Orientational dynamics imparts viscoelasticity and toughness in 3D-printable ordered block copolymer hydrogels

The three-dimensional (3D) processing of hydrogels into mechanically robust, complex volumetric objects is central to applications in load-bearing scaffolds, soft robotics, and biomedical devices. Yet most state-of-the-art tough hydrogel formulations remain incompatible with 3D printing or suffer substantial loss in mechanical properties when 3D-printed. Here we report a rapid (within seconds) photopolymerization-based strategy to form alternating block copolymer networks in situ from oligomeric precursors in an organic solvent, which subsequently self-assemble into ordered nanoscale morphologies upon solvent exchange into water. The resulting block copolymer hydrogels (BCPHs) are capable of dynamic and reversible strain-induced reorganization and exhibit exceptional mechanical properties, combining high stiffness (~1.5 MPa), tensile strength (~900 kPa), toughness (~3.4 kJ m-2), extensibility (~500%), energy dissipation (~20-60%), and rapid (seconds to minutes) recovery under ambient conditions. Mechanical testing, birefringence imaging, and small-angle X-ray scattering experiments are used to elucidate the structurefunction relationships in BCPHs, which include non-affine, orientational dynamics-mediated deformation mechanisms that underpin their viscoelasticity and toughness. Furthermore, we fabricate BCPHs into complex 3D architectures using digital light processing (DLP)-based 3D printing without post-processing that maintain the exceptional mechanical properties of their nonprinted counterparts. Together, this work establishes a facile, modular platform for highly tunable, 3D-printable, viscoelastic, and tough hydrogels.