Impact‐Resistant Hydrogels by Harnessing 2D Hierarchical Structures

With the strengthening capacity through harnessing multi‐length‐scale structural hierarchy, synthetic hydrogels hold tremendous promise as a low‐cost and abundant material for applications demanding unprecedented mechanical robustness. However, integrating high impact resistance and high water content, yet superior softness, in a single hydrogel material still remains a grand challenge. Here, a simple, yet effective, strategy involving bidirectional freeze‐casting and compression‐annealing is reported, leading to a hierarchically structured hydrogel material. Rational engineering of the distinct 2D lamellar structures, well‐defined nanocrystalline domains and robust interfacial interaction among the lamellae, synergistically contributes to a record‐high ballistic energy absorption capability (i.e., 2.1 kJ m−1), without sacrificing their high water content (i.e., 85 wt%) and superior softness. Together with its low‐cost and extraordinary energy dissipation capacity, the hydrogel materials present a durable alternative to conventional hydrogel materials for armor‐like protection circumstances. Bioinspired hydrogels with lobster‐underbelly‐like properties are reported. By engineering the hierarchical structures, synthetic hydrogel materials can be enabled with the lobster‐underbelly‐like combinational properties, including high ballistic resistance, toughness, strength, water content, and superior softness.