Biomimic Conductive Hydrogel Based on Polyphenol-Modified Cellulose Nanocrystals for Flexible Mechano-sensors

Excellent mechanical properties and force-electric coupling are essential for flexible conductive hydrogels, enabling their applications in soft robotics, wearable sensors, and human-machine interfaces. However, such hydrogels often face a fundamental trade-off between mechanical strength and electrical sensitivity. Inspired by the "soft-hard" architecture strategy in biological mechanical tissues and mussel-inspired multimode interacting mechanisms, we report the fabrication of a composite conductive hydrogel with enhanced mechanical strength, fatigue resistance, universal surface adhesion, and highly sensitive mechano-sensing capabilities by incorporating tannic acid-modified cellulose nanocrystals (CNC@TA) into an interpenetrating polyacrylamide/poly(vinyl alcohol)/poly(acrylic acid)/Al³⁺ multinetwork hydrogel matrix. The TA functionalization provides the CNCs with abundant cross-linking and interaction sites, enabling strong bonding with the surrounding matrix through physical entanglements, hydrogen bonding, π-π stacking, and coordination interactions. The hydrogel exhibits universal adhesion to various substrates and achieves well-performed mechanical property with elongation up to 765%, tensile strength around 83 kPa, and toughness around 276 kJ/m³. Simultaneously, the coordinated Al³⁺ ions provide the hydrogel with excellent ionic conductivity and a high strain sensitivity (gauge factor of up to 2.7). With superior mechanical properties and force-electric coupling performance, this hydrogel holds broad application potential in flexible electronics, human-machine interaction devices, and biomimetic materials.