  We use dedicated microfluidic devices to expose soft hydrogel particles to a
rapid change in the externally applied osmotic pressure and observe a
non-monotonic response: After an initial rapid compression the particle slowly
reswells to approximately its original size. Using a simple phenomenological
and a more elaborate poroelastic model, we extract important material
properties from a single microfluidic experiment, including the compressive
modulus, the gel permeability and the diffusivity of the osmolyte inside the
gel. We expect our approach to be relevant to applications such as controlled
release, chromatography, and responsive materials.
