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Bioelectromagnetism

frst observed by John Kerr (1824–1907) about 150 years ago. Kerr was a Scottish physicist, Mathematical

Lecturer of the Free-Church Training College, Glasgow, and the term of “Kerr efect” is named afer

him. Kerr reported electric birefringence observations in various liquids (Kerr, 1875). In this paper, he

presented about electric feld-efects on dust particles (dielectrifed body). When the particles in ben­

zene and carbon disulfde were numerous enough, they formed a chain between the electrodes. Te

chain breaks up violently at the instant discharges. When the particles are few and of the same forms,

they do not produce a chain, and they are presented as a set of sparkling points, which dart hither and

thither through the ventral parts of the electric feld (Kerr, 1875; O’Konski, 1981). In 1927, Ernst Muth,

University of Halle, observed the phenomenon of pearl chain formation by exposing fat emulsions to

high-frequency AC electric feld (Muth, 1927). Ten years later, Paul Liebesny (1881–1962), physician, New

York, was the frst to demonstrate the pearl chain formation of erythrocytes in a high-frequency electric

feld (Liebesny, 1938).

Te pearl chain formation is the phenomenon where two dielectric particles in a homogeneous elec­

tric feld will be attracted to each other forming a dipole and will be oriented in the direction of the

electric feld. Cells will tend to form pearl chain in the direction of the electric feld. In a gradient elec­

tric feld, the pearl chains will protrude from the surface of electrode (Grimnes and Martinsen, 2000).

William Krasny-Ergen presented a theory of the pearl chain formation (Krasny-Ergen, 1936, 1937). He

proposed a theory that explains the pearl chain formation of dispersed particles in terms of potential

energy. However, he made no comparison between theoretical results and experimental data. Later,

Schwan and his colleagues developed a general theory to account for the pearl chain formation of spher­

ical and nonspherical particles in AC felds (Saito and Schwan, 1961; Schwarz et al., 1965; Saito et al.,

1966; Schwan and Sher, 1969). Tey studied for the frst time the pearl chain formation experimentally

and theoretically. Masao Saito (1934–2016), a visiting scientist, later professor at the University of Tokyo,

pointed out that the time constants of pearl chain formations were of the order of a second for a particle

with radius 1 μm, and they were proportional to the cube of the radius. At low felds, the time constants

were not strongly dependent on the feld intensity, but at higher felds, they are inversely proportional to

the square of the feld strength. Large error of the threshold feld strength in experimental works may

occur if the time constants for the pearl chain formations are in the order of hundred of a second, or

minutes when the particles measure a few microns or more in size. Schwan pointed out that a minimal

feld strength is needed to cause feld efects and termed this minimal feld value as the threshold feld

strength Eth. Saito and Schwan presented an equation for Eth for pearl chain formations based on an

expression derived for the potential electrical energy of a particle suspended in a medium of diferent

dielectric properties (Saito and Schwan, 1961; Schwan, 1989). Schwan noted that it could not be applied

with experimental data casting, doubt on the validity of the Saito-Schwan expression for Eth (Schwan,

1989). Later, Sauer pointed out that the equations of the theoretical considerations of Krasny-Ergen,

Saito and Schwan gave only qualitative and semi-quantitative analyses for the pearl chain formation in

special case when the medium and the particles have no dielectric losses (Sauer, 1983). Sauer calculated

the forces on two particles in an electric feld in the case when the medium and the particles have dielec­

tric losses. His calculation successfully predicted the trajectories of the particles during the process of

the pearl chain formation.

Electrorotation refers to the rotation of particles in electric feld. A. A. Teixeira-Pinto, a postdoctoral

Fellow from Portugal in the New England Institute for Medical Research, Connecticut, and his co­

workers noted not only particle pearl chain formation but also particle orientation and observed frst

that an Euglena cell and an amoeba began to rotate when they approached each other in an electric feld

in the radio frequency range (Teixeira-Pinto et al., 1960). Later, A. A. Füredi and I. Ohad, Te Hebrew

University of Jerusalem, Israel, reported the behavior of human erythrocytes in a high-frequency elec­

tric feld (Füredi and Ohad, 1964). Because longer exposure (over 10 seconds) causes damage to cells by

heating for erythrocytes, it was applied for 1–5 seconds. Erythrocytes showed a reversible elongation

which was accompanied by a rotatory motion. Old erythrocytes do not elongate or rotate but can form

chains oriented in the direction of the feld. Electrorotation is used to diferentiate between viable and