Ionic Hydration Engineering Enables Tissue-Like Conductive all-Polymer Hydrogels With Subzero-Temperature Tolerance

Conductive all-polymer hydrogels (c-APHs) face challenges in subzero-temperature applications due to ice-induced mechanical failure and electrical conductivity loss. Here, we present a cryo-compatible c-APH via ionic hydration engineering, integrating poly(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS) nanofibrils into a polyvinyl alcohol (PVA) matrix with Na₂SO₄ mediation. The optimized hydrogel achieves exceptional electrical conductivity (35.0 S/cm at -20°C; 27.2 S/cm at -70°C), tissue-like softness (Young's modulus: 0.5-1.3 MPa at room temperature), and biocompatibility. Salt concentration governs hydrogen-bond dynamics: low Na₂SO₄ content disrupts ice formation while enhancing water-PVA interactions, ensuring flexibility; high concentrations induce PVA aggregation via Hofmeister effects, stiffening the hydrogel. The materials demonstrate multifunctionality, including high charge storage (16.0 mC·cm^-2) and injectable signal transmission (3.04 mC·cm^-2), exceeding Pt, stable electrophysiological monitoring (ECG/EMG), and resilience to 20000 biphasical pulses and 1000 cyclic electrochemical cycles. A proof-of-concept human-machine interface (HMI) using hydrogel-based gloves enables precise robotic control across ambient and subzero-temperature environments (-70°C), validated by real-time gesture recognition and actuation. This work provides a promising way to resolve the long-standing trade-off between subzero-temperature performance and softness in bioelectronics, offering transformative solutions for wearable sensors, neural interfaces, and extreme-environment robotics.