3D printed flexible wearable device generates electricity using body heat

From health monitors and fitness trackers to virtual reality headsets, wearable electronics have become part of our daily lives. Researchers at the University of Washington recently published a paper in the journal Advanced Energy Materials, saying that they have pioneered a flexible wearable thermoelectric device that can convert body heat into electricity. The device has properties that are usually difficult to combine: it is both soft and stretchable, and strong and efficient.

"If we can capture the heat energy that is wasted in the surrounding environment, it's a 100 percent gain," said Mohammed Malakudi, assistant professor of mechanical engineering at the University of Washington. "But to use this energy for self-powered electronic devices, we need higher power density. Stretchable electronics made with 3D printing can improve efficiency and enable seamless integration into wearable devices."

The researchers created a prototype device that remained fully functional even after more than 15,000 stretching cycles at 30 percent strain, which is ideal for wearable electronics and flexible robotics. The device also increased power density by 6.5 times compared to previous stretchable thermoelectric generators.

To create this prototype device, the researchers 3D printed composite materials with engineered functional and structural properties in each layer, and the filler material contains liquid metal alloys that provide high electrical and thermal conductivity. These alloys address the limitations of previous devices, including the inability to stretch, inefficient heat transfer, and complex manufacturing processes. The team also embedded hollow microspheres to direct heat to the semiconductor in the core layer and reduce the weight of the device.

The researchers said they were able to print the device onto stretchable textiles and curved surfaces, suggesting that future devices could be applied to clothing and other objects. A unique aspect of this research is that it covers the entire range from material synthesis to device fabrication and characterization, giving the researchers freedom to design new materials and exercise creativity.