Mechanics of confined swelling in hydrogels

Hydrogels are stimuli responsive materials whose physical-chemical-mechanical properties and responsiveness are tunable; their behavior is similar to those observed in natural living tissues, and their use is promising in a wide range of applications, especially in the biomedical field. In the present study, we investigate experimentally and provide a theoretical interpretation of the swelling phenomenon, both in free (i.e. without constraints) and confined 1-D and 2-D conditions, of poly(acrylamid-co-acrylic acid) hydrogels, in terms of volume ratio increase, of the Flory-Huggins interaction parameter, and the stress state arising in the network. Relying on a theoretical multi-physics-based theory describing fluid diffusion, and mechanics, the swelling process is interpreted and quantitatively discussed, providing new insights in the realm of controlled swelling of hydrogels for their exploitation in new and advanced applications.