Biomedical Engineering Reference
In-Depth Information
from the surrounding environment.
165
The coating can be functionalized by
attaching antibodies, biotin, avidin, streptavidin, protein G, and other mol-
ecules.
4,15-17,131,132,165
Depending upon the molecule on the IOMNP surface,
drugs, receptors, proteins, or nucleic acids can be coupled on the surface for
various medical applications.
The various medical applications of IOMNPs include drug delivery, cellular
labeling/cell separation, tissue repair, magnetic resonance imaging, magnetic
hyperthermia and magnetofection.
4,15-17,160-163,165-174
These medical applica-
tions will ultimately involve humans or other animals, it is imperative to study
toxicity of IOMNPs in appropriate models. A list of commercially available
IOMNPs is given in
Table 8.4
.
The most important considerations in the successful applications of IOM-
NPs in medicine are their biocompatibility and toxicity. Various parameters
to evaluate biocompatibility that include the size of the core and the coatings
(shell), stability, and surface modification. For efficient applications, the IOMNPs
must exhibit high magnetization in order for their translocation in a living sys-
tem to be controlled as close as necessary to the targeted pathologic tissue with
an external magnetic field.
175
The other important consideration for the IOMNPs for medical applica-
tions is internalization into specific cells or cell uptake which may be compro-
mised by (a) short blood half-life of the NPs, (b) non-specific targeting, and
(c) low cell internalization efficiency.
176
Different studies have been reported
on the control of the size and surface properties of IOMNPs to improve these
areas.
165,170,177
The most common molecules used for stabilizing IOMPNs are
surfactants such as oleic acid, lauric acid, alkane sulphonic acids, and alkane
phosphonic acids.
178
A method to prepare hydrophobic IOMNPs is the use of
alpha-cyclodextrin by host-guest interactions making the NMs able to disperse
from organic to aqueous solution.
173
This is also achieved by using an amphiphi-
lic polymer shell
179
such as poly (ethylene-co-vinyl acetate), polyvinylpyrrol-
idone (PVP), polylactic-co-glycolic acid (PLGA), polyethylene glycol (PEG),
or polyvinyl alcohol (PVA) have also been used as coating materials in aqueous
suspension.
174
The IOMNPs are coated with these amphiphilic polymers that
introduce amines or carboxyl groups creating an internal hydrophobic structure
enveloping the organic soluble iron oxide core and a hydrophilic outer layer
making the IOMNPs water soluble. Other materials such as gelatin, dextran,
polylactic acids, starch, albumin, liposomes, chitosan, and ethyl cellulose have
been used in modifying IOMNPs for drug delivery.
Although iron oxide particles are known to be non-toxic, some of the coating
materials used to make them water soluble could be toxic. For instance, silica
is known to be biocompatible but not biodegradable.
165
Amorphous silica coat-
ing on magnetite NMs that results in silica-coated core-shell particles when
dispersed in aqueous suspensions showed negative charge above the isoelectric
point of silica which is at pH ~ 2.
171
The interactions of IOMNPs with biologi-
cal fluids can lead to increased formation of free hydroxyl radicals and reactive
