Polymerizable deep eutectic solvent assisted facile preparation of lignin hydrogel with high transparency, adhesion and environmental tolerance for flexible electronics

Environmental factors strongly restrict the applications of hydrogel sensors. Conventional approaches enhance environmental tolerance through functional additives, but they inevitably compromise hydrogels' structural integrity and functional synergy. Herein, we developed an integrated strategy based on polymerizable deep eutectic solvent (PDES). The choline chloride-acrylic acid PDES simultaneously extracted lignin from agroforestry waste while functioning as a reactive monomer reservoir, enabling by-product minimization, process simplification, and concurrently achievement of functional coordination and structural regulation in the hydrogel. The PDES lignin exhibited light coloration that enhanced the transparency of the hydrogel. In addition, it endowed the hydrogel with excellent UV resistance and multi-surface adhesion. Benefiting from the high ionic concentration and abundant hydrogen bonding network within the PDES system, the hydrogel demonstrated remarkable conductivity, self-healing capabilities and excellent environmental stability (−20 °C or 25 °C, over six months). The PDES/lignin hydrogel-based flexible strain sensor exhibited a wide detection range (2 %–300 % strain), rapid response (60 ms at 40 % strain), and suitable gauge factors (GF = 2.22–5.96), along with fatigue resistance and reliable human/machine signal monitoring capabilities. These synergistic properties allow the PDES/lignin hydrogel to serve as an effective material for wearable sensors and human-machine interfaces in demanding environments such as winter sports and geological exploration.