Printable Polar Silicone Elastomers for Healable Super-capacitive Strain Sensors

Soft strain sensors with high sensitivity and the ability to recover from damages are required in the emerging field of self-healing soft robotics. Here, we developed printable supercapacitive strain sensors that can heal upon moderate heating (75 °C for 10 min) and exhibit a 30 times higher sensitivity than PDMS-based sensors. For the sensor's core layer and electrode, we use a nitrile-functional polysiloxane that contains an active ionic initiator and can heal by siloxane equilibration at elevated temperatures. Supercapacitive strain sensors prepared from the elastomer are highly sensitive at low strains of 0–30%, enabled by the electric double-layer formation of the ionic initiator. After healing, the sensors exhibit nearly unaltered performance in tensile testing. Due to the thermoreversible nature of the elastomer network, we can print patterned core layers with different microstructures by direct ink writing. The capacitive sensors based on these microstructured films reach a higher sensitivity and linearity than those based on unstructured films. Finally, we integrate the sensor into a soft robotic finger and validate the sensor's ability to determine the bending angle by motion capture. Our technology can provide new opportunities to equip soft robotic devices with custom-printed, healable strain sensors.