Sunday, July 15, 2007

How Gecko Toes Stick

From the American Scientist

The powerful, fantastic adhesive used by geckos is made of nanoscale hairs that engage tiny forces, inspiring envy among human imitators

Kellar Autumn

Geckos can run up smooth walls or cross inverted surfaces with seeming ease. How do they do it? Author Autumn describes recent research in his lab and others that tells the tale. It turns out that gecko toe pads are sticky because they contain extraordinary structures that act together as a smart adhesive. But gecko toes work nothing like pressure-sensitive adhesives (found on adhesive tape), which are soft enough to flow and make intimate, continuous surface contact. Instead, gecko toes bear ridges covered with arrays of stiff, hairlike setae. Each seta branches into hundreds of tiny endings that touch the surface and engage intermolecular van der Waals forces. Together, the 6.5 million setae on a 50-gram gecko generate enough force to support the weight of two people. Furthermore, gecko toes detach within milliseconds, stick to nearly every material, and neither stay dirty nor self-adhere.
See also Kellar Autumn's page, which also includes a slide show on the various ways animals have evolved to adhere to surfaces.

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