Adhesive mimics gecko toe hairs: Berkeley engineers create gravity-defying bonding agent.

A new anti-sliding adhesive developed by engineers at the University of California, Berkeley, may be the closest man-made material yet to mimic the remarkable gecko toe hairs that allow the tiny lizard to scamper along vertical surfaces and ceilings.

The researchers say that such an adhesive could one day be used to outfit a small robot that could climb up walls.

Taking a cue from the millions of hairs covering a gecko's toes, researchers squeezed 42 million hard plastic microfibers onto each square centimeter of material and loaded it with various weights. They found that on a smooth, clean, vertical surface, two square centimeters of the synthetic adhesive could hold 400 grams (0.88 pounds). At the same time, the adhesive easily lifts off with minimal force and no residue.

Scientists have long marveled at the gravity-defying feats of the gecko, and a number of research teams across the world are working on duplicating the lizard's adhesive forces. Ron Fearing, UC Berkeley professor of electrical engineering and computer sciences and head of the research team developing the new material, notes that previous research on gecko-like adhesives has focused on the strength of the adhesion. He said that the ease of attachment and detachment are equally important when developing a material that can be used practically for scaling vertical walls and ceilings.

What sets this new gecko-inspired adhesive apart from its predecessors is that it is directional, only "sticking" when it slides along a smooth surface, not when it is pressed down.

"This difference is critical because if you're climbing up vertical surfaces, you can't afford to use a lot of energy pressing down into the surface to stick," said Fearing. "Using force to attach also requires force to detach. A gecko running uphill may be attaching and detaching its feet 20 times a second, so it'd get very tired if it had to work hard to pull its feet off at every step."

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