Chameleons can change their colors thanks to photonic crystals in their skin. As they tense or relax their muscles, the light reflects in a different pattern, resulting in a change of color. The problem with synthetic color-changing skin is in the hydrogel that the photonic crystals are packed into: After expanding and contracting, the large amount of crystals would cause the medium to seize up. Khalid Salaita and his colleagues have solved this problem by concluding that less is more.
The team watched time-lapse videos of chameleons' phase-shifting skin and realized that the reptiles have fewer skin cells with photonic crystals than previously thought. By packing fewer photonic crystals in a thin layer of hydrogel, and then placing that slice on a larger layer of colorless hydrogel, the smart skin can expand and contract without issue. As the temperature changes or sunlight hits the surface, the material changes color.
ACS Nano, a peer-reviewed journal focused on nanotechnology where this study was published, notes that smart skin may have applications in camouflage, signaling and anti-counterfeiting. MIT's color-changing ink, meanwhile, could let users change patterns and colors of their shoes, cars and more. Picking a color for an expensive gadget like a smartphone can be a stressful one; you're going to have to live with that choice for years. But with smart skin, we may eventually be able to change the colors of our gadgets as frequently as we swap out our wallpaper backgrounds.