A secretive octopus, yesterday

Octopus skin inspires programmable ‘camouflaging’ material

Engineers at Cornell University have invented a stretchable surface with programmable 3D texture morphing, a synthetic ‘camouflaging skin’ inspired by studying and modelling behaviours of the skin of the octopus and the cuttlefish.

For the octopus and cuttlefish, the ability to instantaneously change their skin colour and pattern to blend into their surrounding environment is a key part of their camouflage abilities. They can also morph their skin into a textured 3D surface, to portray a ragged outline that mimics seaweed, coral or other seabed object that it wants to use for camouflage.

The Cornell team, led by James Pikul and Robert Shepherd, along with collaborator and cephalopod biologist Roger Hanlon of the Marine Biological Laboratory (MBL), based its pneumatically activated material on the 3D ‘bumps’ - or papillae - that cephalopods can express in one-fifth of a second for dynamic camouflage and then just as quickly retract to swim away without the papillae imposing hydrodynamic drag.

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

Papillae are examples of what is known as a muscular hydrostat - biological structures that consist of muscle with no skeletal support, such as the human tongue.

“The degrees of freedom in the papillae system are really beautiful,” Hanlon says. “In the European cuttlefish, there are at least nine sets of papillae that are independently controlled by the brain. 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 engineers' breakthrough was to develop synthetic tissue groupings that allow programmable, 2D stretchable materials to both extend and retract a range of target 3D shapes.

“Engineers have developed a lot of sophisticated ways to control the shape of soft, stretchable materials, but we wanted to do it in a simple way that was fast, strong, and easy to control,” says Pikul, assistant professor in the Department of Mechanical Engineering and Applied Mechanics at the University of Pennsylvania.

“We were drawn by how successful cephalopods are at changing their skin texture, so we studied and drew inspiration from the muscles that allow cephalopods to control their texture and implemented these ideas into a method for controlling the shape of soft, stretchable materials.”

The material could be morphed to reflect light in its 2D spaces and absorb light in its 3D shapes. “That would have applications in any situation where you want to manipulate the temperature of a material,” Hanlon says.

The team published the report on its controllable soft actuator in the October 13 issue of Science.

The unique skills and abilities of the humble octopus are inspiring a number of biomimetic innovations. The field of robotics in particular is drawing inspiration from the creature, such as studying the highly effective propulsion methods of the octopus in order to make underwater drones faster and analysing octopus tentacles to create a more flexible robot arm that is able to perform keyhole surgery more dextrously.

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