Elastic Pore Asymmetry Causes Flow Rectification

The human body is approximately 70% water and has many pathways and channels to transport fluid, such as pores, which are found throughout the body. Biological tissues are not rigid or perfectly symmetric. If a pore deforms asymmetrically, an oscillating pressure difference across the pore may drive more flow in one direction than another, resulting in a net flow, even if the net pressure is zero. One potential example of this is in the brain’s cerebrospinal and interstitial transport system, which plays a crucial role in clearing the brain’s waste, and where the fluid flows through gaps between astrocyte endfeet. To explore the possibility that these gaps act as flow rectifiers, we performed in vitro experiments and computational simulations of flow through an asymmetric pore driven by an oscillating pressure, designed to model flow through astrocyte endfeet. We observed flow rectification and quantified the resulting flow rates. We identified the geometric and material parameters that have the largest impact on flow rectification. These parameters could help design efficient bio-inspired passive valves.