Electroporation of mammalian cells in a microfluidic channel with geometric variation

A Pioneer Review on Lactoferrin-Conjugated Extracellular Nanovesicles for Targeting Cellular Melanoma: Recent Advancements and Future Prospects

Melanoma, a highly aggressive form of skin cancer, presents a formidable challenge in terms of treatment due to its propensity for metastasis and resistance to conventional therapies. The development of innovative nanocarriers for targeted drug delivery has opened new avenues in cancer therapy. Lactoferrin-conjugated extracellular nanovesicles (LF-EVs) have emerged as a promising vehicle in the targeted treatment of cellular melanoma, owing to their natural biocompatibility, enhanced bioavailability, and ability to traverse biological barriers effectively. This review synthesizes recent advancements in the use of LF-EVs as a novel drug delivery system for melanoma, emphasizing their unique capacity to enhance cellular uptake through LF's receptor-mediated endocytosis pathways. Key studies demonstrate that LF conjugation significantly increases the specificity of extracellular nanovesicles for melanoma cells, minimizes off-target effects, and promotes efficient intracellular drug release. Furthermore, we explore how LF-EVs interact with the tumor microenvironment, potentially inhibiting melanoma progression and metastasis while supporting antitumor immune responses. Future prospects in this field include optimizing LF conjugation techniques, improving the scalability of LF-EV production, and integrating multifunctional payloads to target drug resistance mechanisms. This review highlights the potential of LF-EVs to transform melanoma treatment strategies, bridging current gaps in therapeutic delivery and paving the way for personalized and less invasive melanoma therapies.

An experimental and theoretical study on cell swelling for osmotic imbalance induced by electroporation

The cellular membrane serves as a pivotal barrier in regulating intra- and extracellular matter exchange. Disruption of this barrier through pulsed electric fields (PEFs) induces the transmembrane transport of ions and molecules, creating a concentration gradient that subsequently results in the imbalance of cellular osmolality. In this study, a multiphysics model was developed to simulate the electromechanical response of cells exposed to microsecond pulsed electric fields (μsPEFs). Within the proposed model, the diffusion coefficient of the cellular membrane for various ions was adjusted based on electropore density. Cellular osmolality was governed and described using Van't Hoff theory, subsequently converted to loop stress to dynamically represent the cell swelling process. Validation of the model was conducted through a hypotonic experiment and simulation at 200 mOsm/kg, revealing a 14.2% increase in the cell's equivalent radius, thereby confirming the feasibility of the cell mechanical model. With the transmembrane transport of ions induced by the applied μsPEF, the hoop stress acting on the cellular membrane reached 179.95 Pa, and the cell equivalent radius increased by 11.0% when the extra-cellular medium was supplied with normal saline. The multiphysics model established in this study accurately predicts the dynamic changes in cell volume resulting from osmotic imbalance induced by PEF action. This model holds theoretical significance, offering valuable references for research on drug delivery and tumor microenvironment modulation.

Three-dimensional array of microbubbles sonoporation of cells in microfluidics

Sonoporation is a popular membrane disruption technique widely applicable in various fields, including cell therapy, drug delivery, and biomanufacturing. In recent years, there has been significant progress in achieving controlled, high-viability, and high-efficiency cell sonoporation in microfluidics. If the microchannels are too small, especially when scaled down to the cellular level, it still remains a challenge to overcome microchannel clogging, and low throughput. Here, we presented a microfluidic device capable of modulating membrane permeability through oscillating three-dimensional array of microbubbles. Simulations were performed to analyze the effective range of action of the oscillating microbubbles to obtain the optimal microchannel size. Utilizing a high-precision light curing 3D printer to fabricate uniformly sized microstructures in a one-step on both the side walls and the top surface for the generation of microbubbles. These microbubbles oscillated with nearly identical amplitudes and frequencies, ensuring efficient and stable sonoporation within the system. Cells were captured and trapped on the bubble surface by the acoustic streaming and secondary acoustic radiation forces induced by the oscillating microbubbles. At a driving voltage of 30 Vpp, the sonoporation efficiency of cells reached 93.9% ± 2.4%.

High-definition electroporation: Precise and efficient transfection on a microelectrode array

Intracellular delivery is critical for a plethora of biomedical applications, including mRNA transfection and gene editing. High transfection efficiency and low cytotoxicity, however, are often beyond the capabilities of bulk techniques and synonymous with extensive empirical optimization. Moreover, bulk techniques are not amenable to large screening applications. Here, we propose an expeditious workflow for achieving optimal electroporation-based intracellular delivery. Using the multiplexing ability of a high-definition microelectrode array (MEA) chip, we performed a sequence of carefully designed experiments, multiple linear regression modelling and validation to obtain optimal conditions for on-chip electroporation of primary fibroblasts. Five electric pulse parameters were varied to generate 32 different electroporation conditions. The effect of the parameters on cytotoxicity and intracellular delivery could be evaluated with just two experiments. Most successful electroporation conditions resulted in no cell death, highlighting the low cytotoxicity of on-chip electroporation. The resulting delivery models were then used to achieve dosage-controlled delivery of small molecules, delivery of Cas9-GFP single-guide RNA complexes and transfection with an mCherry-encoding mRNA, resulting in previously unreported high-efficiency, single-cell transfection on MEAs: cells expressed mCherry on 81% of the actuated electrodes, underscoring the vast potential of CMOS MEA technology for the transfection of primary cells.

Possible Synergies of Nanomaterial-Assisted Tissue Regeneration in Plasma Medicine: Mechanisms and Safety Concerns

Cold atmospheric plasma and nanomedicine originally emerged as individual domains, but are increasingly applied in combination with each other. Most research is performed in the context of cancer treatment, with only little focus yet on the possible synergies. Many questions remain on the potential of this promising hybrid technology, particularly regarding regenerative medicine and tissue engineering. In this perspective article, we therefore start from the fundamental mechanisms in the individual technologies, in order to envision possible synergies for wound healing and tissue recovery, as well as research strategies to discover and optimize them. Among these strategies, we demonstrate how cold plasmas and nanomaterials can enhance each other's strengths and overcome each other's limitations. The parallels with cancer research, biotechnology and plasma surface modification further serve as inspiration for the envisioned synergies in tissue regeneration. The discovery and optimization of synergies may also be realized based on a profound understanding of the underlying redox- and field-related biological processes. Finally, we emphasize the toxicity concerns in plasma and nanomedicine, which may be partly remediated by their combination, but also partly amplified. A widespread use of standardized protocols and materials is therefore strongly recommended, to ensure both a fast and safe clinical implementation.

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.

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 nonlinear electrokinetic flows in insulator-based dielectrophoresis: From induced charge to Joule heating effects

Insulator-based dielectrophoresis (iDEP) has been increasingly used for particle manipulation in various microfluidic applications. It exploits insulating structures to constrict and/or curve electric field lines to generate field gradients for particle dielectrophoresis. However, the presence of these insulators, especially those with sharp edges, causes two nonlinear electrokinetic flows, which, if sufficiently strong, may disturb the otherwise linear electrokinetic motion of particles and affect the iDEP performance. One is induced charge electroosmotic (ICEO) flow because of the polarization of the insulators, and the other is electrothermal flow because of the amplified Joule heating in the fluid around the insulators. Both flows vary nonlinearly with the applied electric field (either DC or AC) and exhibit in the form of fluid vortices, which have been utilized to promote some applications while being suppressed in others. The effectiveness of iDEP benefits from a comprehensive understanding of the nonlinear electrokinetic flows, which is complicated by the involvement of the entire iDEP device into electric polarization and thermal diffusion. This article is aimed to review the works on both the fundamentals and applications of ICEO and electrothermal flows in iDEP microdevices. A personal perspective of some future research directions in the field is also given.

Passive Dielectrophoretic Focusing of Particles and Cells in Ratchet Microchannels

Focusing particles into a tight stream is critical for many microfluidic particle-handling devices such as flow cytometers and particle sorters. This work presents a fundamental study of the passive focusing of polystyrene particles in ratchet microchannels via direct current dielectrophoresis (DC DEP). We demonstrate using both experiments and simulation that particles achieve better focusing in a symmetric ratchet microchannel than in an asymmetric one, regardless of the particle movement direction in the latter. The particle focusing ratio, which is defined as the microchannel width over the particle stream width, is found to increase with an increase in particle size or electric field in the symmetric ratchet microchannel. Moreover, it exhibits an almost linear correlation with the number of ratchets, which can be explained by a theoretical formula that is obtained from a scaling analysis. In addition, we have demonstrated a DC dielectrophoretic focusing of yeast cells in the symmetric ratchet microchannel with minimal impact on the cell viability.

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.

An Electroporation Device with Microbead-Enhanced Electric Field for Bacterial Inactivation

This paper presents an electroporation device with high bacterial inactivation performance (~4.75 log removal). Inside the device, insulating silica microbeads are densely packed between two mesh electrodes that enable enhancement of the local electric field strength, allowing improved electroporation of bacterial cells. The inactivation performance of the device is evaluated using two model bacteria, including one Gram-positive bacterium (Enterococcus faecalis) and one Gram-negative bacterium (Escherichia coli) under various applied voltages. More than 4.5 log removal of bacteria is obtained for the applied electric field strength of 2 kV/cm at a flowrate of 4 mL/min. The effect of microbeads on the inactivation performance is assessed by comparing the performance of the microbead device with that of the device having no microbeads under same operating conditions. The comparison results show that only 0.57 log removal is achieved for the device having no microbeads—eightfold lower than for the device with microbeads.

Cell lysis via acoustically oscillating sharp edges

In this article, we demonstrate an acoustofluidic device for cell lysis using the acoustic streaming effects induced by acoustically oscillating sharp-edged structures. The acoustic streaming locally generates high shear forces that can mechanically rupture cell membranes. With the acoustic-streaming-derived shear forces, our acoustofluidic device can perform cell lysis in a continuous, reagent-free manner, with a lysis efficiency of more than 90% over a range of sample flow rates. We demonstrate that our acoustofluidic lysis device works well on both adherent and non-adherent cells. We also validate it using clinically relevant samples such as red blood cells infected with malarial parasites. Additionally, the unique capability of our acoustofluidic device was demonstrated by performing downstream protein analysis and gene profiling without additional washing steps post-lysis. Our device is simple to fabricate and operate while consuming a relatively low volume of samples. These advantages and other features including the reagent-free nature and controllable lysis efficiency make our platform valuable for many biological and biomedical applications, particularly for the development of point-of-care platforms.

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.

Microfluidic Irreversible Electroporation-A Versatile Tool to Extract Intracellular Contents of Bacteria and Yeast

Exploring the dynamic behavior of cellular metabolism requires a standard laboratory method that guarantees rapid sampling and extraction of the cellular content. We propose a versatile sampling technique applicable to cells with different cell wall and cell membrane properties. The technique is based on irreversible electroporation with simultaneous quenching and extraction by using a microfluidic device. By application of electric pulses in the millisecond range, permanent lethal pores are formed in the cell membrane of Escherichia coli and Saccharomyces cerevisiae, facilitating the release of the cellular contents; here demonstrated by the measurement of glucose-6-phosphate and the activity of the enzyme glucose-6-phosphate dehydrogenase. The successful application of this device was demonstrated by pulsed electric field treatment in a flow-through configuration of the microfluidic chip in combination with sampling, inactivation, and extraction of the intracellular content in a few seconds. Minimum electric field strengths of 10 kV/cm for E. coli and 7.5 kV/cm for yeast S. cerevisiae were required for successful cell lysis. The results are discussed in the context of applications in industrial biotechnology, where metabolomics analyses are important.

3D Nanochannel Array for High-Throughput Cell Manipulation and Electroporation

Electroporation has been one of the most commonly used physical methods for gene/drug delivery. Compared to other nonviral counterparts, electroporation enables optimization of delivery efficiency by tuning the electric field applied on cells. Commercial electroporation, however, results in stochastic transfection and significant cellular damage mostly due to its "bulk" environment. In this chapter, we introduce nanoelectroporation (NEP) which has demonstrated living cell transfection in a highly controllable manner. In NEP, the electric field can be precisely focused on a single cell positioned on nanochannels. Safe single-cell electroporation as well as "electrophoretic" molecular delivery can be achieved on the same device. This system achieves significantly higher transfection efficiency and cellular viability than commercial systems. This device is unique in that it can efficiently deliver genetic molecules (e.g., DNAs, RNAs) that exceed 10 kbp in size. The NEP device based on a 3D nanochannel array prototype was fabricated using cleanroom techniques. For achieving precise cell to nanochannel pairing, three on-chip high-throughput manipulation technologies were developed, that is, magnetic tweezers (MT), dielectrophoresis (DEP), and thin-film microfluidics.

Correlation Between Optical Fluorescence and Microwave Transmission During Single-Cell Electroporation

OBJECTIVE

Multimodal characterization of a mammalian cell by optical and microwave techniques simultaneously during electroporation.

METHODS

Using a coplanar waveguide with a Jurkat cell trapped in the middle of its center conductor, continuous waves at 100 kHz of different amplitudes were applied for 20 s, while microwave transmission coefficients at 9 GHz were measured every 0.4 s.

RESULTS

The onset of electroporation was indicated by abrupt changes in both fluorescence intensity and transmission coefficient. Additionally, in measurements that lasted 300 s, the transmission coefficient was found to recover to the pre-poration level, while the fluorescence intensity remained different. Since the cells were confirmed viable through post-poration staining, the recovery of the transmission coefficient suggested reversible electroporation.

CONCLUSION

These experimental results showed that the transmission coefficient could serve as a label-free indicator of cell membrane permeability during and after electroporation. Furthermore, it could be used to expeditiously differentiate reversible electroporation from the irreversible one.

SIGNIFICANCE

This study should aid fundamental analysis of cell physiology, as well as molecular delivery, in cell engineering and electrotherapy.

Integration of marker-free selection of single cells at a wireless electrode array with parallel fluidic isolation and electrical lysis

We present integration of selective single-cell capture at an array of wireless electrodes (bipolar electrodes, BPEs) with transfer into chambers, reagent exchange, fluidic isolation and rapid electrical lysis in a single platform, thus minimizing sample loss and manual intervention steps. The whole process is achieved simply by exchanging the solution in a single inlet reservoir and by adjusting the applied voltage at a pair of driving electrodes, thus making this approach particularly well-suited for a broad range of research and clinical applications. Further, the use of BPEs allows the array to be scalable to increase throughput. Specific innovations reported here include the incorporation of a leak channel to balance competing flow paths, the use of 'split BPEs' to create a distinct recapture and electrical lysis point within the reaction chamber, and the dual purposing of an ionic liquid as an immiscible phase to seal the chambers and as a conductive medium to permit electrical lysis at the split BPEs.

Intracellular Delivery by Membrane Disruption: Mechanisms, Strategies, and Concepts

Intracellular delivery is a key step in biological research and has enabled decades of biomedical discoveries. It is also becoming increasingly important in industrial and medical applications ranging from biomanufacture to cell-based therapies. Here, we review techniques for membrane disruption-based intracellular delivery from 1911 until the present. These methods achieve rapid, direct, and universal delivery of almost any cargo molecule or material that can be dispersed in solution. We start by covering the motivations for intracellular delivery and the challenges associated with the different cargo types-small molecules, proteins/peptides, nucleic acids, synthetic nanomaterials, and large cargo. The review then presents a broad comparison of delivery strategies followed by an analysis of membrane disruption mechanisms and the biology of the cell response. We cover mechanical, electrical, thermal, optical, and chemical strategies of membrane disruption with a particular emphasis on their applications and challenges to implementation. Throughout, we highlight specific mechanisms of membrane disruption and suggest areas in need of further experimentation. We hope the concepts discussed in our review inspire scientists and engineers with further ideas to improve intracellular delivery.

Recent advances in the use of microfluidic technologies for single cell analysis

The inherent heterogeneity in cell populations has become of great interest and importance as analytical techniques have improved over the past decades. With the advent of personalized medicine, understanding the impact of this heterogeneity has become an important challenge for the research community. Many different microfluidic approaches with varying levels of throughput and resolution exist to study single cell activity. In this review, we take a broad view of the recent microfluidic developments in single cell analysis based on microwell, microchamber, and droplet platforms. We cover physical, chemical, and molecular biology approaches for cellular and molecular analysis including newly emerging genome-wide analysis.

Microfluidic Electroporation-Facilitated Synthesis of Erythrocyte Membrane-Coated Magnetic Nanoparticles for Enhanced Imaging-Guided Cancer Therapy

Biomimetic cell membrane-coated nanoparticles (CM-NPs) with superior biochemical properties have been broadly utilized for various biomedical applications. Currently, researchers primarily focus on using ultrasonic treatment and mechanical extrusion to improve the synthesis of CM-NPs. In this work, we demonstrate that microfluidic electroporation can effectively facilitate the synthesis of CM-NPs. To test it, Fe₃O₄ magnetic nanoparticles (MNs) and red blood cell membrane-derived vesicles (RBC-vesicles) are infused into a microfluidic device. When the mixture of MNs and RBC-vesicles flow through the electroporation zone, the electric pulses can effectively promote the entry of MNs into RBC-vesicles. After that, the resulting RBC membrane-capped MNs (RBC-MNs) are collected from the chip and injected into experimental animals to test the in vivo performance. Owing to the superior magnetic and photothermal properties of the MN cores and the long blood circulation characteristic of the RBC membrane shells, core-shell RBC-MNs were used for enhanced tumor magnetic resonance imaging (MRI) and photothermal therapy (PTT). Due to the completer cell membrane coating, RBC-MNs prepared by microfluidic electroporation strategy exhibit significantly better treatment effect than the one fabricated by conventional extrusion. We believe the combination of microfluidic electroporation and CM-NPs provides an insight into the synthesis of bioinpired nanoparticles to improve cancer diagnosis and therapy.

A Review on Macroscale and Microscale Cell Lysis Methods

The lysis of cells in order to extract the nucleic acids or proteins inside it is a crucial unit operation in biomolecular analysis. This paper presents a critical evaluation of the various methods that are available both in the macro and micro scale for cell lysis. Various types of cells, the structure of their membranes are discussed initially. Then, various methods that are currently used to lyse cells in the macroscale are discussed and compared. Subsequently, popular methods for micro scale cell lysis and different microfluidic devices used are detailed with their advantages and disadvantages. Finally, a comparison of different techniques used in microfluidics platform has been presented which will be helpful to select method for a particular application.

Size Specific Transfection to Mammalian Cells by Micropillar Array Electroporation

Electroporation serves as a promising non-viral gene delivery approach, while its current configuration carries several drawbacks associated with high-voltage electrical pulses and heterogeneous treatment on individual cells. Here we developed a new micropillar array electroporation (MAE) platform to advance the electroporation-based delivery of DNA and RNA probes into mammalian cells. By introducing well-patterned micropillar array texture on the electrode surface, the number of pillars each cell faces varies with its plasma membrane surface area, despite their large population and random locations. In this way, cell size specific electroporation is conveniently carried out, contributing to a 2.5~3 fold increase on plasmid DNA transfection and an additional 10–55% transgene knockdown with siRNA probes, respectively. The delivery efficiency varies with the number and size of micropillars as well as their pattern density. As MAE works like many single cell electroporation are carried out in parallel, the electrophysiology response of individual cells is representative, which has potentials to facilitate the tedious, cell-specific protocol screening process in current bulk electroporation (i.e., electroporation to a large population of cells). Its success might promote the wide adoption of electroporation as a safe and effective non-viral gene delivery approach needed in many biological research and clinical treatments.

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.

Continuous-flow multi-pulse electroporation at low DC voltages by microfluidic flipping of the voltage space topology

Concerns over biosafety, cost, and carrying capacity of viral vectors have accelerated research into physical techniques for gene delivery such as electroporation and mechanoporation. Advances in microfabrication have made it possible to create high electric fields over microscales, resulting in more efficient DNA delivery and higher cell viability. Continuous-flow microfluidic methods are typically more suitable for cellular therapies where a large number of cells need to be transfected under sterile conditions. However, the existing continuous-flow designs used to generate multiple pulses either require expensive peripherals such as high-voltage (>400 V) sources or function generators, or result in reduced cell viability due to the proximity of the cells to the electrodes. In this paper, we report a continuous-flow microfluidic device whose channel geometry reduces instrumentation demands and minimizes cellular toxicity. Our design can generate multiple pulses of high DC electric field strength using significantly lower voltages (15-60 V) than previous designs. The cells flow along a serpentine channel that repeatedly flips the cells between a cathode and an anode at high throughput. The cells must flow through a constriction each time they pass from an anode to a cathode, exposing them to high electric field strength for short durations of time (the "pulse-width"). A conductive biocompatible poly-aniline hydrogel network formed in situ is used to apply the DC voltage without bringing the metal electrodes close to the cells, further sheltering cells from the already low voltage electrodes. The device was used to electroporate multiple cell lines using electric field strengths between 700 and 800 V/cm with transfection efficiencies superior than previous flow-through designs.

Flow-Through Electroporation of HL-60 White Blood Cell Suspensions using Nanoporous Membrane Electrodes

A flow-through electroporation system, based on a novel nanoporous membrane/electrode design, for the delivery of cell wall-impermeant molecules into model leukocytes, HL-60 promyelocytes, was demonstrated. The ability to apply low voltages to cell populations, with nm-scale concentrated electric field in a periodic array, contributes to high cell viability. With applied biases of 1-4V, delivery of target molecules was achieved with 90% viability and up to 65% transfection efficiency. More importantly, the system allowed electrophoretic pumping of molecules from a microscale reservoir across the membrane/electrode system into a microfluidic flow channel for transfection of cells, a design that can reduce reagent amount by eightfold compared to current strategies. The flow-through system, which forces intimate membrane/electrode contact by using a 10μm channel height, can be easily scaled-up by adjusting the microfluidic channel geometry and/or the applied voltage pulse frequency to control cell residence times at the cell membrane/electrode interface. The demonstrated system shows promise in clinical applications where low-cost, high cell viability and high volume transfection methods are needed without the risk of viral vectors. In particular genetic modification of freely mobile white blood cells to either target disease cells or to express desired protein/enzyme biomolecules is an important target platform enabled by this device system.

Electrical lysis of cells for detergent-free droplet assays

Efficient lysis is critical when analyzing single cells in microfluidic droplets, but existing methods utilize detergents that can interfere with the assays to be performed. We demonstrate robust cell lysis without the use of detergents or other chemicals. In our method, cells are exposed to electric field immediately before encapsulation in droplets, resulting in cell lysis. We characterize lysis efficiency as a function of control parameters and demonstrate compatibility with enzymatic assays by measuring the catalysis of β-glucosidase, an important cellulase used in the conversion of biomass to biofuel. Our method enables assays in microfluidic droplets that are incompatible with detergents.

Microfluidic Screening of Electric Fields for Electroporation

Electroporation is commonly used to deliver molecules such as drugs, proteins, and/or DNA into cells, but the mechanism remains poorly understood. In this work a rapid microfluidic assay was developed to determine the critical electric field threshold required for inducing bacterial electroporation. The microfluidic device was designed to have a bilaterally converging channel to amplify the electric field to magnitudes sufficient to induce electroporation. The bacterial cells are introduced into the channel in the presence of SYTOX^®, which fluorescently labels cells with compromised membranes. Upon delivery of an electric pulse, the cells fluoresce due to transmembrane influx of SYTOX^® after disruption of the cell membranes. We calculate the critical electric field by capturing the location within the channel of the increase in fluorescence intensity after electroporation. Bacterial strains with industrial and therapeutic relevance such as Escherichia coli BL21 (3.65 ± 0.09 kV/cm), Corynebacterium glutamicum (5.20 ± 0.20 kV/cm), and Mycobacterium smegmatis (5.56 ± 0.08 kV/cm) have been successfully characterized. Determining the critical electric field for electroporation facilitates the development of electroporation protocols that minimize Joule heating and maximize cell viability. This assay will ultimately enable the genetic transformation of bacteria and archaea considered intractable and difficult-to-transfect, while facilitating fundamental genetic studies on numerous diverse microbes.

A Flow-Through Cell Electroporation Device for Rapidly and Efficiently Transfecting Massive Amounts of Cells in vitro and ex vivo

Continuous cell electroporation is an appealing non-viral approach for genetically transfecting a large number of cells. Yet the traditional macro-scale devices suffer from the unsatisfactory transfection efficiency and/or cell viability due to their high voltage, while the emerging microfluidic electroporation devices is still limited by their low cell processing speed. Here we present a flow-through cell electroporation device integrating large-sized flow tube and small-spaced distributed needle electrode array. Relatively large flow tube enables high flow rate, simple flow characterization and low shear force, while well-organized needle array electrodes produce an even-distributed electric field with low voltage. Thus the difficulties for seeking the fine balance between high flow rate and low electroporation voltage were steered clear. Efficient in vitro electrotransfection of plasmid DNA was demonstrated in several hard-to-transfect cell lines. Furthermore, we also explored ex vivo electroporated mouse erythrocyte as the carrier of RNA. The strong ability of RNA loading and short exposure time of freshly isolated cells jointly ensured a high yield of valid carrier erythrocytes, which further successfully delivered RNA into targeted tissue. Both in vitro and ex vivo electrotransfection could be accomplished at high cell processing speed (20 million cells per minute) which remarkably outperforms previous devices.

Stiffness-Independent Highly Efficient On-Chip Extraction of Cell-Laden Hydrogel Microcapsules from Oil Emulsion into Aqueous Solution by Dielectrophoresis

A dielectrophoresis (DEP)-based method achieves highly efficient on-chip extraction of cell-laden microcapsules of any stiffness from oil into aqueous solution. The hydrogel microcapsules can be extracted into the aqueous solution by DEP and interfacial tension forces with no trapped oil, while the encapsulated cells are free from electrical damage due to the Faraday cage effect.

Polymer Coatings in 3D-Printed Fluidic Device Channels for Improved Cellular Adherence Prior to Electrical Lysis

This paper describes the design and fabrication of a polyjet-based three-dimensional (3D)-printed fluidic device where poly(dimethylsiloxane) (PDMS) or polystyrene (PS) were used to coat the sides of a fluidic channel within the device to promote adhesion of an immobilized cell layer. The device was designed using computer-aided design software and converted into an .STL file prior to printing. The rigid, transparent material used in the printing process provides an optically transparent path to visualize endothelial cell adherence and supports integration of removable electrodes for electrical cell lysis in a specified portion of the channel (1 mm width × 0.8 mm height × 2 mm length). Through manipulation of channel geometry, a low-voltage power source (500 V max) was used to selectively lyse adhered endothelial cells in a tapered region of the channel. Cell viability was maintained on the device over a 5 day period (98% viable), though cell coverage decreased after day 4 with static media delivery. Optimal lysis potentials were obtained for the two fabricated device geometries, and selective cell clearance was achieved with cell lysis efficiencies of 94 and 96%. The bottleneck of unknown surface properties from proprietary resin use in fabricating 3D-printed materials is overcome through techniques to incorporate PDMS and PS.

Magnetic tweezers-based 3D microchannel electroporation for high-throughput gene transfection in living cells

A novel high-throughput magnetic tweezers-based 3D microchannel electroporation system capable of transfecting 40 000 cells/cm(2) on a single chip for gene therapy, regenerative medicine, and intracellular detection of target mRNA for screening cellular heterogeneity is reported. A single cell or an ordered array of individual cells are remotely guided by programmable magnetic fields to poration sites with high (>90%) cell alignment efficiency to enable various transfection reagents to be delivered simultaneously into the cells. The present technique, in contrast to the conventional vacuum-based approach, is significantly gentler on the cellular membrane yielding >90% cell viability and, moreover, allows transfected cells to be transported for further analysis. Illustrating the versatility of the system, the GATA2 molecular beacon is delivered into leukemia cells to detect the regulation level of the GATA2 gene that is associated with the initiation of leukemia. The uniform delivery and a sharp contrast of fluorescence intensity between GATA2 positive and negative cells demonstrate key aspects of the platform for gene transfer, screening and detection of targeted intracellular markers in living cells.

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.

Focusing of mammalian cells under an ultrahigh pH gradient created by unidirectional electropulsation in a confined microchamber†Electronic supplementary information (ESI) available: Figures S1-S5 and videos S1-S2. See DOI: 10.1039/c4sc00319eClick here for additional data file.Click here for additional data file.Click here for additional data file

A new method is demonstrated for focusing mammalian cells in free solution in a closed microfluidic chamber by applying unidirectional electric pulses.

The transport and manipulation of cells in microfluidic structures are often critically required in cellular analysis. Cells typically make consistent movement in a dc electric field in a single direction, due to their electrophoretic mobility or electroosmotic flow or the combination of the two. Here we demonstrate that mammalian cells focus to the middle of a closed microfluidic chamber under the application of unidirectional direct current pulses. With experimental and computational data, we show that under the pulses electrochemical reactions take place in the confined microscale space and create an ultrahigh and nonlinear pH gradient (∼2 orders of magnitude higher than the ones in protein isoelectric focusing) at the middle of the chamber. The varying local pH affects the cell surface charge and the electrophoretic mobility, leading to focusing in free solution. Our approach provides a new and simple method for focusing and concentrating mammalian cells at the microscale.

The use of skin models in drug development

Three dimensional (3D) tissue models of the human skin are probably the most developed and understood in vitro engineered constructs. The motivation to accomplish organotypic structures was driven by the clinics to enable transplantation of in vitro grown tissue substitutes and by the cosmetics industry as alternative test substrates in order to replace animal models. Today a huge variety of 3D human skin models exist, covering a multitude of scientific and/or technical demands. This review summarizes and discusses different approaches of skin model development and sets them into the context of drug development. Although human skin models have become indispensable for the cosmetics industry, they have not yet started their triumphal procession in pharmaceutical research and development. For drug development these tissue models may be of particular interest for a) systemically acting drugs applied on the skin, and b) drugs acting at the site of application in the case of skin diseases or disorders. Although quite a broad spectrum of models covering different aspects of the skin as a biologically acting surface exists, these are most often single stand-alone approaches. In order to enable the comprehensive application into drug development processes, the approaches have to be synchronized to allow a cross-over comparison. Besides the development of biological relevant models, other issues are not less important in the context of drug development: standardized production procedures, process automation, establishment of significant analytical methods, and data correlation. For the successful routine use of engineered human skin models in drug development, major requirements were defined. If these requirements can be accomplished in the next few years, human organotypic skin models will become indispensable for drug development, too.

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.

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.

Thermal loading in flow-through electroporation microfluidic devices

Thermal loading effects in flow-through electroporation microfluidic devices have been systematically investigated by using dye-based ratiometric luminescence thermometry. Fluorescence measurements have revealed the crucial role played by both the applied electric field and flow rate on the induced temperature increments at the electroporation sections of the devices. It has been found that Joule heating could raise the intra-channel temperature up to cytotoxic levels (>45 °C) only when conditions of low flow rates and high applied voltages are applied. Nevertheless, when flow rates and electric fields are set to those used in real electroporation experiments we have found that local heating is not larger than a few degrees, i.e. temperature is kept within the safe range (<32 °C). We also provide thermal images of electroporation devices from which the heat affected area can be elucidated. Experimental data have been found to be in excellent agreement with numerical simulations that have also revealed the presence of a non-homogeneous temperature distribution along the electroporation channel whose magnitude is critically dependent on both applied electric field and flow rate. Results included in this work will allow for full control over the electroporation conditions in flow-through microfluidic devices.

Sequential multi-molecule delivery using vortex-assisted electroporation

We developed an on-chip microscale electroporation system that enables sequential delivery of multiple molecules with precise and independent dosage controllability into pre-selected identical populations of target cells. The ability to trap cells with uniform size distribution contributed to enhanced molecular delivery efficiency and cell viability. Additionally, the system provides real-time monitoring ability of the entire delivery process, allowing timely and independent modification of cell- and molecule-specific electroporation parameters. The precisely controlled amount of inherently membrane-impermeant molecules was transferred into human cancer cells by varying electric field strengths and molecule injection durations. The proposed microfluidic electroporation system's improved viability and comparable gene transfection efficiency to that of commercial systems suggest that the current system has great potential to expand the research fields that on-chip electroporation techniques can be used in.

Physical methods for intracellular delivery: practical aspects from laboratory use to industrial-scale processing

Effective intracellular delivery is a significant impediment to research and therapeutic applications at all processing scales. Physical delivery methods have long demonstrated the ability to deliver cargo molecules directly to the cytoplasm or nucleus, and the mechanisms underlying the most common approaches (microinjection, electroporation, and sonoporation) have been extensively investigated. In this review, we discuss established approaches, as well as emerging techniques (magnetofection, optoinjection, and combined modalities). In addition to operating principles and implementation strategies, we address applicability and limitations of various in vitro, ex vivo, and in vivo platforms. Importantly, we perform critical assessments regarding (1) treatment efficacy with diverse cell types and delivered cargo molecules, (2) suitability to different processing scales (from single cell to large populations), (3) suitability for automation/integration with existing workflows, and (4) multiplexing potential and flexibility/adaptability to enable rapid changeover between treatments of varied cell types. Existing techniques typically fall short in one or more of these criteria; however, introduction of micro-/nanotechnology concepts, as well as synergistic coupling of complementary method(s), can improve performance and applicability of a particular approach, overcoming barriers to practical implementation. For this reason, we emphasize these strategies in examining recent advances in development of delivery systems.