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At least 289 records · Page 16Linked to original sources
PubMed2005

Effect of dynamic loading on the frictional response of bovine articular cartilage.

The objective of this study was to test the hypotheses that (1) the steady-state friction coefficient of articular cartilage is significantly smaller under cyclical compressive loading than the equilibrium friction coefficient under static loading, and decreases as a function of loading frequency; (2) the steady-state cartilage interstitial fluid load support remains significantly greater than zero under cyclical compressive loading and increases as a function of loading frequency. Unconfined compression tests with sliding of bovine shoulder cartilage against glass in saline were carried out on fresh cylindrical plugs (n=12), under three sinusoidal loading frequencies (0.05, 0.5 and 1 Hz) and under static loading; the time-dependent friction coefficient mu(eff) was measured. The interstitial fluid load support was also predicted theoretically. Under static loading mu(eff) increased from a minimum value (mu(min)=0.005+/-0.003) to an equilibrium value (mu(eq)=0.153+/-0.032). In cyclical compressive loading tests mu(eff) similarly rose from a minimum value (mu(min)=0.004+/-0.002, 0.003+/-0.001 and 0.003+/-0.001 at 0.05, 0.5 and 1 Hz) and reached a steady-state response oscillating between a lower-bound (mu(lb)=0.092+/-0.016, 0.083+/-0.019 and 0.084+/-0.020) and upper bound (mu(ub)=0.382+/-0.057, 0.358+/-0.059, and 0.298+/-0.061). For all frequencies it was found that mu(ub)>mu(eq) and mu(lb)<mu(eq)(p<0.05). Under cyclical compressive loading the interstitial fluid load support was found to oscillate above and below the static loading response, with suction occurring over a portion of the loading cycle at steady-state conditions. All theoretical predictions and most experimental results demonstrated little sensitivity to loading frequency. On the basis of these results, both hypotheses were rejected. Cyclical compressive loading is not found to promote lower frictional coefficients or higher interstitial fluid load support than static loading.

Adaptation, Physiological↗
PubMed2005

Effect of swing phase load on metal-on-metal hip lubrication, friction and wear.

There is renewed interest in metal-on-metal (MOM) total hip replacements (THRs), however, variable wear rates have been observed clinically. It is hypothesised that changes in soft tissue tensioning during surgery may alter loading of THRs during the swing phase of gait leading to changes in fluid film lubrication, friction and wear. This study aimed to assess the effect of swing phase load on the lubrication, friction and wear of MOM hip replacements. Theoretical lubrication modelling was carried out using elastohydrodynamic theory. All the governing equations were solved numerically for the lubricant film thickness between the articulating surfaces under the transient dynamic conditions with low and high swing phase loads. Friction testing was completed using a single axis pendulum simulator, simplified loading cycles were applied with low and high swing phase loads. MOM hip replacements were tested in a hip simulator, modified to provide different swing phase loading regimes; a low (100 N) and a high load (as per ISO 14242-1; 280 N). Results demonstrated that the performance of MOM bearings is highly dependent on swing phase load. Hence, changes in the tension of the tissues at surgery and variations in muscle forces may increase swing phase load, reduce lubrication, increase friction and accelerate wear. This may explain some of the variations that have been observed with clinical wear rates.

Arthroplasty, Replacement, Hip↗
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↗
PubMed2001

Frictional heating of total hip implants. Part 1: measurements in patients.

Hip implants heat up due to friction during long lasting, high loading activities like walking. Thermal damage in the surrounding soft and hard tissues and deteriorated lubrication of synovial fluid could contribute to implant loosening. The goal of this study was to determine the implant temperatures in vivo under varying conditions. Temperatures and contact forces in the joints were measured in seven joints of five patients using instrumented prostheses with alumina ceramic heads and telemetry data transmission. The peak temperature in implants with polyethylene cups rose up to 43.1 degrees C after an hour of walking but varied considerably individually. Even higher temperatures at the joints are probable for patients with higher body weight or while jogging. The peak temperature was lower with a ceramic cup, showing the influence of friction in the joint. During cycling the peak temperatures were lower than during walking, proving the effect of force magnitudes on the produced heat. However, no positive correlation was found between force magnitude and maximum temperature during walking. Other individual parameters than just the joint force influence the implant temperatures. Based on the obtained data and the available literature about thermal damage of biological tissues a detrimental effect of friction induced heat on the stability of hip implants cannot be excluded. Because the potential risk for an individual patient cannot be foreseen, the use and improvement of low friction implant materials is important.

Aged↗
PubMed2003

Friction between human finger flexor tendons and pulleys at high loads.

A method was developed to indirectly measure friction between the flexor tendons and pulleys of the middle and ring finger in vivo. An isokinetic movement device to determine maximum force of wrist flexion, interphalangeal joint flexion (rolling in and out) and isolated proximal interphalangeal (PIP) joint flexion was built. Eccentric and concentric maximum force of these three different movements where gliding of the flexor tendon sheath was involved differently (least in wrist flexion) was measured and compared. Fifty-one hands in 26 male subjects were evaluated. The greatest difference between eccentric and concentric maximum force (29.9%) was found in flexion of the PIP joint. Differences in the rolling in and out movement (26.8%) and in wrist flexion (14.5%) were significantly smaller. The force of friction between flexor tendons and pulleys can be determined by the greater difference between eccentric and concentric maximum force provided by the same muscles in overcoming an external force during flexion of the interphalangeal joints and suggests the presence of a non-muscular force, such as friction. It constitutes of 9% of the eccentric flexion force in the PIP joint and therefore questions the low friction hypothesis at high loads.

Adolescent↗
PubMed2004

Analysis of effects of friction on the deformation behavior of soft tissues in unconfined compression tests.

Frictionless specimen/platen contact in unconfined compression tests has traditionally been assumed in determining material properties of soft tissues via an analytical solution. In the present study, the suitability of this assumption was examined using a finite element method. The effect of the specimen/platen friction on the mechanical characteristics of soft tissues in unconfined compression was analyzed based on the published experimental data of three different materials (pigskin, pig brain, and human calcaneal fat). The soft tissues were considered to be nonlinear and viscoelastic; the friction coefficient at the contact interface between the specimens and platens was assumed to vary from 0.0 to 0.5. Our numerical simulations show that the tissue specimens are, due to the specimen/platen friction, not compressed in a uniform stress/strain state, as has been traditionally assumed in analytical analysis. The stress of the specimens obtained with the specimen/platen friction can be greater than those with the frictionless specimen/platen contact by more than 50%, even in well-controlled test conditions.

Adipose Tissue↗
PubMed2003

A local friction model to develop microscopic transport parameters for membrane-soluble ions in bilayer membranes.

Charged membrane-soluble ions in bilayer membranes move between opposing interfacial states on application of an electric field. The kinetics of this transition is modeled as discrete state electrophoresis using a Langevin formulation that focuses on local velocities at points along the spatial trajectory of the ion. These local velocities are used to establish both the decay time for the transition and the activation energy profile along the trajectory. The local velocities depend on local frictional coefficients. These coefficients are developed from the molecular structure along the trajectory by introducing a microscopic frictional force. This frictional force is produced by the lateral displacement of segments of the surrounding membrane molecules as the ion passes. The displaced molecular chains produce a non-linear resistive force that translates into a frictional force directly proportional to both ion radius and velocity.

Electrochemistry↗
PubMed1997

Evaluation of frictional resistance in esthetic brackets.

The purpose of this study was to measure the frictional forces generated between composite, ceramic, and metal brackets and selected wire alloy-size combinations with elastomeric and stainless steel ligatures in a dry environment. Four types of composite, one ceramic, one sapphire, and one metal bracket were tested with stainless steel, nickel-titanium, and beta-titanium wires. The testing was performed with two wire sizes in the 0.018-inch slot brackets and three wire sizes in the 0.022-inch slot bracket. The recently introduced composite brackets were found to offer lower frictional resistance than the ceramic and stainless steel brackets, regardless of the wire size, wire alloy, and type of ligation. The wire alloy with the least friction was stainless steel, followed by beta-titanium and nickel-titanium. Mean variability in friction, as reflected by the magnitude of the standard deviations, was 2.7 to 3 times more with the stainless steel ligation than the elastomeric ligation.

Bicuspid↗
PubMed1999

Comparison of frictional resistance in titanium and stainless steel brackets.

This study measures and compares the level of frictional resistance generated between titanium and stainless steel brackets. Both 0.018 and 0.022 inch slot size edgewise brackets were tested with different sized rectangular stainless steel wires in a specially designed apparatus. The frictional resistance was measured on Instron Universal testing machine (Instron Corp, Canton, Mass) with a 10 pound load cell. The specimen population was composed of 180 brackets and 180 wire specimens. A completely randomized design (one way) ANOVA was used to test for significant differences among the three bracket/wire types in the 0.018 and 0.022 inch slot sizes. This was followed by the Student Newman Keuls Multiple Comparison of means ranking at P < .05 to determine differences between the different groups. The titanium brackets showed lower static and kinetic frictional force as the wire size increased, whereas stainless steel brackets showed higher static and kinetic frictional force as the wire size increased.

Analysis of Variance↗
PubMedDate not supplied

Low-profile dynamic splints: a solution to the friction problem.

To find a solution to the problem of friction between the nylon fishing line and the outrigger of a low-profile dynamic splint, a jig was manufactured to bend notches in 2.5-mm copper-coated welding rod. This type of outrigger was compared with an adjustable stainless-steel outrigger to determine which of the two types produces the least amount of friction. As one of each type of outrigger was covered with a layer of Teflon paint, four different outriggers were compared with each other: welding rod only, welding rod with Teflon, stainless steel with Teflon, and stainless steel only. Equal traction units were attached to each of the outriggers and the amount of elongation of a 50-mm tension spring was measured when a 300-g weight was hooked onto it. This was compared with the elongation of the same spring when no friction was present. The results show that the Teflon-covered outriggers displayed significantly (on a 5% level) less friction than did the uncovered outriggers. The stainless-steel outrigger with Teflon performed slightly better than the welding-rod outrigger with Teflon. However, there was no significant difference between these two outriggers, and because the welding-rod outrigger is cheaper and more readily available, it is recommended for clinical use.

Equipment Design↗
PubMed1997

Friction between different wire-bracket configurations and materials.

Friction opposes tooth motion whenever sliding mechanics is employed. Understanding what friction is and how to manage it is of paramount importance to the successful practitioner. In this article, the coefficients of friction are summarized between different arch wire-bracket couples as a function of material, geometric, and external parameters. From this vantage point, friction can then be evaluated within the context of other factors that affect sliding-binding and notching.

Dental Alloys↗
PubMed2006

Friction between cellulose surfaces and effect of xyloglucan adsorption.

The forces and friction between cellulose spheres have been measured in the absence and presence of xyloglucan using an atomic force microscope. The forces between cellulose are monotonically repulsive with negligible adhesion after contact is achieved. The friction coefficient is observed to be unusually high in comparison with other nanotribological systems. We have confirmed that xyloglucan adsorbs strongly to cellulose, which results in a much stronger adhesion, which is dependent on the time the surfaces are in contact. Xyloglucan also increases the repulsion on approach of the cellulose surfaces, and the friction is markedly reduced. The apparently incompatible observations of decreased friction in combination with increased adhesion fulfills many of the necessary criteria for a papermaking additive.

Adsorption↗
PubMed2001

Frictional amyloidosis: a study of 10 cases.

Ten patients with macular amyloidosis were studied with particular reference to the role of friction. All 10 patients had a history of prolonged rubbing over a period of 2-5 years with various objects, such as bath sponges, brushes, towels, plant sticks and leaves. The presence of amyloid was confirmed by histochemical stains in six cases and by electron microscopy in four cases. The study confirms the role of friction in the causation of macular amyloidosis and hence, the term 'frictional amyloidosis' aptly describes the condition. The study also emphasizes the need for electron microscopy in the diagnosis of frictional amyloidosis.

Adult↗
PubMed2006

In vitro comparison of frictional torque and torsional resistance of aged conventional gamma-in-nitrogen sterilized polyethylene versus aged highly crosslinked polyethylene articulating against head sizes larger than 32 mm.

BACKGROUND: The advent of highly crosslinked polyethylene has allowed the re-evaluation of the use of femoral heads larger than 32 mm for metal-on-polyethylene total hip arthroplasties. However, the effect of larger heads on the frictional torque of highly crosslinked polyethylene is unknown. METHODS: We performed an in vitro examination of the effect of larger chrome cobalt femoral heads (40 mm diameter) on the frictional torque and torsional resistance of hip articulations on aged liners of polyethylene that were sterilized by gamma rays while in nitrogen, and aged highly crosslinked polyethylene. The frictional torque at the femoral head articulation was usually higher for the highly crosslinked polyethylene than for the conventional polyethylene. The aged conventional liners oxidized considerably, which led to gross failure of the polyethylene at the anti-rotation portion of the rim. The aged crosslinked polyethylene showed no such failures despite the higher frictional torque. INTERPRETATION: Our findings suggest that in terms of torsional resistance to fatigue when studied as a device, rather than as an isolated material, under these conditions, aged highly crosslinked polyethylene is preferable to aged conventional polyethylene.

Arthroplasty, Replacement, Hip↗
PubMed2004

The effect of bone cement particles on the friction of polyethylene and polyurethane knee bearings.

Compliant layer knee joints have been considered for use in an attempt to increase the serviceable life of artificial joints. If designed correctly, these joints should operate within the full-fluid film lubrication regime. However, adverse tribological conditions, such as the presence of bone and bone cement particles, may breach the fluid film and cause surface wear. The frictional behaviour of both polyurethane (PU) and conventional polyethylene (PE) tibial components against a metallic femoral component was therefore assessed when bone cement particles were introduced into the lubricant. The bone cement particles caused a large increase in the frictional torque of both the PE and PU bearings; however, the friction produced by the PU bearings was still considerably lower than that produced by the PE bearings. The volume of bone cement particles between each of the bearings and the resultant frictional torque both decreased over time. This occurred more quickly with the PE bearings but greater damage was caused to the surface of the PE bearings than the PU components.

Biocompatible Materials↗
PubMed2001

A model for evaluating friction during orthodontic tooth movement.

Orthodontic forces for sliding tooth movement during space closure are applied at a distance from the centre of resistance of the teeth. For this reason, the teeth will tip until contacts are established between the archwire and diagonally opposite corners of the bracket wings. They will also rotate until the wire contacts opposite corners of the ligature tie or the buccal shield with self-ligating brackets, and the base of the slot. Frictional forces measured with models that do not enable such movements may therefore not be representative of the clinical condition. To test this hypothesis, a dentoalveolar model that allowed accurate reproduction of the width of a material of similar elastic properties as the periodontal ligament (PDL) was fabricated. In addition, a device was designed that allowed accurate adjustment of the bracket slot in all three planes of space during mounting of the model in an Instron machine. Frictional forces during sliding of ceramic brackets with 0.022 x 0.028-inch bracket slots along 0.019 x 0.025-inch stainless steel wires were tested using models with simulated PDL widths of 0.00, 0.33, 0.67, and 1.00 mm. ANOVA detected a significant effect of PDL width on mean frictional force (P < 0.001). Pairwise comparisons at 0.05 significance level indicated no differences between the models without PDL and those with a width of 0.33 mm, and between models with PDL widths of 0.67 and 1.00 mm. However, the two models with smaller widths produced significantly lower frictional forces.

Analysis of Variance↗
PubMed1995

Clean intermittent catheterization in spinal cord injury patients: long-term followup of a hydrophilic low friction technique.

Clean intermittent self-catheterization is an established option in bladder management of spinal cord injury patients. Several early and a small number of long-term studies have reported good preventive or therapeutic effects on hydronephrosis, vesicourethral reflux, urinary tract infection and incontinence. Most reports describe the use of small catheters and liberal use of jelly but urethral complications, such as strictures and false passages, seem to increase with the length of followup. All 30 spinal cord injury patients in this retrospective study had used disposable hydrophilic, low friction catheters from the early shock phase to a median of 7 years (range 5 to 9). There were 26 upper motor neuron and 4 lower motor neuron lesions. After tap water soaking, the surface layer of the catheter coating has a friction constant more than 10 times lower than that for a regular plastic catheter (Nélaton) with chlorhexidine jelly. There was no hydronephrosis, pyelonephritis or renal scarring. In 3 patients who had decreased the clean intermittent self-catheterization regimen, signs of upper tract dilatation developed but the excretory urogram returned to normal after correction of the regimen. Of 30 patients 12 (40%) maintained sterile urine, while 4 of the remaining 18 with bacteriuria had episodes of urinary sepsis and chronic infections. Two patients had epididymitis. Of 6 men with occasional insertion difficulties when the clean intermittent self-catheterization regimen started after the indwelling catheter had been removed 4 showed yielding signs of strictures during the subsequent clean intermittent self-catheterization regimen. In 1 patient 2 dilation attempts had failed but the patient can perform the clean intermittent self-catheterization regimen. One patient with Crohn's disease had advanced urethral changes in the acute phase but could perform clean intermittent self-catheterization with a small catheter. One patient has had recurrent modifications of the urethral wall but no development of a false passage. The study indicates that patients who use hydrophilic low friction low friction catheters do as well as or better than patients using conventional catheters. Above all, there is no increase in severe urethral complications with time after injury. Progression towards strictures after early urethral trauma seems to be preventable by the use of this catheter.

Adult↗
PubMed2000

Biological microtribology: anisotropy in frictional forces of orthopteran attachment pads reflects the ultrastructure of a highly deformable material.

Evolutionarily optimized frictional devices of insects are usually adapted to attach to a variety of natural surfaces. Orthopteran attachment pads are composed of hexagonal outgrowths with smooth flexible surfaces. The pads are designed to balance the weight of the insect in different positions and on different materials. In a scanning electron microscopy study followed by freezing-substitution experiments, the ultrastructural architecture of the pad material was visualized. In friction experiments, the interaction was measured between the attachment pad and a polished silicon surface. The inner structure of this material contains distally directed rods, branching close to the surface, and spaces filled with fluid. The specific design of the pad material provides a higher frictional force in the distal direction. Frictional anisotropy is more enhanced at higher normal forces and lower sliding velocities. It is concluded that optimal mechanical functionality of biosystems is the result of a combination of surface structuring and material design.

Animals↗