Biomedical Engineering Reference
In-Depth Information
and can dissolve inorganic compounds. In addition, due to their relatively high
boiling points, they offer a wide operating-temperature range for preparing inor-
ganic compounds. Polyols also serve as reducing agents as well as stabilizers to
control particle growth and prevent interparticle aggregation (Laurent et al.
2008
).
Non-aggregated magnetite nanoparticles (7 nm in diameter) were synthesized dur-
ing the reaction of triethylene glycol with Fe(acac)
3
at an elevated temperature (Cai
and Wan
2007
).
Recently a novel synthesis of magnetite nanoparticles based on a flow injection
synthesis (FIS) technique has been developed. The technique consists of continuous
or segmented mixing of reagents under laminar flow regime in a capillary reactor.
The FIS technique has shown some advantages, such as a high reproducibility
because of the plug-flow and laminar conditions, a high mixing homogeneity, and
an opportunity for a precise external control of the process. The obtained magnetite
nanoparticles had a narrow size distribution in the range of 2-7 nm (Laurent et al.
2008
; Salazar-Alvarez et al.
2006
).
Spray and laser pyrolysis, typical representatives of aerosol technologies, are
continuous chemical processes allowing for high rate production of nanoparticles.
In spray pyrolysis, a solution of ferric salts and a reducing agent in organic solvent
is sprayed into a series of reactors, where the aerosol solute condenses and the
solvent evaporates. The resulting dried residue consists of particles whose size
depends upon the initial size of the original droplets. Maghemite particles with size
ranging from 5 to 60 nm with different shapes have been obtained using different
iron precursor salts in alcoholic solution (Laurent et al.
2008
).
A wide variety of chemical reactions accelerated by microwave irradiation of
reactants have been observed. Recently a simple, quick and cost effective micro-
wave method to prepare relatively uniform magnetite nanoparticles (80 ± 5 nm)
directly from Fe
2+
salts has been developed; the formation of magnetic nanoparti-
cles using microwave method requires only a few seconds or minutes. Also magne-
tite nanoparticles doped with silver nanoparticles can be prepared using this
procedure (Zheng et al.
2010
).
Nanosized magnetite powders can also be synthesized via a mechanochemical
reaction. Ball milling of ferrous and ferric chlorides with sodium hydroxide led to
a mixture of magnetite and sodium chloride. To avoid agglomeration, the excess of
NaCl is usually added to the precursor before ball milling. To prepare different size
of particles, the as-milled powders were annealed at temperatures ranging from
100°C to 800°C for 1 h in appropriate atmosphere (Lin et al.
2006
).
3
Stabilization of Magnetic Particles
To obtain biocompatible magnetically responsive materials it is usually necessary
to stabilize the prepared iron oxide nanoparticles by appropriate modification of
their surface or by their incorporation into appropriate biocompatible matrix.
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