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PubMedDate not supplied

Coefficient of friction of ocular surface lubricants for laser in situ keratomileusis.

PURPOSE: The coefficient of friction was empirically derived for a series of commercially available ophthalmic lubricants having potential use during laser in situ keratomileusis (LASIK). METHODS: Measurements were obtained using a modified tensile testing machine. Solutions tested included the artificial tear supplements Polytears-free, Bion Tears, Genteal, Refresh, Cellufresh, Celluvisc, Theratears, and Viscotears gel; and balanced salt solution (BSS). RESULTS: Viscotears carbomer gel had a significantly lower mean coefficient of friction compared to other ophthalmic lubricants tested (P=.002) and the dry plate (P=.005). Addition of 0.1 ml of BSS to 0.025 ml of Celluvisc significantly reduced the coefficent of friction of Celluvisc (P=.01). Polytears, Bion Tears, Genteal, Refresh, Celluvisc, Theratears, and BSS had coefficients of friction significantly higher than that of the dry plate. CONCLUSION: A range of values were obtained for the coefficient of the ophthalmic lubricants tested. Viscotears gel (0.1 ml), and Celluvisc (0.025 ml) + BSS (0.1 ml) had coefficients of friction significantly lower than that of the dry plate.

Friction↗
PubMedDate not supplied

Quantitative methods for evaluating optical and frictional properties of cationic polymers.

This paper presents three quantitative methods to examine gloss, opacity, and friction of cationic polymers. The adsorption of cationic polymers onto hair and skin can be regarded as a thin film coating. Therefore, optical and frictional properties of polymer films are of significant relevance to the applications of cationic polymers in hair care products. Such properties reflect the desirable hair condition attributes consumers seek in shampoo and conditioner products. Using these test methods, polyquaternium-10 and cationic guar samples of varying molecular weight and cationic substitution were compared. The effect of an anionic surfactant, sodium dodecyl sulfate (SDS), on polymer film properties was also investigated. Neat guar hydroxypropyl trimonium chloride imparts less friction than polyquaternium-10 but dulls the substrate employed in this study. The optical data show that polyquaternium-10 provides greater film clarity and gloss than cationic guars. In the presence of SDS, polyquaternium-10 also displays similar or lower friction than cationic guar. The comparative optical and frictional results are in good agreement with the visual assessment of the cationic polymer films. These results clearly demonstrate that polyquaternium-10 exhibits superior film properties in the forms of both neat polymer and polymer/surfactant complex. In addition, microscopic techniques such as scanning electron microscopy (SEM) and atomic force microscopy (AFM) provide powerful explanations for the differences noted between the two popular classes of cationic polymers. The test methods described in this paper can be utilized to differentiate the upper performance potential of cationic polymers. These objective and standardized test methods derived from the coatings industry are not affected by the variability of hair or the formulation complexity of end products. They can be useful tools in the product development process in quickly screening the relative performance of different polymers.

Cations↗
PubMed2003

Method of friction coefficients determining for ternary solutions of non-electrolytes and polymeric membrane.

In this paper, the dependencies between phenomenological coefficients for membrane and friction coefficients for solutes and membrane in the framework of generalised Spiegler-Kedem-Katchalsky model for non-ionic and homogeneous solutions were presented. The matrixes of transformation from phenomenological onto frictional coefficients and from frictional onto phenomenological coefficients were worked out. Besides, the influence of hydration number of solutes on friction and phenomenological coefficients was elaborated. Moreover, the friction coefficients and their dependencies on hydration number of glucose for aqueous glucose solution (binary solution) and glucose solution in aqueous ethanol solution (ternary solution), permeating through flat polymer membrane were presented.

Dialysis↗
PubMed2005

A dynamic friction model for haptic simulation of needle insertion.

This paper describes a new friction model, termed the brush model, suitable for haptic simulations of needle insertion in virtual environments. A novel two-layer surface contact model is presented that provides real-time rendering of friction forces at haptic refresh rates. A significant modification to the brush model is also presented, leading to a new friction model, termed the fixed bristle brush model. Simulation results show that the two models can accurately reflect the experimentally observed friction characteristics. This paper presents a simulation of friction during needle insertion; results agree with the experimental observations.

Computer Simulation↗
PubMed2006

Tribological behaviour of orthodontic archwires under dry and wet sliding conditions in-vitro. I--Frictional behaviour.

OBJECTIVE: To evaluate the frictional behaviour of orthodontic archwires in dry and wet conditions in-vitro. METHODS: Two types of archwire materials were investigated: stainless steel and NiTi. A fretting wear tribometer fitted with an alumina ball was operated at 23 degrees C in three different environments: ambient air with 50 per cent relative humidity, 0.9 wt. per cent sodium chloride solution, and deionised water. RESULTS: NiTi archwires sliding against alumina exhibited high coefficients of friction (about 0.6) in the three environments. Stainless steel archwires sliding against alumina had relatively low coefficients of friction (0.3) in the solutions, but high coefficients (0.8) in air. CONCLUSION: The low frictional forces of the stainless steel wires sliding against alumina in the solutions were due to a lubricating effect of the solutions and corrosion-wear debris. The high frictional forces between the NiTi wires and alumina are attributed to an abrasive interfacial transfer film between the wires and alumina.

Air↗
PubMed2006

The influence of ligation on frictional resistance to sliding during repeated displacement.

OBJECTIVE: To determine if the type of ligation influences the frictional resistance between stainless steel wire and brackets when the wire is subjected to repeated vertical displacements. METHODS: Eight different types of ligation were used to secure a length of stainless steel wire in three stainless steel twin brackets. The wire was subjected to repeated vertical displacements in a simulated extraction space. Eighty per cent of the minimum force required to overcome static friction (F-m) between the wire and brackets was applied to the wire for eight minutes and any sliding measured. RESULTS: Frictional resistance to sliding was least when stainless steel ligatures twisted in a figure 8 pattern until taut then untwisted one quarter turn were used, and greatest when elastomeric modules in a figure 8 pattern (EM8) were used. The F-m difference between fully engaged standard and Super Slick elastomeric modules was significantly different (p = 0.007). The frictional resistance to sliding fell when the wire was secured with either of these two methods and subjected to vertical displacement loads. There was no significant difference in the rate of wire movement between these modules. CONCLUSION: Repeated vertical displacement reduced the frictional resistance to sliding for all methods of ligation except EM8.

Dental Alloys↗
PubMedDate not supplied

Modification of the frictional surfaces of artificial joints.

To overcome the wear problems associated with artificial joint materials, new surface structures with regular patterning were designed and fabricated. The lubrication properties were studied to evaluate the wear of the frictional surfaces. The surface structure was a pattern of "dents" with a diameter of 0.2-1.0 mm and a pitch of 0.6-2.0 mm. The pattern was fabricated on the stainless steel (SUS) surface by a photochemical etching technique with 3 microns depth, and on an ultrahigh molecular weight polyethylene (UHMWPE) surface by mechanical processes. The time dependent changes of frictional force between SUS and UHMWPE were measured, and the surface morphologic changes were observed. The patterned surface showed lower frictional force than the smooth non-patterned surface, and less wear occurred on the patterned sample than on the sample without a pattern. There were optimum sizes for the diameter and the pitch of the pattern. These results demonstrated that lubrication properties could be improved by patterning of the frictional surfaces. The surface patterning was effective in preventing wear of the frictional surface, and the life of an artificial joint could be extended by such patterning.

Biomechanical Phenomena↗
PubMed1979

The volar skin of primates: its frictional characteristics and their functional significance.

Friction of volar skin on wood is not proportional to load in human beings and prosimians, but to load raised to a fractional power. This meets theoretical expectations for the frictional characteristics of convex elastic surfaces. Although this enables small clawless primates to cling to steeper slopes and larger vertical supports than would otherwise be possible, the magnitude of the effect is not great enough to overcome the disadvantages of clawlessness in climbing vertical or steeply-sloping tree trunks and branches. In human subjects, friction appears to be more nearly proportional to load than in small prosimians used as experimental subjects. It is suggested that this is due to the fact that the small animals have discrete, elevated volar pads. Pad coalescence in large primates may be an adaptation for increasing the power to which load must be raised to become proportional to friction; increasing this exponent yields more friction per unit of adduction force on supports that are small relative to the animals' dimensions and weights.

Animals↗
PubMed1985

Swing phase control with knee friction in juvenile amputees.

Above-knee amputees have a slower than normal walking velocity. In conventional prostheses the solution has been to apply knee friction to attempt to match the cadence of the prosthetic limb to the sound limb. Using kinematic data, we investigated the effect of variable knee friction on the swing phase of gait in juvenile amputees. The subjects were instructed to walk at a comfortable pace and were tested repeatedly with varying amounts of knee friction. We found that the excursion of the prosthetic shank as measured by knee range of motion was altered by changing the amount of knee friction. The period of the prosthetic shank remained constant when measured as a physical pendulum and when measured dynamically during gait. Therefore, knee friction is an effective means of providing the amputee with a more symmetrical appearing gait by matching the heel rise of the prosthetic limb to the sound limb. It is not an effective means, however, of matching the cadence of the prosthetic limb to the sound limb.

Artificial Limbs↗
PubMed1996

Friction and stem stiffness affect dynamic interface motion in total hip replacement.

Large cyclic movements between the femoral stem and bone during the first weeks after total hip arthroplasty may hamper bone ingrowth and adversely affect the eventual success of the arthroplasty. Little is known, however, about the magnitude of the motions and its relationship to design and surgical factors. A two-dimensional finite element model of a cementless prosthesis inserted into the proximal femur was constructed to study the effects of two mechanical variables--the stiffness of the implant and the coefficient of friction between bone and implant--on the magnitude of the motions. We investigated the influences of these variables on the subsidence of the prosthesis, the magnitudes of the cyclic motions, and the level of the interface stresses. The presence of friction reduced cyclic motions by about 85% compared with a frictionless interface. Once friction was assumed, varying the coefficient of friction had little effect. The effect of friction on the interface stress state and gross subsidence of the prosthesis was not as great as on cyclic motion. Implant stiffness also affected the magnitudes and distributions of the cyclic motions along the interface. A flexible stem generated motions about three to four times larger proximally than those of a stiff stem, which generated larger motions distally. The influence of stem stiffness on interface stresses and prosthetic subsidence was less than on cyclic motion. The location of the peak shear stresses at the interface around a bonded prosthesis corresponded to the location where cyclic interface motion was maximal for an unbonded prosthesis. However, no direct relationship was found between the magnitudes of peak stresses and the amplitudes of cyclic motions.

Elasticity↗
PubMed1995

Linear and nonlinear stiffness and friction in biological rhythmic movements.

Biological rhythmic movements can be viewed as instances of self-sustained oscillators. Auto-oscillatory phenomena must involve a nonlinear friction function, and usually involve a nonlinear elastic function. With respect to rhythmic movements, the question is: What kinds of nonlinear friction and elastic functions are involved? The nonlinear friction functions of the kind identified by Rayleigh (involving terms such as theta3) and van der Pol (involving terms such as theta2theta), and the nonlinear elastic functions identified by Duffing (involving terms such as theta3), constitute elementary nonlinear components for the assembling of self-sustained oscillators, Recently, additional elementary nonlinear friction and stiffness functions expressed, respectively, through terms such as theta2theta3 and thetatheta2, and a methodology for evaluating the contribution of the elementary components to any given cyclic activity have been identified. The methodology uses a quantification of the continuous deviation of oscillatory motion from ideal (harmonic) motion. Multiple regression of this quantity on the elementary linear and nonlinear terms reveals the individual contribution of each term to the oscillator's non-harmonic behavior. In the present article the methodology was applied to the data from three experiments in which human subjects produced pendular rhythmic movements under manipulations of rotational inertia (experiment 1), rotational inertia and frequency (experiment 2), and rotational inertia and amplitude (experiment 3). The analysis revealed that the pendular oscillators assembled in the three experiments were compositionally rich, braiding linear and nonlinear friction and elastic functions in a manner that depended on the nature of the task.

Adult↗
PubMed1989

[Materials technology research on the problem of friction between bracket and arch].

Orthodontic tooth movement along the arch wire is associated with a frictional force between bracket and wire. There is as yet little certainty as to how much force is lost as a result of friction. Therefore a measuring apparatus was used to measure torque in relation to bracket angulation. In all, five types of wire, each of different dimensions were measured in three brackets of differing widths. The results showed significant differences between the types of wire. As the wire dimensions are increased, so likewise are the frictional forces. Bracket with and frictional force bear an inverse relationship to each other. Frictional force increases the greater the surface roughness of the wire.

Dental Alloys↗
PubMed1996

Work and power outputs determined from pedalling and flywheel friction forces during brief maximal exertion on a cycle ergometer.

Work and power outputs during short-term, maximal exertion on a friction loaded cycle ergometer are usually calculated from the friction force applied to the flywheel. The inertia of the flywheel is sometimes taken into consideration, but the effects of internal resistances and other factors have been ignored. The purpose of this study was to estimate their effects by comparing work or power output determined from the force exerted on the pedals (pedalling force) with work or power output determined from the friction force and the moment of inertia of the rotational parts. A group of 22 male college students accelerated a cycle ergometer as rapidly as possible for 3 s. The total work output determined from the pedalling force (TWp) was significantly greater than that calculated from the friction force and the moment of inertia (TWf). Power output determined from the pedalling force during each pedal stroke (SPp) was also significantly greater than that calculated from the friction force and the moment of inertia. Percentage difference (% diff), defined by % diff = ¿(TWp - TWf)/TWf¿ x 100, ranged from 16.8% to 49.3% with a mean value of 30.8 (SD 9.1)%. It was observed that % diff values were higher in subjects with greater TWp or greater maximal SPp. These results would indicate that internal resistances and other factors, such as the deformation of the chain and the vibrations of the entire system, may have significant effects on the measurements of work and power outputs. The effects appear to depend on the magnitudes of pedalling force and pedal velocity.

Adult↗
PubMed1983

Surface tension of animal cartilage as it relates to friction in joints.

Measurement of the surface tension of articular cartilage and friction experiments were carried out to provide further evidence in support of a new theory regarding the mechanism of friction in joints. To determine the surface tension of cartilage, contact angle measurements were used in conjunction with the equation of state for interfacial tensions. The advancing contact angle between saline drops and articular cartilage was found to be 100 degrees +/- 5 degrees, indicating a highly hydrophobic surface. The corresponding surface tension value was calculated to be 22.5 ergs/cm2. Friction of cartilage against hydrophobic surfaces is shown to be lower than the friction of cartilage against hydrophilic surfaces. All these results further support the theory that lubrication by nonwetting drops occurs in joints and may be responsible for the exceptional friction characteristics of the joints.

Animals↗
PubMed1990

Usefulness of a pericardial friction rub after thrombolytic therapy during acute myocardial infarction in predicting amount of myocardial damage. The TAMI Study Group.

To evaluate the clinical incidence and outcomes of patients with pericarditis after thrombolytic therapy, 810 patients were prospectively studied during acute myocardial infarction (AMI). Pericarditis was defined as the presence of a pericardial friction rub during the hospital course. Only 5% of patients developed a rub during AMI, a low percent compared with that in the prethrombolytic era. A pericardial friction rub more often occurred in the setting of an anterior wall AMI. Patients with, compared to those without, a pericardial friction rub had lower ejection fractions (45 vs 51%, p = 0.002); worse regional left ventricular function (-3.2 vs 2.7, standard deviation per chord); higher in-hospital mortality (15 vs 6%, p = 0.056); a higher frequency of power failure (83 vs 57%); a higher frequency of anterior wall location of the AMI (53% of cases, p = 0.002); and a higher frequency of 3-vessel disease. Therefore, although the frequency of a pericardial friction rub was low (5%) compared with that in the prethrombolytic era, its occurrence denotes more extensive myocardial damage with a worse clinical outcome. Perhaps with successful reperfusion of the infarct-related vessel, transmural myocardial necrosis is prevented and with it the development of pericarditis. Cardiac tamponade did not occur clinically in any patient who developed a pericardial friction rub.

Female↗
PubMed1990

Low-friction hydrophilic surface for medical devices.

A hydrophilic polymer surface was developed exhibiting excellent low frictional property, namely slipperiness, when in contact with water or physiological fluid due to the reaction of epoxy-containing poly(vinyl pyrrolidone) with the polyamino compound formed on the surface of the substrate. Epoxy-containing poly(vinyl pyrrolidone) was obtained by the copolymerization of vinyl pyrrolidone as a hydrophilic component, glycidyl acrylate as a binding component to the substrate, and vinyl acetate to preserve the strength of the coating layer. The surface friction coefficient depends on the molecular weight of the coated hydrophilic copolymer. It was demonstrated that a molecular weight of 400,000 or more is essential to achieve excellent low surface friction. Using rabbit models, polyurethane catheters, both with and without the hydrophilic low friction coating, were evaluated for surface friction coefficient and blood compatibility. As a result, in the case of coated catheters, no lesions of the intima of the blood vessels and no thrombus formations on the surfaces of the catheters were observed. However, the non-coated catheters injured the intima of the blood vessels and severe thrombus formation was found on their surfaces.

Animals↗
PubMed1991

Static frictional force and surface roughness of nickel-titanium arch wires.

Surface roughness and static frictional force resistance of orthodontic arch wires were measured. Nine nickel-titanium alloy arch wires were studied. One beta-titanium alloy wire, one stainless steel alloy wire, and one cobalt-chromium alloy wire were included for comparison. Arithmetic average roughness in micrometers was measured with a profilometer. Frictional force resistance was quantified by pushing wire segments through the stainless steel self-ligating brackets of a four-tooth clinical model. The cobalt-chromium alloy and the nickel-titanium alloy wires, with the exception of Sentalloy and Orthonol, exhibited the lowest frictional resistance. The stainless steel alloy and the beta-titanium alloy wires showed the highest frictional resistance. The stainless steel alloy wire was the smoothest wire tested, whereas NiTi, Marsenol, and Orthonol were the roughest. No significant correlation was found between arithmetic average roughness and frictional force values.

Chromium Alloys↗
PubMed2004

Reproducible lateral force microscopy measurements for quantitative comparisons of the frictional and chemical properties of nanostructures.

Atomic force microscopy (AFM) is a widely used technique for characterizing the topography and frictional properties of nanostructures. Inherent misalignments between the AFM cantilever and the feedback hardware lead to crosstalk between topography data and lateral force microscopy (LFM) data. Because the degree of crosstalk depends on the positioning of the cantilever, LFM and topography data of the same structure can vary from one experiment to the next. For nanostructures with large LFM contrast, errors as large as 50% in topography and LFM can be observed. This paper describes an empirical strategy for correcting this alignment error. The technique is used to characterize the frictional properties of scanning probe-induced oxide nanostructures and the hydrogen-terminated Si(111) surfaces on which they are patterned. Reproducible differences in the frictional properties of the oxide nanostructures patterned on HF-treated and NH4F-treated Si(111) surfaces are observed and attributed to the mixed-hydride versus monohydride termination of each surface. The observed frictional contrast is consistent with known differences in surface reactivity and demonstrates how LFM measurements can provide insight into the frictional and chemical properties of nanostructures

Journal Article↗