Fatigue-resistant and tough double network granular elastomers

Elastomers can be designed to constitute stretchable, compliant materials that can also bear some load. This combination of assets renders them attractive for the fabrication of soft robots, soft electronics wearables, and numerous soft biomedical devices. Unfortunately, single network elastomers suffer from a stiffness-toughness compromise. This compromise can be addressed by formulating multi-network elastomers. However, single and multi-network elastomers typically suffer from a toughness-fatigue trade-off that severely limits their use in dynamic applications. In this paper, we demonstrate that granular double network elastomers (DNGEs) composed of jammed stiff elastomer microparticles that are firmly connected through a much softer 2nd network combine toughness and fatigue resistance: their locally varying composition enables DNGEs to efficiently and reversibly dissipate energy if stretched to moderate strains, imparting them a good fatigue resistance. Yet, if stretched to high strain, DNGEs can efficiently dissipate energy through reversible and irreversible mechanisms, imparting them a high toughness. Leveraging the 3D printability of the material, we vary the local composition to combine stiffness, toughness and fatigue resistance within one elastomer, a feature that could thus far not be achieved for this material class. We foresee these DNGEs to increase the lifetime of many elastomer-based structures and enable new applications in soft robotics, soft electronics, wearables and biomedicine, which are currently limited by the stiffness-toughness-fatigue resistance trade-off of currently available soft materials suffer from.