Octopi and cuttlefish are masters of disguise. Within a fraction of a second, they can morph their tissue and seamlessly blend with their surroundings, becoming indistinguishable from a rock or coral, for example. Taking cues from nature, researchers at Cornell University have devised their own ‘camouflage skin’ which stretches and morphs in 3D. The skin can be programmed to take all sorts of shapes.

An example of the inflated membrane programmed to form stone shapes. Credit: J.H. Pikul et al., Science (2017).

An example of the inflated membrane programmed to form stone shapes. Credit: J.H. Pikul et al., Science (2017).

The secret to cephalopods’ unrivaled camouflage lies within 3D bumps on the surface of their skin called papillae. In one-fifth of a second, the papillae can rise or retract, swiftly and reversibly morphing the animal’s surface into various textures like those belonging to seaweed or coral. The primary reason why the soft-bodied mollusks evolved this ability is for defense. Their flexible body has no bones so they can escape into small cracks, rocks, crevices, and even into bottles and cans from the seafloor. They can also use jet propulsion to quickly move through the water and escape predators. At the end of the day, however, these animals invested the most resources into camouflage because it pays off better to stay inconspicuous rather than constantly evade predators.

octopus camouflage

Simply amazing! Credit: Giphy.

In the closeup video below you can get a glimpse of how the papillae are actuated.

Cornell engineers worked closely with cephalopod biologists to design a controllable soft octopus-inspired actuator, reporting in the journal Science. First, cephalopod biologist Roger Hanlon and colleagues thoroughly described the papillae, which are muscular hydrostats — biological structures that perform an action and consist only of muscle with no bony frame. The human tongue is another prime example of a muscular hydrostat.

“Lots of animals have papillae, but they can’t extend and retract them instantaneously as octopus and cuttlefish do,” says Hanlon, who is the leading expert on cephalopod dynamic camouflage. “These are soft-bodied molluscs without a shell; their primary defense is their morphing skin.”

“The degrees of freedom in the papillae system are really beautiful,” Hanlon said in a press release. “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.”

After nailing down the structure, function, and biomechanics of the cephalopod papillae, Cornell engineers developed synthetic tissue groupings that can be programmed to extend and retract. In order to closely mimic cephalopods as much as possible, the artificial papillae were constructed from a fiber mesh embedded inside a silicone elastomer. An algorithm determines how the pattern is set in the mesh using a laser so the final 3D shape of the ‘skin’ reaches the desired configuration. The silicone is simply inflated to turn the skin into a 3D object like a rock or the Graptoveria amethorum plant, as researchers demonstrated.

“Theoretically, you could do this really, really quick — milliseconds,” says study coauthor James Pikul.

This is not the first attempt at artificial dynamic camouflage. In 2014, Chinese researchers developed a thin, flexible 4-layer material that autonomously that changes appearance to match surroundings.

The method allows soft, stretchable materials to morph from 2D to a desired 3D shape, with a wide range of applications. For instance, the material can be tuned to reflect light in its 2D form and absorb light when it morphs into a 3D shape, which can be very useful when you want to manipulate temperature. Dynamic camouflage is also appealing to the Army Research Office which funded this research.