Anion–π Interaction‐Regulated Ion Generation and High Piezoionic Response in Ultrasoft Low‐Salinity Hydrogels

Abstract

ABSTRACT Anion–π interactions play important roles in underwater cohesion and selective ion recognition and transport in biological systems. Inspired by these functions, we report the first hydrogel system employing anion–π interactions as a design motif for piezoionic energy conversion. Unlike conventional piezoionic hydrogels that typically employ relatively stiff matrices (10 −7 –10 −4 Pa −1 ) and concentrated salts (≥1 M), our system achieves efficient mechanoelectrical conversion in an ultrasoft hydrogel under low‐salinity conditions. Anion–π interactions serve as dynamic cohesive crosslinking motifs, imparting injectability, self‐healing, and ultrasoft tissue compliance (10 −3 –10 −2 Pa −1 ), while the cooperative aromatic–phosphate environment is proposed to regulate the separation of water‐derived ionic species. Hydrated protonic species may associate with aromatic motifs through cation–π interactions strengthened by adjacent phosphate groups, increasing the lifetime of charge‐separated protonic and hydroxide‐containing ions. Under deformation‐induced pressure gradients, poroelastic solvent redistribution is proposed to preferentially transport mobile hydroxide‐containing species, producing ionic transport asymmetry and a high piezoionic coefficient of 7.8 mV kPa −1 , with 70.6 mV voltage and 32.1 µA current at ≤0.15 M salt. This combination enables minimally invasive delivery, conformal tissue contact, biomechanical monitoring, and stimulation‐level voltage generation. This work highlights anion–π interactions as a versatile strategy for developing next‐generation soft ion‐conducting materials with combined mechanical and electromechanical properties.