1. Department of Biology, Lewis and Clark College, Portland, Oregon 97219, USA
2. Department of Mechanical Engineering, Stanford University, Stanford, California 94305, USA
3. Department of Integrative Biology, University of California at Berkeley, Berkeley, California 94720, USA
4. Department of Electrical Engineering and Computer Science, University of California at Berkeley, Berkeley , California 94720, USA

Correspondence to: Robert J. Full³ Correspondence and requests for materials should be addressed to R.J.F. (e-mail: Email: rjfull@socrates.berkeley.edu).

Abstract

Geckos are exceptional in their ability to climb rapidly up smooth vertical surfaces^{1, 2, 3}. Microscopy has shown that a gecko's foot has nearly five hundred thousand keratinous hairs or setae. Each 30–130 m long seta is only one-tenth the diameter of a human hair and contains hundreds of projections terminating in 0.2–0.5 m spatula-shaped structures^{2, 4}. After nearly a century of anatomical description^{2, 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 forces^{8, 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.