Highly Robust, Sensitive, Antifreezing, and Drying-Tolerant Polyacrylamide/Gelatin/Zr⁴⁺ Hydrogels as Flexible Strain Sensors

The immersion method in which metal ions were used to toughen macromolecular chains to avoid the failure of hydrogel synthesis due to the rapid formation of coordination bonds in the gel precursor was often used to develop a robust gel. However, the uneven distribution of ions inside the hydrogel was harmful for its sensing performance by soaking. Herein, a robust polyacrylamide/gelatin/ZrOCl2·8H2O (PG-Zr4+) hydrogel was developed by a straightforward strategy to toughen gelatin chains with Zr4+. The PG-Zr4+ hydrogel held not only a high transparency (73%), robust fracture strength (0.842 MPa), and outstanding toughness (4 MJ m–3) but also fast self-recovery and satisfactory conductivity. Furthermore, the crystallization peak of the PG-Zr4+ hydrogel disappeared at −60 to 25 °C with the introduction of dimethyl sulfoxide (DMSO) as a cryoprotectant; it could still exhibit stable electrical responses to weak stimuli of 1% strain at −20 °C for 24 h. Surprisingly, when simply assembled into a strain sensor with a gauge factor (GF) of 5.817, it was capable of precise real-time monitoring of both subtle pronunciation signals and drastic joint movements. This work opened the door to develop flexible wearable devices with multiple advantages.