Date: Sep 28, 2012 Author: John Mangels Source: cleveland.com (
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John Mangels, The Plain Dealer By John Mangels, The Plain Dealer
on September 28, 2012 at 8:00 PM, updated September 29, 2012 at 1:16 PM
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Gecko on glass.JPGView full sizeGus Chan, The Plain DealerGeckos' unique dry-adhesive toe pads allow them to cling, walk and even sleep upside-down on glass and other slippery surfaces.
Gecko on glass.JPGView full sizeGus Chan, The Plain DealerGeckos' unique dry-adhesive toe pads allow them to cling, walk and even sleep upside-down on glass and other slippery surfaces.
But water could be geckos' kryptonite. Sure, staying put on a dry glass pane is impressive. How about when the surface is damp, or the gecko's feet are soaking wet?
That's what Stark and her UA colleagues are out to test. Their project is part of an emerging, revolutionary field called biomimicry, or bio-inspiration, in which scientists mine nature for tools and techniques to solve human problems.
Drawing on its deep experience manipulating polymers -- the natural and manmade molecules that make up much of what we encounter in everyday life -- UA is becoming a hub of bio-inspiration research. Its scientists are working on harnessing the strength of spider silk, deciphering the iridescent sheen of bird feathers and understanding the ingenious self-assembly of bones and sea shells.
Earlier this month, the university's provost and vice president for research committed to spend $4 million during the next two-plus years on biomimicry research and innovation. The money will be used to establish a biomimicry research center, hire additional faculty and staff, and attract more biomimicry research funding.
UA also has partnered with the Great Lakes Biomimicry Collaborative, a new organization that plans to promote bio-inspired design as an economic development tool for the region.
And the university has launched an "integrated bioscience" doctorate program to cross-train scientists in biology and disciplines such as materials science, physics, computers and engineering. The blend gives Stark and other students the tools and mind-set to tackle complex research that bridges the divide between living and artificial systems, like adapting geckos' natural stickiness for commercial uses.
If scientists can overcome some major technological challenges to making gecko-like surfaces -- and they're getting closer -- the payoffs could be huge: surgical and industrial adhesives that work when wet; wall-climbing robots for surveillance and rescue work; fumble-proof sports gloves; and sticky patches for micro-electronics that eliminate solder while helping an iPad or smartphone run cooler.
A UA spinoff company founded by Polymer Science Department Chairman Ali Dhinojwala is gearing up to make specialized "gecko tape," and the university hopes to spawn other businesses and seed existing ones with its bio-inspired graduates.
"Our goal is to have students create or be involved in new startups in the area," said UA biologist Peter Niewiarowski, who will lead the new biomimicry initiative and collaborates with Dhinojwala on gecko research. "That's the holy grail."
With Gordon hitched up to a small motor and perched on a moistened pane of glass, a sort of lizard tractor pull begins.
As the motor tugs his harness, the gecko's feet stay firmly planted, but the rest of his body stretches. His mottled olive and orange chest heaves a bit under the strain. A digital sensor ticks off the rising force it takes to stay put. Finally, the adhesion bonding Gordon's toes to the glass gives way, and he slides backward.
Sticking to it
Geckos' amazing stickiness has fascinated people for centuries. In 350 B.C., Aristotle praised their acrobatic climbing. A 17th century Hindu legend holds that a warrior named Tanaji roped himself to a lizard to scale a steep cliff wall and attack an enemy's fort.
Though it's unlikely a gecko could hoist a man (the Hindu legend involved a larger monitor lizard), lab tests by University of Massachusetts biologist Duncan Irschick show that a gecko can hold as much as 250 percent of its body weight, or about 4.5 pounds, while clinging on a smooth vertical surface. That's like the Cavaliers' Kyrie Irving being able to stick to the backboard glass with Anderson Varejao and Daniel Gibson hanging on his back.
How geckos achieve that phenomenal adhesion has been the target of research for more than a century. Scientists gradually narrowed the list of potential gecko adhesive suspects. They ruled out methods found elsewhere in nature: static electricity that makes socks cling in the dryer; suction cups like those on tree frogs' feet; interlocking mechanisms such as cockleburr nettles, which inspired the invention of Velcro; and the gluey mucus secretions that stick garden slugs to leaves, and barnacles to ship' hulls.
The answer surfaced only a decade ago, and there are still unresolved questions about certain details of the process. Gathering clues has required the world's most powerful microscopes, which let researchers peer into the nanometer realm, seeing structures as small as a single atom.
When those microscopes were trained on a gecko's foot, they revealed a stunningly complex landscape.
Each of the lizard's five toe pads has a series of what appear to the naked eye as solid, raised ridges, like the treads on a sneaker. Closer inspection shows the ridges really are forests of tiny, densely packed hairs, called setae. Each hair is no more than four-thousandths of an inch long and is made of beta-keratin protein, the same stiff stuff as in birds' beaks, porcupine quills, turtle shells and human fingernails. A single gecko toe pad has more than a quarter-million of the hairs.
At extreme magnification, each setae branches like a broccoli stalk into hundreds of even finer filaments called spatulae. The spatulae fibers are slightly curved, and they end in flat, triangular nubs 100 times smaller than a dust mite.
In 2002, biologist Kellar Autumn of Oregon's Lewis & Clark College and a student, Anne Peattie, finally pegged the source of geckos' cling -- a wispy, barely there force called van der Waals attraction. It's a temporary bond between individual molecules in the gecko's toe and those in the surface the toe touches. The attraction occurs only when the molecules are extremely close to one another, no more than a couple of nanometers apart. That's about one-45,000th of the thickness of a piece of paper.
In theory, pressing your palm against a window pane ought to activate van der Waals attraction and let you clamber up the glass. But at the nanometer level, the skin on your palm and the even the glass's seemingly smooth surface are as jagged and rough as the Himalayas. Precious little of the two surfaces actually comes into close contact, so there's minuscule van der Waals attraction.
But as Autumn and his colleagues found, evolution has provided geckos and a few other types of lizards with a unique solution, one that enabled them to climb out of reptiles' typical ground-dwelling realm and exploit new habitats.
The hundreds of millions of tips on the flexible toe hairs fit in almost every nook and cranny of whatever the gecko steps on. The sheer number of stalks and their ability to match the varying surface contour vastly multiply the van der Waals effect. The gecko easily sticks.
Autumn calculated that if all the hair tips attached simultaneously, a typical gecko could withstand 293 pounds of pulling force. Some hairs are unmoored, but enough are in contact at any one time to make the gecko an extraordinary climber, able to ascend as fast as 2 miles an hour.
The gecko adhesion system is not only highly effective, it's also smart. The hair stalks are slightly curved, giving geckos the ability to turn their stickiness on and off. The curvature keeps the tips at enough of an angle that they don't automatically trigger the van der Waals effect. The hairs' default position is "unsticky."
To activate the adhesion, the gecko plants and slightly drags its foot. That straightens the hair stalks and kicks in the van der Waals force. To unstick, the gecko curls its toes upward, restoring the natural hair curvature and breaking the adhesion. Geckos can do this in the blink of an eye, casually sticking and unsticking their feet while at a dead run.
The chemical composition of the hairs prevents them from sticking to each other and losing effectiveness. The hairs also shed dirt and, to an extent, water droplets. That gives geckos a naturally self-cleaning, reusable, water-resistant, user-controlled adhesive that makes tape and glue manufacturers drool.
Micro-hair moment
In 2002, UA's Dhinojwala attended an adhesion conference in New Hampshire and listened to Autumn describe what he'd learned about how geckos stick.
Dhinojwala is a polymer guy, not a biologist. His specialty is understanding how synthetic polymer surfaces behave, particularly when they're exposed to extreme temperatures, water and friction. But what Autumn was describing about the behavior of a natural surface -- the millions of micro-hairs on a gecko's toes -- got his attention.
"Several of us . . . had our own ideas about how to mimic the structure that was found in geckos," Dhinojwala said. "When I came back from the meeting, that's where the inspiration started. Polymers [were] a great choice."
UA's experience with polymers stretches back to the early 1900s and the university's close ties with the tire industry. Tire makers Goodyear, Firestone and Goodrich were headquartered in Akron, the "Rubber City," serving the burgeoning auto business.
Rubber is a natural polymer, but without additives, it's brittle and doesn't perform well in heat or cold. UA offered courses in rubber chemistry beginning in 1909 and started its Rubber Technical Institute in 1942 to help develop synthetic rubber. Since then, the university's polymer focus has expanded far beyond the tire industry, into areas such as electronics, protective coatings and bio-materials. Its College of Polymer Science and Polymer Engineering, established in 1988, is internationally respected.
Early efforts to make synthetic gecko hairs used tiny, painstakingly fabricated plastic strands that were cast in ultra-small molds. In 2003, a team led by physicist Andre Geim of Britain's University of Manchester was able to produce a fingernail-size fragment of gecko tape using the method.
Its sticking power was close to that of the lizard's, and the scientists got lots of news coverage by illustrating their research paper with a Spider-Man toy stuck to a glass pane with their gecko tape. They thought about covering a volunteer's hands with the stuff and having him dangle from one of the lab's windows.
But making that much gecko tape would have taken a long time and cost thousands of dollars, Geim told a BBC Online interviewer. The stunt might also have been risky. Geim, who went on to win the 2010 Nobel Prize in physics for other polymer work, reported that many of the plastic hairs on his fledgling gecko tape wilted or broke after just a few uses, ruining its adhesion.
Geim recommended experimenting with fibers that were more flexible and durable. At UA, Dhinojwala turned to a special kind of polymer called carbon nanotubes.
As the name implies, carbon nanotubes are minuscule hollow cylinders. Their walls are made of one-atom-thick sheets of carbon, the constituent of coal, diamonds and pencil lead. Using heat and some additives, researchers can grow carbon nanotubes like hairs -- an easier process than molding plastic nanofibers.
By 2007, working with scientists at New York's Rensselaer Polytechnic Institute, Dhinojwala's team had grown carbon nanotube hairs even thinner than those on a gecko's toes. By tightly bunching the hairs, the researchers were able to create a piece of gecko tape that was 10 times stickier than Geim's plastic-strand tape and four times stickier than a gecko's natural toe-hairs.
A patch of the stuff a little larger than a cell phone button could support nearly 9 pounds of weight. It could stick to glass, mica, even Teflon. Like a gecko's hairs, it didn't take much effort to unstick the carbon nanotubes. And they didn't break, meaning the adhesive effect didn't wear off.
As an important bonus, the carbon-based nanohairs conduct heat. In addition to being sticky, the adhesive patch acts like a little radiator.
"Heat management is one of the biggest challenges for the electronics industry," Dhinojwala said. "The light-emitting diode industry is really suffering right now because the life of the LED is controlled by the heat. You overheat and it goes away. The processors right now in an iPad are getting hot. They have to figure out how to cool it off. That's what we think will be our biggest shot."
Gecko-inspired tapes can't be made as inexpensively as traditional adhesives, but the ability to shed heat could provide a niche in the competitive market. ADAP Nanotech LLC, the Akron-based start-up company Dhinojwala founded in 2009 with one of his former graduate students, Sunny Sethi, got $250,000 in funding this year from Cleveland technology accelerator JumpStart Inc. It plans to begin commercial sales in 2013.
Natural collaboration
For manmade gecko adhesives to be successful, they have to work as well as -- or even better than -- their natural counterparts. That means functioning in real-world conditions, in dirt, water and weather extremes, just as geckos do. Creating the ideal adhesive requires an understanding not just of polymers, but also of geckos.
While polymer expert Ali Dhinojwala was working on synthetic gecko hair, a lizard expert was working just a block away on the UA campus to decipher reptiles' behavior and physiology.
Biologist Peter Niewiarowski -- whose first research paper back in 1989 had been about gecko metabolism -- had just been tapped to run the university's new integrated bioscience program, which blends traditional biology training with other science and engineering fields. It seemed natural for Niewiarowski and Dhinojwala to team up, not just because their gecko interests dovetailed but because it exemplified what the new interdisciplinary doctorate program was about.
Normally, "the way these [collaborations] come together is kind of haphazard," Niewiarowski said. "With the integrated bioscience program, we're trying to create more opportunities to bring people together."
The initial collaboration of the two professors and their students quickly paid off, with research findings in 2008 that shed new light on how temperature and humidity affect geckos' ability to stick. (The results are complicated, but basically, humidity boosts geckos' adhesion at lower but not higher temperatures.)
Alyssa Stark had enrolled in the integrated bioscience program just after that study was published. The Californian, whose undergraduate degree is in animal biology, wanted to use polymer science to expand her understanding of how natural systems work. "I'm in the polymer science capital of the world," she said. "I liked the idea of being a bit of a guinea pig."
Stark continued the UA gecko team's research on water effects and played a role in a surprising discovery that showed the value of its integrated approach.
While working in a darkened lab, cleaning the glass sheets that geckos walk on during adhesion experiments, Stark noticed some faint residue on the panes. "I usually just washed it off," she said. "The polymer students were like, 'What is that? It looks like a footprint.' "
The researchers hadn't expected geckos to leave any footprints on a surface like glass, since their toe pads stay so clean. Working together, the biologists, polymer scientists and chemists did some fancy analysis that revealed the residue was a thin layer of lipids, the stuff nature uses for protective membranes, among other things.
The UA researchers aren't sure why geckos would leave a ghostly trail of lipid footprints, but it adds a wrinkle to the adhesion story. Dhinojwala suspects wear and damage protection may be involved -- something the university knows a lot about from its tire research.
"If you make something really sticky and you try to peel it off, you tend to create damage," he said. In a gecko, "maybe there is a mechanism where you put a little sacrificial layer -- it could be lipid or a combination of lipid and something we have not yet figured out -- which allows [the gecko's hairs] to have adhesion but not catastrophic breaking. That's one of the very simple mechanisms we use in designing tires. A tire essentially leaves a carbon layer behind every time you roll."
While such discoveries eventually may lead to more-durable gecko tape, or other yet-unimagined products, the UA researchers say there's a greater purpose: producing young scientists like Alyssa Stark who can change the way universities and companies conceive new ideas.
"If we do biomimicry and it's just making gecko tape and spider threads and that is the only meaning, I think we're losing focus," Dhinojwala said. "If students have been exposed to that milieu of innovation and interactive teams . . . that's our product, not just making a tape. They'll teach and inspire more innovation."
