Grip Performance Affected by Water-Induced Wrinkling of Fingers

Lin, Hsin Ta; Hong, T.; Li, Wang Long

doi:10.1007/s11249-015-0515-4

Cited by 12 publications

(10 citation statements)

References 22 publications

(28 reference statements)

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“…Everyone has experienced wrinkly fingers after an extended exposure to water. These wrinkles have been proposed as an evolutionary mechanism for a better grip of wet objects 23,40 . However, besides experimental observations 7,55,33 or mathematical theories 31,53,58,16 there is still not a clear agreement whether this is a result of the contraction of the hypodermis ( the 'shrink' model), the effect of epidermal swelling (the 'swell' model),…”

Section: Discussionmentioning

confidence: 99%

Mechanics Reveals the Biological Trigger in Wrinkly Fingers

Saéz

Zöllner

2016

Ann Biomed Eng

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Fingertips wrinkle due to long exposure to water. The biological reason for this morphological change is unclear and still not fully understood. There are two main hypotheses for the underlying mechanism of fingertip wrinkling: the 'shrink' model (in which the wrinkling is driven by the contraction of the lower layers of skin, associated with the shrinking of the underlying vasculature), and the 'swell' model (in which the wrinkling is driven by the swelling of the upper layers of the skin, associated with osmosis). In reality, contraction of the lower layers of the skin and swelling of the upper layers will happen simultaneously. However, the relative importance of these two mechanisms to drive fingertip wrinkling also remains unclear. Simulating the swelling in the upper layers of skin alone, which is associated with neurological disorders, we found that wrinkles appeared above an increase of volume of [Formula: see text] Therefore, the upper layers can not exceed this swelling level in order to not contradict in vivo observations in patients with such neurological disorders. Simulating the contraction of the lower layers of the skin alone, we found that the volume have to decrease a [Formula: see text] to observe wrinkles. Furthermore, we found that the combined effect of both mechanisms leads to pronounced wrinkles even at low levels of swelling and contraction when individually they do not. This latter results indicates that the collaborative effect of both hypothesis are needed to induce wrinkles in the fingertips. Our results demonstrate how models from continuum mechanics can be successfully applied to testing hypotheses for the mechanisms that underly fingertip wrinkling, and how these effects can be quantified.

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Section: Discussionmentioning

confidence: 99%

Mechanics Reveals the Biological Trigger in Wrinkly Fingers

Saéz

Zöllner

2016

Ann Biomed Eng

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“…Although some reported experimental data in literature vary significantly, there is general consensus that both the dependence of the apparent contact area A 0 and the ridge contact area A R on the normal force can be fitted to power functions according to Equation (5). Given exponents corresponding to the apparent contact area in the low force regime range between 0.36 and 0.42 and those corresponding to the ridge contact area range between 0.42 and 0.58 (Warman and Ennos, 2009;van Kuilenburg et al, 2013a;Lin et al, 2015;Dzidek et al, 2017;. Taking into account that the relationship between area and load depends on many things like the fingerpad inclination angle, measurement methods (ink printing or optical method), environmental conditions (temperature and humidity) and individual properties of the finger (influenced by age and gender of subjects) the differences in exponents are still relatively small.…”

Section: Application To Fingerpad In Contact With Capacitive Screenmentioning

confidence: 99%

Macroscopic Modeling of Fingerpad Friction Under Electroadhesion: Possibilities and Limitations

Heß

Forsbach

2020

Front. Mech. Eng.

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Electrovibration is one of the key technologies in surface haptics. By inducing controlled electrostatic forces, the friction within a sliding contact between the human finger and a capacitive screen is modulated, which in turn gives effective tactile feedback to the user. Such powerful haptic displays can be built into mobile phones, tablets, navigation devices, games consoles and many other devices of consumer electronics. However, due to the layered structure and complex material of human skin, the underlying contact mechanical processes have not yet been fully understood. This work provides new continuum-based approaches to macroscopic modeling of the electro-adhesive frictional contact. A solution of pure normal contact between a human finger and a rigid, smooth plane under electroadhesion is derived by applying Shull's compliance method in the extended regime of large deformations. Based on these results and assuming pressure-controlled friction, a model for the sliding electro-adhesive contact is developed, which adequately predicts the friction force and coefficient of friction over the whole range of relevant voltages and applied normal forces. The experimentally observed area reduction caused by the tangential force is incorporated in a more empirical than profound contact mechanical way. This effect is studied with the help of a two-dimensional finite element model of the fingertip, assuming non-linear elastic material for the skin tissue. Although the simulations are restricted to non-adhesive tangential contacts, they show a significant reduction of the contact area, which is caused by large deformations of the non-linear elastic material around the distal phalanx. This result indicates that adhesion is only of secondary importance for the area reduction.

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“…Some optical measurements of the apparent area found in the literature report also an exponent close to 2/3 [34], consistent with the theory. Other fingertip studies found various exponents for the area within the apparent area of contact (i.e., at a smaller scale), one that is ≈ 2/3 [35], another is ≈ 1/2 [31], and ≈ 0.4 [36]. These differences could be attributed to variations in measurement method but also to fingertips mechanical parameters.…”

Section: A Friction-modulation Does Not Reduce Contact Area Homogeneouslymentioning

confidence: 95%

How to Measure the Area of Real Contact of Skin on Glass

Huloux

Willemet

Wiertlewski

2021

IEEE Trans. Haptics

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The contact between the fingertip and an object is formed by a collection of micro-scale junctions, which collectively constitute the real contact area. This real area of contact is only a fraction of the apparent area of contact and is directly linked to the frictional strength of the contact (i.e., the lateral force at which the finger starts sliding). As a consequence, a measure of this area of real contact can help probe into the mechanism behind the friction of skin on glass. In this article, we present two methods to measure the variations of contact area; one that improves upon a tried-and-true fingertip imaging technique to provide ground truth, and the other that relies on the absorption and reflection of acoustic energy. To achieve precise measurements, the ultrasonic method exploits a recently developed model of the interaction that incorporates the non-linearity of squeeze film levitation. The two methods are in good agreement (ρ = 0.94) over a large range of normal forces and vibration amplitudes. Since the real area of contact fundamentally underlies fingertip friction, the methods described in the article have importance for studying human grasping, understanding friction perception, and controlling surface-haptic devices.

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Grip Performance Affected by Water-Induced Wrinkling of Fingers

Cited by 12 publications

References 22 publications

Mechanics Reveals the Biological Trigger in Wrinkly Fingers

Mechanics Reveals the Biological Trigger in Wrinkly Fingers

Macroscopic Modeling of Fingerpad Friction Under Electroadhesion: Possibilities and Limitations

How to Measure the Area of Real Contact of Skin on Glass

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