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INTEGR. COMP. BIOL., 42:10811090 (2002) Mechanisms of Adhesion in Geckos1

Summary: 1081
INTEGR. COMP. BIOL., 42:10811090 (2002)
Mechanisms of Adhesion in Geckos1
Department of Biology, Lewis & Clark College, Portland, Oregon 97219
SYNOPSIS. The extraordinary adhesive capabilities of geckos have challenged explanation for millennia,
since Aristotle first recorded his observations. We have discovered many of the secrets of gecko adhesion,
yet the millions of dry, adhesive setae on the toes of geckos continue to generate puzzling new questions and
valuable answers. Each epidermally-derived, keratinous seta ends in hundreds of 200 nm spatular tips,
permitting intimate contact with rough and smooth surfaces alike. Prior studies suggested that adhesive
force in gecko setae was directly proportional to the water droplet contact angle ( ) , an indicator of the
free surface energy of a substrate. In contrast, new theory suggests that adhesion energy between a gecko
seta and a surface (WGS) is in fact proportional to , and only for 60 . A reanalysis of prior(1 cos )
data, in combination with our recent study, support the van der Waals hypothesis of gecko adhesion, and
contradict surface hydrophobicity as a predictor of adhesion force. Previously, we and our collaborators
measured the force production of a single seta. Initial efforts to attach a seta failed because of improper 3D
orientation. However, by simulating the dynamics of gecko limbs during climbing (based on force plate data)
we discovered that, in single setae, a small normal preload, combined with a 5 m displacement yielded a
very large adhesive force of 200 microNewton ( N), 10 times that predicted by whole-animal measurements.


Source: Autumn, Kellar - Department of Biology, Lewis and Clark College


Collections: Engineering; Materials Science; Biology and Medicine