Centrifugal Draining Tests for Permeability Determination

Despite its relevance, permeability measurements have received comparatively little attention, and reported values for the same tissue can span several orders of magnitude, partly due to experimental challenges related to sample clamping, the definition of a reference geometry, and tissue inhomogeneity. With our new method, liquid efflux from a hydrated tissue sample is induced by centrifugal force. In a typical experiment, thin tissue samples are centrifuged at high speed, causing liquid to drain from the sample under the resulting centrifugal body forces, where the mass loss is measured at defined time intervals. A series of additional characterisations allows the identification of the sample's reference area, mean thickness and solid volume fraction. Because the driving force is a volumetric body force rather than an externally applied boundary condition, the method is largely insensitive to irregularities in sample geometry and does not require tight mechanical clamping — a key source ofuncertainty in conventional permeation and compression experiments.

The hydraulic permeability is quantified through an inverse analysis based on a quadriphasic computational model of the tissue [1], which accounts for the solid, liquid and dissolved ionic phases and their interactions. Simulations of the centrifugation experiment are fitted to the measured mass–time curves to identify parameters of a volume-dependent model of hydraulic permeability.