Hierarchically aligned heterogeneous core-sheath hydrogels.

Natural materials with highly oriented heterogeneous structures are often lightweight but strong, stiff but tough and durable. Such an integration of diverse incompatible mechanical properties is highly desired for man-made materials, especially weak hydrogels which are lack of high-precision structural design. Herein, we demonstrate the fabrication of hierarchically aligned heterogeneous hydrogels consisting of a compactly crosslinked sheath and an aligned porous core with alignments of nanofibrils at multi-scales by a sequential self-assembly assisted salting out method. The produced hydrogel offers ultrahigh mechanical properties among the reported hydrogels, elastomers and natural materials, including a toughness of 1031 MJ · m, strength of 55.3 MPa, strain of 3300%, stiffness of 6.8 MPa, fracture energy of 552.7 kJ · m and fatigue threshold of 40.9 kJ · m. Furthermore, such a tough and strong hydrogel facilely achieves stable regeneration and rapid adhesion owing to the highly crystallized and aligned network structure. The regenerated specimen presents the reinforced strength, toughness and fatigue resistance over 10 regeneration cycles. This work provides a simple method to produce hydrogels with bioinspired heterostructures and combinational properties for real applications.