Scientists from Harvard University and the Marine Biological Laboratory (MBL) now believe that bioinspired human camouflage and color-shifting products could be invented by exploiting some of the capabilities of cuttlefish (Sepia officinalis) – small, marine animals that belong to the Cephalopoda class.
Despite their name, cuttlefish are actually mollusks, possessing eight arms and two tentacles that are lined with suckers. It also has three hearts, responsible for circulating its blue-green blood, and a unique, doughnut-shaped brain. The creature is highly intelligent, with a surprisingly complex brain; of all the invertebrates, the cuttlefish has one of the largest brain-to-body size ratios identified.
Known as the “chameleon of the sea,” the cuttlefish can quickly change both its skin color, pattern and shape, at will. This helps cuttlefish to produce a deimatic display to temporarily distract any potential predators, thereby allowing them to evade danger, or to scare off possible threats. In addition, this ability enables the cuttlefish to mimic its surroundings, as well as communicate with fellow cuttlefish.
The latest research findings were published in the Journal of the Royal Society Interface, entitled The Structure-Function Relationships of a Natural Nanoscale Photonic Device in Cuttlefish Chromatophores. Researchers from Harvard-MBL reported new details on the intricate biomolecular nanophotonic system that facilitates the cuttlefish’s camouflaging abilities.
Kevin Kit Parker, a professor at Harvard School of Engineering and Applied Sciences (SEAS), and a member at the Wyss Institute for Biologically Inspired Engineering, states that the mystery of adaptive camouflage has long been solved. However, today’s challenge lies in reverse-engineering such a system to develop an economically viable, synthetic system, “… amenable to mass manufacturing.” Just some of the applications include military camouflage and use in materials for a variety of consumer products, including cosmetics and electronics.
How Cuttlefish Achieve Adaptive Camouflage
The cuttlefish’s color-shifting function is created by clusters of chromatophores – pigment-containing, light-reflecting organelles that are found at the cellular level. Chromatophores have been discovered in a wide array of animals, including amphibians, cephalopods, crustaceans, reptiles and even bacteria. In cuttlefish, the neurally-regulated chromatophores ensure the creatures can change their appearance, based upon the visual clues around them.
To achieve this, three optical components are arranged in a series of layers, consisting of leucophores, iridophores and chromatophores. The leucophore contains crystalline purines that are used to reflect light, uniformly, over the entire visible spectrum. Meanwhile, iridophore cells (a.k.a. guanophores) boast sacs of reflective plates that can cause an optical effect, known as Rayleigh scattering, and emit blue or green colors.
According to coauthor Leila F. Deravi, a researcher in bioengineering at Harvard SEAS, this stratification enables the skin of the cuttlefish to selectively absorb or reflect different wavelengths of light. Based upon the team’s new research, Deravi claims that chromatophores should no longer be regarded as mere selective color filters. Instead, she claims their results show that they contain “luminescent protein nanostructures,” ensuring the organism can make quick and complex changes to its skin pigmentation.
Each chromatophore expands when the cuttlefish needs to make changes to their appearance, with the surface area increasing up to 500 percent. The team demonstrated the presence of tethered pigment granules that regulated their appearance though absorbance, fluorescence and reflection. Professor Evelyn Hu, who coauthored the latest paper, indicates that cuttlefish have an incredibly ingenious means of changing appearance – one that has yet to be replicated in manufactured displays and represents a considerable challenge for engineers to replicate:
“… 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.”
Based upon the afore-mentioned findings, the team refutes previous suggestions that cephalopod chromatophores are composed solely of visual pigments. Instead, perturbations to granular architecture helps to change the optical properties, highlighting a role for nanostructure in the optical response of chromatophores.
Roger Hanlon and colleagues from the Marine Biological Laboratory in Woods Hole, Massachusetts, also participated in the latest research. Hanlon believes that unlocking the mysteries of the interplay between each of the cuttlefish’s pigments and reflectors is key to applying the color actuation principles to science and engineering. He explains that the study has yielded intriguing information about the tethering of the individual pigment granules, which could be of future benefit.
Meanwhile, Parker – a Army reservist who was called to Afghanistan on two occasions – recently discussed some of the more controversial applications of the research team’s latest cuttlefish study:
“Throughout history, people have dreamed of having an ‘invisible suit’… Nature solved that problem, and now it’s up to us to replicate this genius so, like the cuttlefish, we can avoid our predators.”
By James Fenner