Chameleon-inspired stretchable e-skin changes color when touched

September 14, 2015 by Lisa Zyga feature
The chameleon-inspired e-skin’s two main components are a pressure-sensitive polymer (“pyramid layer”) and an electrochromic polymer. At bottom left, the two chemical structures of the electrochromic polymer are shown that emit red and blue light, respectively. (Ambanja panther chameleon and hand images from 123rf.com) Credit: Chou, et al. ©2015 Macmillan Publishers Limited

(Phys.org)—Researchers at Stanford University have fabricated a stretchable, color-changing, pressure-sensitive material–basically the closest thing yet to an artificial chameleon skin. Touching the new electronic skin (e-skin) with varying amounts of pressure causes it to change colors, as the pressure indirectly alters the chemical structure, and subsequently the optical properties, of the "electrochromic" material. The e-skin could have applications in interactive wearable devices, artificial prosthetics, and smart robots.

Previously, similar materials have been fabricated that can change color, and a few of these are even touch-sensitive, but so far none has also been stretchable. The new e-skin combines all three of these properties for the first time.

"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 along with the applied pressure duration," Ho-Hsiu Chou of Stanford University, who is first author of the study, told Phys.org. "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 main components: a stretchable microstructured that can modify its voltage upon an applied pressure, and a stretchable electrochromic polymer that can be either red or blue, depending on the applied voltage.

The researchers demonstrated how the e-skin works by using an item not commonly found in most engineering labs: a teddy bear. They attached the pressure-sensitive polymer to the bear's paw, and connected it to the electrochromic polymer which they mounted on the bear's 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. Once the handshake is removed, the polymer again turns red, but a stronger handshake (about 200 kPa) causes it to turn pale blue.

What's happening, as the researchers explain, is a multi-step process that ultimately changes the chemical structure of the electrochromic polymer into a different chemical structure that emits light at a different wavelength, or color. Pressure from the handshake causes a drop in the electrical resistance of the pressure-sensitive polymer (which is connected to a low-voltage power supply) by up to several orders of magnitude. The drop in resistance increases the voltage to the electrochromic polymer and oxidizes the material, slightly altering its . Although the structural change is small, it causes a large change in the material's light absorption spectrum, which can be quickly reversed by releasing the pressure.

When attached to a teddy bear, the e-skin changes color upon a handshake, since the pressure-sensitive polymer is attached to the paw. Credit: Chou, et al. ©2015 Macmillan Publishers Limited

While the electrochromic polymer used here can only switch between shades of red and blue, the researchers expect that other electrochromic polymers can be designed to exhibit a wide range of colors that can be modulated by various pressures. This could lead to a wide variety of applications.

"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 ," 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.

"Because the e-skin's color change can also be in turn utilized to distinguish and quantify the magnitude of pressure we applied, the other potential application is that we can integrate the system into any surface where we want to know the magnitude of pressure applied on it. Also, the e-skin can provide the camouflage function for prosthetics and . In addition, the stretchable system allows it to attach on curvilinear or dynamic surfaces well, while conventional rigid devices cannot. This advantage can reduce the interface between the device and human body."

As the e-skin has the potential to find use in a wide variety of consumer applications, the researchers addressed the fact that the material contains carbon nanotubes, which have raised concerns about toxicity and carcinogenicity because they have similar shapes as asbestos. Here, the carbon nanotubes are sprayed onto the pressure-sensitive polymer and play an important role in controlling the resistance response to pressure. Fortunately, the carbon nanotubes used here are relatively short and small in diameter, whereas studies have shown that longer and thicker carbon nanotubes induce more DNA damage and inflammation. Still, the researchers recommend that the system be encapsulated in stretchable materials, such as silicone, as a safety precaution.

"Another important target is to make the whole system biodegradable since the device is applied on the human," Chou said.

Explore further: Bridging sensory gap between artificial and real skin

More information: Ho-Hsiu Chou, et al. "A chameleon-inspired stretchable electronic skin with interactive colour changing controlled by tactile sensing." Nature Communications. DOI: 10.1038/ncomms9011

Related Stories

Bridging sensory gap between artificial and real skin

December 10, 2014

"Smart" prosthetics still has a long road ahead. In the human, skin-based mechanoreceptors and thermoreceptors gather information streams from the environment but it is not so easy to create artificial skin for people in ...

UCLA engineers create fully stretchable OLED

August 27, 2011

(PhysOrg.com) -- Engineers at the University of California, Los Angeles, have created the first fully stretchable organic light-emitting diode (OLED). The researchers devised a way of creating a carbon nanotube and polymer ...

Recommended for you

Scientific advances can make it easier to recycle plastics

November 17, 2017

Most of the 150 million tons of plastics produced around the world every year end up in landfills, the oceans and elsewhere. Less than 9 percent of plastics are recycled in the United States, rising to about 30 percent in ...

The spliceosome—now available in high definition

November 17, 2017

UCLA researchers have solved the high-resolution structure of a massive cellular machine, the spliceosome, filling the last major gap in our understanding of the RNA splicing process that was previously unclear.

Ionic 'solar cell' could provide on-demand water desalination

November 15, 2017

Modern solar cells, which use energy from light to generate electrons and holes that are then transported out of semiconducting materials and into external circuits for human use, have existed in one form or another for over ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.