Silk Fibroin-Based Antifreezing and Highly Conductive Hydrogel for Sensing at Ultralow Temperature

Hydrogels with a combination of mechanical flexibility and good electrical conductivity hold significant potential for various applications. Nonetheless, it is inevitable that water-based conductive hydrogels lose their elasticity and conductivity at extremely low temperatures, severely limiting their utilization in ultralow temperature environments, such as those for Arctic/Antarctic exploration. In this study, we developed a conductive hydrogel based on a double network cross-linking strategy that incorporated silk fibroin (SF) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) within a lithium bromide (LiBr) solution, which shows exceptional antifreezing (-108 °C freezing point) and excellent conductivity (16.33 S m^-1). The obtained SF/PEDOT:PSS/LiBr (SPL) hydrogel shows a stable and reliable response to a wide range of deformations (compression: 0.5-60%; tensile: 1.0-100%), with a short response/recovery time of approximately 70 ms. More importantly, the hydrogel displays well-maintained conductivity, robust mechanical properties, and dependable sensing capabilities, even under temperatures as low as -80 °C. For proof of concept, we demonstrated the applications of the SPL hydrogel in detecting body movements, monitoring climate conditions, and ensuring information security in ultralow temperature environments. The results indicate that the antifreezing hydrogel is a promising candidate for fabricating flexible sensors, particularly well-suited for use in challenging ultralow temperature scenarios.