By now, we have seen how technology is inspired by the natural world in so many ways. This time, researchers from Cambridge University's Cavendish Laboratory report that they have synthesized artificial chromatophores-those cells that help chameleons and some species of squid during instances when they need active camouflage.
In animals, the chromatophores are transparent cells that contain fibers that move pigments around by expansion and contraction. When a chameleon is relaxed the cells are expanded, thus the pigment is spread out and visible. But when it wants to blend in with the colors of its environment, the cells contract causing fibers in the chromatophores to be squeezed together and their cells would appear transparent.
Co-first authors Andrew Salmon and Sean Cormier, together with their colleagues explained how they went about the synthesis of the material in Advance Optical Materials. First, they coated minute particles of gold with acrylic polymer shells, which were essential to the project as they can store and eject water. They then squeezed the gold particles into microdroplets of water suspended in oil.
"Loading the nanoparticles into the microdroplets allows us to control the shape and size of the clusters, giving us dramatic color changes," explained Salmon.
The particles behaved similarly with chromatophores in a way that they expand to show color and contract to hide their color. In the natural world, what drives the expansion-contraction mechanism was biology and the animal's survival instinct. Here, the driving force would be a set temperature of 89.6 degree Fahrenheit-that is 32 degree Celsius. Above this temperature, the polymer shell expels all stored water, which in turn forces nanoparticles to compress tightly, causing the material to turn blue. At lower temperatures, the polymer shell would absorb the water and expand, changing the color of the material to red.
Aside from the material's reaction to heat or changes in temperature, the researchers have also observed a change in material behavior when shown to light. Exposure to it would cause the nanoparticles to appear as though they were swimming in different ways, respective of the light's intensity.
"This work is a big advance in using nanoscale technology to do biomimicry," said co-first author Cormier. "We're now working to replicate this on roll-to-roll films so that we can make meters of color-changing sheets. Using structured light we also plan to use the light-triggered swimming to 'herd' droplets. It will be really exciting to see what collective behaviors are generated."
As of now, the researchers are working on a single layer of particles, so the change in color is only from blue to red or red to blue. In the future, they hope to develop multilayered materials using various nanoparticle materials so that the product could change color dynamically.
