Using smart materials to mimic squid and zebrafish camouflage

Inspired by extraordinary camouflaging abilities of organisms such as squid and zebrafish, a group of researchers from the University of Bristol have created artificial muscles that can change their state and appearance at the push of a button, and demonstrated two different transforming mechanisms that could lead to new clothes with camouflaging tricks analogous to those seen in nature.

“We have taken inspiration from nature’s designs and exploited the same methods to turn our artificial muscles into striking visual effects”, said Dr Jonathan Rossiter, Senior Lecturer in the Department of Engineering Mathematics.

The soft, stretchy, artificial muscles are based on chromatophores – specialist cells found in amphibians, fish, reptiles and cephalopods. These cells contain pigments of colors that are responsible for the animals’ remarkable color-changing effects. University of Bristol researchers decided to mimic two different mechanisms used by squids and zebrafishes.

A typical color-changing cell in a squid has a central sac containing granules of pigment. The sac is surrounded by a series of muscles and when the cell is ready to change color, the brain sends a signal to the muscles and they contract. The contracting muscles make the central sacs expand and create the optical effect which makes the squid look like it is changing color.

The researchers mimicked this effect with dielectric elastomers (DEs) – smart materials, usually made of a polymer, which are connected to an electric circuit and expand when a voltage is applied. They return to their original shape when they are short circuited.

On the other hand, the cells in the zebrafish contain a small reservoir of black pigmented fluid that, when activated, travels to the skin surface and spreads out. The natural dark spots on the surface of the zebrafish therefore appear to get bigger and the desired optical effect is achieved.

The zebrafish cells were mimicked using two glass microscope slides sandwiching a silicone layer. Two pumps, made from flexible DEs, were positioned on both sides of the slide and were connected to the central system with silicone tubes; one pumping opaque white spirit, the other a mixture of black ink and water.

“Our artificial chromatophores are both scalable and adaptable and can be made into an artificial compliant skin which can stretch and deform, yet still operate effectively. This means they can be used in many environments where conventional ‘hard’ technologies would be dangerous, for example at the physical interface with humans, such as smart clothing”, said Rossiter.

For more information, you can read the article published in journal Bioinspiration and Biomimetics: “Biomimetic chromatophores for camouflage and soft active surfaces”.

The lead author of the article is Dr Jonathan Rossiter, and his co-authors are Bryan Yap and Dr Andrew Conn, Lecturer in the Department of Mechanical Engineering.