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.
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.
Chains of nanogold – forged with atomic precision
23.09.2016 | Suomen Akatemia (Academy of Finland)
Self-assembled nanostructures hit their target
23.09.2016 | King Abdullah University of Science and Technology
The Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP has been developing various applications for OLED microdisplays based on organic semiconductors. By integrating the capabilities of an image sensor directly into the microdisplay, eye movements can be recorded by the smart glasses and utilized for guidance and control functions, as one example. The new design will be debuted at Augmented World Expo Europe (AWE) in Berlin at Booth B25, October 18th – 19th.
“Augmented-reality” and “wearables” have become terms we encounter almost daily. Both can make daily life a little simpler and provide valuable assistance for...
With the help of artificial intelligence, chemists from the University of Basel in Switzerland have computed the characteristics of about two million crystals made up of four chemical elements. The researchers were able to identify 90 previously unknown thermodynamically stable crystals that can be regarded as new materials. They report on their findings in the scientific journal Physical Review Letters.
Elpasolite is a glassy, transparent, shiny and soft mineral with a cubic crystal structure. First discovered in El Paso County (Colorado, USA), it can also be...
For the first time, Fraunhofer IKTS shows additively manufactured hardmetal tools at WorldPM 2016 in Hamburg. Mechanical, chemical as well as a high heat resistance and extreme hardness are required from tools that are used in mechanical and automotive engineering or in plastics and building materials industry. Researchers at the Fraunhofer Institute for Ceramic Technologies and Systems IKTS in Dresden managed the production of complex hardmetal tools via 3D printing in a quality that are in no way inferior to conventionally produced high-performance tools.
Fraunhofer IKTS counts decades of proven expertise in the development of hardmetals. To date, reliable cutting, drilling, pressing and stamping tools made of...
At AKL’16, the International Laser Technology Congress held in May this year, interest in the topic of process control was greater than expected. Appropriately, the event was also used to launch the Industry Working Group for Process Control in Laser Material Processing. The group provides a forum for representatives from industry and research to initiate pre-competitive projects and discuss issues such as standards, potential cost savings and feasibility.
In the age of industry 4.0, laser technology is firmly established within manufacturing. A wide variety of laser techniques – from USP ablation and additive...
Every three years, the plastics industry gathers at K, the international trade fair for plastics and rubber in Düsseldorf. The Fraunhofer Institute for Laser Technology ILT will also be attending again and presenting many innovative technologies, such as for joining plastics and metals using ultrashort pulse lasers. From October 19 to 26, you can find the Fraunhofer ILT at the joint Fraunhofer booth SC01 in Hall 7.
K is the world’s largest trade fair for the plastics and rubber industry. As in previous years, the organizers are expecting 3,000 exhibitors and more than...
23.09.2016 | Event News
20.09.2016 | Event News
16.09.2016 | Event News
23.09.2016 | Life Sciences
23.09.2016 | Health and Medicine
23.09.2016 | Life Sciences