Caterina Merla

Quantitative assessment of dielectric parameters for membrane lipid bi-layers from RF permittivity measurements

In this article, we propose and validate theoretical and experimental methods to quantitatively assess the Debye dielectric model of membrane lipid bi-layers. This consists of two steps: permittivity measurements of biological solutions (liposomes), and estimation of the model parameters by inverse application of the Effective Medium Theory. The measurements are conducted in the frequency domain between 100 MHz and 2 GHz using a modified coaxial connector, at the temperatures of 27 and 30 degrees C. Estimations have been performed using a three-layered model based on the Maxwell-Wagner formulation. Debye parameters (mean value +/- standard error) found from fitting experimental data are: epsilon(s) = 11.69 +/- 0.09, epsilon(infinity) = 4.00 +/- 0.07, f(relax) = 179.85 +/- 6.20 MHz and epsilon(s) = (1.1 +/- 0.1) x 10(-7) S/m. This model can be used in microdosimetric studies aiming to precisely determine the E-field distribution in a biological target down to the single cell level. In this context the use of an accurate membrane dielectric model, valid through a wide frequency range, is particularly appropriate.

A 3-D Microdosimetric Study on Blood Cells: A Permittivity Model of Cell Membrane and Stochastic Electromagnetic Analysis

This paper describes a microdosimetric study on erythrocytes in two parts: an assessment of the membrane dielectric model from permittivity measurements of erythrocyte solutions and its uncertainty, and a quasi-static electromagnetic (EM) analysis solving the Laplace equation, both analytically and numerically. To evaluate the role of the estimated uncertainty, a stochastic EM solution has been conducted; our results highlight the fundamental role of the dielectric modeling on the reliability of electric field values in the cell membrane. Numerical data, from 3-D cell models, confirm the dependence of the electric field distribution on the extra-cellular field polarization.

Microdosimetry in the Microwave Range: A Quantitative Assessment at Single Cell Level

Recently, growing attention has been devoted to microwave (MW) microdosimetry studies. Electromagnetic (EM) field at cell level is a complex function of frequency, shape, dielectric properties, and of the conditions of irradiation. The aim of this work is to quantitatively assess the role of the various parameters involved in the problem using both analytical and numerical , assessing the relevance of these computational techniques as well. As a main result, the crucial role played by the cell dielectric model has been demonstrated.

A microwave microdosimetric study on blood cells: Estimation of cell membrane permittivity and parametric EM analysis

In the study of the interaction of RF and MW fields with biological systems particular attention has been recently devoted to microdosimetric research. In this paper a microdosimetric study on erythrocytes is proposed. Facing this topic, two fundamental steps are needed: the set up of a proper membrane dielectric model valid up to the RF and MW range, and the set up of an appropriate EM solution on the cell environment. Concerning the first point, an accurate estimation of the membrane dielectric model and of its uncertainty has been performed, from permittivity measurements of erythrocytes solutions. Focusing on the second point, a quasi-static EM analysis solving the Laplace equation has been chosen. An analytical approach has been applied on simplified spherical cell geometry, while a numerical solver has been used for erythrocyte shaped cell. In this context the fundamental role of the dielectric membrane modeling on results reliability has been highlighted.

Coplanar waveguide with defected ground structure for nanosecond subcellular electroporation

Compact measurement setup and test structure for nanosecond electroporation of biological cells were demonstrated. The test structure was based on a coplanar waveguide with a defected ground structure that afforded broadband impedance match with little dispersion or parasitic. The defected ground structure with a 10-µm gap formed a microchamber to readily accept biological solutions and to allow the measurement to be quickly performed before the solution evaporated or the cell activity changed. The measured results in conjunction with detailed electromagnetic analysis of a three-layer spherical cell model showed that the present measurement setup was capable of delivering a nanosecond 0.1-V potential across a plasmatic membrane. This transmembrane potential, although an order of magnitude lower than the typical threshold for membrane poration, could be increased by using nanosecond pulses with order-of-magnitude higher amplitude or 10-ns pulses with three times higher amplitude.

A Wire Patch Cell for “in vitro” exposure at the Wi-Fi frequencies

An in vitro exposure system, based on a Wire Patch Cell (WPC) and operating in the whole band of the Wi-Fi signal, has been fabricated and characterized. The system enables the contemporary exposure of four 35 mm Petri dishes and can be inserted into a commercial incubator. Results of both simulations and measurements indicate a good behavior in the band. The mean efficiency, in terms of Specific Absorption Rate (SAR) in the biological sample for 1 W of input power, is higher than 0.75 (W/kg)/W. The homogeneity of the SAR distribution inside each Petri dish is above 70 % in the lowest layer of the biological solution, indicating the optimal employment of the system for the exposure of cell monolayers.

Nanosecond pulsed electric field (nsPEF): A microdosimetry study at single cell level

Exposure of cell lines and tissues to nanosecond pulsed electric fields has been associated to a number of biological relevant phenomena, suggesting the plasmatic membrane as one of the main interaction targets. In this context, a microdosimetric study able to predict trans-membrane potential and pore number distribution on the membrane seems to be particularly interesting. Thus to obtain these quantities, a quasi-static electromagnetic solution coupled with and asymptotic electroporation model is solved on a three-layered spherical cell. Consequently the role played by including or disregarding Debye description as well as by adopting different dielectric membrane models on such observables is discussed.