Could a new conductive ink mean wearable electronics?


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Are wearable electronics the next big thing? Researchers at the University of Tokyo have developed a new kind of ink that can be printed on textiles to form a highly conductive and stretchable connection. Given the flexibility of the material, activity trackers, heart rate monitors and other gadgets might literally become part of your workout gear. The new ink will enable manufacturers of sportswear and underwear to incorporate sensing devices for measuring a range of biological indicators such as heart rate and muscle contraction.


Ink capability

Right now, electronics — such as transistors, LEDs and solar panels — can be printed on plastic or paper surfaces but these materials tend to be rigid. Using soft, stretchable materials would mean a new generation of wearable devices that fit comfortably on the human body. Until now, it has proved difficult to create an ink that is highly conductive as well as sufficiently stretchy without using a complicated multistep printing process.

But a research group at the University of Tokyo's Graduate School of Engineering led by Professor Takao Someya has developed an greatly improved elastic conducting ink that can be easily printed on textiles and patterned using only a single printing step. The ink is made using silver flakes, fluorine rubber and an organic solvent and it is highly conductive even when it is stretched to more than three times its original length. Previous inks have only been able to extend to more than two and a half times their original length.


Ink complete

Electrodes, wires, and via holes can be printed by a single step printing process. The muscle activity sensor was produced by printing once on each side of the material's surface. © 2015 Someya Laboratory.

Using the new ink, the group created a wristband muscle activity sensor by printing an elastic conductor on a sportswear material and attaching it to an amplifier circuit. The sensor can measure physical activity by detecting electrical signals from muscles over an area of 16 square centimeters.

"Our team aims to develop comfortable wearable devices," says Someya. "This ink was developed as part of this endeavor. The biggest challenge was obtaining high conductivity and stretchability with a simple one-step printing process. We were able to achieve this by use of a surfactant that allowed the silver flakes to self-assemble at the surface of the printed pattern, ensuring high conductivity." Comfortable, stretchable, wearable devices? Maybe that Apple watch is already looking a little old.