Investigation of the friction and surface degradation of innovative chondroplasty materials against articular cartilage

Understanding the wear of the biomaterial-cartilage interface is vital for the development of innovative chondroplasty. The aim of this study was to investigate a number of biphasic materials as potential chondroplasty biomaterials. Simple geometry friction and wear studies were conducted using bovine articular cartilage pins loaded against a range of single-phase and biphasic materials. The frictions of each biomaterial was compared within simple and protein-containing lubricants. Longer-term continuous sliding tests within a protein containing lubricant were also conducted at various loading conditions to evaluate the friction and degradation for each surface. All single-phase materials showed a steady rise in friction, which was dependent on the loss of interstitial fluid load support from the opposing cartilage pin. All biphasic materials demonstrated a marked reduction in friction when compared with the single-phase materials. It is postulated that the biphasic nature of each material allowed an element of fluid load support to be maintained by fluid rehydration and expulsion. In the longer-term study, significant differences in the articular cartilage pin (surface damage) between the positive control (stainless steel) and the negative control (articular cartilage) was found. The potential biphasic chondroplasty materials produced a reduction in articular cartilage pin damage when compared with the single-phase materials. The changes in surface topography of the cartilage pin were associated with increased levels of friction achieved during the continuous wear test. The study illustrated the importance of the biphasic properties of potential chondroplasty materials, and future work will focus on the optimization of biphasic properties as well as long-term durability, such that materials will more closely mimic the biotribology of natural articular cartilage.     

Boundary Lubrication of Steel Surfaces with Borate,Phosphorus, and Sulfur Containing Lubricants at Relatively Low and Elevated Temperatures

Prolonging the life of engineering components through lubricant formulation to achieve better wear resistance and higher oxidation stability is of paramount importance to many mechanical systems, such as automotive gears and bearings. This can be accomplished with formulated lubricants that limit the generation of wear debris causing severe abrasion and protect the contacting surfaces through the formation of wear-resistant tribofilms. In this study, a ball-on-disk tribometer was used to characterize the friction and wear properties of steel surfaces slid in the boundary lubrication regime. An experimental scheme was developed to allow the statistical screening of various lubricant formulations. Sliding experiments were performed in baths of different lubricants at relatively low and elevated temperatures, approximately 32 and 100°C, respectively, under conditions of constant load and sliding speed. Surface profilometry, optical microscopy, and scanning electron microscopy were used to characterize the dominant friction and wear mechanisms. The tribological properties were found to strongly depend on the temperature and the additives (e.g., borate, phosphorus, and sulfur) present in the blended lubricants. The superior high-temperature wear performance of the lubricant with the higher borate content is indicative of the formation of a durable tribofilm that reduces metal-to-metal adhesion, material transfer, and surface plowing by wear debris.     

Influence of hyaluronic acid on the time-dependent friction response of articular cartilage under different conditions

Therapeutic lubricant injections of hyaluronic acid are a relatively recent treatment for osteoarthritis. Their efficacy, however, in vivo has been subject to much debate. Frictional properties of cartilage-cartilage contacts under both static and dynamic loading conditions have been investigated, using healthy cartilage and cartilage with a physically disrupted surface, with and without the addition of a therapeutic lubricant, hyaluronic acid. Most of the cartilage friction models produced typical time-dependent loading curves, with a rise in static friction with loading time. For the dynamic loading conditions the rise in friction with loading time was dependent on the spatial (and time) variation in the load on the cartilage plate. For sliding distances of 4 mm or greater, when the cartilage plate was unloaded during sliding, the dynamic friction remained low whereas, with shorter sliding distances, the dynamic friction increased with increasing loading time. Static friction was higher than dynamic friction (under the same tribological conditions). The 'damaged' cartilage models produced higher friction than healthy cartilage under equivalent tribological conditions. It was shown that hyaluronic acid was an effective boundary lubricant for articular cartilage under static conditions with both healthy and damaged cartilage surfaces. Hyaluronic acid was less effective under dynamic conditions. However, these dynamic conditions had low friction values with the control lubricant because of the effectiveness of the intrinsic biphasic lubrication of the cartilage. It was only under the tribological conditions in which the cartilage friction was higher and rising with increasing loading time because of depletion of the intrinsic biphasic lubrication, that the role of hyaluronic acid as an effective therapeutic lubricant was demonstrated.     

A rig test to measure friction and wear of heavy duty diesel engine piston rings and cylinder liners using realistic lubricants

Laboratory tests to evaluate piston ring and cylinder liner materials for their friction and wear behavior in realistic engine oils are described to support the development of new standard test methods. A ring segment was tested against a flat specimen of gray cast iron typical of cylinder liners. A wide range of lubricants including Jet A aviation fuel, mineral oil, and a new and engine-aged, fully formulated 15W40 heavy duty oil were used to evaluate the sensitivity of the tests to lubricant condition. Test temperatures ranged from 25 to 100 °C. A stepped load procedure was used to evaluate friction behavior using a run-in ring segment. At 100 °C, all lubricants showed boundary lubrication behavior, however, differences among the lubricants could be detected. Wear tests were carried out at 240 N for 6 h at 100 °C with new ring segments. The extent of wear was measured by weight loss, wear volume and wear depth using a geometric model that takes into account compound curvatures before and after testing. Wear volume by weight loss compared well with profilometry. Laboratory test results are compared to engine wear rates.     

The lubrication effect of hyaluronic acid and chondroitin sulfate on the natural temporomandibular cartilage under torsional fretting wear

The aim of this study is to investigate the lubrication of hyaluronic acid (HA) and chondroitin sulfate (CS) on the condylar cartilage of the temporomandibular joint. The wear behaviour of bovine condyle cartilage was explored against a zirconia ball with different lubrications under torsional fretting mode. The worn cartilage morphologies were observed using scanning electron microscopy and hemotoxylin and eosin staining. The results indicated that HA or CS could significantly lower the friction torque and dissipated energy of fretting interface and reduce the damage of the articular cartilage surface compared to the control (phosphate‐buffered saline). The mixture (HA and CS) could provide better protection for the cartilage layer. Absence of good lubrication in overloading torsional fretting process caused excessive cartilage wear. High concentration and high molecular weight HA or CS acted as good boundary lubricants, and the lubrication effect of their mixture was better due to their synergistic function. Copyright © 2014 John Wiley & Sons, Ltd.     

Nanocomposite UHMWPE–CNT Polymer Coatings for Boundary Lubrication on Aluminium Substrates

The boundary lubrication regime plays a very important role in determining the life span of any of the two mating parts under liquid-lubricated conditions. It is during the start\stop cycles when insufficient fluid is available to fully separate the surfaces in relative motion and thus unusual wear takes place; a case of boundary lubrication. The aim of this work is to study the feasibility of using polymer coatings as boundary lubricants. This study investigates the friction and wear properties of ultra-high molecular weight polyethylene (UHMWPE) films coated on aluminium substrates under dry and base oil (without any additives)-lubricated conditions. In order to increase the load bearing capacity of the UHMWPE coatings, 0.1 wt% of single-walled carbon nanotubes are added. Experiments are carried out on a custom-built tribometer simulating a line contact between a polymer-coated cylindrical Al surface (shaft) and a flat uncoated Al plate as the counterface. The experimental parameters such as the normal load and the sliding speed are selected to simulate the boundary and mixed lubrication regimes for comparison purposes. Specific wear rates of the polymer films and bare Al surface under lubricated conditions are also calculated. Stribeck curves have been generated to evaluate the effectiveness of the pristine UHMWPE and the nanocomposite coatings in the various regimes of lubrication, especially the boundary lubrication regime. It is observed that the selected polymer coatings are effective in protecting the metallic surfaces without causing any observable oil contamination with wear debris.     

三种固液复合润滑系统的真空边界润滑特性

为研究MoS2/815Z、MoS2/RP4751和MoS2/RIPP4758三种固液复合润滑体系在真空边界润滑工况下的润滑特性,对三种固液复合润滑体系进行了真空往复滑动摩擦试验和真空螺旋轨道摩擦(SOT)试验研究,并对SOT试验后的球盘摩擦副平盘表面进行扫描电镜(SEM)和X射线能量色散谱仪(EDS)分析.试验结果表明...     

The Failure and Damage Mechanisms Under Friction of Copper in the EHL and Mixed EHL Regions

Recently, friction and wear behaviour of Copper (Cu)–steel pairs rubbed under different lubrication conditions were studied. The Stribeck curve was used to identify the different regimes of friction of copper with different virgin grain sizes: the elasto-hydrodynamic lubrication (EHL), mixed lubrication and boundary lubrication (BL) regimes. The aim of this work is the detailed analysis of the damage evolution under friction in the EHL and mixed EHL regions. The effects of load on the friction and the wear and damage mechanisms have been studied. The surfaces of Cu samples before and after friction have been analysed using SEM and AFM techniques as well as roughness and hardness measurements. It was shown that the mechanisms of damage and failure of Cu samples under friction in the EHL region are similar to the damage and failure mechanisms in Very High Cycle Fatigue. Friction in the EHL region is accompanied by initiation and coalescence of pores and microcracks. The effects of the coalescence of pores and microcracks observed in the EHL region are enlarged with a subsequent loading in the mixed EHL region. The effect of the loading rate on the transition from the EHL to BL region has been studied. It was shown that decreasing the loading rate increases significantly the load of the transition from the EHL to BL region. The pore and microcrack coalescence remain as the dominant damage mechanism under friction in the mixed EHL region with the low loading rate, while a lot of ploughing tracks and large delaminated regions appeared on the surface of Cu sample after friction with the higher loading rate.     

Boundary lubrication in vivo

Evidence is reviewed for the concept that the body employs essentially the same lubrication system in many sites in the body where tissues slide over each other with such ease. This system consists of fluid adjacent to surfaces coated with an oligolamellar lining of surface-active phospholipid (SAPL) acting as a back-up boundary lubricant wherever the fluid film fails to support the load--a likely event at physiological velocities. Particular attention is paid to the load-bearing joints, where the issue of identifying the vital active ingredient in synovial fluid is reviewed, coming down--perhaps predictably--in favour of SAPL. It is also explained how Lubricin and hyaluronic acid (HA) could have 'carrier' functions for the highly insoluble SAPL, while HA has good wetting properties needed to promote hydrodynamic lubrication of a very hydrophobic articular surface by an aqueous fluid wherever the load permits. In addition to friction and wear, release is included as another major role of boundary lubricants, especially relevant in environments where proteins are found, many having adhesive properties. The discussion is extended to a mention of the lubrication of prosthetic implants and to disease states where a deficiency of boundary lubricant is implicated, particular attention being paid to osteoarthritis.     

Nanodiamond-Based Nanolubricants: Investigation of Friction Surfaces

Synergistic compositions of detonation nanodiamond (DND) particles with polytetrafluoroethylene and molybdenum dialkyldithiophosphate were used in ring-on-ring, four-ball, and block-on-ring tests as an additive to polyalphaolefins and engine oils. Modest to significant reductions in the friction coefficients, wear, or both were observed. In the wear scars produced in the block-on-ring tests, the friction surfaces were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and profilometry. Significant polishing effects of the friction surfaces in lubricants containing DND were revealed in SEM observations and roughness measurements. The roughness of the scar surfaces produced in the presence of DND additives was about 35% lower than the roughness of the scars observed in pure oil experiments.     

人工关节材料的表面润滑设计与应用

人工关节的摩擦磨损问题仍然是基础研究中最重要的问题,借助表面改性技术改善假体的摩擦学性能是人工关节未来发展的必经之路。从润滑角度考虑,对假体关节材料摩擦性能的研究主要集中在表面功能化润滑结构设计以及新型仿生润滑剂研究两方面。针对功能化润滑结构,介绍表面织构设计以及聚合物刷的应用,分析表面织构参数对不同运动工况下摩擦副摩擦性能的影响,阐述表面织构的润滑机制;总结不同种类的聚合物刷结构对摩擦体系耐磨性能的调控,阐明"刷型"结构在摩擦界面的水润滑特点,提出环境介质对聚合物刷结构及性质的影响作用。针对关节润滑剂,介绍传统的关节滑液组分向聚合物仿生润滑剂的拓展。指出微/纳结构的嵌套设计与协同润滑以及润滑剂结构仿生与功能仿生的结合,将是未来的重要发展方向。     

一种新型摩擦材料在水润滑下的摩擦学性能研究

采用环块式摩擦磨损实验研究了一种新型摩擦材料在水润滑状态下不同载荷与转速对试样摩擦学性能的影响,并对比干摩擦条件下的摩擦学性能变化,借助磨损表面形貌观察分析其磨损机理。实验结果表明:水润滑条件下,摩擦系数随着载荷的增大而减小,随着转速的提高先增加后减小;磨损率随着载荷与转速的提高都减小。相同载荷与转速下,干摩擦时磨损机理以磨粒磨损和黏着磨损为主,而水润滑条件下水形成边界润滑,磨损机理以磨粒磨损和轻微的黏着磨损为主;水润滑条件下摩擦系数和磨损率均低于干摩擦,主要是由于水起到了润滑和冷却的作用,阻止了转移膜的形成,并在材料表面形成水膜起到了边界润滑的作用。     

Sb2S3和MoS2的协同作用对摩擦材料摩擦性能的影响

采用MPX-2000型磨损试验机和定速摩擦实验机分别测试不同载荷及不同温度下固体润滑剂Sb2 S3和MOS2对摩擦材料摩擦性能的影响,探讨2种固体润滑剂的协同作用;采用扫描电镜分析摩擦材料磨损后摩擦表面的微观形貌.结果表明,固体润滑剂Sb2 S3和MoS2具有良好的协同效应,可大大改善摩擦材料的摩擦性能,这是因为MOS2和Sb2 S3分别在制动过程中的低温段和高温段起到良好的润滑作用.当Sb2S3的体积分数为6%,MoS2的体积分数为3%时,摩擦材料的摩擦性能最佳.     

聚四氟乙烯纤维基层压材料的摩擦学行为研究

以无碱玻璃纤维布作为基材,以浸渍有聚四氟乙烯的棉纤维布为表层,以环氧树脂为黏合剂,经热压制备聚四氟乙烯纤维基层压材料;采用 MRH-03型高速环－块摩擦磨损试验机研究其在空气、纯水、海水介质中的摩擦学行为,利用扫描电镜观察并分析磨损表面的形貌及摩擦形式。结果表明,与基底材料相比,增加聚四氟乙烯棉纤维布后,材料的摩擦性能有明显的改善;加入水作为润滑介质后,由于水膜边界润滑的作用,特别是由于海水作为润滑介质时摩擦产生的淤泥状的 Mg （OH）2和 CaCO3的自润滑作用,摩擦因数和磨损率进一步减小。     

Influence of temperature on tribological behaviour of ionic liquids as lubricants and lubricant additives

Ionic liquids are low‐melting‐point salts composed entirely of ions, and many of them are liquids at room temperature. In recent years, studies have indicated that they might be good candidates for lubricants, either in neat or additive form. In this work, a sulfate‐based ionic liquid with a pyrollidinium cation was studied as neat lubricant and as additive for glycerol in lubrication of steel–steel contacts. Glycerol was chosen as the base oil because of its high polarity, which allows full miscibility with polar ionic liquids. Tests were performed on an oscillating friction and wear tribometer. The coefficients of friction and wear were measured. The tests were run at room temperature, 50 °C, 100 °C and 150 °C. By using profilometry, optical microscopy, scanning electron microscope and atomic force microscopy (AFM) analyses, it was shown that the ionic liquid plays an important role in the friction and wear reduction, as well as in the smoothening of the worn surface. Copyright © 2013 John Wiley & Sons, Ltd.     

Comparison of friction and lubrication of different hip prostheses

It is well documented that an important cause of osteolysis and subsequent loosening of replacement hip joints is polyethylene wear debris. To avoid this, interest has been renewed in metal-on-metal and ceramic-on-ceramic prostheses. Various workers have assessed the lubrication modes of different joints by measuring the friction at the bearing surfaces, using different lubricants. Measurements of friction factors of a series of hip prostheses were undertaken using carboxymethyl cellulose (CMC) fluids, silicone fluids, synovial fluid and different concentrations of bovine serum as the lubricant. The experimental results were compared with theoretical predictions of film thicknesses and lubrication modes. A strong correlation was observed between experiment and theory when employing CMC fluids or silicone fluids as the lubricant. Mixed lubrication was found to occur in the metal-on-metal (CoCrMo/CoCrMo) joints with all lubricants at a viscosity within the physiological range. This was also the case for the metal-on-plastic (CoCrMo/ultra-high molecular weight polyethylene) joints. The ceramic-on-ceramic (Al2O3/Al2O3) joints, however, exhibited full fluid film lubrication with the synthetic lubricants but mixed lubrication with the biological lubricants. Employing a biological fluid as the lubricant affected the friction to varying degrees when compared with the synthetic lubricants. In the case of the ceramic-on-ceramic joints it acted to increase the friction factor tenfold; however, for the metal-on-metal joints, biological fluids gave slightly lower friction than the synthetic lubricants did. This suggests that, when measuring friction and wear of artificial joints, a standard lubricant should be used.     

纳米K2Ti4O9晶须增强型固体润滑涂层在切削加工中的应用

为了减少切削加工中切削液的排放 ,改善环境 ,本研究用固体润滑剂代替切削液。在高温摩擦试验机上对四种固体润滑剂进行了摩擦试验和效果对比 ,筛选出纳米钛酸钾增强型复合固体润滑剂 ;将其涂覆在刀具表面进行 4 0Cr钢切削试验 ,干切削中切削速度为 14 0m/min时涂层刀具的后刀面磨损量是未涂层刀具的 1/ 6 ,比使用切削液时的磨损量也略有降低 ;随着切削速度的升高 ,涂层刀具的后刀面磨损量有所增加 ,但仍比未涂层的低 ,比使用润滑液的有所增高。AFM、SEM和EDX对摩擦表面的分析结果表明 :固体润滑膜涂覆在刀具表面 ,可改善刀具的润滑状况 ,有效地防止切屑和刀具的粘附 ,明显减少刀具的磨损     

石墨干膜润滑剂在碳钢表面摩擦磨损性能试验研究*

传统油或脂润滑剂在极端工况环境下无法满足碳钢类零件的减摩要求,采用干膜润滑剂是提高极端工况环境下碳钢表面摩擦磨损性能的可行性方法。采用超声波分散方法制备以石墨粉末为基体的干膜润滑剂,使用压力喷涂技术使其沉积在碳钢试件表面,在端面摩擦试验仪中开展干摩擦和石墨干膜润滑剂润滑下摩擦磨损性能对比性试验研究。试验结果表明：石墨干膜润滑剂在碳钢表面的沉积效果较好,沉积的石墨干膜润滑剂具有较好的润滑性能,可以有效地保护碳钢表面不被过度磨损;喷涂石墨干膜润滑剂的碳钢试件的工作寿命随着压力载荷和主轴转速的增大而缩短,负载和滑动速度的联合作用会加速涂层向稳定方向的过渡;磨损过程中形成的微观润滑剂颗粒会形成颗粒流润滑,适当添加石墨颗粒粉末可能会延长润滑剂正常发挥减摩作用的时间。制备的石墨干膜润滑剂为碳钢在极端工况环境下的减摩提供了支持。     

Next generation lubrication system for weapons

Current weapon system lubricants have performance limitations in extreme climatic conditions, specifically in sand and dust and cold environments. An alternative solid lubricant based lubrication system was investigated and validated using the ASTM subscale tests. The solid lubricants were selected and evaluated based on weapon system lubrication requirements. The solid lubrication systems were evaluated for coefficient of friction, wear, load carrying capacity, endurance (wear) life and corrosion resistance. The novel lubrication system showed superior subscale performance compared to current gun lubricants. It has the potential to provide much better performance than current gun lubricants, especially in sand, cold and humid environments.     

Development of a high-vacuum wear test apparatus mounted in a scanning electron microscope

The lubrication of sliding components in vacuum conditions offers unique challenges. High vacuum precludes the use of many conventional liquid lubricants because of vaporisation, while the lack of a naturally-occurring oxide film on metal surfaces may cause instant seizure following the failure of a lubricant. Solid lubricants, such as molybdenum disulphide and tungsten disulphide, are also used, but are less effective than more complex liquid lubrication mechanisms. New surface treatment processes, such as diamond-like carbon (DLC), are becoming available and may further reduce wear. The purpose of the present paper is to describe an apparatus that can evaluate solid lubricants under a wide range of contact conditions at vacua down to 3 × 10⁻⁷ Torr. The wear test stage is mounted in the chamber of a Scanning Electron Microscope (SEM), which allows real-time high magnification photography of the contact area. The complete stage may be moved in three planes to facilitate observation of the complete contact area. Realtime measurement of applied load and friction coefficient is also provided.