The non-contact-based determination of the membrane permeability to water and dimethyl sulfoxide of cells virtually trapped in a self-induced micro-vortex.

Abstract

The cell-membrane permeabilities of a cell type toward water (<i>L</i>_p) and cryoprotective agents (<i>P</i>_s) provide crucial cellular information for achieving optimal cryopreservation in the biobanking industry. In this work, cell membrane permeability was successfully determined <i>via</i> directly visualizing the transient profile of the cell volume change in response to a sudden osmotic gradient instantaneously applied between the intracellular and extracellular environments. A new micro-vortex system was developed to virtually trap the cells of interest in flow-driven hydrodynamic circulation passively formed at the expansion region in a microfluidic channel, where trapped cells remain in suspension and flow with the streamline of the localized vortex, involving no physical contact between cells and the device structure; furthermore, this supports a pragmatic assumption of 100% sphericity and allows for the calculation of the active surface area of the cell membrane for estimating the actual cell volume from two-dimensional images. For an acute T-cell lymphoma cell line (Jurkat), moderately higher values (<i>L</i>_p = 0.34 μm min^-1 atm^-1 for a binary system, and <i>L</i>_p = 0.16 μm min^-1 atm^-1 and <i>P</i>_s = 0.55 × 10^-3 cm min^-1 for a ternary system) were measured than those obtained from prior methods utilizing contact-based cell-trapping techniques, manifesting the influence of physical contact on accuracy during the determination of cell membrane permeability.