Double-Network Physical Cross-Linking Strategy To Promote Bulk Mechanical and Surface Adhesive Properties of Hydrogels

Development of mechanically strong and adhesive hydrogels with self-recovery and self-healing properties is important for many applications but has proven to be very challenging. Here, we reported a double-network design strategy to synthesize a fully physically cross-linked double-network (DN) hydrogel, consisting of the first gelatin network and the second poly(N-hydroxyethyl acrylamide) network where both networks were mainly cross-linked by hydrogen bonds. The resultant gelatin/pHEAA hydrogels exhibited high mechanical property (tensile stress of 1.93 MPa, tensile strain of 8.22, tearing energy of 4584 J/m2), fast self-recovery at room temperature (toughness/stiffness recovery of 70.2%/68.0% after 10 min resting), and good self-healing property (self-healed tensile stress/strain of 0.62 MPa/3.2 at 60 °C for 6 h). More importantly, gelatin/pHEAA hydrogels also exhibited strong surface adhesion on different hydrophilic solid surfaces, as indicated by high adhesion energy (i.e., interfacial toughness) of...