The chameleonic cuttlefish acted as a model for a group of scientists to design colour changing materials. (Photo: Dwayne Meadows, NOAA/NMFS/OPR)
Scientists learn camouflage techniques from cuttlefish
Friday, September 14, 2012, 23:20 (GMT + 9)
Engineers at the University of Bristol in the UK have created soft materials that mimic the cuttlefish’s colour-changing skin, leading to the design of “smart clothing,” which would take camouflage to a new level.
What allows the cuttlefish to blend into nearly any background – whether it is by turning a light tan when swimming along the sandy seafloor or displaying crude black and white squares on its skin when placed in a tank with a black-and-white checkerboard pattern – are millions of specialised cells packed under its skin called chromatophores. These contain miniature sacs full of black, brown, yellow or other coloured pigment.
As the cuttlefish’s brain instructs the skin to change colour, muscles surrounding the sacs quickly contract, stretching the sacs and letting the pigment inside extend across a larger surface area, thus changing the colour and pattern of the skin. Cuttlefish are able to transform in this way at lightning speed to evade predators, sneak up on prey or attract mates.
Engineers Jonathan Rossiter and Andrew Conn attempted to replicate this process by creating artificial chromatophores out of small devices called dielectric elastomer actuators (DEA), which consist of a thin, rubberised membrane positioned between two flexible electrodes connected to a power supply. When the power is turned on, the electrodes take on opposite charges, attract each other and squeeze the rubber membrane, BBC reports.
To allow for a colour-changing effect, Rossiter and Conn built a clear “artificial skin” studded with circular DEAs, each of which carried a thin disc of black rubber placed between two circular electrodes. When the power is turned on, the electrodes squash the black membranes, which then expand in surface area.
“You have a small spot, and you apply electricity and it becomes a big spot,” Rossiter said.
By expanding all these black spots simultaneously, it looks like the skin is suddenly darkening. The change happens within “tens of milliseconds.”
The researchers also tried to model a second colour-changing animal: the zebrafish, which can make itself appear darker thanks to cells known as melanophores, which contain reservoirs of black fluid. Muscle contractions pump this fluid to the skin’s surface, where the liquid spreads out and darkens the fish.
As this process is triggered by hormones and not directly by the brain, it takes longer than it does in cuttlefish. In the engineers’ experiment with an artificial ink cell, it took a few seconds to achieve a camouflage effect.
Rossiter said the next step is to refine the bio-inspired chromataphores and to network increasing amounts of them together.
“We’ll put these things together to produce larger arrays and at the same time we’ll miniaturise them,” he said.
By layering different chromatophores and pigment cells, the team was able to create a soft material that could realize various sophisticated effects, such as multiple colour changes and moving patterns that appear to flow across the fabric.
Such colour-changing materials could be used in the military – but also to make ourselves more conspicuous while biking in traffic, for example.
By Natalia Real