The Slow Motion of Rigid Particles Through Hydrogels*

We report the results of an experimental investigation into the slow motion of rigid particles through concentrated collections of hydrated hydrogels. The experiment is analogous to a simple falling bob viscometer where the viscous fluid has been replaced by a material with complex properties. Surprising systematic behaviour is uncovered and apparent connections with Stokes and elastoviscoplastic flows are revealed. However, clear differences with these standard flows are also found and the origin of these appears to lie in a surprising dependence on end boundary conditions.