Camouflage allows soldiers to blend into their surroundings, but the Operational Camouflage Pattern (OCP) adopted by the US Army falls well short of the stealth capabilities of the squid and other cephalopods. That's why a team of researchers, led by Leila Deravi, at Northeastern University have turned to these creatures in an attempt to uncover their secrets and see if they can be mimicked.

The sea can be an extremely savage place, with one animal eating another only to be gobbled up by a third – sometimes while it's still eating the first. It's small wonder then that over hundreds of millions of years the underwater world has become a giant laboratory of offensive and defensive technologies locked in a perpetual arms race.

One of the most effective defenses developed by sea creatures is camouflage and the most adept practitioners are the cephalopods – a class of tentacled mollusks that includes squid, octopi, cuttlefish, and the nautilus. These make up not only the largest and most intelligent of the mollusks, but also species that have an ability to change their color and even their skin texture in so quick and fine a manner that it essentially borders on invisibility – at least when it comes to potential predators.

The cephalopods' remarkable stealth is achieved by means of tiny muscular organs called chromatophores, which contain hundreds of thousands of pigment granules that are 150 times smaller than the width of a human hair. These incorporate a folding membrane that can hide or reveal them in a fraction of a second and, along with similar organs, provide the animals with an amazing degree of control over their color and iridescence.

These chromatophores come in shades of red, yellow, brown, and orange. Underneath these is a layer of iridophores that reflect light like a biological mirror. By combining the properties of the chromatophores and the iridophores, an advanced cephalopod like the cuttlefish can reflect all colors of visible light.

To better understand and mimic this mechanism, Deravi's team, in cooperation with the US Army Natick Soldier Research, Development, and Engineering Center, isolated and examined the pigment granules, which they found can be layered and reorganized to create an extensive pallet of colors.

The team then used these granules to make ultra-thin films and spools of fibers that are rich in colors. When these are backed by a mirror layer, the resulting scattering of light enhanced the color effect – a property that Deravi says could one day find an application in solar cell design.

However, the most important application may be in textiles. Not only do the pigment granules offer the promise of stunning new colors for the fashion trade, but they have the greater promise of creating wearable, flexible screens and textiles that are capable of adaptive coloration. In other words, battle fatigues that can turn a soldier into a combat cuttlefish able to better blend with their surroundings.

"For more than a decade, scientists and engineers have been trying to replicate this process and build these devices that can color match, color change, and camouflage just like the cephalopods, but many of them come nowhere near the speed or dynamic range of color that the animals can display," says Deravi. "Cephalopods have evolved to incorporate these specific pigment granules for a reason, and we're starting to piece together what that reason is."

The research was published in Advanced Optical Materials.

Source:
Northeastern University
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