Camouflaged membrane invented that hides like an octopus
No other animal has mastered camouflage like the octopus. The mightiest of these morphing creatures, the mimic octopus, contorts its body into a thin ribbon and adopts the colors of a venomous sea serpent to scare predators away. Divers have seen mimic octopuses masquerade as lion fish, sea stars, shrimp and anemones. When peckish, the octopus takes the form of a lusty crab. Crustaceans fooled by the display end up eaten.
Materials scientists and engineers also have fallen under the octopuses' spell. A team of Cornell University researchers, with the aid of octopus expert Roger Hanlon, successfully mimicked the mimic using sheets of rubber and mesh.
As they report in a study published Thursday in the journal Science, the researchers created a thin membrane that contorts into complex 3-D shapes - much like the shape-shifting skin of an octopus. The membranes can inflate in seconds to the shapes of everyday objects, such as potted plants or a cluster of stones.
Octopuses are covered in muscly bundles called papillae, Hanlon and his colleagues documented in the Journal of Morphology in 2014. The papillae go slack when an octopus wants to decrease the drag of water against skin, allowing it to speed away in a hurry. Contractions cause fleshy nubs to appear, and the skin bulges. Octopuses can match the texture of seaweed so closely they become almost invisible.
Itai Cohen, a materials expert at Cornell and an author of the new study, said he was awed by videos of the shape-shifters.
He and fellow Cornell researcher Robert Shepherd assigned James Pikul the grunt work of figuring it out.
"For a few decades, scientists and engineers have been trying to control the shape of soft, stretchable materials," said Pikul, a graduate student at the time of this research and now an assistant professor at the University of Pennsylvania.
But cheaply fabricating these materials proved difficult.
Success brought together two concepts: the musculature of the octopus with the mechanics of blowing up a balloon. The trick was to cut concentric rings into a thin surface of silicone rubber and mesh. Inflating the rubber caused the membrane to contort following the shape of the cuts.
Programming the laser cuts in just the right way enabled the rubber to inflate not only outwardly, like a kickball, but as a 3-D structure with concave regions. It's a bit like the sculptures made by twisting together sausageshaped balloons.
Except, in this case, it's all one membrane.