"Molecular bridge" anchoring: A strategy to harmonize conductivity and toughness in cellulose-conjugated polymer hydrogels for high-performance flexible bioelectronics.

To address the core challenge of balancing electrical conductivity, mechanical toughness, and biocompatibility in flexible bioelectronic electrodes, this study proposes a PAM molecular bridge directional coupling strategy. We in situ fabricated a CCNFs/PEDOT: PSS-co-PAM (PSM) composite hydrogel, with linear CMC as a control. Via multiscale characterization and molecular dynamics (MD) simulations, we clarified key structure-property links. PAM segments act as "molecular bridges," conferring flexibility and biocompatibility, while their amide groups form high-density hydrogen bonds with CCNF's ordered carboxyl groups. This anchors the 3D rigid CCNF framework to PEDOT: PSS chains, thereby optimizing stress transfer and charge transport. In contrast, CMC's linear structure and ether-linked carboxyl groups yield weak interfacial interactions. MD simulations confirmed the CCPSM system has 1.6× more hydrogen bonds, 3.36× higher interaction energy, and 63.4% lower water diffusion vs. CMC. CCPSM-5 exhibits 2.16 S/m conductivity, 5.7× higher toughness (3.165 MJ·m-3), 1.2× higher elongation (746%), plus excellent adhesion, anti-swelling, and dynamic electrical stability on glass and dry/wet skin. As a bioelectrode, it outperforms commercial Ag/AgCl in EMG/ECG signal fidelity and RMS, enabling precise multi-joint motion monitoring. This work resolves the conductivity-mechanical trade-off by leveraging CCNF's 3D reinforcement and interfacial coupling, offering a novel design paradigm for high-performance flexible bioelectronics.