Biomedical Engineering Reference
In-Depth Information
the thermal decomposition method of Sun
et al.
[16, 17] disperse well in organic
solvents such as hexane and toluene. The addition of MPEG-COOH to the reaction
mixture during the thermal decomposition of Fe(acac)
3
resulted in nanoparticles
which were water-soluble due to the presence of surface-bound MPEG [18]. The
solubility and surface properties of the nanoparticles are critical factors in deter-
mining the biomedical applicability. For example, a comparison of the effect of
uncoated, dextran-, and albumin-coated MNPs prepared using the coprecipitation
method on fi broblasts
in vitro
showed distinct differences in particle uptake and
cellular response [11]. The uncoated MNPs were largely internalized by the fi bro-
blasts, resulting in eventual cell death. A similar result was obtained with the
dextran-coated particles, while the albumin-coated particles resulted in cell prolif-
eration. The modifi cation of the surfaces of MNPs to mediate their interactions
with cells will be discussed in greater detail later in the chapter.
10.3
Magnetic Nanoparticles with Polymeric Shell
One of the major challenges faced when using MNPs
in vivo
is their rapid elimina-
tion from the bloodstream by the mononuclear phagocyte system (MPS), which
comprises the bone marrow progenitors, blood monocytes and tissue macro-
phages. Unfortunately, this rapid clearance of MNPs by the MPS prevents them
from reaching the target cells. Hence, in order to increase the MNPs' circulation
time in the bloodstream they can be modifi ed with a polymeric coating so as to
minimize plasma protein adsorption and render them less susceptible to clearance
by the macrophages [4]. The polymer can also provide a platform for the attach-
ment of targeting ligands which are crucial for site- specifi c targeting required for
imaging, drug delivery, and hyperthermia applications.
The discussion of magnetic core-polymer shell nanoparticles synthesis will be
divided into subsections focusing on the different methods of preparation. The
techniques described here apply to the synthesis of single magnetic nanoparticles
with polymeric shells. It should be noted that polymer-coated MNPs are commer-
cially available as magnetic resonance contrast agents (e.g., Feridex, Endorem,
Resovist); these products are primarily coated with dextran or dextran derivatives,
and their specifi c preparation methods will not be described here.
10.3.1
Coating with Polymer During MNP Synthesis
10.3.1.1
Dextran - Coated MNP s via the Coprecipitation Method
As noted in Section 10.2, MNPs with polymer coatings may be prepared
in situ
during the nucleation and growth of the Fe
3
O
4
. This simultaneous process is often
referred to as the “one-pot” method. One of the earliest studies using such a tech-
nique was that conducted by Molday and MacKenzie [9] who, reacted ferrous
chloride with ferric chloride under alkaline condition in the presence of dextran
