The art of paper cutting becomes the science of wearable devices

Novel synthetic strategy supports development of flexible wearable electronics, including a humidity dosimeter ideal for detecting airborne droplets from coughs or sneezes.

This schematic illustration shows a humidity dosimeter detecting droplets that originate from sneezes and coughs. (Image courtesy of D’Arcy Lab.)

Stretchability is an important feature in wearable electronics and portable sensors, but the materials typically used to build energy storage devices don’t usually like to be stretched. To overcome this obstacle, materials scientists have had to come up with creative solutions. Enter Kirigami. Traditionally the art of paper cutting, this intricate 3D artform provides a clever approach to developing wearable electronics.

Kirigami engineering produces a supportive structure that can be stretched repeatedly while the active material responsible for electronic properties is not actually stretched. Though Kirigami techniques have been applied in earlier research on flexible and stretchable electrodes, a team in Washington University’s Institute of Materials Science & Engineering and the Department of Chemistry in Arts & Sciences has developed a new synthetic approach to wearable humidity dosimeters – cost-effective disposable devices that can measure the dose of aerosolized droplets encountered by the wearer – and stretchable supercapacitors. Their findings, including possible applications in detecting airborne droplets from coughs or sneezes, were published March 31 in the Journal of Materials Chemistry A.

The humidity dosimeter can be attached to a surgical mask in its 2D state (top), then it stretches to accommodate 3D deformation during wear without losing its electrochemical capabilities, as shown here by lead author Yifan Diao (bottom). (Images courtesy of D’Arcy Lab.)

“Our unique synthetic strategy relies on rust-based vapor-phase polymerization,” explained lead author Yifan Diao, a graduate student in IMSE working with chemist Julio D’Arcy. “This allows us to achieve superior electronic and electrochemical performance by depositing conducting polymer nanofibers layer by layer directly on pre-cut Kirigami substrates, which hadn’t been done before. Our approach enables exquisite control of the electrode’s electroactive performance without causing any damage to the nanofibrillar morphology. Moreover, our approach enables deposition of multiple nanofibrillar materials.”

The team’s novel strategy for synthesizing the active material responsible for storing energy and for sensing hydrated saliva aerosols comes with additional benefits. “Our approach obviates the need for multiple synthetic steps because we produce nanofibers of a conducting polymer directly on the surface of a supportive material that makes Kirigami engineering possible,” said D’Arcy, assistant professor of chemistry. “The synthetic technique we reported advances the field of Kirigami because we can deposit a high packing density of nanofibers without templates, and we have simplified the route for attaining high surface area electrodes that enhance the performance of electronic devices.”

With their new technique, the team envisions combining different polymers in the same device, which will enable them to increase the energy stored in their stretchable supercapacitors. Combining materials will also allow them to develop reusable sensors with heightened sensitivity, expanding the range of aerosol droplet sizes that can be detected as well as the speed of detection. 

“Of course, a two-for-one device would be a holy grail where our supercapacitors can also power the sensors that we develop,” D’Arcy added. “This next generation of our stretchable and wearable device would have a dual function – sensing and energy storage – and would therefore be able to have a longer lifetime.”