Ellipsoidal Cell Model Research Articles

Effect of microstructure on dynamic compressive behavior of cellular materials

It is known that the microstructure of cellular materials has a significant impact on their compressive properties. To study these phenomena, a hierarchical Poisson disk sampling algorithm and Voronoi partitioning were used to create a 3D numerical analysis model of cellular materials. In this study, we prepared random, periodic, and ellipsoidal cell models to investigate the effects of cell shape randomness and oblateness. Numerical experiments were performed using the finite element method solver RADIOSS. In the numerical analysis, an object collided with the cellular materials at a velocity of 25 m/s. The results showed that the flow stress of the random cell model was higher than that of the periodic cell model. Further, it was found that the aspect ratio of the cell shape has a significant impact on the mechanical properties of cellular materials.

Effect Of Temperature On The Electrorotation Behavior Of Human Red Blood Cells

The dielectric parameters of Human Red Blood Cells (HRBCs) were investigated by Electrorotation (ER). Suspended HRBCs were exposed to rotating electric fields in the range from 50 kHz to 250 MHz in a rectangular 4–electrode microchip chamber. ER spectra was recorded at external conductivities ranging from 0.02 – 3.00 S/m. The electrode structures were fabricated on glass chips by laser ablation of a platinum layer. Different measuring temperatures were used. At low conductivities, the temperature of the microscopic stage was kept constant by a thermostat. At higher medium conductivities, the additional temperature increase in the measuring volume due to Joule heating was registered. Measured data in the range from 20 to 35°C were then sorted according to different temperature classes of a width of 5 K. The first and the second characteristic peak frequencies of ER were plotted over medium conductivity and interpreted using an oblate single shell model with a dispersive cytoplasm and temperature dependent electric cell parameters. Key words: Erythrocyte, AC-electrokinetics, impedance, dispersion, ellipsoidal cell model, electric cell properties

A study of the electric field distribution in erythrocyte and rod shape cells from direct RF exposure

This paper shows the importance of using realistic cell shapes with the proper geometry and orientation to study the mechanisms of direct cellular effects from radiofrequency (RF) exposure. For this purpose, the electric field distribution within erythrocyte, rod and ellipsoidal cell models is calculated by using a finite element technique with adaptive meshing. The three cell models are exposed to linearly polarized electromagnetic plane waves of frequencies 900 and 2450 MHz. The results show that the amplification of the electric field within the membrane of the erythrocyte shape cell is more significant than that observed in other cell geometries. The results obtained show the dependence of the induced electric field distribution on frequency, electrical properties of membrane and cytoplasm and the orientation of the cell with respect to the applied field. The analysis of the transition of an erythrocyte shape to an ellipsoidal one shows that a uniformly shelled ellipsoid model is a rough approximation if a precise simulation of bioeffects in cells is desired.

Spectral Representation Theory for Dielectric Behavior of Nonspherical Cell Suspensions**The project supported by the Research Grants Council of the Hong Kong SAR Government

Recent experiments revealed that the dielectric dispersion spectrum of fission yeast cells in a suspension was mainly composed of two sub-dispersions. The low-frequency sub-dispersion depended on the cell length, while the high-frequency one was independent of it. The cell shape effect was simulated by an ellipsoidal cell model but the comparison between theory and experiment was far from being satisfactory. Prompted by the discrepancy, we proposed the use of spectral representation to analyze more realistic cell models. We adopted a shell-spheroidal model to analyze the effects of the cell membrane. It is found that the dielectric property of the cell membrane has only a minor effect on the dispersion magnitude ratio and the characteristic frequency ratio. We further included the effect of rotation of dipole induced by an external electric field, and solved the dipole-rotation spheroidal model in the spectral representation. Good agreement between theory and experiment has been obtained.

Dielectric behaviour of non-spherical cell suspensions

Recent experiments revealed that the dielectric dispersion spectrum of fission yeast cells in a suspension was mainly composed of two sub-dispersions. The low-frequency sub-dispersion depended on the cell length, whereas the high-frequency one was independent of it. The cell shape effect was qualitatively simulated by an ellipsoidal-cell model. However, the comparison between theory and experiment was far from being satisfactory. In an attempt to close up the gap between theory and experiment, we considered the more realistic cells of spherocylinders, i.e. circular cylinders with two hemispherical caps at both ends. We have formulated a Green function formalism for calculating the spectralrepresentation of cells of finite length. The Green function can be reduced because of the azimuthal symmetry of the cell. This simplification enables us to calculate the dispersionspectrum and hence assess the effect of cell structure on thedielectric behaviour of cell suspensions.

Analysis of the influence of the cell geometry, orientation and cell proximity effects on theelectric field distribution from direct RF exposure

This paper shows the importance of using a cell model with the proper geometry, orientation andinternal structure to study possible cellular effects from direct radiofrequency exposure. For thispurpose, the electric field intensity is calculated, using the finite element numerical technique, insingle- and multilayer spherical, cylindrical and ellipsoidal mammalian cell models exposed tolinearly polarized electromagnetic plane waves of frequencies 900 and 2450 MHz. An extensiveanalysis is performed on the influence that the cell geometry and orientation with respect to theexternal field have in the value of the electric field induced in the membrane and cytoplasm. Wealso show the significant role that the cytoplasmic and extracellular bound water layers play indetermining the electric field intensity for the cylindrical and ellipsoidal cell models. Finally, astudy of the mutual interactions between cells shows that polarizing effects between cellssignificantly modify the values of field intensity within the cell.

Dielectric analysis for estimation of oil content in the mycelia ofMortierella alpina

The dielectric behavior of the filamentous fungi Mortierella alpina SAM2104 and 1S-4, which produce polyunsaturated fatty acid enriched oil in the mycelia, was investigated. During the cultivation carried out in a 10-kL fermentor for 12-15 days, the relative permittivity and conductivity of the broth were measured in the frequency range of 100 kHz to 30 MHz. The dielectric parameters, i.e., the amplitude of dielectric relaxation (Deltaepsilon) and the characteristic frequency (f(c)), were obtained by fitting the Cole-Cole equation to the observed dielectric relaxation, and the conductivity of the medium (kappa(a)) was also measured. The value of Deltaepsilon gradually increased from the second day through the end of cultivation, suggesting that volume fraction of the cell increased with oil accumulation. The conductivity of the cytoplasm (kappa(i)) was calculated from the experimental values of f(c) and kappa(a), using a theoretical equation based on an ellipsoidal cell model. As a result, good correlation between the calculated kappa(i) and the oil content was obtained. These findings indicate that dielectric analysis enables us to estimate the oil content in the mycelia of oleaginous fungi and also provides a useful tool for monitoring cell growth and for controlling the cultivation process.

Effect of cell shape on dielectric behavior of fission yeast

In order to study the effect of cell shape on dielectric behavior of cell suspensions, a temperature sensitive cell division cycle mutant, cdc25-22, of Schizosaccharomyces pombe was used, whose cell length was varied by cultivating at the restrictive temperature. The dielectric dispersion of the cells in suspension was mainly composed of two subdispersions. The low-frequency subdispersion depended on the cell length, whereas the high-frequency subdispersion was independent of it. The cell shape effect was qualitatively simulated by an ellipsoidal cell model.

Electrorotation of non-spherical cells: Theory for ellipsoidal cells with an arbitrary number of shells

Theoretical expressions for electrorotation are derived for an ellipsoidal cell model with an arbitrary number of confocal shells. The theory for a spherical cell model with an arbitrary number of shells can be obtained as a special case of the present theory. Theoretical expressions are presented for several ellipsoidal cell models which are relevant to biological cells. The effects of cell shape and size on the electrorotation spectrum are discussed in detail for the case of the ellipsoidal single-shell model under the conditions that seem appropriate for biological cells.