Dielectrophoretic Separation of Live and Dead Monocytes Using 3D Carbon-Electrodes

Proposal and performance evaluation of a new parallel plate continuous cell separation device using dielectrophoresis

Along with the rapid development of cellular biological research in recent years, there has been an urgent need for a high-speed, high-precision method of separating target cells from a highly heterogeneous cell population. Among the various cell separation technologies proposed so far, dielectrophoresis (DEP)-based approaches have shown particular promise because they are noninvasive to cells. We have developed a new DEP-based device to separate large numbers of live and dead cells of the human mammary cell line MCF10A. In this study, we validated the separation performance of this device. The results showed the successful separation of a higher percentage of cells than in previous studies, with a separation efficiency higher than 90%. In the past, there have been no confirmed cases in which a separation rate of over 90% and high-speed processing of a large number of cells were simultaneously achieved. It was shown that the proposed device can process large numbers of cells at high speed and with high accuracy.

Dielectrophoretic separation and purification: From colloid and biological particles to droplets

It is indispensable to realize the high level of purification and separation, so that objective particles, such as malignant cells, harmful bacteria, and special proteins or biological molecules, could satisfy the high precise measurement in the pharmaceutical analysis, clinical diagnosis, targeted therapy, and food defense. In addition, this could reveal the intrinsic nature and evolution mechanisms of individual biological variations. Consequently, many techniques related to optical tweezers, microfluidics, acoustophoresis, and electrokinetics can be broadly used to achieve micro- and nano-scale particle separations. Dielectrophoresis (DEP) has been used for various manipulation, concentration, transport, and separation processes of biological particles owing to its early development, mature theory, low cost, and high throughput. Although numerous reviews have discussed the biological applications of DEP techniques, comprehensive descriptions of micro- and nano-scale particle separations feature less frequently in the literature. Therefore, this review summarizes the current state of particle separation attention to relevant technological developments and innovation, including theoretical simulation, microchannel structure, electrode material, pattern and its layout. Moreover, a brief overview of separation applications using DEP in combination with other technologies is also provided. Finally, conclusions, future guidelines, and suggestions for potential promotion are highlighted.

Nonlinear Electrokinetic Methods of Particles and Cells

Nonlinear electrokinetic phenomena offer label-free, portable, and robust approaches for particle and cell assessment, including selective enrichment, separation, sorting, and characterization. The field of electrokinetics has evolved substantially since the first separation reports by Arne Tiselius in the 1930s. The last century witnessed major advances in the understanding of the weak-field theory, which supported developments in the use of linear electrophoresis and its adoption as a routine analytical technique. More recently, an improved understanding of the strong-field theory enabled the development of nonlinear electrokinetic techniques such as electrorotation, dielectrophoresis, and nonlinear electrophoresis. This review discusses the operating principles and recent applications of these three nonlinear electrokinetic phenomena for the analysis and manipulation of particles and cells and provides an overview of some of the latest developments in the field of nonlinear electrokinetics.

Capillarity Enabled Large-Array Liquid Metal Electrodes for Compact and High-Throughput Dielectrophoretic Microfluidics

Dielectrophoresis (DEP) particle separation has label-free, well-controllable, and low-damage merits. Sidewall microelectrodes made of liquid metal alloy (LMA) inherits the additional advantage of thick electrodes to generate impactful DEP force. However, existing LMA electrode-based devices lack the ability to integrate large-array electrodes in a compact footprint, severely limiting flow rate and thus throughput. Herein, a facile and versatile method is proposed to integrate high-density thick LMA electrodes in microfluidic devices, taking advantage of the passive control ability of capillary burst valves (CBVs). CBVs with carefully designed burst pressures are co-designed in microfluidic channels, allowing self-assembly of LMA electrode array through simple hand-push injection. The arrayed electrode configuration brings the accumulative DEP deflection effect. Specifically, The fabricated 5000 pairs of sidewall electrodes in a compact chip are demonstrted to achieve ten times higher throughput in DEP deflection. The 5000-electrode-pair device is applied to successfully separate four mixed samples, including human peripheral blood mononuclear cells and A549 cells with the flow rate of 70 µL min-1. It is envisioned that this work can greatly facilitate LMA electrode array fabrication and offer a robust and versatile platform for DEP separation applications.

Microfluidic Blood Separation: Key Technologies and Critical Figures of Merit

Blood is a complex sample comprised mostly of plasma, red blood cells (RBCs), and other cells whose concentrations correlate to physiological or pathological health conditions. There are also many blood-circulating biomarkers, such as circulating tumor cells (CTCs) and various pathogens, that can be used as measurands to diagnose certain diseases. Microfluidic devices are attractive analytical tools for separating blood components in point-of-care (POC) applications. These platforms have the potential advantage of, among other features, being compact and portable. These features can eventually be exploited in clinics and rapid tests performed in households and low-income scenarios. Microfluidic systems have the added benefit of only needing small volumes of blood drawn from patients (from nanoliters to milliliters) while integrating (within the devices) the steps required before detecting analytes. Hence, these systems will reduce the associated costs of purifying blood components of interest (e.g., specific groups of cells or blood biomarkers) for studying and quantifying collected blood fractions. The microfluidic blood separation field has grown since the 2000s, and important advances have been reported in the last few years. Nonetheless, real POC microfluidic blood separation platforms are still elusive. A widespread consensus on what key figures of merit should be reported to assess the quality and yield of these platforms has not been achieved. Knowing what parameters should be reported for microfluidic blood separations will help achieve that consensus and establish a clear road map to promote further commercialization of these devices and attain real POC applications. This review provides an overview of the separation techniques currently used to separate blood components for higher throughput separations (number of cells or particles per minute). We present a summary of the critical parameters that should be considered when designing such devices and the figures of merit that should be explicitly reported when presenting a device's separation capabilities. Ultimately, reporting the relevant figures of merit will benefit this growing community and help pave the road toward commercialization of these microfluidic systems.

A High-Throughput Microfluidic Cell Sorter Using a Three-Dimensional Coupled Hydrodynamic-Dielectrophoretic Pre-Focusing Module

Dielectrophoresis (DEP) is a powerful tool for label-free sorting of cells, even those with subtle differences in morphological and dielectric properties. Nevertheless, a major limitation is that most existing DEP techniques can efficiently sort cells only at low throughputs (<1 mL h-1). Here, we demonstrate that the integration of a three-dimensional (3D) coupled hydrodynamic-DEP cell pre-focusing module upstream of the main DEP sorting region enables cell sorting with a 10-fold increase in throughput compared to conventional DEP approaches. To better understand the key principles and requirements for high-throughput cell separation, we present a comprehensive theoretical model to study the scaling of hydrodynamic and electrostatic forces on cells at high flow rate regimes. Based on the model, we show that the critical cell-to-electrode distance needs to be ≤10 µm for efficient cell sorting in our proposed microfluidic platform, especially at flow rates ≥ 1 mL h-1. Based on those findings, a computational fluid dynamics model and particle tracking analysis were developed to find optimum operation parameters (e.g., flow rate ratios and electric fields) of the coupled hydrodynamic-DEP 3D focusing module. Using these optimum parameters, we experimentally demonstrate live/dead K562 cell sorting at rates as high as 10 mL h-1 (>150,000 cells min-1) with 90% separation purity, 85% cell recovery, and no negative impact on cell viability.

Continuous Flow Separation of Live and Dead Cells Using Gravity Sedimentation

The separation of target cell species is an important step for various biomedical applications ranging from single cell studies to drug testing and cell-based therapies. The purity of cell solutions is critical for therapeutic application. For example, dead cells and debris can negatively affect the efficacy of cell-based therapies. This study presents a cost-effective method for the continuous separation of live and dead cells using a 3D resin-printed microfluidic device. Saccharomyces cerevisiae yeast cells are used for cell separation experiments. Both numerical and experimental studies are presented to show the effectiveness of the presented device for the isolation of dead cells from cell solutions. The experimental results show that the 3D-printed microfluidic device successfully separates live and dead cells based on density differences. Separation efficiencies of over 95% are achieved at optimum flow rates, resulting in purer cell populations in the outlets. This study highlights the simplicity, cost-effectiveness, and potential applications of the 3D-printed microfluidic device for cell separation. The implementation of 3D printing technology in microfluidics holds promise for advancing the field and enabling the production of customized devices for biomedical applications.

New Generation Dielectrophoretic-Based Microfluidic Device for Multi-Type Cell Separation

This study introduces a new generation of dielectrophoretic-based microfluidic device for the precise separation of multiple particle/cell types. The device features two sets of 3D electrodes, namely cylindrical and sidewall electrodes. The main channel of the device terminates with three outlets: one in the middle for particles that sense negative dielectrophoresis force and two others at the right and left sides for particles that sense positive dielectrophoresis force. To evaluate the device performance, we used red blood cells (RBCs), T-cells, U937-MC cells, and Clostridium difficile bacteria as our test subjects. Our results demonstrate that the proposed microfluidic device could accurately separate bioparticles in two steps, with sidewall electrodes of 200 µm proving optimal for efficient separation. Applying different voltages for each separation step, we found that the device performed most effectively at 6 Vp-p applied to the 3D electrodes, and at 20 Vp-p and 11 Vp-p applied to the sidewall electrodes for separating RBCs from bacteria and T-cells from U937-MC cells, respectively. Notably, the device's maximum electric fields remained below the cell electroporation threshold, and we achieved a separation efficiency of 95.5% for multi-type particle separation. Our findings proved the device's capacity for separating multiple particle types with high accuracy, without limitation for particle variety.

A correlation of conductivity medium and bioparticle viability on dielectrophoresis-based biomedical applications

Dielectrophoresis (DEP) bioparticle research has progressed from micro to nano levels. It has proven to be a promising and powerful cell manipulation method with an accurate, quick, inexpensive, and label-free technique for therapeutic purposes. DEP, an electrokinetic phenomenon, induces particle movement as a result of polarization effects in a nonuniform electrical field. This review focuses on current research in the biomedical field that demonstrates a practical approach to DEP in terms of cell separation, trapping, discrimination, and enrichment under the influence of the conductive medium in correlation with bioparticle viability. The current review aims to provide readers with an in-depth knowledge of the fundamental theory and principles of the DEP technique, which is influenced by conductive medium and to identify and demonstrate the biomedical application areas. The high conductivity of physiological fluids presents obstacles and opportunities, followed by bioparticle viability in an electric field elaborated in detail. Finally, the drawbacks of DEP-based systems and the outlook for the future are addressed. This article will aid in advancing technology by bridging the gap between bioscience and engineering. We hope the insights presented in this review will improve cell suspension medium and promote DEP-viable bioparticle manipulation for health-care diagnostics and therapeutics.

Microfluidic Systems for Blood and Blood Cell Characterization

A laboratory blood test is vital for assessing a patient's health and disease status. Advances in microfluidic technology have opened the door for on-chip blood analysis. Currently, microfluidic devices can reproduce myriad routine laboratory blood tests. Considerable progress has been made in microfluidic cytometry, blood cell separation, and characterization. Along with the usual clinical parameters, microfluidics makes it possible to determine the physical properties of blood and blood cells. We review recent advances in microfluidic systems for measuring the physical properties and biophysical characteristics of blood and blood cells. Added emphasis is placed on multifunctional platforms that combine several microfluidic technologies for effective cell characterization. The combination of hydrodynamic, optical, electromagnetic, and/or acoustic methods in a microfluidic device facilitates the precise determination of various physical properties of blood and blood cells. We analyzed the physical quantities that are measured by microfluidic devices and the parameters that are determined through these measurements. We discuss unexplored problems and present our perspectives on the long-term challenges and trends associated with the application of microfluidics in clinical laboratories. We expect the characterization of the physical properties of blood and blood cells in a microfluidic environment to be considered a standard blood test in the future.

Dielectrophoretic characterization of macrophage phenotypes

Different macrophage phenotypes play important roles in diverse biological processes and diseases. In this study, we have characterized the dielectrophoretic responses of human monocytes and macrophage phenotypes: nonactivated (M0), pro-inflammatory (M1), and pro-healing (M2a). Dielectrophoretic responses of cells change as a function of frequency of the applied electric field. We measured the crossover frequency at which cells transition from negative to positive dielectrophoresis (DEP) or vice versa using interdigitated electrodes. For these characterization experiments, we also developed a new low-conductivity media formulation that retained 100% of the initial viability for 1 h. Human THP1 monocytes showed a distinguishable DEP response from mature macrophages. M1 macrophages also showed a distinct DEP response compared to M0 and M2a macrophages. No clear distinction could be drawn between M0 and M2a. The median values of the crossover frequencies of monocytes, M0, M1, and M2a were 38, 21, 11, and 23 kHz, respectively. Membrane capacitances of these cells were calculated consequently, and the values were 0.0111, 0.0128, 0.0244, and 0.0117 F/m² for monocytes, M0, M1, and M2a, respectively. These results show how bioelectric properties are influenced by changes in macrophage phenotype.

Analysis of U87 glioma cells by dielectrophoresis

Glioblastoma multiforme is the most aggressive and invasive brain cancer consisting of genetically and phenotypically altering glial cells. It has massive heterogeneity due to its highly complex and dynamic microenvironment. Here, electrophysiological properties of U87 human glioma cell line were measured based on a dielectrophoresis phenomenon to quantify the population heterogeneity of glioma cells. Dielectrophoretic forces were generated using a gold-microelectrode array within a microfluidic channel when 3 V_pp and 100, 200, 300, 400, 500 kHz, 1, 2, 5, and 10 MHz frequencies were applied. We analyzed the dielectrophoretic behavior of 500 glioma cells, and revealed that the crossover frequency of glioma cells was around 140 kHz. A quantifying dielectrophoretic movement of the glioma cells exhibited three distinct glioma subpopulations: 50% of the glioma cells experienced strong, 30% of the cells were spread in the microchannel by moderate, and the rest of the cells experienced very weak positive dielectrophoretic forces. Our results demonstrated the dielectrophoretic spectra of U87 glioma cell line. Dielectrophoretic responses of glioma cells linked population heterogeneity to membrane properties of glioma cells rather than their size distribution in the population.

Rational Design and Numerical Analysis of a Hybrid Floating cIDE Separator for Continuous Dielectrophoretic Separation of Microparticles at High Throughput

Dielectrophoresis (DEP) enables continuous and label-free separation of (bio)microparticles with high sensitivity and selectivity, whereas the low throughput issue greatly confines its clinical application. Herein, we report a novel design of the DEP separator embedded with cylindrical interdigitated electrodes that incorporate hybrid floating electrode layout for (bio)microparticle separation at favorable throughput. To better predict microparticle trajectory in the scaled-up DEP platform, a theoretical model based on coupling of electrostatic, fluid and temperature fields is established, in which the effects of Joule heating-induced electrothermal and buoyancy flows on particles are considered. Size-based fractionation of polystyrene microspheres and dielectric properties-based isolation of MDA-MB-231 from blood cells are numerically realized, respectively, by the proposed separator with sample throughputs up to 2.6 mL/min. Notably, the induced flows can promote DEP discrimination of heterogeneous cells. This work provides a reference on tailoring design of enlarged DEP platforms for highly efficient separation of (bio)samples at high throughput.

Multiphysics microfluidics for cell manipulation and separation: a review

Multiphysics microfluidics, which combines multiple functional physical processes in a microfluidics platform, is an emerging research area that has attracted increasing interest for diverse biomedical applications. Multiphysics microfluidics is expected to overcome the limitations of individual physical phenomena through combining their advantages. Furthermore, multiphysics microfluidics is superior for cell manipulation due to its high precision, better sensitivity, real-time tunability, and multi-target sorting capabilities. These exciting features motivate us to review this state-of-the-art field and reassess the feasibility of coupling multiple physical processes. To confine the scope of this paper, we mainly focus on five common forces in microfluidics: inertial lift, elastic, dielectrophoresis (DEP), magnetophoresis (MP), and acoustic forces. This review first explains the working mechanisms of single physical phenomena. Next, we classify multiphysics techniques in terms of cascaded connections and physical coupling, and we elaborate on combinations of designs and working mechanisms in systems reported in the literature to date. Finally, we discuss the possibility of combining multiple physical processes and associated design schemes and propose several promising future directions.

Inertial Microfluidic Purification of CAR-T-Cell Products

Chimeric antigen receptor T (CAR-T) cell therapy is rapidly becoming a frontline cancer therapy. However, the manufacturing process is time-, labor- and cost-intensive, and it suffers from significant bottlenecks. Many CAR-T products fail to reach the viability release criteria set by regulators for commercial cell therapy products. This results in non-recoupable costs for the manufacturer and is detrimental to patients who may not receive their scheduled treatment or receive out-of-specification suboptimal formulation. It is demonstrated here that inertial microfluidics can, within minutes, efficiently deplete nonviable cells from low-viability CAR-T cell products. The percentage of viable cells increases from 40% (SD ± 0.12) to 71% (SD ± 0.09) for untransduced T cells and from 51% (SD ± 0.12) to 71% (SD ± 0.09) for CAR-T cells, which meets the clinical trials' release parameters. In addition, the processing of CAR-T cells formulated in CryStor yields a 91% reduction in the amount of the cryoprotectant dimethyl sulfoxide. Inertial microfluidic processing has no detrimental effects on the proliferation and cytotoxicity of CAR-T cells. Interestingly, ≈50% of T-regulatory and T-suppressor cells are depleted, suggesting the potential for inertial microfluidic processing to tune the phenotypical composition of T-cell products.

A flow-through microfluidic chip for continuous dielectrophoretic separation of viable and non-viable human T-cells

Effective methods for rapid sorting of cells according to their viability are critical in T cells based therapies to prevent any risk to patients. In this context, we present a novel microfluidic device that continuously separates viable and non-viable T-cells according to their dielectric properties. A dielectrophoresis (DEP) force is generated by an array of castellated microelectrodes embedded into a microfluidic channel with a single inlet and two outlets; cells subjected to positive DEP forces are drawn toward the electrodes array and leave from the top outlet, those subjected to negative DEP forces are repelled away from the electrodes and leave from the bottom outlet. Computational fluid dynamics is used to predict the device separation efficacy, according to the applied alternative current (AC) frequency, at which the cells move from/to a negative/positive DEP region and the ionic strength of the suspension medium. The model is used to support the design of the operational conditions, confirming a separation efficiency, in terms of purity, of 96% under an applied AC frequency of 1.5 × 10⁶  Hz and a flow rate of 20 μl/h. This work represents the first example of effective continuous sorting of viable and non-viable human T-cells in a single-inlet microfluidic chip, paving the way for lab-on-a-chip applications at the point of need.

A critical review on the fabrication techniques that can enable higher throughput in dielectrophoresis devices

The sorting of targeted cells in a sample is a cornerstone of healthcare diagnostics and therapeutics. This work focuses on the use of dielectrophoresis for the selective sorting of targeted bioparticles in a sample and how the lack of throughput has been one important practical challenge to its widespread practical implementation. Increasing the cross-sectional area of a channel can lead to higher flow rates and thus the capability to process a larger sample volume per unit of time. However, the required electric field gradient that is generated by polarized electrodes drastically decreases as one moves away from the electrodes. Hence, the scaling up of the channel cross section must be done asymmetrically. One desires a channel aspect ratio AR = height/width that is much smaller or much larger than 1. Since reducing footprint of the DEP device is important to ensure affordability, the use of channels with AR>>1 is desired. This creates the challenge to fabricate electrodes on the sidewalls of multiple channels with AR>>1, or a channel embedding an array of electrodes with a gap in between them with AR >>1. This critical review first details the motivation for using three-dimensional (3D) DEP devices to improve throughput and then describes selected techniques that have been used to fabricate them. Techniques include electrodeposition, deep etching, thick-film photolithography, and co-fabrication. Electrode materials addressed include metals, silicon, carbon, PDMS-based composites as well as conductive polymers and fluids.

Integration of a Dielectrophoretic Tapered Aluminum Microelectrode Array with a Flow Focusing Technique

We present the integration of a flow focusing microfluidic device in a dielectrophoretic application that based on a tapered aluminum microelectrode array (TAMA). The characterization and optimization method of microfluidic geometry performs the hydrodynamic flow focusing on the channel. The sample fluids are hydrodynamically focused into the region of interest (ROI) where the dielectrophoresis force (F_DEP) is dominant. The device geometry is designed using 3D CAD software and fabricated using the micro-milling process combined with soft lithography using PDMS. The flow simulation is achieved using COMSOL Multiphysics 5.5 to study the effect of the flow rate ratio between the sample fluids (Q₁) and the sheath fluids (Q₂) toward the width of flow focusing. Five different flow rate ratios (Q₁/Q₂) are recorded in this experiment, which are 0.2, 0.4, 0.6, 0.8 and 1.0. The width of flow focusing is increased linearly with the flow rate ratio (Q₁/Q₂) for both the simulation and the experiment. At the highest flow rate ratio (Q₁/Q₂ = 1), the width of flow focusing is obtained at 638.66 µm and at the lowest flow rate ratio (Q₁/Q₂ = 0.2), the width of flow focusing is obtained at 226.03 µm. As a result, the flow focusing effect is able to reduce the dispersion of the particles in the microelectrode from 2000 µm to 226.03 µm toward the ROI. The significance of flow focusing on the separation of particles is studied using 10 and 1 µm polystyrene beads by applying a non-uniform electrical field to the TAMA at 10 V_PP, 150 kHz. Ultimately, we are able to manipulate the trajectories of two different types of particles in the channel. For further validation, the focusing of 3.2 µm polystyrene beads within the dominant F_DEP results in an enhanced manipulation efficiency from 20% to 80% in the ROI.

Methods of Generating Dielectrophoretic Force for Microfluidic Manipulation of Bioparticles

Manipulation of microscale bioparticles including living cells is of great significance to the broad bioengineering and biotechnology fields. Dielectrophoresis (DEP), which is defined as the interactions between dielectric particles and the electric field, is one of the most widely used techniques for the manipulation of bioparticles including cell separation, sorting, and trapping. Bioparticles experience a DEP force if they have a different polarization from the surrounding media in an electric field that is nonuniform in terms of the intensity and/or phase of the electric field. A comprehensive literature survey shows that the DEP-based microfluidic devices for manipulating bioparticles can be categorized according to the methods of creating the nonuniformity via patterned microchannels, electrodes, and media to generate the DEP force. These methods together with the theory of DEP force generation are described in this review, to provide a summary of the methods and materials that have been used to manipulate various bioparticles for various specific biological outcomes. Further developments of DEP-based technologies include identifying materials that better integrate with electrodes than current popular materials (silicone/glass) and improving the performance of DEP manipulation of bioparticles by combining it with other methods of handling bioparticles. Collectively, DEP-based microfluidic manipulation of bioparticles holds great potential for various biomedical applications.

Perspectives on C-MEMS and C-NEMS biotech applications

Carbon microelectromechanical system (C-MEMS) and carbon nanoelectromechanical system (C-NEMS) have been identified as promising technologies for a range of biotech applications, including electrochemical biosensors, biofuel cells, neural probes, and dielectrophoretic cell trapping. Research teams around the world have devoted more and more time to this field. After almost two decades of efforts on developing C-MEMS and C-NEMS, a review of the relevant progress and addressing future research opportunities and critical issues is in order. This review first introduces C-MEMS and C-NEMS fabrication processes that fall into two categories: photolithography- and non-photolithography- based techniques. Next, a detailed discussion of the state of the art, and technical challenges and opportunities associated with C-MEMS and C-NEMS devices used in biotech applications are presented. These devices are discussed in the relevant sub-sections of biosensors, biofuel cells, intracorporeal neural probe, dielectrophoresis cell trapping, and cell culture. The review concludes with an exposition of future perspectives in C-MEMS and C-NEMS.

Dynamically controlled dielectrophoresis using resonant tuning

Electrically polarizable micro- and nanoparticles and droplets can be trapped using the gradient electric field of electrodes. But the spatial profile of the resultant dielectrophoretic force is fixed once the electrode structure is defined. To change the force profile, entire complex lab-on-a-chip systems must be re-fabricated with modified electrode structures. To overcome this problem, we propose an approach for the dynamic control of the spatial profile of the dielectrophoretic force by interfacing the trap electrodes with a resistor and an inductor to form a resonant resistor-inductor-capacitor (RLC) circuit. Using a dielectrophoretically trapped water droplet suspended in silicone oil, we show that the resonator amplitude, detuning, and linewidth can be continuously varied by changing the supply voltage, supply frequency, and the circuit resistance to obtain the desired trap depth, range, and stiffness. We show that by proper tuning of the resonator, the trap range can be extended without increasing the supply voltage, thus preventing sensitive samples from exposure to high electric fields at the stable trapping position. Such unprecedented dynamic control of dielectrophoretic forces opens avenues for the tunable active manipulation of sensitive biological and biochemical specimen in droplet microfluidic devices used for single-cell and biochemical reaction analysis.

Latest Updates on the Advancement of Polymer-Based Biomicroelectromechanical Systems for Animal Cell Studies

Biological sciences have reached the fundamental unit of life: the cell. Ever-growing field of Biological Microelectromechanical Systems (BioMEMSs) is providing new frontiers in both fundamental cell research and various practical applications in cell-related studies. Among various functions of BioMEMS devices, some of the most fundamental processes that can be carried out in such platforms include cell sorting, cell separation, cell isolation or trapping, cell pairing, cell-cell communication, cell differentiation, cell identification, and cell culture. In this article, we review each mentioned application in great details highlighting the latest advancements in fabrication strategy, mechanism of operation, and application of these tools. Moreover, the review article covers the shortcomings of each specific application which can open windows of opportunity for improvement of these devices.

Characterization and Separation of Live and Dead Yeast Cells Using CMOS-Based DEP Microfluidics

This study aims at developing a miniaturized CMOS integrated silicon-based microfluidic system, compatible with a standard CMOS process, to enable the characterization, and separation of live and dead yeast cells (as model bio-particle organisms) in a cell mixture using the DEP technique. DEP offers excellent benefits in terms of cost, operational power, and especially easy electrode integration with the CMOS architecture, and requiring label-free sample preparation. This can increase the likeliness of using DEP in practical settings. In this work the DEP force was generated using an interdigitated electrode arrays (IDEs) placed on the bottom of a CMOS-based silicon microfluidic channel. This system was primarily used for the immobilization of yeast cells using DEP. This study validated the system for cell separation applications based on the distinct responses of live and dead cells and their surrounding media. The findings confirmed the device’s capability for efficient, rapid and selective cell separation. The viability of this CMOS embedded microfluidic for dielectrophoretic cell manipulation applications and compatibility of the dielectrophoretic structure with CMOS production line and electronics, enabling its future commercially mass production.

On the design, functions, and biomedical applications of high-throughput dielectrophoretic micro-/nanoplatforms: a review

As an efficient, rapid and label-free micro-/nanoparticle separation technique, dielectrophoresis (DEP) has attracted widespread attention in recent years, especially in the field of biomedicine, which exhibits huge potential in biomedically relevant applications such as disease diagnosis, cancer cell screening, biosensing, and others. DEP technology has been greatly developed recently from the low-flux laboratory level to high-throughput practical applications. In this review, we summarize the recent progress of DEP technology in biomedical applications, including firstly the design of various types and materials of DEP electrode and flow channel, design of input signals, and other improved designs. Then, functional tailoring of DEP systems with endowed specific functions including separation, purification, capture, enrichment and connection of biosamples, as well as the integration of multifunctions, are demonstrated. After that, representative DEP biomedical application examples in aspects of disease detection, drug synthesis and screening, biosensing and cell positioning are presented. Finally, limitations of existing DEP platforms on biomedical application are discussed, in which emphasis is given to the impact of other electrodynamic effects such as electrophoresis (EP), electroosmosis (EO) and electrothermal (ET) effects on DEP efficiency. This article aims to provide new ideas for the design of novel DEP micro-/nanoplatforms with desirable high throughput toward application in the biomedical community.

Microscale nonlinear electrokinetics for the analysis of cellular materials in clinical applications: a review

This review article presents a discussion of some of the latest advancements in the field of microscale electrokinetics for the analysis of cells and subcellular materials in clinical applications. The introduction presents an overview on the use of electric fields, i.e., electrokinetics, in microfluidics devices and discusses the potential of electrokinetic-based methods for the analysis of liquid biopsies in clinical and point-of-care applications. This is followed by four comprehensive sections that present some of the newest findings on the analysis of circulating tumor cells, blood (red blood cells, white blood cells, and platelets), stem cells, and subcellular particles (extracellular vesicles and mitochondria). The valuable contributions discussed here (with 131 references) were mainly published during the last 3 to 4 years, providing the reader with an overview of the state-of-the-art in the use of microscale electrokinetic methods in clinical analysis. Finally, the conclusions summarize the main advancements and discuss the future prospects.

Toward low-voltage dielectrophoresis-based microfluidic systems: A review

Dielectrophoretically driven microfluidic devices have demonstrated great applicability in biomedical engineering, diagnostic medicine, and biological research. One of the potential fields of application for this technology is in point-of-care (POC) devices, ideally allowing for portable, fully integrated, easy to use, low-cost diagnostic platforms. Two main approaches exist to induce dielectrophoresis (DEP) on suspended particles, that is, electrode-based DEP and insulator-based DEP, each featuring different advantages and disadvantages. However, a shared concern lies in the input voltage used to generate the electric field necessary for DEP to take place. Therefore, input voltage can determine portability of a microfluidic device. This review outlines the recent advances in reducing stimulation voltage requirements in DEP-driven microfluidics.

Single Cell Level Dielectrophoretic Responses & Dielectrophoretic Deformations of Monocytes to Quantify Population Heterogeneity

Single-cell dielectrophoretic movement and dielectrophoretic deformation of monocyte cells were interrogated applying 20 V_pp, 50 kHz to 1 MHz signal in the 3D carbon electrode array. Heterogeneity of the monocyte population is shown in terms of the crossover frequencies, translational movement, and deformation index of the cells. The results presented that crossover range for monocytes was 100 kHz - 200 kHz, the translational movement of the cells was rapidly altered when the initial positions of the cells were in the negative dielectrophoretic region. Finally, the deformation index of the monocyte population varied from 0.5 to 1.5.

Recent advances in microfluidic technologies for separation of biological cells

Cell separation has always been a key topic in academic research, especially in the fields of medicine and biology, due to its significance in diagnosis and treatment. Accurate, high-throughput and non-invasive separation of individual cells is key to driving the development of biomedicine and cellular biology. In recent years, a series of researches on the use of microfluidic technologies for cell separation have been conducted to solve bio-related problems. Hence, we present here a comprehensive review on the recent developments of microfluidic technologies for cell separation. In this review, we discuss several cell separation methods, mainly including: physical and biochemical method, their working principles as well as their practical applications. We also analyze the advantages and disadvantages of each method in detail. In addition, the current challenges and future prospects of microfluidic-based cell separation were discussed.

Quantifying Heterogeneity According to Deformation of the U937 Monocytes and U937-Differentiated Macrophages Using 3D Carbon Dielectrophoresis in Microfluidics

A variety of force fields have thus far been demonstrated to investigate electromechanical properties of cells in a microfluidic platform which, however, are mostly based on fluid shear stress and may potentially cause irreversible cell damage. This work presents dielectric movement and deformation measurements of U937 monocytes and U937-differentiated macrophages in a low conductive medium inside a 3D carbon electrode array. Here, monocytes exhibited a crossover frequency around 150 kHz and presented maximum deformation index at 400 kHz and minimum deformation index at 1 MHz frequencies at 20 V_peak-peak. Although macrophages were differentiated from monocytes, their crossover frequency was lower than 50 kHz at 10 V_peak-peak. The change of the deformation index for macrophages was more constant and lower than the monocyte cells. Both dielectric mobility and deformation spectra revealed significant differences between the dielectric responses of U937 monocytes and U937-differentiated macrophages, which share the same origin. This method can be used for label-free, specific, and sensitive single-cell characterization. Besides, damage of the cells by aggressive shear forces can, hence, be eliminated and cells can be used for downstream analysis. Our results showed that dielectric mobility and deformation have a great potential as an electromechanical biomarker to reliably characterize and distinguish differentiated cell populations from their progenitors.

Dielectrophoretic Immobilization of Yeast Cells Using CMOS Integrated Microfluidics

This paper presents a dielectrophoretic system for the immobilization and separation of live and dead cells. Dielectrophoresis (DEP) is a promising and efficient investigation technique for the development of novel lab-on-a-chip devices, which characterizes cells or particles based on their intrinsic and physical properties. Using this method, specific cells can be isolated from their medium carrier or the mixture of cell suspensions (e.g., separation of viable cells from non-viable cells). Main advantages of this method, which makes it favorable for disease (blood) analysis and diagnostic applications are, the preservation of the cell properties during measurements, label-free cell identification, and low set up cost. In this study, we validated the capability of complementary metal-oxide-semiconductor (CMOS) integrated microfluidic devices for the manipulation and characterization of live and dead yeast cells using dielectrophoretic forces. This approach successfully trapped live yeast cells and purified them from dead cells. Numerical simulations based on a two-layer model for yeast cells flowing in the channel were used to predict the trajectories of the cells with respect to their dielectric properties, varying excitation voltage, and frequency.

Facile template-free synthesis of multifunctional 3D cellular carbon from edible rice paper

Edible rice paper wrapper is found to be an interesting precursor of a porous and light-weight carbon material. During pyrolysis, material samples show significant differences in length change, displaying typical 20–25% shrinking in the in-plane directions, and strongly expanding (up to 500%) across their out-of-plane direction. This results in a template-free synthesis of a 3D network of cellular carbon material. The out-of-plane expansion also allows for fabrication of 3D shapes of cellular carbon material from the 2D precursor. The rice paper derived carbon material features a hierarchical porosity, resulting in a specific surface area ranging from 6 m² g⁻¹ to 239 m² g⁻¹ depending on the synthesis temperature. The carbon material has a density of 0.02–0.03 g cm⁻³, and a higher modulus-density ratio than reported for other cellular carbon materials. It is mechanically stiff and exhibits excellent fire-resistant properties.

Edible rice paper wrapper is found to be an interesting precursor for template-free synthesis of lightweight, stiff, and fire-resistant 3D cellular carbon material.

Characterization of the Dielectrophoretic Response of Different Candida Strains Using 3D Carbon Microelectrodes

Bloodstream infection with Candida fungal cells remains one of the most life-threatening complications among hospitalized patients around the world. Although most of the cases are still due to Candida albicans, the rising incidence of infections caused by other Candida strains that may not respond to traditional anti-fungal treatments merits the development of a method for species-specific isolation of Candida. To this end, here we present the characterization of the dielectrophoresis (DEP) response of Candida albicans, Candida tropicalis and Candida parapsilosis. We complement such characterization with a study of the Candida cells morphology. The Candida strains exhibited subtle differences in their morphology and dimensions. All the Candida strains exhibited positive DEP in the range 10-500 kHz, although the strength of the DEP response was different for each Candida strain at different frequencies. Only Candida tropicalis showed positive DEP at 750 kHz. The current results show potential for manipulation and enrichment of a specific Candida strain at specific DEP conditions towards aiding in the rapid identification of Candida strains to enable the effective and timely treatment of Candida infections.

Examination of the dielectrophoretic spectra of MCF7 breast cancer cells and leukocytes

The detection of circulating tumor cells (CTCs) in blood is crucial to assess metastatic progression and to guide therapy. Dielectrophoresis (DEP) is a powerful cell surface marker-free method that allows intrinsic dielectric properties of suspended cells to be exploited for CTC enrichment/isolation from blood. Design of a successful DEP-based CTC enrichment/isolation system requires that the DEP response of the targeted particles should accurately be known. This paper presents a DEP spectrum method to investigate the DEP spectra of cells without directly analyzing their membrane and cytoplasmic properties in contrast to the methods in literature, which employ theoretical assumptions and complex modeling. Integrating electric field simulations based on DEP theory with the experimental data enables determination of the DEP spectra of leukocyte subpopulations, polymorphonuclear and mononuclear leukocytes, and MCF7 breast cancer cells as a model of CTC due to their metastatic origin over the frequency range 100 kHz-50 MHz at 10 V_pp . In agreement with earlier findings, differential DEP responses were detected for mononuclear and polymorphonuclear leukocytes due to the richness of the cell surface features and morphologies of the different leukocyte types. The data reveal that the strength of the DEP force exerted on MCF7 cells was particularly high between 850 kHz and 20 MHz. These results illustrate that the proposed technique has the potential to provide a generic platform to identify DEP responses of different biological particles.

Automated "pick and transfer" of targeted cells using dielectrophoresis

Selective manipulation of single cells is an important step in sample preparation for biological analysis. A highly specific and automated device is desired for such an operation. An ideal device would be able to selectively pick several single cells in parallel from a heterogeneous population and transfer those to designated sites for further analysis without human intervention. The robotic manipulator developed here provides the basis for development of such a device. The device in this work is designed to selectively pick cells based on their inherent properties using dielectrophoresis (DEP) and automatically transfer and release those at a transfer site. Here we provide proof of concept of such a device and study the effect of different parameters on its operation. Successful experiments were conducted to separate Candida cells from a mixture with 10 μm latex particles and a viability assay was performed for separation of viable rat adipose stem cells (RASCs) from non-viable ones. The robotic DEP device was further used to pick and transfer single RASCs. This work also discusses the advantages and disadvantages of our current setup and illustrates the future steps required to improve the performance of this robotic DEP technology.

Nondimensional Streaming Dielectrophoresis Number for a System of Continuous Particle Separation

Cell sorting methods are required in numerous healthcare assays. Although flow cytometry and magnetically actuated sorting are widespread techniques for cell sorting, there is intense research on label-free techniques to reduce the cost and complexity of the process. Among label-free techniques, dielectrophoresis (DEP) offers the capability to separate cells not only on the basis of size but also on their membrane capacitance. This is important because it enables cell discrimination on the basis of specific traits such as viability, identity, fate, and age. StreamingDEP refers to the continuous sorting of cells thanks to the generation of streams of targeted particles by equilibrating the drag and DEP forces acting on targeted particles. In this work, we provide an analytical expression for a streamingDEP number toward enabling the a priori design of DEP devices to agglomerate targeted particles into streams. The nondimensional streamingDEP number (SDN) obtained in this analysis is applied to experiments with 1 μm polystyrene particles and Candida cells. On the basis of these experiments, three characteristic zones are mapped to different values of the SDN: (1) physical capture thanks to DEP for 0 < SDN < 0.6; (2) streaming due to DEP for 0.6 < SDN < 1; (3) elution without experiencing DEP for SDN > 1.

A review of sorting, separation and isolation of cells and microbeads for biomedical applications: microfluidic approaches

We have reviewed the microfluidic approaches for cell/particle isolation and sorting, and extensively explained the mechanism behind each method.

Microfluidic device embedding electrodes for dielectrophoretic manipulation of cells-A review

Microfluidic device embedding electrodes realizes cell manipulation with the help of dielectrophoresis. Cell manipulation is an important technology for cell sorting and cell population purification. Till now, the theory of dielectrophoresis has been greatly developed. Microfluidic devices with various arrangements of electrodes have been reported from the beginning of the single non-uniform electric field to the later multiple physical fields. This paper reviews the research status of microfluidic device embedding electrodes for cell manipulation based on dielectrophoresis. Firstly, the working principle of dielectrophoresis is explained. Next, cell manipulation approaches based on dielectrophoresis are introduced. Then, different types of electrode arrangements in the microfluidic device for cell manipulation are discussed, including planar, multilayered and microarray dot electrodes. Finally, the future development trend of the dielectrophoresis with the help of microfluidic devices is prospected. With the rapid development of microfluidic technology, in the near future, high precision, high throughput, high efficiency, multifunctional, portable, economical and practical microfluidic dielectrophoresis will be widely used in the fields of biology, medicine, agriculture and so on.

Glassy Carbon: A Promising Material for Micro- and Nanomanufacturing

When certain polymers are heat-treated beyond their degradation temperature in the absence of oxygen, they pass through a semi-solid phase, followed by the loss of heteroatoms and the formation of a solid carbon material composed of a three-dimensional graphenic network, known as glassy (or glass-like) carbon. The thermochemical decomposition of polymers, or generally of any organic material, is defined as pyrolysis. Glassy carbon is used in various large-scale industrial applications and has proven its versatility in miniaturized devices. In this article, micro and nano-scale glassy carbon devices manufactured by (i) pyrolysis of specialized pre-patterned polymers and (ii) direct machining or etching of glassy carbon, with their respective applications, are reviewed. The prospects of the use of glassy carbon in the next-generation devices based on the material's history and development, distinct features compared to other elemental carbon forms, and some large-scale processes that paved the way to the state-of-the-art, are evaluated. Selected support techniques such as the methods used for surface modification, and major characterization tools are briefly discussed. Barring historical aspects, this review mainly covers the advances in glassy carbon device research from the last five years (2013⁻2018). The goal is to provide a common platform to carbon material scientists, micro/nanomanufacturing experts, and microsystem engineers to stimulate glassy carbon device research.

Continuous removal of small nonviable suspended mammalian cells and debris from bioreactors using inertial microfluidics

Removing nonviable cells from a cell suspension is crucial in biotechnology and biomanufacturing. Label-free microfluidic cell separation devices based on dielectrophoresis, acoustophoresis, and deterministic lateral displacement are used to remove nonviable cells. However, their volumetric throughputs and test cell concentrations are generally too low to be useful in typical bioreactors in biomanufacturing. In this study, we demonstrate the efficient removal of small (<10 μm) nonviable cells from bioreactors while maintaining viable cells using inertial microfluidic cell sorting devices and characterize their performance. Despite the size overlap between viable and nonviable cell populations, the devices demonstrated 3.5-28.0% dead cell removal efficiency with 88.3-83.6% removal purity as well as 97.8-99.8% live cell retention efficiency at 4 million cells per mL with 80% viability. Cascaded and parallel configurations increased the cell concentration capacity (10 million cells per mL) and volumetric throughput (6-8 mL min-1). The system can be used for the removal of small nonviable cells from a cell suspension during continuous perfusion cell culture operations.

Label-Free Rapid Separation and Enrichment of Bone Marrow-Derived Mesenchymal Stem Cells from a Heterogeneous Cell Mixture Using a Dielectrophoresis Device

Bone marrow-derived mesenchymal stem cells (BMSCs) are an important cell resource for stem cell-based therapy, which are generally isolated and enriched by the density-gradient method based on cell size and density after collection of tissue samples. Since this method has limitations with regards to purity and repeatability, development of alternative label-free methods for BMSC separation is desired. In the present study, rapid label-free separation and enrichment of BMSCs from a heterogeneous cell mixture with bone marrow-derived promyelocytes was successfully achieved using a dielectrophoresis (DEP) device comprising saw-shaped electrodes. Upon application of an electric field, HL-60 cells as models of promyelocytes aggregated and floated between the saw-shaped electrodes, while UE7T-13 cells as models of BMSCs were effectively captured on the tips of the saw-shaped electrodes. After washing out the HL-60 cells from the device selectively, the purity of the UE7T-13 cells was increased from 33% to 83.5% within 5 min. Although further experiments and optimization are required, these results show the potential of the DEP device as a label-free rapid cell isolation system yielding high purity for rare and precious cells such as BMSCs.

An integrated microfluidic platform for size-selective single-cell trapping of monocytes from blood

Reliable separation and isolation of target single cells from bodily fluids with high purity is of great significance for an accurate and quantitative understanding of the cellular heterogeneity. Here, we describe a fully integrated single-blood-cell analysis platform capable of size-selective cell separation from a population containing a wide distribution of sizes such as diluted blood sample and highly efficient entrapment of single monocytes. The spiked single U937 cells (human monocyte cell line) are separated in sequence by two different-sized microfilters for removing large cell clumps, white blood cells, and red blood cells and then discriminated by dielectrophoretic force and isolated individually by downstream single-cell trapping arrays. When 2% hematocrit blood cells with a final ratio of 1:1000 U937 cells were introduced under the flow rate of 0.2 ml/h, 400 U937 cells were trapped sequentially and deterministically within 40 s with single-cell occupancy of up to 85%. As a proof-of-concept, we also demonstrated single monocyte isolation from diluted blood using the integrated microfluidic device. This size-selective, label-free, and live-cell enrichment microfluidic single blood-cell isolation platform for the processing of cancer and blood cells has a myriad of applications in areas such as single-cell genetic analysis, stem cell biology, point-of-care diagnostics, and cancer diagnostics.

Quantitative Investigation for the Dielectrophoretic Effect of Fluorescent Dyes at Single-Cell Resolution

Most of the microscopy-based, quantitative assays rely on fluorescent dyes. In this study, we investigated the impact of fluorescent dyes on the dielectrophoretic response of the mammalian cells. The dielectrophoretic measurements were performed to quantify whether the fluorescent dyes alter the dielectrophoretic properties of the cells at single-cell resolution. Our results present that when 10 V_pp electric field is applied, the fluorescent-labeled cells experienced the crossover frequency at 8-10 kHz, whereas the label-free cells exhibited at 16-18 kHz.