They've made electronics that can bend. They've made electronics that can stretch. And, now, they've made electronics that can be subjected to any complex deformation, including twisting.

Professors Yonggang Huang (Northwestern University's McCormick School of Engineering and Applied Science) and John Rogers (University of Illinois at Urbana-Champaign), have improved their “pop-up” technology to create circuits that can be twisted. Such electronics could be used in places where flat, unbending electronics would fail, like the human body.

Their research appeared in the Proceedings of the National Academy of Sciences and is available for purchase at pnas.org. Electronic components historically have been flat and unbendable because silicon, the principal component of all electronics, is brittle and inflexible. Any significant bending or stretching renders an electronic device useless.

Huang and Rogers developed a method to fabricate stretchable electronics that increases the stretching range (as much as 140%) and allows the user to subject circuits to extreme twisting. The researchers expect the emerging technology to advance flexible sensors, transmitters, photovoltaic and microfluidic devices, and other applications, including wearable health monitors for temperature, pulse rate, and blood oximetry; cardiac monitors for locating and treating arrhythmias; and neural monitors for monitoring brain disorders, cognition, and possibly as a machine-human interface.

“Essentially, any time one wants to integrate electronics or sensors with the human body, one needs the system to be soft and tissue-like, in a mechanical sense,” says Huang.

The partnership — Huang focuses on theory and Rogers focuses on experiments — has resulted in a one-dimensional, stretchable form of single-crystal silicon that can be stretched in one direction without altering its electrical properties. They've also made stretchable integrated circuits. The results appeared in the journal, Science (sciencemag.org), published by the American Association for the Advancement of Science.

The researchers went on to develop a technology that allowed circuits to be placed on a curved surface. That technology uses an array of circuit elements approximately 100 micrometers square and connected by metal “pop-up bridges.” The circuit elements are so small that when placed on a curved surface, they don't bend; similar to how buildings don't bend on the Earth's curved surface. The system works because these elements were connected by metal wires that popped up when bent or stretched. The research was a cover article in Nature (nature.com).

In the research reported in PNAS, Huang and Rogers took their pop-up bridges and made them into an “S” shape, which, in addition to bending and stretching, have enough give that they can be twisted.

“For a lot of applications related to the human body - like placing a sensor on the body - an electronic device needs not only to bend and stretch but also to twist,” says Huang. “So we improved our pop-up technology to accommodate this. Now it can accommodate any deformation.”

Huang and Rogers are now focusing their research on another important application of this technology - solar panels. The pair published a cover article in Nature Materials (nature.com/materials) describing a new process of creating very thin silicon solar cells that can be combined in flexible and transparent arrays.

The work on twistable electronics was supported by the National Science Foundation and the U.S. Department of Energy.