Hydrogels are cross-linked, water-based polymer networks with reversible swelling, tunable porosity, elasticity, toughness, stiffness, and flexibility. The global market for hydrogels was valued 25.2 billion U.S. dollars in 2021 and is projected to reach 45.2 billion U.S. dollars by 2030 with major product segments in personal care and hygiene (sanitary pads, diapers), pharmaceuticals and healthcare, contact lenses and agriculture. In academic research, hydrogels are commonly applied in tissue engineering and regenerative medicine, additive manufacturing, drug delivery, as (bio)sensors, underwater adhesives, actuators or soft robots, in information storage, or photonics. Each application area requires a careful adjustment of the microstructural features of the hydrogel in order to engineer the material with suitable macroscopic mechanical properties. This connection between the physicochemical properties on a molecular level and the mechanical properties of the macroscopic object is commonly known as the structure-property relationship. Understanding the structure-property relationship of a material is of critical importance to predict material behavior and, therefore, has enabled researchers to engineer and design innovative hydrogel materials.