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

TL;DR

This paper introduces a microfluidic method to measure solute permeability and reflection coefficients of hydrogel membranes by analyzing transient osmotic flows, providing insights into membrane transport properties.

Contribution

The study presents a novel microfluidic approach to simultaneously measure permeability and reflection coefficients, and applies it to hydrogel membranes to determine their molecular weight cut-off.

Findings

Measured solute permeability and reflection coefficients of hydrogel membranes.

Determined the dependence of transport parameters on solute molecular weight.

Estimated the molecular weight cut-off of the hydrogel membranes.

Abstract

We first highlight theoretically a microfluidic configuration that allows to measure two fundamental parameters describing mass transport through a membrane: the solute permeability coefficient $\mathcal{L}_D$, and the associated reflection coefficient $\sigma$. 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 \textit{in situ} measurements of osmotically-induced flows. These experiments enable us to estimate $\mathcal{L}_D$ and $\sigma$ 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.