Working harder, getting stronger: Self-healing polymers attempt to restore mechanical strength after deformation. Polymer gels tend to be too soft for this to occur. Matsuda et al. generated self-healing hydrogels composed of a double-network material (see the Perspective by Craig). A mechanical stress breaks the more brittle of the two networks, while the other retains stability. On breakage, the fractured chains create radical initiators that polymerize new network material. With repeated network breakage and a supply of monomers, the gel gets stronger. Science , this issue p. 504 ; see also p. 451

Natural structural materials (such as tendons and ligaments) are comprised of multiscale hierarchical architectures, with dimensions ranging from nano‐ to macroscale, which are difficult to mimic synthetically. Here a bioinspired, facile method to fabricate anisotropic hydrogels with perfectly aligned multiscale hierarchical fibrous structures similar to those of tendons and ligaments is reported. The method includes drying a diluted physical hydrogel in air by confining its length direction. During this process, sufficiently high tensile stress is built along the length direction to align the polymer chains and multiscale fibrous structures (from nano‐ to submicro‐ to microscale) are spontaneously formed in the bulk material, which are well‐retained in the reswollen gel. The method is useful for relatively rigid polymers (such as alginate and cellulose), which are susceptible to mechanical signal. By controlling the drying with or without prestretching, the degree of alignment, size of superstructures, and the strength of supramolecular interactions can be tuned, which sensitively influence the strength and toughness of the hydrogels. The mechanical properties are comparable with those of natural ligaments. This study provides a general strategy for designing hydrogels with highly ordered hierarchical structures, which opens routes for the development of many functional biomimetic materials for biomedical applications.