When most people think of wearable devices, they think of smart watches, smart glasses, fitness trackers, even smart clothing. These devices, part of a fast-growing market, have two things in common: They all need an external power source, and they all require exacting manufacturing processes. Until now.

Yanliang Zhang, associate professor of aerospace and mechanical engineering at the University of Notre Dame, and doctoral student Yipu Du have created an innovative hybrid printing method -- combining multi-material aerosol jet printing and extrusion printing -- that integrates both functional and structural materials into a single streamlined printing platform. Their work was recently published in Nano Energy.

Zhang and Du, in collaboration with a team at Purdue University led by professor Wenzhuo Wu, also have developed an all-printed piezoelectric (self-powered) wearable device.

Using their new hybrid printing process, the team demonstrated stretchable piezoelectric sensors, conformable to human skin, with integrated tellurium nanowire piezoelectric materials, silver nanowire electrodes and silicone films. The devices printed by the team were then attached to a human wrist, accurately detecting hand gestures, and to an individual's neck, detecting the individual's heartbeat. Neither device used an external power source.

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