Thermal and NIR controlled flexible switching devices using a smart conductive composite hydrogel approach

Flexible switching devices with multi-stimulus responsive abilities have shown promising applications as smart materials in the tissue regeneration fields. Herein, a composite hydrogel-based flexible switch system was successfully designed by integrating the nano-sized conductive CNC@PPy (cellulose nanocrystal decorated with polypyrrole (PPy)) and CNC@PDA (cellulose nanocrystal decorated with polydopamine (PDA)) composite particles into the thermal sensitive poly N-isopropyl acrylamide (PNIPAM) hydrogels. The resulting composite hydrogels exhibited enhanced elastic modulus (∼29.5 kPa), superior conductivity (∼1.1 S/m), self-healing, and thermo- and NIR-responsive abilities. Particularly, the incorporated CNC@PDA and CNC@PPy particles within the hydrogel matrix by hydrogen bonds could not only provide a more continuous transporting path for electrons, but also further improve the photothermal conversion efficiency of the composite hydrogel system, in which the temperature increased by 47.6 °C within 10 min under NIR irradiation, and high NIR light-responsive sensitivity with a volume change of 30% within 2 min. Moreover, these composite hydrogels were developed to serve thermo- and NIR light-responsive switchers effectively, which showed excellent stimulus-responsive sensitivities. In all, this work provided a new strategy for designing the multi-stimulus responsive smart hydrogels, which demonstrated excellent potential to serve as remotely controllable switch devices in biomaterials and tissue regeneration.