Evidence for self-cleaning in gecko setae

Abstract

A tokay gecko can cling to virtually any surface and support its body mass with a single toe by using the millions of keratinous setae on its toe pads. Each seta branches into hundreds of 200-nm spatulae that make intimate contact with a variety of surface profiles. We showed previously that the combined surface area of billions of spatulae maximizes van der Waals interactions to generate large adhesive and shear forces. Geckos are not known to groom their feet yet retain their stickiness for months between molts. How geckos manage to keep their feet clean while walking about with sticky toes has remained a puzzle until now. Although self-cleaning by water droplets occurs in plant and animal surfaces, no adhesive has been shown to self-clean. In the present study, we demonstrate that gecko setae are a self-cleaning adhesive. Geckos with dirty feet recovered their ability to cling to vertical surfaces after only a few steps. Self-cleaning occurred in arrays of setae isolated from the gecko. Contact mechanical models suggest that self-cleaning occurs by an energetic disequilibrium between the adhesive forces attracting a dirt particle to the substrate and those attracting the same particle to one or more spatulae. We propose that the property of self-cleaning is intrinsic to the setal nanostructure and therefore should be replicable in synthetic adhesive materials in the future.adhesion ͉ contact mechanics ͉ locomotion ͉ reptilia ͉ nanotechnology

Frictional and elastic energy in gecko adhesive detachment

“…Both PSAs and geckos adhere primarily by van der Waals (vdW) forces (Autumn et al 2002;Creton 2003) and have effective elastic moduli below 100 kPa (Dahlquist 1969;Pocius 2002;Autumn et al 2006c), but gecko setae stand in stark contrast to PSAs in their anisotropy ) and self-cleaning (Hansen & Autumn 2005) properties. PSAs are used commonly for both industrial and home applications.…”

Gecko-Inspired Carbon Nanotube-Based Self-Cleaning Adhesives

“…It has been suggested that this same hairy carpet on the gecko feet also plays an important role in self-cleaning. 12 Some of the other systems found in nature that exhibit self-cleaning properties are the leaves of lotus and lady's mantle plants. 18 The surface of lotus leaves have two levels of microscopic roughness ( Figure 1B).…”

“…17 Even though the surface properties of the spatulas are not known, the hierarchical structure of gecko feet makes the macroscopic structure superhydrophobic. 12 Significant effort in developing synthetic materials inspired by gecko feet show comparable, and in some cases better, shear resistance than natural gecko feet. 2,[6][7][8][9]11 Still, these measurements were done in controlled environments and limited self-cleaning data of these synthetic materials were reported.…”

A bio-inspired flexible fiber array with an open radial geometry for highly efficient liquid transfer

“…7 It has also been suggested that the nanowire-structured bristles of gecko feet enable high adhesion to solid and liquid drops arising from the wetting-induced structure rebuilding of the nanowire array. 8,9 Such natural phenomena have inspired materials scientists to more closely examine the wetting behavior of fibrous media, [10][11][12][13] resulting in the development of numerous bio-inspired artificial fibrous systems with special wettability properties. To date, most endeavors have focused on developing either anisotropic fibers for water collection 4,5 and pumping 14 or a vertically aligned fiber array for controllable morphologies through capillarity-induced self-assembly.…”