Octopuses, squids, cuttlefish and other cephalopods are often called the chameleons of the sea for their dazzling ability to instantly change textures and colour patterns of their skin in response to the complex marine environment. For a long time, this property of cephalopods has inspired awe and wonder. Now researchers are getting closer than ever to creating camouflage materials that mimic these astonishing creatures.
Scientists from the US and China created a flexible camouflage sheet that can change colour to match its surroundings. To achieve that, the researchers copied the remarkable three-layered structure of the cephalopod skin. The results of the study are published in the PNAS journal.
The camouflage sheet consists of a grid made of 1 mm cells. The top layer is filled with temperature-controlled dye, which can instantly switch from black to white when a certain temperature is reached. The middle layer contains special actuators that produce an electric current, which raises the temperature and triggers the change. Finally, the bottom layer comprises an array of photosensors, responsible for detecting changes in light and transmitting them to the actuators. You can watch a demo of how the sheet works below.
Despite the overall similarity in the layered design, the working mechanism of the sheet is, of course, completely different from the working mechanism of the cephalopod skin.
In cephalopods, colour pigments are contained in small sacs called chromatophores. The sacs are driven by muscle contraction. When relaxed, these sacs shrink and become practically invisible. However, when contracted, their surface significantly expands, thus making them visible. Interestingly, the muscles can also change the texture of the skin, for instance, from flat to bumpy.
This peculiarity of cephalopod design was explored in another recent study, published in Nature Communications. The researchers developed a paper-thin, elastic film that can simultaneously change texture and colour on demand.
The film is made of elastomer, a flexible and stretchable polymer. An important property of elastomers is that they can dynamically change texture under voltage. Stephen Craig, Duke University Professor of Chemistry and one of the leaders of the study, explains how the film works:
“The texturing and deformation of the elastomer further activates special mechanically responsive molecules embedded in the elastomer, which causes it to fluoresce or change color in response to voltage changes. Once you release the voltage, both the elastomer and the molecules return to their relaxed state – like the cephalopod skin with muscles relaxed.”
Although both studies are nowhere near the complexity and colour range of cephalopods’ skin, they represent a huge step in the development of dynamic camouflaging materials and make us wonder where this technology will eventually end up.