Recreating the hematon: microfabrication of artificial haematopoietic stem cell microniches in vitro using dielectrophoresis

The Role of Dielectrophoresis for Cancer Diagnosis and Prognosis

Liquid biopsy is emerging as a potential diagnostic tool for prostate cancer (PC) prognosis and diagnosis. Unfortunately, most circulating tumor cells (CTC) technologies, such as AdnaTest or Cellsearch®, critically rely on the epithelial cell adhesion molecule (EpCAM) marker, limiting the possibility of detecting cancer stem-like cells (CSCs) and mesenchymal-like cells (EMT-CTCs) that are present during PC progression. In this context, dielectrophoresis (DEP) is an epCAM independent, label-free enrichment system that separates rare cells simply on the basis of their specific electrical properties. As compared to other technologies, DEP may represent a superior technique in terms of running costs, cell yield and specificity. However, because of its higher complexity, it still requires further technical as well as clinical development. DEP can be improved by the use of microfluid, nanostructured materials and fluoro-imaging to increase its potential applications. In the context of cancer, the usefulness of DEP lies in its capacity to detect CTCs in the bloodstream in their epithelial, mesenchymal, or epithelial-mesenchymal phenotype forms, which should be taken into account when choosing CTC enrichment and analysis methods for PC prognosis and diagnosis.

Multi-particle interaction in AC electric field driven by dielectrophoresis force

When the dielectrophoresis technology is used to manipulate micron-sized particles, the interaction between particles should not be ignored because of the particle-particle interaction. Especially, when multiple particles (number of particles is above 2) are simultaneously manipulated, the interaction between neighboring particles will affect the results of the manipulation. This research investigates the interaction of particles caused dielectrophoresis effect by the Arbitrary Lagrangian-Eulerian (ALE) method based on the hypothesis of the thin layer of the electric double layer at the microscale. The mathematics model can be solved simultaneously by the finite element method for the AC electric field, the flow field around the suspended particles and the particle mechanics at the micrometer scale. In this study, the particle conductivity and the direction of the electric field are investigated, we find that particle conductivity and electric field direction pose an impact on particle movement, and the research reveal the law of microparticle dielectrophoresis movement, which could offer theoretical and technology support to profoundly understand the precise manipulation of particles in microfluidic chips by the dielectrophoresis effect.

Dielectrophoresis as a tool for electrophysiological characterization of stem cells

Dielectrophoresis (DEP), a nonlinear electrokinetic technique caused by Maxwell-Wagner interfacial polarization of neutral particles in an electrolyte solution, is a powerful cell manipulation method used widely for various applications such as enrichment, trapping, and sorting of heterogeneous cell populations. While conventional cell characterization and sorting methods require tagging or labeling of cells, DEP has the potential to manipulate cells in a label-free way. Due to its unique ability to characterize and sort cells without the need of labeling, there is renewed interest in using DEP for stem cell research and regenerative medicine. Stem cells have the potential to differentiate into various lineages, but achieving homogeneous cell phenotypes from an initially heterogeneous cell population is a challenge. Using DEP to efficiently and affordably identify, sort, and enrich either undifferentiated or differentiated stem cell populations in a label-free way would advance their potential uses for applications in tissue engineering and regenerative medicine. This review summarizes recent, significant research findings regarding the electrophysiological characterization of stem cells, with a focus on cellular dielectric properties, i.e., permittivity and conductivity, and on studies that have obtained these measurements using techniques that preserve cell viability, such as crossover frequency. Potential applications for DEP in regenerative medicine are also discussed. Overall, DEP is a promising technique and, when used to characterize, sort, and enrich stem cells, will advance stem cell-based regenerative therapies.

Droplet Microfluidics for the ex Vivo Expansion of Human Primary Multiple Myeloma Cells

We previously reported a new approach for micromanipulation and encapsulation of human stem cells using a droplet-based microfluidic device We demonstrated the possibility of encapsulating and culturing difficult-to-preserve primary human hematopoietic stem cells using an engineered double layered bead composed by an inner layer of alginate and an outer layer of puramatrix constructed using a soft technology without the use of any external force. In this work, we use this micro manipulation technique to build a 3D scaffold as a biomimetic model to recapitulate the niche of patient-derived multiple myeloma cells (MM cell) using a multilayered 3D tissue scaffold constructed in a microfluidic device and cultured in 10% FBS culture medium. In the current study, we included the use of this biomimetic model comprising supporting human Mesenchymal stem cells to show the mid-term survival of MM cells in the proposed structures. We found that the generated microniches were suitable for the maintenance of MM cells with and without supporting cells. Additionally, cultured MM cells in droplets were exposed to both Bortezomib and Lenalidomide to test their toxicity in the cultured patient derived cells. Results indicate that the maintained MM cells were consistently responding to the applied medication, opening a wide field of possibilities to use the presented micro device as an ex vivo platform for drug screening.

Bone marrow hematons: An access point to the human hematopoietic niche

To understand the complex interactions between hematopoietic stem cells and the bone marrow niche, a human experimental model is needed. Our hypothesis is that hematons are an appropriate ex vivo model of human bone marrow. We analyzed the hierarchical hematopoietic cell content and the tissue organization of single hematons from healthy donors. Most (>90%) hematons contained precursors of all cell lineages, myeloid progenitors, and LTC-ICs without preferential commitment. Approximately, half of the hematons could generate significant levels of lympho-myeloid hematopoiesis after transplantation in an NSG mouse model, despite the low absolute numbers of transplanted CD34⁺ cells. Mesenchymal STRO-1⁺ and/or CD271⁺ cells formed a critical network that preserved hematon cohesion, and STRO-1⁺ cells colocalized with most hematopoietic CD34⁺ cells (68%). We observed an influence of age and gender. These structures represent a particularly attractive model for studying the homeostasis of the bone marrow niche and pathological changes that occur during diseases.

Dielectrophoresis for bioparticle manipulation

As an ideal method to manipulate biological particles, the dielectrophoresis (DEP) technique has been widely used in clinical diagnosis, disease treatment, drug development, immunoassays, cell sorting, etc. This review summarizes the research in the field of bioparticle manipulation based on DEP techniques. Firstly, the basic principle of DEP and its classical theories are introduced in brief; Secondly, a detailed introduction on the DEP technique used for bioparticle manipulation is presented, in which the applications are classified into five fields: capturing bioparticles to specific regions, focusing bioparticles in the sample, characterizing biomolecular interaction and detecting microorganism, pairing cells for electrofusion and separating different kinds of bioparticles; Thirdly, the effect of DEP on bioparticle viability is analyzed; Finally, the DEP techniques are summarized and future trends in bioparticle manipulation are suggested.

Dynamic microparticle manipulation with an electroosmotic flow gradient in low-frequency alternating current dielectrophoresis

In this study, the potential of low-frequency AC insulator-based DEP (iDEP) was explored for the separation of polystyrene microparticles and yeast cells. An EOF gradient was generated by employing an asymmetrical, 20 Hz AC electrical signal in an iDEP device consisting of a microchannel with diamond-shaped insulating posts. Two types of samples were analyzed, the first sample contained three types of polystyrene particles with different diameters (0.5, 1.0, and 2.0 μm) and the second sample contained two types of polystyrene particles (1.0 and 2 μm) and yeast cells (6.3 μm). This particular scheme uses a tapered AC signal that allows for all particles to be trapped and concentrated at the insulating post array, as the signal becomes asymmetrical (more positive), particles are selectively released. The smallest particles in each sample were released first, since they require greater dielectrophoretic forces to remain trapped. The largest particles in each sample were released last, when the applied signal became cyclical. A dielectropherogram, which is analogous to a chromatogram, was obtained for each sample, demonstrating successful separation of the particles by showing "peaks" of the released particles. These separations were achieved at lower applied potentials than those reported in previous studies that used solely direct current electrical voltages. Additionally, mathematical modeling with COMSOL Multiphysics was carried out to estimate the magnitude of the dielectrophoretic and EOF forces acting on the particles considering the low-frequency, asymmetrical AC signal used in the experiments. The results demonstrated the potential of low-frequency AC-iDEP systems for handling and separating complex mixtures of microparticles and biological cells.

Modeling and simulation of dielectrophoretic particle-particle interactions and assembly

Electric field induced particle-particle interactions and assembly are of great interest due to their useful applications in micro devices. The behavior of particles becomes more complex if multiple particles interact with each other at the same time. In this paper, we present a numerical study of two dimensional DC dielectrophoresis based particle-particle interactions and assembly for multiple particles using a hybrid immersed interface-immersed boundary method. The immersed interface method is employed to capture the physics of electrostatics in a fluid media with suspended particles. Particle interaction based dielectrophoretic forces are obtained using Maxwell's stress tensor without any boundary or volume integration. This electrostatic force distribution mimics the actual physics of the immersed particles in a fluid media. The corresponding particle response and hydrodynamic interactions are captured through the immersed boundary method by solving the transient Navier-Stokes equations. The interaction and assembly of multiple electrically similar and dissimilar particles are studied for various initial positions and orientations. Numerical results show that in a fluid media, similar particles form a chain parallel to the applied electric field, whereas dissimilar particles form a chain perpendicular to the applied electric field. Irrespective of initial position and orientation, particles first align themselves parallel or perpendicular to the electric field depending on the similarity or dissimilarity of particles. The acceleration and deceleration of particles are also observed and analyzed at different phases of the assembly process. This comprehensive study can be used to explain the multiple particle interaction and assembly phenomena observed in experiments.

Gelatin methacrylate as a promising hydrogel for 3D microscale organization and proliferation of dielectrophoretically patterned cells

Establishing the 3D microscale organization of cells has numerous practical applications, such as in determining cell fate (e.g., proliferation, migration, differentiation, and apoptosis) and in making functional tissue constructs. One approach to spatially pattern cells is by dielectrophoresis (DEP). DEP has characteristics that are important for cell manipulation, such as high accuracy, speed, scalability, and the ability to handle both adherent and non-adherent cells. However, widespread application of this method is largely restricted because there is a limited number of suitable hydrogels for cell encapsulation. To date, polyethylene glycol-diacrylate (PEG-DA) and agarose have been used extensively for dielectric patterning of cells. In this study, we propose gelatin methacrylate (GelMA) as a promising hydrogel for use in cell dielectropatterning because of its biocompatibility and low viscosity. Compared to PEG hydrogels, GelMA hydrogels showed superior performance when making cell patterns for myoblast (C2C12) and endothelial (HUVEC) cells as well as in maintaining cell viability and growth. We also developed a simple and robust protocol for co-culture of these cells. Combined application of the GelMA hydrogels and the DEP technique is suitable for creating highly complex microscale tissues with important applications in fundamental cell biology and regenerative medicine in a rapid, accurate, and scalable manner.

Formation of embryoid bodies using dielectrophoresis

Embryoid body (EB) formation forms an important step in embryonic stem cell differentiation invivo. In murine embryonic stem cell (mESC) cultures EB formation is inhibited by the inclusion of leukaemic inhibitory factor (LIF) in the medium. Assembly of mESCs into aggregates by positive dielectrophoresis (DEP) in high field regions between interdigitated oppositely castellated electrodes was found to initiate EB formation. Embryoid body formation in aggregates formed with DEP occurred at a more rapid rate-in fact faster compared to conventional methods-in medium without LIF. However, EB formation also occurred in medium in which LIF was present when the cells were aggregated with DEP. The optimum characteristic size for the electrodes for EB formation with DEP was found to be 75-100 microns; aggregates smaller than this tended to merge, whilst aggregates larger than this tended to split to form multiple EBs. Experiments with ESCs in which green fluorescent protein (GFP) production was targeted to the mesodermal gene brachyury indicated that differentiation within embryoid bodies of this size may preferentially occur along the mesoderm lineage. As hematopoietic lineages during normal development derive from mesoderm, the finding points to a possible application of DEP formed EBs in the production of blood-based products from ESCs.

Cellular dielectrophoresis: applications to the characterization, manipulation, separation and patterning of cells

Over the past decade, dielectrophoresis (DEP) has evolved into a powerful, robust and flexible method for cellular characterization, manipulation, separation and cell patterning. It is a field with widely varying disciplines, as it is quite common to see DEP integrated with a host of applications including microfluidics, impedance spectroscopy, tissue engineering, real-time PCR, immunoassays, stem-cell characterization, gene transfection and electroporation, just to name a few. The field is finally at the point where analytical and numerical polarization models can be used to adequately describe and characterize the dielectrophoretic behavior of cells, and there is ever increasing evidence demonstrating that electric fields can safely be used to manipulate cells without harm. As such, DEP is slowly making its way into the biological sciences. Today, DEP is being used to manipulate individual cells to specific regions of space for single-cell assays. DEP is able to separate rare cells from a heterogeneous cell suspension, where isolated cells can then be characterized and dynamically studied using nothing more than electric fields. However, there is need for a critical report to integrate the many new features of DEP for cellular applications. Here, a review of the basic theory and current applications of DEP, specifically for cells, is presented.

Lab-on-a-chip devices as an emerging platform for stem cell biology

The advent of stem cell based therapies has brought regenerative medicine into an increased focus as a part of the modern medicine practice, with a potential to treat a myriad of intractable diseases in the future. Stem cells reside in a complex microenvironment presenting them with a multitude of potential cues that are chemical, physical, and mechanical in nature. Conventional techniques used for experiments involving stem cells can only poorly mimic the physiological context, and suffer from imprecise spatial and temporal control, low throughput, lack of scalability and reproducibility, and poor representation of the mechanical and physical cell microenvironment. Novel lab-on-a-chip platforms, on the other hand, can much better mimic the complexity of in vivo tissue milieu and provide a greater control of the parameter variation in a high throughput and scalable manner. This capability may be especially important for understanding the biology and cementing the clinical potential of stem cell based therapies. Here we review microfabrication- and microfluidics-based approaches to investigating the complex biology of stem cell responses to changes in the local microenvironment. In particular, we categorize each method based on the types of controlled inputs it can have on stem cells, including soluble biochemical factors, extracellular matrix interactions, homotypic and heterotypic cell-cell signaling, physical cues (e.g. oxygen tension, pH, temperature), and mechanical forces (e.g. shear, topography, rigidity). Finally, we outline the methods to perform large scale observations of stem cell phenotypes and high-throughput screening of cellular responses to a combination of stimuli, and many new emerging technologies that are becoming available specifically for stem cell applications.

Creation of arrays of cell aggregates in defined patterns for developmental biology studies using dielectrophoresis

It is shown that dielectrophoresis--the movement of particles in non-uniform electric fields--can be used to create engineered skin with artificial placodes of different sizes and shapes, in different spatial patterns. Modeling of the electric field distribution and image analysis of the cell aggregates produced showed that the aggregation is highly predictable. The cells in the aggregates remain viable, and reorganization and compaction of the cells in the aggregates occurs when the artificial skin is subsequently cultured. The system developed could be of considerable use for the in vitro study of developmental processes where local variations in cell density and direct cell-cell contacts are important.