Effect of the shape of human erythrocytes on the evaluation of the passive electrical properties of the cell membrane

Improved Hematology Analysis Based on Microfluidic Impedance Spectroscopy: Erythrocyte Orientation and Anisotropic Dielectric Properties of Flowing Blood

Electrochemical impedance spectroscopy has great potential for laboratory blood tests. The overall aim of this study is to develop a microfluidic sensor for determining the physical properties and hematological parameters of blood based on its dielectric spectra. Impedance was measured in flowing blood to prevent aggregation and sedimentation at frequencies between 40 Hz and 110 MHz. Two major factors make accurate analysis of impedance spectra difficult: forced orientation of erythrocytes in a microchannel and hemoglobin hydration. A theoretical approach based on the effective medium theory was applied to find the preferred erythrocyte orientation and dielectric properties of blood components. The cytoplasm of erythrocytes was considered a colloidal suspension of hemoglobin molecules surrounded by a double hydration shell. The proposed preferred orientation factor demonstrates that approximately 66% of the erythrocytes in the microfluidic channel have a random distribution and approximately 34% of them occupy random positions and are oriented along the blood flow. The experiments did not reveal any significant changes in the preferred orientation factor when the blood flow rate changed from 2 to 20 mL/h. Finally, several hematological parameters of blood samples were determined (erythrocyte count, hemoglobin level, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration). A comparison of routine hematological studies and the developed technique proves its effectiveness.

Electro-deformation spectroscopy: A unified method for simultaneous electrical and mechanical characterization of single cells

The intrinsic electrical and mechanical properties of cells are not only valuable biophysical markers reflective of physiological conditions but also play important roles in the development and progression of human diseases. Existing single-cell techniques are restricted to assessing either mechanical or electrical properties. We introduce the development of electro-deformation spectroscopy (EDS), namely the frequency-dependent electro-deformation, as a new method for simultaneous electrical and mechanical characterization of individual cells in suspension. To facilitate the practical use of this technology, we developed a testing procedure that evaluates red blood cells (RBCs) directly from whole blood in a simple microfluidic system, employing an electric field magnitude of 34 kV/m over a frequency range of 15 MHz to 100 kHz. The EDS measurement is performed under stationary conditions without special cell stabilization, at a moderate throughput of 50-100 cells per minute. We develop an experimental-computational framework to decouple cell electromechanics by optimizing the most suitable parameters of the relative permittivity of cell membrane, cytoplasm electrical conductivity, and membrane shear modulus. This technique, tested on RBCs from 4 healthy human samples, revealed membrane relative permittivity of 3.6 - 5.8, membrane shear modulus of 2.2 - 2.8 µN/m, and cytoplasm conductivity of 0.47 - 0.81 S/m. EDS analysis identifies the marked intrasample heterogeneity and individual variability in both cellular electrical and mechanical properties. The EDS framework can be readily used to test RBCs across different species, pathological states, and other cell types of similar structures as RBCs. STATEMENT OF SIGNIFICANCE: This work introduces electro-deformation spectroscopy (EDS) as a unified method for simultaneous electrical and mechanical characterization of single cells in suspension. This is the first-of-its-kind technology for such purposes. EDS can be performed in a simple microfluidic system with minimal sample preparation, making it a convenient and powerful tool for label-free, non-invasive single-cell analysis. We validate the applicability of EDS by measuring the intrasample heterogeneity and individual variability based on the electromechanical parameters of interest for human red blood cells. Single-cell EDS has the potential to enable rapid and reliable detection of cellular changes by diseases or drug treatments and provide insights into the fundamental bioelectromechanical mechanisms of cellular adaptation and dysfunction. This work advances the field of single-cell analysis and contributes to the development of biomaterials and biotechnologies based on cellular electromechanics.

Dielectric spectroscopy of red blood cells in sickle cell disease

Hypoxia-induced polymerization of sickle hemoglobin and the related ion diffusion across cell membrane can lead to changes in cell dielectric properties, which can potentially serve as label-free, diagnostic biomarkers for sickle cell disease. This article presents a microfluidic-based approach with on-chip gas control for the impedance spectroscopy of suspended cells within the frequency range of 40 Hz to 110 MHz. A comprehensive bioimpedance of sickle cells under both normoxia and hypoxia is achieved rapidly (within ∼7 min) and is appropriated by small sample volumes (∼2.5 μL). Analysis of the sensing modeling is performed to obtain optimum conditions for dielectric spectroscopy of sickle cell suspensions and for extraction of single cell properties from the measured impedance spectra. The results of sickle cells show that upon hypoxia treatment, cell interior permittivity and conductivity increase, while cell membrane capacitance decreases. Moreover, the relative changes in cell dielectric parameters are found to be dependent on the sickle and fetal hemoglobin levels. In contrast, the changes in normal red blood cells between the hypoxia and normoxia states are unnoticeable. The results of sickle cells may serve as a reference to design dielectrophoresis-based cell sorting and electrodeformation testing devices that require cell dielectric characteristics as input parameters. The demonstrated method for dielectric characterization of single cells from the impedance spectroscopy of cell suspensions can be potentially applied to other cell types and under varied gas conditions.

Electrochemical Impedance Characterization of Blood Cell Suspensions. Part 1: Basic Theory and Application to Two-Phase Systems

Electrochemical impedance spectra of composite materials contain information on the topological arrangement, volume fraction, and shape of particles, as well as the dielectric properties of the matrix and particles. The objective of this study is to investigate how these parameters affect the dielectric spectrum and what reliable information can be extracted from experimental data. The main attention was focused on systems with dielectric behavior similar to that of human blood. Mostly plasma and erythrocytes determine the dielectric properties of whole blood. Erythrocytes suspended in plasma can be considered as three-phase systems with single-shelled particles. A theoretical approach based on the effective medium theory is developed for calculating the effective permittivity and conductivity of three-phase composites at a wide frequency range (from 0 to 1 GHz). A finite-difference method is applied to model three-dimensional periodic structures. A special case of two-phase materials is used to demonstrate the influence of the shape and arrangement of particles on dielectric properties. Theoretical and numerical approaches are applied to two-phase composites with spherical, spheroidal and biconcave particles and are compared with each other and with published data. It is shown that two-phase composites exhibit only β-dispersion. In contrast to the quasi-static limit, the wide-bandwidth impedance spectroscopy makes it possible to distinguish between disordered and regular arrangements of spheroidal and biconcave particles. The results can be used to analyze the dielectric properties of blood, which is very promising for various medical applications. This study of two-phase composites can be further extended to three-phase composites.

Quick, Single-Frequency Dielectric Characterization of Blood Samples of Pediatric Cancer Patients by a Cylindrical Capacitor: Pilot Study

In this paper, as an application in biometrics, the electrical capacitance of normal and cancerous blood samples is experimentally determined in order to test the null hypothesis that the electrical capacitance of the two samples differs. The samples taken from healthy donors and patients diagnosed with different types of hematologic cancer are examined by a cylindrical capacitor with blood as its dielectric. The capacitance of these samples is measured at room temperature and a single frequency of 120 Hz, well below the frequency where β -dispersion starts, using a simple LCR meter device. The measurements indicate that the capacitance of the blood increases under applied electric field for a short period of time and asymptotically reaches its steady-state value. The measured values for the healthy group agreed with previous data in the literature. By the use of the unpaired two-tailed T-test, it is found that cancerous blood has higher values of capacitance when compared to normal samples ( p < 0.05 ). The reasons that might lead to such alterations are discussed from a biological perspective. Moreover, based on correlation calculations, a strong negative association is observed between blood capacitance and red blood cell (RBC) count in each group. Furthermore, sensitivity (SE) and specificity (SP) analysis demonstrates that for a threshold value between 15 and 17 for the capacitance value, both SE and SP are 100%. These preliminary findings on capacitance values may pave the way for the development of inexpensive and easy-to-use diagnosis tools for hematologic cancers at medical facilities and for in-home use, especially for children.

Dielectric characterization of hepatocytes in suspension and embedded into two different polymeric scaffolds

The dielectric and conductometric properties of hepatocytes in two different environments (in aqueous suspension and embedded into polymeric scaffolds) have been investigated in the frequency range from 1 kHz to 2 GHz, where the interfacial electrical polarization gives rise to marked dielectric relaxation effects. We analyzed the dielectric behavior of hepatocytes in complete medium aqueous suspensions in the light of effective medium approximation for heterogeneous systems and hepatocytes cultured into two different highly porous and interconnected polymeric structures. In the former case, we have evaluated the passive electrical parameters associated with both the plasmatic and nuclear membrane, finding a general agreement with the values reported elsewhere, based on a partially different analysis of the experimental spectra. In the latter case, we have evaluated the cell growth into two different polymeric scaffolds made of alginate and gelatin with a similar pore distribution and similar inter-connectivity. Based on a qualitative analysis of the dielectric spectra, we were able to provide evidence that alginate scaffolds allow an overall survival of cells better than gelatin scaffold can do. These indications, confirmed by biological tests on cell viability, suggest that hepatocytes embedded in alginate scaffolds are able to perform liver specific functions even over on extended period of time.

Dipole relaxation in erythrocyte membrane: involvement of spectrin skeleton

Polarization of spectrin-actin undermembrane skeleton of red blood cell (RBC) plasma membranes was studied by impedance spectroscopy. Relatedly, dielectric spectra of suspensions that contained RBCs of humans, mammals (bovine, horse, dog, cat) and birds (turkey, pigeon, duck), and human RBC ghost membranes were continuously obtained during heating from 20 to 70°C. Data for the complex admittance and capacitance were used to derive the suspension resistance, R, and capacitance, C, as well as the energy loss as a function of temperature. As in previous studies, two irreversible temperature-induced transitions in the human RBC plasma membrane were detected at 49.5°C and at 60.7°C (at low heating rate). The transition at 49.5°C was evident from the abrupt changes in R, and C and the fall in the energy loss, due to dipole relaxation. For the erythrocytes of indicated species the changes in R and C displayed remarkable and similar frequency profiles within the 0.05-13MHz domain. These changes were subdued after cross-linking of membranes by diamide (0.3-1.3mM) and glutaraldehyde (0.1-0.4%) and at the presence of glycerol (10%). Based on the above results and previous reports, the dielectric changes at 49.5°C were related to dipole relaxation and segmental mobility of spectrin cytoskeleton. The results open the possibility for selective dielectric thermolysis of cell cytoskeleton.

Dielectric properties of microvillous cells simulated by the three-dimensional finite-element method

Most of biological cells have microvilli on their surfaces, which significantly influence their dielectric properties. The complex permittivity of a cubical system containing a spherical cell model with cylindrical projections was calculated over a frequency range of 10 kHz to 100 MHz using the three-dimensional finite-element method. The spectra of the complex permittivity consisted of low- and high-frequency relaxation processes which were respectively attributed to the polarization of the membranes covering the projections and the spherical body. Conventional analysis based on the spherical shell model was applied to the simulated spectra to discuss the effects of cell surface morphology on the electric parameters estimated for the plasma membrane and the cytoplasm.

The dielectric behavior of nonspherical biological cell suspensions: an analytic approach

The influence of the cell shape on the dielectric and conductometric properties of biological cell suspensions has been investigated from a theoretical point of view presenting an analytical solution of the electrostatic problem in the case of prolate and oblate spheroidal geometries. The model, which extends to spheroidal geometries the approach developed by other researchers in the case of a spherical geometry, takes explicitly into account the charge distributions at the cell membrane interfaces. The presence of these charge distributions, which govern the trans-membrane potential DeltaV, produces composite dielectric spectra with two contiguous relaxation processes, known as the alpha-dispersion and the beta-dispersion. By using this approach, we present a series of dielectric spectra for different values of the different electrical parameters (the permittivity epsilon and the electrical conductivity sigma, together with the surface conductivity gamma due to the surface charge distribution) that define the whole behavior of the system. In particular, we analyze the interplay between the parameters governing the alpha-dispersion and those influencing the beta-dispersion. Even if these relaxation processes generally occur in well-separated frequency ranges, it is worth noting that, for certain values of the membrane conductivity, the high-frequency dispersion attributed to the Maxwell-Wagner effect is influenced not only by the bulk electrical parameters of the different adjacent media, but also by the surface conductivity at the two membrane interfaces.

Dielectric screening of early differentiation patterns in mesenchymal stem cells induced by steroid hormones

In the framework of this study, target identification and localization of differentiation patterns by means of dielectric spectroscopy is presented. Here, a primary pre-osteoblastic bone marrow-derived MBA-15 cellular system was used to study the variations in the dielectric properties of mesenchymal stem cells while exposed to differentiation regulators. Using the fundamentals of mixed dielectric theories combined with finite numerical tools, the permittivity spectra of MBA-15 cell suspensions have been uniquely analyzed after being activated by steroid hormones to express osteogenic phenotypes. Following the spectral analysis, significant variations were revealed in the dielectric properties of the activated cells in comparison to the untreated populations. Based on the differentiation patterns of MBA-15, the electrical modifications were found to be highly correlated with the activation of specific cellular mechanisms which directly react to the hormonal inductions. In addition, by describing the dielectric dispersion in terms of transfer functions, it is shown that the spectral perturbations are well adapted to variations in the electrical characteristics of the cells. The reported findings vastly emphasize the tight correlation between the cellular and electrical state of the differentiated cells. It therefore emphasizes the vast abilities of impedance-based techniques as potential screening tools for stem cell analysis.

The role of GLUT1 in the sugar-induced dielectric response of human erythrocytes

We propose a key role for the glucose transporter 1 (GLUT1) in mediating the observed changes in the dielectric properties of human erythrocyte membranes as determined by dielectric spectroscopy. Cytochalasin B, a GLUT1 transport inhibitor, abolished the membrane capacitance changes in glucose-exposed red cells. Surprisingly, D-fructose, known to be transported primarily by GLUT5, exerted similar membrane capacitance changes at increasing D-fructose concentrations. In order to evaluate whether the glucose-mediated membrane capacitance changes originated directly from intracellularly bound adenosine triphosphate (ATP) or other components of the glycolysis process, we studied the dielectric responses of swollen erythrocytes with a decreased ATP content and of nucleotide-filled ghosts. Resealed ghosts containing physiological concentrations of ATP yielded the same glucose-dependent capacitance changes as biconcave intact red blood cells, further supporting the finding that ATP is the effector of the glucose-mediated dielectric response where the ATP concentration is also the mediating factor in swollen red blood cells. The results suggest that ATP binding to GLUT1 elicits a membrane capacitance change that increases with the applied concentration gradient of D-glucose. A simplified model of the membrane capacitance alteration with glucose uptake is proposed.

Effect of shape on the dielectric properties of biological cell suspensions

In this note, we analyze the effect of cell shape on the dielectric and conductometric behavior of biological cell suspension, in a frequency range where the interfacial polarization characteristic of highly heterogeneous systems occurs. We consider two different families of curves, both of them capable of generating a variety of symmetric or asymmetric shapes, ranging from oval, to dog-bone like, to lemniscate curves. These curves, which differ from those generally employed in dielectric models of biological cell suspensions, describe in principle different cells including discocytes, cup-shaped cells, pear-shaped cells, dumbbells and cells with spherical protrusions or invaginations. Our analysis, based on a numerical solution of the Laplace equation by means of boundary element methods, is carried out in the attempt of separating the contributions associated with the different electrical properties of the dielectric media involved from the ones mainly associated with the shape of the cell. We determine the dielectric strength of the dielectric dispersion for a variety of cell shapes and the phenomenological correlation between this parameter of the relaxation and the cell geometry is briefly discussed and commented.

A new method for the preperative and analytical electrophoresis of cells

In this paper, a new method is described for the horizontal electrophoresis of cells on a density cushion under near-isopycnic conditions. When cell sedimentation is minimized, the electrophoresis of red blood cells (RBC) used as model cells within an anti-convective porous matrix (with pores over 300 μm in diameter) was capable of separating a mixture of human and chicken RBC according to their electrophoretic mobilities. Samples taken from the separated RBC bands show over 90% purity for each species. The simultaneous electrophoresis of several RBC samples carried out under identical conditions permitted the use of comparative data based on the electrophoretic mobility of cells which differ in their surface properties. We believe that this relatively simple system, in which cell sedimentation and convection are minimized, has the potential to be modified and adapted for the separation of other cell types/organelles.

Parameters characterizing acid-base equilibria between cell membrane and solution and their application to monitoring the effect of various factors on the membrane

The cell membrane is an extremely complicated object. It participates in a large number of equilibria. For this reason, it is impossible to determine the parameters of all of them. It is the purpose of this work to define a limited number of averaged parameters in order to describe the equilibria between cell membrane components and environmental components. These parameters are the total acidic functional group concentration as well as the basic group concentration and their association constants with hydrogen or hydroxyl ions. The parameters were determined using the pH dependence of the electric surface charge density. The usefulness of these parameters was checked by studying the effect of green tea on liver cells in ethanol poisoning. Ethanol provokes an increase in concentration of functional groups, positively and negatively charged, as well as an increase in the basic groups association constant and a decrease in acidic groups association constant. Administering green tea partly compensates the changes provoked by ethanol poisoning. The parameters proposed in this work, C(TA), C(TB), K(AH) and K(BOH), are suited for monitoring the changes caused by various factors.