Squid-inspired material 'first step' towards military bio-stealth tech
A squid-inspired infrared camouflage could one day help soldiers escape detection on night-time missions.
The stealthy substance, created from a protein called reflectin, can be dynamically retuned to different wavelengths of light, allowing a hypothetical wearer to choose what types of light to reflect or absorb.
"This tenability allows our films to reversibly disappear and reappear when visualised with an infrared imaging camera," write the University of California Irvine team behind the research, in a paper published in .
Squids and octopi, collectively described by the term cephalopods, have been investigated for some time by researchers interested in their incredible camouflaging abilities. Take for example this video of an octopus turning white after being tossed inside a boat of the same colour.
Mimicking their abilities could give militaries the edge when it comes to stealth technology -- indeed in 2009 the US Office for Naval Researchawarded millions of dollars to Duke University for research into squid and octopus camouflage.
One piece of the puzzle is the way the cells are structured on their skin. The way they layer skin cells allows for something called structural colour, which is when colour does not arise out of a property of a cell itself, like the pigmentation in humans, but rather colour arises from the way light refracts when it hits the surface.
In the longfin inshore squid examined in the paper, layers of high refractive index (meaning light travels slowly) cells are separated by layers of low refractive index empty space -- by alternating the distance between layers of cells, the squid is able to retune which wavelengths of light it reflects and therefore change its colour.
To mimic this ability, the researchers took the protein found in those high refractive index cells, reflectin, and grew it in a bacteria culture. They then placed the resulting protein film on top of thin films of graphene oxide and silicon dioxide.
By applying either water vapour or an acid solution, they were able to swell the proteins on the film, which altered the wavelengths of light the film reflected, allowing the researches to "tune" the film.
The wavelength range of the film was found to be between 400nm and 1200nm, well within the range of infrared imaging equipment, which functions in the range 700nm to 1200nm.
This experimental research is of course a long way from being used in the field, but in the paper the authors argue that it represents "a crucial first step" towards developing new bio-inspired stealth technology.