Net Flow Through Soft Porous Media Generated by Periodic Mean-Zero Pressure Gradient

Characterization of fluid transport through soft porous media is crucial to understanding and predicting mass transport in a variety of biological and industrial contexts. Recent studies have shown complex hysteretic behavior in the material deformation of soft porous media, which leads to a variable, nonlinear relationship between fluid flux and pressure gradients such that Darcy's law is insufficient. We add fluorescent microspheres to fluid passing through a bed of densely-packed hydrogel particles and track their motion to simultaneously characterize the fluid flow and porous media deformation. When subjected to asymmetric, mean-zero temporally periodic pressure gradients, a non-zero directional flow is observed through the porous media. We quantify the magnitude of the directional flow as a function of the pressure gradient and time scale of pressure variation. Our observations offer insight into potential mechanisms of fluid transport for numerous biological systems, such as the interstitial spaces of the body and brain tissues.