A novel ultralow conductivity electromanipulation buffer improves cell viability and enhances dielectrophoretic consistency

Hyler AR, Hong D, Davalos RV, Swami NS, Schmelz EM. A novel ultralow conductivity electromanipulation buffer improves cell viability and enhances dielectrophoretic consistency. Electrophoresis. 2021; https://doi.org/10.1002/elps.202000324

Cell separation has become a critical diagnostic, research, and treatment tool for personalized medicine. Despite significant advances in cell separation, most widely used applications require the use of multiple, expensive antibodies to known markers in order to identify subpopulations of cells for separation. Dielectrophoresis (DEP) provides a biophysical separation technique that can target cell subpopulations based on phenotype without labels and return native cells for downstream analysis. One challenge in employing any DEP device is the sample being separated must be transferred into an ultralow conductivity medium, which can be detrimental in retaining cells’ native phenotypes for separation. Here, we measured properties of traditional DEP reagents and determined that after just 12 h of exposure and subsequent culture, cells’ viability was significantly reduced below 50%. We developed and tested a novel buffer (Cyto Buffer) that achieved 6 weeks of stable shelf-life and demonstrated significantly improved viability and physiological properties. We then determined the impact of Cyto Buffer on cells’ dielectric properties and morphology and found that cells retained properties more similar to that of their native media. Finally, we vetted Cyto Buffer's usability on a cell separation platform (Cyto R1) to determine combined efficacy for cell separations. Here, more than 80% of cells from different cell lines were recovered and were determined to be >70% viable following exposure to Cyto Buffer, flow stimulation, electromanipulation, and downstream collection and growth. The developed buffer demonstrated improved opportunities for electrical cell manipulation, enrichment, and recovery for next generation cell separations.

Benign (A) and malignant (B) cell lines’ viability following prolonged exposure to traditional electromanipulation buffer in comparison to native media (control). Cells were exposed to buffer for up to 3 h then metabolism was tested after cells were reseeded and grown for 48 h. Values shown are mean ± SEM where * indicate statistical significance (* p < 0.05, **p < 0.01, ***p < 0.001) in comparison to the control.

(A) Schematic overview of the Cyto R1 Platform components used in this work. The core technology employs a contactless dielectrophoresis (cDEP) microfluidic device (B) interfaced with electronics and fluidics systems. Experiments are then visualized on an inverted microscope with laptop-based software control. The cDEP device is constructed in a single layer out of COC containting 20 μm pillars and a 14 μm membrane that allows electrical fields to pass but retains separation of the sample and the liquid electrodes (cDEP).