[ Watch the Video: What Mechanisms Are Behind Cuttlefish Camouflage? ]
Brett Smith for redOrbit.com – Your Universe Online
Capable of producing zebra-like camouflage or ‘hypnotic’ color oscillations, the skin of the cuttlefish has long fascinated scientists looking to unlock its secrets. Now, a new study from Harvard University has revealed a natural nanoscale photonic device that allows the so-called ‘chameleon of the sea’ to dynamically change its colors.
“Nature solved the riddle of adaptive camouflage a long time ago,” said study author Kevin Kit Parker, a professor of bioengineering and applied physics at the Harvard. “Now the challenge is to reverse-engineer this system in a cost-efficient, synthetic system that is amenable to mass manufacturing.”
By using pigmented organs called chromatophores, the cephalopod can change the look of its skin in response to visual stimuli. Scientists have been unable to understand the biological, chemical, and optical mechanics behind this adaptive coloration.
To change skin color, the cuttlefish uses a system of vertically arranged optical components: the leucophore, a light scatterer that spreads light evenly over the visible spectrum; the iridophore, a reflector made from thin films; and the chromatophore. This layered system allows the cuttlefish skin to selectively absorb or reflect light of different colors, the researchers said.
“Chromatophores were previously considered to be pigmentary organs that acted simply as selective color filters,” said study author Leila F. Deravi, a research associate in bioengineering at Harvard. “But our results suggest that they play a more complex role; they contain luminescent protein nanostructures that enable the cuttlefish to make quick and elaborate changes in its skin pigmentation.”
When the cuttlefish changes its skin color, each chromatophore expands – changing the surface area of each by as much as 500 percent. In the new study, which was published in the Journal of the Royal Society Interface, researchers revealed that fully-expanded chromatophore has two factors related to maintaining skin color intensity: the presence of certain proteins – reflectin and crystallin – in pigment granules and pigment layers as thin as three granules that maintain optical effectiveness – effectively functioning as nanoscale photonic elements.
“The cuttlefish uses an ingenious approach to materials composition and structure, one that we have never employed in our engineered displays,” said co-author Evelyn Hu, a professor of applied physics and of electrical engineering at Harvard.
“It is extremely challenging for us to replicate the mechanisms that the cuttlefish uses,” she added. “For example, we cannot yet engineer materials that have the elasticity to expand 500 times in surface area. And were we able to do so, the richness of color of the expanded and unexpanded material would be dramatically different – think of stretching and shrinking a balloon.”
“The cuttlefish may have found a way to compensate for this change in richness of color by being an ‘active’ light emitter (fluorescent), not simply modulating light through passive reflection,” Hu said.
By studying the cuttlefish skin, the researchers say they hope to engineer new types of military camouflage.
“Throughout history, people have dreamed of having an ‘invisible suit,'” said Parker, an Army reservist who completed two tours of duty in Afghanistan. “Nature solved that problem, and now it’s up to us to replicate this genius so, like the cuttlefish, we can avoid our predators.”