Adhesive force of a single gecko foot-hair

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Abstract
Geckos are exceptional in their ability to climb rapidly up smooth vertical surfaces1,2,3. Microscopy has shown that a gecko's foot has nearly five hundred thousand keratinous hairs or setae. Each 30–130 µm long seta is only one-tenth the diameter of a human hair and contains hundreds of projections terminating in 0.2–0.5 µm spatula-shaped structures2,4. After nearly a century of anatomical description2,4,5,6, here we report the first direct measurements of single setal force by using a two-dimensional micro-electro-mechanical systems force sensor7 and a wire as a force gauge. Measurements revealed that a seta is ten times more effective at adhesion than predicted from maximal estimates on whole animals. Adhesive force values support the hypothesis that individual seta operate by van der Waals forces8,9. The gecko's peculiar behaviour of toe uncurling and peeling2 led us to discover two aspects of setal function which increase their effectiveness. A unique macroscopic orientation and preloading of the seta increased attachment force 600-fold above that of frictional measurements of the material. Suitably orientated setae reduced the forces necessary to peel the toe by simply detaching above a critical angle with the substratum.