Multiscale Cellulose-Enhanced Zwitterionic Hydrogels Based on Electrostatic Regulation for the Strain Sensor and Human Motion Monitoring

Zwitterionic hydrogels have gained prominence in flexible electronics for their biocompatibility. However, their applications are hindered by weak mechanical strength and low conductivity. Herein, we proposed an innovative strategy for fabricating multiscale cellulose-modified zwitterionic hydrogels through electrostatic regulation. The hydrogels employed poly(vinyl alcohol) and [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide matrix, where the dispersion-aggregation architecture of anionic carboxymethyl cellulose sodium and cationic polyethylenimine-modified cellulose nanocrystals (PEI@CNC) was precisely controlled via protons. Furthermore, the zwitterionic hydrogels were fabricated through the cyclic freezing-thawing process and in situ zwitterionic monomer polymerization. The results demonstrate that the incorporation of PEI@CNC leads to synergistic enhancement in mechanical properties and ionic conductivity. The tensile strength and ionic conductivity of the DPCC-0.25 sample are 8.4 times and 2.2 times those of the original hydrogel, respectively. This is attributed to the dynamic hydrogen bonding and electrostatic interactions in the porous network based on ionized cellulose. Moreover, the hysteresis area in the tensile cyclic tests at 100% strain is negligible, indicating excellent elasticity. Its strain-sensing capability exhibits hysteresis-free resistive responses across 1%-400% strains with stable cyclability and real-time accuracy. DPCC-0.25-based sensors effectively monitor human body movements. In summary, this study provides new insights into the regulation of polysaccharide dispersion-aggregation structures and the fabrication of multifunctional ionic hydrogels.