Gecko
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Geckos have amazing adhesive abilities that allow them to climb nearly any surface. This is due to the microscopic hairs called setae that cover their toes. Each seta branches into thousands of even smaller spatulae tips that are only 200 nanometers wide. Studies have shown that gecko adhesion is caused by van der Waals forces between these spatulae tips and surfaces. A single seta can even lift weights hundreds of times greater than its own. Researchers have been working to understand and replicate this extraordinary natural adhesion mechanism.
Gecko
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- 4. Los geckos son pequeños lagartos de tamaño moderado que pertenecen a la familia Gekkonidae y se encuentran en climas calientes a través del mundo. Los dedos del pie del gecko han atraído mucho la atención, pues adhieren a una variedad amplia de superficies, sin el uso de líquidos o tensión superficial. Los estudios recientes de las cerdas (setae) de los dedos del gecko demuestran que las fuerzas atractivas que sostienen geckos a las superficies son interacciones de van der Waals (entre los setae finalmente divididos y las superficies ellos mismos )
- 9. 1: Proc Natl Acad Sci U S A. 2002 Sep 17;99(19):12252-6. Epub 2002 Aug 27. Related Articles , Links Evidence for van der Waals adhesion in gecko setae. Autumn K , Sitti M , Liang YA , Peattie AM , Hansen WR , Sponberg S , Kenny TW , Fearing R , Israelachvili JN , Full RJ . Department of Biology, Lewis & Clark College, Portland, OR 97219, USA. autumn@lclarke.edu Geckos have evolved one of the most versatile and effective adhesives known. The mechanism of dry adhesion in the millions of setae on the toes of geckos has been the focus of scientific study for over a century. We provide the first direct experimental evidence for dry adhesion of gecko setae by van der Waals forces, and reject the use of mechanisms relying on high surface polarity, including capillary adhesion. The toes of live Tokay geckos were highly hydrophobic, and adhered equally well to strongly hydrophobic and strongly hydrophilic, polarizable surfaces. Adhesion of a single isolated gecko seta was equally effective on the hydrophobic and hydrophilic surfaces of a microelectro-mechanical systems force sensor. A van der Waals mechanism implies that the remarkable adhesive properties of gecko setae are merely a result of the size and shape of the tips, and are not strongly affected by surface chemistry. Theory predicts greater adhesive forces simply from subdividing setae to increase surface density, and suggests a possible design principle underlying the repeated, convergent evolution of dry adhesive microstructures in gecko, anoles, skinks, and insects. Estimates using a standard adhesion model and our measured forces come remarkably close to predicting the tip size of Tokay gecko seta. We verified the dependence on size and not surface type by using physical models of setal tips nanofabricated from two different materials. Both artificial setal tips stuck as predicted and provide a path to manufacturing the first dry, adhesive microstructures.
- 23. Synthetic gecko tape, developed by scientists at the University of Manchester in England, may have the ability to adhere a human from a horizontal plane. A small section of the tape was used on the action figure depicted at top. The secret to the tape (shown under electron micrograph, bottom) is that it emulates the hairs on the feet of a gecko.
- 26. As far as lizards go, geckos are pretty amazing. Terrifically successful -- there are 850 different gecko species -- the gecko body is also quite energy-efficient. One species, the Frog Eyed Gecko from the Gobi desert, can move more than three times as far per unit energy than other creatures of similar size. But what makes geckos truly amazing is their uncanny ability to stick to pretty much any surface. Gecko feet adhesion " leaves no residue, is directional, detaches without measurable forces, is self-cleaning, and works underwater, in a vacuum, and on nearly every surface material and profile ." In 2002 , biologist Kellar Autumn at Lewis & Clark University in Oregon discovered that the adhesion came from van der Waals Forces, minute molecular-scale attraction, (spider feet work in a similar, albeit simpler, manner ). Each gecko foot is covered with millions of tiny hairs, or setae , which branch in to nanoscale tips, or spatulae ; each seta is strong enough to lift 20mg. The combined adhesive power of a gecko's four feet is over 90 lbs.
- 27. Geckos climb vertical and even inverted surfaces with ease using millions of micron-scale adhesive foot-hairs on each toe. Each foot-hair splits into hundreds of tips only 200 nanometers in diameter, permitting intimate contact with rough and smooth surfaces alike. Geckos' adhesive microstructure requires minimal attachment force, leaves no residue, is directional, detaches without measurable forces, is self-cleaning, and works underwater, in a vacuum, and on nearly every surface material and profile. We took a single gecko foot hair (seta) and made the first direct measurement of its adhesive function. These tiny setae are only as long as 2 diameters of a human hair. That’s 100 millionths of a meter long. Each seta ends in up to 1000 even tinier tips. The tips are only 200 billionths of a meter wide –below the wavelength of visible light. We used a microscopic force sensor designed by Tom Kenny at Stanford to measure the tiny forces of adhesion of the gecko seta.
- 28. We discovered that the seta is 10 times more adhesive than predicted from prior measurement on whole animals. The adhesive is so strong that a single seta can lift the weight of an ant 200 µN = 20 mg. A million setae could lift the weight of a child (20kg, 45lbs). A million setae could easily fit onto the area of a Dime. The combined attraction of a billion spatulae is a thousand times more than a gecko needs to hang from the ceiling. Maximum potential force of 2,000,000 setae on 4 feet of a gecko = 2,000,000 x 200 micronewton = 400 newton = 40788 grams force, or about 90 lbs! This is 600 times greater sticking power than friction alone can account for. Weight of a Tokay gecko is approx. 50 to 150 grams. These exciting results were published in the journal Nature v. 405: 681-685 .
- 29. Our discovery explains how it is that any gecko can hold up its entire body weight with only a single finger. If the adhesive is so strong, how do they get their feet off? We also discovered how to make the seta detach.We found that if we increased the angle the seta makes to the surface, it just pops off! We think the tip peels off like tape. What is the molecular mechanism that makes gecko setae so sticky? Your hair (hopefully) isn't sticky, so what makes geckos' foot-hairs adhesive? Recently, we provided direct support for the van der Waals hypothesis of gecko adhesion, and rejected surface polarity as a predictor of adhesion force, as suggested previously. These results inspired the fabrication of synthetic foot-hair tips that adhere, and was the cover story in the Proceedings of the National Academy of Sciences, USA 99(19): 12252-12256 . http://www.pnas.org/content/vol99/issue19/cover.shtml