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?”
http://ngm.nationalgeographic.com/2008/04/biomimetics/tom-mueller-text.html
