Biomedical Engineering Reference
In-Depth Information
magnetic fi elds and enable the noninvasive control of various cellular functions.
Although this method was fi rst described during the 1950s by Francis Crick [9], it
was not studied further until the 1980s by Valberg and others [10-15]. Based on
these earlier fi ndings, Ning Wang and Donald Ingber developed the technique of
“ magnetic twisting cytometry ” ( MTC ). By coating magnetic microparticles with
ligands targeted at different receptors on the cell surface, and then applying and
measuring the magnetic fi elds required to “twist” the magnetically blocked par-
ticles, it was possible to study the mechanical linkage between the cell membrane
receptor and the cytoskeletal network [16]. Since then, basic scientifi c experiments
have been performed on a variety of cell types using different particles and coat-
ings to investigate mechanotransduction [17 - 25] .
In addition to twisting magnetically blocked microparticles and nanoparticles,
it is also possible to “pull” the particles towards a magnetic fi eld source, provided
that there is a gradient to the fi eld [2]. Magnetic nanoparticles will be attracted to
such a fi eld according to the equation:
1
(
)
F
=−
χχ
V
B
(
∇
B
)
(8.1)
mag
2
1
μ
0
where
F
mag
is the force on the magnetic particle,
χ
2
is the volume magnetic sus-
ceptibility of the magnetic particle,
χ
1
is the volume magnetic susceptibility of the
surrounding medium,
o
is the magnetic permeability of free space,
V
is the par-
ticle volume,
B
is the magnetic fl ux density in Tesla (T),
μ
∇
B
is fi eld gradient, which
can be reduced to
z
.
This attractive force (sometimes in combination with torque), when applied to
magnetic nanoparticles which are attached in some way to cell membrane recep-
tors or cellular components, presents opportunities to employ magnetic actuation
in a way that may be used to control specifi c cellular processes (Figure 8.1).
It is well established that mechanical forces infl uence cellular function, most
likely through their effects on mechanosensitive ion channels. The differentiation
∂
B
/
∂
x
,
∂
B
/
∂
y
,
∂
B
/
∂
B
B
B
=0
(a)
(b)
B
=0
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Figure 8.1
Schematic representation of magnetic
nanoparticle-based ion channel activation. (a) By general
membrane stretch/deformation; (b) By targeted ion channel
attachment and actuation. Figure adapted from Ref. [8].
