By Gail Dutton

Electroporation is an established method to remove unwanted cells from heterogenous cell samples, extract cell components, and transport molecules across cell membranes. Targeting individual cells, however, requires presorting or single-cell technologies and often damages the cells.

In contrast, in a proof-of-concept study, researchers at the Fraunhofer Institute for Cell Therapy and Immunology showed that they could electroporate predetermined cells identified in real-time based on the high-quality microscopic analysis of fluorescent cells. The benefits of applying highly localized electric fields rather than bulk electroporation are increased control and reproducibility.

The team, led by Michael Kirschbaum, PhD, group manager of microfluidic cell processing and cell analytics, stained the 10 µm-diameter target cells with green fluorescence and the non-target cells with blue fluorescence. Their small size allowed individual cells to be porated selectively, as long as the cell spacing also was at least 50 µm. After poration, the cells were flushed from the chip and collected in a 96-well plate.

Good specificity

This method achieved more than 90% specificity, an average poration rate greater than 50%, and throughput as high as 7,200 cells per hour. The theoretical maximum flow rate is about 18,000 cells per hour. In terms of sensitivity, stronger electroporation pulses led to better poration rates. Unfortunately, the stronger pulses decreased cell vitality. After three days, nearly 20% of the cells pulsed at 9kV/cm-1 were viable, compared to approximately 40% at 7kV/cm-1 and 90% at 5kV/cm-1.

Chip performance decreased over time, the paper reported. “Usually, we used each chip for three experiments, with a total of about 20,000 processed cells,” Kirschbaum and first author Felix Pfisterer, diploma engineer, told GEN.

The scientists said they are considering a disposable version of the microfluidic chips while also contemplating ways to increase their durability. Options may include “increasing the thickness of the poration electrode, applying protective coatings, or optimizing the pulse shape to achieve the highest poration effects at the lowest voltage.”

Future experiments may be designed “showing the system’s ability for cell transfection or extraction of intracellular material at single-cell resolution,” noted Kirschbaum and Pfisterer, adding that this method is easy and cost effective, using mainly off-the-shelf equipment. It can be easily parallelized and handle multiple types of cellular targets, they added.

Before it can be commercialized, they said, optimization is needed. That includes increasing throughput and adapting the method to enable sterilization, as well as scaling the production lines.

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