  We investigate pattern transformations of periodic hydrogel systems that are
triggered by swelling-induced structural instabilities. The types of
microstructures considered in the present work include single-phase and
two-phase voided hydrogel structures as well as reinforced hydrogel thin films.
While the observed transformations of the single-phase structures show good
agreement with experimental findings, the two-phase materials provide novel
patterns associated with wrinkling of internal surfaces. Furthermore, an
extensive parametric study on the reinforced hydrogel thin films reveals new
opportunities for the design of complex out-of-plane surface modes caused by
swelling-induced instabilities. Next to the mentioned buckling-type
instabilities, we encountered the development of micro-creases at the internal
surfaces of periodic media before the loss of strong ellipticity of effective
moduli.
