Geckos are able to scurry up walls and across ceilings thanks to two million microscopic hairs on their toes that glom onto surfaces in a way that has given engineers an idea for a novel synthetic adhesive that is both dry and self-cleaning.
In a paper in this week's issue of Nature, University of California, Berkeley, biologist Robert J. Full, Lewis and Clark College biologist Kellar Autumn and their colleagues report the first measurement of the forces that these hairs, or setae (see' tee), exert on a surface.
Working with the "Cadillac" of the gecko world, a Tokay gecko (Gekko gecko) native to Southeast Asia, the team of biologists and engineers showed that the combined adhesive force of all the tiny hairs lining the gecko's toes is 10 times greater than the maximum force reportedly needed to pull a live gecko off the wall. Geckos apparently use only a fraction of the hairs at one time, though they have been known to hang from the ceiling by one toe.
The key seems to be the hundreds to thousands of tiny pads at the tip of each hair. These pads, called spatulae, measure only about ten millionths of an inch across. Yet, they get so close to the surface that weak interactions between molecules in the pad and molecules in the surface become significant. The combined attraction of a billion pads is a thousand times more than the gecko needs to hang on the wall.
"These billion spatulae, which look like broccoli on the tips of the hairs, are outstanding adhesives," said Full, a professor of integrative biology and head of the Poly-PEDAL (Performance, Energetics, Dynamics, Animal Locomotion) Laboratory at UC Berkeley. "Geckos have developed an amazing way of walking that rolls these hairs onto the surface, and then peels them off again, just like tape. But it's better than tape."
"Getting yourself to stick isn't really that difficult, it's getting off that is the problem," noted Autumn, a former postdoctoral student in Full's laboratory who now is
Contact: Robert Sanders
University of California - Berkeley