Bioinspired Self-Adhesive Multifunctional Lubricated Coating for Biomedical Implant Applications.

In the realm of clinical applications, the concern surrounding biomedical device-related infections (BDI) is paramount. To mitigate the risk associated with BDI, enhancing surface characteristics such as lubrication and antibacterial efficacy is considered as a strategic approach. This study delineated the synthesis of a multifunctional copolymer, embodying self-adhesive, lubricating, and antibacterial properties, achieved through free radical polymerization and a carbodiimide coupling reaction. The copolymer was adeptly modified on the surface of stainless steel 316L (SS316L) substrates by employing a facile dip-coating technique. Comprehensive characterizations were performed by using an array of analytical techniques including Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, optical interferometry, scanning electron microscopy, and atomic force microscopy. Nanoscale tribological assessments revealed a notable reduction in the value of the friction coefficient of the copolymer-coated SS316L substrates compared to bare SS316L samples. The coating demonstrated exceptional resistance to protein adsorption, as evidenced in protein contamination models employing bovine serum albumin and fibrinogen. The bactericidal efficacy of the copolymer-modified surfaces was significantly improved against pathogenic strains such as Staphylococcus aureus and Escherichia coli. Additionally, in vitro evaluations of blood compatibility and cellular compatibility underscored the remarkable anticoagulant performance and biocompatibility. Collectively, these findings indicated that the developed copolymer coating represented a promising candidate, with its facile modification approach, for augmenting lubrication and antifouling properties in the field of biomedical implant applications.

Bioinspired film-terminated ridges for enhancing friction force on lubricated soft surfaces.

Enhancing friction force in lubricated, compliant contacts is of particular interest due to its wide application in various engineering and biological systems. In this study, we have developed bioinspired surfaces featuring film-terminated ridges, which exhibit a significant increase in lubricated friction force compared to flat samples. We propose that the enhanced sliding friction can be attributed to the energy dissipation at the lubricated interface caused by elastic hysteresis resulting from cyclic terminal film deformation. Furthermore, increasing inter-ridge spacing or reducing terminal film thickness are favorable design criteria for achieving high friction performance. These findings contribute to our understanding of controlling lubricated friction and provide valuable insights into surface design strategies for novel functional devices.

Bottlebrush Polymers for Articular Joint Lubrication: Influence of Anchoring Group Chemistry on Lubrication Properties.

The role of carboxylic, aldehyde, or epoxide groups incorporated into bottlebrush macromolecules as anchoring blocks (or cartilage-binding blocks) is investigated by measuring their lubricating properties and cartilage-binding effectiveness. Mica modified with amine groups is used to mimic the cartilage surface, while bottlebrush polymers functionalized with carboxylic, aldehyde, or epoxide groups played the role of the lubricant interacting with the cartilage surface. We demonstrate that bottlebrushes with anchoring blocks effectively reduce the friction coefficient on modified surfaces by 75-95% compared to unmodified mica. The most efficient polymer appears to be the one with epoxide groups, which can react spontaneously with amines at room temperature. In this case, the value of the friction coefficient is the lowest and equals 0.009 ± 0.001, representing a 95% reduction compared to measurements on nonmodified mica. These results show that the presence of the functional groups within the anchoring blocks has a significant influence on interactions between the bottlebrush polymer and cartilage surface. All synthesized bottlebrush polymers are also used in the preliminary lubrication tests carried out on animal cartilage surfaces. The developed materials are very promising for future in vivo studies to be used in osteoarthritis treatment.

Effects of dispersing media on the rheological and tribological properties of basil seed mucilage-based thickened liquids.

The development of thickening powders for the management of dysphagia is imperative due to the rapid growth of aging population and prevalence of the dysphagia. One promising thickening agent that can be used to formulate dysphagia diets is basil seed mucilage (BSM). This work investigates the effects of dispersing media, including water, milk, skim milk, and apple juice, on the rheological and tribological properties of the BSM-thickened liquids. Shear rheology results revealed that the thickening ability of BSM in these media in ascending order is milk < skim milk ≈ apple juice < water. On the other hand, extensional rheology demonstrated that the longest filament breakup time was observed when BSM was dissolved in milk, followed by skim milk, water, and apple juice. Furthermore, tribological measurements showed varying lubrication behavior, depending on the BSM concentration and dispersing media. Dissolution of BSM in apple juice resulted in the most superior lubrication property compared with that in other dispersing media. Overall, this study provides insights on BSM's application as a novel gum-based thickening powder in a range of beverages and emphasizes how important it is for consumers to have clear guidance for the use of BSM in dysphagia management.

Review on Cutting Fluids: Formulation, Chemistry and Deformulation.

This comprehensive review offers a chemical analysis of cutting fluids, delving into both their formulation and deformulation processes. The study covers a wide spectrum of cutting fluid formulations, ranging from simple compositions predominantly comprising oils, whether mineral or vegetable, to emulsions. The latter involves the integration of surfactants, encompassing both nonionic and anionic types, along with a diverse array of additives. Concerning oils, the current trend leans towards the use of vegetable oils instead of mineral oils for environmental reasons. As vegetable oils are more prone to oxidation, chemical alterations, the addition of antioxidant may be necessary. The chemical aspects of the different compounds are scrutinized, in order to understand the role of each component and its impact on the fluid's lubricating, cooling, anti-wear, and anti-corrosion properties. Furthermore, the review explores the deformulation methodologies employed to dissect cutting fluids. This process involves a two-step approach: separating the aqueous and organic phases of the emulsions by physical or chemical treatments, and subsequently conducting a detailed analysis of each to identify the compounds. Several analytical techniques, including spectrometric or chromatographic, can be employed simultaneously to reveal the chemical structures of samples. This review aims to contribute to the improvement of waste treatment stemming from cutting fluids. By gathering extensive information about the formulation, deformulation, and chemistry of the ingredients, there is a potential to enhance the waste management and disposal effectively.

A biomimetic lubricating nanosystem for synergistic therapy of osteoarthritis.

Failure of articular cartilage lubrication and inflammation are the main causes of osteoarthritis (OA), and integrated treatment realizing joint lubrication and anti-inflammation is becoming the most effective treat model. Inspired by low friction of human synovial fluid and adhesive chemical effect of mussels, our work reports a biomimetic lubricating system that realizes long-time lubrication, photothermal responsiveness and anti-inflammation property. To build the system, a dopamine-mediated strategy is developed to controllably graft hyaluronic acid on the surface of metal organic framework. The design constructs a biomimetic core-shell structure that has good dispersity and stability in water with a high drug loading ratio of 99%. Temperature of the solution rapidly increases to 55 °C under near-infrared light, and the hard-soft lubricating system well adheres to wear surfaces, and greatly reduces frictional coefficient by 75% for more than 7200 times without failure. Cell experiments show that the nanosystem enters cells by endocytosis, and releases medication in a sustained manner. The anti-inflammatory outcomes validate that the nanosystem prevents the progression of OA by down-regulating catabolic proteases and pain-related genes and up-regulating genes that are anabolic in cartilage. The study provides a bioinspired strategy to employ metal organic framework with controlled surface and structure for friction reduction and anti-inflammation, and develops a new concept of OA synergistic therapy model for practical applications.

Adhesion-Lubrication Paradox of Articular Cartilage.

The friction of solids is primarily understood through the adhesive interactions between the surfaces. As a result, slick materials tend to be nonstick (e.g., Teflon), and sticky materials tend to produce high friction (e.g., tires and tape). Paradoxically, cartilage, the slippery bearing material of human joints, is also among the stickiest of known materials. This study aims to elucidate this apparent paradox. Cartilage is a biphasic material, and the most cited explanation is that both friction and adhesion increase as load transfers from the pressurized interstitial fluid to the solid matrix over time. In other words, cartilage is slippery and sticky under different times and conditions. This study challenges this explanation, demonstrating the strong adhesion of cartilage under high and low interstitial hydration conditions. Additionally, we find that cartilage clings to itself (a porous material) and Teflon (a nonstick material), as well as other surfaces. We conclude that the unusually strong interfacial tension produced by cartilage reflects suction (like a clingfish) rather than adhesion (like a gecko). This finding is surprising given its unusually large roughness, which typically allows for easy interfacial flow and defeats suction. The results provide compelling evidence that cartilage, like a clingfish, conforms to opposing surfaces and effectively seals submerged contacts. Further, we argue that interfacial sealing is itself a critical function, enabling cartilage to retain hydration, load support, and lubrication across long periods of inactivity.

Tablet ejection: A systematic comparison between force, static friction, and kinetic friction.

The magnitude of the frictional forces during the ejection of porous pharmaceutical tablets plays an important role in determining the occurrence of tabletting defects. Here, we perform a systematic comparison between the maximum ejection force, static friction coefficient, and kinetic friction coefficient. All of these metrics have different physical meanings, corresponding to different stages of ejection. However, experimental limitations have previously complicated comparisons, as static and kinetic friction could not be measured simultaneously. This study presents a method for simultaneously measuring the maximum ejection force, static friction coefficient, and kinetic friction coefficient in situ during tablet ejection in routine compaction simulator experiments. Using this method, we performed a systematic comparison, including variations of (1) ejection speed, (2) compaction pressure, (3) material, and (4) lubrication method. The relative importance of each variable is discussed in detail, including how ejection speed alone can be a decisive factor in tablet chipping. The reliability of the newly developed method is supported by excellent agreement with previous studies and finite element method (FEM) simulations. Finally, we discuss the suitability of friction coefficients derived from Janssen-Walker theory and explanations for the phenomenon of die-wall static friction coefficients with apparent values far above unity.

Natural product of angelica essential oil developed as a stable Pickering emulsion for joint interface lubrication.

Development of high-performance joint injection lubricants has become the focus in the field of osteoarthritis treatment. Herein, natural product of angelica essential oil combined with the graphene oxide were prepared to the stable Pickering emulsion as a biological lubricant. The tribological properties of the Pickering emulsion under different friction conditions were studied. The lubricating mechanism was revealed and the biological activities were evaluated. Results showed that the prepared Pickering emulsion displayed superior lubrication property at the Ti6Al4V biological material interface. The maximum friction reduction and anti-wear abilities of the Pickering emulsion were improved by 36% and 50% compared to water, respectively. This was primarily due to the action of the double-layer lubrication films composed of the graphene oxide and angelica essential oil molecules. It was worth noting that the friction reduction effect of the Pickering emulsion at the natural cartilage interface was higher about 19% than that of HA used in clinic for OA commonly. In addition, the Pickering emulsion also displayed antioxidant activity and cell biocompatibility, showing a good clinical application prospect in the future.

Effects of speculum lubrication on cervical smears for cervical cancer screening: A double blind randomized clinical trial.

BACKGROUND: Speculum lubrication may help to reduce the pain experienced during Pap-smear collection and hence increase uptake of cervical cancer screening and repeat testing, but there are fears of its interference with cytological results. AIM: To determine and compare the adequacy of cervical cytology smears and the mean pain scores of women undergoing cervical cancer screening with or without speculum lubrication. METHODS: This was a randomised controlled study of 132 women having cervical cancer screening at a tertiary hospital in Nigeria. Sixty-six participants were randomly assigned to the 'Gel' and 'No Gel' groups, respectively. Pap smears were collected from each participant with a lubricated speculum ('Gel group') or a non-lubricated speculum ('No Gel group'). The primary outcome measures were the proportion of women with unsatisfactory cervical cytology smears and the mean numeric rating scale pain scores, while the secondary outcome measures were the proportion of women who were willing to come for repeat testing and the cytological diagnosis of Pap-smear results. RESULTS: The baseline socio-demographic variables were similar in both groups. There was no significant difference in the proportion of unsatisfactory cervical smear results between the two groups (13.6% vs. 21.2%, p = 0.359). However, the mean pain scores were significantly lower in the gel group than in the no gel group (45.04 vs. 87.96; p<0.001). An equal proportion of the participants in each group (90.9% vs. 90.9%; p > 0.999) were willing to come for repeat cervical smears in the future. CONCLUSION: Speculum lubrication did not affect the adequacy of cervical smears but significantly reduced the pain experienced during pap smear collection. Also, it did not significantly affect the willingness to come for repeat cervical smears in the future. TRIAL REGISTRATION: The trial was registered with the Pan-African Clinical Trial Registry with a unique identification and registration number: PACTR2020077533364675.

Study on the evaluation method of cigarette astringency in the simulated oral environment.

Cigarettes with pronounced astringency can diminish consumers' enjoyment. However, due to the complex composition of cigarettes, quantifying astringency intensity accurately has been challenging. To address this, research was conducted to develop a method for assessing astringency intensity in a simulated oral environment. The astringency intensity of four cigarette brands was determined using the standard sensory evaluation method. The mainstream smoke absorbing solution (MS) was prepared by simulating the cigarette smoking process, and its physicochemical properties (such as total phenol content and pH levels) were analyzed. The lubrication properties of the five solutions were tested using the MFT-5000 wear tester, and factors influencing cigarette astringency were examined. The findings showed that total phenol content and pH of MS were positively and negatively correlated with astringency intensity, respectively. Particularly, the lubrication properties of MS were significantly correlated with astringency intensity, and the correlation coefficient was affected by load and speed during testing. The study concluded that coefficient of friction was a more reliable measure for assessing the extent of astringency in cigarettes than the total phenol content and pH of MS, offering new insights into astringency evaluation and development of high-grade cigarettes.

Brushing Up on Cartilage Lubrication: Polyelectrolyte-Enhanced Tribological Rehydration.

This study presents new insights into the potential role of polyelectrolyte interfaces in regulating low friction and interstitial fluid pressurization of cartilage. Polymer brushes composed of hydrophilic 3-sulfopropyl methacrylate potassium salt (SPMK) tethered to a PEEK substrate (SPMK-g-PEEK) are a compelling biomimetic solution for interfacing with cartilage, inspired by the natural lubricating biopolyelectrolyte constituents of synovial fluid. These SPMK-g-PEEK surfaces exhibit a hydrated compliant layer approximately 5 µm thick, demonstrating the ability to maintain low friction coefficients (µ ∼ 0.01) across a wide speed range (0.1-200 mm/s) under physiological loads (0.75-1.2 MPa). A novel polyelectrolyte-enhanced tribological rehydration mechanism is elucidated, capable of recovering up to ∼12% cartilage strain and subsequently facilitating cartilage interstitial fluid recovery, under loads ranging from 0.25 to 2.21 MPa. This is attributed to the combined effects of fluid confinement within the contact gap and the enhanced elastohydrodynamic behavior of polymer brushes. Contrary to conventional theories that emphasize interstitial fluid pressurization in regulating cartilage lubrication, this work demonstrates that SPMK-g-PEEK's frictional behavior with cartilage is independent of these factors and provides unabating aqueous lubrication. Polyelectrolyte-enhanced tribological rehydration can occur within a static contact area and operates independently of known mechanisms of cartilage interstitial fluid recovery established for converging or migrating cartilage contacts. These findings challenge existing paradigms, proposing a novel polyelectrolyte-cartilage tribological mechanism not exclusively reliant on interstitial fluid pressurization or cartilage contact geometry. The implications of this research extend to a broader understanding of synovial joint lubrication, offering insights into the development of joint replacement materials that more accurately replicate the natural functionality of cartilage.

Novel biomimetic macromolecules system for highly efficient lubrication, ROS scavenging and osteoarthritis treatment.

The early stages of osteoarthritis (OA) in the joints are typically characterized by two key factors: the dysfunction of articular cartilage lubrication and inflammation resulting from the excessive production of reactive oxygen species (ROS). Synthetic injectable macromolecular materials present great potential for preventing the progression of early OA. In this study, to mimic the excellent lubricity of brush-like aggregates found in natural synovial fluid, we develop a novel macromolecular biolubricant (CS-PS-DA) by integrating adhesion and hydration groups onto backbone of natural biomacromolecules. CS-PS-DA exhibits a strong affinity for cartilage surfaces, enabling the formation of a stable lubrication layer at the sliding interface of degraded cartilages to restore joint lubrication performance. In vitro results from ROS scavenging and anti-inflammatory experiments indicate the great advantage of CS-PS-DA to decrease the levels of proinflammatory cytokines by inhibiting ROS overproduction. Finally, in vivo rats OA model demonstrates that intra-cavitary injection of CS-PS-DA could effectively resist cartilage wear and mitigated inflammation in the joints. This novel biolubricant provides a new and timely strategy for the treatment of OA.

Supramolecular 3 in 1: A Lubrication and Co-Delivery System for Synergistic Advanced Osteoarthritis Therapy.

The complexity, heterogeneity, and drug resistance of diseases necessitate a shift in therapeutic paradigms from monotherapy to combination therapy, which could augment treatment efficiency. Effective treatment of advanced osteoarthritis (OA) requires addressing three key factors contributing to its deterioration: chronic joint inflammation, lubrication dysfunction, and cartilage-tissue degradation. Herein, we present a supramolecular nanomedicine of multifunctionality via molecular recognition and self-assembly. The employed macrocyclic carrier, zwitterion-modified cavitand (CV-2), not only accurately loads various drugs but also functions as a therapeutic agent with lubricating properties for the treatment of OA. Kartogenin (KGN), a drug for articular cartilage regeneration and protection, and flurbiprofen (FP), an anti-inflammatory agent, were coloaded onto CV-2 assembly, forming a supramolecular nanomedicine KGN&FP@CV-2. The three-in-one combination therapy of KGN&FP@CV-2 addresses the three pathological features for treating OA collectively, and thus provides long-term therapeutic benefits for OA through sustained drug release and intrinsic lubrication in vivo. The multifunctional integration of macrocyclic delivery and therapeutics provides a simple, flexible, and universal platform for the synergistic treatment of diseases involving multiple drugs.

Self-Lubricating, Living Contact Lenses.

The increasing prevalence of dry eye syndrome in aging and digital societies compromises long-term contact lens (CL) wear and forces users to regular eye drop instillation to alleviate discomfort. Here a novel approach with the potential to improve and extend the lubrication properties of CLs is presented. This is achieved by embedding lubricant-secreting biofactories within the CL material. The self-replenishable reservoirs autonomously produce and release hyaluronic acid (HA), a natural lubrication and wetting agent, long term. The hydrogel matrix regulates the growth of the biofactories and the HA production, and allows the diffusion of nutrients and HA for at least 3 weeks. The continuous release of HA sustainably reduces the friction coefficient of the CL surface. A self-lubricating CL prototype is presented, where the functional biofactories are contained in a functional ring at the lens periphery, outside of the vision area. The device is cytocompatible and fulfils physicochemical requirements of commercial CLs. The fabrication process is compatible with current manufacturing processes of CLs for vision correction. It is envisioned that the durable-by-design approach in living CL could enable long-term wear comfort for CL users and minimize the need for lubricating eye drops.

Astringency and its sub-qualities: a review of astringency mechanisms and methods for measuring saliva lubrication.

Astringency is an important mouthfeel attribute that influences the sensory experiences of many food and beverage products. While salivary lubricity loss and increased oral friction were previously believed to be the only astringency mechanisms, recent research has demonstrated that nontactile oral receptors can trigger astringency by responding to astringents without mechanical stimulation. Various human factors have also been identified that affect individual responses to astringents. This article presents a critical review of the key research milestones contributing to the current understanding of astringency mechanisms and the instrumental approaches used to quantify perceived astringency intensity. Although various chemical assays or physical measures mimic in-mouth processes involved in astringent mouthfeel, this review highlights how one chemical or physical approach can only provide a single measure of astringency determined by a specific mechanism. Subsequently, using a single measurement to predict astringency perception is overly idealistic. Astringency has not been quantified beyond the loss of saliva lubrication; therefore, nontactile receptor-based responses must also be explored. An important question remains about whether astringency is a single perception or involves distinct sub-qualities such as pucker, drying, and roughness. Although these sub-quality lexicons have been frequently cited, most studies currently view astringency as a single perception rather than dividing it into sub-qualities and investigating the potentially independent mechanisms of each. Addressing these knowledge gaps should be an important priority for future research.

Understanding mechanisms behind the oily mouthcoating perception of pure vegetable oils using tribology.

Tribology is the science of measuring friction between surfaces. While it has been widely used to investigate texture sensations of food applications, it is seldom applied in pure edible oil systems. In this research, we measured friction, viscosity, and solid fat content (SFC) of nine vegetable oils at 30 and 60°C. Polarized static microscopy was used to assess crystal formation between 60 and 30°C. Descriptive sensory analysis and quantification of oral oil coatings were performed on the oils at 60°C. Expressing the friction factor of oil over the Hersey number (calculated using high sheer-viscosity values) showed no differences in friction between 30 and 60°C, except for shea stearin. Static microscopy revealed crystallization occurred at 30°C for shea stearin, whereas no or few crystals were present for other oils. At 30°C, friction at 1 × 10-2 m/s showed an inverse correlation with SFC (R = -0.95) and with high shear rate viscosity (R = -0.84), as well as an inverse correlation (R = -0.73) with "oily mouthcoating" perception. These results suggest that friction could be a predictor of fat-related perceptions of simple oil systems. Additionally, we hypothesize that the presence of crystals in oils could lower friction via a ball-bearing lubrication mechanism.

Comparative Study on the Lubrication Mechanism and Performance of Two Representative Ionic and Nonionic Self-Adhesive Polymer Coatings.

Surface modification of lubricating coatings on biomedical devices is a pivotal strategy to improve the overall performance and clinical efficacy, significantly reducing friction between devices and human tissues and mitigating tissue damage during intervention and long-term implantation. Recently, various hydrophilic polymeric materials have been used for achieving surface functionalization, endowing the biomedical device with excellent superlubrication performance. N-Vinylpyrrolidone (NVP) and 2-methacryloyloxyethyl phosphorylcholine (MPC) are two typical representatives of nonionic and zwitterionic materials. However, there is still a research gap in a comparative study of the lubrication mechanisms and properties between them. In this study, a bioinspired and dopamine-assisted codeposition technique was used to fabricate biomimetic hydrophilic coatings, including P(DMA-NVP) and P(DMA-MPC), on polyurethane. To achieve a thorough comparative analysis of the self-adhesive coating performance, 3 M ratios of the copolymers were synthesized and comprehensive material evaluations were conducted. Additionally, surface morphology, hydrophilicity, and lubrication at both the microscale and macroscale were performed. It was found that both hydrophilic coatings exhibited good stability. The P(DMA-MPC) coating, due to the ability to attract and bind a large number of water molecules, demonstrated superior lubrication effects compared to the P(DMA-NVP) coating. The study provides an in-depth understanding of the lubrication behavior of the self-adhesive coatings to enhance the functionality and application in biomedical engineering.

Enzymatic digestion does not compromise sliding-mediated cartilage lubrication.

Articular cartilage's remarkable low-friction properties are essential to joint function. In osteoarthritis (OA), cartilage degeneration (e.g., proteoglycan loss and collagen damage) decreases tissue modulus and increases permeability. Although these changes impair lubrication in fully depressurized and slowly slid cartilage, new evidence suggests such relationships may not hold under biofidelic sliding conditions more representative of those encountered in vivo. Our recent studies using the convergent stationary contact area (cSCA) configuration demonstrate that articulation (i.e., sliding) generates interfacial hydrodynamic pressures capable of replenishing cartilage interstitial fluid/pressure lost to compressive loading through a mechanism termed tribological rehydration. This fluid recovery sustains in vivo-like kinetic friction coefficients (µk<0.02 in PBS and <0.005 in synovial fluid) with little sensitivity to mechanical properties in healthy tissue. However, the tribomechanical function of compromised cartilage under biofidelic sliding conditions remains unknown. Here, we investigated the effects of OA-like changes in cartilage mechanical properties, modeled via enzymatic digestion of mature bovine cartilage, on its tribomechanical function during cSCA sliding. We found no differences in sliding-driven tribological rehydration behaviors or µk between naïve and digested cSCA cartilage (in PBS or synovial fluid). This suggests that OA-like cartilage retains sufficient functional properties to support naïve-like fluid recovery and lubrication under biofidelic sliding conditions. However, OA-like cartilage accumulated greater total tissue strains due to elevated strain accrual during initial load application. Together, these results suggest that elevated total tissue strains-as opposed to activity-mediated strains or friction-driven wear-might be the key biomechanical mediator of OA pathology in cartilage. STATEMENT OF SIGNIFICANCE: Osteoarthritis (OA) decreases cartilage's modulus and increases its permeability. While these changes compromise frictional performance in benchtop testing under low fluid load support (FLS) conditions, whether such observations hold under sliding conditions that better represent the joints' dynamic FLS conditions in vivo is unclear. Here, we leveraged biofidelic benchtop sliding experiments-that is, those mimicking joints' native sliding environment-to examine how OA-like changes in mechanical properties effect cartilage's natural lubrication. We found no differences in sliding-mediated fluid recovery or kinetic friction behaviors between naïve and OA-like cartilage. However, OA-like cartilage experienced greater strain accumulation during load application, suggesting that elevated tissue strains (not friction-driven wear) may be the primary biomechanical mediator of OA pathology.