Gecko adhesion: Structure, function, and applications

Geckos attach and detach their adhesive toes in milliseconds while running with reckless abandon on nearly any surface. The adhesive on gecko toes differs dramatically from that of conventional adhesives. Conventional pressure-sensitive adhesives (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 fibers (setae) formed from stiff, hydrophobic keratin that act as a bed of angled springs with an effective stiffness similar to that of PSAs. Setae are Setaecleaning 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. Thus, gecko setae resist inappropriate bonding and are capable of easy and rapid attachment and detachment. Engineered adhesive nanostructures inspired by geckos may become the glue of the future-and perhaps the screw of the future as well.