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T. Vemulkar and R. P. Cowburn
the nanoparticles that are moving away from the superparamagnetic regime. In the
20 nm and above range for iron oxide nanoparticles, the dominant heating process
is frictional losses with the fluid due to stirring and the particles are no longer superparamagnetic. This is because the magnetic moment of the larger particles cannot be
switched by the field magnitude typically used for hyperthermia [70]. The combination of multiple heating mechanisms, the finite size distribution in nanoparticle
formulations [72] and effects such as anisotropy distributions [73–75] and interparticle dipolar interactions [75, 76] has made a comprehensive theoretical model of
heat losses in magnetic particle systems quite elusive.
15.1.1.4 Mechanical Actuation
While initial work by F. Crick et al. used magnetic nanoparticles to investigate the
microrheology of cell cytoplasm [77], the field has progressed to the point where
functionalized blocked magnetic nanoparticles have been attached to individual integrin receptors on the cell membrane. Using a rotating magnetic field, the blocked
particles applied torque to the cell membrane providing insight into the mechanical
properties of the cytoskeleton [78]. Beyond providing a means to probe mechanical
properties, the mechanical actuation of cells via membrane receptors can have significant downstream consequences [79], going as far as to influence gene transcription
within the cell [80]. The reader will find [35] that provides a thorough overview of
mechanical actuation techniques for cell behavioural modification.
There is also interest in mechanical actuation of cells from a clinical perspective.
An area of interest is the directed mediation of mesenchymal stem cell (MSC) differentiation. MSCs differentiate into the various skeletal tissue structures and are a very
relevant cell type for tissue engineering and regeneration to grow replacement tissue
for a patient. The mechanical loading the cells experience is crucial to the differentiation process [81–83]. Using magnetic nanoparticles to condition cells allows for the
mechanical stimulation of cells without a three-dimensional tissue scaffold which is
important for the tissue engineering post the culture process [82].
Since mechanical forces can stimulate cells, the forces and torques they exert can
also be used to destroy cells by damaging the cytoskeleton [84] or cellular components
[85]. There has been work on using iron oxide nanoparticles to destroy cancer cells,
where spherical- and rod-shaped iron oxide nanoparticles in an oscillating field have
been shown to destroy human cervical cancer cells in vitro [84]. This field, however,
has recently received significant attention when highly effective glioblastoma cell
killing was demonstrated using a new class of magnetic particle [36]—lithographically defined micro- and nanoparticles which will be discussed further on in this
chapter.
T. Vemulkar and R. P. Cowburn
the nanoparticles that are moving away from the superparamagnetic regime. In the
20 nm and above range for iron oxide nanoparticles, the dominant heating process
is frictional losses with the fluid due to stirring and the particles are no longer superparamagnetic. This is because the magnetic moment of the larger particles cannot be
switched by the field magnitude typically used for hyperthermia [70]. The combination of multiple heating mechanisms, the finite size distribution in nanoparticle
formulations [72] and effects such as anisotropy distributions [73–75] and interparticle dipolar interactions [75, 76] has made a comprehensive theoretical model of
heat losses in magnetic particle systems quite elusive.
15.1.1.4 Mechanical Actuation
While initial work by F. Crick et al. used magnetic nanoparticles to investigate the
microrheology of cell cytoplasm [77], the field has progressed to the point where
functionalized blocked magnetic nanoparticles have been attached to individual integrin receptors on the cell membrane. Using a rotating magnetic field, the blocked
particles applied torque to the cell membrane providing insight into the mechanical
properties of the cytoskeleton [78]. Beyond providing a means to probe mechanical
properties, the mechanical actuation of cells via membrane receptors can have significant downstream consequences [79], going as far as to influence gene transcription
within the cell [80]. The reader will find [35] that provides a thorough overview of
mechanical actuation techniques for cell behavioural modification.
There is also interest in mechanical actuation of cells from a clinical perspective.
An area of interest is the directed mediation of mesenchymal stem cell (MSC) differentiation. MSCs differentiate into the various skeletal tissue structures and are a very
relevant cell type for tissue engineering and regeneration to grow replacement tissue
for a patient. The mechanical loading the cells experience is crucial to the differentiation process [81–83]. Using magnetic nanoparticles to condition cells allows for the
mechanical stimulation of cells without a three-dimensional tissue scaffold which is
important for the tissue engineering post the culture process [82].
Since mechanical forces can stimulate cells, the forces and torques they exert can
also be used to destroy cells by damaging the cytoskeleton [84] or cellular components
[85]. There has been work on using iron oxide nanoparticles to destroy cancer cells,
where spherical- and rod-shaped iron oxide nanoparticles in an oscillating field have
been shown to destroy human cervical cancer cells in vitro [84]. This field, however,
has recently received significant attention when highly effective glioblastoma cell
killing was demonstrated using a new class of magnetic particle [36]—lithographically defined micro- and nanoparticles which will be discussed further on in this
chapter.