Page 162 - Bio Engineering Approaches to Cancer Diagnosis and Treatment

160 CHAPTER 7 Application of magnetic and electric fields for cancer therapy

nanocarrier to the desired part of the tissue [10]. This is because the surface force has
a linear relationship with the radius of the nanocarriers and the magnetic force varies
with the third power of the nanocarriers radius.
High magnetism characteristic: Nanocarriers with high magnetism are suitable
for precise delivery of the nanocarriers to the targeted tissue [9]. Therefore, higher
magnetism causes the hysteresis and residual losses of the nanocarriers, the main
sources of heat production, to be high.
Long lifespan characteristic: When foreign substances enter the blood circula-
tion system, the immune system quickly detects and eliminates them. This immune
system also applies to injected nanoparticles and shortly detects and repels them.
The duration of identification and repulsion depends on the size of the nanoparticles
and their surface properties. By choosing the appropriate surface for nanoparticles,
the absorption of nanoparticles by the immune system is delayed. In general, larger
nanoparticles are eliminated earlier by the immune system [10]. Based on in vitro
results, the resistance time in the blood plasma for a type of iron oxide nanoparticles
(diameter of 100 nm) was reported to be about 30 min [10]. Gamarra et al. [11] deter-
mined experimentally the detection and elimination of iron oxide nanoparticles with
dextran coatings in mice. Also, they measured the concentration of nanoparticles in
the rat.
Hydrophobic characteristic: Hydrophobic nanocarriers are carriers that do not
mix with water. Generally, the release of hydrophobic nanocarriers is more homoge-
neous in the blood plasma than other types of carriers. Suitable coatings of nanocar-
riers prevent them from oxidation and bonding. A great deal of research is focused
on obtaining suitable nanoparticles for medical applications [9]. Dobrovolskaia et al.
studied the effect of 12 types of PAMAM dendrimers coatings on the human plate-
lets in vitro [12]. Regarding the above properties, polyethylene glycol molecule is
most used to prevent the operation of the immune system. Of course, carbon and
silica coatings are also other options for nanoparticle coatings that have their own
properties [9].
Considering the required characteristics and the production cost, nanocarriers
based on iron oxide is most suitable for medical applications [5,9]. Chertok et al.
showed that iron oxide nanocarriers are also good for delivering the drug to the brain
tumors [13].

7.2 Bioengineering application of electromagnetic fields
It is well known that electromagnetic fields along with electrical conductor materi-
als lead to an increase in temperature by means of Joule effect or energy deposition.
Also, they might induce the same effects on human body structures. Actually, the
electromagnetic fields, with the same mechanisms, induce current density or heat
in human body [14]. These interactions are used in medical treatments. To reach
better therapeutic effect, human body tissue heating is used for hyperthermia, drug
delivery as well as muscle contractions or nerve stimulation. Advanced research in