Highly-Stretchable Biomechanical Strain Sensor using Printed Liquid Metal Paste

Stretchable electronic circuits and systems will be critical for future wearable devices and smart textiles, where existing rigid and flexible fabrication approaches severely limit conformal deformation. This is especially true for wearable sensors and actuators, critical for emerging physical human-machine interfaces and stretchable electrical interconnects. In this work, we present a 3D-printed, highly-stretchable strain sensor that uses a modified liquid metal paste to provide high-strain conductors. This approach provides near-zero hysteresis compared with nanotube-based inks, and improved conductivity over carbon- and metal-based inks, both critical for integration of soft sensors with stretchable measurement circuitry. We present an approach for fabrication of the wearable sensors and demonstrate stable conductivity of the liquid metal paste with near-zero hysteresis over 375 cycles at 200% strain. The device is demonstrated for measurement of elbow flexion angle, providing proof-of-concept of the approach for biomechanical sensor applications and wearable human-machine interfaces.