Borrowing from nature's best ideas

[Al-khiyal]

July 31, 2007 -- Forty-five million years ago an unfortunate fly got stuck in some tree sap and met a sticky end. Today the same fly is responsible for increasing energy efficiency in solar cells. By studying the fly's eye, scientists have developed a new kind of light-capturing material.

Meanwhile, over in Namibia, an unwitting desert beetle is helping farmers to irrigate their fields and airports to clear their runways of fog. When a fog rolls in across the Namib desert the beetle does a handstand and collects fog droplets on its specially adapted shell. The droplets dribble down into the beetle's mouth, providing it with a well-earned drink. By studying the structure of the beetle's shell scientists have developed a synthetic material that is also capable of mopping up fog.

A tenebrionid beetle, a water collector beetle.
Scientists studying these beetles have developed a material
to collect water for desert irrigation systems
and to help clear airport runways of fog

These discoveries are just a couple of examples from a burgeoning scientific field known as biomimetics – copying good designs from nature. Increasingly scientists and engineers are realising that nature, with the benefit of millions of years of evolution, holds the key to some of the very best ideas.

And not only does nature have the best ideas, she wastes nothing and uses minimal energy. Unlike human factories, nature doesn't usually require high temperatures or pressures to make most of her products; she has found ways of making the most of what is available.

So what are the most promising biomimetic designs? What about the future, where viruses and bacteria are put to work on the production line, creating anything from shimmering lipstick to specialised glass. Can we harness the power of nature?

Geckel


A gecko clinging to mussel shell.
Geckos and mussels are being used to make an underwater adhesive.
Geckel adhesive combines the wet adhesive properties of mussel adhesive proteins
with the dry adhesive strategy of the gecko

Sometimes the best designs come from more than one creature. A recent paper in Nature reveals how scientists have taken inspiration from the acrobatic powers of geckos and the suction power of mussels to create a new kind of underwater super-glue – 'geckel'.

Geckos are brilliant at scurrying up walls and across ceilings and their hairy feet have inspired a number of new, super-sticky adhesives. However, one major problem with gecko-based glues is that they fail on wet surfaces.

Phillip Messersmith, from Northwestern University in the United States, and his colleagues were studying what enables mussels to cling onto rocks when inspiration struck. "It hit me that maybe we could apply what we know about mussels to make gecko adhesion work underwater," he said.

Mussels and geckos work in totally different ways when it comes to sticking power. Geckos rely on very fine hairs covering the surface of their feet. Each hair is split at its ends and it is the intermolecular forces between these hairs, known as van der Waals forces, that enable geckos to defy gravity and dangle from the ceiling. Meanwhile, mussels make use of chemicals to keep their grip, secreting a sticky protein out of their foot.

Dr Messersmith and his colleagues have taken the best parts of both designs to create an entirely new waterproof adhesive. A surface covered in minuscule silicone pillars mimics the gecko's foot, while a thin covering of a synthetic polymer mimics the sticky mussel protein.

Currently they are considering medical applications such as plasters and bandages that won't wash off in the shower. "Adhesive tapes made out of geckel could be used to replace sutures for wound closure and might also be useful as a water resistant adhesive for bandages and drug-delivery patches," Dr Messersmith said.

Eventually geckel could have applications in underwater exploration, helping underwater vehicles to crawl over difficult terrain.

[Al-khiyal]

Butterfly blusher


Male and female Morpho butterflies.
Human-made replicas of the optical structures
found in iridescent blue Morpho butterfly wings
(used as an antenna or anti-reflection coating for radar)
are 1,000 times the size of their natural counterparts


High magnification image of the scales
on a Blue Morpho butterfly's wing.
Current work focuses on butterfly scales
by identifying the cells in chrysalises
that later develop to produce scales in adults,
dissecting them and separating them in the lab

It is always difficult to predict where biomimetic science is going to lead. For Andrew Parker, a zoologist at London's Natural History Museum, eye shadow and lipstick were the last things on his mind when he started studying butterflies. "I was interested in how the butterfly creates an iridescent effect," Professor Parker said.

By studying butterfly wings under high-powered microscopes and building models of their wings, Prof Parker worked out that it is the layered structure which produces the colourful shimmer.

"The layering creates a strong iridescent effect, but the addition of a second structure means that the wavelength doesn't change much with viewing angle, meaning that it stays the same colour where ever you view it from," Prof Parker explained.

Cosmetics and paints are also applied in layers and Prof Parker realised that this might be an area where the butterfly effect could be exploited. Now he is working with Procter & Gamble to try and create lipsticks, blushers and eye shadows that mimic the elusive shimmer you see on a butterfly's wing.

Sagra beetle - an example of iridescence in insects


A work by Franziska Schenk, an artist in residence at the Natural History Museum.
She uses newly developed irridescent paints to paint realistic pictures of animals and insects

Fossil power

Biomimetic inspiration doesn't always have to come from living creatures.
It was during a chance visit to Poland's Museum of the Earth in Warsaw in 1995, when Prof Parker spotted the 45 million-year-old fly sitting in its amber grave. Peering at a magnified image of the fly he noticed an unusual structure in the eyes. "I could see very fine striations – a series of ridges and grooves," he said.

Back in the lab, Prof Parker built a model of the fly's eye and investigated how it responded to light. "Instead of reflecting light we found that these parallel ridges encouraged light to pass through," he said.

For the fly this specialised eye would have enabled it to soak up light coming from all different angles, helping it to see clearly in low light levels.

Now, just over 10 years later, the fossilised fly's eye has become the design-basis for a new kind of light-capturing material. By mimicking the structure using modern materials, Prof Parker and his colleagues have been able to recreate a synthetic version. When pasted onto solar panels these synthetic fly eyes increase energy capture by 10%.

Flies in amber, 45 million years old, with perfectly preserved eyes.
The anti-reflective quality of flies' eyes has been used to make solar panels capture more energy


Scanning electron micrograph image of a 45 million year old fly's eye,
showing 4 facets, each with the anti-reflector on the surface

Putting viruses to good use

One of the biggest stumbling blocks for many of these biomimetic ideas is finding a cheap way of mass producing the mimicked material. "Natural structures are very complex and so they are difficult and expensive to make. Normally it is only feasible to make tiny amounts," Prof Parker said.

To roll things out on a larger scale, Prof Parker is currently looking at the possibility of using living cells. "Rather than developing complicated and expensive engineering techniques, we can let nature do the hard work," he said. In June 2007, Prof Parker published a paper in Nature Nanotechnology, outlining some of his ideas.

Most recently he has been working with a single-celled organism called a diatom, to try and grow iridescent structures with commercial interest. By feeding the diatoms different diets Prof Parker has been able to manipulate the way they grow their shells. A nickel-rich diet made the holes in their shell a little larger and produced a similar optical effect to the original fly's eye.

Viruses and bacteria also hold huge potential. "They can self-assemble and you can keep growing them into something as large as you want," Prof Parker said. Already Prof Parker has discovered that this is a simple and inexpensive process, but the challenge is to get the cells to embed themselves in the material you want to use.

If he can overcome this hurdle then viruses, bacteria and other tiny creatures could become the engineers and builders of the future. No genetic engineering is required, just a change in diet and perhaps a few growth hormones to pep them up. What is more, there is no need for the high pressures and temperatures or toxic chemical sludges required in ordinary factories. Unlike engineered materials, these natural structures are biodegradable. These tiny organisms look set to be the eco-friendly workforce of tomorrow.

Scanning Electron Micrograph of a diatom.
These are the single-celled organisms used to make nanostructures.
By using single-celled organisms such as diatoms and viruses,
these newly developed special surfaces could be produced by the tonne

Borrowing from nature's best ideas

[Al-khiyal]

A mussel clings fast to a sheet of Teflon

October 18, 2007 -- The uncanny stickiness of mussels has inspired a brainy new approach to creating a universal adhesive coating, researchers say.

Mussels secrete a complex cocktail of proteins to latch on to just about any surface, explained study co-author Phillip Messersmith, a biomedical engineer at Northwestern University in Evanston, Illinois.

Messersmith and colleagues found that the two most prominent ingredients in this cocktail are the same as those in dopamine, a chemical messenger in the brain.

So the researchers wanted to find out if they could use dopamine to make an adhesive coating that matches the mussels' natural stickiness.

First they added a drop of pure dopamine to a beaker of water that had the same acidity as seawater.

In this solution the dopamine molecules went through chemical changes that caused them to link together and form new, larger molecules known as polymers.

This so-called polydopamine substance was remarkably sticky, the researchers found. Any object put in the new solution got coated with a thin, adhesive film.

"It pretty much worked well on just about any material that we tried," Messersmith said. "It is really tremendously simple."

The results appear this week in the journal Science.

The researchers found that the dopamine-based glue could be used to make a variety of additional materials stick to objects, creating a host of functional applications.

For example, applying certain materials over a sticky object could prevent an object from becoming contaminated—a handy feature for medical instruments.

Secondary exposure to a copper nitrate solution would give an object a metallic sheen, useful in electronics such as flexible displays.

In another application, water polluted with mercury or lead could be passed through a column of beads coated in the adhesive. The metals would stick to the beads, allowing clean water to flow out the other side.

"Each of these applications involves pretty much the same first step but a different second step," Messersmith noted.

He and his colleagues are now trying to determine the limits of the technology and where to focus their development efforts.

Herbert Waite is a marine biologist at the University of California, Santa Barbara, who studies how each ingredient in the mussels' protein cocktail comes together to make the mollusks so sticky.

He said Messersmith's team deserves credit for reducing the complex ingredients to "two very simple features" to make their sticky coating.

"It's nice that the mussel inspired it with its own highly evolved adhesive technology," he said, "but it isn't the same thing as mussel adhesion."

If a mussel just squirted dopamine, the chemical would simply diffuse into the large volume of surrounding seawater, he noted.

"What works for man would not have worked for the mussel."

Mussels' mighty grip inspires dopamine-based glue

[Al-khiyal]

October 20, 2007 -- Mussels are delicious when cooked in a white wine broth, but they also have two other well-known qualities before they're put in a pot: they stick to virtually all inorganic and organic surfaces, and they stick with amazing tenacity.

Northwestern University biomedical engineer Phillip B. Messersmith already has developed a material that mimics the strength of the bonds; now he has produced a versatile coating method that mimics the mussels' ability to attach to a wide variety of objects.

Messersmith and his research team, in a study to be published in the October 19 issue of the journal Science, report that a broad variety of materials can be coated and functionalized through the application of a surface layer of polydopamine.

Potential applications of the simple and inexpensive method include flexible electronics, such as bendable and flexible displays, biosensors, medical devices, marine anti-fouling coatings, and water processing and treatment, such as removing heavy metals from contaminated water.

Key to the coating method is the small molecule dopamine, commonly known as a neurotransmitter. Dopamine, it turns out, is a good mimic of the essential components of mussel adhesive proteins, and the researchers use it as a building block for polymer coatings. (Dopamine itself is not found in mussels.) So, like a mussel, Messersmith's coating sticks to anything.

"This is an astonishingly simple and versatile approach to functional surface modification of materials," said Messersmith, professor of biomedical engineering at Northwestern's McCormick School of Engineering and Applied Science, who led the research. "We dissolve dopamine, which we buy at low cost, in a beaker of water exposed to air. We adjust the water's pH to marine pH, about 8.5, put in an object and several hours later it's coated with a thin film of polydopamine. That's it."

Solid objects of any size and shape can be immersed in the solution. (The dopamine solution is very dilute - only two milligrams of dopamine per one milliliter of water.) At marine pH, there are chemical changes in the dopamine molecule that result in polymerization of the molecules together to form a polymer, polydopamine, which coats the object. The polymer is fairly similar to what is found in the mussel adhesive protein.

And to make things more interesting, the polydopamine coating, in turn, provides a very chemically reactive surface onto which the researchers can deposit a second coating. And because the surface is so reactive in so many different ways, a wide variety of second coatings can be applied.

"We take advantage of that reactivity to apply the second layer," said Messersmith. "As a simple example, I could put an iPod in the dopamine solution, and a thin polydopamine coating would form. Then I could take it out and put it in a metal salt solution and form a coating of copper or silver."

This second coating, depending on what it is, promises to take researchers and industry in multiple directions as far as applications go. In addition to cladding objects with metal coatings, this includes inhibiting biofouling of materials (such as for medical devices), engineering surfaces to support biospecific interactions with cells (such as for culture and expansion of stem cells) and applying self-assembled monolayers to nonmetal surfaces (such as for biosensors).

Messersmith and his colleagues tested the two-step process on 25 different substrate materials (but not an iPod) with a wide range of characteristics representing all major classes of materials, from hydrophobic to hydrophilic, from inorganic to organic, as well as the traditionally difficult material Teflon, all with positive results. They then demonstrated deposition of metal and organic coatings and self-assembled monolayers onto the polydopamine coating.

"Existing methods for modifying material surfaces are fairly restricted to specific materials - what works well on glass would not work well on gold," said Messersmith. "Our method is a much more general strategy for a variety of surfaces. We haven't found a material to which we can't apply polydopamine."

In addition to Messersmith, other authors of the paper, titled "Mussel-inspired surface chemistry for multifunctional coatings," are Haeshin Lee (lead author) and Shara M. Dellatore, both graduate students, and William M. Miller, professor of chemical and biological engineering, all from Northwestern.

Sticky mussels inspire biomedical engineer yet again

[Al-khiyal]

Diamond-like crystals discovered in Brazilian beetle solve issue for future optical computers

May 21, 2008 (ScienceDaily) — Researchers have been unable to build an ideal "photonic crystal" to manipulate visible light, impeding the dream of ultrafast optical computers. But now, University of Utah chemists have discovered that nature already has designed photonic crystals with the ideal, diamond-like structure: They are found in the shimmering, iridescent green scales of a beetle from Brazil.

"It appears that a simple creature like a beetle provides us with one of the technologically most sought-after structures for the next generation of computing," says study leader Michael Bartl, an assistant professor of chemistry and adjunct assistant professor of physics at the University of Utah. "Nature has simple ways of making structures and materials that are still unobtainable with our million-dollar instruments and engineering strategies."

The study by Bartl, University of Utah chemistry doctoral student Jeremy Galusha and colleagues is set to be published in a forthcoming edition of the journal Physical Review E.

The beetle is an inch-long weevil named Lamprocyphus augustus. The discovery of its scales' crystal structure represents the first time scientists have been able to work with a material with the ideal or "champion" architecture for a photonic crystal.

"Nature uses very simple strategies to design structures to manipulate light - structures that are beyond the reach of our current abilities," Galusha says.

Bartl and Galusha now are trying to design a synthetic version of the beetle's photonic crystals, using scale material as a mold to make the crystals from a transparent semiconductor.

The scales can't be used in technological devices because they are made of fingernail-like chitin, which is not stable enough for long-term use, is not semiconducting and doesn't bend light adequately.

The University of Utah chemists conducted the study with co-authors Lauren Richey, a former Springville High School student now attending Brigham Young University; BYU biology Professor John Gardner; and Jennifer Cha, of IBM's Almaden Research Center in San Jose, California.

Quest for the ideal or 'champion' photonic crystal

Researchers are seeking photonic crystals as they aim to develop optical computers that run on light (photons) instead of electricity (electrons). Right now, light in near-infrared and visible wavelengths can carry data and communications through fiberoptic cables, but the data must be converted from light back to electricity before being processed in a computer.

The goal - still years away - is an ultrahigh-speed computer with optical integrated circuits or chips that run on light instead of electricity.

"You would be able to solve certain problems that we are not able to solve now," Bartl says. "For certain problems, an optical computer could do in seconds what regular computers need years for."

Researchers also are seeking ideal photonic crystals to amplify light and thus make solar cells more efficient, to capture light that would catalyze chemical reactions, and to generate tiny laser beams that would serve as light sources on optical chips.

"Photonic crystals are a new type of optical materials that manipulate light in non-classic ways," Bartl says. Some colors of light can pass through a photonic crystal at various speeds, while other wavelengths are reflected as the crystal acts like a mirror.

Bartl says there are many proposals for how light could be manipulated and controlled in new ways by photonic crystals, "however we still lack the proper materials that would allow us to create ideal photonic crystals to manipulate visible light. A material like this doesn't exist artificially or synthetically."

The ideal photonic crystal - dubbed the "champion" crystal - was described by scientists elsewhere in 1990. They showed that the optimal photonic crystal - one that could manipulate light most efficiently - would have the same crystal structure as the lattice of carbon atoms in diamond. Diamonds cannot be used as photonic crystals because their atoms are packed too tightly together to manipulate visible light.

When made from an appropriate material, a diamond-like structure would create a large "photonic bandgap," meaning the crystalline structure prevents the propagation of light of a certain range of wavelengths. Materials with such bandgaps are necessary if researchers are to engineer optical circuits that can manipulate visible light.

On the path of the beetle: From BYU to Belgium and Brazil

The new study has its roots in Richey's science fair project on iridescence in biology when she was a student at Utah's Springville High School. Gardner's group at BYU was helping her at the same time Galusha was using an electron microscope there and learned of Richey's project.

Richey wanted to examine an iridescent beetle, but lacked a complete specimen. So the researchers ordered Brazil's Lamprocyphus augustus from a Belgian insect dealer.

The beetle's shiny, sparkling green color is produced by the crystal structure of its scales, not by any pigment, Bartl says. The scales are made of chitin, which forms the external skeleton, or exoskeleton, of most insects and is similar to fingernail material. The scales are affixed to the beetle's exoskeleton. Each measures 200 microns (millionths of a meter) long by 100 microns wide. A human hair is about 100 microns thick.

Green light - which has a wavelength of about 500 to 550 nanometers, or billionths of a meter - cannot penetrate the scales' crystal structure, which acts like mirrors to reflect the green light, making the beetle appear iridescent green.

Bartl says the beetle was interesting because it was iridescent regardless of the angle from which it was viewed - unlike most iridescent objects - and because a preliminary electron microscope examination showed its scales did not have the structure typical of artificial photonic crystals.

"The color and structure looked interesting," Bartl says. "The question was: What was the exact three-dimensional structure that produces these unique optical properties?"

The Utah team's study is the first to show that "just as atoms are arranged in diamond crystals, so is the chitin structure of beetle scales," he says.

Galusha determined the 3-D structure of the scales using a scanning electron microscope. He cut a cross section of a scale, and then took an electron microscope image of it. Then he used a focused ion beam - sort of a tiny sandblaster that shoots a beam of gallium ions - to shave off the exposed end of the scale, and then took another image, doing so repeatedly until he had images of 150 cross-sections from the same scale.

Then the researchers "stacked" the images together in a computer, and determined the crystal structure of the scale material: a diamond-like or "champion" architecture, but with building blocks of chitin and air instead of the carbon atoms in diamond.

Next, Galusha and Bartl used optical studies and theory to predict optical properties of the scales' structure. The prediction matched reality: green iridescence.

Many iridescent objects appear that way only when viewed at certain angles, but the beetle remains iridescent from any angle. Bartl says the way the beetle does that is an "ingenious engineering strategy" that approximates a technology for controlling the propagation of visible light.

A single beetle scale is not a continuous crystal, but includes some 200 pieces of chitin, each with the diamond-based crystal structure but each oriented a different direction. So each piece reflects a slightly different wavelength or shade of green.

"Each piece is too small to be seen individually by your eye, so what you see is a composite effect," with the beetle appearing green from any angle, Bartl explains.

Scientists don't know how the beetle uses its color, but "because it is an unnatural green, it's likely not for camouflage," Bartl says. "It could be to attract mates."

The study was funded by the National Science Foundation, American Chemical Society, the University of Utah and Brigham Young University.

[Bent_Bladi]

words cannot describe my awe/amazement at these "discoveries" ... wow, all we had to do is open our eyes