Science

Scientists get new insight into the mystery of how lizard feet stay sticky

in great shape , A close-up picture of the toe pad of the Tokay lizard. They have many tiny hairs per foot called setae, each of which splits into hundreds of tiny hairs called spatulas. These help to maximize contact with the surface.

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Geckos are known to be expert climbers, able to climb any surface thanks to the tiny hair-like structures on the bottom of their feet. Researchers at the National Institute of Standards and Technology (NIST), along with collaborators in Oregon, Denmark and Germany, took a closer look at those structures using the high-energy synchrotron, revealing that they are an ultra-thin layer of lipid molecules. are coated with. In an upright orientation, according to a recent paper published in the journal Biology Letters.

Those tiny microscopic hairs are called setae, each of which splits into hundreds of tiny hairs called spatulas. It has long been known that on the microscopic size scale, the so-called van der Waals forces – the attractive and repulsive forces between two dipole molecules – become important.

Essentially, the clumps of tiny hairs on the gecko’s legs move so close to the contours in the walls and ceilings that electrons from the molecules of the gecko hair and electrons from the molecules of the wall interact with each other and create an electromagnetic attraction. . This enables geckos to climb smooth surfaces such as glass with ease. Spiders, cockroaches, beetles, bats, tree frogs, and lizards all have differently shaped sticky footpads that use these same forces.

Geckos and their unusual legs have long been of great interest to scientists. For example, in 2013, scientists at the University of California, Santa Barbara, designed a reusable dry adhesive inspired by the gecko’s feet, which easily clings to smooth surfaces, adheres firmly when pushed forward and backward. When pulled towards, it slips. The secret to that directionality was the angle and shape of the half-cylinder fibers fabricated in the silicone-based adhesive. Pushing the flat side down creates a larger surface area for the glass to stick to. Pulling the fibers down from the circular side reduces the surface area that the adhesive can easily slip off.

In 2020, Berkeley scientists investigated why soft, hairy gecko toes tend to “stick” in only one direction. Pull one leg in one direction and the gecko’s toes will come to the surface. Release the foot and the toes will “peel off” in the opposite direction, although this does not prevent the agile lizard from walking in any way. Scientists found that the faster geckos climb uphill, the faster they can run sideways, thanks to their ability to realign their toes. Having multiple toes helps geckos adjust to clinging to slippery or irregular surfaces. Those toes that maintained contact with the surface were able to shift orientation and distribute the load better. And because toes are softer, animals can more easily conform to rough surfaces.

Despite what we have learned, little is known about the detailed surface chemistry of gecko toe pads, especially setae. So the authors of this latest paper set out to learn more, with particular interest in water’s potentially major role in surface adhesion. “Much was already known about how SETE works mechanically,” said NIST physicist and co-author Cherno Jay. “We now have a better understanding of how they work in terms of their molecular structure.”

According to the authors, recent studies have indicated the presence of water-repellent lipid molecules in gecko footprints and arrays of gecko setae (they can also be found in the epidermis of reptiles arranged in a brick-and-mortar pattern). . NIST’s synchrotron microscope is well suited for taking a closer look at molecular structure because it is able not only to identify molecules on the surface of three-dimensional objects, but also to reveal where they are located. And how are they oriented.

That thin film of lipid (just a nanometer thick) could act to push away any water under the spatula, the authors speculate, allowing the spatula to make close contact with the surface, allowing the gecko to linger on wet surfaces. Helps you maintain your grip. In addition, the settee and spatula are made of keratin protein, much like the proteins in human hair and nails. The analysis revealed that the alignment of the keratin fibers is in the direction of the setae, which may be how they resist friction.

Gecko Feet has inspired many intriguing applications in the past, including a sticky tape, the aforementioned adhesive, a “stickybot” climbing robot with synthetic settees, and even (I kid you not) a strapless bra. Design is included. go and others, Imagine “gecko boots” that can cling to wet surfaces, or “gecko gloves” to get a better grip on wet equipment as possible applications of their latest research.

“The most exciting thing to me about this biological system is that everything is completely optimized at every scale, from macro to micro to molecular,” said co-author Stanisaw Gorb, a biologist at the University of Kiel in Germany. “This could help biomimetic engineers know what to do next.”

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