LAUSR

Hydrogels, water‐rich polymer networks, are important materials for application as structural biomaterials. More water‐rich networks are typically less mechanically robust, which is manifested as softness and low stress to fracture. Unusually, jellyfish mesoglea exhibits paradoxical combination of high stiffness and strength with ultrahigh water content. Here, it is discovered that jellyfish mesoglea possesses a long‐range‐ordered laminated membranous network, which features crystal orientation along membrane plane and collagen chain spanning at the junction of membranes. Such a laminated membranous network is in favor of resistance to deformation, as well as transmission and dispersion of stress for culminating in good mechanical robustness. Fabrication of chitosan hydrogel with jellyfish mesoglea‐like network is further demonstrated by pre‐constructing a random membranous network via evaporation‐induced phase separation, followed by aligning and crystallizing the membranes via combination of in‐plane stretching and sodium hydroxide treatment. The obtained hydrogel exhibits a combination of high modulus (5.2 MPa) and strength (6.5 MPa) with ultrahigh water content (91.8 wt.%), exceeding that of other synthetic and even biological hydrogels. This work offers not only a structural concept but also a feasible way for making hydrogels that overcome traditional trade‐off between good mechanical robustness and ultrahigh water content.