Clarification of electrical current importance in plasma gene transfection by equivalent circuit analysis

Abstract

We have been developing a method of plasma gene transfection that uses microdischarge plasma (MDP) and is highly efficient, minimally invasive, and safe. Using this technique, electrical factors (such as the electrical current and electric field created through processing discharge plasma) and the chemical factors of active species and other substances focusing on radicals are supplied to the cells and then collectively work to introduce nucleic acids in the cell. In this paper, we focus on the electrical factors to identify whether the electric field or electrical current is the major factor acting on the cells. More specifically, we built a spatial distribution model that uses an electrical network to represent the buffer solution and cells separately, as a substitute for the previously reported uniform medium model (based on the finite element method), calculated the voltage and electrical current acting on cells, and examined their intensity. Although equivalent circuit models of single cells are widely used, this study was a novel attempt to build a model wherein adherent cells distributed in two dimensions were represented as a group of equivalent cell circuits and analyzed as an electrical network that included a buffer solution and a 96-well plate. Using this model, we could demonstrate the feasibility of applying equivalent circuit network analysis to calculate electrical factors using fewer components than those required for the finite element method, with regard to electrical processing systems targeting organisms. The results obtained through this equivalent circuit network analysis revealed for the first time that the distribution of voltage and current applied to a cellular membrane matched the spatial distribution of experimentally determined gene transfection efficiency and that the electrical current is the major factor contributing to introduction.

Fig 1. Plasma exposure area of a gene transfection device using microdischarge plasma.

Fig 2. Equivalent circuit comprising a single cell, its surrounding TE/PBS buffer solution, and a 96-well plate.

Fig 3

(a) Distribution of voltage/electrical current propagating along a distributed constant line parallel to the GND electrode, and (b) the associated ladder-shaped circuit simulating this.

Fig 4. Equivalent circuit network modeling buffer solution, cells, and a 96-well plate for plasma gene transfection.

Fig 5

(a) Diagram showing the nth component from the cell layer in the equivalent circuit network. (b) Multiple cells are included in a single component. (c) The dimension in the radial direction was determined such that it maintains the ratio of the heights of the cell layer (H_c) and cellular membrane layer (H_m).

Fig 6

Distribution in the radial direction of the effective values of (a) the electric field and (b) electrical current density.

Fig 7

Distribution in the radial direction of the effective values of the electrical current density for (a) the cell (J_c) and (b) the TE/PBS buffer solution (J_b), and normalized gene transfection efficiency (η) [31]. The electrical current density in the TE/PBS buffer solution derived from finite element method [31] is also shown in Fig 7C.

Fig 8

Distribution of effective values in the radial direction for (a) the voltage applied to the cellular membrane and (b) the electrical current flowing to the cell. The blue shaded regions in (a) and (b) indicate the action potential (approximately 0.1 V or lower) induced through normal cell activity and the electrical current value (of the order of 1 nA) caused by membrane transport through the ion channel, respectively. The red shaded region indicates the voltage (approximately 0.5 V or higher) wherein the cellular membrane would be damaged.