Gecko adhesion: evolutionary nanotechnology

Abstract

If geckos had not evolved, it is possible that humans would never have invented adhesive nanostructures. Geckos use millions of adhesive setae on their toes to climb vertical surfaces at speeds of over 1 m s K1 . Climbing presents a significant challenge for an adhesive in requiring both strong attachment and easy rapid removal. Conventional pressure-sensitive adhesives (PSAs) are either strong and difficult to remove (e.g. duct tape) or weak and easy to remove (e.g. sticky notes). The gecko adhesive differs dramatically from conventional adhesives. Conventional PSAs are soft viscoelastic polymers that degrade, foul, self-adhere and attach accidentally to inappropriate surfaces. In contrast, gecko toes bear angled arrays of branched, hair-like setae formed from stiff, hydrophobic keratin that act as a bed of angled springs with similar effective elastic modulus to that of PSAs. Setae are self-cleaning and maintain function for months during repeated use in dirty conditions. Setae are an anisotropic 'frictional adhesive' in that adhesion requires maintenance of a proximally directed shear load, enabling either a tough bond or spontaneous detachment. Gecko-like synthetic adhesives may become the glue of the future-and perhaps the screw of the future as well.

The influence of surface energy on the self-cleaning of insect adhesive devices

“…However, until recently no adhesive organs were known to have self-cleaning capabilities (Hansen and Autumn, 2005). Models of the mechanical attachment of gecko setae suggest that they are able to self-clean through energetic disequilibrium between the adhesive forces attracting the contaminating particle to the adhesive setae and those attracting it towards the substrate (Autumn and Gravish, 2008). Essentially, bringing the fouled contact organ into contact with a surface that has a greater attraction to contaminating particles than the device leads to the removal of the particles from the adhesive organ.…”

Influence of Packing Density and Surface Roughness of Vertically-Aligned Carbon Nanotubes on Adhesive Properties of Gecko-Inspired Mimetics

“…1,3−6 These bioinspired artificial analogues are of potential interest for applications in industrial fixtures, 7 tissue adhesives, 8 or climbing robots, 9 especially where traditional adhesives (e.g., glue or tape) have proved to be inadequate. 10 A suitable synthetic adhesive requires a design that ensures the structure intimately conforms to rough surfaces, while is rigid enough not to collapse under their own weight. In doing this, essential structural parameters including diameter, length, and aspect ratio of the hairs need to be optimized for the desired ultimate adhesive performance.…”

Facile synthesis of superhydrophobic TiO2/polystyrene core-shell microspheres

“…It is significant that when the water droplets are getting close to the surface, the water is repelled and could hardly adhere to the surface until it eventually sticks to the surface. The van der Waals' mechanism of the gecko suggests that the remarkable adhesion property of the gecko's setae is mainly the result of the size and shape of its tips and is not strongly affected by chemical properties of the surface [37]. At the same time, according to the capillary mechanism, each micro-orifice produces a miniscule capillary force.…”