Mechanism Of Boundary Lubrication Research Articles

Boundary-lubricated biomaterials with drug delivery for osteoarthritis treatment

AbstractThe good lubrication ability of articular cartilage holds significant importance in our daily lives. Osteoarthritis (OA), the most prevalent degenerative joint disease, causes cartilage damage, increased friction, and inflammation. However, the current clinical treatments for OA exhibit some defects. Recently, the sustained drug release systems with lubricating function have attracted considerable attention for treating OA. This review introduces the lubrication mechanism of cartilage, focusing particularly on the boundary lubrication mechanism. The research progress of boundary-lubricated biomaterials with drug delivery, including microcarriers, hydrogels, and nanoparticles in the treatment of OA by improving inter-articular lubrication and relieving inflammation is discussed and summarized. The efficacy and challenges of boundary-lubricated biomaterials with drug delivery in the treatment of OA are summarized, and the prospects are also discussed.

Experimental study on boundary lubricity of superficial area of articular cartilage and synovial fluid

The boundary lubrication mechanism at the articulating surface of natural synovial joints has been the subject of much discussion in tribology. In this study, to elucidate the lubricating function of the superficial area of articular cartilage and synovial fluid (SF), cartilage specimens were processed with four different treatments: gentle and severe washing with detergent, incubation in NaCl solution, and trypsin digestion to selectively remove certain constituents from the cartilage surface. Subsequently, the frictional characteristics were examined in phosphate-buffered saline (PBS) and SF against glass. Angularly reciprocating sliding tests with a spherical glass probe and square articular cartilage specimens were performed at low contact loads in the mN range to extract the frictional behavior in the superficial area of the cartilage specimens. Meanwhile, the cartilage surface was observed to confirm the effects of treatments on the morphology of the cartilage surface using a fluorescence microscope and water-immersion methods. The coefficient of friction (COF) of the prepared cartilage specimens was varied from 0.05 to over 0.3 in PBS. However, a certain group of cartilage specimens exhibited a low COF of less than 0.1 with limited variation. For the low COF group of specimens, all four treatments increased the COF in PBS to different extents, and fluorescence microscopy revealed that the integrity of the cartilage surface was deteriorated by treatments. This means that the intact cartilage surface had lubricating constituents to maintain low friction, and the removal of such constituents resulted in the loss of the intrinsic boundary lubricity of the cartilage surface. The variation in the COF of the cartilage specimens was suppressed in SF because it had a clear boundary lubrication effect on the cartilage surface. The lubricating effect of SF could be confirmed even after degenerative treatment.

Boundary slip and lubrication mechanisms of organic friction modifiers with effect of surface moisture

Surface moisture or humidity impacting the lubrication property is a ubiquitous phenomenon in tribological systems, which is demonstrated by a combination of molecular dynamics (MD) simulation and experiment for the organic friction modifier (OFM)-containing lubricant. The stearic acid and poly-α-olefin 4cSt (PAO4) were chosen as the OFM and base oil molecules, respectively. The physical adsorption indicates that on the moist surface water molecules are preferentially adsorbed on friction surface, and even make OFM adsorption film thoroughly leave surface and mix with base oil. In shear process, the adsorption of water film and desorption OFM film are further enhanced, particularly under higher shear rate. The simulated friction coefficient (that is proportional to shear rate) increases firstly and then decreases with thickening water film, in good agreement with experiments, while the slip length shows a contrary change. The wear increases with humidity due to tribochemistry revealing the continuous formation and removal of Si-O-Si network. The tribological discrepancy of OFM-containing lubricant in dry and humid conditions is attributed to the slip plane’s transformation from the interface between OFM adsorption film and lubricant bulk to the interface between adsorbed water films. This work provides a new thought to understand the boundary lubrication and failure of lubricant in humid environments, likely water is not always harmful in oil lubrication systems.

Effect of Sliding Velocity on UHMWPE and VEXLPE Friction Against CoCr in Multidirectional, Serum Lubricated Conditions

Abstract The recently introduced four-station friction RandomPOD device was utilized in multidirectional, circular translation pin-on-disk (CTPOD) tests. The effect of sliding velocity on friction with orthopaedic bearing materials was studied. The tests included UHMWPE and VEXLPE pins against polished CoCr disks in serum lubrication at 37 °C. In the constant velocity tests, the sliding velocities used were from 5 to 50 mm/s at intervals of 5 mm/s. The test length with each velocity was 24 h. In the constant acceleration tests, the velocity steadily increased from 0 to 50 mm/s in 24 h. In all tests, the sample size was 4. No strong effect of velocity on friction was observed. This indicated a boundary lubrication mechanism. With sliding velocities above 10 mm/s, VEXLPE showed significantly lower friction than UHMWPE. The finding was in agreement with earlier dynamic RandomPOD tests. Clinically, the use of VEXLPE may result in lower frictional heating.

Construction and Tribological Properties of Biomimetic Cartilage-Lubricating Hydrogels.

Articular cartilage provides ultralow friction to maintain the physiological function of the knee joint, which arises from the hierarchical complex composed of hyaluronic acid, phospholipids, and lubricin, covering the cartilage surface as boundary lubrication layers. Cartilage-lubricating polymers (HA/PA and HA/PM) mimicking this complex have been demonstrated to restore the lubrication of cartilage via hydration lubrication, thus contributing to the treatment of early osteoarthritis (OA) in vivo. Here, biomimetic cartilage-lubricating hydrogels (HPX/PVA) were constructed by blending HA/PA and HA/PM (HPX) with polyvinyl alcohol (PVA) to improve the boundary lubrication and wear properties, so that the obtained hydrogels may offer a solution to the main drawbacks of PVA hydrogels used as cartilage implants. The HPX/PVA hydrogels exhibited good physicochemical and mechanical properties through hydrogen-bonding interactions, and showed lower friction and wear under the boundary lubrication and fluid film lubrication mechanisms, which remained when the hydrogels were rehydrated. Our strategy may provide new insights into exploring cartilage-inspired lubricating hydrogels.

Novel Boundary Lubrication Mechanisms from Molecular Pillows of Lubricin Brush-Coated Graphene Oxide Nanosheets.

There are numerous biomedical applications where the interfacial shearing of surfaces can cause wear and friction, which can lead to a variety of medical complications such as inflammation, irritation, and even bacterial infection. We introduce a novel nanomaterial additive comprised of two-dimensional graphene oxide nanosheets (2D-NSCs) coated with lubricin (LUB) to reduce the amount of tribological stress in biomedical settings, particularly at low shear rates where boundary lubrication dominates. LUB is a glycoprotein found in the articular joints of mammals and has recently been discovered as an ocular surface boundary lubricant. The ability of LUB to self-assemble into a "telechelic" brush layer on a variety of surfaces was exploited here to coat the top and bottom surfaces of the ultrathin 2D-NSCs in solution, effectively creating a biopolymer-coated nanosheet. A reduction in friction of almost an order of magnitude was measured at a bioinspired interface. This reduction was maintained after repeated washing (5×), suggesting that the large aspect ratio of the 2D-NSCs facilitates effective lubrication even at diluted concentrations. Importantly, and unlike LUB-only treatment, the lubrication effect can be eliminated over 15 rinsing cycles, suggesting that the LUB-coated 2D-NSCs do not exhibit any binding interactions with the shearing surfaces. The effective lubricating properties of the 2D-NSCs combined with full reversibility through rinsing make the LUB-coated 2D-NSCs an intriguing candidate as a lubricant for biomedical applications.

Tribological behavior of black phosphorus nanosheets as water-based lubrication additives

Black phosphorus (BP) with a layered structure has been used gradually as a lubrication additive in the tribological area. In this study, BP powders are produced via an easy method of high-energy ball milling using red phosphorus as a raw material. Subsequently, BP nanosheets are prepared via liquid exfoliation in N-methyl pyrolidone solvent. The tribological behavior of BP nanosheets as water-based lubrication additives (BP-WL) is evaluated under Ti6Al4V (TC4)/GCr15 contact. The results suggest that the 70 mg/L BP-WL sample exhibits excellent lubrication performance, whose coefficient of friction (COF) and ball wear rate reduced by 32.4% and 61.1%, respectively, compared with those of pure water. However, as the load increased, the tribological properties of BP-WL reduced gradually because of the agglomeration of BP nanosheets. Based on tribological experiments and worn surface analysis, boundary lubrication mechanisms are proposed. The friction reduced, which is primarily attributed to the low interlaminar shear and adsorption of BP nanosheets. In addition, a tribochemical reaction film comprising TiO2, Al2O3, and Fe2O3 effectively protects the surface of titanium alloy/steel from wear. This new water-based lubrication additive can be used to process titanium alloys.

Comparative study on microstructure, bio-tribological behavior and cytocompatibility of Cr-doped amorphous carbon films for Co–Cr–Mo artificial lumbar disc

Cr-doped amorphous carbon (a-C:Cr) film is a promising protective coating to extend the lifetime of Co–Cr–Mo implants. Here, a-C:Cr films with the same doping concentration of Cr and thickness are deposited on Co–Cr–Mo substrates using the closed-field unbalanced magnetron sputtering (UBMS) and the plasma-enhanced chemical vapor deposition (PECVD) methods. A comparative study on the microstructure, bio-tribological behavior, and cytocompatibility of two kinds of a-C:Cr films in the air and different simulated body fluids is conducted. Microstructural analysis results show that the a-C:Cr films prepared by UBMS and PECVD methods belong to graphite-like carbon (GLC) and diamond-like carbon (DLC) films, respectively. Nanohardness of the UBMS a-C:Cr film is found to be lower than that of the PECVD counterpart. However, the UBMS a-C:Cr film exhibits better lubrication, lower wear depth and lower wear volume under all the three simulated body fluids, because of the slight polishing wear and boundary lubrication mechanisms. Moreover, both kinds of a-C:Cr films significantly improve the cytocompatibility of Co–Cr–Mo substrate alloy.

A Tribological Study of Effect of Lubricants and Lubrication Mechanisms in Rolling Process: A Review

The rolling process had been used in every aspect of our life. Various types of sections like tee, angle, channel, railway track, sheets, foils of different mate-rial are made by rolling process. The quality of the product depends upon the various characteristics of rolling parameters. At the junction, the key role played by lubricants for saving energy and properties of the material in contact. Re-searchers are putting continuous efforts into the tribological analysis and developing new lubricants for the rolling process according to the material. The authors had reviewed the lubricants used in different rolling processes and found out a diverse range of lubricants. Various ecologically safe and effective lubricants had been reviewed. Lubrication performance testing tribometer for testing of tribological properties of lubricants had been reviewed. Hydrodynamic, mixed and boundary lubrication mechanisms had been found in different rolling conditions. The use of lubricants was found helpful in reducing power consumption in rolling and good quality products, hence the cost

Correlation Between the Adsorption and the Nanotribological Performance of Fatty Acid-Based Organic Friction Modifiers on Stainless Steel

Surface adsorption of amphiphilic molecules is a vital mechanism of boundary lubrication on stainless steel surfaces. The self-assembly of four fatty acid-based organic friction modifiers in two alkane solvents and their adsorption onto stainless steel surfaces was investigated using Dynamic Light Scattering and Quartz Crystal Balance with Dissipation, respectively. These properties were related to the friction force between a sharp tip and the steel surface measured using Lateral Force Microscopy. The molecular structures of the organic friction modifiers were chosen in order to study the effects of unsaturation and number of alkyl chains as well as the composition of the polar head groups on their assembly in solution, adsorption, and nanotribological behavior. Sorbitan monooleate and dioleate adsorb as monolayers with their alkyl chains either in the upright or tilted configuration, depending on their concentration. If large supramolecular structures were present in the solvent, i.e., for sorbitan monolaurate and glycerol monooleate, micelle adsorption and rearrangement on the surface and multilayer formation took place, respectively. A correlation between the adsorption rate constant and the coefficient of friction of the organic friction modifiers was revealed in these studies, with the coefficient of friction decreasing with an increase in the adsorption rate.

Boundary lubrication properties and contact mechanism of carbon/MoS2 based nanolubricants under steel/steel contact

Lubrication mechanism of some carbon-based nanoparticles is unresolved and needs proper attention. In this work, friction and wear properties of carbon/MoS2 solid lubricants are tested in the boundary lubrication regime and further compared with oil-based binary and ternary nanolubricants. Results show that MWCNT and fullerene have high values of friction coefficient and wear rate in a dry medium. However, in lubricated medium with fomblin oil, they comply with the boundary lubrication mechanism and provide low friction and wear. The binary and ternary nanolubricants of oil-graphene, oil-MoS2, and oil-graphene-MoS2, oil-graphene-fullerene have provided enhanced wear and friction performance due to a build-up of a tribofilm between the contact zones. The interfacial contact mechanism depends on aggregation and particle rolling for dry and lubrication contact, respectively.

Boundary Lubricating Properties of Black Phosphorus Nanosheets in Polyalphaolefin Oil

As a novel layered material, black phosphorus (BP) shows unexpected characteristics in many aspects including tribological application. In this work, BP was prepared through ball milling from red phosphorus (RP). The boundary lubricating properties of the BP nanosheets were investigated on a ball-on-disk tribometer as lubricating additives in polyalphaolefin oil. The micromorphologies, concentration, and composition of the typical chemical elements on the worn surfaces were measured by the 3D laser scanning microscope, scanning electron microscope, and X-ray photoelectron spectrometer, respectively. The results show that bulk BP can be found after RP was milled at 500 rpm for 36 h. The Raman intensity of the BP increased initially and then decreased with the increase in milling time, and the maximum intensity can be obtained at 60 h. The BP nanosheets displayed excellent antifriction and anti-wear performances as lubricating additives in PAO6 oil for steel/steel contact in boundary lubrication regime. The boundary lubrication mechanism of the BP nanosheets is dominated by the physical slippery effect of the laminated nanosheets and the tribofilm on the rubbing surfaces.

Articular cartilage: Hydrophilic and boundary layered lubrication mechanism with phospholipid - (lubricin, hyaluronan) participation

Articular cartilage: Hydrophilic and boundary layered lubrication mechanism with phospholipid - (lubricin, hyaluronan) participation

Boundary Lubrication Behavior and Mechanism Analysis of Oil-Water Emulsion

Boundary Lubrication Behavior and Mechanism Analysis of Oil-Water Emulsion

Elastic Lubricious Effect of Solidlike Boundary Films in Oil-Starvation Lubrication

Herein, a boundary lubrication (BL) mechanism based on the carbon-based tribofilms formed via Ni(Cu)-catalytic dehydrogenation of hydrocarbon oils was queried by performing standard ball-on-disk tr...

Shaft seal operated in boundary lubrication mechanism

Shaft seal operated in boundary lubrication mechanism

Study on Boundary Lubrication Properties and Lubrication Mechanism in Combined Condition of MoP and ZnDTP

Study on Boundary Lubrication Properties and Lubrication Mechanism in Combined Condition of MoP and ZnDTP

A low friction, biphasic and boundary lubricating hydrogel for cartilage replacement.

This paper presents the synthesis, characterisation and preliminary tribological testing of a new biomaterial that aims to recreate the primary chondral lubrication mechanisms: boundary and biphasic lubrication. This work has demonstrated that the introduction of an established zwitterionic, biomimetic boundary lubricant can improve the frictional properties of an ultra-tough hydrogel. This new biomaterial, when used as a partial joint replacement bearing material, may help avoid damage to the opposing chondral surface-which has been reported as an issue for other non-biomimetic partial joint replacement materials. Alongside the synthesis of a novel biomaterial focused on complementing the lubrication mechanisms of cartilage, your readership will gain insights into effective mechanical and tribological testing methods and materials characterisation methods for their own biomaterials.

Stick-Slip Friction Reveals Hydrogel Lubrication Mechanisms.

The lubrication behavior of the hydrated biopolymers that constitute tissues in organisms differs from that outlined by the classical Stribeck curve, and studying hydrogel lubrication is a key pathway to understand the complexity of biolubrication. Here, we have investigated the frictional characteristics of polyacrylamide (PAAm) hydrogels with various acrylamide concentrations, exhibiting Young's moduli (E) that range from 1 to 40 kPa, as a function of applied normal load and sliding velocities by colloid probe lateral force microscopy. The speed-dependence of the friction force shows an initial decrease in friction with increasing velocity, while, above a transition velocity V*, friction increases with speed. This study reveals two different boundary lubrication mechanisms characterized by distinct scaling laws. An unprecedented and comprehensive study of the lateral force loops reveals intermittent friction or stick-slip above and below V*, with characteristics that depend on the hydrogel network, applied load, and sliding velocity. Our work thus provides insight into the closely tied parameters governing hydrogel lubrication mechanisms, and stick-slip friction.

Cross-Sectional Imaging of Boundary Lubrication Layer Formed by Fatty Acid by Means of Frequency-Modulation Atomic Force Microscopy.

To observe in situ the adsorption of fatty acid onto metal surfaces, cross-sectional images of the adsorption layer were acquired by frequency-modulation atomic force microscopy (FM-AFM). Hexadecane and palmitic acid were used as the base oil and typical fatty acid, respectively. A Cu-coated silicon wafer was prepared as the target substrate. The solvation structure formed by hexadecane molecules at the interface between the Cu substrate and the hexadecane was observed, and the layer pitch was found to be about 0.6 nm, which corresponds to the height of hexadecane molecules. This demonstrates that hexadecane molecules physically adsorbed onto the surface due to van der Waals forces with lying orientation because hexadecane is a nonpolar hydrocarbon. When hexadecane with palmitic acid was put on the Cu substrate instead of pure hexadecane, an adsorption layer of palmitic acid was observed at the interface. The layer pitch was about 2.5-2.8 nm, which matches the chain length of palmitic acid molecules well. This indicates that the original adsorption layer was monolayer or single bilayer in the local area. In addition, a cross-sectional image captured 1 h after observation started to reveal that the adsorbed additive layer gradually grew up to be thicker than about 20 nm due to an external stimulus, such as cantilever oscillation. This is the first report of in situ observation of an adsorbed layer by FM-AFM in the tribology field and demonstrates that FM-AFM is useful for clarifying the actual boundary lubrication mechanism.