Octopus skin yields bright discovery
Natural proteins act as super reflectors.
The molecules that make octopus skin so successful as a dynamic camouflage could provide materials scientists with a new way to make super-reflective materials.
Octopus, squid and cuttlefish have developed sophisticated skins so they can hide in an ocean full of hungry predators. Roger Hanlon at the Marine Biological Laboratory, Woods Hole, Massachusetts and colleagues took a close look at this skin and identified a new group of proteins with remarkable properties.
Hanlon's team discovered that the bottom layer of octopus skin, made up of cells called leucophores, is composed of a translucent, colourless, reflecting protein. "Protein reflectors are very odd in the animal kingdom," says Hanlon, who is a zoologist.
What's even more odd is just how reflective these proteins are they reflect all wavelengths of light that hit at any angle. "This is beautiful broadband reflection," Hanlon told the Materials Research Society at their meeting in Boston last month.
The result is a material that looks startlingly white in white light, and blue in the bluish light found beneath the waves. "These cells also match the intensity of the prevalent light," says Hanlon's research associate Lydia Mathger. All this helps the creatures to blend into their surroundings.
Closer inspection of a cuttlefish shows that some parts of the skin have enhanced reflective properties thanks to flat platelets called iridophores in the layer lying on top of the leucophores. In the brightest spots, the number of iridophores matches the number of leucophores one for one.
"The flat platelets are enhancing the brightness of the whiteness," Hanlon says. But just how they're doing that is unclear. "These are very complex 3-D cells," Hanlon says. They require further investigation, he says.
Ryan Kramer, at the Air Force Research Laboratory in Ohio, is investigating reflectin, the only known reflective protein that has been fully genetically sequenced. Hanlon's work does show that leucophores are proteins, says Kramer. Perhaps they are themselves a type of reflectin.
Once the proteins involved and their optical properties are fully understood, there could be applications far more diverse than simply mimicking an octopus's camouflage, says Hanlon. Better optical fibres could be made, for example, with super-reflective compounds.
Hanlon sees his discoveries as a call to arms for materials scientists to find applications for the bounty being discovered by zoologists. He's sure they'll find a use for it: after all, he says, the military is always interested in playing with light.
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