We’ve all probably experienced a moment when we envied a chameleon’s ability to blend into the background—say, after a gaffe at the office holiday party. As it turns out, chameleons change their skin color in response to all kinds of stimuli: physical threats, temperature changes, and the animal’s moods. What if humans could harness that same ability?
That could one day be a reality, thanks to a new material that mimics the “fantastic and complex” ability of chameleons, a material developed by UC Berkeley engineer Connie Chang-Hasnain and her two graduate students, Li Zhu and James Ferrara.
Most colors are produced by pigments, which absorb some wavelengths of light and reflect others back to the human eye. This reflected light produces the colors we see. A red flower, for example, will absorb all the light in the spectrum except red lightwaves, which are bounced back. Chameleons, however, can shift their hues by changing how light interacts with the three-dimensional structure of their skin.
A chameleon’s skin is latticed with a layer of tiny guanine crystals that reflect light. These small structures are embedded in cells that can swell and contract, changing the distance between the crystals. As the crystals move, the length of the lightwaves they reflect changes, thus changing the color of the animal’s skin.
Instead of using a grid of crystals, the Berkeley team developed a technique to stamp ridges onto a strip of silicon 1,000th the thickness of a dollar bill. They then embedded this material into an elastic silicone “skin.” By stretching the skin, the scientists can change the distance between the ridges. As with the skin of a chameleon, that changes the wavelength of the light reflecting on the material’s surface, thus changing the color of the silicone. From some angles, the silicone looks clear; from others, it reflects bright green or orange. The result is an iridescent surface almost like the wings of a butterfly.
The next step, says Chang-Hasnain, will be to stamp squares rather than ridges on the silicon base layer. Although more difficult to do, this would allow the material to change color when pulled in different directions. For now, the material has potential applications in a variety of fields—for instance, as a medical biosensor or a gauge of structural instability, where inspiration from nature could one day save lives.