BIOMEDICAL APPLICATIONS V: INFLUENCE OF CARBON NANOTUBES IN NEURONAL LIVING NETWORKS - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 167

Neural network activity was investigated using single-cell patch-clamp
recordings. The frequency of spontaneous postsynaptic currents (PSCs) of
neurons deposited on the glass coverslips covered with MWNTs displayed
a sixfold increase in comparison with the control substrate constituted of
hippocampal neurons seeded directly on glass coverslips. The generation
of PSCs was indicative of functional synapse formation. However, the height
and half-width of action potentials of the neurons grown on both substrates
were not signiicantly different. In addition, other electrophysiological
characteristics of the neurons grown on the MWNT-coated substrates were
nearly similar to those grown on the control substrate, in particular the resting
membrane potential, input resistance and capacitance values. In summary,
puriied MWNTs obtained via a functionalisation/defunctionalisation
sequence were demonstrated to be suitable growth surfaces for neurons.
They boosted neuronal electrical signalling by promoting an increase in the
eficacy of neuronal signal transmission. The authors pointed out that this
effect was not attributable to differences in neuronal survival, morphology or
passive membrane properties, but that it possibly represented a consequence
of the properties of the SWNT substrates.
Pappas et al. also examined the use of functionalised SWNTs as substrate
for neuronal attachment and growth. 55 They demonstrated that neurons
were electrically coupled to SWNTs. Using the diazonium salt approach 56
SWNTs were functionalised to introduce 4-benzoic acid or 4- tert -butylphenyl
functional groups on the nanotube surface. Transparent, conductive SWNT-
polyethylene terephthalate (PET) ilms were prepared via pre-dispersion of
the SWNTs in water by using 1% SDS. As already reported, 46 neuroblastoma
× glioma NG108 was used as model of neuronal cell. The highest cell growth
and neurite extension of NG108 occurred on unmodiied SWNT substrates,
with decreasing growth on 4- tert -butylphenyl SWNT and 4-benzoic acid
SWNT substrates. The neuronal cells were viable according to the vital
dye calcein test. On the basis of acute attachment assays, SWNT substrates
were found to display a more dramatic effect on cell attachment than on cell
proliferation. It should be noted that cell adhesion is critical for cell survival.
In fact, functional groups on the nanotube surface inhibited cell attachment.
These results support those obtained by Haddon and coworkers on the
inluence of the surface charge of CNTs on neurite outgrowth where negatively
charged functional groups at physiological pH or pristine MWNTs induced a
reduction of the neurite outgrowth, in comparison with positively charged
substrates. 11 The neuronal cells were then electrically stimulated through the
SWNT-PET substrates. NG108 and rat primary peripheral neurons showed
robust voltage-activated currents. These results suggested that CNTs can be
a physiologically compatible substrate to be incorporated into devices for
electrical stimulation of neurons.