Book excerpt: Hydrogels are polymer networks embedded in a solvent which is usually predominantly water. Due to the solvent diffusion and rearrangement of the polymer network, hydrogels exhibit poroelastic and viscoelastic behaviors. The two behaviors are usually coupled and may influence other mechanical properties, such as fracture. While there is much work on modeling and simulation of poroelasticity, viscoelasticity, and fracture, there is still a need for more experimental work that explores the response of the material and the calibration of the material response. In this dissertation, three large suites of experiments were performed under nonhomogeneous conditions to characterize the linear and nonlinear poroelasticity, viscoelasticity, and fracture in gelatin-based hydrogels. First, the poroelasticity of gelatin-based hydrogel of two different compositions is examined through drying and swelling experiments, achieved by adjusting the humidity levels in an environmentally controlled enclosure. The deformation of the specimens was quantified through Digital Image Correlation. The experimental measurements were compared with the simulations based on the Finite Element Method (FEM) implemented on the public domain code FEniCS, to provide a way to calibrate the material parameters both for linear and nonlinear poroelasticity. Second, the coupled poroelastic and viscoelastic behaviors of hydrogels were explored through simultaneous swelling/drying and creep experiments also in a controlled environment. This work showed that the decomposition of the volumetric and isochoric deformation provides a way to separate the poroelastic and viscoelastic behaviors. According to the experimental results, the volumetric deformation was dominated by water diffusion, and isochoric deformation was influenced by both viscoelasticity and poroelasticity. A nonlinear poroviscoelastic theory was developed based on a two-potential formulation under a thermodynamic framework, that successfully captured the coupled power-law creep and swelling/drying behaviors. Finally, the fracture behavior of hydrogels was explored under various conditions through poroelastic diffusion and viscoelastic creep. The viscoelastic J-like integral based on Schapery's theory was calculated from the measured displacement field and served as a characteristic parameter for crack growth in quasi-steady conditions. To further explore the poroelastic influence on the crack tip, fracture tests of immersed-crack-tip conditions were performed, which showed that water diffusion decreased the fracture energy