Water-borne fabrication of stretchable and durable microfibers for high performance underwater strain sensors.

The development of stretchable strain sensors having high linearity and sensitivity, low hysteresis, and fast response to reliably monitor fast human motion is challenging. In this study, hydrogel-based strain sensors in the form of microfibers comprising tough double-network hydrogels or organogels and multi-walled carbon nanotubes (CNTs) are fabricated using aqueous microfluidic devices. Owing to the shear thinning effect on the microchannel, the CNTs can be aligned parallel to the flow direction, which increases the linearity of the sensor up to a strain of 400% and provides high durability over 50,000 strain cycles at 300% elongation. Owing to the negligible hysteresis, high resolution of 0.1%, and low response time of ~30 ms, the strain sensors enable the quantitative conversion of the measured resistance change to the extent of stimulus as well as the simple detection of the motion. The developed sensors can be stably used to detect human motion in real-time in both air and water. Furthermore, the developed material system demonstrates the potential for use in the fabrication of pressure sensors.