Imagine a uniform that changes color like a chameleon to match the surrounding environment, allowing a soldier to remain camouflaged while moving from the desert to the sea. Sandia National Laboratories researchers have demonstrated that, in theory, they could cause synthetic materials to change color like chameleons or certain fish species.
They believe their work could lead to color-changing material in five to 10 years. Demonstrating that color changes are possible in the lab is the first step toward developing camouflage clothing that works at the nanoscale level, said principal investigator George Bachand. Nanoscale refers to atomic and molecular scale _ the head of a pin is about a million nanometers, for example.
"Just the ability to change those two states (colors) back and forth allows us now to understand how to do that in an artificial environment," said Bachand, whose background is in bioengineering. "It's the first proof we can do it."
That will allow materials engineers to move forward to create materials with color-changing properties, he said.
"The long-term goal and payoff has a number of different applications, both in civilian applications as well as military ones," Bachand said. "There's always this concept of the national labs being involved in highly secret, covert work they can't talk about, but a lot of work ... has many facets that can affect our lives."
The idea of developing materials that could sense their environment and change to fit it seemed like a good target, said Bachand, who has worked on the process for most of his eight years with Sandia.
"What really are some things nature and living systems can do better than our manmade systems can? One of the great aspects nature has evolved is the ability to sense and adapt to the environment," he said. That biological property could lead to materials that change with surrounding conditions _ not just color, but in the longer range, properties such as breathability or temperature control, he said.
A typical spring day in New Mexico, for example, starts out cold and gets warm. Instead of people dressing in layers, Bachand envisions a shirt that changes its thermal properties.
Or for military use, he envisions a material that's able to allow air exchange for comfort but changes if it comes into contact with a chemical warfare agent "so it doesn't allow that to cross the material boundary."
Sandia's work, mimicking biology, relies on a basic cellular fuel called ATP, which releases energy as it breaks down. About half that energy is absorbed by the motor proteins _ tiny proteins within a cell that are responsible for moving materials around.
Sandia's work takes motor proteins from a living cell and puts them into a system that uses a glass slide or a silicon surface such as those used for making computer chips, along with an artificial pigment crystal for color change, Bachand said. He likens it to a complex of railroad tracks within a single cell, with the motor protein serving as the locomotive to move things.
Color-changing fish have specific cells in their skin that use motor proteins to aggregate or disperse pigment particles. Bringing the cells tightly together or spreading them out changes the color on the fish, Bachand said. Think of it like an ink jet printer that uses red, yellow and blue to make a black spot. Taking those individual droplets and dispersing them along a page produces a much different color from putting them together on a tiny spot. In the long run, motor proteins won't be used to produce a camouflage fabric because they require liquid to function, Bachand said. But the work with such proteins shows it's possible to create that kind of change outside a living system, he said.
Henry Hess, a professor in the University of Florida's department of materials science and engineering who researches biomolecular motors, said he believes the path Bachand is pursuing has advantages. "One is, of course, we know it works because we see it used by fish and other animals to camouflage themselves. Second, it's really a materials response and not a device," Hess said in a telephone interview from his office.
Hess, who has worked with Bachand in the past, cited the evolution of the bright red uniforms of the 18th century to the gray uniforms of the Civil War to today's patterned uniforms. "This is sort of the 21st century approach to creating material that can be dramatically adapted," he said. A paper describing Sandia's research was published in the journal Biotechnology and Bioengineering last October. The work also was the subject of a cover article in the December 2 edition of the journal Advanced MatAP
While nature uses complex signalling mechanisms to make colors change, Sandia had to come up with a simpler way of turning the motor on and off. Researchers linked a metal atom to the sides of the protein, immobilising it to keep pigment particles in one state or the other _ as if someone walking along a railroad track had their feet frozen in place, he said.
"It physically keeps it from moving and keeps the color where we want it," Bachand said. The process also is reversible. Clothing that automatically camouflages will depend on scientists' ability to develop a series of engineered pigment crystals in nanosize, Bachand said.
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