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

ABSTRACT 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 Na 2 SO 4 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 Na 2 SO 4 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.