Strong hydrogels through precisely oriented crystallization regulation

Achieving high mechanical strength and environmental stability is critical for hydrogels in demanding engineering scenarios. Crystalline hydrogels hold promise because their crystallites act as physical crosslinks and energy dissipators; however, precise control over crystalline architecture remains underexplored. Inspired by industrial thermoplastic processing, we report an ASGS strategy for crystalline hydrogels that integrates alkali-induced chain activation (A), ultra-stretching-driven orientation (S), and glycerol-seawater-mediated densification (GS). Alkali treatment yields moderate initial crystallinity with refined nascent crystallites. Ultra-stretching establishes a highly oriented chain network, and subsequent densification achieves maximum crystallinity and highly oriented crystallites. The resultant hydrogels, in the fully hydrated state, combine a tensile strength of 160.0 MPa, a modulus of 746.0 MPa, and a fracture energy of 26.4 kJ·m⁻². The corresponding plastic reaches 414.2 MPa tensile strength while retaining flexibility. This thermoplastic-inspired crystallization engineering provides a scalable paradigm for fabricating strong and stable crystalline hydrogels, promising for load-bearing and harsh underwater engineering applications.