Anti-freezing and robust Ag-MOFs@PVA/XG hydrogel for flexible sensing and robotic state monitoring

Flexible sensors are essential for human-machine interfaces and bioinspired intelligent robotics, yet achieving a balance between mechanical robustness and high sensitivity at lower temperatures remains a challenge. Herein, a multifunctional hydrogel sensor (PG₂/Ag-MOFs-XG) was fabricated through physical crosslinking of polyvinyl alcohol (PVA) and xanthan gum (XG) in glycerol (Gly) and deionized water mixture via freeze-thaw circulation and NaCl crosslinking. The in situ growth of Ag-MOFs on XG molecular chains is facilitated by the electrostatic interactions between the hydroxyl groups and the carboxyl groups of XG and Ag⁺, restricting molecular chain movement, thereby enhancing comprehensive properties. The PG₂/Ag-MOFs-XG hydrogel exhibits outstanding mechanical properties across a broad temperature range, with a 101 % increase in tensile strength (from 0.583 MPa to 1.17 MPa) at 25 °C and a 112 % increase (from 0.352 MPa to 0.746 MPa) at -18 °C, compared to the pure PVA hydrogel. Additionally, it demonstrates exceptional sensitivity to stretching (GF = 3.65) and compression (S = 3.38 × 10^-2 kPa^-1). Furthermore, the hydrogel functions as a flexible sensor for monitoring human motion, assessing industrial robot performance, and detecting the tightness of robotic components. This work offers valuable insights into the development of portable, highly sensitive, and flexible sensors for intelligent robotics.