Jenny Jun Yue Zhang
WRIT340
Illumin Paper
From biology to technology: biomimicry in modern engineering
Abstract
Biomimicry is the emulation of natural systems in order to solve engineering problems with
similar applications. The modern realm of biomimicry has reached well past exterior mechanical
emulations such as the plane and the submarine. Our insight into the macroscopic and microscopic
world, coupled with the energy constraints of our generation, has pushed biomimetic engineering
towards optimizing existing technologies through natural mechanisms. This article will present a
sampling of recent biomimetic engineering developments that have made our current technology
more efficient.
Introduction
David Letterman has tried this on TV: wear a suit made of industrial strength Velcro and
leap onto an inflatable Velcro wall—and try to stick. Despite its unassuming appearance, a twoinch square of Velcro can hold a 175lb person on a wall.
The invention of Velcro is one of the most well known applications of biomimicry in
engineering. The hook-and-loop fastener is the brainchild of Swiss engineer George de Mestral,
who uncovered the concept when pondering the tenacity with which burrs clung to his dog’s
hair. [2] Like the little seedpod hitchhikers, Velcro consists of one part tiny stiff plastic hooks
that will catch anything with a loop, and another part loosely woven nylon fiber that acts much
like the hair of Mestral’s dog. It took Mestral eight years to commercialize Velcro fasteners
despite its simple concept—the effective transformation of a biological mechanism into mass
synthesized product is not an easy task. [2]
http://24.media.tumblr.com/tumblr_lw3yvnSaBg1qk01v6o3_500.jpg
Figure 1. The hook and loop mechanism of Velcro fasteners
Biomimetic engineering didn’t start to gain traction as an official academic discipline
until early 1990s. Today, it is a highly interdisciplinary field that involves people anywhere
from computer scientists, physicists, chemists, and philosophers working alongside biologists
and engineers. [1] However, it’s an easy misconception that biomimetic engineering attempts to
merely replicate the biological system in synthetic ways. As MIT chemical engineers stated:
“You don’t have to reproduce a lizard skin to make a water collection device, or a moth eye to
make an anti-reflective coating. The natural structure provides a clue to what is useful in a
mechanism, but maybe you can do it better.” [2] To engineers, nature is merely the starting
point of technology. As we gain insight into the macroscopic and microscopic world, biomimetic
technology may emulate a chemical process, or even just a concept of a mechanism, and will not
necessarily appear like their biological inspiration.
It is the common belief that nature has found “the path of least resistance” to every
function through billion years of evolution. Today, biomimetic research is re-evaluating many of
our existing technology through the lenses of nature in order to improve their efficiency. The
following three examples—the new digital screen inspired by butterfly wings, the self cleaning
coating inspired by lotus leaves, and the aerodynamic car inspired by the boxfish—are all
recent biomimetic engineering projects that utilize a natural mechanism to produce a more
sustainable alternative to an existing technology.
Structural Colors in Butterfly Wings: A New Generation of Display Technology
http://www.extremetech.com/wp-content/uploads/2012/01/mirasol-640x353.jpg
Figure 2. A preliminary tablet model using the Mirasol technology.
In today’s competitive market for display technology, every company is vying for a
balance between energy use, visibility, and color quality in both still and moving images. Liquid
crystal displays (LCD) achieve vibrant color at the cost of energy consumption, while colored eink is still waiting on its faster and full color advancement. Meanwhile, there is another
blossoming technology that utilizes a concept radically different from all existing giants in the
field, and its inspiration came from a small butterfly.
The inspiration
Observe the wings of a morphos butterfly: its color holds a subtle iridescence and
changes hues when viewed at different angles. The coloring of their wings is not from pigments,
but rather a result of the bending of light through the complicated cell structures in the
butterfly’s wing tissues. The tissues are comprised of layers upon layers of transparent fiber
and air cuticles. Instead of absorbing and reflecting only a certain light wavelength as pigments
and dyes do, these cuticles can both cancel out and reflect selective wavelengths to achieve a
full range of colors. This kind of dynamic coloring is called structural color. [3] [4]
http://www.asknature.org/images/uploads/strategy/1d00d97a206855365c038d57832ebafa/morpho_feature.jpg
Figure 2. layered cuticles that produce structural coloring on the wings of a morphos butterfly
The technology
The new Mirasol technology sought to emulate the butterfly wing’s ability to
dynamically control wavelength interactions. The wing cuticles are mimicked by micro-scale
plates with a tiny separation between them. Both plates are conductive; the top is a thin film on
a transparent glass substrate, while the bottom is a reflective membrane (figure 3). Current
passing through the plates can control the gap between plates through electrostatic repulsion,
and thus control the absorption of red, yellow, and blue light. When no current is passing
through a plate, its default state is closed, which absorbs no light and corresponds to a black
display. [5]
http://www.mirasoldisplays.com/how-it-works
Figure 3. The assembly of micro-scale plates used in Mirasol displays
To assemble complex colors, a large array of these plates is fabricated in layers not
unlike the butterfly’s tissues. Strips of these plates will form the pixels on the display screen.
The unique color corresponding to the gap in each plate is overlaid to achieve complex colors
(figure 4). The plate separation can be adjusted a thousand times a second, creating color that’s
faster than e-ink but at a lower energy cost than LCD. What’s better, the Mirasol screen absorbs
sunlight, so it’s both antiglare and energy saving. [5]
http://www.mirasoldisplays.com/how-it-works
Figure 4. The Mirasol display combines trips of micro-sized plates to display complex color.
The future
The preliminary models of the Mirasol screen have already been adopted by some cell
phone companies and e-readers in Asia. As the technology matures, engineers are working to
improve the coordination between digital signals and final display in order to achieve fast and
smooth video performance. [4] The Mirasol screen heralds the new generation of structural
display technology. The full color energy-sipping tablet may soon become reality.
The Lotus Effect: nanotechnology in self-cleaning and easy-cleaning materials
Outside the field of display technology, another well-known example of biomimicry is in
materials engineering. For this field, the search for a durable, self-cleaning, and repellent
coating has endless incentives; from paint, to architectural and machine exteriors, to camping
and other recreational products, self-cleaning surfaces can reduce the labor cost and extend a
material’s life cycle. For this magic surface, the inspiration is even more humble than the
butterfly—it is the lotus.
The inspiration
In many eastern cultures, the lotus is a symbol of purity. As it turns out, this reputation
is well deserved. The lotus leaves have a super-hydrophobic effect: water does not wet it, but
instead rolls off the leaves, carrying dirt and soot with it. This famous self-cleaning effect was
discovered by botanist Wilhelm Barthlott in 1973, and later patented as the “Lotus Effect.” [6]
http://www.biomimicryinstitute.org/images/stories/lotus_detail2.jpg
Figure 5. Water droplets sitting on the tips of nano-scale wax crystals on the lotus leaf.
The secret to super-hydrophobicity lies in a nano-textured surface. A combination of
tiny, nipple-like wax crystals around one nanometer in diameter is systematically arranged
throughout the lotus leaf surface (it will take thousands of these wax crystals just to cover the
diameter of a strand of human hair). In fact, the water droplet is only in contact with about 23% of the area covered by the droplet. [6] The interplay of surface tension and low contact area
causes the water to ball up and sit on the tip of the wax crystals (figure 5). This nano-scale
roughness is essential to self-cleaning; on a smoother surface, water will simply slide rather
than roll, thus drastically reducing its ability to pick up surface impurities. [6]
The technology
When the lotus effect was first discovered in 1973, nanotechnology was not yet
advanced enough to enable engineers to utilize the concept. But now, with the advancement of
nanotechnology and the Sol-Gel method, engineers can produce controlled growth and
aggregation of nano-crystals.
The Sol-Gel method involves a unique fluid solution that will slowly change from liquid
to gel, and finally be eliminated from the crystal structure through chemical drying. Initially, the
individual crystal particles are suspended in the liquid, and as the fluid morphology changes to
gel, crystals form through slow linking of the suspended particles. Dipping compatible materials
into the Sol-Gel solution can therefore produce a thin film coating with nano-sized pores and
protrusions. [6]
Today, engineers use this technology in repellent paint for industrial housing, which
uses silicon nanoparticles suspended in resin to form a super-hydrophobic surface. Other
engineers are utilizing composite materials such as polypropylene (a kind of plastic found in
textiles and banknotes) to create matrixes of nanoparticles and deposit them on fabric surfaces.
[7]
GreenShield is one such recent coating technology that combines nanoparticles of
composites and fluorocarbons in order to create super-hydrophobic fabrics. These fabrics are
extremely stain and water resistant (figure 6), and heralds a new market for parasols, sails,
tents, and even housing materials. [7] Combining particles on a nano-scale enable engineers
http://www.asknature.org/images/uploads/strategy/714e970954253ace485abf1cee376ad8/greenshield_feature.jpg
Figure 6. GreenShield coats textile fibers with liquid repelling nanoparticle, reducing the need to use
environmentally dangerous fluorocarbons. Here red wine, water, and soy sauce is shown rolling on
GreenShield fabric.
to reduce fluorocarbon usage by 90%. [7] Fluoro-chemicals, though a necessary component in
most repellent coatings, is a chronic toxin that bio-accumulates in the body and persists in the
environment. Therefore the technology of nano-scale surfaces is making the repellent coating
industry much more environmental friendly.
The future
For the future, the main challenge for super-hydrophobic surfaces is a balance between
cost, application, and longevity. Self-cleaning buildings would be a good payback, but selfcleaning tablecloths? Not so much. The deposition of lotus effect coatings can still be relatively
unstable on extremely smooth surfaces. [6] Engineers continue to seek out more suitable
nanoparticles that will withstand the caustic damages present in nature.
Aerodynamics of a boxfish: the engineering of the Mercedes-Benz bionic car
Returning to the realm of the visible, the natural grace of biological structures still
inspire some of our most effective transportation designs. In 2005, DaimlerChrysler presented
the preliminary model for the most aerodynamic car in its compact class—the bionic car. But
the sleekness of this car does not boast its design inspiration from agile animals such as the
dolphin or the shark, but instead from a funny looking little fish.
The inspiration
Although the boxfish has an angular appearance, it’s a surprisingly agile swimmer. With
a stiff outer coat comprised of hexagonal bone plates, the fish can withstand very high pressures
while at the same time navigate with minimal dorsal movement. [9]
http://images.gizmag.com/gallery_lrg/4133_80605113337.jpg
Figure 7. Aerodynamic study of the boxfish body in free flow. The new Mercedes bionic car has almost
exactly duplicated this aerodynamic structure.
In free flow, the body of the boxfish has a drag coefficient as low as 0.06. [9] The drag
coefficient measures the resistance of an object to the flow of air or fluid, and the coefficient of a
teardrop, which is widely recognized as the ideal streamlined form, is only 0.02 lower than that
of the boxfish. When engineers scoured nature for a model, the structure of the boxfish
immediately stood out as a combination of good space, energy efficiency and passenger safety.
The technology
Following the boxfish body almost contour by contour, the bionic car design boasts a
drag coefficient of 0.19 (even a smaller Honda Civic has a drag coefficient of 0.31). This places
the car about 65% more aerodynamic than average compact cars, and makes it one of the
world’s most aerodynamic car designs today. [9]
To minimize weight and maximize structural strength, engineers also model their
reinforcement system after the hexagonal skeletal structure of the boxfish. Using the Soft Kill
Option, which is a computer simulation that configures the body and suspension components of
the car, engineers can better identify areas of high stress. [8] This way, materials can be made
thinner in lower load areas, while highly stressed areas (such as the car door) are reinforced
with a honeycomb structure. The end product is a car with 40% increase in stiffness and a 30%
decrease in weight. [8]
http://www.carbodydesign.com/archive/2008/03/01-mercedes-benz-bionic-car-at-the-moma/
Figure 8. Soft Kill simulation reduced materials used in lower load areas while reinforcing highly
stressed areas.
The future
The bionic car may very well be the desired model for our future automobiles. The
combination of aerodynamic design, light weight, and fuel efficient engine gives the car a
dazzling fuel range of 70 miles per gallon, which ultimately makes the car 20% more
economical than other compact models today. [8]
Conclusion: A Brave New World?
The three examples given here are but a sampling of the endless applications of
biomimetic engineering. Today, biomimetic applications have expanded to realms of even
architecture and renewable energy. In Zimbabwe, midrise buildings are modeled after termite
mounds, which utilizes air draft alone to maintain an interior temperature around 31 degrees
Celsius despite fluctuations of outside temperature from 3 to 42 degrees. Also, windmill blades
are modeled after the aerodynamic shape of shake fins and coated with sharkskin inspired
paint to increase its wind energy utilization.
Gradually, biomimetic engineering is redefining the traditional “heat, beat, and treat”
procedure of manufacturing, in which raw materials are heated with enormous amounts of
energy, twisted into shape through heavy machinery, and finally strengthened through
chemical treatments. More and more, technology is becoming smaller scaled, more efficient, and
more environmentally friendly through the direct or indirect application of biomimicry.
However, the task to translate nature’s solution into technology will always remain a
challenge that requires innovative simplifications. As engineer Mark Cutkosky, the Co-Director
for the Center of Research Design at Stanford University, says, “The price that we pay for
complexity at small scales is vastly higher than the price nature pays…and nature is fabulously,
wantonly complex.” We may yet encounter many cases, such as the lotus effect, in which the
concept emerges before current technology can successfully transform it into a commercialized
product. But as technological advances turn more and more scientific concepts into reality, we
will witness a whole new dimension to our current technologies lead by biomimetic
engineering.
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