Jiafeng Yao

Spatial concentration distribution analysis of cells in electrode-multilayered microchannel by dielectric property measurement

The spatial concentration distribution of cells in a microchannel is measured by combining the dielectric properties of cells with the specific structure of the electrode-multilayered microchannel. The dielectric properties of cells obtained with the impedance spectroscopy method includes the cell permittivity and dielectric relaxation, which corresponds to the cell concentration and structure. The electrode-multilayered microchannel is constructed by 5 cross-sections, and each cross-section contains 5 electrode-layers embedded with 16 micro electrodes. In the experiment, the dielectric properties of cell suspensions with different volume concentrations are measured with different electrode-combinations corresponding to different electric field distributions. The dielectric relaxations of different cell concentrations are compared and discussed with the Maxwell-Wagner dispersion theory, and the relaxation frequencies are analysed by a cell polarization model established based on the Hanai cell model. Moreover, a significant linear relationship with AC frequency dependency between relative permittivity and cell concentration was found, which provides a promising way to on-line estimate cell concentration in microchannel. Finally, cell distribution in 1 cross-section of the microchannel (X and Y directions) was measured with different electrode-combinations using the dielectric properties of cell suspensions, and cell concentration distribution along the microchannel (Z direction) was visualized at flowing state. The present cell spatial sensing study provides a new approach for 3 dimensional non-invasive online cell sensing for biological industry.

Noninvasive online measurement of particle size and concentration in liquid–particle mixture by estimating equivalent circuit of electrical double layer

ABSTRACT Three electrical elements (i.e., resistance, capacitance, and relaxation frequency) of electrical double layer (EDL) formed around particles have been extracted by a measuring–fitting combination for a novel noninvasive online measurement technique of particle size and concentration in a liquid–particle mixture. The measuring–fitting combination means measuring the impedances with electrical-impedance spectroscopy (EIS) method, and fitting the equivalent circuit with Levenberg–Marquardt method. The liquid–particle mixture in the impedance measurement is made of sodium chloride solution and stainless particles; the equivalent circuit is established corresponding to the contents in the liquid–particle mixture. As a result, the influence of the particle size and concentration on the electrical elements in the EDL which are the resistance, capacitance, and relaxation frequency in the EDL are clarified and discussed. This method is useful for determination of the particle size and concentration in liquid–particle mixture.

Investigation of particle inertial migration in high particle concentration suspension flow by multi-electrodes sensing and Eulerian-Lagrangian simulation in a square microchannel

The inertial migration of neutrally buoyant spherical particles in high particle concentration (αpi  > 3%) suspension flow in a square microchannel was investigated by means of the multi-electrodes sensing method which broke through the limitation of conventional optical measurement techniques in the high particle concentration suspensions due to interference from the large particle numbers. Based on the measured particle concentrations near the wall and at the corner of the square microchannel, particle cross-sectional migration ratios are calculated to quantitatively estimate the migration degree. As a result, particle migration to four stable equilibrium positions near the centre of each face of the square microchannel is found only in the cases of low initial particle concentration up to 5.0 v/v%, while the migration phenomenon becomes partial as the initial particle concentration achieves 10.0 v/v% and disappears in the cases of the initial particle concentration αpi  ≥ 15%. In order to clarify the influential mechanism of particle-particle interaction on particle migration, an Eulerian-Lagrangian numerical model was proposed by employing the Lennard-Jones potential as the inter-particle potential, while the inertial lift coefficient is calculated by a pre-processed semi-analytical simulation. Moreover, based on the experimental and simulation results, a dimensionless number named migration index was proposed to evaluate the influence of the initial particle concentration on the particle migration phenomenon. The migration index less than 0.1 is found to denote obvious particle inertial migration, while a larger migration index denotes the absence of it. This index is helpful for estimation of the maximum initial particle concentration for the design of inertial microfluidic devices.

Application of Process Tomography to Multiphase Flow Measurement in Industrial and Biomedical Fields: A Review

This paper reviews the latest development and emerging technologies on the application of process tomography to multiphase flow measurement in industrial and biomedical fields. In the industrial applications, electrical resistance tomography and electrical capacitance tomography are popularly applied in multiphase flow measurement dependent on the electrical properties of the objects. In particular, applications to circulating fluidized bed, trickle-bed reactor and temperature measurement are discussed. In the biomedical applications, in most cases, measurement is conducted in a static condition. Two latest applications in flowing condition are reviewed, which are thrombus detection in blood flow and cell sensing with a microfluidic device. Finally, the challenges to process tomography for multiphase flow measurement on industrial and biomedical applications are addressed.

Development of electrical impedance tomography system for cell sedimentation detection in electrode-multilayered microchannel

Electrical Impedance Tomography (EIT) System has been developed for cell sedimentation detection in the present study. In this paper, the EIT system was evaluated by simulation and experiments. In the simulation, 3 image reconstruction algorithms were employed, which are GVSPM (Generalized Vector Sampled Pattern Matching), Tikhonov Regularization (TK) and Projected Landweber Iteration (PLW). GVSPM was found to be the optimum algorithm for image reconstruction due to its faster calculation and higher image correlation (/e). In the experiments, measurements of the cell distribution of two-phase flow which consist of yeast cells and purified water in the micro channel were conducted with a range of frequencies to find the optimum frequency for image reconstruction by GVSPM. Images of cell distribution reconstructed by GVSPM in three cross-sections showed that cells sediment at the bottom of the micro channel. The present study provides a successful approach for cell distribution sensing in microfluidics.

Influence of particle size on the exit effect of a full-scale rolling circulating fluidized bed

ABSTRACT This paper investigated the influence of particle size on the exit effect of a full-scale rolling circulating fluidized bed (CFB) by using the Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) method. The gas–solid two-phase flow of the full-scale rolling CFB was compared with that of a simplified rolling CFB. Thus, the exit effect of the full-scale rolling CFB was clarified. In the air phase, a peak of air axial velocity vya was observed when the full-scale rolling CFB reached the maximum angular displacement. The particle phase possessed back mixing and radial exchange phenomena at the top and bottom of the full-scale rolling CFB, respectively. However, those phenomena were not obvious at the top and bottom of the simplified rolling CFB. The mechanism of the above-mentioned exit effect was then clarified by analyzing the forces acting on the particles under different particle sizes. Finally, the increases in particle size lead to the intensification of the peak of vya, particle back mixing, and radial exchange phenomena. Therefore, the intensity of the exit effect of the gas–solid two-phase flow increased as the particle size increased. The results suggested that the small particles had the potential to promote the purification rate of the full-scale rolling CFB on account of its small exit effect.

Distinct Motion of GFP-Tagged Histone Expressing Cells Under AC Electrokinetics in Electrode-Multilayered Microfluidic Device

The distinct motion of GFP-tagged histone expressing cells (Histone-GFP type cells) has been investigated under ac electrokinetics in an electrode-multilayered microfluidic device as compared with Wild type cells and GFP type cells in terms of different intracellular components. The Histone-GFP type cells were modified by the transfection of green fluorescent protein-fused histone from the human lung fibroblast cell line. The velocity of the Histone-GFP type cells obtained by particle tracking velocimetry technique is faster than Wild type cells by 24.9% and GFP type cells by 57.1%. This phenomenon is caused by the more amount of proteins in the intracellular of single Histone-GFP type cell than that of the Wild type and GFP type cells. The more amount of proteins in the Histone-GFP type cells corresponds to a lower electric permittivity ϵc of the cells, which generates a lower dielectrophoretic force exerting on the cells. The velocity of Histone-GFP type cells is well agreed with Eulerian–Lagrangian two-phase flow simulation by 4.2% mean error, which proves that the fluid motion driven by thermal buoyancy and electrothermal force dominates the direction of cells motion, while the distinct motion of Histone-GFP type cells is caused by dielectrophoretic force. The fluid motion does not generate a distinct drag motion for Histone-GFP type cells because the Histone-GFP type cells have the same size to the Wild type and GFP type cells. These results clarified the mechanism of cells motion in terms of intracellular components, which helps to improve the cell manipulation efficiency with electrokinetics.

Analysis of dynamic cell movement under AC electric field in 3D multi-layered microchannel

In the field of regenerative medicine, it is expected to separate disease-causing cells from healthy cells by electrical method with label-free and high efficiency. The purpose of this study is to find the differences of speeds between disease-causing cells and healthy cells under alternating current electric field in 3D multi-layered microchannel. We prepared intracellular charge-differed two cell types: wild type cells (WT) and wild type cells with green fluorescent protein (GFP)-histone (GFP-HT). The cell dynamic movement of each type was detected by cell tracking. We found a difference between WT velocity and GFP-HT velocity around supplying electrode and discussed by particle tracking velocimetry. The present results provide a great significance for separation of disease-causing cells from healthy cells in the microchannel.

Experimental study on dielectric properties of yeast cells in micro channel by impedance spectroscopy

Impedance spectroscopy has been proved to be a useful technique for analyzing heterogeneous systems, especially biological cell suspensions and tissues because of its capacity of non-invasive measurement. In the present paper, experiments were conducted to study the dielectric properties of yeast cells by Impedance Spectroscopy. The capacitance of the suspension of yeast cells was measured and the relative permittivity and the dielectric loss were calculated. As the concentration of yeast cells increased, the relative permittivity and the dielectric loss were also increased. In addition, the relative permittivity and the dielectric loss of living cells were higher than that of the dead ones. Finally, we concluded that it is possible to sense the status and the concentration of cell suspension by impedance spectroscopy.