Transient osmotic flows in a microfluidic channel: measurements of solute permeability and reflection coefficients of hydrogel membranes†

We first highlight theoretically a microfluidic configuration that allows to measure two fundamental parameters describing mass transport through a membrane: the solute permeability coefficient _D, and the associated reflection coefficient σ. This configuration exploits the high confinement of microfluidic geometries to relate these two coefficients to the dynamics of a transient flow induced by forward osmosis through a membrane embedded in a chip. We then applied this methodology to hydrogel membranes photo-crosslinked in a microchannel with in situ measurements of osmotically-induced flows. These experiments enable us to estimate _D and σ and their dependence on the molecular weight of the solute under consideration, ultimately leading to a precise estimate of the molecular weight cut-off of these hydrogel membranes.