Frequency discretization in dielectrophoretic assisted cell sorting arrays to isolate neural cells

Cellular subpopulations identified using an ensemble average of multiple dielectrophoresis measurements

While the average value measurement approach can successfully analyze and predict the general behavior and biophysical properties of an isogenic cell population, it fails when significant differences among individual cells are generated in the population by intracellular changes such as the cell cycle, or different cellular responses to certain stimuli. Detecting such single-cell differences in a cell population has remained elusive. Here, we describe an easy-to-implement and generalizable platform that measures the dielectrophoretic cross-over frequency of individual cells by decreasing measurement noise with a stochastic method and computing ensemble average statistics. This platform enables multiple, real-time, label-free detection of individual cells with significant dielectric variations over time within an isogenic cell population. Using a stochastic method in combination with the platform, we distinguished cell subpopulations from a mixture of drug-untreated and -treated isogenic cells. Furthermore, we demonstrate that our platform can identify drug-treated isogenic cells with different recovery rates.

Scaling up stem cell production: harnessing the potential of microfluidic devices

Stem cells are specialised cells characterised by their unique ability to both self-renew and transform into a wide array of specialised cell types. The widespread interest in stem cells for regenerative medicine and cultivated meat has led to a significant demand for these cells in both research and practical applications. Despite the growing need for stem cell manufacturing, the industry faces significant obstacles, including high costs for equipment and maintenance, complicated operation, and low product quality and yield. Microfluidic technology presents a promising solution to the abovementioned challenges. As an innovative approach for manipulating liquids and cells within microchannels, microfluidics offers a plethora of advantages at an industrial scale. These benefits encompass low setup costs, ease of operation and multiplexing, minimal energy consumption, and the added advantage of being labour-free. This review presents a thorough examination of the prominent microfluidic technologies employed in stem cell research and explores their promising applications in the burgeoning stem cell industry. It thoroughly examines how microfluidics can enhance cell harvesting from tissue samples, facilitate mixing and cryopreservation, streamline microcarrier production, and efficiently conduct cell separation, purification, washing, and final cell formulation post-culture.

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.

Cell Surface N-Glycans Influence Electrophysiological Properties and Fate Potential of Neural Stem Cells

Understanding the cellular properties controlling neural stem and progenitor cell (NSPC) fate choice will improve their therapeutic potential. The electrophysiological measure whole-cell membrane capacitance reflects fate bias in the neural lineage but the cellular properties underlying membrane capacitance are poorly understood. We tested the hypothesis that cell surface carbohydrates contribute to NSPC membrane capacitance and fate. We found NSPCs differing in fate potential express distinct patterns of glycosylation enzymes. Screening several glycosylation pathways revealed that the one forming highly branched N-glycans differs between neurogenic and astrogenic populations of cells in vitro and in vivo. Enhancing highly branched N-glycans on NSPCs significantly increases membrane capacitance and leads to the generation of more astrocytes at the expense of neurons with no effect on cell size, viability, or proliferation. These data identify the N-glycan branching pathway as a significant regulator of membrane capacitance and fate choice in the neural lineage.

Microtechnology applied to stem cells research and development

Microfabrication and microfluidics contribute to the research of cellular functions of cells and their interaction with their environment. Previously, it has been shown that microfluidics can contribute to the isolation, selection, characterization and migration of cells. This review aims to provide stem cell researchers with a toolkit of microtechnology (mT) instruments for elucidating complex stem cells functions which are challenging to decipher with traditional assays and animal models. These microdevices are able to investigate about the differentiation and niche interaction, stem cells transcriptomics, therapeutic functions and the capture of their secreted microvesicles. In conclusion, microtechnology will allow a more realistic assessment of stem cells properties, driving and accelerating the translation of regenerative medicine approaches to the clinic.

Separation of neural stem cells by whole cell membrane capacitance using dielectrophoresis

Whole cell membrane capacitance is an electrophysiological property of the plasma membrane that serves as a biomarker for stem cell fate potential. Neural stem and progenitor cells (NSPCs) that differ in ability to form neurons or astrocytes are distinguished by membrane capacitance measured by dielectrophoresis (DEP). Differences in membrane capacitance are sufficient to enable the enrichment of neuron- or astrocyte-forming cells by DEP, showing the separation of stem cells on the basis of fate potential by membrane capacitance. NSPCs sorted by DEP need not be labeled and do not experience toxic effects from the sorting procedure. Other stem cell populations also display shifts in membrane capacitance as cells differentiate to a particular fate, clarifying the value of sorting a variety of stem cell types by capacitance. Here, we describe methods developed by our lab for separating NSPCs on the basis of capacitance using several types of DEP microfluidic devices, providing basic information on the sorting procedure as well as specific advantages and disadvantages of each device.

Particle separation by phase modulated surface acoustic waves

High efficiency isolation of cells or particles from a heterogeneous mixture is a critical processing step in lab-on-a-chip devices. Acoustic techniques offer contactless and label-free manipulation, preserve viability of biological cells, and provide versatility as the applied electrical signal can be adapted to various scenarios. Conventional acoustic separation methods use time-of-flight and achieve separation up to distances of quarter wavelength with limited separation power due to slow gradients in the force. The method proposed here allows separation by half of the wavelength and can be extended by repeating the modulation pattern and can ensure maximum force acting on the particles. In this work, we propose an optimised phase modulation scheme for particle separation in a surface acoustic wave microfluidic device. An expression for the acoustic radiation force arising from the interaction between acoustic waves in the fluid was derived. We demonstrated, for the first time, that the expression of the acoustic radiation force differs in surface acoustic wave and bulk devices, due to the presence of a geometric scaling factor. Two phase modulation schemes are investigated theoretically and experimentally. Theoretical findings were experimentally validated for different mixtures of polystyrene particles confirming that the method offers high selectivity. A Monte-Carlo simulation enabled us to assess performance in real situations, including the effects of particle size variation and non-uniform acoustic field on sorting efficiency and purity, validating the ability to separate particles with high purity and high resolution.

Compartmentalized Microfluidic Platforms: The Unrivaled Breakthrough of In Vitro Tools for Neurobiological Research

Microfluidic technology has become a valuable tool to the scientific community, allowing researchers to study fine cellular mechanisms with higher variable control compared with conventional systems. It has evolved tremendously, and its applicability and flexibility made its usage grow exponentially and transversely to several research fields. This has been particularly noticeable in neuroscience research, where microfluidic platforms made it possible to address specific questions extending from axonal guidance, synapse formation, or axonal transport to the development of 3D models of the CNS to allow pharmacological testing and drug screening. Furthermore, the continuous upgrade of microfluidic platforms has allowed a deeper study of the communication occurring between different neuronal and glial cells or between neurons and other peripheral tissues, both in physiological and pathological conditions. Importantly, the evolution of microfluidic technology has always been accompanied by the development of new computational tools addressing data acquisition, analysis, and modeling.

Concurrent shear stress and chemical stimulation of mechano-sensitive cells by discontinuous dielectrophoresis

Microfluidic platforms enable a variety of physical or chemical stimulation of single or multiple cells to be examined and monitored in real-time. To date, intracellular calcium signalling research is, however, predominantly focused on observing the response of cells to a single mode of stimulation; consequently, the sensitising/desensitising of cell responses under concurrent stimuli is not well studied. In this paper, we provide an extended Discontinuous Dielectrophoresis procedure to investigate the sensitising of chemical stimulation, over an extensive range of shear stress, up to 63 dyn/cm(2), which encompasses shear stresses experienced in the arterial and venus systems (10 to 60 dyn/cm(2)). Furthermore, the TRPV4-selective agonist GSK1016790A, a form of chemical stimulation, did not influence the ability of the cells' to remain immobilised under high levels of shear stress; thus, enabling us to investigate shear stress stimulation on agonism. Our experiments revealed that shear stress sensitises GSK1016790A-evoked intracellular calcium signalling of cells in a shear-stimulus dependent manner, as observed through a reduction in the cellular response time and an increase in the pharmacological efficacy. Consequently, suggesting that the role of TRPV4 may be underestimated in endothelial cells-which experience high levels of shear stress. This study highlights the importance of conducting studies at high levels of shear stress. Additionally, our approach will be valuable for examining the effect of high levels of shear on different cell types under different conditions, as presented here for agonist activation.

Separation and assisted patterning of hippocampal neurons from glial cells using positive dielectrophoresis

In this work, we describe the separation of embryonic mouse hippocampal neurons from glial cells using a positive dielectrophoresis (DEP) process. Here, we have implemented a cell trapping-favorable, cell suspension solution with low conductivity. It enables positive dielectrophoresis for hippocampal neurons (thereby attracting them to the electrodes), while resulting in negative dielectrophoresis for glial cells (repelling them from the electrodes). We have systematically performed a mathematical simulation and analysis to anticipate the DEP frequency at which hippocampal neurons and glial cells are separated. Simulated DEP crossover frequencies have been experimentally verified, and new, refined glial dielectric and physical properties are suggested that better reflect the experimental results obtained. DEP movements of neurons and glial cells in targeted separation media were experimentally analyzed, under the specified electric signal. Additionally, we have confirmed our modeling results by selectively trapping neurons over electrodes on a custom-made, multi-electrode array (MEA), resulting in active recruitment of neurons over the stimulation and recording sites. This technique is a valuable addition to the toolbox for creating more functional and versatile multi-electrode arrays.

Continuous-flow sorting of stem cells and differentiation products based on dielectrophoresis

This paper presents a continuous-flow microfluidic device for sorting stem cells and their differentiation progenies. The principle of the device is based on the accumulation of multiple dielectrophoresis (DEP) forces to deflect cells laterally in conjunction with the alternating on/off electric field to manipulate the cell trajectories. The microfluidic device containing a large array of oblique interdigitated electrodes was fabricated using a combination of standard and soft lithography techniques to generate a PDMS-gold electrode construct. Experimental testing with human mesenchymal stem cells (hMSC) and their differentiation progenies (osteoblasts) was carried out at different flow rates, and clear separation of the two populations was achieved. Most of the osteoblasts experiencing stronger DEP forces were deflected laterally and continuously, following zig-zag trajectories, and moved towards the desired collection outlet, whereas most of the hMSCs remained on the original trajectory due to weaker DEP forces. The experimental measurements were characterized and evaluated quantitatively, and consistent performance was demonstrated. Collection efficiency up to 92% and 67% for hMSCs and osteoblasts, respectively, along with purity up to 84% and 87% was obtained. The experimental results established the feasibility of our microfluidic DEP sorting device for continuous, label-free sorting of stem cells and their differentiation progenies.

Increasing label-free stem cell sorting capacity to reach transplantation-scale throughput

Dielectrophoresis (DEP) has proven an invaluable tool for the enrichment of populations of stem and progenitor cells owing to its ability to sort cells in a label-free manner and its biological safety. However, DEP separation devices have suffered from a low throughput preventing researchers from undertaking studies requiring large numbers of cells, such as needed for cell transplantation. We developed a microfluidic device designed for the enrichment of stem and progenitor cell populations that sorts cells at a rate of 150,000 cells/h, corresponding to an improvement in the throughput achieved with our previous device designs by over an order of magnitude. This advancement, coupled with data showing the DEP-sorted cells retain their enrichment and differentiation capacity when expanded in culture for periods of up to 2 weeks, provides sufficient throughput and cell numbers to enable a wider variety of experiments with enriched stem and progenitor cell populations. Furthermore, the sorting devices presented here provide ease of setup and operation, a simple fabrication process, and a low associated cost to use that makes them more amenable for use in common biological research laboratories. To our knowledge, this work represents the first to enrich stem cells and expand them in culture to generate transplantation-scale numbers of differentiation-competent cells using DEP.

Membrane biophysics define neuron and astrocyte progenitors in the neural lineage

Neural stem and progenitor cells (NSPCs) are heterogeneous populations of self-renewing stem cells and more committed progenitors that differentiate into neurons, astrocytes, and oligodendrocytes. Accurately identifying and characterizing the different progenitor cells in this lineage has continued to be a challenge for the field. We found previously that populations of NSPCs with more neurogenic progenitors (NPs) can be distinguished from those with more astrogenic progenitors (APs) by their inherent biophysical properties, specifically the electrophysiological property of whole cell membrane capacitance, which we characterized with dielectrophoresis (DEP). Here, we hypothesize that inherent electrophysiological properties are sufficient to define NPs and APs and test this by determining whether isolation of cells solely by these properties specifically separates NPs and APs. We found NPs and APs are enriched in distinct fractions after separation by electrophysiological properties using DEP. A single round of DEP isolation provided greater NP enrichment than sorting with PSA-NCAM, which is considered an NP marker. Additionally, cell surface N-linked glycosylation was found to significantly affect cell fate-specific electrophysiological properties, providing a molecular basis for the cell membrane characteristics. Inherent plasma membrane biophysical properties are thus sufficient to define progenitor cells of differing fate potential in the neural lineage, can be used to specifically isolate these cells, and are linked to patterns of glycosylation on the cell surface.

Automated long-term monitoring of parallel microfluidic operations applying a machine vision-assisted positioning method

As microfluidics has been applied extensively in many cell and biochemical applications, monitoring the related processes is an important requirement. In this work, we design and fabricate a high-throughput microfluidic device which contains 32 microchambers to perform automated parallel microfluidic operations and monitoring on an automated stage of a microscope. Images are captured at multiple spots on the device during the operations for monitoring samples in microchambers in parallel; yet the device positions may vary at different time points throughout operations as the device moves back and forth on a motorized microscopic stage. Here, we report an image-based positioning strategy to realign the chamber position before every recording of microscopic image. We fabricate alignment marks at defined locations next to the chambers in the microfluidic device as reference positions. We also develop image processing algorithms to recognize the chamber positions in real-time, followed by realigning the chambers to their preset positions in the captured images. We perform experiments to validate and characterize the device functionality and the automated realignment operation. Together, this microfluidic realignment strategy can be a platform technology to achieve precise positioning of multiple chambers for general microfluidic applications requiring long-term parallel monitoring of cell and biochemical activities.

Electrokinetic confinement of axonal growth for dynamically configurable neural networks

Axons in the developing nervous system are directed via guidance cues, whose expression varies both spatially and temporally, to create functional neural circuits. Existing methods to create patterns of neural connectivity in vitro use only static geometries, and are unable to dynamically alter the guidance cues imparted on the cells. We introduce the use of AC electrokinetics to dynamically control axonal growth in cultured rat hippocampal neurons. We find that the application of modest voltages at frequencies on the order of 10(5) Hz can cause developing axons to be stopped adjacent to the electrodes while axons away from the electric fields exhibit uninhibited growth. By switching electrodes on or off, we can reversibly inhibit or permit axon passage across the electrodes. Our models suggest that dielectrophoresis is the causative AC electrokinetic effect. We make use of our dynamic control over axon elongation to create an axon-diode via an axon-lock system that consists of a pair of electrode 'gates' that either permit or prevent axons from passing through. Finally, we developed a neural circuit consisting of three populations of neurons, separated by three axon-locks to demonstrate the assembly of a functional, engineered neural network. Action potential recordings demonstrate that the AC electrokinetic effect does not harm axons, and Ca(2+) imaging demonstrated the unidirectional nature of the synaptic connections. AC electrokinetic confinement of axonal growth has potential for creating configurable, directional neural networks.

Advancing practical usage of microtechnology: a study of the functional consequences of dielectrophoresis on neural stem cells

The integration of microscale engineering, microfluidics, and AC electrokinetics such as dielectrophoresis has generated novel microsystems that enable quantitative analysis of cellular phenotype, function, and physiology. These systems are increasingly being used to assess diverse cell types, such as stem cells, so it becomes critical to thoroughly evaluate whether the systems themselves impact cell function. For example, engineered microsystems have been utilized to investigate neural stem/progenitor cells (NSPCs), which are of interest due to their potential to treat CNS disease and injury. Analysis by dielectrophoresis (DEP) microsystems determined that unlabeled NSPCs with distinct fate potential have previously unrecognized distinguishing electrophysiological characteristics, suggesting that NSPCs could be isolated by DEP microsystems without the use of cell type specific labels. To gauge the potential impact of DEP sorting on NSPCs, we investigated whether electric field exposure of varying times affected survival, proliferation, or fate potential of NSPCs in suspension. We found short-term DEP exposure (1 min or less) had no effect on NSPC survival, proliferation, or fate potential revealed by differentiation. Moreover, NSPC proliferation (measured by DNA synthesis and cell cycle kinetics) and fate potential were not altered by any length of DEP exposure (up to 30 min). However, lengthy exposure (>5 min) to frequencies near the crossover frequency (50-100 kHz) led to decreased survival of NSPCs (maximum ∼30% cell loss after 30 min). Based on experimental observations and mathematical simulations of cells in suspension, we find that frequencies near the crossover frequency generate an induced transmembrane potential that results in cell swelling and rupture. This is in contrast to the case for adherent cells since negative DEP frequencies lower than the crossover frequency generate the highest induced transmembrane potential and damage for these cells. We clarify contrasting effects of DEP on adherent and suspended cells, which are related to the cell position within the electric field and the strength of the electric field at specific distances from the electrodes. Modeling of electrode configurations predicts optimal designs to induce cell movement by DEP while limiting the induced transmembrane potential. We find DEP electric fields are not harmful to stem cells in suspension at short exposure times, thus providing a basis for developing DEP-based applications for stem cells.

Efficient dielectrophoretic cell enrichment using a dielectrophoresis-well based system

Whilst laboratory-on-chip cell separation systems using dielectrophoresis are increasingly reported in the literature, many systems are afflicted by factors which impede "real world" performance, chief among these being cell loss (in dead spaces, attached to glass and tubing surfaces, or sedimentation from flow), and designs with large channel height-to-width ratios (large channel widths, small channel heights) that make the systems difficult to interface with other microfluidic systems. In this paper, we present a scalable structure based on 3D wells with approximately unity height-to-width ratios (based on tubes with electrodes on the sides), which is capable of enriching yeast cell populations whilst ensuring that up to 94.3% of cells processed through the device can be collected in tubes beyond the output.

Investigation of hypoxia-induced myocardial injury dynamics in a tissue interface mimicking microfluidic device

Myocardial infarction is a major cause of morbidity and mortality worldwide. However, the methodological development of a spatiotemporally controllable investigation of the damage events in myocardial infarction remains challengeable. In the present study, we describe a micropillar array-aided tissue interface mimicking microfluidic device for the dynamic study of hypoxia-induced myocardial injury in a microenvironment-controllable manner. The mass distribution in the device was visually characterized, calculated, and systematically evaluated using the micropillar-assisted biomimetic interface, physiologically relevant flows, and multitype transportation. The fluidic microenvironment in the specifically functional chamber for cell positioning and analysis was successfully constructed with high fluidic relevance to the myocardial tissue. We also performed a microenvironment-controlled microfluidic cultivation of myocardial cells with high viability and regular structure integration. Using the well-established culture device with a tissue-mimicking microenvironment, a further on-chip investigation of hypoxia-induced myocardial injury was carried out and the varying apoptotic responses of myocardial cells were temporally monitored and measured. The results show that the hypoxia directionally resulted in observable cell shrinkage, disintegration of the cytoskeleton, loss of mitochondrial membrane potential, and obvious activation of caspase-3, which indicates its significant apoptosis effect on myocardial cells. We believe this microfluidic device can be suitable for temporal investigations of cell activities and responses in myocardial infarction. It is also potentially valuable to the microcontrol development of tissue-simulated studies of multiple clinical organ/tissue disease dynamics.