Lignin-Ethylene\nGlycol Improved Hydrogel with Antifreezing\nand Antiswelling Properties As a Flexible Sensor for Underwater Motion\nMonitoring

Conductive hydrogels have great potential\nas flexible sensors for\nmotion monitoring. However, their practical applications are still\nlimited due to the poor functional stability of high-water-content\nhydrogels at low temperatures and in wet environments. In this paper,\na hydrogel composite system was synthesized with various hydrogen-bonding\ninteractions. The main strategy was to introduce ethylene glycol (EG)\nand alkaline lignin (AL) into a polymer network. Except for EG, a\nmoderate amount of AL (2 wt %) significantly enhanced the freeze resistance\nof the hydrogel. Moreover, the antiswelling ability of hydrogel improved\nsignificantly (the optimal swelling rate was 10%) with the introduction\nof AL. After a long-term immersion of the hydrogel in water, no change\nin mechanical properties (elongation at break > 300%, tensile strength\n> 0.13 MPa), frost resistance (−25.88 °C), and conductivity\n(0.18 S/m) were observed. Notably, the hydrogel sensor could accurately\ndetect human and aquatic organisms’ movements in water. The\nsensor was also assembled into a wireless sensing device to transmit\ninformation via Bluetooth technology and display an electromyography\nsignal equivalent to that of a commercial Ag/AgCl gel electrode. This\ngreen, low-cost, and sustainable antifreezing and antiswelling hydrogel\nsensor exhibits great potential in low-temperature and underwater\nsensing applications.