Effects of humidity on the mechanical properties of gecko setae

Prowse, Michael S.; Wilkinson, Matt; Puthoff, Jonathan B.; Mayer, G.; Autumn, Kellar

doi:10.1016/j.actbio.2010.09.036

Cited by 89 publications

(114 citation statements)

References 28 publications

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“…Additionally, it is also possible that adhesive setae themselves are affected differently by water than those of other species. This may include reduction of the setal modulus due to hydration (Prowse et al, 2011;Puthoff et al, 2010). In this context, Puthoff and colleagues questioned whether species from dry climates would suffer impaired adhesion due to the low humidity of their environment (Puthoff et al, 2010).…”

Section: Discussionmentioning

confidence: 99%

“…Studies of the potential effects of water on gecko adhesion are increasing (Huber et al, 2005b;Sun et al, 2005;Niewiarowski et al, 2008;Pesika et al, 2009;Prowse et al, 2011;Stark et al, 2012Stark et al, , 2013Stark et al, , 2014a, although, to date, all have focused on static adhesive performance. In contrast, work on dynamic performance seems to be restricted to investigations related to atmospheric humidity rather than surface water and has not been investigated in whole animal experiments (Puthoff et al, 2010(Puthoff et al, , 2013Gravish et al, 2010).…”

Section: Discussionmentioning

confidence: 99%

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Run don't walk: locomotor performance of geckos on wet substrates

Stark

Ohlemacher

Knight

et al. 2015

Journal of Experimental Biology

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The gecko adhesive system has been under particular scrutiny for over a decade, as the field has recently attracted attention for its application to bio-inspired design. However, little is known about how the adhesive system behaves in ecologically relevant conditions. Geckos inhabit a variety of environments, many of which are characterized by high temperature, humidity and rain. The van der Waals-based gecko adhesive system should be particularly challenged by wet substrates because water can disrupt the intimate contact necessary for adhesion. While a few previous studies have focused on the clinging ability of geckos on wet substrates, we tested a dynamic performance characteristic, sprint velocity. To better understand how substrate wettability and running orientation affect locomotor performance of multiple species on wet substrates, we measured average sprint velocity of five species of gecko on substrates that were either hydrophilic or intermediately wetting and oriented either vertically or horizontally. Surprisingly, we found no indication that wet substrates impact average sprint velocity over 1 m, and rather, in some species, sprint velocity was increased on wet substrates rather than reduced. When investigating physical characteristics and behavior that may be associated with running on wet substrates, such as total number of stops, slips and wet toes at the completion of a race, we found that there may be habitat-related differences between some species. Our results show that in general, unlike clinging and walking, geckos running along wet substrates suffer no significant loss in locomotor performance over short distances.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Run don't walk: locomotor performance of geckos on wet substrates

Stark

Ohlemacher

Knight

et al. 2015

Journal of Experimental Biology

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“…At relatively low temperatures, the response is strong and positive, but at high temperatures it is negligible. The effect of humidity on mechanical properties of individual setae may provide a partial answer: setae become softer in high humidity, which may provide more surface area for adhesive contact (Puthoff et al, 2010;Prowse et al, 2011). Although increased adhesive surface area may significantly contribute to increased adhesion in high humidity, it is still unclear why there is a complex interaction between temperature and humidity (Niewiarowski et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

The effect of surface water and wetting on gecko adhesion

Stark

Sullivan

Niewiarowski

2012

Journal of Experimental Biology

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SUMMARYDespite profound interest in the mechanics and performance of the gecko adhesive system, relatively few studies have focused on performance under conditions that are ecologically relevant to the natural habitats of geckos. Because geckos are likely to encounter surfaces that are wet, we used shear force adhesion measurements to examine the effect of surface water and toe pad wetting on the whole-animal performance of a tropical-dwelling gecko (Gekko gecko). To test the effect of surface wetting, we measured the shear adhesive force of geckos on three substrate conditions: dry glass, glass misted with water droplets and glass fully submerged in water. We also investigated the effect of wetting on the adhesive toe pad by soaking the toe pads prior to testing. Finally, we tested for repeatability of the adhesive system in each wetting condition by measuring shear adhesion after each step a gecko made under treatment conditions. Wetted toe pads had significantly lower shear adhesive force in all treatments (0.86±0.09N) than the control (17.96±3.42N), as did full immersion in water (0.44±0.03N). Treatments with droplets of water distributed across the surface were more variable and did not differ from treatments where the surface was dry (4.72±1.59N misted glass; 9.76±2.81N dry glass), except after the gecko took multiple steps. These findings suggest that surface water and the wetting of a geckoʼs adhesive toe pads may have significant consequences for the ecology and behavior of geckos living in tropical environments.

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“…At the atomic scale, surfaces are pulled together by van der Waals interactions that produce forces per unit area that are orders of magnitude larger than atmospheric pressure (1). This leads to strong adhesion of small objects, such as Gecko setae (2,3) [capillary forces may also contribute to Gecko adhesion in humid environments (4,5)] and engineered mimics (6), and unwanted adhesion is the main failure mechanism in microelectromechanical systems with moving parts (7). Although tape and gecko feet maintain this strong adhesion at macroscopic scales, few of the objects we encounter are sticky.…”

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confidence: 99%

Contact between rough surfaces and a criterion for macroscopic adhesion

Pastewka

Robbins

2014

Proc. Natl. Acad. Sci. U.S.A.

273

238

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At the molecular scale, there are strong attractive interactions between surfaces, yet few macroscopic surfaces are sticky. Extensive simulations of contact by adhesive surfaces with roughness on nanometer to micrometer scales are used to determine how roughness reduces the area where atoms contact and thus weakens adhesion. The material properties, adhesive strength, and roughness parameters are varied by orders of magnitude. In all cases, the area of atomic contact is initially proportional to the load. The prefactor rises linearly with adhesive strength for weak attractions. Above a threshold adhesive strength, the prefactor changes sign, the surfaces become sticky, and a finite force is required to separate them. A parameter-free analytic theory is presented that describes changes in these numerical results over up to five orders of magnitude in load. It relates the threshold adhesive strength to roughness and material properties, explaining why most macroscopic surfaces do not stick. The numerical results are qualitatively and quantitatively inconsistent with classical theories based on the Greenwood−Williamson approach that neglect the range of adhesion and do not include asperity interactions.surface roughness | contact mechanics S urfaces are adhesive or "sticky" if breaking contact requires a finite force. At the atomic scale, surfaces are pulled together by van der Waals interactions that produce forces per unit area that are orders of magnitude larger than atmospheric pressure (1). This leads to strong adhesion of small objects, such as Gecko setae (2, 3) [capillary forces may also contribute to Gecko adhesion in humid environments (4, 5)] and engineered mimics (6), and unwanted adhesion is the main failure mechanism in microelectromechanical systems with moving parts (7). Although tape and gecko feet maintain this strong adhesion at macroscopic scales, few of the objects we encounter are sticky. Indeed, our world would come to a halt if macroscopic objects adhered with an average pressure equal to that from van der Waals interactions.The discrepancy between atomic and macroscopic forces has been dubbed the adhesion paradox (8). Experiments show that a key factor underlying this paradox is surface roughness, which reduces the fraction of surface atoms that are close enough to adhere (8-11). Quantitative calculations of this reduction are extremely challenging because of the complex topography of typical surfaces, which have bumps on top of bumps on a wide range of scales (12, 13). In many cases, they can be described as self-affine fractals from a lower wavelength λ s of order nanometers to an upper wavelength λ L in the micrometer to millimeter range (10,14).The traditional Greenwood−Williamson (GW) (15) approach for calculating nonadhesive contact of rough surfaces approximates their complex topography by a set of spherical asperities of radius R. The distribution of asperity heights is assumed to be either exponential or Gaussian, and the long-range elastic interactions between different asperities...

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Effects of humidity on the mechanical properties of gecko setae

Cited by 89 publications

References 28 publications

Run don't walk: locomotor performance of geckos on wet substrates

Run don't walk: locomotor performance of geckos on wet substrates

The effect of surface water and wetting on gecko adhesion

Contact between rough surfaces and a criterion for macroscopic adhesion

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