To develop the artificial muscles, Rossiter and his colleagues looked at several biological mechanisms responsible for color-shifting in cuttlefish, squid and octopus.
In cephalopods, like cuttlefish and squid, sacs on the surface of the skin that are filled with dark, granular particles help the animals change color. When the muscles surrounding each sac contract, they stretch the sacs and create much larger dark spots. The color change happens fast, although the area of the color is limited by how far the skin can stretch.
"The cephalopod looks at its environment to decide on an appropriate body pattern," explained Lydia Mäthger, a marine biologist at Woods Hole, who is not a part of the Bristol team.
Mäthger explained that cells in the skin called chromatophores create the brown, red and yellow tones in body patterns, but cephalopods use other cells, like light reflectors, to create greens and blues.
In a separate family, the Zebrafish use a completely different mechanism to change the color of their skin. They have a reservoir of dark liquid several layers under their skin. They squeeze their muscles and that squeezes the liquid up to the surface, changing the color of their skin.