  Inspired by the cellular design of plant tissue, we present a new approach to
make versatile, tough, highly water-swelling composites. We embed highly
swelling hydrogel particles inside tough, water-permeable, elastomeric
matrices. The resulting composites, which we call \emph{hydroelastomers}, show
little softening as they swell, and have excellent fracture properties that
match those of the best-performing, tough hydrogels. Our composites are
straightforward to fabricate, based on commercial materials, and can easily be
molded or extruded to form shapes with complex swelling geometries.
Furthermore, there is a large design space available for making
hydroelastomers, since one can use any hydrogel as the dispersed phase in the
composite, including hydrogels with stimuli-responsiveness. These features
should make hydroelastomers excellent candidates for use in soft robotics and
swelling-based actuation, or as shape-morphing materials, while also being
useful as hydrogel replacements in a wide range of other fields.
