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Surprising Science

Check out This Stretchable Cloaking Device Modeled After Octopus Skin

It’s fascinating how an octopus’s skin does this and how these scientists recreated it.
Credit: Getty Images.

We often see movies where a villain (or hero) has a cloaking device. They can appear or disappear at will. Such a foe is exceedingly difficult to reckon with, as one might imagine. Researchers from several American institutions have announced the invention of a certain material that could be used to make such a device. It’s a 3D camouflage “skin,” modeled after an octopus’s.

These cephalopods can change not only their skin color, but the shape and texture  as well. The octopus’s skin can change from a 2D surface to a 3D textured one in a fraction of a second. Drab, ragged seaweed, colorful, bumpy coral, and more, are easy for the octopus to emulate and blend into seamlessly. Researchers say because of this, they are infamously hard to catch.

Certain bodies below the surface of their skin known as papillae give them the capability. Papillae are an example of a muscular hydrostat. This is a muscle bereft of skeletal support. The human tongue is one such example. Octopi papillae rise out of the skin to mimic different colors and textures and then retract in an instant, to allow the octopus to swim away, without the detriment of drag. This ability is so important marine biologists say, because it’s one of their only defenses against predators.

Catch a glimpse of this soft robot here:

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Credit: Cornell University.

Robert Shepard is an assistant professor of mechanical and aerospace engineering at Cornell University. He and James Pikul at the University of Pennsylvania, led the study. They were aided by Cornell physics professor Itai Cohen, and biologist and cephalopod expert Roger Hanlon. The results of this study were published in the journal Science.  Hanlon was on the research team who first discovered how papillae work.

Hanlon told Science Daily:

The degrees of freedom in the papillae system are really beautiful. In the European cuttlefish, there are at least nine sets of papillae that are independently controlled by the brain. And each papilla goes from a flat, 2D surface through a continuum of shapes until it reaches its final shape, which can be conical or like trilobes or one of a dozen possible shapes. It depends on how the muscles in the hydrostat are arranged.

The muscle groupings under an octopus’s skin have within them an erector muscle. This squeezes the other muscles downward, causing a protrusion to form on the surface. Inflate a balloon and it takes a round shape. But tie a rope around it perhaps a third of the way down and you’ll get a finger-like protrusion. Group these very tightly together and through pressure control, you can make any 3D surface you wish. Release the pressure, and the protrusions go flat.

See the robot in one of its iterations here:

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Credit: Cornell University.

Their method is now known as CCOARSE – Circumferentially Constrained and Radially Stretched Elastomer. They plan to patent it. “Engineers have developed a lot of sophisticated ways to control the shape of soft, stretchable materials,” Prof. Pikul said. “But we wanted to do it in a simple way that was fast, strong, and easy to control.” Researchers first took a sturdy fiber mesh and cut into concentric circles, using a laser.

These were covered in a stretchy material, called a silicone elastomer, which were grouped together like papillae. Hanlon calls it a “classic example of bio-inspired engineering.” The fiber mesh allows for precise control. While a simple algorithm tells the robot what shape to make. So far, the scientists were able to mimic stones in a riverbed and a certain type of succulent plant (Graptoveria amethorum).

The CCOARSE protrusions are very accurate, coming within 10% of algorithm projections. Next up, the researchers want to find out how they can change the material’s color and texture. More precise patterning is also desired. They think they can accomplish this with higher-resolution laser patterning.

The robot as a plant:

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Credit: Cornell University. 

Shepard now has a 300 gallon tank in his lab. He plans to study the octopus closely. And he wants to use these observations to inform future robot models. The Army Research Office funded the study. It says it’s interested in this tech for camouflage purposes. But researchers say, they specifically made the process easily reproducible so it would be accessible to hobbyists, as well as those in academia and industry. Now, Shepard is manipulating the protrusions not with air but electrical current, which he say allows him to shape them in the same way and with the same amount of control.

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