Soft materials, though often shadowed by their hard counterparts such as plastics, concrete or metals, are indispensable in daily life. Among them, elastomers are particularly promising for emerging technologies, including soft robotics and flexible biomedical devices, where their softness enables safer interaction and greater freedom of movement. Their lightweight and energy efficiency also contribute to reducing the carbon footprint of devices. However, the broader adoption of elastomers in high-performance applications remains limited due to an inherent trade-off between stiffness and toughness, as well as processing challenges. The development of elastomers that combine high mechanical performance with compatibility for additive manufacturing is therefore highly desirable.

This thesis introduces a new 3D printable elastomeric system: double network granular elastomers (DNGEs). DNGEs consist of a first elastomeric network confined within microparticles that are interconnected by a second network. By adjusting the composition of both networks, elastomers with mechanical properties that can be tuned across an unprecedented range were produced. The microparticles impart 3D printability, enabling the fabrication of complex elastomeric structures with locally varying compositions and mechanical properties that can deform in a pre-defined fashion. Furthermore, DNGEs exhibit enhanced fracture toughness and fatigue resistance compared to their bulk counterparts. This improvement is attributed to the locally varying compositions and architecture that facilitate reversible energy dissipation through efficient stress transfer between the two networks as well as crack deflection at the microparticles. Under compression, DNGEs demonstrate high energy dissipation alongside rapid shape recovery, making them suitable damping materials. To reduce the environmental impact of DNGEs, recyclable DNGEs (rDNGEs) were developed by introducing dynamic covalent bonds into the second network. Thereby, rDNGEs could be decomposed into microparticles that can be processed into rDNGEs exhibiting almost identical mechanical properties as the virgin counterparts.

Altogether, this thesis establishes DNGEs as a new class of 3D printable elastomers that combine strength, toughness and durability while offering pathways toward recyclability. These materials open up new opportunities in soft robotics, biomedical devices and protective systems, illustrating how enhancement of soft materials can lead to new technologies with improved performance, durability and reduced environmental footprint.