A Green Strategy for the Ultrafast Synthesis of Functional Hydrogels Toward Intelligent Human–Machine Interfaces

Abstract

With the rapid development of flexible electronics, there is an increasing demand for hydrogel‐based sensors with rapid fabrication, robust mechanical performance, and stable sensing behavior. Herein, a green and ultrafast self‐catalytic strategy is developed to fabricate a multifunctional hydrogel based on tannic acid‐coated cellulose nanofibers (TA‐CNF), Fe 3+ , polyacrylic acid (PAA), and glycerol. The gelation process is completed within 5 s under ambient conditions, driven by a Fe 3+ ‐TA‐mediated redox cycle that continuously generates free radicals to initiate polymerization without external thermal or UV stimuli. In this system, TA‐CNF provides abundant catechol groups for redox reactions and strong adhesion, Fe 3+ enables dynamic coordination cross‐linking and ionic conductivity, while glycerol enhances antifreezing and water‐retention properties, resulting in a synergistically reinforced three‐dimensional network. The obtained hydrogel exhibits excellent mechanical properties with a tensile strength of 212 kPa and elongation at break of 1200%, as well as rapid conductive self‐healing (93% recovery within 105 ms). As a strain sensor, it demonstrates high sensitivity with a gauge factor ranging from 1.50 to 6.29 over a wide strain range (0%–600%), fast response and recovery times of 111 and 174 ms, respectively, and outstanding cyclic stability over 2000 cycles. Additionally, the hydrogel shows reliable pressure‐sensing performance with a maximum gauge factor of 17.98 under compression. Owing to these properties, the hydrogel can be effectively applied in wearable sensors for monitoring human motion and physiological signals, thereby providing a scalable and sustainable strategy for the rapid preparation of high‐performance bio‐based hydrogels for intelligent human–machine interfaces.