Micro-electroporation of mesenchymal stem cells with alternating electrical current pulses

Nanotechnology at the crossroads of stem cell medicine

Nanotechnology in stem cell medicine is an interdisciplinary field which has gained a lot of interest recently. This domain addresses key challenges associated with stem cell medicine such as cell isolation, targeted delivery, and tracking. Nanotechnology-based approaches, including magnetic cell sorting, fluorescent tagging, and drug or biomolecule conjugation for delivery, have enhanced precision in stem cell isolation and guided cell migration, increasing the therapeutic potential. Recent studies have focused on using nanomaterials and scaffolds to drive stem cell differentiation by activating specific molecular pathways, achieved through embedding biomolecules within the scaffold or through the scaffold's material composition and structure alone. These innovations hold promise in therapeutic applications across various diseases, including cancer stem cell targeting, neurodegenerative disorders, pre-eclampsia, cardiovascular conditions, and organoid development. This review examines recent advancements in the field, explores potential applications like biosensors and nanochips, and highlights the challenges and research gaps.

2D electrical admittance lattice model of biological cellular system for modeling electroporation

In this work, a new modeling approach is presented to obtain a two-dimensional transport lattice of a biological cellular system for the calculation of the potential distribution throughout the system and investigation of the corresponding membrane electroporation. The presented model has been obtained by a modified bilayer model of the cell membrane. This modified membrane model allows for an effective inclusion of the shape of the cell membrane in the potential calculation. The results of the model have shown good agreement with the results of the well-known Schwan equation and COMSOL Multiphysics for the circular cell. The simulation results show that both membranes of a mitochondrion can be simultaneously electroporated by an alternating voltage source with frequencies between 1 MHz and 1 GHz.

Pulsed Field Ablation: A Comprehensive Update

One of the recent advancements in the field of cardiac electrophysiology is pulsed field ablation (PFA). PFA is a novel energy modality that does not rely on thermal processes to achieve ablation which, in turn, results in limited collateral damage to surrounding structures. In this review, we discuss the mechanisms, safety, efficacy, and clinical applications of PFA for the management of atrial and ventricular arrhythmias. We also summarize the published pre-clinical and clinical studies regarding this new technology.

Non-viral gene delivery to human mesenchymal stem cells: a practical guide towards cell engineering

In recent decades, human mesenchymal stem cells (hMSCs) have gained momentum in the field of cell therapy for treating cartilage and bone injuries. Despite the tri-lineage multipotency, proliferative properties, and potent immunomodulatory effects of hMSCs, their clinical potential is hindered by donor variations, limiting their use in medical settings. To address this challenge, gene delivery technologies have emerged as a promising approach to modulate the phenotype and commitment of hMSCs towards specific cell lineages, thereby enhancing osteochondral repair strategies. This review provides a comprehensive overview of current non-viral gene delivery approaches used to engineer MSCs, highlighting key factors such as the choice of nucleic acid or delivery vector, transfection strategies, and experimental parameters. Additionally, it outlines various protocols and methods for qualitative and quantitative evaluation of their therapeutic potential as a delivery system in osteochondral regenerative applications. In summary, this technical review offers a practical guide for optimizing non-viral systems in osteochondral regenerative approaches. hMSCs constitute a key target population for gene therapy techniques. Nevertheless, there is a long way to go for their translation into clinical treatments. In this review, we remind the most relevant transfection conditions to be optimized, such as the type of nucleic acid or delivery vector, the transfection strategy, and the experimental parameters to accurately evaluate a delivery system. This survey provides a practical guide to optimizing non-viral systems for osteochondral regenerative approaches.

M-TUBE enables large-volume bacterial gene delivery using a high-throughput microfluidic electroporation platform

Conventional cuvette-based and microfluidics-based electroporation approaches for bacterial gene delivery have distinct advantages, but they are typically limited to relatively small sample volumes, reducing their utility for applications requiring high throughput such as the generation of mutant libraries. Here, we present a scalable, large-scale bacterial gene delivery approach enabled by a disposable, user-friendly microfluidic electroporation device requiring minimal device fabrication and straightforward operation. We demonstrate that the proposed device can outperform conventional cuvettes in a range of situations, including across Escherichia coli strains with a range of electroporation efficiencies, and we use its large-volume bacterial electroporation capability to generate a library of transposon mutants in the anaerobic gut commensal Bifidobacterium longum.

New horizons in developing cell lysis methods: A Review

Cell lysis is an essential step in many studies related to biology and medicine. Based on the scale and medium that cell lysis is carried out, there are three main types of the cell lysis: 1) lysis of the cells in the surrounding environment, 2) lysis of the isolated or cultured cells and 3) Single cell lysis. Conventionally, several cell lysis methods have been developed, such as freeze-thawing, bead beating, incursion in liquid nitrogen, sonication and enzymatic and chemical based approaches. In recent years, various novel technologies have been employed to develop new methods of cell lysis. The aim of studies in this field is to introduce more precise and efficient tools or to reduce the costs of cell lysis procedures. Nanostructure based lysis methods, acoustic oscillation, electrical current, irradiation, bacteria-mediated cell lysis, magnetic ionic liquids, bacteriophage genes, monolith columns, hydraulic forces and steam explosion are some examples of new developed cell lysis methods. Beside the significant advances in this field, there are still many challenges and the tools must be further improved. This article is protected by copyright. All rights reserved.

Recent Advances in Microscale Electroporation

Electroporation (EP) is a commonly used strategy to increase cell permeability for intracellular cargo delivery or irreversible cell membrane disruption using electric fields. In recent years, EP performance has been improved by shrinking electrodes and device structures to the microscale. Integration with microfluidics has led to the design of devices performing static EP, where cells are fixed in a defined region, or continuous EP, where cells constantly pass through the device. Each device type performs superior to conventional, macroscale EP devices while providing additional advantages in precision manipulation (static EP) and increased throughput (continuous EP). Microscale EP is gentle on cells and has enabled more sensitive assaying of cells with novel applications. In this Review, we present the physical principles of microscale EP devices and examine design trends in recent years. In addition, we discuss the use of reversible and irreversible EP in the development of therapeutics and analysis of intracellular contents, among other noteworthy applications. This Review aims to inform and encourage scientists and engineers to expand the use of efficient and versatile microscale EP technologies.

Recent advances in microfluidic-based electroporation techniques for cell membranes

Electroporation is a fundamental technique for applications in biotechnology. To date, the ongoing research on cell membrane electroporation has explored its mechanism, principles and potential applications. Therefore, in this review, we first discuss the primary electroporation mechanism to help establish a clear framework. Within the context of its principles, several critical terms are highlighted to present a better understanding of the theory of aqueous pores. Different degrees of electroporation can be used in different applications. Thus, we discuss the electric factors (shock strength, shock duration, and shock frequency) responsible for the degree of electroporation. In addition, finding an effective electroporation detection method is of great significance to optimize electroporation experiments. Accordingly, we summarize several primary electroporation detection methods in the following sections. Finally, given the development of micro- and nano-technology has greatly promoted the innovation of microfluidic-based electroporation devices, we also present the recent advances in microfluidic-based electroporation devices. Also, the challenges and outlook of the electroporation technique for cell membrane electroporation are presented.

Microfluidic and Nanofluidic Intracellular Delivery

Innate cell function can be artificially engineered and reprogrammed by introducing biomolecules, such as DNAs, RNAs, plasmid DNAs, proteins, or nanomaterials, into the cytosol or nucleus. This process of delivering exogenous cargos into living cells is referred to as intracellular delivery. For instance, clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 gene editing begins with internalizing Cas9 protein and guide RNA into cells, and chimeric antigen receptor-T (CAR-T) cells are prepared by delivering CAR genes into T lymphocytes for cancer immunotherapies. To deliver external biomolecules into cells, tools, including viral vectors, and electroporation have been traditionally used; however, they are suboptimal for achieving high levels of intracellular delivery while preserving cell viability, phenotype, and function. Notably, as emerging solutions, microfluidic and nanofluidic approaches have shown remarkable potential for addressing this open challenge. This review provides an overview of recent advances in microfluidic and nanofluidic intracellular delivery strategies and discusses new opportunities and challenges for clinical applications. Furthermore, key considerations for future efforts to develop microfluidics- and nanofluidics-enabled next-generation intracellular delivery platforms are outlined.

Microfluidic electrical cell lysis for high-throughput and continuous production of cell-free varicella-zoster virus

Varicella-zoster virus (VZV), the causative agent of varicella and herpes zoster, is highly cell-associated and spreads via cell-to-cell contact in tissue culture. The lack of cell-free VZV hampers studies on VZV biology as well as antiviral and vaccine development. In the present study, a poly(methylmethacrylate) microfluidic device integrated with arrays of microelectrode was fabricated to continuously electrolyse VZV-infected cells to produce cell-free viruses. By designing multiple constrictions and microelectrode arrays, a high electric field is focused on the constricted region of the microchannel to disrupt large numbers of virus-infected cells with high-throughput on a microfluidic platform. Plaque assay and scanning electron microscopy were conducted to quantify and characterize cell-free VZV produced using the microfluidic continuous-flow electrical cell lysis device. The process of microfluidic electrical cell lysis followed by subsequent filtration and virus concentration process yielded a 1.4-2.1 × 10⁴ plaque-forming units (PFUs) per mL of cell-free VZV from 7.0 × 10⁶ VZV-infected human foreskin fibroblasts (HFF) cells. The high electric field formed inside a microfluidic channel combined with the continuous-flow of virus-infected cells within the microchannel enabled the rapid and efficient production of high-titer cell-free virus in large quantities with relatively low input of the voltage.

Review of Microfluidic Methods for Cellular Lysis

Cell lysis is a process in which the outer cell membrane is broken to release intracellular constituents in a way that important information about the DNA or RNA of an organism can be obtained. This article is a thorough review of reported methods for the achievement of effective cellular boundaries disintegration, together with their technological peculiarities and instrumental requirements. The different approaches are summarized in six categories: chemical, mechanical, electrical methods, thermal, laser, and other lysis methods. Based on the results derived from each of the investigated reports, we outline the advantages and disadvantages of those techniques. Although the choice of a suitable method is highly dependent on the particular requirements of the specific scientific problem, we conclude with a concise table where the benefits of every approach are compared, based on criteria such as cost, efficiency, and difficulty.

Microfluidic single-cell analysis-Toward integration and total on-chip analysis

Various types of single-cell analyses are now extensively used to answer many biological questions, and with this growth in popularity, potential drawbacks to these methods are also becoming apparent. Depending on the specific application, workflows can be laborious, low throughput, and run the risk of contamination. Microfluidic designs, with their advantages of being high throughput, low in reaction volume, and compatible with bio-inert materials, have been widely used to improve single-cell workflows in all major stages of single-cell applications, from cell sorting to lysis, to sample processing and readout. Yet, designing an integrated microfluidic chip that encompasses the entire single-cell workflow from start to finish remains challenging. In this article, we review the current microfluidic approaches that cover different stages of processing in single-cell analysis and discuss the prospects and challenges of achieving a full integrated workflow to achieve total single-cell analysis in one device.

Single-Cell Point Constrictions for Reagent-Free High-Throughput Mechanical Lysis and Intact Nuclei Isolation

Highly localized (point) constrictions featuring a round geometry with ultra-sharp edges in silicon have been demonstrated for the reagent-free continuous-flow rapid mechanical lysis of mammalian cells on a single-cell basis. Silicon point constrictions, robust structures formed by a single-step dry etching process, are arranged in a cascade along microfluidic channels and can effectively rupture cells delivered in a pressure-driven flow. The influence of the constriction size and count on the lysis performance is presented for fibroblasts in reference to total protein, DNA, and intact nuclei levels in the lysates evaluated by biochemical and fluoremetric assays and flow-cytometric analyses. Protein and DNA levels obtained from an eight-constriction treatment match or surpass those from a chemical method. More importantly, many intact nuclei are found in the lysates with a relatively high nuclei-isolation efficiency from a four-constriction treatment. Point constrictions and their role in rapid reagent-free disruption of the plasma membrane could have implications for integrated sample preparation in future lab-on-a-chip systems.

Synchronized Electromechanical Shock Wave-Induced Bacterial Transformation

We report a simple device that generates synchronized mechanical and electrical pressure waves for carrying out bacterial transformation. The mechanical pressure waves are produced by igniting a confined nanoenergetic composite material that provides ultrahigh pressure. Further, this device has an arrangement through which a synchronized electric field (of a time-varying nature) is initiated at a delay of ≈85 μs at the full width half-maxima point of the pressure pulse. The pressure waves so generated are incident to a thin aluminum-polydimethylsiloxane membrane that partitions the ignition chamber from the column of the mixture containing bacterial cells (Escherichia coli BL21) and 4 kb transforming DNA. A combination of mechanical and electrical pressure pulse created through the above arrangement ensures that the transforming DNA transports across the cell membrane into the cell, leading to a transformation event. This unique device has been successfully operated for efficient gene (∼4 kb) transfer into cells. The transformation efficacy of this device is found comparable to the other standard methods and protocols for carrying out the transformation.

Microfluidic approaches for cell-based molecular diagnosis

The search for next-generation biomarkers has enabled cell-based diagnostics in a number of disciplines ranging from oncology to pharmacogenetics. However, cell-based diagnostics are still far from clinical reality due to the complex assays and associated protocols which typically require cell isolation, lysis, DNA extraction, amplification, and detection steps. Leveraging recent advances in microfluidics, many biochemical assays have been translated onto microfluidic platforms. We have compared and summarized recent advances in modular approaches toward the realization of fully-integrated, cell-based molecular diagnostics for clinical and point-of-care applications.

Non-electrolytic microelectroporation

Micro and nano technologies are of increasing importance in microfluidics devices used for electroporation (electroporation - the permeabilization of the cell membrane with brief high electric field pulses). Electrochemical reactions of electrolysis occur whenever an electric current flows between an electrode and an ionic solution. It can have substantial detrimental effects, both on the cells and solutions during the electroporation. As electrolysis is a surface phenomenon, between electrodes and solution, the extent of electrolysis is increased in micro and nano electroporation over macro-electroporation, because the surface area of the electrodes in micro and nano electroporation is much larger. A possible way to eliminate the electrolytic effect is to develop non-electrolytic microelectroporation by coating the microelectroporation devices with a dielectric insulating layer. In this study, we examine the effect of a dielectric insulating layer on the performance of a singularity microelectroporation device that we have recently designed. Using numerical analysis, we study the effects of various design parameters including, input sinusoidal voltage amplitude and frequency, geometrical configuration and material electrical properties on the electroporation performance of the non-electrolytic microelectroporation device. In the simulation, we used properties of four real dielectric materials and four solutions of interest for microelectroporation. We characterized the effect of various design parameters of relevance to singularity based microelectroporation, on non-electrolytic microelectroporation. Interestingly, we found that the system behaves in some aspects as a filter and in many circumstances saturation of performance is reached. After saturation is reached, changes in parameters will not affect the performance of the device.

Irreversible electroporation ablation for atrial fibrillation

Atrial fibrillation (AF) is one of the most important problems in modern cardiology. Thermal ablation therapies, especially radiofrequency ablation (RF), are currently "gold standard" to treat symptomatic AF by localized tissue necrosis. Despite the improvements in reestablishing sinus rhythm using available methods, both success rate and safety are limited by the thermal nature of procedures. Thus, while keeping the technique in clinical practice, safer and more versatile methods of removing abnormal tissue are being investigated. This review focuses on irreversible electroporation (IRE), a nonthermal ablation method, which is based on the unrecoverable permeabilization of cell membranes caused by short pulses of high voltage/current. While still in its preclinical steps for what concerns interventional cardiac electrophysiology, multiple studies have shown the efficacy of this method on animal models. The observed remodeling process shows this technique as tissue specific, triggering apoptosis rather than necrosis, and safer for the structures adjacent the myocardium. So far, proposed IRE methodologies are heterogeneous. The number of devices (both generators and applicators), techniques, and therapeutic goals impair the comparability of performed studies. More questions regarding systemic safety and optimal processes for AF treatment remain to be answered. This work provides an overview of the electroporation process, and presents different results obtained by cardiology-oriented research groups that employ IRE ablation, with focus of AF-related targets. This contribution on the topic aspires to be a practical guide to approach IRE ablation for cardiac arrhythmias, and to highlight controversial features and existing knowledge, to provide background for future improved experimentation with IRE in arrhythmology.

Simultaneous electroporation and dielectrophoresis in non-electrolytic micro/nano-electroporation

It was recently shown that electrolysis may play a substantial detrimental role in microfluidic electroporation. To overcome this problem, we have developed a non-electrolytic micro/nano electroporation (NEME) electrode surface, in which the metal electrodes are coated with a dielectric. A COMSOL based numerical scheme was used to simultaneously calculate the excitation frequency and dielectric material properties dependent electric field delivered across the dielectric, fluid flow, electroporation field and Clausius-Mossotti factor for yeast and E. coli cells flowing in a channel flow across a NEME surface. A two-layer model for yeast and a three-layer model for E. coli was used. The numerical analysis shows that in NEME electroporation, the electric fields could induce electroporation and dielectrophoresis simultaneously. The simultaneous occurrence of electroporation and dielectrophoresis gives rise to several interesting phenomena. For example, we found that a certain frequency exists for which an intact yeast cell is drawn to the NEME electrode, and once electroporated, the yeast cell is pushed back in the bulk fluid. The results suggest that developing electroporation technologies that combine, simultaneously, electroporation and dielectrophoresis could lead to new applications. Obviously, this is an early stage numerical study and much more theoretical and experimental research is needed.

Sine wave electropermeabilization reveals the frequency-dependent response of the biological membranes

The permeabilization of biological membranes by electric fields, known as electroporation, has been traditionally performed with square electric pulses. These signals distribute the energy applied to cells in a wide frequency band. This paper investigates the use of sine waves, which are narrow band signals, to provoke electropermeabilization and the frequency dependence of this phenomenon. Single bursts of sine waves at different frequencies in the range from 8 kHz-130 kHz were applied to cells in vitro. Electroporation was studied in the plasma membrane and the internal organelles membrane using calcium as a permeabilization marker. Additionally, a double-shell electrical model was simulated to give a theoretical framework to our results. The electroporation efficiency shows a low pass filter frequency dependence for both the plasma membrane and the internal organelles membrane. The mismatch between the theoretical response and the observed behavior for the internal organelles membrane is explained by a two-step permeabilization process: first the permeabilization of the external membrane and afterwards that of the internal membranes. The simulations in the model confirm this two-step hypothesis when a variable plasma membrane conductivity is considered in the analysis. This study demonstrates how the use of narrow-band signals as sine waves is a suitable method to perform electroporation in a controlled manner. We suggest that the use of this type of signals could bring a simplification in the investigations of the very complex phenomenon of electroporation, thus representing an interesting option in future fundamental studies.

Microscale Symmetrical Electroporator Array as a Versatile Molecular Delivery System

Successful developments of new therapeutic strategies often rely on the ability to deliver exogenous molecules into cytosol. We have developed a versatile on-chip vortex-assisted electroporation system, engineered to conduct sequential intracellular delivery of multiple molecules into various cell types at low voltage in a dosage-controlled manner. Micro-patterned planar electrodes permit substantial reduction in operational voltages and seamless integration with an existing microfluidic technology. Equipped with real-time process visualization functionality, the system enables on-chip optimization of electroporation parameters for cells with varying properties. Moreover, the system’s dosage control and multi-molecular delivery capabilities facilitate intracellular delivery of various molecules as a single agent or in combination and its utility in biological research has been demonstrated by conducting RNA interference assays. We envision the system to be a powerful tool, aiding a wide range of applications, requiring single-cell level co-administrations of multiple molecules with controlled dosages.

Avoiding the side effects of electric current pulse application to electroporated cells in disposable small volume cuvettes assures good cell survival

Background

The harmful side effects of electroporation to cells due to local changes in pH, the appearance of toxic electrode products, temperature increase, and the heterogeneity of the electric field acting on cells in the cuvettes used for electroporation were observed and discussed in several laboratories. If cells are subjected to weak electric fields for prolonged periods, for example in experiments on cell electrophoresis or galvanotaxis the same effects are seen. In these experiments investigators managed to reduce or eliminate the harmful side effects of electric current application.

Methods

For the experiments, disposable 20 μl cuvettes with two walls made of dialysis membranes were constructed and placed in a locally focused electric field at a considerable distance from the electrodes. Cuvettes were mounted into an apparatus for horizontal electrophoresis and the cells were subjected to direct current electric field (dcEF) pulses from a commercial pulse generator of exponentially declining pulses and from a custom-made generator of double and single rectangular pulses.

Results

More than 80% of the electroporated cells survived the dcEF pulses in both systems. Side effects related to electrodes were eliminated in both the flow through the dcEF and in the disposable cuvettes placed in the focused dcEFs. With a disposable cuvette system, we also confirmed the sensitization of cells to a dcEF using procaine by observing the loading of AT2 cells with calceine and using a square pulse generator, applying 50 ms single rectangular pulses.

Conclusions

We suggest that the same methods of avoiding the side effects of electric current pulse application as in cell electrophoresis and galvanotaxis should also be used for electroporation. This conclusion was confirmed in our electroporation experiments performed in conditions assuring survival of over 80% of the electroporated cells. If the amplitude, duration, and shape of the dcEF pulse are known, then electroporation does not depend on the type of pulse generator. This knowledge of the characteristics of the pulse assures reproducibility of electroporation experiments using different equipment.

Micro-/nanoscale electroporation

Electroporation has been one of the most popular non-viral technologies for cell transfection. However, conventional bulk electroporation (BEP) shows significant limitations in efficiency, cell viability and transfection uniformity. Recent advances in microscale-electroporation (MEP) resulted in improved cell viability. Further miniaturization of the electroporation system (i.e., nanoscale) has brought up many unique advantages, including negligible cell damage and dosage control capabilities with single-cell resolution, which has enabled more translational applications. In this review, we give an insight into the fundamental and technical aspects of micro- and nanoscale/nanochannel electroporation (NEP) and go over several examples of MEP/NEP-based cutting-edge research, including gene editing, adoptive immunotherapy, and cellular reprogramming. The challenges and opportunities of advanced electroporation technologies are also discussed.

A novel electroporation system for efficient molecular delivery into Chlamydomonas reinhardtii with a 3-dimensional microelectrode

Electroporation is one of the most widely used transfection methods because of its high efficiency and convenience among the various transfection methods. Previous micro-electroporation systems have some drawbacks such as limitations in height and design, time-consuming and an expensive fabrication process due to technical constraints. This study fabricates a three dimensional microelectrode using the 3D printing technique. The interdigitated microstructure consisting of poly lactic acid was injected by a 3D printer and coated with silver and aluminum with a series of dip-coatings. With the same strength of electric field (V cm⁻¹), a higher efficiency for molecular delivery and a higher cellular viability are achieved with the microelectrode than with a standard cuvette. In addition, this study investigates chemicophysical changes such as Joule heating and dissolved metal during electroporation and showed the micro-electroporation system had less chemicophysical changes. It was concluded that the proposed micro-electroporation system will contribute to genetic engineering as a promising delivery tool, and this combination of 3D printing and electroporation has many potential applications for diverse designs or systems.

A review of basic to clinical studies of irreversible electroporation therapy

The use of irreversible electroporation (IRE) for cancer treatment has increased sharply over the past decade. As a nonthermal therapy, IRE offers several potential benefits over other focal therapies, which include 1) short treatment delivery time, 2) reduced collateral thermal injury, and 3) the ability to treat tumors adjacent to major blood vessels. These advantages have stimulated widespread interest in basic through clinical studies of IRE. For instance, many in vitro and in vivo studies now identify treatment planning protocols (IRE threshold, pulse parameters, etc.), electrode delivery (electrode design, placement, intraoperative imaging methods, etc.), injury evaluation (methods and timing), and treatment efficacy in different cancer models. Therefore, this study reviews the in vitro, translational, and clinical studies of IRE cancer therapy based on major experimental studies particularly within the past decade. Further, this study provides organized data and facts to assist further research, optimization, and clinical applications of IRE.

On-chip lysis of mammalian cells through a handheld corona device

On-chip lysis is required in many lab-on-chip applications involving cell studies. In these applications, the complete disruption of the cellular membrane and a high lysis yield is essential. Here, we present a novel approach to lyse cells on-chip through the application of electric discharges from a corona handheld device. The method only requires a microfluidic chip and a low-cost corona device. We demonstrate the effective lysis of BHK and eGFP HCT 116 cells in the sub-second time range using an embedded microelectrode. We also show cell lysis of non-adherent K562 leukemia cells without the use of an electrode in the chip. Cell lysis has been assessed through the use of bright-field microscopy, high-speed imaging and cell-viability fluorescence probes. The experimental results show effective cell lysis without any bubble formation or significant heating. Due to the simplicity of both the components involved and the lysis procedure, this technique offers an inexpensive lysis option with the potential for integration into lab-on-a-chip devices.

Model of pore formation in a single cell in a flow-through channel with micro-electrodes

Microfluidic channels with embedded micro-electrodes are of growing use in devices that aim to electroporate single cells. In this article we present an analysis of pore evolution in a single cell passing by two planar electrodes that are separated by a nano-gap. The cell experiences an electric field that changes in time, as it goes over the electrodes in the channel. The nano-gap between the electrodes enhances the electric field's strength in the micro-channel, thus enabling the use of low potential difference between the electrodes. By computing the electric field on the surface of the cell we can calculate the pore density, as predicted by the model described by Krassowska and Filev (Biophys. J. 92(2):404-417, 2007). The simulation presented in this article is a useful tool for planning and executing experiments of single-cell electroporation in flow-through devices. We demonstrate how different parameters, such as cell size and the size of the gap between the electrodes, change the pore density and show how electroporation between micro-electrodes on the same plane is different from conventional electroporation between facing electrodes.

Emerging microfluidic devices for cell lysis: a review

Intracellular components containing information about genetic and disease characteristics are key substances to clinical diagnostics. Cell lysis is therefore a crucial step for efficient extraction and the subsequent analysis of intracellular components. With the advent of advanced manufacturing techniques, a number of micro systems have been proposed and applied for manipulating cells on chips. In this paper, we review emerging microfluidic devices for cell lysis. Different lysis mechanisms and related techniques are compared. The technical details, advantages, and limitations of various microfluidic devices are discussed.

Alternating electric field capacitively coupled micro-electroporation

Electroporation of biological solutions is typically performed using galvanically coupled electrodes and the administration of high-voltage, direct current (DC) pulses.

Microfluidic electroporation for cellular analysis and delivery

Electroporation is a simple yet powerful technique for breaching the cell membrane barrier. The applications of electroporation can be generally divided into two categories: the release of intracellular proteins, nucleic acids and other metabolites for analysis and the delivery of exogenous reagents such as genes, drugs and nanoparticles with therapeutic purposes or for cellular manipulation. In this review, we go over the basic physics associated with cell electroporation and highlight recent technological advances on microfluidic platforms for conducting electroporation. Within the context of its working mechanism, we summarize the accumulated knowledge on how the parameters of electroporation affect its performance for various tasks. We discuss various strategies and designs for conducting electroporation at the microscale and then focus on analysis of intracellular contents and delivery of exogenous agents as two major applications of the technique. Finally, an outlook for future applications of microfluidic electroporation in increasingly diverse utilities is presented.

Microfluidic electro-sonoporation: a multi-modal cell poration methodology through simultaneous application of electric field and ultrasonic wave

A microfluidic device that simultaneously applies the conditions required for microelectroporation and microsonoporation in a flow-through scheme toward high-efficiency and high-throughput molecular delivery into mammalian cells is presented. This multi-modal poration microdevice using simultaneous application of electric field and ultrasonic wave was realized by a three-dimensional (3D) microelectrode scheme where the electrodes function as both electroporation electrodes and cell flow channel so that acoustic wave can be applied perpendicular to the electric field simultaneously to cells flowing through the microfluidic channel. This 3D microelectrode configuration also allows a uniform electric field to be applied while making the device compatible with fluorescent microscopy. It is hypothesized that the simultaneous application of two different fields (electric field and acoustic wave) in perpendicular directions allows formation of transient pores along two axes of the cell membrane at reduced poration intensities, hence maximizing the delivery efficiency while minimizing cell death. The microfluidic electro-sonoporation system was characterized by delivering small molecules into mammalian cells, and showed average poration efficiency of 95.6% and cell viability of 97.3%. This proof of concept result shows that by combining electroporation and sonoporation together, significant improvement in molecule delivery efficiency could be achieved while maintaining high cell viability compared to electroporation or sonoporation alone. The microfluidic electro-sonoporation device presented here is, to the best of our knowledge, the first multi-modal cell poration device using simultaneous application of electric field and ultrasonic wave. This new multi-modal cell poration strategy and system is expected to have broad applications in delivery of small molecule therapeutics and ultimately in large molecule delivery such as gene transfection applications where high delivery efficiency and high viability are crucial.

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.

Flow-through comb electroporation device for delivery of macromolecules

We present a microfluidic electroporation device with a comb electrode layout fabricated in polydimethylsiloxane (PMDS) and glass. Characterization experiments with HeLa cells and fluorescent dextran show efficient delivery (∼95%) with low toxicity (cell viability ∼85%) as well as rapid pore closure after electroporation. The activity of delivered molecules is also verified by silencing RNA (siRNA) studies that demonstrate gene knockdown in GFP expressing cells. This simple, scalable approach to microfluidic, flow-through electroporation could facilitate the integration of electroporation modules within cell analysis devices that perform multiple operations.

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.

Low-frequency ac electroporation shows strong frequency dependence and yields comparable transfection results to dc electroporation

Conventional electroporation has been conducted by employing short direct current (dc) pulses for delivery of macromolecules such as DNA into cells. The use of alternating current (ac) field for electroporation has mostly been explored in the frequency range of 10kHz-1MHz. Based on Schwan equation, it was thought that with low ac frequencies (10Hz-10kHz), the transmembrane potential does not vary with the frequency. In this report, we utilized a flow-through electroporation technique that employed continuous 10Hz-10kHz ac field (based on either sine waves or square waves) for electroporation of cells with defined duration and intensity. Our results reveal that electropermeabilization becomes weaker with increased frequency in this range. In contrast, transfection efficiency with DNA reaches its maximum at medium frequencies (100-1000Hz) in the range. We postulate that the relationship between the transfection efficiency and the ac frequency is determined by combined effects from electrophoretic movement of DNA in the ac field, dependence of the DNA/membrane interaction on the ac frequency, and variation of transfection under different electropermeabilization intensities. The fact that ac electroporation in this frequency range yields high efficiency for transfection (up to ~71% for Chinese hamster ovary cells) and permeabilization suggests its potential for gene delivery.

Genetic modification of mesenchymal stem cells

Mesenchymal stem cells (MSC) are currently considered the most promising type of adult stem cells for therapeutic applications, because they can be easily isolated from the bone marrow and other tissues, and manipulated for different applications. The genetic transformation of MSC using genes that enhance their homing ability, as well as their proliferation and survival capacities when transplanted to sites of injury, is an important alternative to improve MSC function, especially for tissue regeneration. This chapter describes protocols for the transformation of MSC using plasmid vectors by lipofection and electroporation, as well as retroviral vectors representing viral transformations.

A laminar flow electroporation system for efficient DNA and siRNA delivery

By introducing a hydrodynamic mechanism into a microfluidics-based electroporation system, we developed a novel laminar flow electroporation system with high performance. The laminar buffer flow implemented in the system separated the cell suspension flow from the electrodes, thereby excluding many unfavorable effects due to electrode reaction during electroporation, such as hydrolysis, bubble formation, pH change, and heating. Compared to conventional microfluidic electroporation systems, these improvements significantly enhanced transfection efficiency and cell viability. Furthermore, successful electrotransfection of plasmid DNA and, more importantly, synthetic siRNA, was demonstrated in several hard-to-transfect cell types using this system.

Optical injection of mammalian cells using a microfluidic platform

The use of a focused laser beam to create a sub-micron hole in the plasma membrane of a cell (photoporation), for the selective introduction of membrane impermeable substances (optical injection) including nucleic acids (optical transfection), is a powerful technique most commonly applied to treat single cells. However, particularly for femtosecond photoporation, these studies have been limited to low throughput, small-scale studies, because they require sequential dosing of individual cells. Herein, we describe a microfluidic photoporation system for increased throughput and automated optical injection of cells. Hydrodynamic focusing is employed to direct a flow of single-file cells through a focused femtosecond laser beam for photoporation. Upon traversing the beam, a number of transient pores potentially open across the extracellular membrane, which allows the uptake of the surrounding fluid media into the cytoplasm, also containing the chosen injection agent. The process is entirely automated and a rate of 1 cell/sec could readily be obtained, enabling several thousand cells to be injected per hour using this system. The efficiency of optically injecting propidium iodide into HEK293 mammalian cells was found to be 42 ± 8%, or 28 ± 4% taking into account the requirement of post-injection viability, as tested using Calcein AM. This work now opens the way for combining photoporation with microfluidic analyses, sorting, purification or on-chip cell culture studies.

Single-cell electroporation

Single-cell electroporation (SCEP) is a relatively new technique that has emerged in the last decade or so for single-cell studies. When a large enough electric field is applied to a single cell, transient nano-pores form in the cell membrane allowing molecules to be transported into and out of the cell. Unlike bulk electroporation, in which a homogenous electric field is applied to a suspension of cells, in SCEP an electric field is created locally near a single cell. Today, single-cell-level studies are at the frontier of biochemical research, and SCEP is a promising tool in such studies. In this review, we discuss pore formation based on theoretical and experimental approaches. Current SCEP techniques using microelectrodes, micropipettes, electrolyte-filled capillaries, and microfabricated devices are all thoroughly discussed for adherent and suspended cells. SCEP has been applied in in-vivo and in-vitro studies for delivery of cell-impermeant molecules such as drugs, DNA, and siRNA, and for morphological observations.

Irreversible electroporation for microbial control of drugs in solution

The purpose of this study was to examine the feasibility of using irreversible electroporation (IRE) as a non-chemical method for eliminating microorganisms of liquid drugs. The studied drug was a topical ophthalmic medication, a pharmaceutical field in which the problem of microbial contamination has not yet been adequately solved, especially in the case of eye drops prescribed for chronic use. Commercially available Hylo-Comod preservative-free eye drop solution was subjected to contamination with Escherichia coli bacteria (10(6) colony forming units/mL). Electroporation parameters for bacterial control were investigated by comparing the effects of electrical fields of 5.4, 7.2, and 10 kV/cm, delivered as 100-micros square pulses at 1 Hz in sequences of 10 pulses, 20 pulses, or 20 pulses delivered as four sets of five pulses with 1-min intervals between each set. Microorganism survival after treatment was determined by pour plate counting. Effects of the treatment parameters on temperature and pH were recorded. Bacterial survival was lowest (0.14% +/- 0.03%) after application of 20 pulses delivered as four separate sets. With that application mode, the solution remained at pH 7.5 and the temperature rose to 35.6 degrees +/- 0.2 degrees C. Because IRE can be efficiently delivered under conditions that avoid the potentially deleterious effects of electrical pulses on temperature and pH, it appears to be a feasible method for bacterial control of drugs in solution. The principles established in this study can be applied to any drug in solution and optimized individually according to the solution's composition.