A Multifunctional Waterborne Polyurethane-Based Flexible Wearable Sensor Integrating Self-Healing, Flame Retardancy, and Strain–Temperature Sensing with Adhesion, Self-Cleaning, and Antifouling Properties

Waterborne polyurethane (WPU) is a promising material for flexible wearable sensors owing to its tunable structure, excellent mechanical properties, and facile multifunctionalization. However, compatibility issues between WPU and conductive components often limit the integration of additional functionalities, especially flame retardancy. Herein, a WPU-based multifunctional and dual-mode flexible wearable sensor (xLSPdWPU) with both flame-retardant and self-healing properties was fabricated by incorporating lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as a conductive component into a multilevel double cross-linking network (MDCN). Film performance was synergistically optimized by regulating the interactions among MDCN, LiTFSI, and the WPU matrix. Owing to the MDCN structure, 30LSPdWPU retains adequate mechanical performance (6.38 MPa) for sensing applications after LiTFSI incorporation, along with a high self-healing efficiency (90.8% after 3 h under mild conditions) and good recyclability. Benefiting from phytic acid, metal ions, diselenide bonds, and LiTFSI, 30LSPdWPU also shows excellent flame retardancy and antibacterial activity against Staphylococcus aureus (95.7%) and Escherichia coli (99.8%). Notably, 30LSPdWPU enables strain-temperature dual-mode sensing for monitoring human joint movements and subtle body-temperature variations, while its adhesion, self-cleaning, and antifouling properties further support human motion sensing applications. This work offers a versatile strategy for developing multifunctional wearable sensors for integrated health monitoring.