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High modulus, toughness, and fatigue resistance are usually difficult to be obtained simultaneously in rubbery materials. Here, we report that by superimposing the nanophase separation structure in double network (DN) elastomers using immiscible polymers, the modulus, fracture energy, and energy release rate of fatigue threshold are enhanced all together by 13, 5, and 5 times, respectively. We reveal that the interplay between the DN structure and the nanophase separation structure brings two effects synergistically: (1) formation of nanoclusters overstresses and homogenizes the sacrificial network, thereby remarkably increasing the modulus and yielding stress and (2) the nanoclusters act as viscoelastic nanofillers dissipating energy and pinning the crack propagation, thereby significantly enhancing toughness and fatigue resistance. This work provides a facile approach to superimpose high-order structures in DN materials for excellent mechanical performance. The clarified synergetic effects should be universal for DN materials made of immiscible polymers. We believe that this work will facilitate more studies on elastomers and gels along this line.

Supermacroporous hydrogels, possessing sponge-like structure and permeability, have drawn significant atten-tion for their bioengineering and biomedical applications. However, their mechanical weakness due to their low-density structure is one of their biggest limitations. This work reports a multi-step cryogelation technique, which does not require special equipment, for preparing tough supermacroporous hydrogels on the basis of the double-network (DN) strategy. The produced supermacroporous DN gels possess interconnected pores with pore sizes of 50–230 μm. They also show a com-pressive modulus of up to ~100 kPa, which is 2- to 4-times higher than that of the corresponding supermacroporous single-network (SN) gels, and compressive strength of up to 1 MPa at 80% compression. The supermacroporous DN cryogels are also stretchable with a work of extension of up to 38 kJ m-3, which is 1 to 2 orders larger than that of the SN cryogels. The high stiffness and stretchability distinguish them from other types of cryogels. Supermacroporous triple-network (TN) gels and DN gels composed of different polymer combinations are also prepared. The technique presented herein is suitable for pre-paring supermacroporous DN gels from various polymers; hence, it is promising in meeting bioengineering and biomedical demands.