Fatigue-resistant and tough double network granular elastomers.

Elastomers can be engineered as stretchable, compliant materials capable of bearing load, making them attractive for soft robotics, wearable electronics, and biomedical devices. Unfortunately, single-network elastomers are constrained by a stiffness-toughness compromise. While multinetwork elastomers can mitigate this limitation, tough multinetwork elastomers typically exhibit a limited fatigue resistance. Here, we demonstrate that double-network granular elastomers (DNGEs) composed of stiff elastomer microparticles connected through a softer second network combine toughness and fatigue resistance. Their locally varying composition and structure enable DNGEs to efficiently deconcentrate stress and repetitively dissipate energy if stretched to moderate strains, imparting them a good fatigue resistance. Leveraging the three-dimensional printability of DNGEs, we spatially vary the composition to combine stiffness, toughness, and fatigue resistance within one elastomer. We anticipate that DNGEs will unlock opportunities in soft robotics, wearables, and biomedicine, where current soft materials remain limited by the stiffness-toughness-fatigue resistance trade-off.