The ability to rapidly change the color and texture of skin in order to avoid predators is found in cephalopods, a class of mollusks that includes octopuses, squids, and cuttlefish. Materials scientists have been seeking to replicate the cephalopods’ ability to see the environment and change to blend in with it for years. Two papers published this week have taken steps toward achieving that goal. While both projects received funding from the Department of Defense’s Office of Naval Research, each team took a unique approach to the problem.
The team from Rice University led by Naomi Halas used aluminum nanoparticles to create a display panel that could be used to create a variety of intense colors for camouflage. The display was described in the Proceedings of the National Academy of Sciences (PNAS). Xuanhe Zhao's team at MIT developed a flexible material that can change color and texture via remote control. This project was published in Nature Communications.
The display panel from Rice has pixels that are only five microns wide, which is around 40 times smaller than pixels used in high-end LCDs. Though they be but little, they are fierce. Each pixel contains hundreds of aluminum nanorods that have been very carefully arranged. Manipulating the height and spacing between the nanorods generates dozens of colors that are much more vibrant than previous aluminum nanorod displays. Because the color is generated from the positioning of the nanorods, the colors will not fade over time, giving the system longevity.
The cephalopod skin from MIT does not get its coloring from displays, but from passing electricity through a flexible polymer known as an elastomer. When the voltage is cranked up, the skin creates bright fluorescent patterns. Additionally, the flat skin begins to contract and create a bumpy texture. The ability to change texture also acts as an anti-foul measure, removing over 90 percent of the organisms that attempt to grow on the surface. This is especially important for naval vessels, as the buildup of barnacles, algae, mollusks, and other marine life can damage the hull and impede the vessel’s performance over time.
Rice’s nanorod display would allow for precise coloring that could replicate every detail of the landscape and create a realistic camouflage that can be changed when needed. While aluminum is an inexpensive material to work with, the nanorods also need to be very precisely added via electron-beam deposition, which makes it hard to produce in large quantities. The team will now begin working on getting the color to change automatically based on the material’s ability to recognize colors in its surroundings.
The flexibility of MIT’s skin would allow it to be used on a number of surfaces, expanding what can be camouflaged. Additionally, the electro-active elastomers are relatively easy to manufacture. However, MIT’s skin is capable of generating only a few fluorescent colors and textures. While the team states that the color and texture possibilities could be expanded in the future, the system does not allow for multiple colors and shapes to be represented now.
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