Macroscopic Alignment and Structural Fixation of Homogeneous Cross-Linked Polymer Networks for Ultrastrong Hydrogels

Developing ultrastrong hydrogels remains a daunting challenge but is of both practical and fundamental importance for diverse applications of hydrogels. Herein, a simple and general approach is proposed to develop ultrastrong anisotropic hydrogels. Hydrogel precursors are prepared in one step using hydrophobic homogeneous cross-linking via polymerization of aqueous divinylbenzene/sodium acrylate/sodium alginate solutions. The hydrophobic homogeneous cross-linking of poly(sodium acrylate) by divinylbenzene enables antifracture and extremely stretchable features of the precursors, while sodium alginate serves as chelating polymers for structural fixation. The precursors are largely stretched to macroscopical alignment, and then the macroscopically aligned structures are fixed by coordination cross-linking. Correspondingly, the fracture stress (σ), Young's modulus (E), and fracture toughness (G) are 240 times, 10,604 times, and 2.8 times enhanced compared to the precursors, respectively. The obtained anisotropic hydrogels show ultrastrong strength and toughness, with σ of 43.2 MPa, E of 466.6 MPa, G of 173 kJ m–2, and a fatigue threshold of 30 kJ m–2, which outperforms previously reported state-of-art hydrogels with well-designed topologies. The generality of the approach is verified by substituting the hydrophilic monomer, hydrophobic cross-linker, chelating polymers, and multivalent metal ions. The work here sheds new light on topology design and development of versatile ultrastrong hydrogels for diverse applications.