Unlike any other animals, cuttlefish and squid use light to blend into or stand out from their surroundings. Marine scientists believe they do this using tiny sensors all over their skin that help them change color without sending messages to the brain. Exactly how it works is still a mystery.
Roger Hanlon, a senior scientist at the Marine Biological Laboratory in Woods Hole, Mass., is collaborating with bioengineers across the country to develop a material that mimics this camouflage mechanism. The material might be able to hide objects or change the tint of your car. It might even allow buildings to keep cool in the summer and warm in the winter by darkening to absorb heat and lightening to reflect it.
‘Why does it need that?’
In 2010 Hanlon and Lydia Mathger, a researcher in his lab, published a study showing that the same gene that produces light-sensing molecules in the retina was distributed throughout the skin of cuttlefish. The finding was a big surprise.
“When we started, we thought: What on earth is this doing in the skin?” Mathger said. “It’s the same visual pigment as in the eye. Why does it need that?”
The researchers found this gene (for a protein called opsin) concentrated near chromatophores; these tiny organs consist of an elastic sac of red, yellow or black pigment and are tied to muscle fibers. The scientists believe that the protein senses light while the chromatophores change the skin color. The opsin may be acting on its own without brain signaling and may be somehow connected to the chromatophores. Mathger believes the presence of opsin may mean that the otherwise colorblind cuttlefish can “see” a multicolored environment through its skin. But Hanlon and other scientists at Woods Hole and elsewhere are still trying to prove the connection.
Alexandra Kingston, a biology graduate student at the University of Maryland Baltimore County, is exploring the role of opsin in a cuttlefish relative, the long-finned squid. Kingston has found the protein all over the squid’s skin, and she is now looking for retinochrome, another protein that switches opsin on and off.
“It’s a recycling mechanism for the opsin,” Kingston said. “We have the opsin molecules, but do they have the [light-sensing] cells? That’s what we are working on right now.”
Kingston’s adviser, Tom Cronin, says that more sea creatures that use camouflage — such as the flounder and the mantis shrimp — are being found to have light-sensing opsin on their skin.
“Light sensing has lots of different jobs besides vision,” said Cronin, who is collaborating with Hanlon. “It will tell you whether it’s day or night, how shallow you are, how deep you are. It may not be related to camouflage. But what’s surprising is, they use the exact same protein that is in their eye.”
Building electronic skin
While Cronin and Kingston probe the inner workings of squid skin, engineers funded by the Office of Naval Research are trying to make a similar camouflage material out of silicon and circuits. This artificial skin might help the Pentagon make its tanks and submarines disappear or turn a wall into a 3-D television camera, according to Richard Baraniuk, a professor of electrical engineering at Rice University and a collaborator on the project.
“What we are designing is a passive system that interacts with the ambient light, channels the right amount to the right direction so you can camouflage yourself,” Baraniuk said. “It’s not like any kind of imaging device that has ever been designed.”
By harnessing the light-collecting and color-shifting abilities of the undersea animals, Baraniuk and other bioengineers dream of building a thin electronic “skin” that could turn an entire room into a camera, transmitting images of what’s happening there without people knowing it. That might seem a bit creepy, but this technology could also be used to design new kinds of three-dimensional televisions, holographic games and medical imaging devices.
John Rogers, a professor of materials science at the University of Illinois at Champaign-Urbana, is also working on this idea. “Just imagine surfaces that would be wallpapered that turn into a camera,” he said.
The initial prototype would be a black-and-white version that can match its surroundings, Rogers said. Flexible camouflage panels would contain sacs of colored dyes that contract or expand, just like the skin of the squid and cuttlefish.
Clothes that change color
Experts say lots of engineering problems must be solved before we will be able to buy clothing that changes color to match its background. That’s because there are still a lot of things scientists don’t understand about how cuttlefish skin changes color.
That change is the result of a cascade of events influenced by chemical and physical signals from its surroundings, the animal’s own chemical hormones and electrical impulses from the brain, according to Andrea Toa, an assistant professor of nano-engineering at the University of California at San Diego. She says that fabricating a similar cascade won’t be easy.
“Squid have very complex systems,” said Toa, who is not involved in the Office of Naval Research project. “In a camouflage device, you have man-made elements which boil down to an electrical circuit.”
However, researchers including Baraniuk and Rogers point to other advanced devices as evidence that nature and engineering can work together. Scientists in Japan are building “krill-eye,” a wide-angle lens that collects light the way the compound eye of a shrimp does. An Oregon lab is designing “neuromorphic” computer chips that mimic the way the brain’s neurons work — sending messages in spikes of energy instead of a continuous current.
“Whatever we learn from this,” Baraniuk said, “will be applicable way beyond mimicking camouflage.”
Niiler writes about science and technology, and lives in Chevy Chase.