For the octopus and cuttlefish, instantaneously changing their skin color and pattern to disappear into the environment is just part of their camouflage prowess. These animals can also swiftly and reversibly morph their skin into a textured, 3-D surface, giving the animal a ragged outline that mimics seaweed, coral or other objects it detects and uses for camouflage.
This week, engineers at Cornell University report on their invention of stretchable surfaces with programmable 3-D texture morphing, a synthetic “camouflaging skin” inspired by studying and modeling the real thing in octopus and cuttlefish. The engineers, along with collaborator and cephalopod biologist Roger Hanlon of the Marine Biological Laboratory, report on their controllable soft actuator in the Oct. 13 issue of Science.
Led by James Pikul and Rob Shepherd, the team’s pneumatically activated material takes a cue from the 3-D bumps, or papillae, that cephalopods can express in one-fifth of a second for camouflage, and then retract to swim away with minimal hydrodynamic drag.
A live Octopus rebescens expressing its skin papillae. (Copyright Grayson Hanlon)
“Lots of animals have papillae, but they can’t extend and retract them instantaneously as octopus and cuttlefish do,” said 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.”
Papillae are examples of a muscular hydrostat, biological structures consisting 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 3-D papillae in detail.
“The development of this material is an excellent example of the applications that can derive from studying the fundamental biology of marine organisms,” said MBL Director of Research David Mark Welch.
“The degrees of freedom in the papillae system are really beautiful,” Hanlon said. “In the European cuttlefish, at least nine sets of papillae are independently controlled by the brain. And each papilla goes from a flat, 2-D surface through a continuum of shapes until it reaches its final shape, which can be conical or one of a dozen possible shapes. It depends on how the muscles in the hydrostat are arranged.”