Biomedical Engineering Reference
In-Depth Information
OH
+
H
2
N
NH
O
O
Carboxyl-functionalized
magnetic particle
Antibody
Figure 7.6
The amine-carboxylic acid coupling strategy for
binding antibody onto magnetic nanoparticles.
In order to improve the biocompatibility of magnetic nanoparticles, most of
these particles are coated with materials such as carbohydrate, peptides, synthetic
polymers, or inorganic materials (e.g., gold, silica) [38]. Besides, these coating
materials also provide a platform for building organic functionalities on the surface
of the magnetic nanoparticles.
7.3.1.2
Functionalization of Magnetic Nanoparticles
In order to target the receptors on the cell membrane, specific antibodies are bound
on the surface of the nanoparticles. Therefore, nanoparticles with the optimal
surface properties are essential for the stimulation of cells. Typically, nanoparticles
with amine or carboxylic acid groups are used for binding antibodies, as well
as other protein molecules. This is because a simple chemical coupling reaction
canbeappliedbyforminganamidebondbetweentheparticleandtheantibody
molecule (see Figure 7.6).
However, using this procedure, antibody molecules are bound in random
orientation, and therefore some may not be able to target the receptor. The
use of a secondary antibody has been proposed [39]. Although this would ensure
that the antibodies are at the right orientation, the overall size of the particles will
increase and the whole binding procedure becomes very complicated.
7.3.2
Magnetic Stimulation
In general, there are twomain categories for this technique of magnetic stimulation:
magnetic pulling and magnetic twisting cytometry (MTC).
7.3.2.1
Magnetic Pulling
In the mid-1990s, Glogauers and coworkers started to study the effect of an external
magnetic field, generated by a permanent magnet, on cells loaded with iron oxide
magnetic micro- or nanoparticles [40, 41]. In this study, the particles were attached
to integrin receptors on the surface of fibroblast cells. To do that, the magnetic
particles were coated with collagen. Studies using electromagnets have also been
reviewed [42] but this approach is less popular due to the heat generated by the
electromagnet. Such heat may cause uncertainty in cell activities or even damages
on cells. Whether it is a permanent magnet or electromagnet, the principle is to
provide a magnetic field with a high gradient to pull the magnetic particles in a
