A new method for digital design and printing of stretchable, flexible electronics, called Hybrid 3D printing, was developed to integrate soft, conductive inks with a material substrate to create stretchable, wearable electronic devices. Starting from nothing, the printer builds an entire stretchable circuit that blends the mechanical durability of printed components with the robust performance of off-the-shelf electronics.

Hybrid 3D printing uses additive manufacturing to integrate soft, conductive inks with material substrates to create stretchable electronic devices. A potential application is to create sensors to enable better human performance monitoring. (Photo: Harvard Wyss Institute)

In a demonstration, a 3D printer was used to print conductive traces of flexible, silver-infused, thermoplastic polyurethane. A pick-and-place method was then used to set microcontroller chips and LED lights into the flexible substrate, augmented by an empty printer nozzle and vacuum system to create the hybrid system. When tested, the additively manufactured, hybrid-electronic devices were able to maintain function even after being stretched by more than 30 percent from original size.

Skin-worn electronics have the potential to provide feedback on movement, body temperature, fatigue, hydration, and other metrics crucial to understanding performance; however, while skin is inherently soft and stretchable, electronics and sensors are not. Additive manufacturing enables custom design of complex form factors that enable electronics to be integrated into unique places.

The Harvard researchers printed sensors and placed microelectronics onto a spandex sleeve able to respond to the movement of the wearer’s arm. They also created a pressure sensor for shoes, able to sense and monitor gait. AFRL researchers also tested the processes in the lab, and are investigating the possibility of using the same methodologies to build antennas and sensors into structures.

One challenge addresses the powering of the devices, which would require a stretchable battery or other printed power source to be integrated into the manufacturing process.

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