Strategies to Prevent Bacterial Adhesion on Biomaterials - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 189

Static
Vs.
Pulsed field

Magnetic
field
strength

Magnetic field
treatment for
antibacterial
efficiency

Pulsed
characteristics
or bacterial
cell type

Exposure
duration

Figure 7.24 Schematic of characteristics of magnetic fi eld infl uencing
antibacterial effi ciency.

found to vary according to type of fi eld (static or pulsed fi eld), strength
of applied fi eld and exposure duration. Different types of bacteria
respond differently under the same type of external fi eld, as shown in
Figure 7.24.
Two reasons are being proposed: (a) the effect of electromagnetic fi elds
on the permeability of the ionic membrane, and (b) formation of free radi-
cals due to magnetic fi eld [111]. It has been suggested that oxygen

free
radicals are produced due to magnetic fi eld, which react with the ions
in growth medium [113]. It has also been proposed that the bactericidal
might be related to the shape and wall structure of the protein cell. The
E. coli bacterium has a very thin wall thickness of 10 nm, and the mag-
netic fi eld force can therefore easily penetrate the cell wall as shown in
Figure 7.25 [118]. Further, it has been proposed that the effect of mag-
netic fi eld may be different on gram

−

negative bacteria
[119]. As far as the strength of magnetic fi eld is concerned, most of the
experiments are reported to be carried out at fi eld strength of less than
100 mT, while some researchers found positive response of magnetic
fi eld for bacterial infection, but such response is reported to be depen-
dent on exposure duration. In some of the work, low magnetic fi eld was
found to cause bactericidal property in a specifi c bacterial strain, how-
ever, was found ineffi cient for other types of bacterial cells. Such observa-
tions indicate that the magnetic fi eld response is also cell type dependent.
Very few studies are carried out at fi eld strength of more than 100 mT,
where similar types of effects as described above were reported. Schematic
of a external static magnetic fi eld setup used in a study is shown in
Figure 7.26 [113].

− positive and gram −