EMBARGOED FOR RELEASE UNTIL: 5 p.m. Eastern, Monday, January 3, 2005
December 28, 2004
Release #04-05-069

CONTACT:
Kellar Autumn, Associate Professor of Biology
503-768-7205 or 503-869-3641 or autumn@lclark.edu

Tania Thompson, Senior Communications Officer
503-768-7961 or 503-701-3211 or taniat@lclark.edu

(Portland, Ore.)—Duct tape that never loses its stick. Bandages that come off without sticky residue or an “ouch.” Gecko feet may hold the key to the development of synthetic self-cleaning adhesives, according to a biologist from Lewis & Clark College. The research is published in the January 3, 2005 online early edition of the Proceedings from the National Academy of Sciences of the United States, or PNAS (Article #08304: “Evidence for self-cleaning in gecko setae,” W.R. Hansen and K. Autumn).

“How geckos manage to keep their feet clean while walking about with sticky feet has remained a puzzle until now,” said Kellar Autumn, associate professor of biology at Lewis & Clark College. “Geckos don’t groom their feet, and the adhesive on their toes is much too sticky for dirt to be shaken off. Conventional adhesives like tape just get dirtier and dirtier, but we discovered that gecko feet actually become cleaner with repeated use.”

The new research with coauthor Wendy R. Hansen ’01, published in PNAS, found that the microscopic adhesive hairs—or setae—that create the gecko’s adhesive qualities are also the first known self-cleaning adhesive. According to Autumn, gecko setae isolated from the gecko become cleaner by themselves.

“Our mathematical models suggest that self-cleaning in gecko setae is a result of geometry not chemistry,” said Autumn. “This means that synthetic self-cleaning adhesives could be fabricated from a wide variety of materials. The possibilities for future applications of a dry, self-cleaning adhesive are enormous. We envision uses for our discovery ranging from nanosurgery to aerospace applications. Who knows—maybe a gecko-inspired robot with sticky, self-cleaning feet will walk on the dusty surface of Mars someday.”

An interdisciplinary team of researchers, led by Autumn, earlier confirmed speculation that the gecko’s amazing climbing ability depends on weak molecular attractive forces called van der Waals forces, named after a Dutch physicist of the late 1800s. Van der Waals forces are weak electrodynamic forces that operate over very small distances but bond to nearly any material.Autumn’s research team rejected a 30-year-old model based on the adhesion chemistry of water molecules. Instead, the research team demonstrated that a gecko’s ability to stick to surfaces depends on geometry—not chemistry—to synthesize the world’s first gecko-based adhesive microstructure.

The setae (microscopic hairs) on the bottom of gecko’s feet are only as long as two diameters of a human hair. That’s 100-millionths of a meter long. Each seta ends with 1,000 even tinier pads at the tip. These tips, called spatulae, are only 200-billionths of a meter wide—below the wavelength of visible light.In 2002, Ronald Fearing, a researcher at the University of California at Berkeley, was able to produce two artificial hair tips, while Autumn and colleagues concluded that “both artificial setal tips stuck as predicted and provide a path to manufacturing the first dry, adhesive microstructures.” Fearing’s group later made the first array of synthetic gecko hairs with long stalks (6 micron stalk) and relatively large diameters (6 micron diameter).

The team’s research is supported by the National Science Foundation and the Defense Advanced Research Projects Agency (DARPA). More information about Autumn’s research is available online at http://www.lclark.edu/pnas05.

NOTE TO BROADCAST OUTLETS: Gecko b-roll, video news releases, and interview segments with Kellar Autumn are available. Contact Tania Thompson, senior communications officer, for further details at 503-768-7961 or taniat@lclark.edu.

Previous research from the gecko team:

Autumn et al. PNAS 2002:

1. Provides the first direct experimental verification for a van der Waals mechanism of gecko foot-hair adhesion;
2. Predicts foot-hair design based on adhesive theory. Adhesion is enhanced simply by splitting a surface into small protrusions to increase surface density - just what has evolved in nature independently numerous times.
3. Reports the gecko-inspired fabrication of synthetic foot-hair tips that stick. If van der Waals force is the mechanism, then adhesion should depend more on size and shape than on the nature of the surface. Our ability to fabricate artificial foot-hair tips that stick from two different materials strongly supports our experimental and theoretical results.

Autumn et al. Nature 2000:

1. Presented the first measurements of adhesion in a single isolated gecko seta.
2. Found that setae are 10 times as sticky as suggested by previous whole-body measurements.
3. Discovered the mechanical requirements for attachment of a seta.
4. Discovered the mechanical requirements for detachment of a seta.
5. Could not reject vdW forces on theoretical grounds.

For more information:

http://www.lclark.edu/pnas05

http://www.lclark.edu/~autumn/dept/index.html

http://www.pnas.org/content/vol99/issue19/cover.shtml

Autumn, K., M. Sitti, A.M. Peattie, W. Hansen. S. Sponberg, Y.A. Liang, T. Kenny, R. Fearing, J.N. Israelachvili, R.J. Full. 2002. “Evidence for van der Waals adhesion in gecko setae. “PNAS 99(19): 12252-12256. http://www.pnas.org/content/vol99/issue19/cover.shtml

Autumn, K. and A.M.Peattie. 2002. “Mechanisms of adhesion in geckos. Integrative and Comparative Biology.” 42(6): 1081-1090.

Autumn, K., W.-P. Chang, R. Fearing, T. Hsieh, T. Kenny, L. Liang, W. Zesch, R.J. Full. 2000. “Adhesive force of a single gecko foot-hair.” Nature 405:681-685.

M. Sitti and R.S. Fearing,

“Nanomolding Based Fabrication of Synthetic Gecko Foot-Hairs.” IEEE Nano, August 2002, Washington, D.C.