Chameleons are known for their ability to change color. But amazingly, what we see isn't a change in pigment. What's actually going on is a change in millions of microscopic salt crystals just under the chameleon's skin. These photonic crystals have a leg up on regular hues because they can play more than one tune. Depending on how they are arranged, their size and their chemistry, these crystals can scatter light in many different ways.
"When light hits the crystals, some wavelengths are absorbed and some are reflected," KQED explains in a post about how and why chameleons change color. "The result, to our eyes, is the beautiful rainbow of colors on the chameleon's skin. But what we're actually seeing is light that is bouncing off of these tiny crystals."
In fact, those crystals have inspired a new biomimicry breakthrough. Scientists at Emory University have created a smart skin that changes color when exposed to the sun but doesn't also have to change in size.
"Scientists in the field of photonic crystals have been working for a long time to try to create color-changing smart skins for a range of potential applications, such as camouflage, chemical sensing and anti-counterfeiting tags," Khalid Salaita, an Emory professor of chemistry, says in an Emory University story about the breakthrough. "While our work is still in the fundamental stages, we've established the principles for a new approach to explore and build upon."
She and doctoral student Yixiao Dong improved on previous attempts to create smart skin in the lab. They created a hydrogel with two layers, which is how chameleon skin is structured, and that structure gave them the flexibility they needed to create strain-accommodating smart skin (or SASS), which changes color but maintains a near-constant size.
"We've provided a general framework to guide the future design of artificial smart skins," Dong says. "There is still a long way to go for real-life applications, but it's exciting to push the field another step further."
Editor's note: This story has been updated since it was published in September 2015.
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