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

Abstract

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.