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Critter Chemistry

September 22002

Holding Fast

Van der Waals bonding, not capillary adhesion, attaches geckos to ceilings

Sophie Wilkinson

I was on a Hawaiian vacation, lying in bed, and saw a gecko run across the ceiling to attack a large spider,” says Kellar Autumn, assistant professor of biology at Lewis & Clark College, Portland, Ore. The spider fell, but the gecko held fast to the ceiling, setting Autumn to wondering about the mechanism behind the lizard’s staying power. Now, five years later, he and his colleagues “have finally solved a problem that has puzzled scientists—and everyone else—for over a century,” he says.


SELF-ADHESIVE Branched hairs on their toes allow geckos to stick to vertical surfaces.

Autumn, along with electrical engineering professor Ronald S. Fearing and integrative biology professor Robert J. Full of the University of California, Berkeley, and their colleagues, tested adhesion of gecko toes to strongly hydrophobic and hydrophilic polarizable surfaces. Gecko toes, which are highly hydrophobic, are covered with millions of tiny hairs, each tipped with hundreds of projections known as spatulae.

If geckos used the water-based capillary adhesive forces used by insects, frogs, and some mammals, they wouldn’t be able to stick to a strongly hydrophobic surface, the researchers reasoned. They found that the lizard toes adhered equally well to both types of surfaces, indicating that van der Waals bonding rather than capillary adhesion is at work. Their complex makeup means gecko feet have an enormous surface area for the bonding [Proc. Natl. Acad. Sci. USA, published online Aug. 27,].

The research shows that the adhesive properties depend on the size and shape of the spatulae rather than their chemical makeup. Based on these findings,

Autumn says, the team is now designing gecko-inspired dry adhesive microstructures that feature “shafts decorated with lots of small tips.”

The Defense Advanced Research Projects Agency, which supports the research, is interested in such adhesives, as well as applications including climbing robots for search and rescue and space exploration.

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