Nonlinear poroviscoelastic behavior of gelatin-based hydrogel

The mechanical properties of hydrogels involve solvent diffusion as well as viscous dissipation in the network, with the coupling called poroviscoelasticity. To explore the poroviscoelastic behavior, we performed tests on a gelatin-based hydrogel in which poroelastic swelling/drying occurred at controlled humidity levels while simultaneously developing creep deformation under a uniaxial load. These experimental results allowed the decomposition of the deformation into volumetric and isochoric parts, and the inference that volumetric deformation was dominated by poroelastic effects while isochoric deformation was influenced by both viscoelastic and poroelastic effects. We developed a nonlinear model based on an extension of the Flory–Rehner theory of the ternary system and the fractional derivative model of viscoelasticity to capture nonlinear poroviscoelastic behavior. The model was implemented into FEniCS finite element software. Comparisons of numerical simulations based on this model to experimental measurements were used to calibrate material parameters.