3D Printing of Dual-Physical Cross-linking Hydrogel with Ultrahigh Strength and Toughness

3D printing of hydrogels with high intrinsic mechanical performance has significant applications in many fields yet has been proven to be a fundamental challenge. Here, 3D printing of ultrahigh strength hydrogels is achieved by constructing cross-linkingDPC networks based on poly(vinyl alcohol) (PVA) and chitosan (CS). The hybrid ink with moderate rheology for direct ink writing is employed to manufacture complex hydrogel structures, first. Then, the cyclic freezing-thawing followed by sodium citrate solution soaking realize the first network of PVA crystallization and the second one of CS ionic interaction between amino and carboxyl groups. The optimized DPC hydrogel displays a tensile strength of 12.71 +/- 1.32 MPa at a strain of 302.27 +/- 15.70%, Young's modulus of 14.01 +/- 1.35 MPa, and work of extension at fracture W-ext of 22.10 +/- 2.36 MJ m(-3) because of the dominant energy dissipation of the stiff CS ionic network. Moreover, the tearing test supports that this DPC hydrogel possesses a high toughness of 9.92 +/- 1.05 kJ m(-2). This protocol can readily realize not only the hydrogel lattice, honeycomb, and spring, but also secondary-shaping hydrogel objects including whale, octopus, and butterfly via a local DPC strategy. Integrating the advanced 3D-printing technique with high-performance hydrogels uncovers a feasible strategy to broad practical applications in engineering, intelligent machine, and soft robotics.