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At least 19 recordsLinked to original sources

PubMed1995

Friction analysis of kinetic schemes: the friction coefficient.

Friction analysis is proposed as the application of general control analysis to single enzymes to describe the control of elementary kinetic steps on the overall catalytic rate. For each transition, a friction coefficient is defined that measures the sensitivity of the turnover rate to the free energy of the transition state complex of the transition. The latter is captured in a single property of the transition, termed friction, as the geometrical mean of the inverse of the forward and backward rate constants. By definition, the friction coefficient measures the relative change in the turnover rate in response to a small change in the friction. The friction coefficient is the sum of the flux control coefficients of the forward and backward rate constants from general control theory and measures the extent to which an elementary step is rate determining. Two basic rules apply to the friction coefficients: (i) the summation theorem states that summation of the friction coefficients over all the steps in a scheme results in a value of 1, and (ii) the group rule states that grouping of rate constants of similar transitions results in a friction coefficient for the group that is the sum of the friction coefficients of the individual steps in the group. The friction coefficients are derived for a number a kinetic schemes taking the rate equations as the starting point and both rules are demonstrated. In fully coupled systems the friction coefficients of individual steps lie between 0 and 1. In partially uncoupled systems the summation theorem applies to all the rates in the system, however, the summation of subsets of friction coefficients may exceed the value of one, implying negative values for other steps in the scheme. The values of individual friction coefficients lie between -1 and 1. The friction coefficient is redefined in a numerical treatment of the steady state of more complex enzymatic schemes.

Enzymes↗

PubMed1991

Friction ... Friction resistance between edgewise brackets and archwires.

This study quantified the dynamic frictional force encountered when TMA, Orthonol and multistranded stainless steel archwires were pulled a distance of 2mm through ceramic and stainless steel brackets. The current literature is inadequate and incomplete, for example, no data was found on rectangular multistranded archwires. The following factors were investigated: archwire material, archwire size, archwire-to-bracket angulation, bracket material, archwire and bracket slot surface roughness and lubrication in the form of artificial saliva. A total of 156 different combinations were investigated. A universal testing machine was used to pull the ligated archwires through the brackets, and record the friction. A four way analysis of variance with one nesting (archwire size) was carried out on 1,560 measurements to assess the results. All factors and interactions tested were significant in determining friction. Friction was found to increase with: archwire angulation and archwire size (exceptions were seen in some TMA archwires). Friction decreased with lubrication. There was a definite relationship between friction and archwire and bracket material. There was no definite relationship between archwire surface roughness and friction. Highest friction was observed with ceramic bracket and TMA archwire. The range of friction was 1.02 to 9.95 Newtons. The magnitude of the friction recorded is substantially larger than the forces applied in orthodontic movement clinically. It is proposed that the values recorded should be utilised as a means of comparing the effects of different factors, rather than for the quantification of friction in vivo.

Analysis of Variance↗

PubMed2004

Influence of the hydrophobic and hydrophilic characteristics of sliding and slider surfaces on friction coefficient: in vivo human skin friction comparison.

INTRODUCTION: The objective of this study was to investigate whether hydrophilic/hydrophobic balance (Hi/Ho) of the skin surface strongly modifies the friction coefficient (mu). The Hi/Ho balance is determined using the relationship between the critical surface tension gammac (Zisman's principle:which delimits the wetting capacity) and the surface tension of water gammaH2O (water: reference element of Hi/Ho balance). METHOD: Critical surface tension gammac was determined (according to Zisman's principle) through the measurement of advancing contact angle theta of a series of ethanol/water dilutions. Friction coefficient depends on several parameters: types of probe motions (rotational vs. linear), surface roughness and physicochemical parameters of surfaces in contact). In this study, the wettability parameters for six surfaces (human skin forearm, Teflon, silicone impression material 'Silflo', vinyl polysiloxane impression material 'resin' steel and glass) were measured and their influences were compared to friction coefficient mu. RESULTS: This study shows that the higher hydrophobia tendency of the surfaces, the lower friction coefficient. The use of three sliding materials (Teflon, steel and glass) of different Hi/Ho balance confirms the importance of these physicochemical parameters in mu. For example, Teflon with high hydrophobia has a low mu. Friction coefficient increased when hydrophobia of sliding and slider surfaces decreased. CONCLUSION: Friction coefficient value depends on the type of slider surface and its physicochemical properties. In vivo,the friction coefficient may quantify the influence of lubrificant/emolients/moisturizers. For example, the friction coefficient of hydrated skin (through the action of moisturizing products) is higher than the friction coefficient of dry skin. The relationship between the friction coefficient and the Hi/Ho balance can be reversed in the presence of water and sebum on forehead, for example.

Adult↗

PubMed1997

The normal stress effect and equilibrium friction coefficient of articular cartilage under steady frictional shear.

During creep or stress relaxation, articular cartilage exhibits a time-dependent friction coefficient which has been shown to reach an equilibrium value, mu eq, as the tissue deformation equilibrates. This study investigates the frictional properties of articular cartilage explants under steady frictional shear and constant compressive strain after the tissue reaches stress-relaxation equilibrium. The two parameters measured are the normal force and frictional torque, from which the friction coefficient was then calculated. It is shown in this experimental study that: (1) Under a prescribed infinitesimal compressive strain, cartilage supports higher compressive normal stress under steady shear than it does in the absence of frictional shear. Furthermore, the normal stress increases with increasing sliding velocity, resulting in a velocity-dependent value of mu eq. The observed normal stress effectively increases the compressive stiffness of cartilage by a factor up to 3.1. (2) Under a prescribed steady frictional shear both the normal stress and frictional shear stress increase, though not proportionally, with increasing compressive strain, producing a decreasing friction coefficient. (3) This velocity-dependent normal stress effect is also shown to result, at least partly, from intrinsic properties of cartilage. The normal stress effect has not been previously reported for articular cartilage, and represents an intriguing mechanical response not commonly encountered in solids, though common in non-Newtonian fluids.

Animals↗

PubMed2003

In vitro study of frictional forces during sliding mechanics of "reduced-friction" brackets.

This study evaluated the static friction force created between archwires and "reduced-friction" brackets during sliding mechanics. Five different brands of "reduced-friction" brackets were used: group A: NuEdge (TP Orthodontics, LaPorte, Ind); group B: Discovery (Dentaurum, Ispringen, Germany); group C: Synergy (Rocky Mountain Orthodontics, Denver, Colo); group D: Friction Free (American Orthodontics, Sheboygan, Wis); and group E: TIME, a self-ligating bracket (American Orthodontics). Group F (Omni Arch, GAC International, Bohemia, NY) served as a control group. Each group contained 75 stainless steel brackets with.022 x.028-in slots. Three stainless steel wires were tested:.018,.018 x.025, and.019 x.025 in. To take second-order bends into account, the brackets were set at either 5 degrees or 10 degrees to the wires. Each bracket was set in a special device, which was placed on the base of the testing machine. A wire ligated to the bracket was attached to the crosshead of the machine and pulled at a speed of 10 mm/min for a distance of 5 mm. Significant differences were found in the static friction forces among the different groups. Group D (Friction Free) showed the lowest and group E (TIME) showed the highest friction forces (higher than the normal friction brackets [Omni Arch]). This study demonstrates that not all brackets provide "reduced friction," even though the manufacturers describe them as doing so.

Dental Alloys↗

PubMed2003

Static-dynamic friction transition of FRP esthetic orthodontic wires on various brackets by suspension-type friction test.

A new testing apparatus for the measurement of frictional properties was designed and the frictional coefficients were obtained and compared with each other in various combinations of brackets and orthodontic wires, including esthetic fiber-reinforced plastic (FRP) wire that was especially designed and manufactured. Three kinds of wires (stainless steel, nickel-titanium, and FRP) and four brackets (single-crystal alumina, polycrystalline alumina, polycarbonate, and stainless steel) were used. The testing was done under dry and wet conditions. The friction testing equipment was designed to attach the bracket to a C-shaped bar suspended with a variable mass, and sliding along a fixed wire. The transition between static and dynamic friction was measured as a breakaway force, with the use of a universal test machine. In addition to material properties, this testing fixture eliminates geometrical factors, such as the rotational moment at the edge of the bracket slot, deflection of the orthodontic wire, and tension of the ligature wire. Nearly ideal frictional properties between materials are obtained. The frictional properties of FRP wire were similar to those of metal wires on all brackets, except the polycrystalline alumina bracket. The frictional coefficient between the polycrystalline ceramic bracket and FRP wire was larger than that of other combinations. There was little difference in frictional coefficients between dry and wet conditions.

Biocompatible Materials↗

PubMed2004

Frictional forces between lingual brackets and archwires measured by a friction tester.

Frictional resistance tends to rapidly increase as the angle between a bracket and an archwire increases beyond a critical angle. The purpose of this study was to determine a new measuring method with a pin on disk friction tester for the measurement of the frictional force between lingual brackets and archwires. A lingual bracket is different from a labial bracket in dimensions and in some clinical aspects. The influence of artificial saliva was also surveyed. Two brands of lingual brackets and one brand of labial standard bracket with an 0.018-inch slot size were used. Archwires of three alloys (stainless steel [SS], Ormco; beta-Titanium [TM], Ormco; cobalt-chrome, [EL], RMO) with 0.016 x 0.022- and 0.017 x 0.025-inch dimensions were used. Measurements were conducted with an angular velocity of 0.6 degrees/s for 90 seconds and a normal force of 100 g at 25 degrees C in a dry and 34 degrees C in an artificial saliva environment. For SS and EL archwires, the frictional force with the FJT bracket was greater than that with ORM bracket (P < .01). Compared with SS and TM archwires, 0.016 x 0.022-inch EL archwire showed a higher frictional force with two lingual brackets (P < .01). Significant differences in frictional force existed between dry and artificial saliva environments (P < .05), and the effects varied by the bracket-archwire couples. The estimated critical contact angles were greater than the theoretical values. This new method can be a useful protocol for measurement of frictional force because it can measure the frictional force under the conditions of continuous angular change between bracket and archwire.

Chromium Alloys↗

PubMed2002

The evaluation of skin friction using a frictional feel analyzer.

BACKGROUND/AIMS: Sensory evaluation is an important factor for cosmetic products. Several devices for the measurement of sensory properties have been developed in recent years. The objective here is to measure skin surface friction using these devices and examine the correlation with other physiological parameters in order to evaluate the potential of physical measurement of tactile sensation. METHODS: A KES-SE Frictional Analyzer, a commercial device for measurement of surface frictional characteristics, was used in this study. An arm holder was added to this device for measurement on the human forearm. The frictional coefficient (MIU) and its mean deviation (MMD) were used as the parameter to indicate surface friction. The moisture content in the stratum corneum was measured with a Corneometer CM825, the transepidermal water loss with a Tewameter TM210, the viscoelastic properties of the skin with a Cutometer SEM575 and the skin surface pattern by observing the negative replica using silicon rubber. RESULTS: The MIU was not influenced by load; however, it was increased due to water application on the skin. The relationship between MIU and the moisture content in the stratum comeum, between MMD and skin surface pattern and between MMD and viscosity of both normal human forearm skin and SDS (sodium dodecyl sulfate)-induced dry skin were confirmed by statistical analysis in a test on human subjects. There was also a correlation between either MIU or MMD and sensory evaluation in the morning after the application of moisturizing products. CONCLUSION: Human skin surface friction was measured by using a KES-SE Frictional Analyzer. Judging from the correlation between either MIU or MMD and sensory evaluation, we considered this instrumental analysis to be useful for evaluating the tactile impression of human skin.

Biophysics↗

PubMed2001

The role of friction in the measurement of slipperiness, Part 1: friction mechanisms and definition of test conditions.

Friction has been widely used as a measure of slipperiness. However, controversies around friction measurements remain. The purposes of this paper are to summarize understanding about friction measurement related to slipperiness assessment of shoe and floor interface and to define test conditions based on biomechanical observations. In addition, friction mechanisms at shoe and floor interface on dry, liquid and solid contaminated, and on icy surfaces are discussed. It is concluded that static friction measurement, by the traditional use of a drag-type device, is only suitable for dry and clean surfaces, and dynamic and transition friction methods are needed to properly estimate the potential risk on contaminated surfaces. Furthermore, at least some of the conditions at the shoe/floor interface during actual slip accidents should be replicated as test conditions for friction measurements, such as sliding speed, contact pressure and normal force build-up rate.

Accidental Falls↗

PubMed2001

Ice friction in speed skating: can klapskates reduce ice frictional loss?

PURPOSE: Reducing ice friction was one of the motives for developing the klapskate. However, the magnitude of power dissipation that occurs with conventional skates when a skater plantar flexes his ankle and the tip of the blade is pressed into the ice has not been quantified previously. In this study, we examine how ice friction varies during a single stroke with conventional skates and estimate the reduction in ice friction that might be obtained with klapskates. METHODS: Five elite speed skaters performed a series of trials at constant velocity and a series of maximal accelerations. Energy dissipated to ice friction during a stroke with conventional skates was analyzed using an instrumented skate and high-speed 3D kinematic analysis. The energy that would be dissipated when klapskates were used was estimated from the collected data with conventional skates. RESULTS: The estimated difference in power loss between conventional and klapskates was less dramatic than has been suggested frequently. Pressing the tip of the blade into the ice comprises only 0.84 W of the total power dissipated by ice friction (54 W) during constant velocity speed skating. During an all-out acceleration, this power loss reached 4.55 W. CONCLUSION: We conclude that only a minor part of the benefit of klapskates can be attributed to a reduction in ice friction. It is shown that this relatively small increase in ice friction is related to the large length of the skate blade.

Adult↗

PubMed2001

Frictional resistances of metal-lined ceramic brackets versus conventional stainless steel brackets and development of 3-D friction maps.

The frictional resistances of 2 metal-lined ceramic brackets (Luxi and Clarity) were compared with 2 conventional stainless steel brackets (Mini-Taurus and Mini-Twin) in vitro. In method 1, we varied the second-order angulation from 0 degrees to 12 degrees while maintaining the normal or ligature force constant at 0.3 kg; in method 2, we varied the ligature force from 0.1 kg to 0.9 kg while maintaining the angulation at theta = 0 degrees or theta = 11 degrees. The hardware simulated a 3-bracket system in which the interbracket distances were always 18 mm. All couples were evaluated at 34 degrees C using the same size stainless steel archwire (19 x 26 mil) and ligature wire (10 mil). In the passive region, the static and kinetic frictional forces and coefficients of friction were key parameters; in the active region, the static and kinetic binding forces and coefficients of binding were critical parameters. From outcomes of methods 1 and 2, the 4 aforementioned parameters, and a knowledge of the critical contact angle for binding, 3-dimensional friction maps were constructed in the dry and wet states from which the frictional resistances could be determined at any ligature force or second-order angulation. Those 3-dimensional maps show that metal-lined ceramic brackets can function comparably to conventional stainless steel brackets and that 18-kt gold inserts appear superior to stainless steel inserts. As the morphologies of metal inserts are improved, these metal-lined ceramic brackets will provide not only good esthetics among ceramic brackets but also minimal friction among conventionally ligated brackets.

Aluminum Oxide↗

PubMed2002

Deep transverse friction massage for treating tendinitis.

BACKGROUND: Deep transverse friction massage (DTFM) is one of several physiotherapy interventions suggested for the management of pain due to iliotibial band friction syndrome (ITBFS). OBJECTIVES: To assess the effectiveness of DTFM for treating ITBFS observed in runners. SEARCH STRATEGY: We searched the Medline, Embase, Healthstar, Sports Discus, CINAHL, the Cochrane Controlled Trials Register, PEDro, the specialized registry of the Cochrane musculoskeletal group and the Cochrane field of Physical and Related Therapies up to the end of December 2000, using the sensitive search strategy developed by the Cochrane Collaboration. The search was complemented with bibliography searching of the reference list of the trials retrieved from the electronic search. Key experts in the area were contacted for further published and unpublished articles. SELECTION CRITERIA: All randomized controlled trials (RCTs) and controlled clinical trials (CCTs) comparing therapeutic ultrasound against placebo or another active intervention in patients with patellofemoral pain syndrome were selected. DATA COLLECTION AND ANALYSIS: Two reviewers determined the studies to be included based on inclusion and exclusion criteria (LB, VR). Data were independently abstracted by two reviewers (VR, LB), and checked by a third reviewer (BS) using a pre-developed form of the Cochrane Musculoskeletal Group. The same two reviewers, using a validated scale, assessed the methodological quality of the RCTs and CCTs independently. Iliotibial band friction syndrome outcome measures were extracted from the publications. The pooled analysis was performed using weighted mean differences (WMDs) for pain relief as described as 1) daily pain; 2) pain while running and 3) percentage of maximum pain when running. A chi-square test was used to assess heterogeneity among trials. Fixed effects models were used throughout and random effects for outcomes showing heterogeneity. MAIN RESULTS: One RCT, including 17 patients with ITBFS was included. The experimental group (DTFM combined to rest, stretching exercises, cryotherapy and therapeutic ultrasound) (n=9) was compared to the control group (rest, stretching exercises, cryotherapy and therapeutic ultrasound only) (n=8). This trial showed no statistical difference in the three types of pain relief measured after four consecutive sessions of DTFM combined with other physiotherapy modalities for runners. Despite lack of statistical significance, there was a clinically important relative percentage difference in pain while running of 22%. REVIEWER'S CONCLUSIONS: DTFM combined with other physiotherapy modalities did not show consistent benefit over control of pain for runners experiencing ITBFS. These conclusions are limited by the low methodological quality of the one small sample size trial (n=17) included. No conclusions can be drawn about the use or non use of DTFM for the treatment of ITBFS. Future trials, utilizing appropriate methods and adequate sample sizes are needed before conclusions can be drawn regarding the effect of massage on iliotibial band friction syndrome.

Clinical Trials as Topic↗

PubMed1988

Wear, creep, and frictional heating of femoral implant articulating surfaces and the effect on long-term performance--Part II, Friction, heating, and torque.

In Part I, (J.A. Davidson and G. Schwartz, "Wear, creep, and frictional heating of femoral implant articulating surfaces and the effect on long-term performance--Part I, A review," J. Biomed. Mater. Res., 21, 000-000 (1987) it was shown that lubrication of the artificial hip joint was complex and that long-term performance is governed by the combined wear, creep, and to a lesser extent, oxidation degradation of the articulating materials. Importantly, it was shown that a tendency for heating exists during articulation in the hip joint and that elevated temperatures can increase the wear, creep, and oxidation degradation rate of UHMWPE. The present study was performed to examine closely the propensity to generate heat during articulation in a hip joint simulator. The systems investigated were polished Co-Cr-Mo alloy articulating against UHMWPE, polished alumina ceramic against UHMWPE, and polished alumina against itself. Frictional torque was also evaluated for each system at various levels of applied loads. A walking load history was used in both the frictional heating and torque tests. The majority of tests were performed with 5 mL of water lubricant. However, the effect of various concentrations of hyaluronic acid was also evaluated. Results showed frictional heating to occur in all three systems, reaching an equilibrium after roughly 30 min articulation time. Ceramic systems showed reduced levels of heating compared to the cobalt alloy-UHMWPE system. The level of frictional torque for each system ranked similar to their respective tendencies to generate heat. Hyaluronic acid had little effect, while dry conditions and the presence of small quantities of bone cement powder in water lubricant significantly increased frictional torque.

Hip Prosthesis↗

PubMed2006

Investigation of scale effects and directionality dependence on friction and adhesion of human hair using AFM and macroscale friction test apparatus.

Macroscale testing of human hair tribological properties has been widely used to aid in the development of better shampoos and conditioners. Recently, literature has focused on using the atomic force microscope (AFM) to study surface roughness, coefficient of friction, adhesive force, and wear (tribological properties) on the nanoscale in order to increase understanding about how shampoos and conditioners interact with the hair cuticle. Since there are both similarities and differences when comparing the tribological trends at both scales, it is thus recognized that scale effects are an important aspect of studying the tribology of hair. However, no microscale tribological data for hair exists in literature. This is unfortunate because many interactions between hair-skin, hair-comb, and hair-hair contact takes place at microasperities ranging from a few mum to hundreds of mum. Thus, to bridge the gap between the macro- and nanoscale data, as well as to gain a full understanding of the mechanisms behind the trends, it is now worthwhile to look at hair tribology on the microscale. Presented in this paper are coefficient of friction and adhesive force data on various scales for virgin and chemically damaged hair, both with and without conditioner treatment. Macroscale coefficient of friction was determined using a traditional friction test apparatus. Microscale and nanoscale tribological characterization was performed with AFM tips of various radii. The nano-, micro-, and macroscale trends are compared and the mechanisms behind the scale effects are discussed. Since the coefficient of friction changes drastically (on any scale) depending on whether the direction of motion is along or against the cuticle scales, the directionality dependence and responsible mechanisms are discussed.

Adhesiveness↗

PubMed2005

Nanoscale friction: kinetic friction of magnetic flux quanta and charge density waves.

In analogy with the standard macroscopic friction, here we present a comparative study of the friction force felt by moving vortices in superconductors and charge density waves. Using experiments and a model for this data, our observations (1) provide a link between friction at the micro- and macroscopic scales, (2) explain the roundness of the static-kinetic friction transition in terms of thermal fluctuations, particle interactions, and system size (critical-phenomena view), and (3) explain the crossing of the kinetic friction F(k) versus velocity V for our pristine (high density of very weak defects) and our irradiated samples (with lower density of deeper pinning defects).

Journal Article↗

PubMed2001

The role of friction in the measurement of slipperiness, Part 2: survey of friction measurement devices.

This paper seeks to address questions related to friction measurement such as how friction is related to human-centred assessment and actual slipping, and how repeatable friction measurements are. Commonly used devices for slipperiness measurement are surveyed and their characteristics compared with suggested test conditions from biomechanical observations summarized in Part 1. The issues of device validity, repeatability, reproducibility and usability are examined from the published literature. Friction assessment using the mechanical measurement devices described appears generally valid and reliable. However, the validity of most devices could be improved by bringing them within the range of human slipping conditions observed in biomechanical studies. Future studies should clearly describe the performance limitations of any device and its results and should consider whether the device conditions reflect these actual human slipping conditions. There is also a need for validation studies of more devices by walking experiments.

Accidental Falls↗

PubMed2004

Exploiting poly(dimethylsiloxane)-modified tips to evaluate frictional behavior by friction force microscopy.

With the aim of investigating the effect of the surface properties on the friction behavior of self-assembled monolayers, we have modified tipless atomic force microscopy (AFM) cantilevers with a poly(dimethylsiloxane) (PDMS) lens. The friction coefficient using the silicon tip is strongly influenced by the mechanical properties of the substrate monolayer because hard, sharp silicon tips penetrate the surface of organic monolayers. However, the friction coefficient obtained for the PDMS-modified AFM cantilever is mostly due to the surface properties of the monolayer functional end group, rather than the viscoelastic deformation of the monolayer. The use of the PDMS tip was demonstrated as a novel means to investigate the effect of surface properties on the frictional behavior of self-assembled monolayers with various functional groups with less mechanical deformation.

Journal Article↗

PubMed1979

[Importance of the friction between plate and bone in the anchoring of plates for osteosynthesis. Determination of the coefficient of metal-bone friction in animal in vivo].

In mechanical devices in general the friction plays an important role in force transmission. To find out about the magnitude of frictional forces between internal fixation plate and bone in vivo, simultaneous strain recording in plated bone and instrumented plate were performed. After 3 weeks of implantation the torque applied to a single plate-screw was set to definite levels. Thus it could be determined at what level of screw compression and at what tangential load of the related surface bone-plate, gliding occurred. The coefficient of friction was found to be 0.2 +/- 0.09 (x +/- Sx). It can be concluded that in vivo friction produced at the plate-bone contact surface is able to guarantee stability of fixation.

Animals↗