Highly Stretchable Strain Sensors Comprising Double Network Hydrogels Fabricated by Microfluidic Devices

Strain sensors with high sensitivity and stretchability are required for wearable or implantable sensors to detect human motion. In this study, highly stretchable double-network (DN) of soft polyacrylamide and brittle calcium-alginate microfibers containing poly(3,4-ethylenedioxythiphene)-poly(styrenesulfonate) (PEDOT:PSS) are prepared using microfluidic devices. The resistance changes in response to the stretching of the microfiber due to the connection/partial disconnection of the PEDOT:PSS domains; it could be monitored up to 300% elongation with a resolution of 0.1%. Furthermore, these changes are fully reversible and repeatable over 10 000 cycles of 200% elongation. Owing to such mechanical and electronic properties, DN microfibers are envisioned to be useful in stretchable strain sensors to detect human motion in real time, including bending of the fingers, walking, and running. It is also demonstrated that the developed sensor can be stably used outdoors by measuring the growth of a bamboo planted in a garden.