Biotribology of artificial hip joints

Hip arthroplasty can be considered one of the major successes of orthopedic surgery, with more than 350000 replacements performed every year in the United States with a constantly increasing rate. The main limitations to the lifespan of these devices are due to tribological aspects, in particular the wear of mating surfaces, which implies a loss of matter and modification of surface geometry. However, wear is a complex phenomenon, also involving lubrication and friction. The present paper deals with the tribological performance of hip implants and is organized in to three main sections. Firstly, the basic elements of tribology are presented, from contact mechanics of ball-in-socket joints to ultra high molecular weight polyethylene wear laws. Some fundamental equations are also reported, with the aim of providingthe reader with some simple tools for tribological investigations. In the second section, the focus moves to artificial hip joints, defining materials and geometrical properties and discussing their friction, lubrication and wear characteristics. In particular, the features of different couplings, from metal-on-plastic to metal-on-metal and ceramic-on-ceramic, are discussed as well as the role of the head radius and clearance. How friction, lubrication and wear are interconnected and most of all how they are specific for each loading and kinematic condition is highlighted. Thus, the significant differences in patients and their lifestyles account for the high dispersion of clinical data. Furthermore, such consideration has raised a new discussion on the most suitable in vitro tests for hip implants as simplified gait cycles can be too far from effective implant working conditions. In the third section, the trends of hip implants in the years from 2003 to 2012 provided by the National Joint Registry of England, Wales and Northern Ireland are summarized and commented on in a discussion.

Wettability Modification for Biosurface of Titanium Alloy by Means of Sequential Carburization

Microporous titanium carbide coating was successfully synthesized on medical grade titanium alloy by using sequential carburization.Changes in the surface morphology of titanium alloy occasioned by sequential carburization were characterized and the wettability characteristics were quantified.Furthermore,the dispersion forces were calculated and discussed.The results indicate that sequential carburization is an effective way to modify the wettability of titanium alloy.After the carburization the surface dispersion force of titanium alloy increased from 76.5×10^(-3)J·m^(-2) to 105.5×10^(-3) J·m^(-2),with an enhancement of 37.9 %.Meanwhile the contact angle of titanium alloy decreased from 83° to 71.5°,indicating a significant improvement of wettability,which is much closer to the optimal water contact angle for cell adhesion of 70°.

Study on Biotribological Behavior of the Combined Joint of CoCrMo and UHMWPE/BHA Composite in a Hip Joint Simulator

UHMWPE composites reinforced with Bovine Bone Hydroxyapatite(BHA)in different contents were prepared by heat pressing formation method.A hip joint wear simulator was used to investigate the biotribological behavior of UHMWPE/BHA composite acetabular cups against CoCrMo alloy femoral heads in bovine synovia lubrication at 37±1 ℃.It was found that the addition of BHA powder to UHMWPE can improve the hardness and creep modulus of UHMWPE/BHA composites,and decrease their wear rates under bovine synovia lubrication.When the content of BHA filler particles was up to 30 wt%, UHMWPE/BHA composites demonstrated the well design performances of the surface and biotribological properties.Fatigue, ploughing and slight adhesive wear were the main wear mechanisms for UHMWPE and its composites.In addition,the sizes of wear particles became larger with an increase in BHA powder addition.These results suggest that BHA filler is a desirable component to increase the wear resistance of UHMWPE/BHA composites for biomedical applications.

Biotribological behavior of ultra high molecular weight polyethylene composites containing bovine bone hydroxyapatite

Wear particles of ultrahigh molecular weight polyethylene （UHMWPE） are the main cause of long-term failure of total joint replacements. Therefore, increasing its wear resistance or bioactivity will be very useful in order to obtain high quality artificial joints. In our study, UHMWPE composites filled with the bovine bone hydroxyapatite （BHA） were prepared by the method of compression moulding. A ball-on-disc wear test was carried out with a Universal Micro-Tribometer to investigate the friction and wear behavior of a Si3N4 ceramic ball, cross-sliding against the UHMWPE/BHA composites with human plasma lubrication. At the same time, the profiles of the worn grooves on the UHMWPE/BHA surface were scanned. The experimental results indicate that the addition of BHA to UHMWPE had a significant effect on the biotribological behavior of UHMWPE cross-sliding against the Si3N4 ceramic ball. The addition of BHA powder enhanced the hardness and modulus of elasticity of these composites and decreased the friction coefficients and wear rates under conditions of human plasma lubrication. When the added amount of BHA powders was up to 20%-30%, UHMWPE/BHA composites demonstrated the designed performance of the mechanical properties and biotribological behavior.

Effects of TaN nanoparticles on microstructure,mechanical properties and tribological performance of PEEK coating prepared by electrophoretic deposition

In order to solve the friction,wear and lubrication problems of titanium,a series of TaN/ployether−ether−ketone(PEEK)coatings were developed by electrophoretic deposition,and the effects of TaN nanoparticles on the microstructure,mechanical properties and tribological performance of coatings were explored.Results manifest that the introduction of TaN nanoparticles into PEEK coatings could improve the deposition efficiency,enhance the resistant deform capacity,increase the hardness,elastic modulus and adhesive bonding strength.Compared with the pure PEEK coating,the friction coefficient of P-TN-3 was greatly reduced by 31.25%.The wear resistance of P-TN-3 was also improved in huge boost,and its specific wear rate was decreased from 9.42×10^(−5) to 1.62×10^(−5) mm^(3)·N^(−1)·m^(−1).The homogeneous composite TaN/PEEK coatings prepared by electrophoretic deposition were well-adhered to the titanium alloy substrate,TaN nanoparticles could improve the strength of PEEK coating,and provide wear-resistance protection for titanium alloys.

Anthropomorphic Classification of Tactile Qualities of Woven Fabrics Based on Skin/Textile Friction-Induced Vibrations

The common method classifying tactile qualities of fabrics is indirectly based on their difference of purely mechanical and physical properties. When human skin slides across fabric surfaces, the friction interaction between fabrics and skin will occur and trigger the cutaneouS tactile receptors, which are responsible for perceived tactile sensation. By the extracted features from friction- induced vibration signals, this paper presents an anthropomorphic classification method classifying tactile qualities of fabrics. The friction-induced vibration signals are recorded by a three-axis accelerator sensor, and the entice testing procedure is conducted in an anthropomorphic way to obtain vibration signals. The fast Fourier transform （FFT） is applied to analyzing the recoded signals, and then the classification features are extracted from the FFT data by the neurophysiological properties of tactile receptors. The extracted features are used to classify fabric samples by the softness sensation and the roughness sensation, respectively, and the classification performance is checked by a comparison with those in a sensory evaluation procedure. The results showed that the anthropomorphic objective classification method was precise and efficient to clarify tactile qualities of woven fabrics.

Tribological properties of the beetle leg joints

Tribological properties of femoro-tibial leg joints in two beetles,darkling beetle Zophobas morio and Congo rose chafer Pachnoda marginata were studied.Very low friction of 0.004 was revealed by the direct measurements in the joint.It is assumed that semi-solid lubricant functioning as in technical bearings is one of the leading factors of the friction minimization.Dependence of the surface texture and physical chemical properties(hydrophobicity)on the cuticle friction was analysed.Contribution of the surface texture to the tribological properties of contacting surfaces was examined by the measurement in the tribosystem“contacting surface/glass”.It is supposed that coefficient of friction(COF)decreases with decrease of surface roughness.At the same time,no statistically significant correlation was found between the hydrophobicity of the surface and the value of the friction coefficient.

Elevating mechanical and biotribological properties of carbon fiber composites by constructing graphene-silicon nitride nanowires interlocking interfacial enhancement

Carbon fiber reinforced dual-matrix composites(CHM)including carbon fiber reinforced hydroxyapatite-polymer matrix composites(CHMP)and carbon fiber reinforced hydroxyapatite-pyrolytic carbon matrix composites(CHMC)have great potential application in the field of artificial hip joints,where a combination of high mechanical strength and excellent biotribological property are required.In this work,the graphene-silicon nitride nanowires(Graphene-Si_(3)N_(4)nws)interlocking interfacial enhancement were designed and constructed into CHM for boosting the mechanical and biotribological properties.The graphene and Si_(3)N_(4)nws interact with each other and construct interlocking interfacial enhancement.Benefiting from the Graphene-Si_(3)N_(4)nws synergistic effect and interlocking enhancement mechanism,the mechanical and biotribological properties of CHM were promoted.Compared with CHMP,the shear and compressive strengths of Graphene-Si_(3)N_(4)nws reinforced CHMP were increased by 80.0% and 61.5%,respectively.The friction coefficient and wear rate were reduced by 52.8% and 52.9%,respectively.Compared with CHMC,the shear and compressive strengths of Graphene-Si_(3)N_(4)nws reinforced CHMC were increased by 145.4% and 64.2%.The friction coefficient and wear rate were decreased by 52.3% and 73.6%.Our work provides a promising methodology for preparing Graphene-Si_(3)N_(4)nws reinforced CHM with more reliable mechanical and biotribological properties for use in artificial hip joints.

A review of recent advances in tribology

The reach of tribology has expanded in diverse fields and tribology related research activities have seen immense growth during the last decade.This review takes stock of the recent advances in research pertaining to different aspects of tribology within the last 2 to 3 years.Different aspects of tribology that have been reviewed including lubrication,wear and surface engineering,biotribology,high tem perature tribology,and computational tribology.This review attempts to highlight recent research and also presents future outlook pertaining to these aspects.It may however be noted that there are limitations of this review.One of the most important of these is that tribology being a highly multidisciplinary field,the research results are widely spread across various disciplines and there can be omissions because of this.Secondly,the topics dealt with in the field of tribology include only some of the salient topics(such as lubrication,wear,surface engineering,biotribology,high tem perature tribology,and computational tribology)but there are many more aspects of tribology that have not been covered in this review.Despite these limitations it is hoped that such a review will bring the most recent salient research in focus and will be beneficial for the growing community of tribology researchers.

A review of advances in tribology in 2020–2021

Around 1,000 peer-reviewed papers were selected from 3,450 articles published during 2020–2021,and reviewed as the representative advances in tribology research worldwide.The survey highlights the development in lubrication,wear and surface engineering,biotribology,high temperature tribology,and computational tribology,providing a show window of the achievements of recent fundamental and application researches in the field of tribology.

Slippery Surface of Nepenthes alata Pitcher： The Role of Lunate Cell and Wax Crystal in Restricting Attachment Ability of Ant Camponotus japonicus Mayr

This study attempts to investigate how the slippery surface of Nepenthes alata pitchers restricts the attachment ability of ant Camponotus japonicus Mayr, via climbing behavior observation and friction force measurement. Ants exhibited ineffective climbing behaviors and rather small friction forces when attached to upward-oriented slippery surfaces, but opposite phenomena were shown when on inverted surfaces. Friction forces of intact, claw tip-removed and pad-destroyed ants were measured on intact and de-waxed slippery surfaces, exploring the roles of wax crystals and lunate cells in restricting ant＇s attachment. On downward-directed slippery surfaces, greater forces were exhibited by intact and pad-destroyed ants; on the two slippery sur- faces, pad-destroyed ants presented slightly smaller forces and clawless ants generated considerably smaller forces. Somewhat different force was provided by clawless ants on upward and downward oriented slippery surfaces, and slightly higher force was shown when ants climbed on wax-removed surface. Results indicate that the lunate cells contribute greatly to decrease the friction force, whereas the wax crystals perform a supplementary role. Mechanical analysis suggests that the directionally growing lunate cells possess a sloped structure that effectively prevents the claw＇s mechanical interlock, reducing the ant＇s attachment ability considerably. Our conclusion supports a further interpretation of slippery surface＇s anti-attachment mecha- nism, also provides theoretical reference to develop biomimetic slippery plate to trap agricultural insect.

Influence of synovia constituents on tribological behaviors of articular cartilage

The extremely low friction and minimal wear in natural synovial joints appear to be established by effective lubrication mechanisms based on appropriate combination of articular cartilage and synovial fluid.The complex structure of cartilage composed of collagen and proteoglycan with high water content contributes to high load-carrying capacity as biphasic materials and the various constituents of synovial fluid play important roles in various lubrication mechanisms.However,the detailed differences in functions of the intact and damaged cartilage tissues,and the interaction or synergistic action of synovia constituents with articular cartilage have not yet been clarified.In this study,to examine the roles of synovia constituents and the importance of cartilage surface conditions,the changes in friction were observed in the reciprocating tests of intact and damaged articular cartilage specimens against glass plate lubricated with lubricants containing phospholipid,protein and/or hyaluronic acid as main constituents in synovial fluid.The effectiveness of lubricant constituents and the influence of cartilage surface conditions on friction are discussed.In addition,the protectiveness by synovia constituents for intact articular cartilage surfaces is evaluated.

Instrumented Indentation Investigation on the Viscoelastic Properties of Porcine Cartilage

Articular cartilage lubricates the contact surfaces in human joints and provides a shock-absorbing effect which protects the joint under dynamic loading. However, this shock-absorbing effect is gradually reduced as the result of normal wear, tear and aging-related cartilage loss. Thus, with the increasing average human life expectancy, the issue of joint health has attracted significant interest in recent decades. In developing new materials for the repair or regeneration of damaged articular cartilage, it is essential that the difference in the mechanical properties of healthy and damaged cartilages is well-understood. In the present study, the hardness and Young＇s modulus of damaged and healthy porcine articular cartilage samples are evaluated via a quasi-static nanoindentation technique. A dynamic mechanical analysis method is then applied to determine the viscoelastic properties of the two samples. The results presented in this study provide a useful insight into the mechanical properties of articular cartilage at the mesoscale, and therefore fill an important gap in the literature.

Synthesis of titanium carbide coating on Ti15Mo alloy and its tribological behaviour

Ti15Mo alloy has been regarded as one of the most potential biomedical materials due to its excellent performance.However,the low hardness and poor wear resistance of titanium alloy limit the further application.Therefore,high temperature solid carburising technology was performed on the surface of Ti15Mo alloys to prepare titanium carbide(TiC)coating with graphene(G)as the carburising agent.The microstructure,mechanical properties,and tribological properties of TiC coating under different lubricants were investigated.Results showed that TiC coating was closely bonded to the titanium substrate.The maximum thickness of TiC coating treated with 1150°C was approximately 184.02μm,and the microhardness of alloys treated with 1100°C can achieve 1221.5 HV.All modified Ti15Mo alloys showed improved tribological performance compared to the original samples.The wear mechanisms of modified Ti15Mo alloys were abrasive wear and adhesive wear under the SBF lubricant,and the TiC coating was slightly peeled off.The overall friction coefficient and wear rate under 25%calf serum lubricant were lower than the SBF lubricant,and surface scratches were almost absent,and slight abrasive wear and adhesive wear occurred on the surface.

Finger pad friction and tactile perception of laser treated,stamped and cold rolled micro-structured stainless steel sheet surfaces

Tactile perception is a complex system,which depends on frictional interactions between skin and counter-body.The contact mechanics of tactile friction is governed by many factors such as the state and properties of skin and counter-body.In order to discover the connection between perception and tactile friction on textured stainless steel sheets,both perception experiments (subjective) and tactile friction measurements (objective) were performed in this research.The perception experiments were carried out by using a panel test method to identify the perceived roughness,perceived stickiness and comfort level from the participants.For the friction experiments,tactile friction was measured by a multi-axis force/torque transducer in vivo.The perceived stickiness was illustrated as an effective subjective stimulus,which has a negative correlation to the comfort perception.No significant evidence was revealed to the connection between the perceived roughness and comfort perception,and this relationship may be influenced by the participants' individual experience,gender and moisture level of skin.Furthermore,the kinetic tactile friction was concluded as an objective stimulus to the comfort perception with a negative correlation.

Friction behaviour between a laparoscopic grasper and the large intestine during minimally invasive surgery

Slippage is a common phenomenon between laparoscopic graspers and tissues during minimally invasive surgery,which may lead to inefficient surgical operations,prolonged operation time,and increased patient suffering.The stability factors related to the friction behaviour between laparoscopic graspers and the large intestine,including bio-surface liquids,pulling angle,and surface profile of graspers,were studied.The friction behav-iour at the large intestine-grasper interface was tested using a UMT-II tribometer under the conditions of clamping force of 1-4 N,sliding displacement of 15 mm,and sliding velocity of 2 mm/s to simulate the grasping and pulling operations of soft tissue.The results showed that the bio-surface liquid(serum)of the large intestine significantly decreased the friction coefficient,thus reducing the grasping efficiency.A pulling angle of 15°could generate the peak frictional force and enhance the grasping stability.The frictional force increased with the ratio of the profile surface area of the grasper.These results demonstrate that the grasping stability can be improved by changing either the bio-surface liquid condition or the pulling angle.In addition,a grasper with a larger profile surface area can also prevent slippage due to its significant influence on the pressure distribution and actual contact area for tissue retention.

The influence of lubricant temperature on the wear of total knee replacements

Experimental in vitro simulation can be used to predict the wear performance of total knee replacements.The in vitro simulation should aim to replicate the in vivo loading,motion and environment experienced by the joint,predicting wear and potential failure whilst minimising test artefacts.Experimental wear simulation can be sensitive to envi-ronmental conditions;the environment temperature is one variable which should be controlled and was the focus of this investigation.In this study,the wear of an all‐polymer(PEEK‐OPTIMA™polymer‐on‐UHMWPE)total knee replacement and a conventional cobalt chrome‐on‐UHMWPE implant of similar initial surface topography and geometry were investigated under elevated temperature conditions.The wear was compared to a previous study of the same implants under simulator running temperature(i.e.without heating the test environment).Under elevated temperature conditions,the wear rate of the UHMWPE tibial inserts was low against both femoral component materials(mean<2 mm3/million cycles)and significantly lower(p<0.05)than for investigations at simulator running temperature.Protein precipitation from the lubricant onto the component articulating surfaces is a possible explanation for the lower wear.This study highlights the need to understand the influence of different variables including envi-ronmental temperature to minimise the test artefacts during wear simulation which may affect the wear rates.

One-step method to enhance biotribological properties and biocompatibility of DLC coating by ion beam irradiation

A one-step method was developed to create a highly biocompatible micropatterned surface on a diamond-like carbon(DLC)through irradiation with a nitrogen ion beam and thus enhance the biocompatibility of osseointegrated surfaces and biotribological performance of articular surfaces.The biocompatibility and biotribological mechanisms were analyzed in terms of the structure and morphology of DLC.It was demonstrated that a layer enriched in sp^(3) C-N bonds was formed on the surface of the DLC after nitrogen ion beam irradiation.Moreover,with an increase in the radiation dose,the content of sp^(3) C-N on the DLC surface increased significantly,and the biocompatibility was positively correlated with it.The adhesion of the MC3T3 osteoblasts increased significantly from 32%to 86%under an irradiation dose of 8×10^(15) ions/cm^(2).In contrast,the micropattern had a significant negative effect on the adhesion of the osteoblasts as it physically hindered cell expansion and extension.The micropattern with a depth of 37 nm exhibited good friction properties,and the coefficient of friction was reduced by 21%at relatively high speeds.

Mechanical and Biotribological Properties of PVA/SB Triple-Network Hydrogel for Biomimetic Artificial Cartilage

Poly (vinyl alcohol) hydrogel has been perceived as a promising replacement for articular cartilage due to its superior water-absorption ability and excellent biocompatibility, but its mechanical properties are still insufficient. In this study, the poly (vinyl alcohol)/sodium tetraborate triple-network (PVA/SB TN) hydrogel was developed by repeated freeze–thaw method. Scanning electron microscopy images demonstrated that the structure of as-prepared hydrogels was three-dimensional porous network structure similar to that of natural articular cartilage. Compared to the pure PVA hydrogel, the mechanical performance of the PVA/SB TN hydrogels were improved by 116% and 461% in tensile and compressive strengths, respectively. This was mainly because that the complexation reaction between the PVA and SB strengthened the stability of the hydrogel network. Notably, the biotribological performance of PVA hydrogel has also been improved significantly. Even at high load, the friction coefficient of the PVA/SB TN hydrogel was both very low in calf serum or deionized water. This PVA/SB TN hydrogel with good mechanical property and low friction has high application potential in cartilage repair.

The correlation between biotribological function and structural characteristics of bamboo rat teeth

Chinese bamboo rats consume a diet that consists mainly mechanically demanding bamboo.The ability of the rats to process food depends on the capacity of their teeth to resist wear during biting and chewing.The mechanisms of the bamboo rat teeth were determined by investigating and correlating the structure and tribological properties of the teeth.The rat's incisor has a cutting-edge cusp and outer enamel iron pigmentation,making the teeth harder,more resistant to acid attacks,and improving the resistance to cracking.Additionally,the incisor is designed to self-sharpen.The complex morphology at the macroscale,and the three-dimensional fabric body formed by densely packed rods and inter-rods at the microscale of molar enamel benefit molar rapid capture and effective breaking of bamboo,resisting the high stresses required to process bamboo without wear.The results of the structure-function relations of bamboo rat teeth in this study may provide new ideas for improving plant cutting and grinding tools.