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Secrets to Making Gecko Glue Unlocked

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    NHNE News List Current Members: 679 Subscribe/unsubscribe/archive info at the bottom of this message. ... HOW GECKOS STICK, SECRETS TO MAKING GECKO GLUE
    Message 1 of 1 , Sep 3, 2002
      NHNE News List
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      Lewis & Clark College / Newswise
      August 27, 2002


      PORTLAND, Ore.-- 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

      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

      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.

      Defense Advanced Research Projects Agency (DARPA) supports the research.


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