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

Abstract

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.

Dielectrophoretic enrichment of live chemo-resistant circulating-like pancreatic cancer cells from media of drug-treated adherent cultures of solid tumors

“…Electrode channels were filled with liquefied Field's metal as described previously. 34,35 Briefly, the device was immersed in a water bath at 65 °C and the liquefied Field's metal (RotoMetals) was introduced through a syringe using positive pressure. After complete filling of the electrode channel, the device was allowed to cool at room temperature resulting in solidification of the metal.…”

“…32,33 Our prior work created a set of sequential lateral field non-uniformities orthogonal to the sample flow and extending over the device depth, 34 to enable DEP deflection at 10-20 μL min −1 flow rates, along with an on-chip means for cell exchange into an optimal buffer prior to DEP. 35 Since target CTCs have a more folded cell membrane structure and are larger in size on average than the background blood cells, 36,37 CTCs can be selected over blood cells by positive DEP (pDEP) based on their lower DEP crossover frequency 38,39 due to their larger size and higher membrane capacitance. However, the live chemoresistant PDAC cell subpopulation suspended in the culture media exhibits a wide size distribution that overlaps with dead cells suspended in the media, which includes smaller apoptotic cells and larger necrotic cells from the adherent culture.…”

Microfluidic Blood Separation: Key Technologies and Critical Figures of Merit

“…Buffer preparation requires several steps that take time, lead to sample loss in the washing steps, and can affect blood sample functionality. There are integrated microfluidic devices that change the blood sample medium into a DEP buffer as a stage prior to DEP separation [109]. This approach could avoid sample stress and minimize sample loss by eliminating traditional sample-washing steps.…”

Multichannel Impedance Cytometry Downstream of Cell Separation by Deterministic Lateral Displacement to Quantify Macrophage Enrichment in Heterogeneous Samples

“…[16] Hence, microfluidic separation based on multiple biophysical criteria integrated with on-chip phenotypic analysis at single-cell sensitivity can enhance discrimination of cellular phenotypes and be applied to enrich for minority subpopulations. [17,18,19] This phenotypic information is essential for device design, active control of separation conditions, [20] and sample choice to improve versatility of the workflow [21,22] and discrimination ability of the separation.…”