A hand-held friction meter

Body mapping of skin friction coefficient and tactile perception during the dynamic skin-textile interaction

The clothing fabric and skin interact continuously across the many regions of users' bodies during wear, which can lead to both physical skin damage and discomfort. Therefore, this investigation aimed to explore the regional differences in skin friction, tactile perception, and sensitivity in both females and males during the skin-textile interaction. The static and dynamic friction coefficient and textile perception (texture, stickiness, pleasantness, and discomfort) were measured across the 36 selected testing body areas by using a friction measurement device. The results revealed there was a significant difference in skin friction, tactile perceptions, and sensitivity across the various body regions. The anterior neck had the highest skin friction in both females and males, and participants generally rated higher texture perception in their anterior aspects compared to posterior and lateral regions. There was no significant difference in skin friction, tactile perception ratings, and sensitivity between females and males. Practitioner summary: This study sought to examine regional variations in skin friction, tactile perception, and sensitivity during the skin-textile interaction. There was a significant difference in skin friction, tactile perceptions, and sensitivity across the various body regions and no significant sex effect on skin friction, tactile perception ratings, and sensitivity.

Textiles and Human Skin, Microclimate, Cutaneous Reactions: An Overview

This article overviews research in the interdisciplinary area of textile/skin interaction and related cutaneous intolerance. Microclimate in the skin/clothing system and especially the skin responses relates to the moisture and heat transfer within this system and plays a critical role in skin irritation from textiles. A discussion is then given on skin irritation reactions to textiles, including intolerance caused by chemicals (dyes and finishes) and physical contact/friction. Finally, two skin injuries, blisters and pressure ulcers, which are caused by physical contact, pressure, and friction, are documented. Despite the prevalent problems caused by ill textile/skin interactions, minimal efforts have been devoted to this field. In addition, the in vivo experimental studies infrequently lead to a solid conclusion. The cause may lie in the dramatic variation of skin conditions among individuals as well as among different anatomic sites of the same person. Another reason might be the lack of communications between researchers in the areas of textiles and dermatology.

Development and validation of a new method for measuring friction between skin and nonwoven materials

A new method for measuring the coefficient of friction between nonwoven materials and the curved surface of the volar forearm has been developed and validated. The method was used to measure the coefficient of static friction for three different nonwoven materials on the normal (dry) and over-hydrated volar forearms of five female volunteers (ages 18–44). The method proved simple to run and had good repeatability: the coefficient of variation (standard deviation expressed as a percentage of the mean) for triplets of repeat measurements was usually (80 per cent of the time) less than 10 per cent. Measurements involving the geometrically simpler configuration of pulling a weighted fabric sample horizontally across a quasi-planar area of volar forearm skin proved experimentally more difficult and had poorer repeatability. However, correlations between values of coefficient of static friction derived using the two methods were good ( R = 0.81 for normal (dry) skin, and 0.91 for over-hydrated skin). Measurements of the coefficient of static friction for the three nonwovens for normal (dry) and for over-hydrated skin varied in the ranges of about 0.3–0.5 and 0.9–1.3, respectively. In agreement with Amontons' law, coefficients of friction were invariant with normal pressure over the entire experimental range (0.1–8.2 kPa).

Barefoot-pedestrian tribometry: in vivo method of measurement of available friction between the human heel and the walkway

We have developed an in vivo tribometer for characterizing the friction of a human heel against a planar test surface. The pedestrian steps down on an angled test surface and an observer determines if the person's heel slips. In the simplest variation, the subject simply steps down onto the test surface. The second variation has the standing subject's lower leg constrained to a vertically running carriage, forcing the pedestrian's leg to descend vertically. The third variation has the subject sitting, with an operator raising and lowering the carriage to which the leg is attached. The test surface was fixed at a given angle, a set of repeated tests was run, and the number of tests and slips were recorded. The test-surface angle was incremented through a range that varied from no slips to all slips. We analyzed the data using logistic regression. We found that the unconstrained test subject's logistic-regression curves varied greatly from subject to subject. The standing, constrained subjects were significantly closer to each other, but at the expense of a much higher spread of the angular range. The seated, constrained test subject's results were both extremely close and had extremely low angular spread.

Assessment of elastic parameters of human skin using dynamic elastography

Sonoelastography and transient elastography are two ultrasound-based techniques that facilitate noninvasive characterization of the viscoelastic properties of soft tissues by investigating their response to shear mechanical excitation. Young's modulus is the principle assessment parameter. Because it defines local tissue stiffness, it is of major interest for the medical imaging and cosmetic industries as it could replace subjective palpation by yielding local, quantitative information. In this paper, we describe a new high-resolution device capable of measuring local Young's modulus in very thin layers (1-5 mm) and devoted to the in vivo evaluation of the elastic properties of human skin. It uses an ultrasonic probe (50 MHz) for tracking the displacements induced by a 300 Hz shear wave generated by a ring surrounding the transducer. The displacements are measured using a conventional cross-correlation technique between successive ultrasonic back-scattered echoes. First, this noninvasive technique has been experimentally proven to be accurate for investigating elasticity in different skin-mimicking phantoms. Second, data were acquired in vivo on human forearms. As expected, Young's modulus was found to be higher in the dermis than in the hypodermis and other soft tissues.

Friction coefficient of skin in real-time

BACKGROUND/PURPOSE

Friction studies are useful in quantitatively investigating the skin surface. Previous studies utilized different apparatuses and materials for these investigations but there was no real-time test parameter control or monitoring. Our studies incorporated the commercially available UMT Series Micro-Tribometer, a tribology instrument that permits real-time monitoring and calculation of the important parameters in friction studies, increasing the accuracy over previous tribology and friction measurement devices used on skin.

METHODS

Our friction tests were performed on four healthy volunteers and on abdominal skin samples. A stainless steel ball was pressed on to the skin with at a pre-set load and then moved across the skin at a constant velocity of 5 mm/min. The UMT continuously monitored the friction force of the skin and the normal force of the ball to calculate the friction coefficient in real-time. Tests investigated the applicability of Amonton's law, the impact of increased and decreased hydration, and the effect of the application of moisturizers.

RESULTS

The friction coefficient depends on the normal load applied, and Amonton's law does not provide an accurate description for the skin surface. Application of water to the skin increased the friction coefficient and application of isopropyl alcohol decreased it. Fast acting moisturizers immediately increased the friction coefficient, but did not have the prolonged effect of the slow, long lasting moisturizers.

CONCLUSION

The UMT is capable of making real-time measurements on the skin and can be used as an effective tool to study friction properties. Results from the UMT measurements agree closely with theory regarding the skin surface.

Coefficient of friction: tribological studies in man - an overview

BACKGROUND/PURPOSE

Compared to other studies of skin, relatively few studies have focused on the friction of skin. This work reviews existing skin friction, emphasizing test apparatuses and parameters that have added to information regarding the friction coefficient. This review also outlines what factors are important to consider in future friction studies.

METHODS

Past studies have utilized numerous designs for a test apparatus, including probe geometry and material, as well as various probe motions (rotational vs. linear). Most tests were performed in vivo; a few were performed in vitro and on porcine skin.

RESULTS

Differences in probe material, geometry and smoothness affect friction coefficient measurements. An increase in skin hydration, either through water or through moisturizer application, increases its friction coefficient; a decrease in skin hydration, either through clinical dermatitis or through alcohol addition, decreases the coefficient. Differences are present between anatomical sites. Conflicting results are found regarding age and no differences are apparent as a result of gender or race.

CONCLUSION

Skin friction appears to be dependent on several factors - such as age, anatomical site and skin hydration. The choice of the probe and the test apparatus also influence the measurement.

Biomedical assessment and instrumental evaluation of healthy infant skin

The skin forms a critical structural boundary and a perceptual interface for the organism, yet the definition "healthy skin" is surprisingly difficult to describe. The present study's goal was to generate a technical definition of healthy infant skin by quantifying specific biophysical parameters before and after bathing in infants and correlating such parameters to a perceptual maternal evaluation. Fifty-two healthy infants, 3-6 months old, were evaluated before and after freshwater bathing. Diapered skin had a higher transepidermal water loss (TEWL), surface hydration, moisture accumulation rate (MAT), and friction than nondiapered skin before the bath (p < 0.01). Bathing dramatically altered the biophysical properties at both skin sites, with decreased MAT and lower friction, indicating a drier skin surface (p < 0.01). Visual redness and dryness decreased after bathing (p < 0.01). Blinded grading of optical images showed a significant preference for the skin after bathing (p < 0.01). This study provides the first quantitative technical definition of healthy infant skin with positive correlation to perceptual assessment by independent observers (mothers). The findings support the hypothesis that water binding properties of the stratum corneum are altered by occlusion (diapering) and that bathing introduces acute changes in stratum corneum water interactions, leading to a drier skin surface and a preferred skin appearance.

Frictional properties of human skin: relation to age, sex and anatomical region, stratum corneum hydration and transepidermal water loss

Differences in the dynamic skin friction coefficients (mu) were investigated with respect to age, sex, and anatomical region. A total of 29 volunteers consisting of seven young females, seven old females, seven young males, and eight old males participated in the study. Measurements were obtained from II anatomical regions, namely, the forehead, upper arm, volar and dorsal forearm, postauricular, palm, abdomen, upper and lower back, thigh, and ankle. The friction data were compared with stratum corneum hydration and transepidermal water loss (TEWL). The dynamic friction coefficient did not vary significantly between age and sex groups but varied considerably among the anatomical regions of the body. The forehead and postauricular had the highest mu (0.34 +/- 0.02) while the abdomen had the lowest (0.12 +/- 0.01); the remaining regions had an average mu value of 0.21 +/- 0.01. Similarly, no sex differences were observed for TEWL and stratum corneum hydration. Capacitance was only significantly lower on the palms of the elderly. Regional differences showed a higher state of hydration on the forehead and postauricular as well as the upper arm, upper and lower back when compared with the volar forearm. TEWL was generally lower in the elderly on all anatomical regions except the postauricular and palm. A significant correlation was established between mu and capacitance for most regions. Between mu and TEWL significant correlation was observed only on the palm and thigh. These findings suggest that frictional properties of skin are dependent on more than water content or non-apparent sweating and the role of sebum secretion is suggested as one possible factor.

The effects of wearing diapers on skin

Wearing dry and wet cloth and disposable diaper materials has certain effects on the degree of skin wetness. These, in turn, affect the coefficient of skin friction, the skin's susceptibility to abrasion damage, its permeability, and its support of microbial growth. These effects were explored using an adult model wearing forearm patches. The adult model was validated by comparisons of skin wetness and friction values for infants and adults determined under similar conditions. Skin wetness was proportional to diaper wetness. With increased skin wetness, there were increased coefficients of friction and increased abrasion damage, skin permeability, and microbial growth. Cloth diaper material produced wetter skin than did disposable diaper material at equivalent loadings.

Measurements of friction injuries in man

Repetitive frictional insults over years to human skin result in lichenification, callosites, and clavi (corns). No measurements of the forces involved have been made for callosites or corns. Two reports deal with lichenification produced by repeated rubbing over weeks. By contrast, friction blisters have been seriously studied because they can be produced in minutes and because foot blisters can disable soldiers. Three devices to measure the coefficient of friction of materials on man's skin and eight machines to rub man's skin are reviewed.