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Results for “LUBRICATION”

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At least 307 records · Page 17Linked to original sources

PubMed1986

Drug-excipient interactions resulting from powder mixing. IV: Role of lubricants and their effect on in vitro dissolution.

Two lubricants, magnesium stearate and sodium stearyl fumarate, were compared under identical mixing conditions to study their roles in drug-excipient interactions. After prolonged mixing, sodium stearyl fumarate did not interact with the drug or excipients; as a result, the disintegration time and drug dissolution rate from hand-filled, uncompacted capsules were not adversely affected. In contrast, magnesium stearate did exhibit drug-excipient interactions which resulted in lamination and subsequent adhesion of the lubricant to the drug-crospovidone agglomerates. These interactions adversely affected the disintegration time and drug dissolution rate from hand-filled, uncompacted capsules. Although the initial specific surface area of magnesium stearate was higher than that of sodium stearyl fumarate, flaking of magnesium stearate due to particulate-particulate interactions caused a large increase in the surface area. The adhesion of the magnesium stearate flakes to the drug-crospovidone agglomerates resulted in a decrease in the drug dissolution rate.

Chemistry, Pharmaceutical↗

PubMed2005

[Activity of antiseptic catheter lubricants against methicillin-resistant Staphylococcus aureus (MRSA)].

In recent years, general and urinary tract infections caused by methicillin-resistant Staphylococcus aureus (MRSA) have became an increasing problem worldwide. Catheterization of the urinary bladder is one of the most significant risk factors for MRSA contamination of the urine. In vitro tests have documented the antimicrobial activity of the catheter lubricants Instillagel and Endosgel against MRSA specimens within 5 min. These findings support recommending the use of these lubricants in high-risk patients in hospitals and old people's homes for prophylaxis of MRSA bacteriuria.

Aged↗

PubMed1993

The role of synovial fluid filtration by cartilage in lubrication of synovial joints--I. Mixture model of synovial fluid.

A mathematical model of lubrication of human synovial joints under squeeze-film conditions is presented in this several-part paper. Squeeze-film action leads to a concentration of hyaluronic-acid-protein macromolecular complex in the synovial fluid between the approaching cartilage surfaces as a result of the diffusion of water and low molecular weight substances through the cartilage surfaces or along the gap. Increasing viscosity of synovial fluid delays the approach of these surfaces and the formation of stable gels then protects cartilage, if sliding motion ensues, before fluid film lubrication is restored. In Part I of the present paper synovial fluid is considered as a mixture of two incompressible fluids. The material parameters of this mixture of fluids are found using previously published experimental results. Squeeze-film analysis is carried out for the axially symmetric synovial film.

Cartilage, Articular↗

PubMed1990

Persistence of N-nitrosodiethanolamine contamination in American metal-working lubricants.

The potent carcinogen N-nitrosodiethanolamine (NDELA) was discovered as a contaminant of commercial metal-working lubricants over a decade ago. To determine whether or not improvements in industrial practice suggested in the meantime have eliminated this contamination from United States products, a selection of cutting fluids obtained from the current marketplace was analysed for NDELA content. All six semi-synthetic fluids examined contained NDELA at levels ranging from 0.5 to 4.3 ppm. Three of six petroleum-based lubricants and five of six synthetics also contained significant NDELA (when analysed at a detection limit of 0.03 ppm), at levels of up to 0.16 and 55 ppm, respectively. The mean concentrations were 1.5 ppm for the semi-synthetics, 0.07 ppm for the petroleum-based products, and 11.4 ppm for the synthetic metal-working fluids. While these levels are far below the values of 1-2% by weight (10,000-20,000 ppm) found in some contaminated products 13 years ago, they may nevertheless pose a continuing health risk for the machinists who work with them.

Diethylnitrosamine↗

PubMed2006

Photoinduced phospholipid polymer grafting on Parylene film: advanced lubrication and antibiofouling properties.

Poly(p-xylylene) (Parylene C) coatings have been applied in implantable electronic devices because of their electrical insulation and moisture barrier properties. To provide lubrication and an antibiofouling surface, a biomimetic phospholipid polymer--poly(2-methacryloyloxyethyl phosphorylcholine (MPC))--was grafted from the surface using UV irradiation with benzophenone as an initiator. The poly(MPC) grafting on the Parylene C films was confirmed by attenuated total reflection-Fourier transfer inflated irradiation, X-ray photoelectron spectroscopy and ellipsometry. These analyses indicated that the Parylene C films were completely covered by the poly(MPC)-graft layer with an average thickness of 140 nm under dry condition. The atomic force microscope (AFM) images revealed that the poly(MPC)-graft chains extended under wet condition. However, they formed globular structures under dry condition. Water contact angle measurements revealed a decreased receding angle of 29.5 degrees on the poly(MPC)-grafted surface with a high hysteresis of 41.4 degrees. These results indicate that the poly(MPC)-graft chains gain mobility in a wet environment. The average kinetic friction coefficient of the poly(MPC)-grafted surface in water was 0.018, which was 90% lower than that of the original surface. The in vitro single protein adsorption reduced by over 70% due to the poly(MPC) grafting. The hydrated poly(MPC)-graft chains are considered to provide lubrication and antibiofouling properties. The surface zeta potential measurement clarified the electroneutrality of the poly(MPC)-grafted surface. We concluded that the poly(MPC) grafting from the Parylene C layer significantly improved its surface properties and, subsequently, its biological properties.

Animals↗

PubMed2004

Lubrication regimes in mesothelial sliding.

To function normally, the lungs, heart, and other organs must undergo changes in shape and size, sliding against surrounding body walls. It is not known whether the delicate mesothelial surfaces covering these organs and body wall are in contact during sliding, or if hydrodynamic pressure in the lubricating liquid increases separation between their surfaces. To address this question, we measured the coefficient of friction (mu) of the mesothelial surface of nine rat-abdominal walls sliding in saline on a smooth glass surface. Sliding at physiological velocities of 0.0123-6.14 cm/s with normal stresses of 50-200 Pa, mu varied with velocity (P<0.001). On average, mu was relatively high at low speeds (0.078 at 0.041 cm/s), decreased to a minimum at intermediate speeds (0.034 at 1.23 cm/s), and increased slightly again at higher speeds (0.045 at 6.14 cm/s), consistent with a mixed lubrication regime in which there is at least partial hydrodynamic separation of surfaces. We conclude that mesothelial surfaces, sliding under physiological conditions, are protected from excessive shear by hydrodynamic pressures that increase separation of surfaces.

Abdominal Wall↗

PubMed2006

Ranking without valuing in the face of major uncertainty--the case of the promotion of biodegradable lubricants.

Major benefit uncertainties prevent monetary quantification of some environmental amenities. Replacing mineral lubricants with biodegradable substitutes is shown to be a case in point. However, it is possible to rank the social benefits of substituting mineral lubricants with regard to different applications and environments. As the private costs and benefits of substitution are mainly constant, only a policy that prioritizes full substitution in the applications with the greatest benefits can be efficient. It is shown that regulations requiring substitution in certain fields are likely to fulfil this criterion, while subsidies for production, processing, market introduction and research usually fail to meet the efficiency criterion.

Biodegradation, Environmental↗

PubMed2006

Prediction of lubrication regimes in two-piece metacarpophalangeal prostheses.

Various designs of two-piece finger prosthesis with conforming spherical surfaces have been proposed. These were compared by calculating the lubrication regime for the material combinations and operating conditions expected at the metacarpophalangeal joints of the fingers. Consideration was given to a range of loads from 2 to 50 N, a range of entraining velocities from 0 to 30 mm/s, and a range of prosthesis radii from 3 to 10 mm. This theoretical lubrication analysis indicated that the optimum material combination of those available for two-piece metacarpophalangeal prostheses is in the order: ceramic-on-ceramic; metal-on-metal; pyrocarbon-on-pyrocarbon; and metal-on-polymer. However, it should be recognised that other factors may take precedence when choosing a material combination for a design of finger prosthesis.

Computer Simulation↗

PubMed2004

Experimental verification of the role of interstitial fluid pressurization in cartilage lubrication.

The objective of the current study was to measure the friction coefficient simultaneously with the interstitial fluid load support in bovine articular cartilage, while sliding against glass under a constant load. Ten visually normal 6-mm-diameter cartilage plugs harvested from the humeral head of four bovine shoulder joints (ages 2-4 months) were tested in a custom friction device under reciprocating linear motion (range of translation +/-2 mm; sliding velocity 1 mm/s), subjected to a 4.5 N constant load. The frictional coefficient was found to increase with time from a minimum value of mu min=0.010+/-0.007 (mean+/-SD) to a maximum value of 0.243+/-0.044 over a duration ranging from 920 to 19,870 s (median: 4,560 s). The corresponding interstitial fluid load support decreased from a maximum of 88.8+/-3.8% to 8.7+/-8.6%. A linear correlation was observed between the frictional coefficient and interstitial fluid load support (r2=0.96+/-0.03). These results support the hypothesis that the temporal variation of the frictional coefficient correlates negatively with the interstitial fluid load support and that consequently interstitial fluid load support is a primary mechanism regulating the frictional response in articular cartilage. Fitting the experimental data to a previously proposed biphasic boundary lubrication model for cartilage yielded an equilibrium friction coefficient of mu eq=0.284+/-0.044. The fraction of the apparent contact area over which the solid cartilage matrix was in contact with the glass slide was predicted at phi s=1.7+/-6.3%, significantly smaller than the solid volume fraction of the tissue, phi s=13.8+/-1.8%. The model predictions suggest that mixed lubrication prevailed at the contact interface under the loading conditions employed in this study.

Animals↗

PubMed2004

Friction and lubrication of pleural tissues.

The frictional behaviour of rabbit's visceral pleura sliding against parietal pleura was assessed in vitro while oscillating at physiological velocities and amplitudes under physiological normal forces. For sliding velocities up to 3 cm s(-1) and normal compressive loads up to 12 cm H2O, the average value of the coefficient of kinetic friction (mu) was constant at 0.019 +/- 0.002 (S.E.) with pleural liquid as lubricant. With Ringer-bicarbonate solution, mu was still constant, but significantly increased (Deltamu = 0.008 +/- 0.001; P < 0.001). Under these conditions, no damage of the sliding pleural surfaces was found on light and electron microscopy. Additional measurements, performed also on peritoneum, showed that changes in nominal contact area or strain of the mesothelia, temperature in the range 19-39 degrees C, and prolonged sliding did not affect mu. Gentle application of filter paper increased mu approximately 10-fold and irreversibly, suggesting alteration of the mesothelia. With packed the red blood cells (RBC) between the sliding mesothelia, mu increased appreciably but reversibly on removal of RBC suspension, whilst no ruptures of RBC occurred. In conclusion, the results indicate a low value of sliding friction in pleural tissues, partly related to the characteristics of the pleural liquid, and show that friction is independent of velocity, normal load, and nominal contact area, consistent with boundary lubrication.

Animals↗

PubMed2000

In vitro assessment of the structural integrity of the female condom after multiple wash, dry, and re-lubrication cycles.

Since the introduction of the female condom in the early 90s, there have been numerous reports of reuse of the device. In response to these reports, studies were undertaken to evaluate the safety of female condom reuse. If reuse were shown to be safe, then programmatic costs of introduction of the female condom would be reduced allowing it to be more widely available. This article outlines the results of in vitro structural integrity testing of the female condom after multiple wash, dry, and re-lubrication cycles. Devices were tested up to 10 washes using water leakage, burst, and tensile seam testing. All results were compared to the United States Food and Drug Administration (US FDA) standards for an unused female condom. The results of the structural integrity tests for all 6 washing procedures examined in this study were above the FDA minimum standards for seam strength and burst tests. For the water leakage test, 3 of 6 washing procedures tested passed the required FDA minimum standards (no holes detected). From the results of the study, it seems that washing, drying, and re-lubricating the female condom up to 10 times leads to some deterioration in the structural integrity of the device for specified washing procedures. Further studies are currently being conducted to establish the safety of female condom reuse with respect to microbial retention, structural integrity after in vivo use, and viral permeability.

Single-Use Internal Condom↗

PubMed2001

Characterization of ageing products of ester-based synthetic lubricants by liquid chromatography with electrospray ionization mass spectrometry and by electrospray ionization (tandem) mass spectrometry.

Ageing products of a commercial jet engine oil based on pentaerythritol tetraesters which were formed upon operation in an aviation turbine were detected by electrospray ionization mass spectrometry (ESI-MS) and characterized by LC-ESI-MS. The fatty acid composition of these ageing products was investigated by ESI-MS-MS analysis. The ammonium adducts of the newly formed pentaerythritol tetraester degradation products were found to be suitable parent ions for further structure elucidation work. ESI-MS, LC-ESI-MS and ESI-MS-MS proved to be versatile tools to study the chemical composition (distribution of homologues) as well as the mechanism of ageing of ester based lubricants on a molecular level. Due to its high sensitivity, ESI-MS can also be used to characterize and identify trace levels of ester-based lubricants.

Chromatography, Liquid↗

PubMed2000

The biodegradability and microbial toxicity testing of lubricants--some recommendations.

In recent years there has been a growing demand for information on the biodegradability (fate) and microbial toxicity (effects) of lubricants. This has been driven by the need to comply with environmental legislation and to meet the requirements of ecolabelling schemes, standards and customer specifications for 'environmentally acceptable' lubricants. This paper describes suitable approaches for generating this information under a variety of environmental conditions (e.g. aerobic, anaerobic, freshwater, marine), gives examples of the results obtained and discusses their interpretation. Recommendations on the use of each test are made.

Biodegradation, Environmental↗

PubMed2001

Using medical lubricating jelly in human cadaver eyes to teach ophthalmic surgery.

Attempting to learn phacomemulsification through the severely edematous cornea of a human cadaver eye is often difficult. We propose a method of improving the view of the anterior chamber structures. Medical lubricating jelly is injected into the anterior chamber of a cadaver eye. After 10 minutes, excellent corneal clarity is achieved. There was no change in the corneal edema with the injection of sodium hyaluronate 1.4% (Healon GV as a control. Using medical lubricating jelly in place of viscoelastic material is an inexpensive, effective adjunct in ophthalmic surgical teaching.

Anterior Chamber↗

PubMed2006

Boundary lubrication under water.

Boundary lubrication, in which the rubbing surfaces are coated with molecular monolayers, has been studied extensively for over half a century. Such monolayers generally consist of amphiphilic surfactants anchored by their polar headgroups; sliding occurs at the interface between the layers, greatly reducing friction and especially wear of the underlying substrates. This process, widespread in engineering applications, is also predicted to occur in biological lubrication via phospholipid films, though few systematic studies on friction between surfactant layers in aqueous environments have been carried out. Here we show that the frictional stress between two sliding surfaces bearing surfactant monolayers may decrease, when immersed in water, to as little as one per cent or less of its value in air (or oil). We attribute this to the shift of the slip plane from between the surfactant layers, to the surfactant/substrate interface. The low friction would then be due to the fluid hydration layers surrounding the polar head groups attached to the substrate. These results may have implications for future technological and biomedical applications.

Adhesiveness↗

PubMedDate not supplied

Surface-active phospholipid: a Pandora's box of clinical applications. Part II. Barrier and lubricating properties.

In Part I, it was described how their configuration renders phospholipid molecules surface active and capable of acting at interfaces in addition to the liquid-air interface to which conventional theory has hitherto confined the study of 'surfactant' in the lung. Surface-active phospholipid (SAPL) appears no different to comparable surfactants studied in the physical sciences for the highly desirable properties that their adsorption (reversible binding) can impart to solid surfaces. In Part II, these properties are considered in sites where there is no air. Highly desirable properties include boundary lubrication (lubricity), release (antistick) and the ability of the strongly adsorbed and strongly cohesive SAPL linings to act as barriers against abrasion, corrosion and, possibly, against invasion by microorganisms. As the 'sealant', it could be the true barrier rather than the cells providing its mechanical support. Evidence is reviewed for SAPL providing the gastric mucosal barrier to acid in the stomach and preventing the digestion of Helicobacter pylori until that barrier is broken by bile in the duodenum, where H. pylori cause ulcers. The concept that SAPL provides effortless sliding of many tissues, including pleura, pericardium and peritoneum is reviewed. Particular attention is paid to the load-bearing joints, where a deficiency has been associated with osteoarthritis. The ability of the same SAPL lining to perform multiple roles is discussed in relation to the peritoneum, where it could provide the lubricant/release agent preventing surgical adhesions, while imparting semipermeability to 'the membrane' vital for peritoneal dialysis. In each site, the prophylactic use of exogenous SAPL is discussed for its potential clinical applications.

Animals↗

PubMed2000

Influence of tableting forces and lubricant concentration on the adhesion strength in complex layer tablets.

The strength of adhesion in complex two-layer tablets is assessed using statistical methods with respect to the applied tableting forces for the first layer and for applying the second layer on the first, as well as regarding the fraction of the lubricant. These results, obtained on a single-punch tablet press, are compared with the results for three-layer tablets produced on a rotary press at production scale. The strongest negative influence on adhesion strength was exerted by the amount of lubricant in the central layer. As expected, compression forces for central-layer tableting also had a negative effect, whereas the compression forces for complex layer tableting exerted a positive effect on layer adhesion. The validity of the derived model equation was proved by experiments: It was shown that the adhesion strength in complex layer tablets produced in production scale can be predicted from laboratory-scale experiments. This makes optimization of the formulation and parameter settings at an early stage of development possible.

Adhesiveness↗

PubMed2005

Levels of biochemical constituents of fish associated with water dispersed fractions of used automobile lubricants.

The effects of sublethal concentrations of water-dispersed fractions of used automobile lubricant (Mobil oil SAE 50) on some biochemical constituents in fish were investigated under laboratory conditions. The fish exposed was Tilapia zilli (mean weight: 7.15+/-0.01 g), the sublethal concentrations were 125.00, 62.50, 31.25, 15.63, 7.81, and 0.00 ppm and the exposure period was 10 weeks. There was no mortality in the exposed fish throughout the exposure period; however, the biochemical constituents investigated revealed that the various concentrations led to physiological impairment in the fish, which was directly proportional to concentration and exposure period. Severely reduced feed intake was observed in fish exposed to concentrations of 62.50 and 125.00 ppm. Depletion in protein and lipid reserves, anemia and hyperglycemia were observed in all exposed fish. The implications of water dispersed fractions of used automobile lubricants in the aquatic environment and their effects on fish biodiversity are discussed.

Animals↗