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19 February, 2018 - 13:59 By Tony Quested

Cambridge research aids push for invisibility cloak to protect military aircraft

Cambridge scientists may have helped advance the US Air Force’s search for a Star Trek-style invisibility cloak to help protect military aircraft.

University of Cambridge personnel were part of an international research team that discovered how cephalopods like cuttlefish were able to change their skin and make themselves invisible.

UK and US partners in the research believe this could lead to the development of new classes of soft materials that can be engineered for a wide array of uses in industry, society, and medicine.

The research was largely funded by the US Air Force Office of Scientific Research and the UK Biotechnology and Biological Sciences Research Council.

It was only last year that the chief of the US Air Force’s Air Mobility Command, General Carlton Everhart, urged Silicon Valley technology companies, specialists at the Pentagon’s innovation office and the defence industry in general to find ways of cloaking airborne military jets.

The researchers involved in the latest study say that understanding how cephalopods’ skin changes from a smooth, flat surface to a textured, 3D structure could help in the design of biologically-inspired materials that can themselves be assembled from flat materials.

Professor Roger Hanlon of the Marine Biological Laboratory in Massachusetts said: “This research on neural control of flexible skin, combined with anatomical studies of the novel muscle groups that enable such shape-shifting skin, has applications for the development of new classes of soft materials that can be engineered for a wide array of uses in industry, society, and medicine.

The international team of scientists identified the neural circuits that enable cuttlefish to change their appearance in just the blink of an eye – and discovered that this is similar to the neural circuit that controls iridescence in squids.

Cuttlefish and octopuses can change their appearance in a matter of seconds, camouflaging themselves from predators and enabling them to surprise their prey.

But unlike a number of reptiles and amphibians which merely change colour to blend into their surroundings, these cephalopods are also able to change the physical texture of their skin to match the coarseness of surrounding rocks, coral or seaweed.

Dr Trevor Wardill from the Department of Physiology, Development and Neuroscience at the University of Cambridge, said: “The sea is full of strange and wondrous creatures, but there are few as bizarre and intelligent as octopuses and cuttlefish.

“We’ve seen dozens of examples of these animals suddenly appearing from nowhere, as if they have thrown off an invisibility cloak. How they do this has long remained a mystery.”

The skin of these animals is covered in tiny muscular organs known as ‘chromatophores’ that change colour in response to a signal from the brain. It also has a second set of muscular organs that can be activated to create bumps known as ‘papillae’. When stimulated, each papilla can change the texture of the skin from flat to three dimensional. The papillae can serve several functions, including disguise.

Understanding the nervous system of these creatures and how they manipulate their skin has proved challenging, but scientists from the Marine Biological Laboratory and University of Cambridge now understand how this happens. 

The researchers found that the instruction signal from the cuttlefish’s brain is routed through the stellate ganglion, a peripheral nerve centre. The stellate ganglion houses the giant axon system, so called because it is large enough to see with the naked eye.

It also houses particular motor neurons that control the papillae on the mantle (the cuttlefish’s outer surface). This nerve circuitry is similar to that by which squids control skin iridescence.

The giant axon system, due to its large size of up to 1mm, helped Nobel prize-winning Cambridge scientists Alan Hodgkin and Andrew Huxley, along with Australian scientist John Eccles, figure out how nerve impulses (action potentials) work.

The researcher team also looked in greater detail at the papillae to find out how they manage to hold their shape over a long period of time without a signal. 

They found that the papillae use a mechanism which they describe as being ‘catch-like’. It resembles the ‘catch’ mechanism found in bivalves, such as oysters, mussels, and scallops, which enables the bivalve shell to remain closed without expending much energy.

• Picture credit: Lakshmi Sawitri via Wikimedia Commons

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