Octopus Inspired Camouflage

Researchers have produced a sheet material which
can change colour selectively on demand.

The new design features a grid of 1mm2 cells, containing a thermochromic temperature-driven dye that switches colour on demand. Currently the work which appeared in the journal PNAS responds in black-and-white, but the team hopes that the principles of their design can be extended and that it will have important future applications.

Author Prof. John Rogers, from the University of Illinois, said the new sheet was the fruit of a collaboration between experts in biology, materials, computing and electrical engineering. "Animals in the natural world - particularly cephalopods -octopus, squid and cuttlefish - have really spectacular colour-changing capabilities."

Artificial systems that replicate functional attributes of the skins of cephalopods could offer capabilities in visual appearance modulation with potential utility in consumer, industrial, and military applications. Here the team has demonstrated a complete set of materials, components, fabrication approaches, integration schemes, bio-inspired designs and coordinated operational modes for adaptive optoelectronic camouflage sheets.

Prof. Rogers' team set out to see what could be learned from such natural examples and build a new material based on those insights.

Octopuses, known for their camouflage abilities, use
a special three-layered skin

The flexible material contains 1mm square
colour-changing cells, enabling the material to sense
and adapt its colours akin to the camouflage used
in the 1987 movie Predator.

In particular, they copied the three-layer design seen in the skin of octopuses: the top layer contains the colours, the middle layer drives the colour changes, and the lower layer senses the background patterns to be copied. Each component in the new sheets, however, does its job quite differently from the three layers that do the same job in an octopus's skin.

The bottom layer in the engineered system contains a grid of photo sensors, which detect changes in light and transmit that pattern to "actuators" in the layer above.

These actuators take the place of muscles within octopus skin, which control colour-changing organs in the surface layer.

When the background changes, the cells within the material switch colour within one or two seconds.

The uppermost layer in the artificial version uses a temperature-sensitive pigment, which goes from black to transparent at precisely 47C. That temperature change has to be produced by a current from the actuators underneath.

In particular, the system needs to improve its spatial and colour resolution, and its efficiency - possibly by incorporating solar cells instead of using external power. This could all be done by adapting existing technology, Prof Rogers said, such as that seen in flat-screen displays. In time, this technology could lead the way to producing special 'Ghillie suits' which are able to render an operator invisible.

With an emphasis on biologically inspired engineering, then this research is an interesting indicator of things to come.