Self-healable and recyclable polyurethane-polyaniline hydrogel toward flexible strain sensor

Flexible electronics have been extensively investigated in recent years because of their potential applications in artificial skin, soft robotics, energy storage, healthcare technology, etc. However, since the rigid and brittle nature of the conductive or semi-conductive materials, it's a huge challenge to project stretchable, self-healable and recyclable soft electronics to mimic skin. Herein, the interpenetrating and synergistic dual-network hydrogel of Diels-Alder chemistry-based dynamic polyurethane substrates and polyaniline conductive polymer (PU-DA-1/1-PANI) was prepared and employed as a strain sensor. The PU-DA-1/1-PANI hydrogel exhibited large elongation at break of 500%, soft Young's modulus of 0.3 MPa, and robust tensile strength of 1.1 MPa. Meanwhile, the strain sensors with optimized composition presented an ideal conductivity of 7.9 S m−1, which could monitor the physical motions precisely and repeatedly with a gauge factor (GF) of 2.9. In addition, the mechanical performance and conductivity could be self-healed, which was enabled by the hydrogen bonds, ionic interactions, reversible DA covalent bonds, and rearrangement of polymer chains. Built on the thermally stimuli-responsive nature of the DA covalent cross-linking points, the PU-DA-1/1-PANI composites could be recycled.