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At least 289 records · Page 16Linked to original sources

PubMed2000

Squeeze-film lubrication of the human ankle joint with synovial fluid filtrated by articular cartilage with the superficial zone worn out.

A squeeze-film lubrication model of the human ankle joint in standing that takes into account the fluid transport across the articular surface is presented. Articular cartilage is a biphasic mixture of the ideal interstitial fluid and an elastic permeable isotropic homogeneous intrinsically incompressible matrix. The simple homogeneous model for articular cartilage models the case of early osteoarthritis, when the intact superficial zone of the normal articular cartilage, much stiffer in tension than the bulk material, has been already disrupted or worn out. The calculations indicate for this case that in normal approach motion the lubricating fluid film is quickly depleted and turned into a synovial gel film that is supposed to serve as a boundary lubricant if sliding motion follows

Ankle Joint↗

PubMed1998

Relationship between the conformity and the lubricating ability of synovial joints.

OBJECTIVE: To relate conformity of sliding surfaces with the lubricating ability of synovial joints. DESIGN: Measurement of start-up friction in the stifles of various animals. Assessment of conformity by Hertzian contact area. BACKGROUND: Past studies showed that the start-up friction in synovial joints sharply increased with the loading duration. The reasons why the friction increased and why the increasing rate is different in different joints were, however, not found. METHODS: Nine stifle joints from various animals were used. A robotic arm was used to give the compressive force and the sliding motion to the joint. Start-up friction was measured by a universal force sensor. The principal curvatures of the sliding surfaces were directly measured by a radius-gauge. Hertzian contact area was calculated from the principal curvatures of the sliding surfaces. RESULTS: The duration until the frictional coefficient reached 0.1 was related to the Hertzian contact area. CONCLUSION: The conformity of sliding surfaces is related to the lubrication ability in synovial joints. The squeeze-film mechanism plays an important role in joint lubrication.

Journal Article↗

PubMed2001

Phospholipid composition of articular cartilage boundary lubricant.

The mechanism of lubrication in normal human joints depends on loading and velocity conditions. Boundary lubrication, a mechanism in which layers of molecules separate opposing surfaces, occurs under severe loading. This study was aimed at characterizing the phospholipid composition of the adsorbed molecular layer on the surface of normal cartilage that performs as a boundary lubricant. The different types of phospholipid adsorbed onto the surface of cartilage were isolated by extraction and identified by chromatography on silica gel paper and mass spectroscopy. The main phospholipid classes identified were quantified by a phosphate assay. Gas chromatography and electrospray ionization mass spectrometry were used to further characterize the fatty acyl chains in each major phospholipid component and to identify the molecular species present. Phosphatidylcholine (41%), phosphatidylethanolamine (27%) and sphingomyelin (32%) were the major components of the lipid layer on the normal cartilage surface. For each lipid type, a mixture of fatty acids was detected, with a higher percentage of unsaturated species compared to saturated species. The most abundant fatty acid observed with all three lipid types was oleic acid (C18:1). Additional work to further quantify the molecular species using electrospray ionization mass spectrometry is recommended.

Animals↗

PubMed2000

Powder and capsule filling properties of lubricated granulated cellulose powder.

Granulated powdered cellulose was studied in terms of powder bulk properties and capsule filling performance on a tamp-filling machine with and without the addition of various concentrations of magnesium stearate. Carr's compressibility reached its minimum value at 0.4% magnesium stearate suggesting an improvement of powder flow compared to the unlubricated material. However, shear cell measurements and the use of a powder rheometer indicated that the addition of 0.2% magnesium stearate and more impairs powder flow and does not reduce interparticulate friction. When capsules were filled into hard gelatine capsules at a zero-compression setting, the fill weight and plug density could be predicted from Carr's compressibility index and from the maximum bulk density. The decrease in one and simultaneous increase in the other bulk property with increasing magnesium stearate concentration caused both fill weight and plug density to go through a minimum at a lubricant concentration of 0.4%. When the capsules were filled at maximum compression, however, the addition of lubricant increased the coefficient of fill weight variation significantly, and the plug density remained constant for any added concentration of magnesium stearate. These findings were in agreement with the shear cell and powder rheometer results. However, the optimum lubricant concentration in terms of ease of machine function, which was identified from tamping pressure measurements, was found to be 0.8% magnesium stearate, which was not an optimal concentration for the powder bulk properties.

Capsules↗

PubMed2003

Lubrication by charged polymers.

Long-ranged forces between surfaces in a liquid control effects from colloid stability to biolubrication, and can be modified either by steric factors due to flexible polymers, or by surface charge effects. In particular, neutral polymer 'brushes' may lead to a massive reduction in sliding friction between the surfaces to which they are attached, whereas hydrated ions can act as extremely efficient lubricants between sliding charged surfaces. Here we show that brushes of charged polymers (polyelectrolytes) attached to surfaces rubbing across an aqueous medium result in superior lubrication compared to other polymeric surfactants. Effective friction coefficients with polyelectrolyte brushes in water are lower than about 0.0006-0.001 even at low sliding velocities and at pressures of up to several atmospheres (typical of those in living systems). We attribute this to the exceptional resistance to mutual interpenetration displayed by the compressed, counterion-swollen brushes, together with the fluidity of the hydration layers surrounding the charged, rubbing polymer segments. Our findings may have implications for biolubrication effects, which are important in the design of lubricated surfaces in artificial implants, and in understanding frictional processes in biological systems.

Journal Article↗

PubMed2000

Determination of metals in lubricating oils by flame atomic absorption spectrometry using a single-bore high-pressure pneumatic nebulizer.

The behaviour of a single-bore high-pressure pneumatic nebulizer (SBHPPN) as a tool for the analysis of lubricating oils by flame atomic absorption spectrometry (FAAS) was investigated. The effects of the sample oil content [from 10% to 100% (w/w) oil in 4-methylpentan-2-one, IBMK] and the carrier nature (IBMK and methanol) on the characteristics of the aerosols generated, on the analyte transport efficiency and on the analytical figures of merit in FAAS were studied. A pneumatic concentric nebulizer (PCN) was used for comparison. Increasing the oil content increases the viscosity of the sample. With the PCN this gives rise to coarser aerosols, making it impossible to nebulize samples with an oil content higher than 70% (w/w). Using the SBHPPN, the viscosity of the sample scarcely affects the characteristics of the primary aerosols. Hence, the SBHPPN is able, by using the appropriate carrier, to nebulize pure lubricating oils. Among the carriers tested, IBMK is the most advisable because it is fully miscible with all the oil samples. The SBHPPN provides higher sensitivities and lower limits of detection than the PCN. Compared with a method based on organic dilution, the use of the SBHPPN for the direct analysis of lubricating oils by FAAS makes it possible, in addition to increasing the analysis throughput, to detect elements at lower concentrations. Moreover, the SBHPPN provides similar results to those obtained using a previous acid digestion step.

Journal Article↗

PubMed1985

The molecular structure and lubricating activity of lubricin isolated from bovine and human synovial fluids.

Lubricin was isolated from bovine ankle, metacarpophalangeal and knee and human knee synovial fluids. The lubricins isolated from the bovine joint fluids had the same amino acid and carbohydrate compositions, but differences were observed in the relative molecular masses. The Mr values of bovine metacarpophalangeal and ankle lubricin determined by light-scattering measurements were about 200 000, whereas values of 132 000 and 143 000 were obtained for the bovine knee lubricin. The human knee lubricin had a similar carbohydrate composition to bovine knee lubricin except for the higher glucosamine content, and the amino acid composition differed slightly. The human sample had a lower glutamic acid content and a leucine/isoleucine ratio of 2:1 compared with 1:1 in the bovine. The Mr value of the human knee lubricin (166 000) was also lower than that of the bovine metacarpophalangeal and ankle samples. The Mr value of the bovine knee lubricin determined by sedimentation-equilibrium measurements was 171 000. The length measurements determined by electron microscopy and also the sedimentation measurements showed considerable polydispersity and indicate that the degree of extension of lubricin molecules can vary. Friction measurements showed that the human knee synovial-fluid lubricin had equivalent lubricating ability in a test system in vitro to that observed for lubricin isolated from normal bovine synovial fluids. The lubricating ability of lubricin was concentration-dependent, and each lubricin sample was able to act as a lubricant in vitro in an equivalent manner to whole synovial fluid at concentrations that are thought to occur in vivo.

Amino Acids↗

PubMed2006

Polyurethane unicondylar knee prostheses: simulator wear tests and lubrication studies.

Many materials are used as artificial joint bearing surfaces; these include conventional stainless steel or CoCrMo-on-ultra-high molecular weight polyethylene (UHMWPE), CoCrMo on itself and alumina-on-alumina. However, these joints have a limited lifespan resulting in failure of the prosthesis and the need for revision surgery. A number of materials have been introduced recently in an attempt to overcome these problems. Polycarbonate urethane (PU) is a compliant material that can be used as an artificial joint bearing surface which has been developed to mimic the natural synovial joint more accurately by promoting fluid film lubrication. Tribological tests were performed on CoCrMo-on-PU unicondylar knee prostheses to assess their performance in vitro. The wear produced by these components was considerably lower than that found for conventional joints. They also exhibited low friction and operated close to full-fluid film lubrication with viscosities of lubricant similar to those found in patients with arthritis. These tests gave encouraging results for the tribological performance of this material couple for use as an alternative bearing combination.

Biocompatible Materials↗

PubMed1998

Release of lubricating synovial surfactant by intra-articular steroid.

This study was undertaken to determine whether glucocorticosteroids promote the secretion of lubricating surfactant, i.e. surface-active phospholipid (SAPL), into the joint. A standard clinical dose (100 mg) of methylprednisolone acetate (MPA) in 2.5 ml of saline was injected into the load-bearing right radiocarpal joint of five horses and 2.5 ml of saline injected into each of the contralateral joints used as controls. Synovial fluid (SF) was aspirated from all 10 joints before injection and at intervals of 16 and 32 h after injection, and then analysed by standard methods. All test joints showed an elevated level of SAPL, the increases averaging 112% after 16 h and 76% after 32 h, which were highly significant relative to the control joints. A large increase at 16 h was also found in proteolipid as a possible further marker of surfactant release. Significant quantities of proteolipid were also found in human SF. Since intra-articular steroids can dramatically improve joint mobility in both humans and horses, it is proposed that part of the benefit may be derived from improved lubrication arising from the remarkable ability of SAPL to lubricate under high load. Other possible benefits of elevating surfactant levels in the joints include control of cartilage hydration, promotion of macrophage activity and the ability to scavenge oxygen free radicals.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1999

Lubricating bacteria model for branching growth of bacterial colonies.

Various bacterial strains (e.g., strains belonging to the genera Bacillus, Paenibacillus, Serratia, and Salmonella) exhibit colonial branching patterns during growth on poor semisolid substrates. These patterns reflect the bacterial cooperative self-organization. A central part of the cooperation is the collective formation of a lubricant on top of the agar which enables the bacteria to swim. Hence it provides the colony means to advance towards the food. One method of modeling the colonial development is via coupled reaction-diffusion equations which describe the time evolution of the bacterial density and the concentrations of the relevant chemical fields. This idea has been pursued by a number of groups. Here we present an additional model which specifically includes an evolution equation for the lubricant excreted by the bacteria. We show that when the diffusion of the fluid is governed by a nonlinear diffusion coefficient, branching patterns evolve. We study the effect of the rates of emission and decomposition of the lubricant fluid on the observed patterns. The results are compared with experimental observations. We also include fields of chemotactic agents and food chemotaxis and conclude that these features are needed in order to explain the observations.

Bacteria↗

PubMed2002

Boundary lubrication properties of materials with expansive freezing.

We have performed molecular dynamics simulations of solid-solid contacts lubricated by a model fluid displaying many of the properties of water, particularly its expansive freezing. Near the region where expansive freezing occurs, the lubricating film remains fluid, and the friction force decreases linearly as the shear velocity is reduced. No sign of stick-slip motion is observed, even at the lowest velocities. We give a simple interpretation of these results, and suggest that, in general, good boundary lubrication properties will be found in the family of materials with expansive freezing.

Journal Article↗

PubMed1996

Lubrication of visceral movement and gastric motility by peritoneal surfactant.

Four studies are described as a means of evaluating the hypothesis that surface-active phospholipid (SAPL) enhances the lubrication of gastric motility and visceral movement in general. In the first two studies, a lipid extract from ovine peritoneal rinsings was found to have remarkable antiwear capabilities ex vivo and to reduce friction to a remarkably low level as quantified by a coefficient of kinetic friction of 0.008 +/- 0.002 (n = 10). Moreover, this lipid extract demonstrated both these features of lubrication at high load. In other studies, peritoneal lipid extract was found to be highly surface-active, while many lamellar bodies (LB) have been identified in omentum and, by analogy with the lung and the stomach, would therefore appear to be a source of SAPL. Lubrication by peritoneal surfactant is discussed as another example of a ubiquitous barrier to abrasion and other potential insults common to all visceral surfaces.

Animals↗

PubMed2001

The thixotropic effect of the synovial fluid in squeeze-film lubrication of the human hip joint.

The thixotropic (shear-thinning) effect of the synovial fluid in squeeze-film lubrication of the human hip joint is evaluated, taking into account filtration of the squeezed synovial film by biphasic articular cartilage. A porous, homogeneous, elastic cartilage matrix filled with the interstitial ideal fluid, with the intact superficial zone (of lower permeability and stiffness in compression) already disrupted or worn away, models an early stage of arthritis. Due to a high viscosity of the normal synovial fluid at very low shear rates, the squeezed synovial film at a fixed time after the application of a steady load is found to be much thicker in a small central part of the lubricated contact area. In the remaining part, the film is thin as it corresponds to the Newtonian fluid with the same high-shear-rate viscosity. Filtration is lower for the normal cartilage with the intact superficial zone due to its lower permeability and compression stiffness. But even in the fictitious case of zero filtration, calculations show that the effect of thixotropy on the increase of the minimum synovial film thickness would manifest itself as late as after several tens of seconds since the physiologic load application. At that time, this thickness would be as low as about 0.3 microm. It follows that thixotropy of the normal synovial fluid (and so much more of the inflammatory fluid) is irrelevant in squeeze-film lubrication of both the normal and arthritic human hip joints.

Arthritis, Rheumatoid↗

PubMed1990

Surface-active phospholipid in muscle lymph and its lubricating and adhesive properties.

In order to investigate the role of phospholipid in facilitating lymph flow, "deep-thigh" lymph was collected from ten anesthetized dogs and analyzed for phospholipids using thin-layer chromatography. The lymph was found to be surface active at liquid and at solid surfaces at which it deposited a hydrophobic monolayer in vitro. Extracted phospholipid was found to be an effective release agent as a monolayer, reducing the force of adhesion of 5% protein solutions by 76% according to a standard test for tacky glues. The same monolayers were effective lubricants, reducing friction by 96%; while mixtures of the same phospholipids from synthetic sources gave similar results for release and lubrication. Surfaces in contact with extracellular fluid or lymph in vivo were found to be hydrophobic with a drop of saline on semitendinosus muscle fibers displaying a contact angle of 40.2 degrees +/- 7.2 degrees. The results are considered compatible with the hypothesis that surface-active phospholipid facilitates the flow of lymph; while it could also provide boundary lubrication for sliding of connective tissue in locomotion and for any relative movement of motor units in muscle contraction and fatigue.

Animals↗

PubMed1989

The effect of bacteriostatic lubricant on group B streptococcal cultures of the female genital tract.

The purpose of this prospective investigation was to determine the effect of bacteriostatic lubricant on group B streptococcal cultures obtained from the lower genital tract of pregnant women. Fifty pregnant women with intact membranes who recently had genital tract cultures for group B streptococci were evaluated. The study group consisted of 25 women who had positive cultures, and the control group comprised 25 women who had negative cultures. All patients underwent examination with a sterile nonlubricated speculum within 7 days of the previously obtained cultures. Secretions from the endocervix and from the posterior vaginal wall near the introitus were collected with a sterile cotton-tipped applicator and inoculated directly onto a selective blood agar culture plate. The sterile speculum was removed and a digital examination performed using bacteriostatic lubricant. A second sterile speculum was then inserted into the vagina and another group B streptococcal culture was obtained. There was 100% correlation between the cultures obtained before and after the vaginal examination. We conclude that use of bacteriostatic lubricant does not alter the recovery of group B streptococci from the genital tract of pregnant women with intact membranes.

Chlorhexidine↗

PubMed1985

Long-term mortality study of oil refinery workers. IV. Exposure to the lubricating-dewaxing process.

A retrospective cohort mortality study of 1,008 male oil refinery workers who ever worked on the lubricating-dewaxing process of the lube oil department and who have been followed for a period of 43 years is presented. These workers were exposed to a number of solvents, primarily methyl ethyl ketone [(MEK) CAS: 78-93-3] and toluene (CAS: 108-88-3), but at levels far below the current Occupational Safety and Health Administration's standard. The standardized mortality ratio (SMR) for all causes (0.70) and the SMR for cancer (0.86) are much lower than unity when they are compared to the mortality experience of the U.S. population. Also observed in this study were 8 prostate cancer deaths (4.4 expected) with an SMR of 1.82, which was not statistically significant (P = .16). Seven of these 8 prostate cancer deaths occurred among nonwhite males, who showed an SMR of 2.47 (P = 0.53). However, only 1 prostate cancer death was seen among workers specifically assigned to the MEK units. The remaining deaths occurred among maintenance workers who had lube oil department-wide assignments. This cancer risk increased with increasing duration of employment in the lube oil department. A latency of 20 years or more was also observed for these prostate cancer deaths. In this study the processing of lubricating oils was found to be at least as important as the MEK solvents, and department-wide maintenance workers were as much at risk as the MEK unit workers. In view of this finding and findings obtained by others, it seems prudent to continue to study lubricating-dewaxing process workers, including the medical monitoring of all such workers for prostate cancer.

Butanones↗

PubMed1980

[Viscosity of synovial fluid and possible artificial lubricants (author's transl)].

The viscosity of "normal" post mortem synovial fluid, and synovial fluid samples of knee joints affected by various joint diseases (inflammatory and non inflammatory) was investigated and compared with flow curves of Hyaluronic acid and Polyacrylamide solutions. The viscoelastic behaviours of synovial fluid seems to be of great importance for the lubrication mechanism of the joints. Differing results of the viscoelastic properties could be determined in different joint diseases. As a result of these changes the lubrication mechanism is impaired and this leads to cartilage wear. Solutions of Polyacrylamide and Hyaluronic acid have been investigated as model-substances, the former showing rheological properties similar to normal synovial fluid. Their application as an artificial lubricant has been investigated.

Acrylic Resins↗

PubMed2004

Lubrication and wear properties of grafted polyelectrolytes, hyaluronan and hylan, measured in the surface forces apparatus.

Hyaluronan is believed to have an important function in the boundary biolubrication of articular cartilage. Using a Surface Forces Apparatus, we tested the tribological properties of surface bound, rather than "free" hyaluronan. The grafting process of the polyelectrolyte included either a biological route via an HA-binding protein or a chemical reaction to covalently bind the polymer to a lipid bilayer coated surface. In another reaction, we constructed a surface with covalently grafted hylan (crosslinked hyaluronan). We studied the normal and shear forces between these surfaces. None of the systems demonstrated comparable lubrication to that found between cartilage surfaces except at very low loads. Both grafted hyaluronan and hylan generated coefficients of friction between 0.15 and 0.3. Thus, the polysaccharide, which is a constituent of the lamina splendens (outermost cartilage layer), is not expected to be the responsible molecule for the great lubricity of cartilage; however, it may contribute to the load bearing and wear protection of these surfaces. This was concluded from the results with hylan, where a thin gel layer was sufficient to shield the underlying surfaces from damage even at applied pressures of over 200 atmospheres during shear. Our study shows that a low coefficient of friction is not a requirement for, or necessarily a measure of, wear protection.

Aluminum Silicates↗