Page 184 - Computational Modeling in Biomedical Engineering and Medical Physics

Magnetic drug targeting 173

inserted near the diseased tissue. At each release of MD, the ferromagnetic implant is
magnetized by an external magnetic field, leading to a much more effective trap of
MNPs (Iacob and Chiriac, 2004; Avilés et al., 2005; Avilés et al., 2008). Moreover, the
PM itself may be implanted right in the patient's tumor region and not at the surface of
the body. The invasiveness of this technique is confined to a single surgical intervention
to implant either the ferromagnetic insert and, or the magnet, which is an improvement
over an ordinary method, where the drug MNPs are injected deep into the tissue. A dis-
advantage would be the difficulty for the drug to cross the wall of the blood vessel to
reach the desired location, but this is a common concern with MDT.
Another, quite new, slightly modified extra corpus application of this MDT princi-
ple, is the purification of bone marrow cells contaminated with tumor cells (Roots-
Weiß et al., 1997), using immunomagnetic particles (Saiyed et al., 2003).

6.2 Magnetic nanoparticles for magnetic drug targeting

MNPs are promised to be used in various biological or medical applications, for early
diagnosis of maladies, noninvasive imaging and for drug development, but also for
controlled drug delivery systems that have the ability to minimize negative systemic
side effects. They comprise polymeric micelles, dendrimers, liposomes, inorganic and
polymeric nanoparticles, quantum dots, etc. (Hawk’s, 2020). All these were tested pre-
clinically and clinically for targeted medication, for gene delivery or for improving
diagnostic imaging. Properties existing only at the nanoscale, such as the enhanced
fluorescence emission of semiconductor crystals (as in the case of quantum dots) or the
magnetic properties of the MNPs, recommend these materials for medical imaging or
targeted medication applications (Neuberger et al., 2005).

Magnetic properties of materials used in designing the magnetic drug
targeting medication
Iron oxide MNPs with various coatings are more and more used in in vivo applica-
tions for reason that they are small enough to be carried through the circulatory or
lymphatic system, and at the same time they can be attached to cells, or even they can
be inserted into cells, and then transported altogether. When combined with drugs or
genes, these particles can transform the viability of the cell or alter the transcription
process (Brown, 2020).
According to their magnetic susceptibility, these materials are classified in diamagnetic,
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with negative susceptibility (χ 10 , i.e., they slightly repulse an external magnetic
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field), paramagnetic (χ 10 ...10 ), and ferromagnetic (χ 50...10 )(Fig. 6.1).
Diamagnetic and paramagnetic properties vanish when the external magnetic field
is removed, whereas the ferromagnetic materials properties persist—they make, in fact,
the PMs. The maximum value of the magnetization is termed saturation magnetization