Squid Inspired Camouflage Coatings

The pencil squid, uncamouflaged. Photo by Steve Dunleavy.
The pencil squid, on the rare occasion it chooses to stand out. Photo by Steve Dunleavy.

By Kate Wheeling
BU News Service

Camouflage patterned uniforms help soldiers vanish into their surroundings during the day, but at night, under infrared imaging, those same uniforms stand out against the environments they were fashioned to resemble. Now researchers at the University of California-Irvine and Caltech found a novel solution to this problem in the animal kingdom’s master of camouflage – the pencil squid.

Squid use a combination of reflective and pigmented cells to control skin coloration and blend into the background. The reflective cells create red, orange, yellow, green and blue color based on the angle that light hits them – the same process makes soap bubbles appear to change color in sunlight. Brown, red and yellow pigmented cells overlay the reflective cells and filter the light that reaches them. Squid use these two cell types in concert to produce colors than span the entire visible spectrum. Researchers zeroed in on a protein called reflectin, a main component of squid reflective cells and demonstrated its practical applications for stealth technologies in a study published July 30 in Advanced Materials.

The team, led by Alon Gorodetsky, Assistant Professor at UCI, created reflectin-coated thin films with tunable reflectance properties – they could manipulate the films to make them appear and disappear under infrared light. To begin, the team engineered E. coli to express a copy of the reflectin protein – a common strategy in protein engineering to produce and purify large quantities of a desired protein. They integrated purified reflectin onto glass by a process akin to spackling a wall. An adhesive layer between the glass and protein coating ensured the protein stuck to the glass and spread out uniformly. Glass is one of many materials options for this technology. This adhesive layer could be used to integrate the protein with virtually anything – plastic, paper, or even cloth. Once assembled, the thin films appeared orange under visible light, but it was their color under infrared light that interested the researchers.

The team then used a chemical trigger, acetic acid vapor, to tune the reflectance of the films over a large wavelength range – beyond what squid can even do, according to Lydia Maethger, an Assistant Research Scientist at the Marine Biological Laboratory in Woods Hole. Researchers compared the infrared reflectance of the films to leaves, which reflect in the infrared and thus appear red when viewed with infrared cameras. When the researchers looked at the reflectin-coated glass with infrared cameras it appeared black. But when they exposed it to acetic acid vapor it appeared red. These changes were reversible, meaning that Gorodetsky and his team could alter the reflectance to match multiple environments.

This is only the first step towards the application of biological camouflage coatings. “Now we need to modify our approach to develop something that’s a little bit more robust and easier to use,” explains Gorodetsky. Acetic acid vapor triggers a reflectance shift well in the lab, but it’s not the best option for the real world. The group plans to look for other chemical or mechanical approaches to induce the same reflectance changes.

Camouflage coatings also need to stand up to the elements. While Maethger is impressed with the tunable range the researchers achieved, she cautions, “If this kind of thing is to be used in the field, it would have to be able to handle a lot of stress.” This isn’t a hard problem to solve according to Gorodetsky. Reflectin is already fairly tough and the thin films could be strengthened by cross linking the proteins.

But robustness won’t be a problem at all if the technology develops the way Gorodetsky envisions it now, “Really I see it as a disposable coating, maybe even something you could put in an aerosol can and spray yourself with and then once you no longer need camouflage, you just get rid of it” by wiping it off or changing clothes.

Can Giant Squid Get the Bends?

Professors Erling Sivertsen and Svein Haftorn measure a 9.2 meter giant squid found at Ranheim in Trondheim, Norway,  2 October 1954. Photo courtesy of NTNU Museum of Natural History and Archaeology.
Professors Erling Sivertsen and Svein Haftorn measure a 9.2 meter giant squid found at Ranheim in Trondheim, Norway, 2 October 1954. Photo courtesy of NTNU Museum of Natural History and Archaeology.

By Cassie Martin
BU News Service

In January, footage of the elusive giant squid in its natural habitat aired on the Discovery Channel. Researchers captured the video in July 2012, more than a mile and a half below the surface 600 miles south of Tokyo, Japan. The last time anyone saw a giant squid alive was in 2006, when Japanese researchers caught a 25-foot female squid and brought it to the surface to photograph, but it died soon after. For a creature that usually lives 3,300 feet underwater, coming to the surface is deadly. Is it possible that the squid was a victim of the bends, an illness common to scuba divers?

The answer is no. The bends, also known as decompression illness, occurs when the diver is put under immense external pressure from deep dives then rises to the surface too quickly. The sudden release of pressure forces dissolved gasses inhaled from the atmosphere, like nitrogen, to bubble up in tissue and blood effectively starving the body of oxygen.

Giant squid don’t inhale nitrogen from the atmosphere; in fact, they don’t have a trace of gas in them. Many invertebrates use gas bladders to float and move deep underwater. However, giant squid are unique. Because the pressure in their habitat is so high, a gas bladder would implode. Since there is no gas for pressure to act on, giant squid cannot get the bends. But they have to keep afloat somehow. Instead of gas, squid re-purpose ammonium ions from their waste to keep buoyant in the water column. Ammonium ions are lighter than the sodium ions in seawater, so they avoid sinking to the sea floor or floating to the surface by adjusting the concentration of ions.

But if they aren’t affected by pressure, then why can’t they survive at the surface? Giant squid thrive in a deep, cold, and dark environment. Oxygen is hard to find deep beneath the ocean surface, but cold water has a high affinity for holding dissolved oxygen, which the squid needs to survive. The shallower the water gets, the warmer it gets and the less dissolved oxygen it holds. If a squid surfaced, its blood would become de-oxygenated and it would likely suffocate to death.

However, there is evidence that the giant squid’s mortal enemy, the sperm whale, is susceptible to decompression illness. Sperm whales are ferocious hunters of giant squid—the beaks of squid have been found in the stomachs of beached whales and scars from battle have been observed on their bodies. Whales will dive as deep as 10,500 feet and stay down for an hour or more. If they rise too quickly, nitrogen bubbles will form and cause bone damage. According to researchers at Woods Hole Oceanographic Institute, that’s just the hazard of doing business. Researchers inspected a collection of sperm whale bones spanning more than a hundred years. The researchers noticed the bones all had one thing in common—pitting and lesions, indicating the whales may have suffered chronic but mild decompression illness.