Researchers from Illinois University (US) have developed a material which can perform a black/white camouflage. The material reproduces the skin structure of cephalopods such as octopus, which can change the color of their skin (metachrosis) and assume the same color as their surroundings.
Animals Changing Color: Metachrosis
Some animals, such as reptiles or cephalopods (i.e. squids, octopus, cuttlefishes), show the ability to change the color of the surface of their skin depending on the surroundings. Scientifically this phenomenon is known as metachrosis.
The principle behind metachrosis is the presence of a chromatophore, a pigment inside an intracellular sac, which can reflect the light. The animal can change the position of the sac, and hence the interaction of the pigment with the light. When this happens, you can see the color change.
Cephalopods control sac position via muscles. The brain controls mechanical action, such as expansion and/or contraction, which creates that change in color.
Cephalopods can use metachrosis for camouflage, to assume the same color as their surroundings.
Artificially Reproducing Metachrosis
There is a great interest in artificially reproducing metachrosis, i.e. to make materials which function according to the same principles as cephalopod skin. Materials with these characteristics could have several important industrial and military applications.
Scientists from the University of Illinois (US) made a very significant step in this direction, In fact, they made a material which mimics the structure of cephalopod skin. The research was conducted in cooperation with other universities in the US and China; the results were published in the Proceedings of the National Academy of Science (PNAS) on the 18th of August 2014.
Decoded Science spoke to Professor John Rogers, leading scientist of this work. He explains how the material was made.
“Our devices include several different functional layers, by analogy to the structure of the skin of an octopus.
The top layer includes a chemistry, known as a leucodye, that can be reversibly switched from colored to colorless upon small changes in temperature. Our particular dye goes from black to colorless at 47 oC. A supporting layer of a roughened silver (Ag) film provides a bright white, reflective background. These first two layers play a role equivalent to that of the cromatophore in cephalopods.
The next layer consists of a distributed array of ultrathin silicon diodes as thermal actuators to control the leucodyes; this layer corresponds to the muscles of the cephalopods, which can control the movement of the chromatophore, and hence induce the color change.
Finally, at the base layer, we included an array of photodetectors to sense color / light and from the surroundings. In cephalopods this function is performed by some specific proteins in the skin.”
Black to White Camouflage
To check the system, Professor Rogers and his coworkers used a mask which allowed the passage of the light only to some areas of the material.
In the parts hit by the light, the background color changed, becoming white; this change was “felt” by the photochemical sensors at the bottom. These, in turn, activated the silicon diode which generated a small electric current; this led to an increase in temperature, which went above 47 oC. The higher temperature caused a change in the dye, which went from black to white.
The experiment can be seen in the short movie below.
According to Professor Rogers:
“Our system provides basic function, in the sense of offering ability to match simple black and white patterns . We all know that nature (i.e. cephalopods) can do much more than that! However, we believe that this first step is important, as we showed that it is possible to reproduce metachrosis.
Our current work focuses on improvements that will allow color reproduction, more efficient operation, faster switching, higher resolution, etc. These first results establish some foundational concepts that will be valuable for further developments in this area.”
The future is going to look pretty interesting.
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