Biomedical Engineering Reference
In-Depth Information
soluble SWNTs. To conirm this hypothesis, the intracellular Ca
2+
levels in
cultured individual neurons were monitored. The experiments involved
depolarisation of neurons via HiK
+
-induced intracellular Ca
2+
accumulation
in neurons. PEG-functionalised SWNTs were found to provoke a reduction of
the intracellular Ca
2+
accumulation in a dose-dependent manner. Therefore,
the SWNT-PEG copolymer could act as blocker of Ca
2+
channels by inhibiting
the depolarisation-dependent inlux of Ca
2+
. Evidence that CNTs can affect
the function of ion channels, such as potassium channels, has already been
reported.
16
The inluence of the electrical conductivity of CNT ilms on the neuronal
growth characteristics was recently studied by Haddon and coworkers.
17
The CNT ilms were prepared by spraying an aqueous dispersion of SWNT-
PEG with an airbrush onto glass coverslips heated at 160 °C. The electrical
conductivity was controlled by varying the thickness of the nanotube
ilm. Hippocampal rat neurons were then cultured on these substrates.
The positive calcein labelling of cells was indicative of cell viability. By
comparison with PEI-coated coverslips used as control, the total outgrowth
of each neuron (i.e., summed length of all processes and their branches) was
superior in neurons grown on the 10 nm thick SWNT-PEG ilms. However,
other parameters of neuronal growth such as the total number of processes
and neurites originating from the cell body were unchanged for each neuron.
In addition, by increasing the nanotube ilm thickness to 30 and 60 nm, thus
allowing for higher conductivity, these effects disappeared since the neurite
outgrowth was unaffected.
In summary, Haddon
et al.
demonstrated that SWNT-based substrates,
having a narrow range of electrical conductivity, supported neurite
outgrowth, with a decrease in the number of growth cones but an increase in
cell body area.
Other research groups also reported the use of CNTs as substrate for
neuronal growth. Shimizu
et al.
functionalised MWNTs with neurotrophins
(a family of proteins that induce survival, development and functions of
neurons), in particular with a nerve growth factor (NGF) or brain-derived
neurotrophic factor (BDNF).
18
The aim of this study was to regulate the
differentiation and survival of neurons.
Neurotrophins are key proteins for the differential function of neurons.
They are endogenous soluble proteins regulating the survival,
19
growth and
function
20
of neurons. Neurotrophins belong to a class of growth factors,
secreted proteins, which are capable of signalling particular cells to survive,
differentiate or grow.
21
They may stimulate the synthesis of proteins in
either axonal or dendritic compartments, thus allowing synapses to exert
local control over the complement of proteins expressed at individual
synaptic sites.
22
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