Multi-hydrogen bond induced double crosslinked network based on WPU/BC/MWCNTs for high ductility and reliable electronic skin for multimodal health monitoring

Abstract

Flexible electronic skins (e-skins) that offer high sensitivity, durability, and long-term stability are essential for wearable sensing applications; however, achieving a balance between conductivity, mechanical flexibility, and stability remains a significant challenge. This study, addresses these issues by developing a highly elastic, waterborne polyurethane (WPU) composite incorporating bacterial cellulose (BC) and multi-walled carbon nanotubes (MWCNTs). The abundant hydroxyl groups in BC form strong hydrogen bonds with polyurethane, resulting in a dual cross-linking network that mechanical strength and facilitates MWCNTs dispersion through hydrophilic-hydrophobic synergy, thereby significantly improving electrical conductivity. In addition, BC modulates the crystallinity of the composite, directly affecting both its mechanical properties and electrical performance. Consequently, the WPU-BC composite film exhibited a tensile strength of 43.6 MPa, 700 % elongation at break, and toughness of 122 MJ/m³, demonstrating outstanding mechanical properties. Furthermore, the MWCNTs/WPU-BC composite film exhibited high conductivity (24.67 S/cm), rapid response time (152.4 ms), and minimal performance degradation after 2000 stretching cycles. These synergistic properties enable flexible e-skins to consistently capture bioelectrical and biomechanical signals over extended periods, highlighting their potential as multimodal health monitoring systems. This study underscores the effective modulation of composite microstructures via hydrogen bonding and crystallinity control, providing a novel approach for developing durable, sensitive, and biocompatible e-skins. This strategy addresses critical challenges in soft-sensor applications.