Biomedical Engineering Reference
In-Depth Information
implemented in order to explore the controversial aspect of carbon nanotube
toxicity, which manifests itself due to carbon nanotubes blocking ion channels
in the membrane, causing increased cell oxidative stress, reduced cell adhesion,
or apoptosis.
A recent improvement in such prosthetic medical devices involved growing
carbon nanotubes on a biocompatible Pt catalyst.
21
The new material shows
less cellular degeneration due to oxidative stress as the main product of the Pt
catalyzed oxygen reduction is water. This is ideal for guiding the axon regen-
eration through tubes made of materials such as chitosan, a biocompatible and
biodegradable natural material that can provide, as a gel sponge, a suitable
scaffold for nerve regeneration.
d
n
4
t
3
n
g
|
0
4.4.2 Nanoribbons for Sensing Cellular Deformation
Although the electrical response of neurons to applied voltage has been studied
extensively, mechanical response has been largely ignored, even if it might
advance the studies on cellular function and physiology, especially in the area
of axon elongation and dendritic formation. Using piezoelectric nanoribbons
made of PbZr or Ti
1-x
O
3
, it was found that the cells deflect by 1 nm when 120
mV is applied to the cell membrane. Such depolarization induces changes in the
membrane tension so that it is accommodating the stimulus by equalizing the
overall pressure across the membrane through a process resembling converse
flexoelectricity.
22
Figure 4.8 shows piezoelectric nanoribbons suspended over a trench as
nanobeams to maximize deflection. The use of an underlying substrate of
transparent MgO as well as transparent indium tin oxide (ITO) electrodes
facilitates backside chip visualization during electrophysiology measurements.
The electrodes are electrically isolated by a coating of SiN
x
to ensure no cross-
signal response when the chip is placed into solution. PC12 cells were cultured on
the piezoelectric chip, and those cells located on the nanobeam arrays were patch-
clamped with a standard glass electrode for membrane voltage stimulation.
n
3
.
4.5 Challenges and Future Perspective of
Nanotechnologies in Neuroscience
It is not clear how neurons interact with nanostructures, why they continue to
function when impaled by nanospears from all directions and how they heal
when confined in nanoscaffolds. Reports on the toxicity of nanomaterials are
extremely controversial. However, if any such undesirable effect can be
minimized and these new materials can contribute to brain regeneration and
repair, the outcome might be a positive one for the future. Like the minia-
turized submarine crew in the 1966 movie Fantastic Voyage, smart nanodevices
may one day be sent beyond the blood-brain barrier to perform lifesaving
surgery inside the brain tissue and to destroy cancerous brain tumors with
extreme precision and in a minimally invasive mode, by delivering the necessary
drug and then leaving the body in a harmless way. It would represent a less
