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Published: April 2008

Biomimetics

Boxfish Hdr

Biomimetics: Design by Nature

What has fins like a whale, skin like a lizard, and eyes like a moth? The future of engineering.

By Tom Mueller
Photograph by Robert Clark

One cloudless midsummer day in February, Andrew Parker, an evolutionary biologist, knelt in the baking red sand of the Australian outback just south of Alice Springs and eased the right hind leg of a thorny devil into a dish of water. The maneuver was not as risky as it sounds: Though covered with sharp spines, the lizard stood only about an inch high at the shoulder, and it looked up at Parker apprehensively, like a baby dinosaur that had lost its mother. It seemed too cute for its harsh surroundings, home to an alarmingly high percentage of the world's most venomous snakes, including the inland taipan, which can kill a hundred people with an ounce of its venom, and the desert death adder, whose name pretty well says it all. Fierce too is the landscape itself, where the wind hissing through the mulga trees feels like a blow dryer on max, and the sun seems three times its size in temperate climes. Constant reminders that here, in the driest part of the world’s driest inhabited continent, you’d better have a good plan for where your next drink is coming from.

This the thorny devil knows, with an elegance and certainty that fascinated Parker beyond all thought of snakebite or sunstroke. “Look, look!” he exclaimed. “Its back is completely drenched!” Sure enough, after 30 seconds, water from the dish had wicked up the lizard’s leg and was glistening all over its prickly hide. In a few seconds more the water reached its mouth, and the lizard began to smack its jaws with evident satisfaction. It was, in essence, drinking through its foot. Given more time, the thorny devil can perform this same conjuring trick on a patch of damp sand—a vital competitive advantage in the desert. Parker had come here to discover precisely how it does this, not from purely biological interest, but with a concrete purpose in mind: to make a thorny-devil-inspired device that will help people collect lifesaving water in the desert.

A slender English academic with wavy, honey-blond hair beneath a wide-brimmed sun hat, Parker busied himself with eyedroppers, misters, and various colored powders, the better to understand the thorny devil’s water-collecting alchemy. Now and then he made soft, bell-like, English-academic sounds of surprise and delight. “The water’s spreading out incredibly fast!” he said, as drops from his eyedropper fell onto the lizard’s back and vanished, like magic. “Its skin is far more hydrophobic than I thought. There may well be hidden capillaries, channeling the water into the mouth.” After completing his last experiment, we gathered up his equipment and walked back to our Land Cruiser. The lizard watched us leave with a faint look of bereavement. “Seeing the devil in its natural environment was crucial to understanding the nature of its adaptations—the texture of the sand, the amount of shade, the quality of the light,” Parker said as we drove back to camp. “We’ve done the macro work. Now I’m ready to look at the microstructure of its skin.”

A research fellow at the Natural History Museum in London and at the University of Sydney, Parker is a leading proponent of biomimetics—applying designs from nature to solve problems in engineering, materials science, medicine, and other fields. He has investigated iridescence in butterflies and beetles and antireflective coatings in moth eyes—studies that have led to brighter screens for cellular phones and an anticounterfeiting technique so secret he can’t say which company is behind it. He is working with Procter & Gamble and Yves Saint Laurent to make cosmetics that mimic the natural sheen of diatoms, and with the British Ministry of Defense to emulate their water-repellent properties. He even draws inspiration from nature’s past: On the eye of a 45-million-year-old fly trapped in amber he saw in a museum in Warsaw, Poland, he noticed microscopic corrugations that reduced light reflection. They are now being built into solar panels.

Parker’s work is only a small part of an increasingly vigorous, global biomimetics movement. Engineers in Bath, England, and West Chester, Pennsylvania, are pondering the bumps on the leading edges of humpback whale flukes to learn how to make airplane wings for more agile flight. In Berlin, Germany, the fingerlike primary feathers of raptors are inspiring engineers to develop wings that change shape aloft to reduce drag and increase fuel efficiency. Architects in Zimbabwe are studying how termites regulate temperature, humidity, and airflow in their mounds in order to build more comfortable buildings, while Japanese medical researchers are reducing the pain of an injection by using hypodermic needles edged with tiny serrations, like those on a mosquito’s proboscis, minimizing nerve stimulation.

“Biomimetics brings in a whole different set of tools and ideas you wouldn’t otherwise have,” says materials scientist Michael Rubner of MIT, where biomimetics has entered the curriculum. “It’s now built into our group culture.”

Shortly after our trip to the Australian desert, I met up with Andrew Parker again, in London, to watch the next phase of his research into the thorny devil. Walking from the Natural History Museum’s entrance to his laboratory on the sixth floor, we traversed warehouse-size halls filled with preserved organisms of the most exuberant variety. In one room were waist-high alcohol jars of grimacing sea otters, pythons, spiny echidnas, and wallabies, and one 65-foot-long case containing a giant squid. Other rooms held displays of gaudy hummingbirds, over-the-top toucans and majestic bowerbirds, and shelf after shelf filled with beetles as bright as gemstones: emerald-green scarabs, sapphire-blue Cyphogastras, and opalescent weevils.

To Parker this was not a mere collection of specimens, but “a treasure-trove of brilliant design.” Every species, even those that have gone extinct, is a success story, optimized by millions of years of natural selection. Why not learn from what evolution has wrought? As we walked, Parker explained how the metallic sheen and dazzling colors of tropical birds and beetles derive not from pigments, but from optical features: neatly spaced microstructures that reflect specific wavelengths of light. Such structural color, fade-proof and more brilliant than pigment, is of great interest to people who manufacture paint, cosmetics, and those little holograms on credit cards. Toucan bills are a model of lightweight strength (they can crack nuts, yet are light enough not to seriously impede the bird’s flight), while hedgehog spines and porcupine quills are marvels of structural economy and resilience. Spider silk is five times stronger by weight and vastly more ductile than high-grade steel. Insects offer an embarrassment of design riches. Glowworms produce a cool light with almost zero energy loss (a normal incandescent bulb wastes 98 percent of its energy as heat), and bombardier beetles have a high-efficiency combustion chamber in their posterior that shoots boiling-hot chemicals at would-be predators. The Melanophila beetle, which lays its eggs in freshly burned wood, has evolved a structure that can detect the precise infrared radiation produced by a forest fire, allowing it to sense a blaze a hundred kilometers away. This talent is currently being explored by the United States Air Force.

“I could look through here and find 50 biomimetics projects in half an hour,” Parker said. “I try not to walk here in the evening, because I end up getting carried away and working until midnight.”

In one such late-night creative burst eight years ago, Parker decided to investigate the water-gathering skills of a desert beetle by building an enormous sand dune in his laboratory. This tenebrionid beetle flourishes in the Namib Desert in southwestern Africa, one of the world’s hottest, driest environments. The beetle drinks by harvesting morning fogs, facing into the wind and hoisting its behind, where hydrophilic bumps capture the fog and cause it to coalesce into larger droplets, which then roll down the waxy, hydrophobic troughs between the bumps, reaching the beetle’s mouth. Parker imported several dozen beetles from Namibia, which promptly scampered all over the lab when he opened the box, but eventually settled contentedly on the dune. There, using a hair dryer and various misters and spray bottles, Parker simulated the conditions in the Namib Desert well enough to understand the beetle’s mechanism. He then replicated it on a microscope slide, using tiny glass beads for the bumps and wax for the troughs.

For all nature’s sophistication, many of its clever devices are made from simple materials like keratin, calcium carbonate, and silica, which nature manipulates into structures of fantastic complexity, strength, and toughness. The abalone, for example, makes its shell out of calcium carbonate, the same stuff as soft chalk. Yet by coaxing this material into walls of staggered, nanoscale bricks through a subtle play of proteins, it creates an armor as tough as Kevlar—3,000 times harder than chalk. Understanding the microscale and nanoscale structures responsible for a living material’s exceptional properties is critical to re-creating it synthetically. So today Andrew Parker had arranged to view the skin of a thorny devil museum specimen under a scanning electron microscope, hoping to find the hidden structures that allow it to absorb and channel water so effectively.

With a microscopist at the helm, we soared over the surface of the thorny devil’s skin like a deep-space probe orbiting a distant planet, dipping down now and then at Parker’s request to explore some curious feature of the terrain. There seemed to be little of interest in the Matterhornlike macrostructure of an individual thorn, though Parker speculated that it might wick away heat from the lizard’s body or perhaps help capture the morning dew. Halfway down the thorn, however, he noticed a series of nodules set in rows, which seemed to grade down to a larger water-collection structure. Finally we dove into a crevasse at the base of the thorn and encountered a honeycomb-like field of indentations, each 25 microns across.

“Ah-ha!” Parker exclaimed, like Sherlock Holmes alighting upon a clue. “This is clearly a superhydrophobic surface for channeling water between the scales.” A subsequent examination of the thorny devil’s skin with an instrument called a micro-CT scanner confirmed his theory, revealing tiny capillaries between the scales evidently designed to guide water toward the lizard’s mouth. “I think we’ve pretty well cracked the thorny devil structure,” he said. “We’re ready to make a prototype.”

Enter the engineers. As the next phase in his quest to create a water-collection device inspired by the lizard, Parker sent his observations and experimental results to Michael Rubner and his MIT colleague Robert Cohen, a chemical engineer with whom he has worked on several biomimetics projects in the past. Rubner and Cohen are neatly groomed gentlemen who speak in clipped phrases and look frequently at their watches. While Parker likes to explain his work via a stroll through a botanic garden or by pulling out drawerfuls of bright beetles in a museum, they are more likely to draw a tidy graph of force over time, or flip through a PowerPoint presentation on their laptop. But a pooling of biological insight and engineering pragmatism is vital to success in biomimetics, and in the case of Parker, Cohen, and Rubner, it has led to several promising applications inspired by the Namib beetle and other insects. Using a robotic arm that, in a predetermined sequence, dips slides into a series of nanoparticle suspensions and other exotic ingredients, they have assembled materials layer by layer that have the same special properties as the organisms. Soon they hope to apply the method to create a synthetic surface inspired by thorny devil skin.

Though impressed by biological structures, Cohen and Rubner consider nature merely a starting point for innovation. “You don’t have to reproduce a lizard skin to make a water collection device, or a moth eye to make an antireflective coating,” Cohen says. “The natural structure provides a clue to what is useful in a mechanism. But maybe you can do it better.” Lessons from the thorny devil may enhance the water-collection technology they have developed based on the microstructure of the Namib beetle, which they’re working to make into water-harvesting materials, graffiti-proof paints, and self-decontaminating surfaces for kitchens and hospitals. Or the work may take them in entirely new directions. Ultimately they consider a biomimetics project a success only if it has the potential to make a useful tool for people. “Looking at pretty structures in nature is not sufficient,” says Cohen. “What I want to know is, Can we actually transform these structures into an embodiment with true utility in the real world?”

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