Automatic medium exchange for micro-volume cell samples based on dielectrophoresis

Feasibility of an acoustophoresis-based system for a high-throughput cell washing: application to bioproduction

BACKGROUND AIMS

These last decades have seen the emergence and development of cell-based therapies, notably those based on mesenchymal stromal cells (MSCs). The advancement of these promising treatments requires increasing the throughput of processed cell for industrialization in order to reduce production costs. Among the various bioproduction challenges, downstream processing, including medium exchange, cell washing, cell harvesting and volume reduction, remains a critical step for which improvements are needed. Typically, these processes are performed by centrifugation. However, this approach limits the automation, especially in small batch productions where it is performed manually in open system.

METHODS

An acoustophoresis-based system was developed for cell washing. The cells were transferred from one stream to another via the acoustic forces and were collected in a different medium. The optimal flow rates of the different streams were assessed using red blood cells suspended in an albumin solution. Finally, the impact of acoustic washing on adipose tissue-derived MSCs (AD-MSCs) transcriptome was investigated by RNA-sequencing.

RESULTS

With a single passage through the acoustic device at input flow rate of 45 mL/h, the albumin removal was up to 90% while recovering 99% of RBCs. To further increase the protein removal, a loop washing in two steps was performed and has allowed an albumin removal ≥99% and a red blood cell/AD-MSCs recovery of 99%. After loop washing of AD-MSCs, only two genes, HES4 and MIR-3648-1, were differently expressed compared with the input.

CONCLUSIONS

In this study, we developed a continuous cell-washing system based on acoustophoresis. The process allows a theoretically high cell throughput while inducing little gene expression changes. These results indicate that cell washing based on acoustophoresis is a relevant and promising solution for numerous applications in cell manufacturing.

On‐chip microfluidic buffer swap of biological samples in‐line with downstream dielectrophoresis

Microfluidic cell enrichment by dielectrophoresis, based on biophysical and electrophysiology phenotypes, requires that cells be resuspended from their physiological media into a lower conductivity buffer for enhancing force fields and enabling the dielectric contrast needed for separation. To ensure that sensitive cells are not subject to centrifugation for resuspension and spend minimal time outside of their culture media, we present an on‐chip microfluidic strategy for swapping cells into media tailored for dielectrophoresis. This strategy transfers cells from physiological media into a 100‐fold lower conductivity media by using tangential flows of low media conductivity at 200‐fold higher flow rate versus sample flow to promote ion diffusion over the length of a straight channel architecture that maintains laminarity of the flow‐focused sample and minimizes cell dispersion across streamlines. Serpentine channels are used downstream from the flow‐focusing region to modulate hydrodynamic resistance of the central sample outlet versus flanking outlets that remove excess buffer, so that cell streamlines are collected in the exchanged buffer with minimal dilution in cell numbers and at flow rates that support dielectrophoresis. We envision integration of this on‐chip sample preparation platform prior to or post‐dielectrophoresis, in‐line with on‐chip monitoring of the outlet sample for metrics of media conductivity, cell velocity, cell viability, cell position, and collected cell numbers, so that the cell flow rate and streamlines can be tailored for enabling dielectrophoretic separations from heterogeneous samples.