Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scientists prove how geckos stick, unlock secrets to making artificial gecko glue

27.08.2002


Gecko foot adhering to GaAs semiconductor, demonstrating van der Waals adhesion (Photo by K. Autumn)


Forget about duct tape. Just grab the ’gecko glue’

Geckos, nature’s supreme climbers, can race up a polished glass wall at a meter per second and support their entire body weight from a wall with only a single toe. But the gecko’s remarkable climbing ability has remained a mystery since Artistotle first observed it in fourth century B.C.

Now a team of biologists and engineers has cracked the molecular secrets of the gecko’s unsurpassed sticking power--opening the door for engineers to fabricate prototypes of synthetic gecko adhesive.



"Two millennia later, we have solved the puzzle of how geckos use millions of tiny foot hairs to adhere to even molecularly smooth surfaces such as polished glass," says Kellar Autumn, lead author of an article in this week’s Proceedings of the National Academy of Sciences. Our new data prove once and for all how geckos stick."

Working at Lewis & Clark College, the University of California at Berkeley, the University of California at Santa Barbara, and Stanford University, the interdisciplinary team:

  • confirmed speculation that the gecko’s amazing climbing ability depends on weak molecular attractive forces called van der Waals forces,
  • rejected a competing model based on the adhesion chemistry of water molecules, and
  • discovered that the gecko’s adhesive depends on geometry, not surface chemistry. In other words, the size and shape of the tips of gecko foot hairs--not what they are made of - determine the gecko’s stickiness.

To verify its experimental and theoretical results, the gecko group then used its new data to fabricate prototype synthetic foot-hair tips from two different materials.

"Both artificial setal tips stuck as predicted," notes Autumn, assistant professor of biology at Lewis & Clark College in Portland, Ore. "Our initial prototypes open the door to manufacturing the first biologically inspired dry, adhesive microstructures, which can have widespread applications."

The project required an interdisciplinary team, according to Autumn. Engineers Ronald Fearing and Metin Siiti at the University of California at Berkeley built prototype synthetic gecko foot-hair tips that stick like the real thing. Engineer Jacob Israelachvili at the University of California at Santa Barbara provided the mathematics that led to the prototype’s design. Other team members include biologist Robert Full at the University of California at Berkeley and engineer Thomas Kenny of Stanford University.

Van der Waals force vs. capillary adhesion

The team tested two competing hypotheses: one based on van der Waals force and a second on capillary (water-based) adhesion.

"Our results provide the first direct experimental verification that a short-range molecular attraction called van der Waals force is definitely what makes geckos stick," Autumn emphasizes.

Van der Waals forces, named after a Dutch physicist of the late 1800s, are weak electrodynamic forces that operate over very small distances but bond to nearly any material.

Geckos have millions of setae--microscopic hairs on the bottom of their feet. These tiny setae are only as long as two diameters of a human hair. That’s 100 millionth 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.

"Intermolecular forces come into play because the gecko foot hairs split and allow a billion spatulae to increase surface density and come into close contact with the surface. This creates a strong adhesive force," says Autumn.

A single seta can lift the weight of an ant. A million setae, which could easily fit onto the area of a dime, could lift a 45-pound child. If a gecko used all of its setae at the same time, it could support 280 pounds.

"Our previous research suggested that van der Waals force could explain gecko adhesion. But we couldn’t rule out water adsorption or some other types of water interaction. With our new data, we can finally disprove a 30-year-old theory based on the adhesion of water molecules."

The team’s previous research ruled out two other possible forms of adhesion: suction and chemical bonding.

Geometry vs. chemistry

"The van der Waals theory predicts we can enhance adhesion--just as nature has--simply by subdividing a surface into small protrusions to increase surface density," Autumn explains. "It also suggests that a possible design principle underlies the repeated, convergent evolution of dry adhesive microstructures in geckos, anoles, skinks, and insects. Basically, Mother Nature is packing a whole bunch of tiny things into a given area."

If van der Waals adhesion determines setal force, then geometry and not the material make-up that should dictate the design of setae, the team predicted.

Jacob Israelachvili at the University of California at Santa Barbara applied a mathematical model--the Johnson-Kendall-Roberts theory of adhesion--to predict the size and shape of the setae.

Ronald Fearing at the University of California at Berkeley took the empirical results and nanofabricated synthetic foot-hair tips from two different materials.

"We confirmed it’s geometry, not surface chemistry, that enables a gecko to support its entire body with a single toe," Autumn says.

"This means we don’t need to mimic biology precisely," he explains. "We can apply the underlying principles and create a similar adhesive by breaking a surface into small bumps. These preliminary physical models provide proof that humans can fabricate synthetic gecko adhesive," he says.

"The artificial foot-hair tip model opens the door to manufacturing dry, self-cleaning adhesive that works under water and in a vacuum," according to Autumn, who foresees countless applications for synthetic gecko adhesive--from vacuum areas of clean rooms to outer space.

Jean Kempe-Ware | EurekAlert!
Further information:
http://www.lclark.edu/~autumn/gecko.html
http://www.lclark.edu/~autumn/
http://www.lclark.edu/autumn/PNAS

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

DGIST develops 20 times faster biosensor

24.04.2017 | Physics and Astronomy

Nanoimprinted hyperlens array: Paving the way for practical super-resolution imaging

24.04.2017 | Materials Sciences

Atomic-level motion may drive bacteria's ability to evade immune system defenses

24.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>