Self-healing chitosan-MXene/polyurethane composite films for dual-mode sensing of strain and humidity

Flexible conductive coatings enhance textiles with functions like heating, luminescence, and sensing. However, they tend to break under external forces, limiting long-term use. Here, a waterborne polyurethane containing disulfide bonds and aldehyde groups was synthesized using 2-hydroxyethyl disulfide as a chain extender and vanillin as a chain terminator. The resulting polyurethane was then blended with chitosan-modified Ti₃C₂T_X MXene nanosheets to create a flexible conductive fabric coating. The innovative fabric coating exhibits outstanding mechanical properties and self-healing performance, driven by a synergistic dual dynamic covalent bonding mechanism. Dynamic disulfide bonds within the polyurethane matrix enable main-chain reconstruction, while reversible Schiff base linkages between vanillin and chitosan enhance interfacial healing efficiency. After being developed into sensors, the coating effectively monitored human joint movements in real time, achieving a sensitivity of 8 once the strain exceeded 50%. Furthermore, due to the abundance of -OH and -NH₂ groups on chitosan-modified MXene, the conductive fabric coating sensor exhibited humidity responsiveness. It displayed a high sensitivity of -71%, a rapid response and recovery time of less than 10 s, and a wide sensing range of 33% to 97% relative humidity, thereby facilitating real-time monitoring of respiratory status during physical activity. This flexible coating holds significant potential for functional flexible electronics.