Rapid advances in the biomedical field increasingly often demand soft materials that can be processed into complex 3D shapes while being able to reliably bear significant loads. Granular hydrogels have the potential to serve as artificial tissues because they can be 3D printed into complex shapes and their composition can be tuned over short length scales. Unfortunately, granular hydrogels are typically soft such that they cannot be used for load‐bearing applications. To address this shortcoming, individual microgels can be connected through a percolating network, such that they introduce the double network toughening mechanism into granular hydrogels. However, the influence of the microgel size and concentration on the processing and toughness of microgel‐reinforced hydrogels (MRHs) remains to be elucidated. Here, it is demonstrated that processing and toughness depend on the inter‐microgel connectivity, while the stress at break is solely dependent on the microgel size. These findings offer an in‐depth understanding of how liquid‐ and paste‐like precursors containing soft, deformable microgels can be processed into bulk microstructured soft materials and how the size and concentration of these microgels influence the mechanical properties of microgel‐reinforced hydrogels.

Front Cover: Article number 2200196 by Esther Amstad and co‐workers demonstrates that the stiffness of microgel‐reinforced bulk hydrogels is solely dependent on the microgel volume fraction, whereas their stress at break also depends on the microgel size and their toughness on the intermicrogel connectivity. These insights enable the tuning of the mechanical properties of 3D printable or castable microparticle‐reinforced hydrogels over a much wider range than was previously possible.