Biomedical Engineering Reference
In-Depth Information
2
Nanoparticles Enhanced Magnetic Hyperthermia
2.1
Basic Features
MNPs are a major class of nanoscale materials with the potential to revolutionize
current clinical diagnostic and therapeutic techniques. As early as 1957, Gilchrist
et al. advanced the concept of magnetic targeting hyperthermia, which however
received few attentions for a rather long time. Only when magnetic nanomaterials
developed rapidly was some progress made in this area. Now, MNPs are being
actively used in tumor hyperthermia and as the contrast agents in MRI (Duguet
et al.
2006
) and as carriers for targeted drug delivery. The goal of magnetic hyper-
thermia is to heat specifically and exclusively the local tumor region by means of the
magnetic losses of nanoparticles in an external alternating magnetic field, without
damaging the surrounding healthy tissues. In addition, MNPs will aggregate to
form a larger diameter of the polymer, which effectively blocked the blood vessels
around the tumor at its position to play a role in vascular thrombosis. This can
cut off the blood supply of tumor. What's more, the magnetic field could inhibit the
growth of cancer tissues through some mechanisms, such as impacting biological
magnetic fields of tumor tissue, disrupting its blood and oxygen supply, changing
the functions of cancer cell membrane so that affecting the material exchange,
inhibition of cancer cell proliferation and enhancing the body immune function.
2.1.1
Enhanced Magnetism of MNPs
When MNPs are placed in an external magnetic field, the magnetic field is locally
augmented through atomistic mechanisms in the magnetic material. The magneti-
zation M is written in terms of the applied field H as (Wetzel and Fink
2001
)
MH HH
() ()
=
c
(1)
where,
c
is called magnetic susceptibility. The magnetization M is not linearly
related to the applied field H.
Magnetic induction B is proportional to the sum of the applied H field and the
material magnetization M, that is
B HM
=
m
0
(
+
)
(2)
where,
m
is the magnetic permeability of free space, whose exact value is defined
=ยด
7
-
as
mp
.
The material's magnetic properties depend on its magnetic susceptibility, which
is defined by the ratio of the induced magnetization to the applied magnetic field.
According to the direction and strength of H, magnetic materials can be sorted into
several kinds (
Classes of Magnetic Materials
; Rishi
2008
): diamagnetic, paramagnetic,
4
10
HM
0
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