Bioinspired anti-freezing 3D-printable conductive hydrogel microfibers for highly-sensitive and wide-range detection of ultralow and high strains

Soft strain sensors that can transduce stretch stimuli into electrical readouts are promising as sustainable wearable electronics. However, most strain sensors cannot achieve highly-sensitive and wide-range detection of ultralow and high strains. Inspired by bamboo structures, anti-freezing microfibers made of conductive poly(vinyl alcohol) hydrogel with poly(3,4-ethylenedioxythiphene)-poly(styrenesulfonate) are developed via continuous microfluidic spinning. The microfibers provide unique bamboo-like structures with enhanced local stress to improve both their length change and resistance change upon stretching for efficient signal conversion. The microfibers allow highly-sensitive (detection limit: 0.05% strain) and wide-range (0%–400% strain) detection of ultralow and high strains, as well as features of good stretchability (485% strain) and anti-freezing property (freezing temperature: −41.1 °C), fast response (200 ms), and good repeatability. The experimental results, together with theoretical foundation analysis and finite element analysis, prove their enhanced length and resistance changes upon stretching for efficient signal conversion. By integrating microfluidic spinning with 3D-printing technique, the textiles of the microfibers can be flexibly constructed. The microfibers and their 3D-printed textiles enable high-performance monitoring of human motions including finger bending and throat vibrating during phonation. This work provides an efficient and general strategy for developing advanced conductive hydrogel microfibers as high-performance wearable strain sensors.