Design of moisturizing and frost-resistant ionic hydrogels for multimodal sensing through water-stabilizing effects†

Abstract

Flexible hydrogel-based electronics have gained considerable attention in soft robotics, healthcare management, and electronic skins. However, engineering ionic hydrogel-based sensors capable of simultaneously detecting temperature and humidity is challenging because there is insufficient utilization of dynamic responses of the water matrix within the polymer network to these stimuli. Herein, we present a versatile moisturizing and frost-resistant ionic (MFI) hydrogel that exhibits multimodal sensing of strain, temperature, and humidity. This was achieved by designing a compact hydrogel skeleton that enables precise regulation of water states, such as free and bound water content, through dynamic ion–water interactions. The MFI hydrogel demonstrates impressive mechanical robustness with a toughness of 2.41 MJ m⁻³ by regulating dynamic crosslinks for efficient energy dissipation. Distinct from its counterparts, the MFI hydrogel-based sensor demonstrates multimodal responsiveness by leveraging hydratable ions to stabilize water molecules. This water-stabilizing strategy enables excellent sensing performance, including a wide response range of 0–1300%, good strain linearity (>0.993), and a superior thermal sensitivity of 1.629%/°C with broad temperature (−60 to 80 °C) and humidity (25–70% RH) ranges for detection. Therefore, MFI hydrogels can serve as wearable strain sensors to accurately capture physiological signals such as body temperature, respiration, and pulse. Additionally, they can function as remote-control units for directing vehicle motion paths and vehicle navigation, paving fresh avenues for advanced artificial skins in next-generation smart electronics.