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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. [ABSTRACT FROM AUTHOR]

This work investigates the effect of surface texturing on the coefficient of friction (COF) of tibial inserts (TIs), of total knee replacements (TKRs), using a servomechanical knee simulator operating under the conditions prescribed by ISO 14243-3:2014, which requires strict control of flexion/extension (FE), anterior/posterior displacement (AP), inward/outward rotation (IOR) movements, and load variation. Tests were carried out lubricating with fetal bovine serum solution with a protein concentration of 20 g/L at 37 ± 2 °C. TIs were manufactured by fused deposition modeling (FDM) using polylactic acid (PLA) because of the advantages associated with rapid prototyping and customization. The acquired COF data were analyzed using statistical parametric mapping (SPM) to determine how the surface of the TIs affects the COF, identifying ranges where significant differences occurred. Textured surfaces led to significant reductions in COF during the swing phase of the walking cycle. [ABSTRACT FROM AUTHOR]

Cartilage degeneration is a characteristic of osteoarthritis (OA), which is often observed in aging populations. This degeneration is due to the breakdown of articular cartilage (AC) mechanical and tribological properties primarily attributed to lubrication failure. Understanding the reasons behind these failures and identifying potential solutions could have significant economic and societal implications, ultimately enhancing quality of life. This review provides an overview of developments in the field of AC, focusing on its mechanical and tribological properties. The emphasis is on the role of lubrication in degraded AC, offering insights into its structure and function relationship. Further, it explores the fundamental connection between AC mechano-tribological properties and the advancement of its degradation and puts forth recommendations for strategies to boost its lubrication efficiency. [ABSTRACT FROM AUTHOR]

Several new-generation synthetic biodegradable polymers have been developed specifically for biomedical applications in the last two decades. Polycaprolactone (PCL) was chosen as the polymer matrix in this study because it is known for its ease of synthesis, commercial availability, and excellent biocompatibility. Carbon Quantum Dots (CQDs), one of the carbon nanostructures with superior properties, were used as fillers to produce PCL film nanocomposites with improved biotribological properties. The biotribological behavior of (Sample of KCQDs produced from Rosehip) K-CQDs filled PCL matrix nanocomposite films containing 0.3 and 2.0 wt. % KCQDs filler were investigated in sliding against an alumina (Al2O3) counterface by a constant loading (2.5 N) and sliding speed (1.7 cm s-1) experiments carried out in a reciprocating friction testing machine in 0.154 M isotonic salt solution. PCL/K-CQDs-2.0 film had lower friction coefficient value (0.304) with a 70% decrease, and wear rate (0.00051 mm3/Nm; 65% decrease) compared to PCL/K-CQDs-0.3. The surface images of PCL/K-CQDs-2.0 film after the wear test indicated that the wear width trace and the adhesive wear traces decreased. In addition, the absence of cracks on the worn surface showed that both films were resistant to plastic deformation. [ABSTRACT FROM AUTHOR]

Proteins can adsorb on the surface of materials, such as soft contact lenses (SCLs), and can affect the hydrophobicity, roughness, and surface properties of the contact lenses (CLs), which, in turn, can influence the friction between the lenses and the ocular surface. Excessive friction between contact lenses and the ocular surface can lead to discomfort for the wearer and may cause irritation or inflammation of the cornea, better known as corneal ulcers (keratitis). Bovine Serum Albumin (BSA) is often used as a standard protein in biocompatibility testing of materials, including contact lenses. One standard commercial contact lens was tested under lubricated conditions to access the coefficient of friction (CoF). The contact was lubricated with a tear-like fluid (TLF) solution containing six different concentrations of BSA. In all cases, good linearity of the results of the friction force was verified, suggesting that the first friction law can be applied to determine the value of the coefficient of friction. It was found that friction increases with the increase in protein concentration. [ABSTRACT FROM AUTHOR]

The human jaw is a complex biomechanical system involving different anatomical components and an articulated muscular system devoted to its dynamical activation. The numerous actions exerted by the mandible, such as talking, eating or chewing, make its biomechanical comprehension absolutely indispensable. To date, even if research on this topic has achieved interesting outcomes using in vitro testing, thanks to the development of new apparatus and methods capable of performing more and more realistic experiments, theoretical modeling is still worthy of investigation. In light of this, nowadays, the Finite Element Method (FEM) approach constitutes certainly the most common tool adopted to investigate particular issues concerning stress–strain characterization of the human jaw. In addition, kinematics analyses, both direct and inverse, are also diffuse and reported in the literature. This manuscript aimed to propose a critical review of the most recurrent biomechanical models of the human mandible to give readers a comprehensive overview on the topic. In light of this, the numerical approaches, providing interesting outcomes, such as muscular activation profiles, condylar forces and stress–strain fields for the human oral cavity, are mainly differentiated between according to the joint degrees of freedom, the analytical descriptions of the muscular forces, the boundary conditions imposed, the kind of task and mandible anatomical structure modeling. [ABSTRACT FROM AUTHOR]

With low wear rates shown by contemporary bearing materials of total hip prostheses, the standard deviation of wear rate is relatively high. Therefore, large sample sizes are needed for an adequate power of test. Because wear tests take a long time, it is practical to test several samples simultaneously. A new high-capacity, multidirectional wear test device, called the SuperCTPOD-200, was introduced. A 3 million-cycle wear test with an unprecedented sample size of 200 was performed for VEXLPE. The duration of the test was 6 weeks. The wear factor was normally distributed with a mean ± SD of 1.64 × 10−7 mm3/Nm ± 0.22 × 10−7 mm3/Nm (n = 200). The observation that SD was 13.1% of the mean can be useful in power analyses of future tests with other highly cross-linked polyethylenes. Burnishing was the most typical feature on the worn pins, which was in agreement with clinical findings on retrieved acetabular liners. The present study emphasizes statistics that often plays a minor role only in wear studies. [ABSTRACT FROM AUTHOR]

In recent years, endovascular treatments, in which a treatment device such as a catheter is inserted into a blood vessel to directly approach a lesion, have become increasingly popular worldwide. For safer treatment and further optimization of medical devices, a deeper understanding of the vascular biotribology of the medical devices, biomodels, and blood vessels and an appropriate evaluation method are required. This review paper presents the current state of research on the evaluation of the friction between an intravascular device and a vascular biomodel. We review the experimental conditions, including the sample shape, sliding speed, contact pressure, lubricant, materials, and temperature. Standardized methods should be established for evaluating the friction between an intravascular device and a vascular biomodel.

Tribology is related to all studies on friction, wear, and lubrication. One of the main aims of these studies is a reduction in friction and wear. Tribology is extremely vast, being also multidisciplinary and interdisciplinary. Therefore, it is very difficult to organize the several tribology subjects in an unique way and different classifications have been proposed by different authors. In this work, several subjects treated by tribology are reviewed and organized in six branches: Fundamental Tribology, Tribology of Materials and Lubricants, Micro and Nanotribology, Industrial Tribology, Biotribology, and New Frontiers of Tribology. The main subjects treated by the six branches are briefly reviewed in this paper in order to highlight the vastness of tribology and its important contribution to sustainability. Particularly, friction and wear reductions are strictly related to greater efficiency and material saving, which means less energy losses and material wastes, less pollution and therefore a more sustainable life according to the sustainable development goals. The connections among the latter and the several different tribological subjects are discussed. [ABSTRACT FROM AUTHOR]

The presence of wear of the joint cuticle of the beetle legs is demonstrated experimentally and is represented by abrasive wear. Presence of the abrasive wear in the natural‐habiting beetles of various families is also established. Abrasive wear comprises of both two‐body and three‐body wear as a result of the action of particles that have entered the joint. The presence of the sliding wear in the absence of abrasive particles is not found. The wear effects are represented by microcuttings, indentations, cracking, delamination, brittle fracturing, and destruction of the surface layer (epicuticle). The correlation of quantitative indicators of wear between the types of experimental substrates (paper, wood, sand) and the length of exposure of beetles on a particular substrate turned out to be very weak. It is hypothesized that the lubricating material in the leg joints of beetles may provide an anti‐wear function by binding particles and facilitating their removal thereby reducing surface damage by sharp asperities, and protecting the damaged surface to prevent further wear. [ABSTRACT FROM AUTHOR]

PEEK has been widely used in orthopedic implants for three decades. However, poor hydrophilicity and lower tribological properties are the weaknesses of PEEK that need to be optimized in artificial joint applications. Zwitterionic sulfobetaine methacrylate (SBMA) polyelectrolyte brushes are prepared on the PEEK surface by UV irradiation to improve the hydrophilicity and biotribological properties. The three‐factor and three‐level orthogonal experiments are designed to investigate the effects of monomer concentration, irradiation time, and temperature of the grafting quantity of SBMA on the PEEK surface. The composition of the grafted PEEK specimens is characterized by attenuated total reflection Fourier transform infrared spectroscopy (ATR‐FTIR) and X‐ray photoelectron spectroscopy (XPS). Hydrophilicity and biotribological properties are also characterized. Results show that SBMA is successfully grafted onto the PEEK surface by UV‐induced grafting polymerization, and the effects of the three process parameters on the grafting quantity are ranked as concentration > time > temperature. The hydrophilicity and biotribological properties are significantly improved due to the graft of the hydrophilic PSBMA polyelectrolyte brushes, and the improved biotribological can be attributed to the load‐bearing capacity of PSBMA polyelectrolyte brush and the boundary lubrication formed by the adsorption of water molecules. [ABSTRACT FROM AUTHOR]

This study employs molecular dynamics simulations to explore nanoscale friction behaviour as a function of varying loading and sliding speeds on a developed top-layer articular cartilage contact interface atomistic model. To investigate nanotribological behaviour, sliding speed variations on the normal force, friction force, non-bonded interaction energy and interface temperature is obtained at the inter-cartilage interface. Analysis conducted at high velocity in a simplified tissue-like hydrated environment revealed ice-like dynamic smooth sliding behaviour of protein chains when cartilage interfaces are even 3.8 Å apart. With an increase in velocity, the coefficient of friction (COF) increases significantly in a hydrated environment. Additionally, at lower loads, the effect of sliding velocity is more pronounced than at higher loads. However, results show that articular cartilage adapts to higher load and speed sliding conditions exhibiting lower friction (COF-0.03–1.17) by means of interfacial water rearrangements and protein side-chain non-bonded interactions reducing heavy shear deformation. This is attributed to an alteration in the load-bearing and friction mechanism owing to water rearrangement and adsorption at nanoconfined biointerfaces. This study provides mechanistic insights into friction mechanisms at the cartilage interface which could lead to wear-like conditions under physiological sliding contact conditions, thereby facilitating the design of better implants. [ABSTRACT FROM AUTHOR]

Abstract 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 184.02 μm, 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.

Nanoparticles are promising candidates as direct therapeutics and delivery systems for osteoarthritis treatments, primarily via intraarticular injection, but little is known about the impact on sliding behavior for a soft material surface like cartilage that would be encountered in a joint. Nanoparticle additives have primarily been studied in the context of hard material interfaces, such as metals or metal oxides, where different lubricating or anti-wear mechanisms depend sensitively on chemical composition, size, and concentration. To understand what nanoparticle parameters influence in situ (in a fluid environment) frictional behavior of soft materials, polyacrylamide (PAM) hydrogels were used as a model soft material platform. Friction tests were conducted in a rheometer with a tribology adapter, with PAM hydrogels molded in a petri dish and immersed in different nanoparticle containing fluid environments. A range of nanoparticle compositions were selected to compare broad categories: gold (metal) with a citrate capping ligand, nanodiamond (carbon), and zirconium dioxide (metal oxide). Comparing surface chemistry, concentration, and degree of aggregation, both nanoparticle surface chemistry and nanoparticle solution viscosity were found to modulate in situ hydrogel friction.

This review explores the intersection of tribology and dermatology, explicitly focusing on studying the human skin and drawing inspiration from natural systems. It investigates animal adaptations and their implications for biotribological applications, with examples such as the friction anisotropy and wear tolerance of snakeskin, the healing properties of fish skin and the lotus effect for reducing adhesion in biomedical devices. Understanding human skin presents challenges due to its complex structure and variability influenced by age, gender, race and environment. The paper discusses in vivo and ex vivo measurements, substitute models replicating human skin properties and contact mechanics considerations. It explores contact models, measurement methods and factors impacting skin friction, emphasising the interplay between adhesion and deformation components. Techniques such as atomic force microscopy and the colloidal probe technique provide insights into mechanical properties and molecular interactions. By comprehending the complexities of human skin and its tribological behaviour, researchers can develop innovative solutions in areas ranging from soft robotics to medical research and aerospace technology.

Abstract 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 environmental 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

Abstract The presence of wear of the joint cuticle of the beetle legs is demonstrated experimentally and is represented by abrasive wear. Presence of the abrasive wear in the natural‐habiting beetles of various families is also established. Abrasive wear comprises of both two‐body and three‐body wear as a result of the action of particles that have entered the joint. The presence of the sliding wear in the absence of abrasive particles is not found. The wear effects are represented by microcuttings, indentations, cracking, delamination, brittle fracturing, and destruction of the surface layer (epicuticle). The correlation of quantitative indicators of wear between the types of experimental substrates (paper, wood, sand) and the length of exposure of beetles on a particular substrate turned out to be very weak. It is hypothesized that the lubricating material in the leg joints of beetles may provide an anti‐wear function by binding particles and facilitating their removal thereby reducing surface damage by sharp asperities, and protecting the damaged surface to prevent further wear.

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 184.02 μm, 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. [ABSTRACT FROM AUTHOR]

Dental prostheses are currently a valid solution for replacing potential missing tooth or edentulism clinical condition. Nevertheless, the oral cavity is a dynamic and complex system: occlusal loads, external agents, or other unpleasant events can impact on implants functionality and stability causing a future revision surgery. One of the failure origins is certainly the dynamic loading originated from daily oral activities like eating, chewing, and so on. The aim of this paper was to evaluate, by a numerical analysis based on Finite Elements Method (FEM), and to discuss in a comparative way, firstly, the stress-strain of two different adopted dental implants and, subsequently, their fatigue life according to common standard of calculations. For this investigation, the jawbone was modeled accounting for either isotropic or anisotropic behavior. It was composed of cortical and cancellous regions, considering it completely osseointegrated with the implants. The impact of implants' fixture design, loading conditions, and their effect on the mandible bone was finally investigated, on the basis of the achieved numerical results. Lastly, the life cycle of the investigated implants was estimated according to the well-established theories of Goodman, Soderberg, and Gerber by exploiting the outcomes obtained by the numerical simulations, providing interesting conclusions useful in the dental practice. [ABSTRACT FROM AUTHOR]

Patients with knee osteoarthritis often receive glucocorticoid (GC) or hyaluronic acid (HA) injections to alleviate symptoms. This study evaluated the impact of Triamcinolone Hexacetonide (a GC), HA, and a combination of both on bovine osteochondral grafts exposed to IL-1β and IL-17 in an ex vivo culture. Metabolic activity increased with GC treatment. GCs and GCs/HA counteracted cytokine effects, with gene expressions similar to untreated controls, while HA alone did not. However, HA improved the coefficient of friction after two weeks. The highest friction values were observed in GC-containing and cytokine-treated groups. Cytokine treatment reduced tissue proteoglycan content, which HA could mitigate, especially in the GC/HA combination. This combo also effectively controlled proteoglycan release, supported by reduced sGAG release. Cytokine treatment led to surface cell death, while GCs, HA, or their combination showed protective effects against inflammation. The GC/HA combination had the best overall results, suggesting its potential as a superior treatment option for osteoarthritis. [ABSTRACT FROM AUTHOR]

The radula is the ingesta‐gathering structure in Mollusca. As interface, it has to perform various tasks without functional deterioration caused by wear. Wear prevention is well investigated in mollusks that forage on rocks and that generate high punctual pressure with their hard teeth, which contain high inorganic contents at their tips. In mollusks that forage on softer substrate, such as sand surfaces, and have relatively soft teeth, wear prevention has not been a focus of study before. Here, we studied the teeth of Limnotrochus thomsoni, which are used for raking algae from sand. For comparison, we investigated the soft outer teeth of Lavigeria grandis, which are used in gathering particles after the ingesta is loosed from the rock surface. SEM revealed scratches on all surfaces of the teeth and suggests that every tooth side interacts with abrasive particles during foraging. Analysis of stomach content revealed that sand particles of 10–20 μm diameter are ingested. By EDX/EDS, we studied the composition of the teeth and determined that high proportions of Ca are present on all surfaces, which could be an adaptation to reduce abrasion. Finally, we here present evidence for the existence of a canal within the teeth, which could potentially serve as delivery pathway of minerals during tooth maturation and has not been previously detected in Gastropoda. [ABSTRACT FROM AUTHOR]

A simple model for speed-invariant shear stress in biological aqueous lubrication has been developed based on previous observations of these fluid films and our foundational understanding of these complex fluids. The model revealed that the exponent of the shear-thinning behavior is not a critical parameter in speed invariance. Additionally, due to the localization of fluidization as a result of gradients in concentration through the aqueous gel network, the shear-thinning behavior results in a monotonic decline in viscosity to the high shear-rate viscosity plateau, η∞. Finally, and perhaps somewhat surprising, was the finding that the optimal gradient was the weakest possible gradient. These findings are consistent with our understanding of aqueous lubrication across soft biological interfaces, which is sensitive to the macromolecular quality of the gel-spanning networks and the water content but not the sliding speed. The finding that this speed-invariant shear stress does not require a unique concentration profile reveals a built-in mechanism of biological resilience to maintain lubricity over a wide range of conditions. Gradients in concentration localize fluidization at the lowest concentration regime during sliding. This leads to an expanding shear zone with proportionally thicker fluidized zones for increasing values of sliding speed resulting in roughly equivalent shear rate and shear stress for all sliding speeds [ABSTRACT FROM AUTHOR]

The paper provides a commentary on the theme of "Current and Future Trends in Tribological Research: Fundamentals and Applications", which is a special feature issue commemorating the 10th anniversary of the journal, Lubricants. A historical discourse is provided regarding various aspects of tribology as a multi-disciplinary subject that interacts in an inter-disciplinary manner with many other subjects: multi-body dynamics, thermofluids and heat transfer, contact mechanics, surface science, chemistry, rheology, data science, and biology, to name but a few. Such interactions lead to many important topics including propulsion with different sources of energy, mitigating emissions, palliation of friction, enhancing durability and sustainability, optimization through detailed analysis, and the use of artificial intelligence. Additionally, issues concerning kinetics at various physical scales (from macroscale to microscale onto mesoscale and nanoscale) affecting the kinematics of contacts are discussed. The broad range of considered applications includes vehicular powertrains, rotor bearings, electrical machines, mammalian endo-articular joints, nanobiological attachment/detachment, and locomotion. Current state-of-the-art tribological research is highlighted within a multi-physics, multi-scale framework, an approach not hitherto reported in the open literature. [ABSTRACT FROM AUTHOR]

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 environmental 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 environmental temperature to minimise the test artefacts during wear simulation which may affect the wear rates. [ABSTRACT FROM AUTHOR]

Abstract Background Soft, biological, and bio-inspired materials are often compositionally heterogeneous and structurally anisotropic, and they frequently feature graded or layered organizations. This design complexity enables exceptional ranges in properties and performance yet complicates a fundamental understanding of the contact mechanics. Recent studies of soft gel layers have relied on Hertzian or Winkler foundation (“bed-of-springs”) models to characterize the mechanics but have found neither satisfactory. Objective The contact mechanics of soft gel layers are not yet fully understood. The aim of this work is to develop a simple contact mechanics model tailored for compositionally-graded materials with soft surface layers under high strains and deformations. Methods Concepts from polymer physics, fluid draining, and Winkler foundation mechanics are combined to develop a simple contact mechanics model which relates the applied normal force to the probe radius of curvature, elastic modulus, and thickness of soft surface layers subjected to high strains. Results This simple model was evaluated with two examples of graded surface gel layers spanning multiple length-scales, including commercially available contact lenses and stratified hydrogels. The model captures the nonlinear contact mechanics of highly strained soft aqueous gel layers more closely than either Hertz or Winkler foundation theory while simultaneously enabling a prediction for the thickness of the surface gel layer. Conclusion These results indicate that this simple model can adequately characterize the contact mechanics of highly strained soft aqueous gel layers.

This paper analyses the stick-slip phenomenon in tribosystems that include human skin and biocompatible polyethylene UHMWPE. The study focuses on the theoretical stability conditions of the movement of the UHMWPE polyethylene specimen in contact with human skin, considering the rheological and tribological properties of human skin, the rigidity of the system, and the speed of training. The proposed dynamic model involves the equation of relative motion of the UHMWPE polyethylene specimen relative to the finger, considering the force of friction, axial stiffness, hysteresis damping, and frequency of oscillation. The results can be useful for choosing materials for lower and upper human endoprosthesis and designing robot gripping systems. The paper presents experimental and analytical models and explores the effects of contact pressure, real contact area, and kinetic friction coefficient on the phenomenon. The study aims to improve the understanding of the stick-slip phenomenon and contribute to the development of more reliable tribological systems.

The human hand has evolved to become the most complex and versatile grasping and manipulation tool. The fingers play a crucial role in acquiring information about touched objects through tactile and thermal sensors. Specifically, the fingertips are densely packed with touch and thermal receptors, which have the highest concentration of cells responsible for transmitting stimuli to the brain.

Cartilage degeneration is a characteristic of osteoarthritis (OA), which is often observed in aging populations. This degeneration is due to the breakdown of articular cartilage (AC) mechanical and tribological properties primarily attributed to lubrication failure. Understanding the reasons behind these failures and identifying potential solutions could have significant economic and societal implications, ultimately enhancing quality of life. This review provides an overview of developments in the field of AC, focusing on its mechanical and tribological properties. The emphasis is on the role of lubrication in degraded AC, offering insights into its structure and function relationship. Further, it explores the fundamental connection between AC mechano-tribological properties and the advancement of its degradation and puts forth recommendations for strategies to boost its lubrication efficiency.

Proteins can adsorb on the surface of materials, such as soft contact lenses (SCLs), and can affect the hydrophobicity, roughness, and surface properties of the contact lenses (CLs), which, in turn, can influence the friction between the lenses and the ocular surface. Excessive friction between contact lenses and the ocular surface can lead to discomfort for the wearer and may cause irritation or inflammation of the cornea, better known as corneal ulcers (keratitis). Bovine Serum Albumin (BSA) is often used as a standard protein in biocompatibility testing of materials, including contact lenses. One standard commercial contact lens was tested under lubricated conditions to access the coefficient of friction (CoF). The contact was lubricated with a tear-like fluid (TLF) solution containing six different concentrations of BSA. In all cases, good linearity of the results of the friction force was verified, suggesting that the first friction law can be applied to determine the value of the coefficient of friction. It was found that friction increases with the increase in protein concentration.

The human jaw is a complex biomechanical system involving different anatomical components and an articulated muscular system devoted to its dynamical activation. The numerous actions exerted by the mandible, such as talking, eating or chewing, make its biomechanical comprehension absolutely indispensable. To date, even if research on this topic has achieved interesting outcomes using in vitro testing, thanks to the development of new apparatus and methods capable of performing more and more realistic experiments, theoretical modeling is still worthy of investigation. In light of this, nowadays, the Finite Element Method (FEM) approach constitutes certainly the most common tool adopted to investigate particular issues concerning stress–strain characterization of the human jaw. In addition, kinematics analyses, both direct and inverse, are also diffuse and reported in the literature. This manuscript aimed to propose a critical review of the most recurrent biomechanical models of the human mandible to give readers a comprehensive overview on the topic. In light of this, the numerical approaches, providing interesting outcomes, such as muscular activation profiles, condylar forces and stress–strain fields for the human oral cavity, are mainly differentiated between according to the joint degrees of freedom, the analytical descriptions of the muscular forces, the boundary conditions imposed, the kind of task and mandible anatomical structure modeling.

Nowadays, the dental implant surgery is a sophisticate and accurate sector with techniques increasingly innovative such as rapid prototyping, guided implant surgery and stem cell-based approaches. An example is certainly the use of multiple implants (4–6), instead of several prosthesis in case of human edentulous condition. The aim of this research is to investigate the mechanical behavior of the All-on-Four technique for different boundary conditions such as the value of load, framework material, type and position of implant. The goal was essentially trying to find out, by the application of structural static Finite Element Analysis (FEM), the best design for this specific treatment. After that, a stress-life fatigue numerical analysis was conducted for the optimal configuration in order to estimate the fatigue life in accordance with both Gerber and Goodman mean stress theory. The coupling involved the implants supported by an arch and a human mandible composed of cortical and cancellous part. After the simulations, it was found that the stress/strain field was very sensitive to the boundary conditions imposed. In particular, the position of the implants and the material framework yielded different responses depending on the implant design. Finally the use of ultrashort implants provided a significant decrease in the developed efforts than the long ones if the first premolar position was assumed. More specific, the stress peaks were in the range 100–225MPa for the implants, 300–537MPa for the framework, 50–124MPa for the cortical bone and 3–35MPa for the cancellous bone and they were located essentially in the abutment-framework connection as much as in implant neck-bone coupling. The best design saw the presence of ultra-short implant, first premolar position and Co-Cr alloy as framework material. The fatigue test confirmed the stability of the structure even with dynamic loads, but critical spots were present in the framework. In conclusion, the All-on-Four technique is a valid and safe alternative, even in case of ultrashort implants, for human edentulism care.

Fundamental knowledge about in vivo kinematics and contact conditions at the articulating interfaces of total knee replacements are essential for predicting and optimizing their behavior and durability. However, the prevailing motions and contact stresses in total knee replacements cannot be precisely determined using conventional in vivo measurement methods. In silico modeling, in turn, allows for a prediction of the loads, velocities, deformations, stress, and lubrication conditions across the scales during gait. Within the scope of this paper, we therefore combine musculoskeletal modeling with tribo-contact modeling. In the first step, we compute contact forces and sliding velocities by means of inverse dynamics approach and force-dependent kinematic solver based upon experimental gait data, revealing contact forces during healthy/physiological gait of young subjects. In a second step, the derived data are employed as input data for an elastohydrodynamic model based upon the finite element method full-system approach taking into account elastic deformation, the synovial fluid's hydrodynamics as well as mixed lubrication to predict and discuss the subject-specific pressure and lubrication conditions. [ABSTRACT FROM AUTHOR]

Abstract Background Cartilage is a mechanically highly stressed tissue in the human body and an important part of synovial joints. The joint cartilage is lubricated by synovial fluid with hyaluronic acid (HA) as main component. However, in joints with osteoarthritis HA has a lower concentration and molecular weight compared to healthy joints. In recent years, the intra-articular injection of therapeutic HA lubricant, has become a popular therapy. The effect of HA application on the friction of a complete joint with physiological movement needs to be further determined. Methods The aim of the present study was to evaluate the lubrication effect of the joint by three lubricants (NaCl, fetal calf serum (FCS) and HA) and their effect on the friction in nine complete ovine carpo-metacarpal joints. The joints were mounted on a material testing machine and a physiological movement with 10° rotation was simulated with ascending axial load (100 – 400 N). Specimens were tested native, with cartilage damage caused by drying out and relubricated. Dissipated energy (DE) as a measure of friction was recorded and compared. Results Investigating the effect of axial load, we found significant differences in DE between all axial load steps (p

Abstract 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.

Silicone elastomer medical implants are ubiquitous in medicine, particularly for breast augmentation. However, when these devices are placed within the body, disruption of the natural biological interfaces occurs, which significantly changes the native energy-dissipation mechanisms of living systems. These new interfaces can introduce non-physiological contact pressures and tribological conditions that provoke inflammation and soft tissue damage. Despite their significance, the biotribological properties of implant-tissue and implant-extracellular matrix (ECM) interfaces remain poorly understood. Here, we developed an in vitro model of soft tissue damage using a custom-built in situ biotribometer mounted onto a confocal microscope. Sections of commercially-available silicone breast implants with distinct and clinically relevant surface roughness ( R a = 0.2 ± 0.03 μ m, 2.7 ± 0.6 μ m, and 32 ± 7.0 μ m) were mounted to spherically-capped hydrogel probes and slid against collagen-coated hydrogel surfaces as well as healthy breast epithelial (MCF10A) cell monolayers to model implant-ECM and implant-tissue interfaces. In contrast to the "smooth" silicone implants ( R a < 10 μ m), we demonstrate that the "microtextured" silicone implant (10 < R a < 50 μ m) induced higher frictional shear stress (τ > 100 Pa), which led to greater collagen removal and cell rupture/delamination. Our studies may provide insights into post-implantation tribological interactions between silicone breast implants and soft tissues. [ABSTRACT FROM AUTHOR]

Tetrahedral amorphous carbon (ta‐C) coatings have the potential to protect biomedical implants from wear and increase their service life. This study elucidates the biocompatibility, mechanical properties, adhesion, and wear resistance of ta‐C coatings fabricated by physical vapor deposition on cobalt‐chromium‐molybdenum (CoCr) and titanium (Ti64) alloys as well as ultrahigh molecular weight polyethylene (UHMWPE). Satisfactory cytocompatibility is verified using contact angle and surface tension measurements as well as indirect and direct cell testing. Scratch testing demonstrates excellent adhesion to the substrates and as confirmed by nanoindentation, the coatings represent an up to 13‐fold and 182‐fold increase in hardness on the hard and soft materials. In metal pin‐on‐UHMWPE disk sliding experiments under simulated body fluid lubrication, the wear rates of the disk are reduced by 48% (against CoCr) and 73% (against Ti64) while the pin wear rates are reduced by factors of 20 (CoCr) and 116 (Ti64) compared to uncoated pairings. From optical and laser scanning microscopy, Raman measurements, and particle analyses, it is shown that the underlying substrates remain well protected. Nonetheless, focused ion beam scanning electron microscopy revealed coating process‐related and thermally driven subductions as well as tribologically induced near‐surface fatigue, which can potentially constitute critical wear mechanisms. [ABSTRACT FROM AUTHOR]

Nowadays dental implant surgery is a very diffused technique with a high probability of success. Nevertheless, undesirable events such as the failure of the implant, and in many cases, the loss of the prosthesis can occur, due to the external imposed conditions. The design, the shape and geometry of the implant, the material, the kind of thread and so on, become therefore crucial variables for a longer prosthesis life cycle. This paper aims to investigate in terms of stress/strain by using Finite Element Method (FEM) a novel implant design, with thick shape, length1, in comparison with a classical design implant, characterized by a narrow shape, length >5 mm and diameter/length ratio

Abstract Tetrahedral amorphous carbon (ta‐C) coatings have the potential to protect biomedical implants from wear and increase their service life. This study elucidates the biocompatibility, mechanical properties, adhesion, and wear resistance of ta‐C coatings fabricated by physical vapor deposition on cobalt‐chromium‐molybdenum (CoCr) and titanium (Ti64) alloys as well as ultrahigh molecular weight polyethylene (UHMWPE). Satisfactory cytocompatibility is verified using contact angle and surface tension measurements as well as indirect and direct cell testing. Scratch testing demonstrates excellent adhesion to the substrates and as confirmed by nanoindentation, the coatings represent an up to 13‐fold and 182‐fold increase in hardness on the hard and soft materials. In metal pin‐on‐UHMWPE disk sliding experiments under simulated body fluid lubrication, the wear rates of the disk are reduced by 48% (against CoCr) and 73% (against Ti64) while the pin wear rates are reduced by factors of 20 (CoCr) and 116 (Ti64) compared to uncoated pairings. From optical and laser scanning microscopy, Raman measurements, and particle analyses, it is shown that the underlying substrates remain well protected. Nonetheless, focused ion beam scanning electron microscopy revealed coating process‐related and thermally driven subductions as well as tribologically induced near‐surface fatigue, which can potentially constitute critical wear mechanisms.

The biomedical Ti–13Zr–13Nb bi-phase (α + β) alloy for long-term applications in implantology has recently been developed. The porous oxide nanotubes' (ONTs) layers of various geometries and lengths on the Ti–13Zr–13Nb alloy surface can be produced by anodizing to improve osseointegration. This work was aimed at how anodizing conditions determinatine the micromechanical and biotribological properties of the Ti–13Zr–13Nb alloy. First-generation (1G), second-generation (2G), and third-generation (3G) ONT layers were produced on the Ti–13Zr–13Nb alloy surface by anodizing. The microstructure was characterized using SEM. Micromechanical properties were investigated by the Vickers microhardness test under variable loads. Biotribological properties were examined in Ringer's solution in a reciprocating motion in the ball-on-flat system. The 2D roughness profiles method was used to assess the wear tracks of the tested materials. Wear scars' analysis of the ZrO2 ball was performed using optical microscopy. It was found that the composition of the electrolyte with the presence of fluoride ions was an essential factor influencing the micromechanical and biotribological properties of the obtained ONT layers. The three-body abrasion wear mechanism was proposed to explain the biotribological wear in Ringer's solution for the Ti–13Zr–13Nb alloy before and after anodizing. [ABSTRACT FROM AUTHOR]

The human hand has evolved to become the most complex and versatile grasping and manipulation tool. The fingers play a crucial role in acquiring information about touched objects through tactile and thermal sensors. Specifically, the fingertips are densely packed with touch and thermal receptors, which have the highest concentration of cells responsible for transmitting stimuli to the brain. [ABSTRACT FROM AUTHOR]

This paper analyses the stick-slip phenomenon in tribosystems that include human skin and biocompatible polyethylene UHMWPE. The study focuses on the theoretical stability conditions of the movement of the UHMWPE polyethylene specimen in contact with human skin, considering the rheological and tribological properties of human skin, the rigidity of the system, and the speed of training. The proposed dynamic model involves the equation of relative motion of the UHMWPE polyethylene specimen relative to the finger, considering the force of friction, axial stiffness, hysteresis damping, and frequency of oscillation. The results can be useful for choosing materials for lower and upper human endoprosthesis and designing robot gripping systems. The paper presents experimental and analytical models and explores the effects of contact pressure, real contact area, and kinetic friction coefficient on the phenomenon. The study aims to improve the understanding of the stick-slip phenomenon and contribute to the development of more reliable tribological systems. [ABSTRACT FROM AUTHOR]

During the last decades, metal-based biomaterials have been extensively explored to be used as biocompatible metals for biomedical applications, owing to their superior mechanical properties and corrosion resistance. Consequently, for long-term implanted medical devices, to assure the biomaterials' reliability, functionality, and biocompatibility, studying the various bio-tribological damage mechanisms to obtain the optimum properties is one of the most important goals. In this review, we consider the most important metal-based biomaterials such as stainless steel, alloys of titanium (Ti), cobalt-chromium (Co-Cr), and Nichel-Titatium (Ni-Ti), as well Magnesium (Mg) alloys and with Tantalum (Ta), emphasizing their characteristics, clinical applications, and deterioration over time. The influence of metal elements on biological safety, including significant effects of metal-based biomaterials in dentistry were discussed, considering the perspectives of surface, mechanical properties, corrosion behaviors, including interactions, bio-mechanisms with tissues, and oral environments. In addition, the role of the oral microbiota was explored due to its role in this erosion condition, in order to further understand the mechanism of metal-based biomaterials implanted on the microflora balance of aerobic and anaerobic bacteria in an oral environment. [ABSTRACT FROM AUTHOR]