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The effects of mechanical properties and contact environment conditions on the adhesiveness of the biomimetic adhesive mushroom-shaped micro-structure have been experimentally investigated. The idea is based on the adhesive micro-structures and surfaces inspired by nature after observing the abilities of some animals. Applications are proposed in various fields of engineering and technology. However, to enable unconventional uses of these biomimetic adhesion surfaces, such as in the biomedical field, it is necessary to adjust and optimize their tribological properties (friction, adhesion, and peeling strength) in contact with soft substrates that can simulate the mechanical features of biological tissues. Our work explores the effect of the combinations of the various parameters on the strength of adhesion. Under dry contact conditions, soft counter-faces lead to lower adhesion than hard counter-faces, whereas under wet conditions, soft counter-faces lead to higher adhesion than harder counter-faces.

Biomimetic micro-hexagonal-textured surfaces have sparked interest for their application in fields that demand high friction and adhesion, such as micro-robotics and biomedicine. Despite extensive research conducted on this specific microstructure, its friction behavior against soft counterfaces remains a topic that has not been fully investigated yet. This study examines how micro-hexagon textures behave when they come into contact with engineered and biological materials like gelatin and chicken skin in dry and wet conditions. The results show clearly that under dry contact conditions, flat surfaces generate higher friction compared to hexagon micropattern surfaces. Under wet conditions, hexagon micropattern surfaces generate higher friction compared to flat surfaces. In wet conditions specifically, the static coefficient of friction is up to 13 times greater than that of a flat specimen against glass, up to 11 times greater against gelatin, and up to 6 times greater against chicken skin. For the dynamic coefficient of friction, the patterned surface demonstrates a maximum increase by a factor of 28 against glass, 11 against gelatin, and 5 against chicken skin. These results further develop our knowledge of these hexagon micropattern surfaces and pave the way for their utilization in future technological advancements in which soft and wet counterfaces are to be considered, such as in biomedical applications that can benefit from increased friction in wet conditions for better control and stability.

There are various potential applications of biomimetic adhesive solutions including climbing robotic systems, mobile sensor platforms, and biomedical applications such as patches for external use. Achieving resistance to both normal and tangential loads, however, is a critical issue that still needs to be addressed. Some animals have developed exceptional attachment mechanisms based on combined fibrillar elements of different shapes and functions. Experimental investigation of combined biomimetic adhesive micro-textures on tribological performances such as adhesion, friction, and peeling resistance is needed to apply this idea to the design of an artificial texture having similar “biomimetic” properties. In the present study, we demonstrate that combinations of different shapes of biomimetic adhesive micro-textures show increased efficiency under different contact environments and enable long-term adhesive solutions. Our work sheds light on combinations of different element shapes inspired by nature and their adhesive efficiency as a function of the ratio of each biomimetic element, as well as their spatial repartition.

Myopia patients wear rigid gas-permeable contact lenses during the day to achieve normal vision, but they might feel uncomfortable, since they are made of hard materials that can cause inappropriate friction and adhesion. These forces affect the biological tissues of the cornea and eyelid. In this study, an in vitro rigid gas-permeable contact lens friction testing method was established to mimic the friction between the eyelid and the rigid contact lens. The lens was rubbed against a gelatin membrane to investigate the tribological properties of artificial tear, saline, and two kinds of care solutions using a dedicated experimental setup. The viscosity, pH value, and surface tension of each lubricant was also analyzed. The friction coefficient of the artificial tear solution was the highest: 0.18 for its static friction and 0.09 for its dynamic friction. In contrast, polysaccharide-containing care solution demonstrated the lowest friction coefficient. The viscosity of artificial tear solutions ranged from 0.97 ± 00 to 1.15 ± 0.16 mPa·s, when the shear rate was increased from 19.2 to 192 1/s, while it ranged from 2.26 ± 1.12 to 2.91 ± 0.00 for polysaccharide-containing care solution. Although the physical–chemical properties of various lubricants could not explain the distinct tribological outcomes, the in vitro tribological testing method for rigid gas-permeable lenses was successfully established in this study.

Laser surface texturing is an interesting possibility to tailor materials’ surfaces and thus to improve the friction and wear properties if proper texture feature sizes are selected. In this research work, stainless steel surfaces were laser textured by two different laser techniques, i.e., the direct laser interference patterning by using a nanosecond pulsed Nd:YAG laser and additionally by an ultrashort pulsed femtosecond Ti:Sa. The as-textured surfaces were then studied regarding their frictional response in a specially designed linear reciprocating test rig under lubricated conditions with a fully formulated 15W40 oil. Results show that dimples with smaller diameter lead to a significant reduction in the coefficient of friction compared to the dimples with a larger diameter and surfaces with a grid-like surface pattern produced by direct laser interference patterning.

Here, we developed a technique to assess the workability of sealed-for-life greased rolling bearings after a long-term storage. In this framework, we devised a model of equivalent transition between the conditions of natural ageing under daily and seasonally fluctuating temperature, and the conditions of accelerated thermal ageing at a constant high temperature. The tested bearings were thermally aged, and then their steady state friction and outer ring temperature were examined in a custom high-speed spindle. These results were compared to the performance of a reference new bearing tested under the same loading conditions. Our findings suggest that long-term storage can significantly degrade the performance of sealed-for-life greased rolling bearings. However, a proper running-in can substantially deter the ageing-driven degradation of the bearings.

Studying the lubrication properties of osteoarthritis (OA) synovial fluid (SF) enables an understanding of the boundary lubrication joint, mobility, and friction. However, tribology has never been combined with the clinical reality of the presence of worn particles within the synovial fluid and how they affect the osteoarthritic joints. Part of the problem relates to the tribology methods studying friction by applying inadequate pin-on-disc techniques. In this study, synovial fluid with and without worn particles was studied using a customized tribometer. This method enables opening the contact at the end of each cycle and simulates better contact conditions of a natural knee joint and can thus be applied for evaluating the severity of joint OA and the treatment given to the patient.

Nano- and micro-particles are being increasingly used to tune interfacial frictional properties in diverse applications, from friction modifiers in industrial lubrication to enhanced biological fluids in human osteoarthritic joints. Here, we assessed the tribological properties of a simulated synovial fluid enriched with non-spherical, poly lactic-co-glycolic acid (PLGA) microparticles (µPL) that have been previously demonstrated for the pharmacological management of osteoarthritis (OA). Three different µPL configurations were fabricated presenting a 20 µm × 20 µm square base and a thickness of 5 µm (thin, 5H µPL), 10 µm (10H µPL), and 20 µm (cubical, 20H µPL). After extensive morphological and physicochemical characterizations, the apparent Young’s modulus of the µPL was quantified under compressive loading returning an average value of ∼ 6 kPa, independently of the particle morphology. Then, using a linear two-axis tribometer, the static ( µ s ) and dynamic ( µ d ) friction coefficients of the µPL-enriched simulated synovial fluid were determined in terms of particle configuration and concentration, varying from 0 (fluid only) to 6µ10 5 µPL/mL. The particle morphology had a modest influence on friction, possibly because the µPL were fully squeezed between two mating surfaces by a 5.8 N normal load realizing boundary-like lubrication conditions. Differently, friction was observed to depend on the dimensionless parameter Ω , defined as the ratio between the total volume of the µPL enriching the simulated synovial fluid and the volume of the fluid itself. Both coefficients of friction were documented to grow with Ω reaching a plateau of µ s ∼ 0.4 and µ d ∼ 0.15, already at Ω ∼ 2×10 −3 . Future investigations will have to systematically analyze the effect of sliding velocity, normal load, and rigidity of the mating surfaces to elucidate in full the tribological behavior of µPL in the context of osteoarthritis.

Friction is a genuine issue in the use of many medical devices involving rubbery materials such as plungers in medical syringes. This paper presents a new direction for the reduction of friction in medical syringes based on surface texturing of the rubber plunger. The specimens were prepared by casting poly(vinylsiloxane) (PVS) rubber into a pre-fabricated negative template obtained by 3D printing. Friction tests were performed on a home-made test-rig. It was clearly shown that friction resistance can be considerably manipulated when using textured plungers.

Objectives To compare the lumbosacral nerve distances (LNDs) and sacroiliac joint (SIJ) morphology in individuals with nonspecific chronic low back pain (NSCLBP) and control and examine their correlations with pain and dysfunction in the former. Materials and methods The sample includes 200 adult patients (ranging from 20 to 50 years old) referred for computerized abdominal tomography (CT): 100 individuals with NSCLBP (50 males and 50 females) and 100 individuals without NSCLBP (50 males and 50 females). CT scans were assessed for LNDs, degenerative sacroiliac changes, and joint bridging. Those factors were correlated to the outcomes of three self-reported questionnaires about pain and function (Oswestry, Fear-Avoidance, and Numerical Pain Rating Scale) in the NSCLBP group. Results Individuals with NSCLBP tend to have reduced LNDs from the sacral part of the SIJ compared to controls (males: right Δ = 5.8 mm, left Δ = 6.03 mm; females: right Δ = 7.9 mm, left Δ = 7.73 mm, two-way ANOVA, p < 0.01), with moderate significant negative correlations with all three questionnaires (−0.38 < Pearson’s r < − 0.57, p < 0.02, i.e., reduced LNDs with greater disability and pain). The NSCLBP group had more significant SIJ degeneration severity that moderately correlated with two questionnaires (0.39 < Pearson’s r < 0.66, p < 0.04, i.e., greater SIJ degeneration with greater disability and pain). In males, the existence of SIJ bridging strongly correlated with all three questionnaires (0.38 < Pearson’s r < 0.78, p < 0.03), and in females, only the Fear-Avoidance Questionnaire and Numerical Pain Scale (0.29 < Pearson’s r < 0.41, p < 0.04). Conclusion Compared to controls, individuals with NSCLBP have reduced LNDs and worse SIJ degenerative changes that correlate with function and pain. Key Points • Individuals with nonspecific low back pain tend to have reduced lumbosacral nerve distances than healthy controls. This may be due to entrapments or inflammation of the nerves or surrounding tissues . • Individuals with nonspecific low back pain tend to have more severe degeneration of their sacroiliac joint than healthy controls . • The above findings significantly correlated with the scores of three self-reported questionnaires about pain and function, implicating that they may be of clinical significance .