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The History of Bioelectromagnetism

In 1974, Ulrich Zimmermann, professor at the University of Würzburg, Germany, concluded that

membrane permeabilization occurs when the transmembrane potential reaches a threshold of 1 V

(Zimmermann et al., 1974). Te emphasis was that the result is relevant to irreversible electropora­

tion parameters. Te efects are not thermal. Zimmermann used reversible electroporation to produce

fusion between cells afer exposure to high electric feld pulses (Zimmermann, 1982). In 1982, Neumann

and his co-workers coined the term electroporation to describe the membrane breakdown induced by

electric felds. Tey introduced frst the use of reversible electroporation to insert genes into cells by

pulsed electric felds (Neumann et al., 1982).

Mitsugi Senda (1929–2016), professor at Kyoto University, Japan, and his co-workers reported the frst

study of the electrofusion with two kinds of plant protoplasts (Senda et al., 1979). Tey brought mechani­

cally two protoplasts isolated from cultured cells of Rauwolfa serpentina through two glass capillary

microelectrodes in contact with the adhering protoplasts. To them, they applied an electric impulse

with 5 and 12 μA for a few milliseconds generated by an electric stimulator (Nippon-Koden Co. Ltd.,

MSE-3). Fusion was immediately induced. Tis phenomenon seemed to be related to transient changes

in the membrane state. Tis was a very important milestone in the development of the electrofusion

technique. Zimmermann and Scheurich also had a pioneer approach in electrofusion (Zimmermann

and Scheurich, 1981). Electrofusion is the use of electric pulses to combine cells, allowing the mixing

of their intracellular contents. Te electrofusion has two steps: frst, the connection of two separated

closed-physical contact cell membranes is achieved by dielectrophoresis of the cells in non-uniform AC

electric felds. Next, electrofusion is triggered between adjacent cells by the application of high pulsed

electric felds with very short duration.

Tere have been papers published on cell movement in nonhomogeneous alternating and in rotating

electric felds. Tese phenomena may be used in cell fusion and cell separation (Zimmermann, 1982).

Fundamentally, pulsed electric felds with duration from the order of milliseconds to micro-seconds and

with amplitudes of the order of hundreds to thousands of volts per centimeter was applied across cells. In

the 1990s, the electroporation had extended to include nano-second pulsed electric felds. Nano-second

pulsed electric felds were designed to induce predominately intracellular efects without heating. In

1997, Karl H. Schoenbach, professor at the Old Dominion University, and his co-workers reported on in

vitro study, using very high voltage pulses of submicrosecond duration (Schoenbach et al., 1997, 2001).

Afer the publication of this paper, studies on the use of pulsed electric felds with the duration of some

nano-seconds or tens of nano-seconds were published. Te concept of these researches came from the

ideal that ultra-short pulses could be able to induce electroporation of intracellular membranes struc­

tures without disturbing the cell membrane. Electroporation is also used for food sterilization and for

transfection of yeast, bacteria and plant protoplast in biotechnology. Te reversible electroporation is

a method for drug delivery into tumor cells. In biotechnology, it is useful for microbial deactivation.

If a non-uniform AC electric feld is applied to a cell, it experiences a force which can cause it to

move. Tis efect is known as dielectrophoresis. Te term dielectrophoresis (DEP) refers to the lateral

movement of non-charged dielectric particles in a non-uniform AC electric feld. Dielectrophoresis is

observed when cells are suspended in low conductivity medium and electric felds are applied to the cells

using microelectrodes (20–200 μm in diameter), and AC voltages of 2–20 Vp-p with a frequency in the

range of 10 kHz–100 MHz. Herbert Ackland Pohl, professor at Oklahoma State University, is the pioneer

of the study of dielectrophoresis and its application to the study of cells. In 1966, Pohl and his co-workers

reported the frst demonstration of dielectrophoresis (DEP) of living and death yeast cells (Pohl and

Hawk, 1966). Te theory of DEP of biological particles was presented by Pohl. However, it is said that his

approach cannot be considered to be satisfactory due to the failure of giving reasonable results in the

low-frequency region. Te correct theory for the possible model of cell membrane was given by Schwan.

Dielectrophoresis is simply the movement of cells in inhomogeneous electric feld. During dielectro­

phoresis, charged dipoles are induced in the cell when a weak AC current passes through the membrane

suspension causing the cells between the electrodes to become aligned in chain-like aggregates, referred

to as “pearl chain formation” (Van Wert and Saunders, 1992). Te pearl chain formation was probably