Electrode assemblies used for electroporation of cultured cells

Highly uniform in-situ cell electrotransfection of adherent cultures using grouped interdigitated electrodes

Cell electrotransfection is an effective approach for transferring exogenous molecules into living cells by electric stimulation. The existing in-situ electrotransfection micro-devices for adherent cells exhibit the drawbacks of low transfection efficiency and low cell viability. An important reason for these drawbacks is the unequal exposure of cells to the electric field. It was found that cells growing directly below the energized electrodes experience a much lower electric field intensity when compared to the cells growing below the spacing area of the electrodes, resulting in low transfection with a strip-like pattern. Therefore, a new strategy for the in-situ electrotransfection of adherent cells growing in a standard 12-well plate is proposed in this study. By sequentially energizing electrodes arranged in a nested and non-contact manner, the cells were exposed to an overall equal intensity of the electric field, and thus a higher efficiency of transfection was achieved. The seven cell lines transfected using this method exhibited high transfection efficiency and high cell viability, demonstrating the potential for studying gene function.

Comparison between direct and reverse electroporation of cells in situ: a simulation study

The discovery of the human genome has unveiled new fields of genomics, transcriptomics, and proteomics, which has produced paradigm shifts on how to study disease mechanisms, wherein a current central focus is the understanding of how gene signatures and gene networks interact within cells. These gene function studies require manipulating genes either through activation or inhibition, which can be achieved by temporarily permeabilizing the cell membrane through transfection to deliver cDNA or RNAi. An efficient transfection technique is electroporation, which applies an optimized electric pulse to permeabilize the cells of interest. When the molecules are applied on top of seeded cells, it is called “direct” transfection and when the nucleic acids are printed on the substrate and the cells are seeded on top of them, it is termed “reverse” transfection. Direct transfection has been successfully applied in previous studies, whereas reverse transfection has recently gained more attention in the context of high‐throughput experiments. Despite the emerging importance, studies comparing the efficiency of the two methods are lacking. In this study, a model for electroporation of cells in situ is developed to address this deficiency. The results indicate that reverse transfection is less efficient than direct transfection. However, the model also predicts that by increasing the concentration of deliverable molecules by a factor of 2 or increasing the applied voltage by 20%, reverse transfection can be approximately as efficient as direct transfection.

Automatic system for electroporation of adherent cells growing in standard multi-well plates

In this study an automatic system is presented to perform electroporation, also known as electropermeabilization, on adherent cells. It is an intention of this system to apply electric field pulses directly to cells growing in standard multi-well plates as a step forward to include this technique in standard laboratory protocols. An interdigitated microelectrode assembly constructed with Printed Circuit Board (PCB) is placed closely above the cell monolayer, and in order to avoid direct contact with cells, small micro-separators were included in the structure. Additionally, distribution of current density was modified by filling the gap between adjacent electrodes with a non conductive material as predicted by electric field simulations. This modification helps to concentrate the electric field intensity in the region where cells are present. The device was tested using C2C12 cell line growing adhered in 24 multi-well plates and fluorescent labeled dextran FD20S as the molecule to be delivered. Successful transfection was observed with minimal invasiveness of the operation reducing the stress caused to cells.

Reversible and irreversible electroporation of cell suspensions flowing through a localized DC electric field

Experiments on reversible and irreversible cell electroporation were carried out with an experimental setup based on a standard apparatus for horizontal electrophoresis, a syringe pump with regulated cell suspension flow velocity and a dcEF power supply. Cells in suspension flowing through an orifice in a barrier inserted into the electrophoresis apparatus were exposed to defined localized dcEFs in the range of 0-1000 V/cm for a selected duration in the range 10-1000 ms. This method permitted the determination of the viability of irreversibly electroperforated cells. It also showed that the uptake by reversibly electroperforated cells of fluorescent dyes (calcein, carboxyfluorescein, Alexa Fluor 488 Phalloidin), which otherwise do not penetrate cell membranes, was dependent upon the dcEF strength and duration in any given single electrical field exposure. The method yields reproducible results, makes it easy to load large volumes of cell suspensions with membrane non-penetrating substances, and permits the elimination of irreversibly electroporated cells of diameter greater than desired. The results concur with and elaborate on those in earlier reports on cell electroporation in commercially available electroporators. They proved once more that the observed cell perforation does not depend upon the thermal effects of the electric current upon cells. In addition, the method eliminates many of the limitations of commercial electroporators and disposable electroporation chambers. It permits the optimization of conditions in which reversible and irreversible electroporation are separated. Over 90% of reversibly electroporated cells remain viable after one short (less than 400 ms) exposure to the localized dcEF. Experiments were conducted with the AT-2 cancer prostate cell line, human skin fibroblasts and human red blood cells, but they could be run with suspensions of any cell type. It is postulated that the described method could be useful for many purposes in biotechnology and biomedicine and could help optimize conditions for in vivo use of both reversible and irreversible electroporation.

Design and implementation of a microelectrode assembly for use on noncontact in situ electroporation of adherent cells

In situ electroporation of adherent cells provides significant advantages with respect to electroporation systems for suspension cells, such as causing minimal stress to cultured cells and simplifying and saving several steps within the process. In this study, a new electrode assembly design is shown and applied to in situ electroporate adherent cell lines growing in standard multiwell plates. We designed an interdigitated array of electrodes patterned on copper with printed circuit board technology and covered with nickel/gold. Small interelectrode distances were used to achieve effective electroporation with low voltages. Epoxy-based microseparators were constructed to avoid direct contact with the cells and to create more uniform electric fields. The device was successful in the electropermeabilization of two different adherent cell lines, C2C12 and HEK 293, as assessed by the intracellular delivery of the fluorescent dextran FD20S. Additionally, as a collateral effect, we observed cell electrofusion in HEK 293 cells, thus making this device also useful for performing cell fusion. In summary, we show the effectiveness of this minimally invasive device for electroporation of adherent cells cultured in standard multiwell plates. The cheap technologies used in the fabrication process of the electrode assembly indicate potential use as a low-cost, disposable device.

Efficient electroporation of peptides into adherent cells: investigation of the role of mechano-growth factor in chondrocyte culture

Peptide therapeutics are of increasing interest due to their biological specificity. We used a simple technique to study the efficacy of inducing peptides into adherent chondrocytes by transiently permeabilizing the membrane with electric pulses (in situ electroporation). Mechano-growth factor (MGF) was selected as a model peptide. FITC-labeled MGF was added to cultures of adherent primary chondrocytes grown on ITO coated glass slides. Cells were subjected to 3-9 pulses of 175-275 V and evaluated by flow cytometry. Under optimal conditions, an electroporation efficiency of close to 50% could be achieved. This technique can be used to study the functional domains of intracellular peptides, peptide inhibition of signal transduction and intracrine-mediated effects of peptides in adherent cells.

Electroporation and ultrasound enhanced non-viral gene delivery in vitro and in vivo

Non-viral vectors are less efficient than the use of viral vectors for delivery of genetic material to cells in vitro and especially in vivo. However, viral vectors involve the use of foreign proteins that can stimulate both the innate and acquired immune response. In contrast, plasmid DNA can be delivered without carrier proteins and is non-immunogenic. Plasmid gene delivery can be enhanced by the use of physical methods that aid the passage of the plasmid through the cell membrane. Electroporation and microbubble-enhanced ultrasound are two of the most effective physical delivery methods and these can be applied to a range of different cell types in vitro and a broad range of tissues in vivo. Both techniques also have the advantage that, unlike viral vectors, they can be used to target specific tissues with systemic delivery. Although electroporation is often the more efficient of the two, microbubble-enhanced ultrasound causes less damage and is less invasive. This review provides an introduction to the methodology and summarises the range of cells and tissues that have been genetically modified using these techniques.