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At least 505 records · Page 28Linked to original sources
PubMed2000

Davener's dermatosis: a variant of friction hypermelanosis.

BACKGROUND: As part of our clinical experience we encountered a group of patients from a specific population with a similar peculiar pigmentation over the lower dorsal spine. OBJECTIVE: We investigated these patients to see whether we could determine a common origin. METHODS: Patients meeting the inclusion criteria underwent detailed history and complete physical examination; biopsy specimens from 3 patients were studied. RESULTS: All 13 patients were full-time male students at Orthodox Jewish Talmudic seminaries (Yeshivas). The lesion consisted of an elongated, vertical, midline, hyperpigmented patch with indistinct borders, which was distributed along the skin overlying the bony protuberances of the inferior thoracic and lumbar vertebrae. It was often unrecognized by the patients. Mean body mass index was lower than that for the general population. Histologic study showed a marked diffuse hyperkeratosis and hyperplastic epidermis with diffuse hyperpigmentation. We attributed the phenomenon to friction from the rigid backrests against the cutaneous surface of the lower back generated by the characteristic swaying activity that traditionally accompanies Torah study or "davening" (praying) and termed it Davener's dermatosis. CONCLUSION: We believe this phenomenon represents a new form of benign friction hypermelanosis. This report highlights the importance of a thorough history in patients presenting with pigmented lesions.

Adolescent↗
PubMed2002

Ground reaction forces and frictional demands during stair descent: effects of age and illumination.

Stair descent is an inherently risky and demanding task that older adults often encounter in everyday life. It is believed that slip between the foot or shoe sole and the stair surface may play a role in stair related falls, however, there are no reports on slip resistance requirements for stair descent. The aim of this study was to determine the required coefficient of friction (RCOF) necessary for safe stair descent in 12 young and 12 older adults, under varied illuminance conditions. The RCOF during stair descent was found to be comparable in magnitude and time to that for overground walking, and thus, with adequate footwear and dry stair surfaces, friction does not appear to be a major determinant of stair safety. Illuminance level had little effect on the dependent variables quantified in this study. However, the older participants demonstrated safer strategies than the young during stair descent, as reflected by differences in the ground reaction forces and lower RCOF.

Activities of Daily Living↗
PubMed1997

Estimating the effective Young's modulus of soft tissues from indentation tests--nonlinear finite element analysis of effects of friction and large deformation.

A nonlinear finite element model was developed to investigate the biomechanics of indentation, particularly the influence of friction and large deformation on the calculation of the effective Young's modulus from the cylindrical, flat-ended indentation test of soft tissues. A new kappa table was given for calculation of the effective Young's modulus to account for the effects of layered geometry with consideration of the larger deformation. The results indicate that the effect of friction on the calculation of Young's modulus becomes significant with a large aspect ratio and with a large Poisson's ratio. It is found that the factor kappa increases almost proportionally to the increase of the indentation depth, especially obvious with a larger Poisson's ratio v and a larger aspect ratio a/h.

Elasticity↗
PubMed2006

Step-growth synthesis and interfacial friction properties of surface dendron coatings.

We report a new procedure for synthesizing self-assembled two-tiered coatings comprised of a tethered carbosilane dendron canopy layer over an alkylsilane sublayer. The sublayer is anchored to a silicon substrate, and the areal density of the canopy can be controlled by changing the concentration of reactive vinyl groups on the sublayer surface. The structure of the dendron layer is characterized by angle-resolved X-ray photoelectron spectroscopy (ARXPS), water contact angle, and ellipsometry. Steric hindrance due to close packing of functional groups has a strong effect on the reaction efficiency, and dendron structure can be obtained only in canopies with low areal densities. Lateral force microscopy (LFM) is used to study interfacial friction and adhesion properties of the coatings. Structural variations in the canopy layer are found to play a crucial role in interfacial friction properties of these coatings.

Adsorption↗
PubMed2006

Friction of single polymers at surfaces.

Atomic force microscope (AFM) single molecule force spectroscopy has been used to investigate the friction coefficient of individual polymers adsorbed onto a solid support. The polymer chains were covalently attached to an AFM tip and were allowed to adsorb on a mica surface. Different polymers (ssDNA, polyallylamine) were chosen to cover a range of friction coefficients. During the experiment, the AFM tip was retracted in- and off-plane which results, depending on the chosen conditions, in a desorption of the polymer from the surface, a sliding across the surface, or a combination of both. Thus, the obtained force-extension spectra reveal detailed information on the mobility of a polymer chain on a surface under experimentally accessible conditions. This study demonstrates that absorbed polymers with comparable desorption forces may exhibit drastically different in plane mobility.

Adenylosuccinate Synthase↗
PubMed1995

Cognitive representation of motion: evidence for friction and gravity analogues.

Five experiments examined whether judgments of the locations of horizontally moving targets were influenced by implied friction between the targets and larger stationary surfaces. When targets crashed through a barrier, forward displacement decreased. When targets slid along the upper or lower edge of a single surface, forward displacement decreased. When targets slid along the upper or lower edge of a single surface, forward displacement decreased; when targets slid between the upper and lower edges of different surfaces, forward displacement decreased further. Targets not in contact with a surface exhibited larger forward displacement with greater target velocities, but contact with a surface attenuated or reversed this pattern. When targets slid along the upper edge of a surface, downward displacement increased; when targets slid along the lower edge of a surface, downward displacement reversed. Downward displacements were larger for larger targets, especially after contact with a surface. The data suggest that target representations contain analogues to friction and gravity that influence remembered position.

Adult↗
PubMed2003

Low-friction flows of liquid at nanopatterned interfaces.

With the important development of microfluidic systems, miniaturization of flow devices has become a real challenge. Microchannels, however, are characterized by a large surface-to-volume ratio, so that surface properties strongly affect flow resistance in submicrometre devices. We present here results showing that the concerted effect of wetting properties and surface roughness may considerably reduce friction of the fluid past the boundaries. The slippage of the fluid at the channel boundaries is shown to be greatly increased by using surfaces that are patterned on the nanometre scale. This effect occurs in the regime where the surface pattern is partially dewetted, in the spirit of the 'superhydrophobic' effects that have been discovered at macroscopic scales. Our results show for the first time that, in contrast to common belief, surface friction may be reduced by surface roughness. They also open the possibility of a controlled realization of the 'nanobubbles' that have long been suspected to play a role in interfacial slippage.

Friction↗
PubMed2003

Atomic vacancy-induced friction on the graphite surface: observation by lateral force microscopy.

Lateral force microscopy has been employed to investigate the frictional behaviour of atomic vacancies on the graphite surface. Such a study was only made possible by the controlled expansion of originally single-atom vacancies into multiatom vacancies, employing oxygen plasma etching for this purpose. Enhanced friction was observed on the vacancy regions compared with pristine areas of graphite, the origin of which is examined and discussed.

Friction↗
PubMed1994

A review of the friction of snow skis.

Snow friction results from a mixture of processes. With little meltwater present, the surfaces are partially separated and, when too much water is present, the contact area increases and there may be capillary attachments. Slider thermal conductivity and even colour are very important. Heat is generated by friction and solar radiation absorbtion and is conducted away by both slider and ice particles. The remaining heat is available to generate meltwater which acts as a lubricant. While sliders must be designed for use over a narrow range of snow and weather conditions, polyethylene bases can be structured and waxed to broaden that range. The important processes operate not at the air temperature, but at the ski base temperature, which is highly dependent on such things as snow-surface temperature, load and speed. The roughness elements and contact areas must be characterized before the basic processes can be understood further.

Biomechanical Phenomena↗
PubMed1992

Motion of the bipolar hip prosthesis components. Friction studied in cadavers.

It has been postulated that most hip motion occurs at the inner bearing in bipolar hip prosthesis. However, radiography and cineradiography analyses have shown that the inner bearing is not always the primary articulation. We studied the frictional behavior of bipolar prosthesis and Austin-Moore prostheses and the motion of the bipolar prosthesis using a pendulum apparatus. The primary articulation was altered according to the amount of loading. When a load of 10 kg was applied to the joint, motion occurred at both bearings with friction coefficients 0.061 at the inner bearing and 0.026 at the outer bearing. With loads of over 20 kg, the outer bearing was the primary articulation. The inner bearing was the dominant articulation only when the acetabular cartilage had been removed. Our results suggest that the motion of bipolar prostheses occurs mainly at the outer bearing during normal walking, and that this prosthesis cannot be expected to reduce wear of articular cartilage.

Biomechanical Phenomena↗
PubMed1994

Mortality and cancer incidence of workers exposed to chrysotile asbestos in the friction-products industry.

Three studies provide data on this topic. The largest was at the Ferodo factory in the U.K. There was no evidence of an overall excess in mortality from all causes, and in particular no increase in mortality due to lung cancer. Also, there was no evidence of any dose-response effect for lung cancer. There were 13 mesotheliomas but for 10 of these there had been exposure to crocidolite whilst working on a special contract that only a small minority of the workforce were involved in. Another one had worked in an asbestos-cement factory for 20 years. This left two mesotheliomas, one unconfirmed, for which the only known exposure was to chrysotile asbestos. The second study was of a plant in Connecticut. There was a significant increase in mortality due to respiratory cancer, but this excess was greatest in those with less than 1 year's exposure and was unrelated to cumulative exposure. No mesotheliomas occurred. The third study was of two factories in Ontario manufacturing automotive components. There was a non-significant increase in lung cancer mortality but the majority of these had not worked in the departments where asbestos was used. There were two unconfirmed mesotheliomas, one of whom had worked with friction materials. In conclusion, the three studies show that, if there are any effects on mortality due to working in the manufacture of friction materials, these effects must be small.

Asbestos, Serpentine↗
PubMed2001

A comparative evaluation of coefficient of friction and mechanical properties of commercially available Foley catheters.

Three commercially available urinary catheters were evaluated for their coefficient of friction and mechanical properties, which are two important parameters as far as the intended use is considered. The apparent coefficient of friction was measured from the slope of the force versus normal load graph using an in-house fabricated setup. The mechanical properties like ultimate tensile strength, elongation at break and modulus were evaluated before and after aging in synthetic urine. The swelling behavior of the catheter samples was studied in toluene and found to correlate well with the mechanical properties.

Catheters, Indwelling↗
PubMed2004

Friction melanosis: a clinical, histologic, and ultrastructural study in Jordanian patients.

BACKGROUND: Friction melanosis (FM) is an acquired pigmentary disorder mainly affecting young people. The primary skin regions affected are located over the osseous prominences, especially the clavicular zone and upper back. Our purpose in this study was to report the clinical spectrum, histologic findings, and ultrastructural features of FM in Jordanian patients. METHODS: Thirteen patients with FM (10 women and three men) were studied. The patients were seen at Princess Basma Teaching Hospital in north Jordan between 1999 and 2001. RESULTS: Eleven patients presented with asymptomatic, diffuse, brownish patches and two presented with mottled patches on the skin over the trunk bones and limbs. All had a history of rubbing their skin repeatedly with scrub pads (loofah) or bathroom towels. Ten of the 13 cases were studied histologically. Skin biopsies from four patients were examined ultrastructurally. Both histologic and electron microscopic examination of the biopsies from our patients showed a marked increase in melanin and melanin incontinence, with a lack of amyloid in the upper dermis. CONCLUSIONS: FM is infrequently seen in north Jordan. We believe that repeated frictional trauma from clothing or scrub pads against the skin overlying the bony protuberances is fundamental in its pathogenesis. Other factors, such as scrub pads made of rough material (loofah), dark skin type, and individual variability, may also play a role in the pathogenesis. We advise patients not to use rough scrub pads during bathing, to avoid rubbing the skin overlying the bony prominences, to avoid rubbing vigorously, and to use a soft cotton pad instead.

Administration, Topical↗
PubMed2003

Inhomogeneous cartilage properties enhance superficial interstitial fluid support and frictional properties, but do not provide a homogeneous state of stress.

It has been well established that articular cartilage is compositionally and mechanically inhomogenous through its depth. To what extent this structural inhomogeneity is a prerequisite for appropriate cartilage function and integrity is not well understood. The first hypothesis to be tested in this study was that the depth-dependent inhomogeneity of the cartilage acts to maximize the interstitial fluid load support at the articular surface, to provide efficient frictional and wear properties. The second hypothesis was that the inhomogeneity produces a more homogeneous state of elastic stress in the matrix than would be achieved with uniform properties. We have, for the first time, simultaneously determined depth-dependent tensile and compressive properties of human patellofemoral cartilage from unconfined compression stress relaxation tests. The results show that the tensile modulus increases significantly from 4.1 +/- 1.9 MPa in the deep zone to 8.3 +/- 3.7 MPa at the superficial zone, while the compressive modulus decreases from 0.73 +/- 0.26 MPa to 0.28 +/- 0.16 MPa. The experimental measurements were then implemented with the finite-element method to compute the response of an inhomogeneous and homogeneous cartilage layer to loading. The finite-element models demonstrate that structural inhomogeneity acts to increase the interstitial fluid load support at the articular surface. However, the state of stress, strain, or strain energy density in the solid matrix remained inhomogeneous through the depth of the articular layer, whether or not inhomogeneous material properties were employed. We suggest that increased fluid load support at the articular surface enhances the frictional and wear properties of articular cartilage, but that the tissue is not functionally adapted to produce homogeneous stress, strain, or strain energy density distributions. Interstitial fluid pressurization, but not a homogeneous elastic stress distribution, appears thus to be a prerequisite for the functional and morphological integrity of the cartilage.

Anisotropy↗
PubMed1997

Effects of frictional losses and pulsatile flow on the collapse of stenotic arteries.

High-grade stenosis can produce conditions in which the artery may collapse. A one-dimensional numerical model of a compliant stenosis was developed from the collapsible tube theory of Shapiro. The model extends an earlier model by including the effects of frictional losses and unsteadiness. The model was used to investigate the relative importance of several physical parameters present in the in vivo environment. The results indicated that collapse can occur within the stenosis. Frictional loss was influential in reducing the magnitude of collapse. Large separation losses could prevent collapse outright even with low downstream resistances. However, the degree of stenosis was still the primary parameter governing the onset of collapse. Pulsatile solutions demonstrated conditions that produce cyclic collapse within the stenosis. This study predicts certain physiologic conditions in which collapse of arteries may occur for high-grade stenoses.

Arterial Occlusive Diseases↗
PubMed2005

Diatom bionanotribology--biological surfaces in relative motion: their design, friction, adhesion, lubrication and wear.

Tribology is the branch of engineering that deals with the interaction of surfaces in relative motion (as in bearings or gears): their design, friction, adhesion, lubrication and wear. Continuous miniaturization of technological devices like hard disc drives and biosensors increases the necessity for the fundamental understanding of tribological phenomena at the micro- and nanoscale. Biological systems show optimized performance also at this scale. Examples for biological friction systems at different length scales include bacterial flagella, joints, articular cartilage and muscle connective tissues. Scanning probe microscopy opened the nanocosmos to engineers: not only is microscopy now possible on the atomic scale, but even manipulation of single atoms and molecules can be performed with unprecedented precision. As opposed to this top-down approach, biological systems excel in bottom-up nanotechnology. Our model system for bionanotribological investigations are diatoms, for they are small, highly reproductive, and since they are transparent, they are accessible with different kinds of optical microscopy methods. Furthermore, certain diatoms have proved to be rewarding samples for mechanical and topological in vivo investigations on the nanoscale. There are several diatom species that actively move (e.g. Bacillaria paxillifer forms colonies in which the single cells slide against each other) or which can, as cell colonies, be elongated by as much as a major fraction of their original length (e.g. Ellerbeckia arenaria colonies can be reversibly elongated by one third of their original length). Therefore, we assume that some sort of lubrication of interactive surfaces is present in these species. Current studies in diatom bionanotribology comprise techniques like atomic force microscopy, histochemical analysis, infrared spectrometry, molecular spectroscopy and confocal infrared microscopy.

Cell Adhesion↗
PubMed1995

The effect of artificial saliva on the frictional forces between orthodontic brackets and archwires.

The effect of artificial saliva on the static and kinetic frictional forces of stainless steel (Dentaurum) and polycrystalline ceramic (Transcend) brackets in combination with 0.018-inch round and 0.019 x 0.025-inch Edgewise archwire sizes and stainless steel, nickel-titanium and beta-titanium archwire materials, under a constant ligature force were investigated. In all cases, artificial saliva had the effect of increasing the frictional force when compared with the dry state.

Ceramics↗
PubMedDate not supplied

Friction of the gliding surface. Implications for tendon surgery and rehabilitation.

Finger flexor tendon rehabilitation has come a long way, but further advances are possible. Ideally, a healing tendon should move, but under the minimum load necessary to achieve motion. It is possible to design suture repairs that minimize the friction between tendon and sheath while simultaneously maintaining adequate strength to provide a wide margin of safety during therapy. A looped, four-strand modified Kessler repair is a good example of this type of high-strength, low-friction repair. At the same time, rehabilitation methods can also be optimized. A new modified synergistic motion protocol is described in which wrist flexion and finger extension is alternated with wrist and metacarpophalangeal joint extension and finger interphalangeal joint flexion. Based on evidence from basic science studies, the authors hypothesize that this new protocol will deliver more effective proximal tension on the tendon repair than either passive flexion/active extension or synergistic protocols, and may be useful in patients who are not ready for, or are not reliable with, active motion or place and hold protocols. The scientific basis for these new methods is reviewed, and the concept of the "safe zone" for tendon loading, in which tendon motion occurs without gapping of the repair site, is developed.

Biomechanical Phenomena↗