Electroporation of single cells and tissues with an electrolyte-filled capillary

Expanding CAR-T cell immunotherapy horizons through microfluidics

Chimeric antigen receptor (CAR)-T cell therapies have revolutionized cancer treatment, particularly in hematological malignancies. However, their application to solid tumors is limited, and they face challenges in safety, scalability, and cost. To enhance current CAR-T cell therapies, the integration of microfluidic technologies, harnessing their inherent advantages, such as reduced sample consumption, simplicity in operation, cost-effectiveness, automation, and high scalability, has emerged as a powerful solution. This review provides a comprehensive overview of the step-by-step manufacturing process of CAR-T cells, identifies existing difficulties at each production stage, and discusses the successful implementation of microfluidics and related technologies in addressing these challenges. Furthermore, this review investigates the potential of microfluidics-based methodologies in advancing cell-based therapy across various applications, including solid tumors, next-generation CAR constructs, T-cell receptors, and the development of allogeneic "off-the-shelf" CAR products.

Influence of Anisotropic White Matter on Electroosmotic Flow Induced by Direct Current

Treatment of cerebral edema remains a major challenge in clinical practice and new innovative therapies are needed. This study presents a novel approach for mitigating cerebral edema by inducing bulk fluid transport utilizing the brain’s electroosmotic property using an anatomically detailed finite element head model incorporating anisotropy in the white matter (WM). Three representative anisotropic conductivity algorithms are employed for the WM and compared with isotropic WM. The key results are (1) the electroosmotic flow (EOF) is driven from the edema region to the subarachnoid space under an applied electric field with its magnitude linearly correlated to the electric field and direction following current flow pathways; (2) the extent of EOF distribution variation correlates highly with the degree of the anisotropic ratio of the WM regions; (3) the directions of the induced EOF in the anisotropic models deviate from its isotropically defined pathways and tend to move along the principal fiber direction. The results suggest WM anisotropy should be incorporated in head models for more reliable EOF evaluations for cerebral edema mitigation and demonstrate the promise of the electroosmosis based approach to be developed as a new therapy for edema treatment as evaluated with enhanced head models incorporating WM anisotropy.

Electroosmosis Based Novel Treatment Approach for Cerebral Edema

OBJECTIVE

Cerebral edema characterized as an abnormal accumulation of interstitial fluid has not been treated effectively. We propose a novel edema treatment approach to drive edematous fluid out of the brain by direct current utilizing brain tissue's electroosmotic property.

METHODS

A finite element (FE) head model is developed and employed to assess the feasibility of the approach. First, the capacity of the model for electric field prediction is validated against human experiments. Second, two electrode configurations (S and D-montage) are designed to evaluate the distribution of the electric field, electroosmotic flow (EOF), current density, and temperature across the brain under an applied direct current.

RESULTS

The S-montage is shown to induce an average EOF velocity of 7e-4 mm/s underneath the anode by a voltage of 15 V, and the D-montage induces a velocity of 9e-4 mm/s by a voltage of 5 V. Meanwhile, the brain temperature in both configurations is below 38 °C, which is within the safety range. Further, the magnitude of EOF is proportional to the electric field, and the EOF direction follows the current flow from anode to cathode. The EOF velocity in the white matter is significantly higher than that in the gray matter under the anode where the fluid is to be drawn out.

CONCLUSION

The proposed electroosmosis based approach allows alleviating brain edema within the critical time window by direct current.

SIGNIFICANCE

The approach may be further developed as a new treatment solely or as a complement to existing conventional treatments of edema.

Ultrathin glass fiber microprobe for electroporation of arbitrary selected cell groups

A new type of ultrathin fiber microprobe for selective electroporation is reported. The microprobe is 10 cm long and has a diameter of 350 µm. This microprobe is a low cost tool, which allows electroporation of an arbitrary selected single cell or groups of cells among population with use of a standard microscope and cell culture plates. The microprobe in its basic form contains two metal microelectrodes made of a silver-copper alloy, running along the fiber, each with a diameter of 23 µm. The probe was tested in vitro on a population of normal and cancer cells. Successful targeted electroporation was observed by means of accumulation of trypan blue (TB) dye marker in the cell. The electroporation phenomenon was also verified with propidium iodide and AnnexinV in fluorescent microscopy.

Flow micropillar array electroporation to enhance size specific transfection to a large population of cells

Despite serving as a popular non-viral delivery approach, electroporation carries several drawbacks in its current configurations. We developed a Flow Micropillar-array Electroporation (FME) system to wisely regulate an important transmembrane-determining factor, namely cell size variations among individual cells, to achieve effective transfection. In FME, cells flow through a slit-type microfluidic channel on which carbon electrodes with well-patterned micropillar array texture are integrated as the top and bottom wall. Gravity helps bring cells to the micropillar array surface so that the permeable area on cells in different size populations is specified by their size regardless their random location fact. Without sacrificing cell viability, we demonstrate this FME concept by delivering DNA plasmids to several mammalian cell lines with obvious transfection enhancement when compared to a commercial system (K562: 3.0 folds; A549: 3.3 folds; HeLa: 1.8 folds, COS7: 1.7 folds; 293T: 2.9 folds; mES: 2.5 folds). Moreover, carbon-based electrodes are less expensive, more durable, and convenient for integration with a microfluidic setup which enables rapid and massive transfection capability that many therapeutic application needs. The success of FME may benefit many emerging biological studies and clinical practice that requires effective transfection to a large population of cells in limited processing time.

Scaffold-mediated sequential drug/gene delivery to promote nerve regeneration and remyelination following traumatic nerve injuries

Neural tissue regeneration following traumatic injuries is often subpar. As a result, the field of neural tissue engineering has evolved to find therapeutic interventions and has seen promising outcomes. However, robust nerve and myelin regeneration remain elusive. One possible reason may be the fact that tissue regeneration often follows a complex sequence of events in a temporally-controlled manner. Although several other fields of tissue engineering have begun to recognise the importance of delivering two or more biomolecules sequentially for more complete tissue regeneration, such serial delivery of biomolecules in neural tissue engineering remains limited. This review aims to highlight the need for sequential delivery to enhance nerve regeneration and remyelination after traumatic injuries in the central nervous system, using spinal cord injuries as an example. In addition, possible methods to attain temporally-controlled drug/gene delivery are also discussed for effective neural tissue regeneration.

Pinpoint Delivery of Molecules by Using Electron Beam Addressing Virtual Cathode Display

Electroporation, a physical transfection method to introduce genomic molecules in selective living cells, could be implemented by microelectrode devices. A local electric field generated by a finer electrode can induces cytomembrane poration in the electrode vicinity. To employ fine, high-speed scanning electrodes, we developed a fine virtual cathode pattern, which was generated on a cell adhesive surface of 100-nm-thick SiN membrane by inverted-electron beam lithography. The SiN membrane works as both a vacuum barrier and the display screen of the virtual cathode. The kinetic energy of the incident primary electrons to the SiN membrane was completely blocked, whereas negative charges and leaking electric current appeared on the surface of the dielectric SiN membrane within a region of 100 nm. Locally controlled transmembrane molecular delivery was demonstrated on adhered C2C12 myoblast cells in a culturing medium with fluorescent dye propidium iodide (PI). Increasing fluorescence of pre-diluted PI indicated local poration and transmembrane inflow at the virtual cathode position, as well as intracellular diffusion. The transmembrane inflows depended on beam duration time and acceleration voltage. At the post-molecular delivery, a slight decrease in intracellular PI fluorescence intensity indicates membrane recovery from the poration. Cell viability was confirmed by time-lapse cell imaging of post-exposure cell migration.

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.

Methods for Precisely Localized Transfer of Cells or DNA into Early Postimplantation Mouse Embryos

Manipulation and culture of early mouse embryos is a powerful yet largely under-utilized technology enhancing the value of this model system. Conversely, cell culture has been widely used in developmental biology studies. However, it is important to determine whether in vitro cultured cells truly represent in vivo cell types. Grafting cells into embryos, followed by an assessment of their contribution during development is a useful method to determine the potential of in vitro cultured cells. In this study, we describe a method for grafting cells into a defined site of early postimplantation mouse embryos, followed by ex vivo culture. We also introduce an optimized electroporation method that uses glass capillaries of known diameter, allowing precise localization and adjustment of the number of cells receiving exogenous DNA with both high transfection efficiency and low cell death. These techniques, which do not require any specialized equipment, render experimental manipulations of the gastrulation and early organogenesis-stage mouse embryo possible, allowing analysis of commitment in cultured cell subpopulations and the effect of genetic manipulations in situ on cell differentiation.

Electroosmotic perfusion of tissue: sampling the extracellular space and quantitative assessment of membrane-bound enzyme activity in organotypic hippocampal slice cultures

This review covers recent advances in sampling fluid from the extracellular space of brain tissue by electroosmosis (EO). Two techniques, EO sampling with a single fused-silica capillary and EO push-pull perfusion, have been developed. These tools were used to investigate the function of membrane-bound enzymes with outward-facing active sites, or ectoenzymes, in modulating the activity of the neuropeptides leu-enkephalin and galanin in organotypic-hippocampal-slice cultures (OHSCs). In addition, the approach was used to determine the endogenous concentration of a thiol, cysteamine, in OHSCs. We have also investigated the degradation of coenzyme A in the extracellular space. The approach provides information on ectoenzyme activity, including Michaelis constants, in tissue, which, as far as we are aware, has not been done before. On the basis of computational evidence, EO push-pull perfusion can distinguish ectoenzyme activity with a ~100 μm spatial resolution, which is important for studies of enzyme kinetics in adjacent regions of the rat hippocampus.

A microdevice to locally electroporate embryos with high efficiency and reduced cell damage

The ability to follow and modify cell behaviour with accurate spatiotemporal resolution is a prerequisite to study morphogenesis in developing organisms. Electroporation, the delivery of exogenous molecules into targeted cell populations through electric permeation of the plasma membrane, has been used with this aim in different model systems. However, current localised electroporation strategies suffer from insufficient reproducibility and mediocre survival when applied to small and delicate organisms such as early post-implantation mouse embryos. We introduce here a microdevice to achieve localised electroporation with high efficiency and reduced cell damage. In silico simulations using a simple electrical model of mouse embryos indicated that a dielectric guide-based design would improve on existing alternatives. Such a device was microfabricated and its capacities tested by targeting the distal visceral endoderm (DVE), a migrating cell population essential for anterior-posterior axis establishment. Transfection was efficiently and reproducibly restricted to fewer than four visceral endoderm cells without compromising cell behaviour and embryo survival. Combining targeted mosaic expression of fluorescent markers with live imaging in transgenic embryos revealed that, like leading DVE cells, non-leading ones send long basal projections and intercalate during their migration. Finally, we show that the use of our microsystem can be extended to a variety of embryological contexts, from preimplantation stages to organ explants. Hence, we have experimentally validated an approach delivering a tailor-made tool for the study of morphogenesis in the mouse embryo. Furthermore, we have delineated a comprehensive strategy for the development of ad hoc electroporation devices.

Optimization of single-cell electroporation protocol for forced gene expression in primary neuronal cultures

The development and function of the central nervous system (CNS) are realized through interactions between many neurons. To investigate cellular and molecular mechanisms of the development and function of the CNS, it is thus crucial to be able to manipulate the gene expression of single neurons in a complex cell population. We recently developed a technique for gene silencing by introducing small interfering RNA into single neurons in primary CNS cultures using single-cell electroporation. However, we had not succeeded in forced gene expression by introducing expression plasmids using single-cell electroporation. In the present study, we optimized the experimental conditions to enable the forced expression of green fluorescent protein (GFP) in cultured cerebellar Purkinje neurons using single-cell electroporation. We succeeded in strong GFP expression in Purkinje neurons by increasing the inside diameter of micropipettes or by making the size of the original plasmid smaller by digestion and cyclizing it by ligation. Strong GFP expression in Purkinje neurons electroporated under the optimal conditions continued to be observed for more than 25 days after electroporation. Thus, this technique could be used for forced gene expression in single neurons to investigate cellular and molecular mechanisms of the development, function, and disease of the CNS.

Fast targeted gene transfection and optogenetic modification of single neurons using femtosecond laser irradiation

A prevailing problem in neuroscience is the fast and targeted delivery of DNA into selected neurons. The development of an appropriate methodology would enable the transfection of multiple genes into the same cell or different genes into different neighboring cells as well as rapid cell selective functionalization of neurons. Here, we show that optimized femtosecond optical transfection fulfills these requirements. We also demonstrate successful optical transfection of channelrhodopsin-2 in single selected neurons. We extend the functionality of this technique for wider uptake by neuroscientists by using fast three-dimensional laser beam steering enabling an image-guided "point-and-transfect" user-friendly transfection of selected cells. A sub-second transfection timescale per cell makes this method more rapid by at least two orders of magnitude when compared to alternative single-cell transfection techniques. This novel technology provides the ability to carry out large-scale cell selective genetic studies on neuronal ensembles and perform rapid genetic programming of neural circuits.

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.

Long-lasting single-neuron labeling by in vivo electroporation without microscopic guidance

In order to make a direct link between the morphological and functional study of the nervous system, we established an experimental protocol for labeling individual neurons persistently without microscopic guidance by injecting a plasmid encoding fluorescent protein electroporatively after recording their activity extracellularly. Using a glass pipette filled with electrolyte solution containing a plasmid encoding green fluorescent protein (GFP), single-neuron recording and electroporation were performed on anesthetized rats. When performing the electroporation at the completion of recording, the degree of contact between the target neuron and the electrode tip was adjusted by monitoring the change of the trace of recorded action potentials and the increase of electrode resistance. The expression of GFP and its immunostaining with a polyclonal antibody enabled us to clearly see the basic structural components such as cell bodies, axons, dendrites, and even smaller components such as spines. Identification of the morphological subtypes of neurons was possible with every labeled neuron. The optimum condition for labeling was a 30% increase of the electrode resistance, and the labeling success rate evaluated 3 days after labeling was 40%. The rate evaluated one month after labeling was only slightly lower (33%). We also confirmed experimentally that this recording and labeling procedure can be similarly successful in head-fixed behaving rats. This new experimental protocol will be a breakthrough in systems neuroscience because it makes a direct link between the morphology and behavior-related activity of single neurons.

Nanofountain probe electroporation (NFP-E) of single cells

The ability to precisely deliver molecules into single cells is of great interest to biotechnology researchers for advancing applications in therapeutics, diagnostics, and drug delivery toward the promise of personalized medicine. The use of bulk electroporation techniques for cell transfection has increased significantly in the past decade, but the technique is nonspecific and requires high voltage, resulting in variable efficiency and low cell viability. We have developed a new tool for electroporation using nanofountain probe (NFP) technology, which can deliver molecules into cells in a manner that is highly efficient and gentler to cells than bulk electroporation or microinjection. Here we demonstrate NFP electroporation (NFP-E) of single HeLa cells within a population by transfecting them with fluorescently labeled dextran and imaging the cells to evaluate the transfection efficiency and cell viability. Our theoretical analysis of the mechanism of NFP-E reveals that application of the voltage creates a localized electric field between the NFP cantilever tip and the region of the cell membrane in contact with the tip. Therefore, NFP-E can deliver molecules to a target cell with minimal effect of the electric potential on the cell. Our experiments on HeLa cells confirm that NFP-E offers single cell selectivity, high transfection efficiency (>95%), qualitative dosage control, and very high viability (92%) of transfected cells.

Single-cell juxtacellular transfection and recording technique

Genetic modifications and pharmacological studies enable the analysis of protein function in living cells. While many of these studies investigate the effect of proteins by bulk administration or withdrawal of the protein in complex cellular networks, understanding the more subtle mechanisms of protein function requires fine-tuned changes on a single-cell level without affecting the balance of the system. In order to analyse the consequences of protein modification at the single-cell level, we have developed a single-cell transfection method in the loose patch configuration, which allows juxtacellular recordings of neuronal cells prior to juxtacellular transfection. CA1 pyramidal neurons were selected based on morphological and electrophysiological criteria. Using a patch clamp amplifier which allows sensitive recordings of action currents in the loose seal mode as well as electroporation with high-voltage electrical stimulation the identified neurons were transfected with a combination of specific nucleotides, e.g. siRNA and a plasmid coding for GFP for later cell retrieval. Two days after transfection, whole-cell patch clamp recordings of transfected cells were performed to analyse electrophysiological properties. Action potential firing and synaptic transmission of single electroporated CA1 pyramidal cells were comparable to untransfected cells. Our study presents a method which enables identification of neurons by juxtacellular recording prior to single-cell juxtacellular transfection, allowing subsequent analysis of morphological and electrophysiological parameters several days after the genetic modification.

Electroosmotic push-pull perfusion: description and application to qualitative analysis of the hydrolysis of exogenous galanin in organotypic hippocampal slice cultures

We demonstrate here a method that perfuses a small region of an organotypic hippocampal culture with a solution containing an enzyme substrate, a neuropeptide. Perfusate containing hydrolysis products is continually collected and subsequently analyzed for the products of the enzymatic degradation of the peptide substrate. The driving force for perfusion is an electric field. The fused silica capillaries used as "push" and "pull" or "source" and "collection" capillaries have a ζ-potential that is negative and greater in magnitude than the tissue's ζ-potential. Thus, depending on the magnitudes of particular dimensions, the electroosmotic flow in the capillaries augments the fluid velocity in the tissue. The flow rate is not directly measured; however, we determine it using a finite-element approach. We have determined the collection efficiency of the system using an all d-amino acid internal standard. The flow rates are low, in the nL/min range, and adjustable by controlling the current or voltage in the system. The collection efficiency of the d-amino acid peptide internal standard is variable, increasing with increased current and thus electroosmotic flow rate. The collection efficiency can be rationalized in the context of a Peclet number. Electroosmotic push-pull perfusion of the neuropeptide galanin (gal1-29) through the extracellular space of an organotypic hippocampal culture results in its hydrolysis by ectopeptidase reactions occurring in the extracellular space. The products of hydrolysis were identified by MALDI-MS. Experiments at two levels of current (8-12 μA and 19-40 μA) show that the probability of seeing hydrolysis products (apparently from aminopeptidases) is greater in the Cornu Ammonis area 3 (CA3) than in the Cornu Ammonis area 1 (CA1) in the higher current experiments. In the lower current experiments, shorter peptide products of aminopeptidases (gal13-29 to gal20-19) are seen with greater frequency in CA3 than in CA1 but there is no statistically significant difference for longer peptides (gal3-29 to gal12-29).

Assessment of tissue viability following electroosmotic push-pull perfusion from organotypic hippocampal slice cultures

We have developed a novel sampling technique that allows both introduction and removal of fluid from the extracellular space of living tissue. This method is based on the fluidics of push-pull perfusion but flow is driven by electroosmosis. We have applied this method to organotypic hippocampal cultures. A source capillary is inserted into the tissue and a collection capillary is in contact with the tissue surface through a thin layer of fluid. A voltage is applied across the proximal ends of source and collection capillary. In the applied field, fluid will move from source, into the tissue, and then be collected. In this process, damage to cells may occur. To understand better what sampling conditions influence damage most, we tested various sampling geometries and applied voltages, quantifying damage 16-24 h later using propidium iodide as a cell death marker. We found that damage correlates with both voltage drop and power dissipated in the tissue, but that voltage drop is a better indicator of damage when comparing models in which capillary arrangement and length are different.

An in situ measurement of extracellular cysteamine, homocysteine, and cysteine concentrations in organotypic hippocampal slice cultures by integration of electroosmotic sampling and microfluidic analysis

We demonstrate an all-electric sampling/derivatization/separation/detection system for the quantitation of thiols in tissue cultures. Extracellular fluid collected from rat organotypic hippocampal slice cultures (OHSCs) by electroosmotic flow through an 11 cm (length) × 50 μm (i.d.) sampling capillary is introduced to a simple microfluidic chip for derivatization, continuous flow-gated injection, separation, and detection. With the help of a fluorogenic, thiol-specific reagent, ThioGlo-1, we have successfully separated and detected the extracellular levels of free reduced cysteamine, homocysteine, and cysteine from OHSCs within 25 s in a 23 mm separation channel with a confocal laser-induced fluorescence (LIF) detector. Attention to the conductivities of the fluids being transported is required for successful flow-gated injections. When the sample conductivity is much higher than the run buffer conductivities, the electroosmotic velocities are such that there is less fluid coming by electroosmosis into the cross from the sample/reagent channel than is leaving by electroosmosis into the separation and waste channels. The resulting decrease in the internal fluid pressure in the injection cross pulls flow from the gated channel. This process may completely shut down the gated injection. Using a glycylglycine buffer with physiological osmolarity but only 62% of physiological conductivity and augmenting the conductivity of the run buffers solved this problem. Quantitation is by standard additions. Concentrations of cysteamine, homocysteine, and cysteine in the extracellular space of OHSCs are 10.6 ± 1.0 nM (n = 70), 0.18 ± 0.01 μM (n = 53), and 11.1 ± 1.2 μM (n = 70), respectively. This is the first in situ quantitative estimation of endogenous cysteamine in brain tissue. Extracellular levels of homocysteine and cysteine are comparable with other reported values.

Micro-/nanofluidics based cell electroporation

Non-viral gene delivery has been extensively explored as the replacement for viral systems. Among various non-viral approaches, electroporation has gained increasing attention because of its easy operation and no restrictions on probe or cell type. Several effective systems are now available on the market with reasonably good gene delivery performance. To facilitate broader biological and medical applications, micro-/nanofluidics based technologies were introduced in cell electroporation during the past two decades and their advances are summarized in this perspective. Compared to the commercially available bulk electroporation systems, they offer several advantages, namely, (1) sufficiently high pulse strength generated by a very low potential difference, (2) conveniently concentrating, trapping, and regulating the position and concentration of cells and probes, (3) real-time monitoring the intracellular trafficking at single cell level, and (4) flexibility on cells to be transfected (from single cell to large scale cell population). Some of the micro-devices focus on cell lysis or fusion as well as the analysis of cellular properties or intracellular contents, while others are designed for gene transfection. The uptake of small molecules (e.g., dyes), DNA plasmids, interfering RNAs, and nanoparticles has been broadly examined on different types of mammalian cells, yeast, and bacteria. A great deal of progress has been made with a variety of new micro-/nanofluidic designs to address challenges such as electrochemical reactions including water electrolysis, gas bubble formation, waste of expensive reagents, poor cell viability, low transfection efficacy, higher throughput, and control of transfection dosage and uniformity. Future research needs required to advance micro-/nanofluidics based cell electroporation for broad life science and medical applications are discussed.

Single-cell electroporation using proton beam fabricated biochips

We report the design and fabrication of a novel single cell electroporation biochip featuring high aspect ratio nickel micro-electrodes with smooth side walls between which individual cells are attached. The biochip is fabricated using Proton Beam Writing (PBW), a new direct write lithographic technique capable of fabricating high quality high-aspect-ratio nano and microstructures. By applying electrical impulses across the biochip electrodes, SYTOX® Green nucleic acid stain is incorporated into mouse neuroblastoma (N2a) cells and observed via green fluorescence when the stain binds with DNA inside the cell nucleus. Three parameters; electric field strength, pulse duration, and numbers of pulses have been investigated for the single cell electroporation process. The results indicate high transfection rates as well as cell viability of 82.1 and 86.7% respectively. This single cell electroporation system may represent a promising method for the introduction of a wide variety of fluorophores, nanoparticles, quantum dots, DNAs and proteins into cells.

High-throughput single-cell manipulation in brain tissue

The complexity of neurons and neuronal circuits in brain tissue requires the genetic manipulation, labeling, and tracking of single cells. However, current methods for manipulating cells in brain tissue are limited to either bulk techniques, lacking single-cell accuracy, or manual methods that provide single-cell accuracy but at significantly lower throughputs and repeatability. Here, we demonstrate high-throughput, efficient, reliable, and combinatorial delivery of multiple genetic vectors and reagents into targeted cells within the same tissue sample with single-cell accuracy. Our system automatically loads nanoliter-scale volumes of reagents into a micropipette from multiwell plates, targets and transfects single cells in brain tissues using a robust electroporation technique, and finally preps the micropipette by automated cleaning for repeating the transfection cycle. We demonstrate multi-colored labeling of adjacent cells, both in organotypic and acute slices, and transfection of plasmids encoding different protein isoforms into neurons within the same brain tissue for analysis of their effects on linear dendritic spine density. Our platform could also be used to rapidly deliver, both ex vivo and in vivo, a variety of genetic vectors, including optogenetic and cell-type specific agents, as well as fast-acting reagents such as labeling dyes, calcium sensors, and voltage sensors to manipulate and track neuronal circuit activity at single-cell resolution.

Long-term gene-silencing effects of siRNA introduced by single-cell electroporation into postmitotic CNS neurons

To explore how long the gene-silencing effects of siRNA introduced into postmitotic neurons continue, we transferred siRNA against GFP into GFP-expressing Purkinje and Golgi cells in cerebellar cell cultures by single-cell electroporation. The temporal changes in the intensity of GFP fluorescence in the same electroporated cells were monitored in real time using GFP imaging. Under standard conditions, GFP fluorescence was reduced to under one-tenth of the initial levels 4-7 days after electroporation. Such effects continued at least up to 14 days after electroporation. The effects of siRNAs against endogenous genes also continued for the same period. Thus, this method could be an effective tool for silencing gene expression for a long period in postmitotic neurons.

A novel micropit device integrates automated cell positioning by dielectrophoresis and nuclear transfer by electrofusion

Nuclear transfer (NT) cloning involves manual positioning of individual donor-recipient cell couplets for electrofusion. This is time-consuming and introduces operator-dependent variation as a confounding parameter in cloning trials. In order to automate the NT procedure, we developed a micro-fluidic device that integrates automated cell positioning and electrofusion of isolated cell couplets. A simple two layer micro-fluidic device was fabricated. Thin film interdigitated titanium electrodes (300 nm thick, 250 microm wide and 250 microm apart) were deposited on a solid borosilicate glass substrate. They were coated with a film of electrically insulating photosensitive epoxy polymer (SU-8) of either 4 or 22 microm thickness. Circular holes ("micropits") measuring 10, 20, 30, 40 or 80 microm in diameter were fabricated above the electrodes. The device was immersed in hypo-osmolar fusion buffer and manually loaded with somatic donor cells and recipient oocytes. Dielectrophoresis (DEP) was used to attract cells towards the micropit and form couplets on the same side of the insulating film. Fusion pulses between 80 V and 120 V were applied to each couplet and fusion scored under a stereomicroscope. Automated couplet formation between oocytes and somatic cells was achieved using DEP. Bovine oocyte-oocyte, oocyte-follicular cells and oocyte-fibroblast couplets fused with up to 69% (n = 13), 50% (n = 30) and 78% (n = 9) efficiency, respectively. Fusion rates were comparable to parallel plate or film electrodes that are conventionally used for bovine NT. This demonstrates proof-of-principle that a micropit device is capable of both rapid cell positioning and fusion.

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.

Microfluidic electroporation of tumor and blood cells: observation of nucleus expansion and implications on selective analysis and purging of circulating tumor cells

Circulating tumor cells (CTCs) refer to cells that detach from a primary tumor, circulate in the blood stream, and may settle down at a secondary site and form metastases. The detection and characterization of CTCs are clinically useful for diagnosis and prognosis purposes. However, there has been very little work on purging CTCs from the blood. In this study, we systematically studied electroporation of tumor and blood cells in the context of selective purging and analysis of CTCs, using M109 and mouse blood cells as models. Electroporation is a simple and effective method for disruption of the cell membrane by applying an external electric field. We applied a microfluidic flow-through electroporation to process cells with various electroporation durations and field intensities. With duration of 100-300 ms, we found that the thresholds for electroporation-induced lysis started at 300-400 V cm(-1) for M109, 400-500 V cm(-1) for white blood cells and 1100-1200 V cm(-1) for red blood cells. Due to the substantial difference, we demonstrated the selective electroporation of tumor cells among blood cells and the scale-up of the flow-through electroporation devices for processing samples of millilitre volumes. Using Coherent Anti-stokes Raman Scattering (CARS) and fluorescence microscopy tools, we observed the dramatic increase in the size of the nucleus of a tumor cell in response to the applied field. We suggest that the nucleus expansion is a newly discovered mechanism responsible for rapid tumor cell death resulted from electroporation.

Dendrite formation of cerebellar Purkinje cells

During postnatal cerebellar development, Purkinje cells form the most elaborate dendritic trees among neurons in the brain, which have been of great interest to many investigators. This article overviews various examples of cellular and molecular mechanisms of formation of Purkinje cell dendrites as well as the methodological aspects of investigating those mechanisms.

Control of the release of freely diffusing molecules in single-cell electroporation

Single-cell electroporation using an electrolyte-filled capillary is an emerging technique for transient pore formation in adherent cells. Because adherent cells do not have a simple and consistent shape and because the electric field emanating from the tip of the capillary is inhomogeneous, the Schwan equation based on spherical cells in homogeneous electrical fields does not apply. We sought to determine experimental and cell parameters that influence the outcome of a single-cell electroporation experiment. A549 cells were exposed to the thiol-reactive dye Thioglo-1, leading to green fluorescence from intracellular thiol adducts. Electroporation causes a decrease with time of the intracellular fluorescence intensity of Thioglo-1-loaded cells from diffusive loss of thiol adducts. The transient curves thus obtained are well-described by a simple model originally developed by Puc et al. We find that the final fluorescence following electroporation is related to the capillary tip-to-cell distance and cell size (specifically, 2(A/pi)(1/2) where A is the area of the cell's image in pixels. This quantity is the diameter if the image is a circle). In separate experiments, the relationship obtained can be used to control the final fluorescence following electroporation by adjusting the tip-to-cell distance based on cell size. The relationship was applied successfully to A549 as well as DU 145 and PC-3 cells. Finally, F-tests show that the variability in the final fluorescence (following electroporation) is decreased when the tip-to-cell distance is controlled according to the derived relationship in comparison to experiments in which the tip-cell distance is a constant irrespective of cell size.

Bionanotubule formation from surface-attached liposomes using electric fields

Spontaneous formation of long-range (millimeters) membrane-bound nanotubules from surface-immobilized liposomes is possible by application of modest electric fields (2 -20 V/cm), providing a novel fabrication strategy for these hollow cylindrical structures. Stable tubes generally aligned with the applied electric field were created from liposomes prepared with phosphatidylcholine (PC), phosphatidic acid (PA), phosphoethanolamine (PE), and cholesterol. The minimum voltage which causes nanotubular formation (the onset voltage) and the average number of tubules per liposome of varying composition was examined with fluorescent microscopy using labeled phospholipids. Generally, the onset voltages ranged between 4 and 15 V/cm and depended on the mother vesicle composition. The results of this study suggest that increasing the charged lipid content can decrease the onset voltage. Conversely, a cholesterol content of more than 30% (by mass) was found to hinder extension of lipid tubules. Basic calculations that assume lipid migration and domain formation on the mother liposome as a nucleating site for tubule extension are assessed and suggest this is a reasonable model to describe the mechanism of tubular growth from immobilized liposomes.

Transfer of small interfering RNA by single-cell electroporation in cerebellar cell cultures

RNA interference (RNAi) is a powerful means to investigate functions of genes involved in neuronal differentiation and degeneration. In contrast to widely used methods for introducing small interfering RNA (siRNA) into cells, recently developed single-cell electroporation has enabled transfer of siRNA into single and identified cells. To explore the availability of single-cell electroporation of siRNA in detail, we introduced siRNA against green fluorescent protein (GFP) into GFP-expressing Golgi and Purkinje cells in cerebellar cell cultures by single-cell electroporation using micropipettes. The temporal changes in the intensity of GFP fluorescence in the same electroporated cells were monitored in real-time up to 4 days after electroporation. Several parameters, including tip diameter and resistance of micropipettes, concentrations of siRNA and a fluorescent dye marker, voltage and time of pulses, were optimized to maximize both the efficacy of RNAi and the viability of the electroporated cells. Under the optimal conditions, transfer of GFP siRNA significantly reduced GFP fluorescence in the electroporated cells, whereas that of negative control siRNA had no effects. GFP siRNA was more efficient in Purkinje cells than in Golgi cells. The electroporated Purkinje cells were normal in their morphology, including elaborated dendrites. Thus, the single-cell electroporation of siRNA could be a simple but effective tool for silencing gene expression in individual cells in neuronal primary cultures. In addition, both gene-silencing and off-target effects of siRNA introduced by this method may differ between neuronal cell types, and the parameters of single-cell electroporation should be optimized in each cell type.

Lab-on-a-chip technologies for proteomic analysis from isolated cells

Lab-on-a-chip systems offer a versatile environment in which low numbers of cells and molecules can be manipulated, captured, detected and analysed. We describe here a microfluidic device that allows the isolation, electroporation and lysis of single cells. A431 human epithelial carcinoma cells, expressing a green fluorescent protein-labelled actin, were trapped by dielectrophoresis within an integrated lab-on-a-chip device containing saw-tooth microelectrodes. Using these same trapping electrodes, on-chip electroporation was performed, resulting in cell lysis. Protein release was monitored by confocal fluorescence microscopy.

In Vitro Electrochemistry of Biological Systems

This article reviews recent work involving electrochemical methods for in vitro analysis of biomolecules, with an emphasis on detection and manipulation at and of single cells and cultures of cells. The techniques discussed include constant potential amperometry, chronoamperometry, cellular electroporation, scanning electrochemical microscopy, and microfluidic platforms integrated with electrochemical detection. The principles of these methods are briefly described, followed in most cases with a short description of an analytical or biological application and its significance. The use of electrochemical methods to examine specific mechanistic issues in exocytosis is highlighted, as a great deal of recent work has been devoted to this application.

Bio-chip for spatially controlled transfection of nucleic acid payloads into cells in a culture

Transfection of siRNA and plasmid nucleic molecules to animal, microbial and plant cell cultures is a critical process in various research areas, including drug discovery, functional genomics and basic life science research. Till recent times, transfection of these exogenous molecules have been global in nature i.e. targeting all the cells in a culture and lacking capability to spatially confine the transfection to small populations of cells within a single culture. However, in emerging areas like high-throughput screening of large molecule libraries, there is a critical need to transfect multiple different molecules to locally specified regions of a single cell culture and monitor phenotypical changes in these different cell populations. In this study, we present a cell-based biochip that utilizes a microelectrode array to generate localized current density fields that induce electroporation to a targeted group of cells for site-specific transfection of exogenous molecules. More specifically, we optimize the transfection efficiency and viabilities for spatially controlled transfection of Alexa-Fluor-488 conjugated siRNA molecules into NIH3T3 fibroblast cell cultures. Optimal electroporation parameters are established at current density values ranging between 0.05-0.07 microA microm(-2) for high transfection efficiencies (>60%) while maintaining viability (>80%) on individual microelectrodes. Additionally, exogenous plasmid molecules are electroporated for site-specific GFP expression and monitored over 48 h in-situ. The microelectrode array technology reported here can therefore be potentially used for targeting specific cells in a culture with spatial precision and transfecting siRNA and plasmids. The microfabrication approach lends itself to significant high-throughput applications in drug-discovery research.

Finite element analysis of microelectrotension of cell membranes

Electric fields can be focused by micropipette-based electrodes to induce stresses on cell membranes leading to tension and poration. To date, however, these membrane stress distributions have not been quantified. In this study, we determine membrane tension, stress, and strain distributions in the vicinity of a microelectrode using finite element analysis of a multiscale electro-mechanical model of pipette, media, membrane, actin cortex, and cytoplasm. Electric field forces are coupled to membranes using the Maxwell stress tensor and membrane electrocompression theory. Results suggest that micropipette electrodes provide a new non-contact method to deliver physiological stresses directly to membranes in a focused and controlled manner, thus providing the quantitative foundation for micreoelectrotension, a new technique for membrane mechanobiology.

Nanopipette delivery of individual molecules to cellular compartments for single-molecule fluorescence tracking

We have developed a new method, using a nanopipette, for controlled voltage-driven delivery of individual fluorescently labeled probe molecules to the plasma membrane which we used for single-molecule fluorescence tracking (SMT). The advantages of the method are 1), application of the probe to predefined regions on the membrane; 2), release of only one or a few molecules onto the cell surface; 3), when combined with total internal reflection fluorescence microscopy, very low background due to unbound molecules; and 4), the ability to first optimize the experiment and then repeat it on the same cell. We validated the method by performing an SMT study of the diffusion of individual membrane glycoproteins labeled with Atto 647-wheat germ agglutin in different surface domains of boar spermatozoa. We found little deviation from Brownian diffusion with a mean diffusion coefficient of 0.79 +/- 0.04 microm(2)/s in the acrosomal region and 0.10 +/- 0.02 microm(2)/s in the postacrosomal region; this difference probably reflects different membrane structures. We also showed that we can analyze diffusional properties of different subregions of the cell membrane and probe for the presence of diffusion barriers. It should be straightforward to extend this new method to other probes and cells, and it can be used as a new tool to investigate the cell membrane.

Electroporation: an arsenal of application

Electroporation is a way to induce nanometersized membrane pore for exogenous substances delivery into cytoplasm using an artificial electric field. Now it was widely used for molecules transfer especially in molecular experiments and genetic aspects. In recent years, modern electroporation on the embryo was developed, whose most important point is that it adopts low energy and rectangular pulse that could obtain high transfection efficiency and low damage to the embryo. This paper reviewed on the pool of application: from lab works to human clinical treatments.

Scanning electroporation of selected areas of adherent cell cultures

We present a computer-controlled scanning electroporation method. Adherent cells are electroporated using an electrolyte-filled capillary in contact with an electrode. The capillary can be scanned over a cell culture and locally deliver both an electric field and an electroporation agent to the target area without affecting surrounding cells. The instantaneous size of the targeted area is determined by the dimensions of the capillary. The size and shape of the total electroporated area are defined by these dimensions in combination with the scanning pattern. For example, striped and serpentine patterns of electroporated cells in confluent cultures can be formed. As it is easy to switch between different electroporation agents, the method is suitable for design of cell cultures with complex composition. Finite element method simulations were used to study the spatial distributions of the electric field and the concentration of an electroporation agent, as well as the fluid dynamics related to scanning and flow of electroporation agent from the capillary. The method was validated for transfection by introduction of a 9-base-pair-long randomized oligonucleotide into PC12 cells and a pmaxGFP plasmid coding for green fluorescent protein into CHO and WSS cells.

Effect of cell size and shape on single-cell electroporation

Single-cell electroporation was performed using electrolyte-filled capillaries on fluorescently labeled A549 cells. Cells were exposed to brief pulses (50-300 ms) at various cell-capillary tip distances. Cell viability and electroporation success were measured. In order to understand the variability in single-cell electroporation, logistic regression was used to determine whether the probabilities of cell survival and electroporation depend on experimental conditions and cell properties. Both experimental conditions and cell properties (size and shape) have a significant effect on the outcome. Finite element simulations were used to compare bulk electroporation to single-cell electroporation in terms of cell size and shape. Cells are more readily permeabilized and are more likely to survive if they are large and hemispherical as opposed to small and ellipsoidal with a high aspect ratio. The dependence of the maximum transmembrane potential across the cell membrane on cell size is much weaker than it is for bulk electroporation. Observed survival probabilities are related to the calculated fraction of the cell's surface area that is electroporated. Observed success of electroporation is related to the maximum transmembrane potential achieved.

Generation of focused electric field patterns at dielectric surfaces

We here report on a concept for creating well-defined electric field gradients between the boundaries of capillary electrode (a capillary of a nonconducting material equipped with an interior metal electrode) outlets, and dielectric surfaces. By keeping a capillary electrode opening close to a boundary between a conducting solution and a nonconducting medium, a high electric field can be created close to the interface by field focusing effects. By varying the inner and outer diameters of the capillary, the span of electric field strengths and the field gradient obtained can be controlled, and by varying the slit height between the capillary rim and the surface, or the applied current, the average field strength and gradient can be varied. Field focusing effects and generation of electric field patterns were analyzed using finite element method simulations. We experimentally verified the method by electroporation of a fluorescent dye (fluorescein diphosphate) into adherent, monolayered cells (PC-12 and WSS-1) and obtained a pattern of fluorescent cells corresponding to the focused electric field.

Single-cell electroporation arrays with real-time monitoring and feedback control

Rapid well-controlled intracellular delivery of drug compounds, RNA, or DNA into a cell--without permanent damage to the cell--is a pervasive challenge in basic cell biology research, drug discovery, and gene delivery. To address this challenge, we have developed a bench-top system comprised of a control interface, that mates to disposable 96-well-formatted microfluidic devices, enabling the individual manipulation, electroporation and real-time monitoring of each cell in suspension. This is the first demonstrated real-time feedback-controlled electroporation of an array of single-cells. Our computer program automatically detects electroporation events and subsequently releases the electric field, precluding continued field-induced damage of the cell, to allow for membrane resealing. Using this novel set-up, we demonstrate the reliable electroporation of an array (n = 15) of individual cells in suspension, using low applied electric fields (<1 V) and the rapid and localized intracellular delivery of otherwise impermeable compounds (Calcein and Orange Green Dextran). Such multiplexed electrical and optical measurements as a function of time are not attainable with typical electroporation setups. This system, which mounts on an inverted microscope, obviates many issues typically associated with prototypical microfluidic chip setups and, more importantly, offers well-controlled and reproducible parallel pressure and electrical application to individual cells for repeatability.

Numerical calculations of single-cell electroporation with an electrolyte-filled capillary

An electric field is focused on one cell in single-cell electroporation. This enables selective electroporation treatment of the targeted cell without affecting its neighbors. While factors that lead to membrane permeation are the same as in bulk electroporation, quantitative description of the single-cell experiments is more complicated. This is due to the fact that the potential distribution cannot be solved analytically. We present single-cell electroporation with an electrolyte-filled capillary modeled with a finite element method. Potential is calculated in the capillary, the solution surrounding the cell, and the cell. The model enables calculation of the transmembrane potential and the fraction of the cell membrane that is above the critical electroporation potential. Electroporation at several cell-to-tip distances of human lung carcinoma cells (A549) stained with ThioGlo-1 demonstrated membrane permeation at distances shorter than approximately 7.0 microm. This agrees well with the model's prediction that a critical transmembrane potential of 250 mV is achieved when the capillary is approximately 6.5 microm or closer to the cell. Simulations predict that at short cell-to-tip distances, the transmembrane potential increases significantly while the total area of the cell above the critical potential increases only moderately.

The microfabricated electrokinetic pump: a potential promising drug delivery technique

Directly delivering liquid using direct current power was a dream for 40 years. Now, the electrokinetic pump can accomplish it. This review reports recent developments in microfabricated electrokinetic pump technologies and their applications, and also discusses the electrophoresis pump and elctroosmotic pump, as well as the materials and fabrication methods frequently used for the production of these pump devices. Electrokinetics pumps can be used to deliver pure water, pure polar organic solvents, inorganic buffer and biomacromolecules, with wide applications for the delivery of liquids. These devices have the potential to become drug delivery systems, for the precise, timed and/or targeted delivery of drugs. Future trends, limitations and possibilities are also discussed.