The goal of this Master's thesis is to provide a physical and mathematical model that attempts to describe the deformation process of hydrogels. Hydrogels are commonly defined as three dimensional networks of hydrophilic polymers with the ability to retain a large quantity of water. Nevertheless, describing the deformation process of hydrogels can be challenging. In this thesis, I expose a variational model that is obtained with the Onsager's principle. This principle provides an ideal setting for discretization and numerical analysis.