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At least 91 records · Page 5Linked to original sources

PubMed2007

Differential tissue-on-tissue lubrication by ophthalmic formulations.

Tissue-on-tissue friction testing was used to determine how instillation of hydrophilic polymer-containing formulations between the "blinking" tissues would compare with lubrication by saline, alone, or an oil-emulsion preparation. Best results were obtained for a formulation that contained active demulcents polyethylene glycol (PEG 400) and propylene glycol (PG), as well as a gellable polymer hydroxypropyl guar (HP-Guar) in a borate-buffered solution, in comparison with hydroxypropylcellulose-containing and carboxymethylcellulose-containing formulations. Superior performance of all the formulations was found for lubricating tissue-on-tissue couples, compared with metal-oxide-to-metal oxide interfaces, or metal oxide-to-tissue interfaces. A reciprocating pin-on-disc type friction/wear test device articulated the intimal faces of preserved human umbilical cord vein segments under increasing loads during simulated continuous "eye-blinking" with addition of increasing weights up to 60 g/cm2, simulating maximal eyelid force on the orbital globe. The tissue-on-tissue couples moved from liquid phase lubrication to boundary lubrication. After residual formulations were rinsed away with saline, persistence of low friction at the highest loads was indicative of formulation substantivity. Human umbilical cord vein segments were utilized in saline-wetted tissue-on-tissue couples that showed variable starting coefficients of friction in the range 0.2-0.4, producing moderate tearing and disruption of the interfacial layers above the medial collagen zone. The best-performing formulations instilled to the tissues pre-wetted with saline apparently reacted separately with each tissue face to produce a lower final and persistent coefficient of friction of about 0.05. Scanning electron microscopy and light microscopy of these guar-modified tissue specimens showed only a few superficial tissue disruptions, and some interphase swelling consistent with polymer uptake. The frictional values for lubricated couples having non-tissue members were considerably higher than the coefficients of friction measured for the similarly lubricated tissue-on-tissue couples, emphasizing the requirement that appropriate simulations are critical to obtaining clinically predictive data.

Cornea↗

PubMed1996

Comparison of the size and morphology of UHMWPE wear debris produced by a hip joint simulator under serum and water lubricated conditions.

This paper investigates the effect of lubricant on the size and morphology of ultra-high molecular weight polyethylene (UHMWPE) wear debris produced by a hip joint simulator. Bovine serum and water were chosen as the lubricants for comparison. When bovine serum was used as lubricant, the majority of the wear debris produced was submicron sized and equiaxed or elongated in shape; no transfer film was found on the femoral heads. When water was used as lubricant, large pieces of thin UHMWPE flakes about 2-3 mm across were produced and patches of transfer films were observed on the femoral heads. These large flakes were comprised of numerous smaller thin flakes compacted together. While the size and shape of the wear debris produced with serum lubrication are similar to those reported from clinical studies in total hip replacement, the debris produced with water lubrication bears no resemblance to what has been seen clinically.

Animals↗

PubMed2005

Influence of fatty acid methyl esters from hydroxylated vegetable oils on diesel fuel lubricity.

Current and future regulations on the sulfur content of diesel fuel have led to a decrease in lubricity of these fuels. This decreased lubricity poses a significant problem as it may lead to wear and damage of diesel engines, primarily fuel injection systems. Vegetable oil based diesel fuel substitutes (biodiesel) have been shown to be clean and effective and may increase overall lubricity when added to diesel fuel at nominally low levels. Previous studies on castor oil suggest that its uniquely high level of the hydroxy fatty acid ricinoleic acid may impart increased lubricity to the oil and its derivatives as compared to other vegetable oils. Likewise, the developing oilseed Lesquerella may also increase diesel lubricity through its unique hydroxy fatty acid composition. This study examines the effect of castor and Lesquerella oil esters on the lubricity of diesel fuel using the High-Frequency Reciprocating Rig (HFRR) test and compares these results to those for the commercial vegetable oil derivatives soybean and rapeseed methyl esters.

Brassicaceae↗

PubMed2004

Appropriate radial clearance of ceramic-on-ceramic total hip prostheses to realize squeeze-film lubrication.

OBJECTIVE: Estimation of appropriate radial clearance of ceramic-on-ceramic total hip prostheses to realize squeeze-film lubrication. BACKGROUND: Some clinical results show that severe wear occurs at ceramic-on-ceramic interfaces of total hip prostheses if the design parameters are improper. Appropriate design is required to realize the optimum lubrication of joint prostheses. DESIGN: Squeeze-film thickness of total hip prostheses with different radial clearances was numerically estimated under the physiological conditions of normal walking. METHODS: The changes in the fluid film thickness between ceramic balls and a ceramic cups with radial clearances of various values from 10 to 80 microm were numerically estimated under the assumption of normal walking conditions by means of elastohydrodynamic squeeze-film lubrication theory including the three-dimensional theory of elasticity. RESULTS: The minimum film thickness remained over 0.02 microm during a few walking steps with a radial clearance under 20 microm and a head diameter of 28 mm. On the other hand, the fluid film was squeezed out during a few steps when the radial clearance was greater than 30 microm. CONCLUSIONS: Squeeze-film lubrication can be realized in a ceramic-on-ceramic total hip prosthesis if the radial clearance is smaller than 20 microm on a head of 28 mm diameter. RELEVANCE: Fluid film lubrication is necessary to prevent the severe wear of ceramic joint prostheses. The present investigation shows which radial clearance of ceramic-on-ceramic hip prostheses is appropriate for squeeze-film lubrication under physiological conditions in daily action.

Ceramics↗

PubMed2005

Compaction mechanism and tablet strength of unlubricated and lubricated (silicified) microcrystalline cellulose.

This paper describes the differences in compaction properties between microcrystalline cellulose (MCC) and microcrystalline cellulose co-processed with colloidal silicon dioxide (SMCC). The different compaction parameters are not only compared for the pure materials, but also for the lubricated powders with magnesium stearate. Neither magnesium stearate, nor colloidal silicon dioxide, facilitates extensively the densification of (silicified) microcrystalline cellulose during compaction. The difference in tablet relaxation of MCC and SMCC indicates a small negative effect of colloidal silicon dioxide on the interparticle bonding strength of unlubricated MCC. However, for lubricated MCC a larger increase in tablet relaxation at a high compression speed was found than for lubricated SMCC tablets. Accordingly, the decrease in tablet strength was larger for the MCC tablets than for the SMCC tablets when lubrication was applied. The examination of the tablet strengths of tablets compressed from physical mixtures of MCC with increasing concentrations of colloidal silicon dioxide proved the slightly negative influence of silicon dioxide on the tablet strength of unlubricated MCC tablets and the positive effect of colloidal silicon dioxide addition on the tensile strength of lubricated MCC tablets. Co-processing of MCC with colloidal silicon dioxide showed no extra contribution on the tablet strength of lubricated tablets above the physical mixtures. The interactions between the different materials were further supported by the interaction parameters based on partial solubility parameters.

Cellulose↗

PubMed2006

Effect of bearing geometry and structure support on transient elastohydrodynamic lubrication of metal-on-metal hip implants.

An effective lubrication can significantly reduce wear of metal-on-metal artificial hip joints. The improvement of the lubrication can be achieved through the optimisation of the bearing geometry in terms of a small clearance and/or the structural support such as a polyethylene backing underneath a metallic bearing in a sandwich acetabular cup form. The separate effects of these two factors on fluid film lubrication of 28 mm diameter metal-on-metal total hip joints under walking conditions were numerically investigated in this paper. The results show that a larger lubricant film due to the polyethylene backing can be significantly enhanced by the transient squeeze-film action, particularly during the stance phase, and a similar lubricant film can be developed for both the monolithic cup relying on the smaller clearance and the sandwich cup benefiting from the polyethylene backing. Both cup systems can function in a wide range of lubrication regimes, covering both mixed and fluid film, under the current design and manufacture conditions.

Computer Simulation↗

PubMed2006

Degradation characteristics of waste lubricants under different nutrient conditions.

We investigated the limits and extent of lubricants biodegradation at different nutrient conditions and evaluated several soil biological activities with regard to their usefulness for monitoring the bioremediation process in a soil contaminated with lubricants. To examine the effects of nutrient addition on lubricants biodegradation, a bench-scale investigation was conducted under different nutrient conditions for over 105 days testing period. When nutrients were added to contaminated soil with aged lubricant, great stimulation was occurred in fertilized soil for hydrocarbon degradation activity compared to non-fertilized soil. At the end of the experiment (105 days after), the initial level of contamination (9320+/-343 mg/kg) was reduced by 42-51% in the fertilized soil, whereas, only 18% of the hydrocarbon was eliminated in the non-fertilized soil. The effect of biostimulation of indigenous soil microorganisms declined with time, apparently 42% of the initial concentration of hydrocarbon remained at the end of experiment. Lubricants biodegradation process could be monitored well by soil biological parameters. In fertilized soil, biological parameters (number of HUB, soil respiration, dehydrogenase and catalase activities) were significantly enhanced and correlated with each other, as well as the residual lubricant concentration.

Biodegradation, Environmental↗

PubMed2000

Polymer additive analysis by pyrolysis-gas chromatography. III. Lubricants.

Lubricants are widely used in thermoplastic polymers to increase the overall rate of processing or to improve surface release properties. Because of the low level of lubricants normally used in a polymer, it may not be possible to analyze the additive directly by common spectroscopic or thermal chemical techniques. However, lubricants as well as other additives in the polymer can be qualitatively analyzed by pyrolysis-gas chromatography (Py-GC) after extraction. In this work, several lubricants have been studied to demonstrate that Py-GC is a viable tool to investigate lubricants. The advantages of using Py-GC in the analysis of lubricant have also been discussed.

Chromatography, Gas↗

PubMed2001

The accumulation of polycyclic aromatic hydrocarbons in lubricating oil over time--a comparison of supercritical fluid and liquid-liquid extraction methods.

Optimal extraction conditions including extraction temperature, fluid density of carbon dioxide and concentration of modifier for supercritical fluid extraction (SFE) to extract of 16 2-6-ring polycyclic aromatic hydrocarbons (PAHs) spiked into used lubricating oil collected from a gasoline-driven automobile were determined. A comparison of extraction efficiency 2-6-ring PAHs spiked into the used lubricating oil extracted by SFE and liquid-liquid extraction (LLE) methods was made. Results indicated that recoveries of PAHs extracted by SFE from the used lubricating oil were higher than those by LLE. PAH profiles of lubricating oil samples collected at various driving distances from an old and a new gasoline-driven automobiles were determined by combining SFE, gel permeation chromatography clean up and gas chromatography-mass spectrometry analysis. Results showed that the concentrations of total PAH in lubricating oils collected from both automobiles increased rapidly after oil change. Two- and three-ring PAHs dominated the PAH profiles of oil samples collected from both automobiles. High concentrations of the more toxic 4-6-ring PAHs, were found in the oil samples collected from both automobiles even at a short driving distance after oil change. The concentrations of total PAH in lubricating oil collected from two automobiles driven for a longer distance after oil change were very similar.

Chromatography, Gel↗

PubMed2001

Boundary lubrication by lubricin is mediated by O-linked beta(1-3)Gal-GalNAc oligosaccharides.

Lubrication of mammalian joints is mediated by lubricin, a product of megakaryocyte stimulating factor gene (MSF; GenBank accession #U70136) expression. Lubricin (M(r) approximately 240 kDa) is a mucinous glycoprotein which is 50% (w/w) post-translationally modified with beta(1-3)Gal-GalNAc incompletely capped with NeuAc, and lubricates apposed cartilaginous surfaces in the boundary mode through an unknown mechanism. Both bovine and human lubricin were purified from synovial fluid and digested with recombinant glycosidases. Released oligosaccharides were identified and quantified by fluorophore assisted carbohydrate electrophoresis (FACE). Corresponding digests of human lubricin were also assayed in a friction apparatus oscillating latex rubber against polished glass at a pressure of 0.35 x 10(6) N/m(2) and the coefficient of friction (mu) was measured. Digestion with alpha2,3-neuraminidase decreased lubricating ability by 19.3%. Partial removal of beta(1-3)Gal-GalNAc moieties by endo-alpha-N-acetyl-D-galactosaminidase reduced lubricating ability by 77.2%. Human lubricin digested with combined alpha2,3-neuraminidase and beta1-3,6-galactosidase continued to lubricate at 52.2% of its nominal value. Both bovine and human lubricin released 48.6% and 54.4% of total beta(1-3)Gal-GalNAc sidechains following digestion with endo-alpha-N-acetyl-D-galactosaminidase. Biological boundary lubrication by synovial fluid in vitro is provided primarily by extensive O-linked beta(1-3)Gal-GalNAc.

Acetylgalactosamine↗

PubMed1998

Enzymatic identification of the load-bearing boundary lubricant in the joint.

Bovine articular cartilage and synovial fluid (SF) were co-incubated with one of three enzymes selected to destroy each of the three major contenders for the active ingredient imparting such remarkable load-bearing lubrication to the normal joint. Destroying hyaluronic acid (HA), alias hyaluronan, with hyaluronidase, both frictional and wear tests displayed no significant change in accordance with most previous studies of SF alone. Destroying surface-active phospholipid (SAPL) with phospholipase A2, there was a highly significant dose-dependent compromise of lubrication as recorded on both tests. Trypsin produced a somewhat surprising result in that lubrication of the cartilage actually improved. This result can be interpreted as indicating that lubricin is not the lubricant per se, but, as a water-soluble, macromolecular, proteinaceous carrier for phospholipid, its destruction caused more SAPL to be deposited as the true load-bearing lubricant. These results are discussed in the context that SAPL, lubricin and HA each have specific roles in a comprehensive lubrication system.

Animals↗

PubMed2005

Effect of liquid and paste-type lubricants on torque values during simulated rotary root canal instrumentation.

AIM: To evaluate the effects of lubrication on torque generated during rotary preparation of simulated root canals in dentine using ProFile and ProTaper Nickel-Titanium instruments. METHODOLOGY: Thirty-two 3 mm thick dentine discs were used for this study. Four pilot holes were drilled perpendicularly through each disc. These simulated root canals were filled with water, aqueous 15% ethylenediamine tetraacetic acid (EDTA) or a paste-type lubricant (Glyde). Empty canals served as controls. Peak torque values and apically directed forces of rotary instruments were measured using a specially designed testing platform. Full torsional loads over time were calculated by integration of continuous torque records. Data were compared using analyses of variance with the alpha-type error set at 0.05. RESULTS: Maximum torque values using ProFile instruments were significantly (P < 0.005) reduced by the EDTA solution, whilst no reduction was observed using Glyde. With ProTaper instruments, no lubricant effects on maximum torque values were observed (P = 0.372). Full torsional loads over time were significantly reduced for both ProFile and ProTaper preparation (P < 0.005) by the use of lubrication. The two fluids performed significantly better than paste-based Glyde. All lubricants reduced force when applied to ProTaper by mean reductions ranging from 12 to 54%, whilst Glyde lead to increased force when applied to ProFile. CONCLUSIONS: Under the conditions of this laboratory study, lubrication appeared to be advantageous. Aqueous solutions generally performed better than the paste-type product under investigation, which showed untoward effects when used in conjunction with a rotary instrument with a U-shaped cross-section (ProFile).

Analysis of Variance↗

PubMed2006

A randomized controlled trial: is water better than a standard lubricant in nasendoscopy?

OBJECTIVES: Previous studies have shown that nasendoscopy is made easier with the use of lubrication at the expense of the quality of the view obtained, but had no effect on the discomfort or pain experienced by the patient. We set out to determine whether the advantages of lubrication with a standard lubricant (KY Jelly) could be achieved by using water, without incurring the same disadvantages. DESIGN: Single blind randomized controlled trial. SETTING: Outpatient Departments at two District General Hospitals. PARTICIPANTS: One hundred and fifty participants selected sequentially from patients requiring a nasendoscopy where the endoscope would be passed far enough to view the larynx. Patients requiring topical anaesthetic were excluded. METHODS: Patients were randomly assigned to have either water or standard lubricant applied to the nasendosope prior to nasendoscopy. Levels of pain experienced by the patient were recorded on a visual analogue score as well as visual analogue scores from the clinician for the levels of difficulty in passing the endoscope. All participants who were entered the study completed the study. Endoscopy was performed by all grades of medical staff. MAIN OUTCOME MEASURES: Levels of pain experienced by the participants were assessed by a visual analogue scale. Difficulty of passing the scope was indicated by the endoscopist using a visual analogue scale, as was the quality of image obtained. RESULTS: Endoscopists found the insertion of the endoscope was easier and the image better when water was used rather than KY Jelly. There was no significant difference in reported in levels of pain experienced by the patient. CONCLUSION: Although the use of water as a lubricant during nasendoscopy confers no additional benefit in term of the levels of pain suffered by patients during the procedure, it makes the insertion of the endoscope easier and provides a better quality image than standard lubrication.

Adult↗

PubMed1985

Influence of the granulation technique and starting material properties on the lubricating effect of granular magnesium stearate.

Magnesium stearate has been granulated in four ways to produce lubricant granulations with different properties. The lubricating properties, as well as the tablet properties with the granulated lubricant, were evaluated on tablets prepared from a mixture of dicalcium phosphate, corn starch and microcrystalline cellulose. The lubricating effect of the magnesium stearate granulations showed a similar pattern regardless of the granulation technique used except for a granulation with providone. Increasing the particle size of the magnesium stearate granulation increased the amount of lubricant required to obtain lubrication similar to powdered magnesium stearate. Variations in the specific surface area of the starting materials could be masked by using them in granular form.

Chemistry, Pharmaceutical↗

PubMed1988

Variations in the friction coefficients of tablet lubricants and relationship to their physicochemical properties.

A previously described modified annular shear cell (MASC) has been used to measure the friction coefficients of some powdered tablet lubricants on a steel surface. Commonly used lubricants, as well as others belonging to the stearate group, differed in their friction coefficients at equivalent sample sizes and in the degree of their ability to reduce friction with increasing amounts when evaluated by the apparatus. In all comparisons, magnesium stearate had the lowest friction coefficient. Divalent salts of stearic acid appeared to be better than the other lubricants tested, and among themselves differed only in the extent of their ability to decrease friction. The lubricants also differed in their physical and chemical properties. On evaluation by stepwise regression analysis, such physical properties as projected surface area of lubricant particles, Martin's diameter and bulk density accounted for most of the variation in friction coefficients of the lubricants rather than moisture content or melting point. It could therefore be suggested that particle size and/or surface area parameters be incorporated in product specifications to ensure reproducible functionality.

Chemical Phenomena↗

PubMed1998

Surface tension forces in sleep apnea: the role of a soft tissue lubricant: a randomized double-blind, placebo-controlled trial.

Upper airway obstruction in patients with sleep apnea may occur in the absence of a negative intraluminal upper airway pressure. We hypothesized that surface tension forces may play a role in the pathogenesis of obstructive sleep apnea (OSA), and that a topical soft tissue lubricant might reduce the severity of OSA. Ten male patients (age 49 +/- 10 yr [mean +/- SD]; body mass index [BMI] 31 +/- 5 kg/m2) with OSA (apnea-hypopnea index [AHI] 17 +/- 9) were studied. The arousal index was lower with the lubricant treatment than with placebo (mean difference 8; 95% CI 4 to 11 arousals/h; p = 0.001). The AHI was lower, in each of the 10 patients, on the lubricant treatment than the placebo (mean change 10, 95% CI 6 to 13; p = 0.0003). The lower AHI with lubricant as compared with placebo was present in both supine (mean difference 13; 95% CI 5 to 20; p = 0.006) and nonsupine (mean difference 6; 95% CI 0 to 12; p = 0.05) positions. There was no significant difference in sleep architecture between the lubricant and placebo treatments. Application of a topical lubricant consistently reduced the severity of OSA. This implies a pathogenetic role for surface tension forces in OSA, and a potential role for surface tension-reducing agents in the treatment of OSA.

Bronchi↗

PubMed2004

Effect of lubricant type and concentration on the punch tip adherence of model ibuprofen formulations.

A model formulation, comprising ibuprofen and direct compression lactose (Tablettose 80) was used to assess the influence of two lubricants, magnesium stearate and stearic acid, on punch tip adherence. Lubricant concentrations were varied from 0.25% to 2% w/w. Formulations in the presence and absence of 0.5% w/w colloidal silica (Aerosil 200) were examined, to assess the influence of the glidant on the anti-adherent effects of the lubricants. Differential scanning calorimetry (DSC) was used to examine the effect of the lubricants on the melting temperature of ibuprofen. Tablets were compacted using a single punch tablet press at 10 kN using hard chrome-plated punches or at 40 kN using uncoated steel punches, tooling was 12.5-mm diameter in each case. The upper punch faces were characterized by obtaining Taylor Hobson Talysurf surface profiles. Following compaction, ibuprofen attached to the face was quantified by spectroscopy. At low concentrations of each lubricant, the levels of sticking observed were similar. Whilst sticking increased at magnesium stearate concentrations above 1%, sticking with stearic acid remained relatively constant at all concentrations. DSC revealed that the melting temperature of ibuprofen was lowered by the formation of eutectic mixtures with both lubricants. However, the onset temperature of melting and melting point were lowered to a greater extent with magnesium stearate compared with stearic acid. When using uncoated tooling at 40 kN, the deleterious effects of magnesium stearate on the tensile strength of the tablets also contributed to sticking. When using chrome-plated punches at 10 kN, the tensile strength reduction by the presence of magnesium stearate was less pronounced, as was the level of sticking.

Adhesiveness↗

PubMed2000

Boundary lubrication in vivo.

Evidence is reviewed for the concept that the body employs essentially the same lubrication system in many sites in the body where tissues slide over each other with such ease. This system consists of fluid adjacent to surfaces coated with an oligolamellar lining of surface-active phospholipid (SAPL) acting as a back-up boundary lubricant wherever the fluid film fails to support the load--a likely event at physiological velocities. Particular attention is paid to the load-bearing joints, where the issue of identifying the vital active ingredient in synovial fluid is reviewed, coming down--perhaps predictably--in favour of SAPL. It is also explained how Lubricin and hyaluronic acid (HA) could have 'carrier' functions for the highly insoluble SAPL, while HA has good wetting properties needed to promote hydrodynamic lubrication of a very hydrophobic articular surface by an aqueous fluid wherever the load permits. In addition to friction and wear, release is included as another major role of boundary lubricants, especially relevant in environments where proteins are found, many having adhesive properties. The discussion is extended to a mention of the lubrication of prosthetic implants and to disease states where a deficiency of boundary lubricant is implicated, particular attention being paid to osteoarthritis.

Adsorption↗