Ion-Regulated Hydration Enables Spontaneous Formation of Asymmetric Polymer Networks for Wearable Electronics

Spatial asymmetry enables polymers to exhibit distinct structures and functions across regions; however, current strategies for constructing asymmetric polymers often rely on multistep processing or complex material designs. Here, we report a salting-out strategy in which ion-specific hydration effects induce spontaneous redistribution of water and polymers during gelation, forming a bilayer polymer network. The gel comprises a hydration-rich, loosely packed conductive sensing layer and a dehydration-dominant, densely packed low-adhesion layer, yielding an approximately fourfold adhesion contrast and over one order of magnitude difference in conductivity. The gel maintains stable mechanical performance over 2400 loading-unloading cycles and enables reliable strain sensing across a wide strain range of 5−300%, supporting monitoring of both large-scale body motions and subtle physiological activities, including joint movement, swallowing, and vocalization. These findings demonstrate that ion-regulated phase separation can serve as a versatile route for programming structural and functional asymmetry in polymers for wearable bioelectronics.