Engineers were inspired by animals like octopus which change their camouflage skin color and pattern to disappear. These animals can also reversibly morph their skin into a textured, 3D surface, other objects it detects and uses for camouflage.
A group of engineers at Cornell University along with collaborator and cephalopod biologist Roger Hanlon of the Marine Biological Laboratory (MBL) developed stretchable surfaces with programmable 3D texture morphing. A synthetic camouflaging skin studying and modeling the real thing in octopus and cuttlefish.
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Dynamic camouflage
James Pikul and Robert Shepherd, Led the team’s pneumatically-activated material takes a cue from the 3D bumps, or papillae. That cephalopods can express in one-fifth of a second for dynamic camouflage. Retract to swim away without the papillae imposing hydrodynamic drag. See video of live Octopus rubescens expressing skin papillae
“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 shell the primary defense is morphing skin.”
Papillae are examples of a muscular hydrostat. Biological structures that consist of muscle with no skeletal support such as the human tongue. Hanlon and members of his laboratory, including Justine Allen, now at Brown University, were the first to describe the structure, function, and biomechanics of these morphing 3D papillae in detail.
“The degrees of freedom in the papillae system are really beautiful,” Hanlon says. “In the European cuttlefish, at least nine sets of papillae 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 arranged.” The engineers’ breakthrough to develop synthetic tissue groupings that allow programmable, 2D stretchable materials to both extend and retract range of target 3D shapes.
Reflect light in its 2D spaces and absorb light in its 3D shapes.
Moreover, 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 lead author James Pikul. assistant professor at the University of Pennsylvania. “We driven 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. Implemented these ideas into a method for controlling the shape of soft, stretchable materials.”
“This is a classic example of bio-inspired engineering” with range of potential applications, Hanlon says. The material controllably 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,” he says.
Although, octopus and cuttlefish only express papillae for camouflage purposes, Hanlon says, and not for locomotion, sexual signaling, or aggression. For fast swimming, the animal would benefit from smooth skin. For sexual signaling, it wouldn’t want to look like a big old wart it wants to look attractive.
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However, if it wanted to conduct a fight, the papillae would not be a good visual to put into the fight. Signaling, by definition, has to be highly conspicuous, unambiguous signals. The papillae would only make it the opposite.
