Conductive regenerated silk-fibroin-based hydrogels with integrated high mechanical performances

Regenerated silk fibroin hydrogels (RSF gels) are extensively investigated in the biomedical field. However, the mechanical properties of RSF hydrogels are often weak or brittle, which limits their potential for applications where high strength is required. Herein, strong and tough RSF-based hydrogels with large extensibility and rapid self-recovery property were developed via the double network (DN) concept. RSF/HPAAm DN gels, consisting of a physical RSF/SDS gel as the first network and a physically cross-linked HPAAm as the second network, are fully physical network structures. At optimal conditions, the RSF/HPAAm DN gel exhibited integrated high mechanical properties, including high compressive strength (122 MPa), high tensile strength (σ_f of 1.17 MPa), large extensibility (ε_f of 19.03 mm mm^-1), high toughness (W of 11.75 MJ m^-3 and T of 1769 J m^-2) and rapid self-recovery (61% toughness recovery after 1 min of resting at room temperature). Interestingly, owing to contained sodium dodecyl sulfate (SDS) and NaCl, RSF/HPAAm DN gels also displayed ionic conductivity, which could be used as a strain sensor, a touch screen pen and the electronic skin of artificial robots. We believe that this design strategy as well as our RSF/HPAAm DN gel will provide a new route for achieving high performance RSF-based gels with new functionalities.