratching increased to 0.088 ± 0.018, 0.076 ± 0.0066, and 0.082 ± 0.0049, respectively, all statistically significant increases (p = 0.00059, 0.00005, 0.0115, respectively). In another test series of 44-mm femoral head diameter hips, metal-on-plastic hips with conventional ultrahigh-molecular-weight polyethylene showed the lowest friction at 0.045 ± 0.0085, followed by highly cross-linked with 0.046 ± 0.0035 (not significantly different). In a ceramic-on-plastic design with conventional ultrahigh-molecular-weight polyethylene, higher friction 0.079 ± 0.0070 was measured likely due to that ceramic surface being rougher than usual. Metal-on-metal hips were compared without and with a TiN coating, resulting in 0.049 ± 0.014 and 0.097 ± 0.020 friction factors, respectively (statistically significant, p < 0.001), and the coating wore away on all coated hips eventually. Higher friction mostly correlated with higher wear or damage to femoral heads or implant coatings, except for the highly cross-linked wear resistant ultrahigh-molecular-weight polyethylene which had slightly higher friction, confirming the same finding in other independent studies. This type of friction measurements can help screen for clamping and elevated wear of metal-on-metal and resurfacing total hip replacements, surgical malpositioning, and abraded and otherwise damaged surfaces.
... Generally, stainless steel is the most favourable material to be paired with polymers owing to its resistance to oxidization which prevents any influence on the polymer wear rate by abrasive oxide particles [19]. Tetreault and Kennedy [20] observed that the coefficients of friction are fairly independent of speed at low sliding speeds because the rise in the thermal heat is negligible and does not affect the mechanical characteristics of the polymer surfaces. At high sliding speeds, the coefficient of friction increases rapidly due to the increase in the adhesive component of friction. ...
In this paper, the application of ball burnishing as a new surface treatment process for polymers is investigated. The polymers used were polyoxymethylene (POM) and polyurethane (PUR). The lowest surface roughness value achieved for POM was 0.44μm (45% decrease) and for PUR was 0.46μm (42% decrease). The lowest coefficient of friction value achieved was 0.22 (32.9% decrease) for POM and 0.24 (28.8% decrease) for PUR. The lowest specific wear rate value achieved was 0.31×10−6mm3/Nm (38.6% decrease) for POM and 0.41×10−6mm3/Nm (37.9% decrease) for PUR.
Description
The most current data available on the impact of vibrations and stiffness on test apparatus and machine wear. This comprehensive volume includes wide-ranging examples of machine wear, current experimental and analysis techniques to investigate these effects, as well as an extensive bibliography on the subject. Specific areas addressed:
• How vibrations can reduce or increase wear and friction
• Methods to study vibration effects
• Self-induced vs.machine-induced vibrations
• Evaluating different design parameters on bearing load dynamics
• Increasing spindle life in grinding machines
• Orthopedic biomaterial wear tests
•The effects of ultra sonic vibration on tool life.
In this study, a test scenario for the friction testing of electrically heated shape-memory alloy (SMA) wires against polymer surfaces was developed. As alloy, Nickel-Titanium (Nitinol, NiTi) was specially selected due to its high working capacity, the good corrosion resistance and the quick actor response at low bias forces. As the materials in contact with the actuator must resist friction forces and elevated temperatures up to 200 °C, a combination with high performance polymers is preferable. In many applications, the actuators use redirections to enhance the actuator capabilities or enable the use in complex structures. To better understand and compare the tribological properties of Nitinol against various polymer materials, it was needed to manufacture a customized testing device.
Total knee arthroplasty (TKA) is an end-stage treatment for knee osteoarthritis that relieves pain and loss of mobility, but patient satisfaction and revision rates require improvement. One cause for TKA revision is joint instability, which may be due to improper ligament balancing. A better understanding of the relationship between prosthesis design, alignment, and ligament engagement is necessary to improve component designs and surgical techniques to achieve better outcomes. We investigated the biomechanical effects of ligament model complexity and ligament wrapping during laxity tests using a virtual joint motion simulator. There was little difference in kinematics due to ligament complexity or ligament wrapping.
Following numerous studies demonstrating the ability of nanostructured alpha-alumina filler to reduce the prohibitively high wear rate of polytetrafluoroethylene (PTFE) down to extremely small values (∼10⁻⁷ mm³/Nm) well below those of conventional PTFE micro-composites, alpha-alumina filler was also shown capable, in a couple recent studies, of imparting similar performance to another fluoropolymer, perfluoroalkoxy (PFA) copolymer, which otherwise was similarly lacking wear resistance in the unfilled state. In addition to duplicating such alpha-alumina performance in PFA, in this study such an extreme wear-reducing capability has also been demonstrated using nanocarbon powder, as an example representative of several other forms of nanoscale carbon filler that like alpha-alumina had been shown capable of providing extreme resistance to PTFE. Fluorinated ethylene propylene (FEP) copolymer, whose nanocomposites have not been tribologically explored previously, was thus more fully investigated here with not only alpha-alumina and nanocarbon, but also other nanotube (CNT) and mesoporous forms of nanoscale carbon fillers. In preliminary testing, only the alpha-alumina filler indicated an ability to impart its wear-reducing capability to FEP; a wear rate of ∼0.8 × 10⁻⁶ mm³/Nm was observed at 2 wt% alpha-alumina concentration. While this is an impressive reduction in wear rate, it is not quite as extreme a reduction as that observed in PTFE or PFA. The transport of the extreme wear resistance of nanocarbon powder in PTFE and PFA was even more partial and incomplete in FEP, with the ∼0.3 × 10⁻³ mm³/Nm unfilled FEP wear rate only reduced to ∼10⁻⁵ mm³/Nm, while the CNT and mesoporous carbon fillers were even less effective. Correspondingly, ATR-FTIR spectra from FEP wear surfaces displayed sizable peaks evident of the chelation of chemical interactions known to be associated with wear resistance for PTFE and PFA matrices only in the most wear-resistance alpha-alumina case and to a lesser extent for the nanocarbon. Finally, it is demonstrated that such fillers demonstrate such strongly beneficial effects only in polymers that otherwise lack wear resistance, and may actually be deleterious for polymers such as high density polyethylene (HDPE) already having some inherent wear resistance in their unfilled state.
Background
Instability following reverse shoulder arthroplasty is influenced by various factors such as component design, component positioning, and soft tissue tensioning. Patients may achieve glenohumeral motion beyond initial scapular impingement during activities of daily living which could further compound instability. However, instability/subluxation risk postscapular impingement is not well documented. Conventional range of motion analysis tools cannot account for the restraining effect of soft tissues or subluxation risk after impingement. Using a previously validated finite element analysis approach, the purpose of this study was to investigate the effects of glenoid component lateralization and humeral component angle of inclination (AOI), with or without simulated subscapularis repair, on postimpingement subluxation. We hypothesized that lack of subscapularis repair, a valgus humeral component AOI, and glenoid medialization would all result in greater postimpingement instability.
Methods
A FE model of the shoulder including the subscapularis tendon and middle deltoid was created, incorporating a general representation of a commercial reverse shoulder arthroplasty implant placed under the direction of a fellowship-trained shoulder surgeon. The deltoid and subscapularis were tensioned and wrapped around the reconstructed glenohumeral joint prior to simulating motion. Humeral rotations were then prescribed to simulate external rotation (neutral to 50°), extension (neutral to 50°), adduction (neutral to 30°), and abduction (neutral to 90°). The effects of three glenosphere lateralization offsets (2, 4, and 10 mm) and 2 humeral liner angles of inclination (varus-150° and valgus-155°) on subluxation propensities were investigated with and without the subscapularis tendon present.
Results
Simulated subscapularis repair resulted in 21%-34% less postimpingement subluxation. Presence of the subscapularis provided stability over a greater range of abduction. Impingement-free range of motion was similar regardless of the presence or absence of the subscapularis. The valgus AOI resulted in 23% less subluxation during abduction. During other motions however, the valgus AOI resulted in 67%-110% greater postimpingement subluxation (subscapularis present), which further worsened without the subscapularis.
Conclusion
Implant design modifications to improve stability may not be beneficial for all motions, highlighting the importance of directionality when investigating instability. Liner-bone impingement appears to compound instability/subluxation and the subscapularis appears to restrain postimpingement instability.
Level of evidence
Basic Science Study; Computer Modeling
Publications are reviewed related to the identification of some regularities in relationships between the chemical structures of the repeating unit, the macromolecular chain (linear, branched, crosslinked structures), deviations in structure of repeating unit and structure of polymer bodies, polymer mixtures, tribochemical transformations in polymers, filled systems and the frictional behavior (the friction coefficient and wear) typical for different classes of polymers, such as carbochain, carbocyclochain, heterochain and heterocyclochain polymers.
Ultra-high molecular weight polyethylene (UHMWPE) and Co-Cr alloy are still commonly used bearing materials for total disc replacement (TDR) as well as total joint replacement (TJR). Compared to TJR, in TDR, there are different articulating conditions such as higher contact pressure, shorter sliding distance, and less lubricant, unlike hip and knee joints. In this study, friction and wear phenomena between UHMWPE and Co-Cr alloy were characterized under the wide range of contact pressures including the extremely high contact pressure with limited amount of lubricant in lumbar TDR. All friction and wear tests were conducted by using a Pin-on-Disk type tribo-tester under normal contact pressures of 5, 10, 20, 40, 60 and 80MPa in the repeat pass rotational and the linear reciprocal sliding motions, respectively. UHMWPE cylindrical pins slid against Co-Cr alloy disks in three different kinds of dry, rarely and fully immersed lubricated conditions for friction tests and in a fully immersed lubricated condition for wear tests. For all lubricated conditions, mean coefficients of friction decreased as contact pressure increased. There were statistically significant differences in the mean coefficients of friction among six levels of contact pressures and among three kinds of lubricated conditions. The amount of wear linearly increased as number of sliding cycles increased for all contact pressures, and also it increased as the contact pressure increased. There were statistically significant differences in the wear rates of UHMWPE among six levels of contact pressures. Coefficients of friction of UHMWPE against Co-Cr alloy under very high contact pressure such as 40–80MPa in the lubricated condition were so low as to induce no clinical problem at the bearing surface. For reducing wear of UHMWPE component in TDR, it is necessary to decrease the contact pressure in design as much as possible.
Total joint replacements traditionally employ ultra high molecular weight polyethylene (UHMWPE) as a bearing material due to its desirable material properties and biocompatibility. Failure of these polyethylene bearings can lead to expensive and risky revision surgery, necessitating a better understanding of UHMWPE's tribological properties. A six-station rolling/sliding machine was developed to study the behavior of acccelerated-aged UHMWPE in cylinder-on-cylinder contact. The normal load and sliding/rolling ratio in the oscillatory contacts can be controlled separately for each test station, as can the liquid test environment. Fatigue tests were run on the machine with UHMWPE versus cobalt-chrome cylinders in a distilled water environment at normal contact pressures of approximately 20 MPa. All specimens failed by subsurface cracking during tribotesting on the machine, and the failures were similar to those that occur in-vivo. The fatigue behavior of the polymer was analyzed to determine its relationship to oxidation and stress state in the rolling/sliding cylinder. At the 20 MPa test load, the number of cycles to fatigue failure by subsurface cracking was inversely proportional to the oxidation level. Analysis of the stress levels through the bulk of the polyethylene specimens and their relationship to the material properties provide insight as to why cracks initiate and propagate subsurface.
A range of ultra-high molecular weight polyethylenes have been subjected to water-lubricated, reciprocating sliding wear against a stainless steel counterface under a pressure of 10 MPa at a frequency of 2.5 Hz and a maximum speed of 0.4 m s-1. Transfer of material to the metal counterface during sliding wear involves interlamellar shear of the polymer and results in the development of a highly oriented transfer film. The deformed surface layers of the polymer and the resultant wear debris have been examined using both optical and scanning electron microscopy, differential scanning calorimetry, infrared spectroscopy and x-ray diffraction. Significant differences have been found in the degree of crystallinity, crystallite size and orientation in the deformed surface layers of the polymer and debris compared with those of the bulk polymer. The worn surface of the polymer shows slightly increased crystallinity but the crystallinity of the debris is much higher than that of the bulk whilst the crystallite size is much reduced.
To gain a better understanding of how small amplitude oscillatory motion affects the tribological behaviour of polymers, a study of ultra high molecular weight polyethylene (UHMWPE) sliding against 440C stainless steel was conducted. A new pin on disc friction and wear test system was designed and built for this purpose. Four operating parameters were varied in the test programme: normal load, oscillation amplitude, oscillation frequency, and initial surface roughness of the metallic disc. Wear of the polymer pin and friction coefficient were monitored continuously during each test, and pin and disc surfaces were examined microscopically after the tests. (from authors' abstract)
The friction and wear rates of high density polyethylene (HDPE) and low density polyethylene (LDPE) were measured on steel counterfaces of various roughnesses at a sliding speed of 1 m/s under a load of 10 N. Surface melting of polyethylenes due to frictional heating occurred during steady-state wear under these sliding conditions. The friction of HDPE showed a minimum at a certain roughness and then increased gradually to a constant value as the roughness was increased. The wear on a rough counterface appears to be caused predominantly by abrasion rather than by fatigue and partially by the transfer due to adhesion. The transfer on counterfaces was examined using an optical non-contact profilometer and SEM. The variations in friction and wear with roughness are discussed on the basis of these examinations.
To gain a better understanding of how temperature affects the tribological behavior of polymers in small amplitude motion, a study of ultra high molecular weight polyethylene (UHMWPE) sliding against 440 C stainless steel was conducted. An existing pin-on-disc wear and friction tester was modified to allow independent temperature control of the polymer pin and the steel counterface. The results indicate that wear rate and friction increase with decreasing counterface temperature or increasing pin temperature. Thus, a relationship was found to exist between the temperature gradient and the measured friction and wear rates. Additionally, higher wear rates corresponded to higher friction. The same friction behavior was observed whether the temperatures were set for the entire test or varied dynamically.
Two types of experiments were carried out in this work. In one experiment, the smooth steel sphere was slid on polymer plates at a very low speed. Water reduces to some extent or very much the friction of polymers. In another experiment, the polymer pins were rubbed against the stainless steel disk at various speeds. In the sliding of polymers on the disk without the transferred polymer, reduction of friction generally occurred slightly under boundary lubrication. However, it occurred clearly in some cases on the disk with the transferred polymer. In these experiments, surface roughness plays an important role in boundary lubrication with water. The amount of polymer transferred under lubrication is similar to that transferred in the dry condition. However, the features of worn surfaces of polymers under lubrication are different from those in a dry condition. The mechanism of polymer wear lubrication is discussed on the basis of these findings.
The relationship between contact temperature, friction coefficient, and wear rate was studied here for the case of dry sliding between pin and flat in small amplitude oscillatory motion. In the first part of the study, infrared radiation pyrometry and finite element analysis techniques were used to measure and model surface temperatures in an oscillatory contact. Good agreement was achieved between model predictions and experimental measurements. The model was then applied to an oscillating contact between an ultra-high molecular weight polyethylene pin and a rough stainless steel flat. Temperature predictions for that case were correlated with measured friction coefficients and wear rates. It was found that the polyethylene wear rate decreased as the contact temperature increased. The uniformity and thickness of the transfer films which formed on both counterface and polymer pin were found to be affected by contact temperature. Transfer film behavior was deemed responsible for the influence of contact temperature on wear rate.
The friction and wear behavior of a polymer/metal oscillatory sliding system is largely dictated by the film of polymer which may form on the metallic counterface. This research utilizes scanning electron microscopy as the principal tool for examination of post-test frictional surfaces in an effort to identify the processes of film formation in an ultra-high molecular weight polyethylene pin/440C stainless steel counterface oscillatory pair. Strong adhesive junction formation at contacts leads to fibril drawing upon continued motion. Eventual fibril rupture deposits polyethylene residues upon the counterface and these residues are cumulatively smeared by the pin into a film. An increase in temperature from 15 to 30 degrees C aids the smearing process, forming a smoother film which reduces wear rate by limiting polymer/metal interaction. Comparative tests with polytetrafluoroethylene support earlier conclusions that film peeling due to weaker adhesion results in higher wear rates for PTFE than UHMWPE.
Ultrahigh molecular weight polyethylene (UHMWPE) acetabular cups of total replacement hip joints tend to wear more quickly in vivo than indicated by most laboratory wear tests. The reason for this discrepancy has been attributed to the generation of fine scratches on the surfaces of the stainless steel femoral heads in service.In the present paper an account is given of an investigation of the influence of single imposed imperfections in stainless steel counterfaces upon the wear of UHMWPE wear pins in linear reciprocating wear tests. The imperfections were in the form of either transverse or longitudinal scratches or single indentations, all generated by diamond markers.It has been found that a single transverse scratch can increase the wear rate of the polymer to a remarkable extent; the major factor being the piled-up steel along the edge of the scratch. When the piled-up material was removed by remedial lapping the wear rate returned to its initial value corresponding to the isotropic roughness of the undisturbed counterface. Longitudinal scratches yielded a less marked yet recognizable increase in the wear rate of the polyethylene.Single diamond indentations did not generate piled-up edges of steel and had little effect upon the wear rate of the polymer.The findings demonstrate the severe effect which simple imperfections on a hard counterface can have upon the wear of polymers. Even shallow transverse scratches can increase the wear rate by an order of magnitude. Remedial lapping of the scratched counterfaces, to remove the piled-up material, largely restores the low wear characteristics of the unblemished counterfaces. The study supports the views offered previously in explanation of the difference between in vivo and laboratory wear rates of total replacement hip joints.
In recent years there has been growing interest in the use of high density alumina ceramic material for the femoral ball in association with ultrahigh molecular weight polyethylene (UHMWPE) for the acetabular component in total replacement hip joints.The wear characteristics of UHMWPE pins sliding against a high density alumina ceramic disc in the presence of distilled water in a tri-pin-on-disc machine have been revealed in very long-term experiments reported in this paper. A total sliding distance in excess of 6000 km was achieved and very low mean wear coefficients of the order of 10−8 mm3 N−1 m−1 were recorded.Experiments were also carried out over a shorter sliding distance under dry conditions and the average wear coefficient of 2 × 10−7mm3N−1m−1 was consistent with earlier findings. In these dry tests, comet-like streaks of polyethylene were transferred to the ceramic counterface, but no such transfer was noted during the wet tests. When distilled water was added to the test chamber after a considerable period of dry sliding, the wear coefficient rapidly decreased to about 10−8 mm3 N−1 m−1 and the streaky transfer film disappeared from the ceramic counterface.The possibility of hydrodynamic action between the wear face on the pins and the counterface was investigated by reversing the direction of sliding. Surface topography changes on both the pins and the discs and friction and bulk temperatures of the pins were recorded throughout the tests.It is concluded that the excellent dry wear coefficients of UHMWPE sliding on alumina ceramic counterfaces are about twenty times greater than those experienced by the same materials in the presence of distilled water. The tribological advantage of the ceramic with respect to stainless steel having a similar surface roughness has been confirmed in dry sliding involving UHMWPE, but further work is required to determine whether or not the same advantage can be achieved under wet conditions.
Creep and wear of articulating reconstructed joints is a complex process, resulting in adverse tissue response, decreased range of motion, and eventual revision. As improvements are made in the design and surgical techniques of reconstructed joints, the long-term performance of the articulating system and materials becomes more important, particularly for younger, heavier, and more active patients. One aspect previously ignored in the long-term performance of articulating systems is the tendency for these systems to generate heat during articulation, particularly for extended periods of relatively strenuous activity. The present study reviews the various aspects of joint lubrication, friction, wear, and overall system performance. Local heating can increase the creep, wear, and oxidation degradation of UHMWPE, thus, specific attention is given to the effect that heat generation can have on long-term performance of these systems. Because of the complexity of this issue, the treatment of these various performance aspects is divided into two parts. The present part, Part I, reviews the various aspects of articulation performance. Part II presents results of friction, heating, and torque testing of various metal and ceramic hip systems. Criteria for frictional heating is also presented, along with discussion related to the various heat transfer mechanisms involved with heat dissipation.
In the present study an overall elastohydrodynamic analysis of synovial joints has been coupled with a study of the local, micro-elastohydrodynamic analysis action associated with surface asperities. The locally generated pressures have been found to have a remarkable ability to 'smooth' the initially rough cartilage surfaces as they pass through the loaded region. This analysis yields predictions of film thicknesses several times greater than the (reduced) 'effective' roughness of the opposing cartilage surfaces and, thus, not only brings analysis and experiment into much closer accord, but also offers a new and convincing explanation of the mode of lubrication of nature's remarkable bearings.
Comparative study of friction and wear behavior of UHMWPE during oscillatory sliding on cobalt chrome and titanium alloys in dry and lubricated environments
- Tetreault
Polyethylene wear against titanium alloy compared to stainless steel and cobalt-chrome alloys
- McKellop
The wear characteristics of ultra-high molecular weight polyethylene against a high density aluminum ceramic under wet (distilled water) and dry conditions
- Dowson