Mechanical tough, non-swelling, self-adhesive and highly conductive amphibious hydrogels for motion sensing in complex conditions

Ideal conductive hydrogels with their mechanical ductility, high conductivity and self-adhesion are essential for potential promising application as fascinating sensing materials in wearable electronic devices. Unfortunately, due to the inevitable performance degeneration stemming from swelling features in aqueous conditions, the applicability of hydrogel-based sensors is greatly reduced in aquatic environments. Herein, an amphibious hydrogel with mechanical ductile, self-adhesive, anti-freezing, and high strain sensitivity underwater is developed. The hydrogel produces a rapid self-gelation behavior at ambient conditions (several minutes) through a catechol redox reaction based on lignocellulosic nanofibril-Ag⁺. The tough polymer network by the virtue of strong hydrogen bonding and nano-reinforcement enables the resultant hydrogel with improved mechanical performance. Meanwhile, outstanding properties including high conductivity (2.12 S/m), strain sensing ability (maximum GF: 3.98), good water resistance (equilibrium swelling ratio of 1.2% after 30 d) as well as other solvents, air/underwater adhesiveness, and anti-freezing performance can be obtained simultaneously. A sensor based on such hydrogel can be conveniently conformed and attached to the human limbs for achieving non-invasive, high stability and continuous underwater communications and habits tracking of marine. Briefly, this work provides an innovative route to develop multifunctional integration hydrogel-based flexible devices for information transmission in marine environments.