Simple and Rapid Way to a Multifunctionally Conductive Hydrogel for Wearable Strain Sensors

Conductive hydrogels have gained increasing attention in the field of wearable smart devices. However, it remains a big challenge to develop a multifunctionally conductive hydrogel in a rapid and facile way. Herein, a conductive tannic acid-iron/poly (acrylic acid) hydrogel was synthesized within 30 s at ambient temperature by the tannic acid-iron (TA@Fe³⁺)-mediated dynamic catalytic system. The TA@Fe³⁺ dynamic redox autocatalytic pair could efficiently activate the ammonium persulfate to initiate the free-radical polymerization, allowing the gelation to occur easily and rapidly. The resulting hydrogel exhibited enhanced stretchability (3560%), conductivity (33.58 S/m), and strain sensitivity (gauge factor = 2.11). When damaged, it could be self-healed through the dynamic and reversible coordination bonds between the Fe³⁺ and COO^- groups in the hydrogel network. Interestingly, the resulting hydrogel could act as a strain sensor to monitor various human motions including the huge movement of deformations (knuckle, wrist) and subtle motions (smiling, breathing) in real time due to its enhanced self-adhesion, good conductivity, and improved strain sensitivity. Also, the obtained hydrogel exhibited efficient electromagnetic interference (EMI) shielding performance with an EMI shielding effectiveness value of 24.5 dB in the X-band (8.2-12.4 GHz). Additionally, it displayed antibacterial properties, with the help of the activity of TA.