Mechanically Strong, Tough, and Shape Deformable Poly(acrylamide-co-vinylimidazole) Hydrogels Based on Cu2+ Complexation

Shape deformable hydrogels have drawn great attention due to their wide applications as soft actuators. Here we report a novel kind of mechanically strong, tough, and shape deformable poly(acrylamide-co-vinylimidazole) [poly(AAm-co-VI)] hydrogel prepared by photoinitiated copolymerization and the followed immersing in a Cu2+ aqueous solution. Strong Cu2+ complexation with imidazole groups dramatically enhances the mechanical properties of the hydrogels, whose tensile strength, elastic modulus, toughness, and fracture energy reach up to 7.7 +/- 0.76 MPa, 15.4 +/- 1.2 MPa, 23.2 +/- 2.5 MJ m(-3), and 22.1 +/- 2.3 kJ m(-2), respectively. More impressively, shape deformation (bending) can be easily achieved by coating Cu2+ solution on one side of hydrogel strips. Furthermore, precise control of the shape deformation from 1D to 2D and 2D to 3D can be achieved by adjusting Cu2+ concentration, coating time, region, and one or two side(s) of hydrogel samples. The Cu2+ complexation provides a simple way to simultaneously improve the mechanical properties of hydrogels and enable them with shape deformability. The mechanically strong, tough, and shape deformable hydrogels might be a promising candidate for soft actuators.