Wettability effect on hydraulic permeability of brain white matter

With brain white matter can be considered as a periodic fibrous porous medium mainly consisting of axons and interstitial fluid (ISF), the corresponding hydraulic permeability reflects the resistance of ISF flow in the extracellular space (ECS), thus playing a key role in molecular transport and drug delivery. As the ECS exhibits a typical width of 10-80 nm, the ISF flow poses a microscale flow problem with the wettability effect, which may induce a flow with a slip boundary and hence remains elusive. In this study, we idealized brain white matter as a periodic fibrous porous medium to quantify the effect of wettability on its hydraulic permeability, with fluid viscosity and slip boundary duly accounted for. We found that wettability led to enlarged hydraulic permeability by diminishing the effective viscosity and enlarging the slip length. We also found that, for the square arrangement of axons, wettability had a greater effect on perpendicular permeability relative to the parallel one, while for hexagonally arranged axons, the opposite held. Results presented in this study may provide theoretical guidance for cerebral edema treatment regimens and drug delivery.