Chameleon-inspired stretchable e-skin could give robots the camouflage they need

Developed by experts at Stanford University, a new electric skin (e-skin) has a fabricated stretchable, color-changing, pressure-sensitive material, that is the closest we have seen to an artificial chameleon skin.

Applying varying amounts of pressure to the skin causes it to change colors, as the pressure indirectly alters the chemical structure and optical properties of the “electrochromic” material. The e-skin is intended to make use in interactive wearable devices, artificial prosthetics, and smart robots.

Prior to the e-skin introduction, other materials have been created that can change color, and few have been touch-sensitive, but this is the first to be extremely stretchable. For the first time, this new skin combines all three of these properties.

“We show an all-solution processed chameleon-inspired stretchable electronic skin (e-skin), in which the e-skin color can easily be controlled through varying the applied pressure along with the applied pressure duration,” Ho-Hsiu Chou of Stanford University, who is first author of the study said. “As such, the e-skin's color change can also in turn be utilized to distinguish the pressure applied.”

The e-skin consists of two components: a stretchable micro-structured pressure-sensitive polymer, and a stretchable electrochromic polymer that can emit either red or blue, depending on the applied voltage.

To demonstrate how the e-skin works, the researchers tested it on a teddy bear by attaching the pressure-sensitive polymer to its paw and connecting that to the electrochromic polymer, mounted to its abdomen. The electrochromic polymer first appears red, but after giving the bear a weak handshake (about 50 kilopascals [kPa] of pressure) it turns blue-gray. Removing the handshake causes it to turn red again, and when a stronger handshake is applied (about 200 kPa), it turns pale blue.

“The e-skin can potentially be integrated into the things that we wear and carry, i.e., clothes, smart phones, smart watches, and any other kind of wearable devices,” Chou said. “By integrating with this color-changeable e-skin, you can imagine that all the colors can be integrated into one device, and the user can change it interactively for decoration or to express emotion. Also, the e-skin can provide the camouflage function for prosthetics and smart robots.

In addition, the stretchable system allows the skin to attach on curvilinear or dynamic surfaces, while conventional rigid devices cannot — an advantage that may reduce the interface between the device and human body.”

While the technology is still experimental, it may be able to help us control how smart exoskeletons and robots handle, grip, or press objects, and since it is so stretchy, it would allow us to wrap the e-skin over irregular surfaces.

Via Phys.org