Biomimetic Bilayer‐Structured CNF/GO‐Reinforced CS–PAA Hydrogel for Flexible Strain Sensors

Hydrogels are promising for flexible sensing, yet trade‐offs between sensitivity and mechanics remain a major bottleneck. Drawing inspiration from human skin, we present a bilayer hydrogel design with functionally distinct yet synergistically reinforced layers: an upper GO–CS conductive network for high‐sensitivity strain response, and a lower CNF‐reinforced CS–AA robust scaffold for mechanical support and adhesion. A covalently interpenetrating interface, formed via monomer infiltration–activation, ensures seamless load transfer and electrical synergy while preventing delamination. Selective PDMS encapsulation of the upper layer further confers environmental stability. The resulting hydrogel achieves high stretchability (521.65% strain), high sensitivity (GF = 2.4 over 0%–400% strain), rapid response (<180 ms), and excellent durability (> 2000 cycles). Multisite human motion tests confirm its accurate strain‐sensing performance, underscoring its potential for motion monitoring, health diagnostics, and e‐skin applications.