‘Artificial muscle’ changes colour like octopus skin

Engineers from Rutgers University have developed a 3D-printed smart gel that changes shape when exposed to light and can be utilised as a colour-changing “artificial muscle”.

 The smart gel is inspired by the ability of cephalopods such as octopuses, squid and cuttlefish to change the colour and texture of their skins for camouflage and communication.

In nature, this is achieved via thousands of pigmented skin cells called chromatophores. In order to change the optical properties of these cells, cephalopods distort the elastic sac containing pigment through the contraction of radial muscles enclosing it; this renders the colour more visible. Chromatophores actuating individually can give rise to complex colour patterns on their skin.

The new cephalopod-inspired smart gel is a 3D-printable hydrogel which senses light and changes shape as a result. Hydrogels keep their shape and stay solid despite containing water; they are found in the human body as well as in jelly, contact lenses, menstrual pads, breast implants and nappies.

The engineers incorporated a light-sensing nanomaterial into the hydrogel, transforming it into an artificial muscle which contracts in response to changes in light. This gel – combined with a 3D-printed stretchy material that reveals colours when light changes – changes colour, resulting in the projection of different light patterns.

The engineers hope that these developments could lead to new military camouflage, biophotonic devices, soft robotics and flexible displays.

“Electronic displays are everywhere and despite remarkable advances, such as becoming thinner, larger, and brighter, they’re based on rigid materials, limiting the shapes they can take and how they interface with 3D surfaces,” said Professor Howon Lee, from Rutgers University’s department of mechanical and aerospace engineering. “Our research supports a new engineering approach featuring camouflage that can be added to soft materials and create flexible, colourful displays.”

The next steps for Lee and his colleagues will include boosting the sensitivity, response time, scalability, packaging, and durability of the artificial muscle.