If you’ve ever watched a cephalopod such as a squid changing color, then you’ll know that it’s a pretty amazing process – they can instantly change the appearance of their skin from dark to light and back again, or even create pulsating bands of color that travel across it. They are able to do this thanks to muscles that manipulate the pigmentation of their skin. Now, scientists from the University of Bristol have succeeded in creating artificial muscles and cells, that might someday allow for the same sort of color changes in smart clothing that can camouflage itself against different backgrounds.

The color-changing muscles of squids – along with various fish, reptiles and amphibians – work in unison with specialized cells known as chromatophores. In squids, each of these cells contains a sac, filled with granules of pigment. When the muscles surrounding a chromatophore contract, that colored sac expands, causing it to appear larger to an observer.

Zebrafish, another color-changing animal, take a slightly different approach. Their chromatophores contain a reservoir of liquid pigmentation. When activated, that liquid is pumped through to the skin, where it spreads out like ink.

The U Bristol researchers used dielectric elastomers – soft, stretchy electrically-activated polymers – to create man-made equivalents of both of these systems.

When an electrical current is applied to them, the elastomers themselves expand, creating the same illusion as a squid’s expanding pigment sac. As soon as the current is shut off, they return to their regular state.

The squid-like expanding elastomers

To replicate the zebrafish’s process, an artificial cell was created by sandwiching a silicone bladder between two glass microscope slides. Dielectric elastomers were used to create two pumps, one located on either side of the bladder, and connected to it with silicone tubes. One of those pumps is able to send opaque white spirit into the bladder, while the other can pump in a mixture of black ink and water. By alternately activating the two muscle-pumps with an electrical current, the white and black “pigmentations” can displace one another within the bladder, causing it to appear all-white, all-black, or somewhere in between.

The zebrafish-inspired artificial chromatophore

“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,” said project leader Jonathan Rossiter. “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.”

A paper on the research was published today in the journal Bioinspiration and Biomimetics.

The two types of artificial chromatophores can be seen in action in the video below.

Source: University of Bristol

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