In the quest to develop implantable electronics to monitor the human body from within, flexibility and stretchability have been major hurdles. We’ve seen numerous developments including stretchable LED arrays, an implantable device for measuring the heart’s electrical output, and an electrode array that melts onto the surface of the brain. Now researchers have developed technology that combines a porous polymer and liquid metal that allows electronics to bend and stretch to more than 200 percent their original size.

While Yonggang Huang, Joseph Cummings Professor of Civil and Environmental Engineering and Mechanical Engineering at Northwestern University, and collaborators at the University of Illinois had previously developed electronics offering high stretchability and twistability, they still weren't stretchy enough for many applications. Although the circuits made from solid metals that are currently on the market can withstand a small amount of stretch, their conductivity plummets when they are stretched significant amounts.

“With current technology, electronics are able to stretch a small amount, but many potential applications require a device to stretch like a rubber band,” said Huang, who conducted this latest research with partners at the Korea Advanced Institute of Science and Technology (South Korea), Dalian University of Technology (China), and the University of Illinois at Urbana-Champaign. “With that level of stretchability we could see medical devices integrated into the human body.”

To overcome the conductivity problem, Huang’s team created a highly porous three-dimensional structure using poly(dimethylsiloxane) (PDMS), a polymer material that can stretch to three times its original size. They then placed a liquid metal (EGaIn) inside the pores that allowed electricity to flow consistently through the material, even when stretched excessively.

“By combining a liquid metal in a porous polymer, we achieved 200 percent stretchability in a material that does not suffer from stretch,” Huang said. “Once you achieve that technology, any electronic can behave like a rubber band.”

As well as flexible and stretchable medical devices that can be implanted inside the human body, the technology could also free consumer electronics manufacturers from the rigid designs we’re used to. The technology could pave the way for bendable consumer electronic devices, such as laptops, smartphones and tablets.

A paper on the “rubber-band electronics” technology appears in the journal Nature Communications.