Gecko Inspired Adhesive Sticks, But Isn’t Sticky

January 12, 2008

By Chris Gorski
ISNS Contributor

Inspired by the not-so-sticky-footed gecko lizard’s ability to climb or hang from almost any surface, researchers at the University of California, Berkley, have developed a tape-like adhesive that is strong but also effortless to remove and reattach. It looks like normal cellophane tape, but works in a different way. Once it slides the tiniest fraction of an inch across a surface, the tape’s unique bonding material holds on like an anchor. It is surprisingly strong when weight pulls against it. But release the weight, and this adhesive peels away without resistance, just like a gecko’s foot.

Gecko lizards who seemingly defy gravity as they scramble up walls and hang from ceilings in the warmer regions of the world, are the inspiration behind the new non-sticky tape, but it is physics on the very small scale that makes it work. The adhesive “sticks” to a surface by bonding to it at the atomic level. The atomic bonding allows the tape to be both incredibly strong, yet pull apart almost effortlessly.

The adhesive technology works on smooth surfaces like glass, but future development could make it useful for all sorts of things like sporting goods, medical equipment, and even climbing robots able to scamper up shear cliffs, the Berkley scientists said.

The tape consists of tiny plastic microfibers, mimicking the millions of tiny hairs called setae that cover geckos’ feet. Each of the setae fan out into many more pieces, producing countless tiny hairs that help the gecko grab onto a surface. Surprisingly, gecko feet feel smooth to the touch, and leave behind no sticky residue. The bond, whether on a gecko’s feet or on the new tape, does not grow stronger when pressed against the surface like standard tape.

The hairs on the feet and the microfibers on the new tape actually adhere to an object by what are called Van der Waal’s forces. This is an atomic force that attracts on a scale of very short distances. It also releases easily as the hairs or fibers pull away. Researchers found that geckos attach and release their feet about 15 times per second.

Familiar adhesives like cellophane tape technically incorporate Van der Waal’s forces, but rely primarily on a combination of sticky tangled threads and vacuum pressure (like microscopic suction cups) to stick to objects. These primary factors of cellophane tape contribute about 10,000 times the strength of the Van der Waal’s force.

Despite depending on only that usually tiny force, geckos’ feet bond to surfaces with incredible strength. It is actually thousands of times stronger than the weight of a gecko. This is the kind of strength the researchers are after. The plastic microfibers in their tape generate the same effect as a gecko’s foot. The fibers are miniscule, tightly packed on the tape with 42 million per square centimeter.

The new tape does not feel sticky, but placing it on a surface and pulling it the tiniest fraction of an inch bends the fibers, which bonds them to the surface. The more they slide, the stronger the bond. Releasing the force pulling on the tape weakens the bond, and the tape detaches without any residue or stickiness. It works on smooth surfaces and can be reused. It even grows stronger when reapplied.

This tape is not the first fastener based on a biological phenomenon. The hook and loop design of Velcro is based on burrs from plants that attach to hikers’ pant legs. Other researchers are working on emulating the remarkable ability of mussels to stick to almost any surface, even in the presence of water. There are even other adhesives based on the gecko. This tape, however, is incredibly strong, and the first one that is so easy to attach and detach.

ISNS contributor Chris Gorski is with the American Institute of Physics’ Discoveries and Breakthroughs Inside Science program. He is a news researcher, writer and filmmaker who specializes in science.

***This story is provided for media use by the Inside Science News Service, which is supported by the American Institute of Physics, a not-for-profit publisher of scientific journals. Contact: Jim Dawson, news editor, at jdawson@aip.org.