Size Specific Transfection to Mammalian Cells by Micropillar Array Electroporation

Microfluidic Electroporation Arrays for Investigating Electroporation-Induced Cellular Rupture Dynamics

Electroporation is pivotal in bioelectrochemistry for cellular manipulation, with prominent applications in drug delivery and cell membrane studies. A comprehensive understanding of pore generation requires an in-depth analysis of the critical pore size and the corresponding energy barrier at the onset of cell rupture. However, many studies have been limited to basic models such as artificial membranes or theoretical simulations. Challenging this paradigm, our study pioneers using a microfluidic electroporation chip array. This tool subjects live breast cancer cell species to a diverse spectrum of alternating current electric field conditions, driving electroporation-induced cell rupture. We conclusively determined the rupture voltages across varying applied voltage loading rates, enabling an unprecedented characterization of electric cell rupture dynamics encompassing critical pore radius and energy barrier. Further bolstering our investigation, we probed cells subjected to cholesterol depletion via methyl-β-cyclodextrin and revealed a strong correlation with electroporation. This work not only elucidates the dynamics of electric rupture in live cell membranes but also sets a robust foundation for future explorations into the mechanisms and energetics of live cell electroporation.

Biomaterial-based gene therapy

Gene therapy, a medical approach that involves the correction or replacement of defective and abnormal genes, plays an essential role in the treatment of complex and refractory diseases, such as hereditary diseases, cancer, and rheumatic immune diseases. Nucleic acids alone do not easily enter the target cells due to their easy degradation in vivo and the structure of the target cell membranes. The introduction of genes into biological cells is often dependent on gene delivery vectors, such as adenoviral vectors, which are commonly used in gene therapy. However, traditional viral vectors have strong immunogenicity while also presenting a potential infection risk. Recently, biomaterials have attracted attention for use as efficient gene delivery vehicles, because they can avoid the drawbacks associated with viral vectors. Biomaterials can improve the biological stability of nucleic acids and the efficiency of intracellular gene delivery. This review is focused on biomaterial-based delivery systems in gene therapy and disease treatment. Herein, we review the recent developments and modalities of gene therapy. Additionally, we discuss nucleic acid delivery strategies, with a focus on biomaterial-based gene delivery systems. Furthermore, the current applications of biomaterial-based gene therapy are summarized.

Combinatorial physical methods for cellular therapy: Towards the future of cellular analysis?

The physical energy activated techniques for cellular delivery and analysis is one of the most rapidly expanding research areas for a variety of biological and biomedical discoveries. These methods, such as electroporation, optoporation, sonoporation, mechanoporation, magnetoporation, etc., have been widely used in delivering different biomolecules into a range of primary and patient-derived cell types. However, the techniques when used individually have had limitations in delivery and co-delivery of diverse biomolecules in various cell types. In recent years, a number of studies have been performed by combining the different membrane disruption techniques, either sequentially or simultaneously, in a single study. The studies, referred to as combinatorial, or hybrid techniques, have demonstrated enhanced transfection, such as efficient macromolecular and gene delivery and co-delivery, at lower delivery parameters and with high cell viability. Such studies can open up new and exciting avenues for understanding the subcellular structure and consequently facilitate the development of novel therapeutic strategies. This review consequently aims at summarising the different developments in hybrid therapeutic techniques. The different methods discussed include mechano-electroporation, electro-sonoporation, magneto-mechanoporation, magnetic nanoparticles enhanced electroporation, and magnetic hyperthermia studies. We discuss the clinical status of the different methods and conclude with a discussion on the future prospects of the combinatorial techniques for cellular therapy and diagnostics.

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.

The cell density effect in animal cell-based bioprocessing: Questions, insights and perspectives

One of the main challenges in the development of bioprocesses based on cell transient expression is the commonly reported reduction of cell specific productivity at increasing cell densities. This is generally known as the cell density effect (CDE). Many efforts have been devoted to understanding the cell metabolic implications to this phenomenon in an attempt to design operational strategies to overcome it. A comprehensive analysis of the main studies regarding the CDE is provided in this work to better define the elements comprising its cause and impact. Then, examples of methodologies and approaches employed to achieve successful transient expression at high cell densities (HCD) are thoroughly reviewed. A critical assessment of the limitations of the reported studies in the understanding of the CDE is presented, covering the leading hypothesis of the molecular implications. The overall analysis of previous work on CDE may offer useful insights for further research into manufacturing of biologics.

Stability of the nitroxide biradical AMUPol in intact and lysed mammalian cells

Dynamic Nuclear Polarization (DNP) enhanced solid state NMR increases experimental sensitivity, potentially enabling detection of biomolecules at their physiological concentrations. The sensitivity of DNP experiments is due to the transfer of polarization from electron spins of free radicals to the nuclear spins of interest. Here, we investigate the reduction of AMUPol in both lysed and intact HEK293 cells. We find that nitroxide radicals are reduced with first order reduction kinetics by cell lysates at a rate of ∼ 12% of the added nitroxide radical concentration per hour. We also found that electroporation delivered a consistent amount of AMUPol to intact cells and that nitroxide radicals are reduced just slightly more rapidly (∼15% per hour) by intact cells than by cell lysates. The two nitroxide radicals of AMUPol are reduced independently and this leads to considerable accumulation of the DNP-silent monoradical form of AMUPol, particularly in preparations of intact cells where nearly half of the AMUPol is already reduced to the DNP silent monoradical form at the earliest experimental time points. This confirms that the loss of the DNP-active biradical form of AMUPol is faster than the nitroxide reduction rate. Finally, we investigate the effect of adding N-ethyl maleimide, a well-known inhibitor of thiol (-SH) group-based reduction of nitroxide biradicals in cells, on AMUPol reduction, cellular viability, and DNP performance. Although pre-treatment of cells with NEM effectively inhibited the reduction of AMUPol, exposure to NEM compromised cellular viability and, surprisingly, did not improve DNP performance. Collectively, these results indicate that, currently, the most effective strategy to obtain high DNP enhancements for DNP-assisted in-cell NMR is to minimize room temperature contact times with cellular constituents and suggest that the development of bio-resistant polarization agents for DNP could considerably increase the sensitivity of DNP-assisted in-cell NMR experiments.

Microfluidic mechanoporation for cellular delivery and analysis

Highly efficient intracellular delivery strategies are essential for developing therapeutic, diagnostic, biological, and various biomedical applications. The recent advancement of micro/nanotechnology has focused numerous researches towards developing microfluidic device-based strategies due to the associated high throughput delivery, cost-effectiveness, robustness, and biocompatible nature. The delivery strategies can be carrier-mediated or membrane disruption-based, where membrane disruption methods find popularity due to reduced toxicity, enhanced delivery efficiency, and cell viability. Among all of the membrane disruption techniques, the mechanoporation strategies are advantageous because of no external energy source required for membrane deformation, thereby achieving high delivery efficiencies and increased cell viability into different cell types with negligible toxicity. The past two decades have consequently seen a tremendous boost in mechanoporation-based research for intracellular delivery and cellular analysis. This article provides a brief review of the most recent developments on microfluidic-based mechanoporation strategies such as microinjection, nanoneedle arrays, cell-squeezing, and hydroporation techniques with their working principle, device fabrication, cellular delivery, and analysis. Moreover, a brief discussion of the different mechanoporation strategies integrated with other delivery methods has also been provided. Finally, the advantages, limitations, and future prospects of this technique are discussed compared to other intracellular delivery techniques.

In-Cell Sensitivity-Enhanced NMR of Intact Viable Mammalian Cells

NMR has the resolution and specificity to determine atomic-level protein structures of isotopically labeled proteins in complex environments, and with the sensitivity gains conferred by dynamic nuclear polarization (DNP), NMR has the sensitivity to detect proteins at their endogenous concentrations. However, DNP sensitivity enhancements are critically dependent on experimental conditions and sample composition. While some of these conditions are theoretically compatible with cellular viability, the effects of others on cellular sample integrity are unknown. Uncertainty about the integrity of cellular samples limits the utility of experimental outputs of in-cell experiments. Using several measures, we establish conditions that support DNP enhancements that can enable detection of micromolar concentrations of proteins in experimentally tractable times that are compatible with cellular viability. Taken together, we establish DNP-assisted MAS NMR as a technique for structural investigations of biomolecules in intact viable cells that can be phenotyped both before and after NMR experiments.

Robust three-dimensional nanotube-in-micropillar array electrodes to facilitate size independent electroporation in blood cell therapy

Blood is an attractive carrier for plasmid and RNA-based medicine in cell therapy. Electroporation serves as a favorable delivery tool for simple operation, quick internalization, minimum cell culture involvement, and low contamination risk. However, the delivery outcome of electroporation heavily depends on the treated cells such as their type, size, and orientation to the electric field, not ideal for highly heterogeneous blood samples. Herein, a new electroporation system was developed towards effective transfection to cells in blood regardless of their large diversity. By coupling replica molding and infiltration-coating processes, we successfully configured a three-dimensional electrode comprised of a polymer micropillar array on which carbon nanotubes (CNTs) are partially embedded. During electroporation, cells sag between micropillars and deform to form a conformal contact with their top and side surfaces. The implanted CNTs not only provide a robust conductive coating for polymer micropattern but also have their protruded ends face the cell membrane vertically everywhere with maximum transmembrane potential. Regardless of their largely varied sizes and random dispersion, both individual blood cell type and whole blood samples were effectively transfected with plasmid DNA (85% after 24 h and 95% after 72 h, or 2.5-3.0 folds enhancement). High-dose RNA probes were also introduced, which regulate better the expression levels of exogenous and endogenous genes in blood cells. Besides its promising performance on non-viral delivery routes to cell-related studies and therapy, the involved new fabrication method also provides a convenient and effective way to construct flexible electronics with stable micro/nano features on the surface.

High Throughput and Highly Controllable Methods for In Vitro Intracellular Delivery

In vitro and ex vivo intracellular delivery methods hold the key for releasing the full potential of tissue engineering, drug development, and many other applications. In recent years, there has been significant progress in the design and implementation of intracellular delivery systems capable of delivery at the same scale as viral transfection and bulk electroporation but offering fewer adverse outcomes. This review strives to examine a variety of methods for in vitro and ex vivo intracellular delivery such as flow-through microfluidics, engineered substrates, and automated probe-based systems from the perspective of throughput and control. Special attention is paid to a particularly promising method of electroporation using micro/nanochannel based porous substrates, which expose small patches of cell membrane to permeabilizing electric field. Porous substrate electroporation parameters discussed include system design, cells and cargos used, transfection efficiency and cell viability, and the electric field and its effects on molecular transport. The review concludes with discussion of potential new innovations which can arise from specific aspects of porous substrate-based electroporation platforms and high throughput, high control methods in general.

3D Printed Microneedle Array for Electroporation

In-vitro transfection of cells by electroporation is a widely used approach in cell biology and medicine. The transfection method is highly dependent on the cell culture's electrical resistance, which is strongly determined by differences in the membranes, but also on the morphology of the electrodes. Microneedle (MN)-based electrodes have been used to concentrate the electrical field during electroporation, and therefore maximize its effect on cell membrane permeability. So far, the methods used for the fabrication of MN electrodes have been relatively limited with respect to the needle design. In this work, we provide a method to fabricate MNs using 3D printing, which is a technology that provides a high degree of flexibility with respect to geometry and dimensions. Pyramidal-shaped MN designs were fabricated and tested on HCT116 cancer cells. Customization of the tips of the pyramids permits tailoring of the electrical field in the vicinity of the cell membranes. The fabricated device enables low-voltage (2 V) electroporation, eliminating the need for the use of specialized chemical buffers. The results show the potential of this method, which can be exploited and optimized for many different applications, and offer a very accessible approach for in-vitro electroporation and cell studies. The MNs can be customized to create complex structures, for example, for a multi-culture cell environment.

Biosensors Based on Mechanical and Electrical Detection Techniques

Biosensors are powerful analytical tools for biology and biomedicine, with applications ranging from drug discovery to medical diagnostics, food safety, and agricultural and environmental monitoring. Typically, biological recognition receptors, such as enzymes, antibodies, and nucleic acids, are immobilized on a surface, and used to interact with one or more specific analytes to produce a physical or chemical change, which can be captured and converted to an optical or electrical signal by a transducer. However, many existing biosensing methods rely on chemical, electrochemical and optical methods of identification and detection of specific targets, and are often: complex, expensive, time consuming, suffer from a lack of portability, or may require centralised testing by qualified personnel. Given the general dependence of most optical and electrochemical techniques on labelling molecules, this review will instead focus on mechanical and electrical detection techniques that can provide information on a broad range of species without the requirement of labelling. These techniques are often able to provide data in real time, with good temporal sensitivity. This review will cover the advances in the development of mechanical and electrical biosensors, highlighting the challenges and opportunities therein.

Efficient CRISPR/Cas9-mediated gene editing in Guangdong small-ear spotted pig cells using an optimized electrotransfection method

OBJECTIVES

Guangdong Small-ear Spotted (GDSS) pigs are a pig breed native to China that possesses unfortunate disadvantages, such as slow growth rate, low lean-meat percentage, and reduced feed utilization. In contrast to traditional genetic breeding methods with long cycle time and high cost, CRISPR/Cas9-mediated gene editing for the modification of the pig genome can quickly improve production traits, and therefore this technique exhibits important potential in the genetic improvement and resource development of GDSS pigs. In the present study, we aimed to establish an efficient CRISPR/Cas9-mediated gene-editing system for GDSS pig cells by optimizing the electrotransfection parameters, and to realize efficient CRISPR/Cas9-mediated gene editing of GDSS pig cells.

RESULTS

After optimization of electrotransfection parameters for the transfection of GDSS pig cells, we demonstrated that a voltage of 150 V and a single pulse with a pulse duration of 20 ms were the optimal electrotransfection parameters for gene editing in these cells. In addition, our study generated GDSS pig single-cell colonies with biallelic mutations in the myostatin (MSTN) gene and insulin-like growth factor 2 (IGF2) intron-3 locus, which play an important role in pig muscle growth and muscle development. The single-cell colonies showed no foreign gene integration or off-target effects, and maintained normal cell morphology and viability. These gene-edited, single-cell colonies can in the future be used as donor cells to generate MSTN- and IGF2-edited GDSS pigs using somatic cell nuclear transfer (SCNT).

CONCLUSIONS

This study establishes the foundation for genetic improvement and resource development of GDSS pigs using CRISPR/Cas9-mediated gene editing combined with SCNT.

Construction of a hierarchical gene regulatory network centered around a transcription factor

We have modified a multitude of transcription factors (TFs) in numerous plant species and some animal species, and obtained transgenic lines that exhibit phenotypic alterations. Whenever we observe phenotypic changes in a TF's transgenic lines, we are always eager to identify its target genes, collaborative regulators and even upstream high hierarchical regulators. This issue can be addressed by establishing a multilayered hierarchical gene regulatory network (ML-hGRN) centered around a given TF. In this article, a practical approach for constructing an ML-hGRN centered on a TF using a combined approach of top-down and bottom-up network construction methods is described. Strategies for constructing ML-hGRNs are vitally important, as these networks provide key information to advance our understanding of how biological processes are regulated.

Cell Size-Specific Transfection by Micropillar Array Electroporation

In this study, we reported a new micropillar array electroporation (MAE) platform to accomplish large-scale, size-specific DNA and RNA delivery to mammalian cells for nanomedicine. By introducing well-patterned micropillar array on the electrode surface, the number of micropillars each cell faces varies with the surface area of cell membrane or the size of cells. In this way, cell size-specific electroporation is conveniently done on a large population of cells in despite of their random locations between the two electrodes. The enhancement of this MAE system on the delivery of DNA and RNA probes without sacrifice of cell viability is demonstrated with an average increase of 2.5 to 3-fold on the transfection efficiency of DNA plasmids and additional knockdown of the targeted protein 10-55% more in siRNA delivery when compared to that using a commercial electroporation system. This MAE system works like many single cell electroporation are carried out in parallel, showing potential to bridge the gap between single cell electrophysiology study and in vitro electroporation to a large population of cells.

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.

Intracellular delivery of mRNA to human primary T cells with microfluidic vortex shedding

Intracellular delivery of functional macromolecules, such as DNA and RNA, across the cell membrane and into the cytosol, is a critical process in both biology and medicine. Herein, we develop and use microfluidic chips containing post arrays to induce microfluidic vortex shedding, or μVS, for cell membrane poration that permits delivery of mRNA into primary human T lymphocytes. We demonstrate transfection with μVS by delivery of a 996-nucleotide mRNA construct encoding enhanced green fluorescent protein (EGFP) and assessed transfection efficiencies by quantifying levels of EGFP protein expression. We achieved high transfection efficiency (63.6 ± 3.44% EGFP + viable cells) with high cell viability (77.3 ± 0.58%) and recovery (88.7 ± 3.21%) in CD3 + T cells 19 hrs after μVS processing. Importantly, we show that processing cells via μVS does not negatively affect cell growth rates or alter cell states. We also demonstrate processing speeds of greater than 2.0 × 10⁶ cells s^-1 at volumes ranging from 0.1 to 1.5 milliliters. Altogether, these results highlight the use of μVS as a rapid and gentle delivery method with promising potential to engineer primary human cells for research and clinical applications.

Interfacing Cells with Vertical Nanoscale Devices: Applications and Characterization

Measurements of the intracellular state of mammalian cells often require probes or molecules to breach the tightly regulated cell membrane. Mammalian cells have been shown to grow well on vertical nanoscale structures in vitro, going out of their way to reach and tightly wrap the structures. A great deal of research has taken advantage of this interaction to bring probes close to the interface or deliver molecules with increased efficiency or ease. In turn, techniques have been developed to characterize this interface. Here, we endeavor to survey this research with an emphasis on the interface as driven by cellular mechanisms.

Tracking the Evolution of Transiently Transfected Individual Cells in a Microfluidic Platform

Transient gene expression (TGE) technology enables the rapid production of large amount of recombinant proteins, without the need of fastidious screening of the producing cells required for stable transfection (ST). However, several barriers must be overcome before reaching the production yields using ST. For optimizing the production yields from suspended cells using TGE, a better understanding of the transfection conditions at the single cell level are required. In this study, a universal droplet microfluidic platform was used to assess the heterogeneities of CHO-S population transiently transfected with cationic liposomes (CL) (lipoplexes) complexed with GFP-coding plasmid DNA (pDNA). A single cell analysis of GFP production kinetics revealed the presence of a subpopulation producing higher levels of GFP compared with the main population. The size of high producing (HP) cells, their relative abundance, and their specific productivity were dependent on the charge and the pDNA content of the different lipoplexes: HPs showed increased cell size in comparison to the average population, lipoplexes with positive charge produced more HPs, and lipoplexes carrying a larger amount of pDNA yielded a higher specific productivity of HPs. This study demonstrates the potential for time-resolved single-cell measurements to explain population dynamics from a microscopic point of view.