BIOMEDICAL APPLICATIONS V: INFLUENCE OF CARBON NANOTUBES IN NEURONAL LIVING NETWORKS - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 160

displayed a normal shape. Thus, this study allowed for the formation of
neuronal networks having a normal functionality with pre-deined geometry
due to growth on substrates patterned with CNT islands.
An original method to pattern cultured neuronal networks was reported
by Hanein et al . and was based on the anchoring of neuronal cell clusters
constituted of tens of cells. 39 The anchors aimed at stabilising the neuronal
cell clusters were CNTs or the strong adhesive substrate poly--lysine. The
dynamics of the real-time network formation was monitored by placing
cultures in an environmental chamber under a microscope. The cell
clusters were seen to self-organise by moving away from each other and
bridging gaps with concomitant formation of a neurite bundle between
neighbouring clusters.
Hanein et al. also fabricated CNT-based electrodes by synthesising high-
density CNT islands using CVD on a lithographically deined substrate. 40 A
mixture of cortical neuron and glial cells from rats were plated and cultured
on the surface of the CNT electrode chip. The CNT islands acted as adhesion
agents because of the substrate's roughness, thus favouring the migration
and adhesion of cells onto the electrode surface. High-idelity extracellular
recordings from cultured neuronal cells were then performed. A typical
extracellular signal was obtained with a shape that relected the irst derivative
of the intracellular action potential signal. The signal-to-noise ratio was high
compared with that of a conventional TiN electrode.
It should be noted that one advantage of the CNT electrodes developed
by Hanein et al. over standard microelectrodes is the cell-adhesive nature
of the nanotubes. Neuronal proliferation can thus be induced without
the need for additional adhesion, thereby promoting coating spread
between the electrodes.
Electrical stimulation of primary neurons was reported by Wang and
coworkers, who used vertically aligned MWNTs as microelectrodes. 41
Lithographic patterning of the catalyst allowed the control of the size
and location of the MWNT pillars. The MWNT-based microelectrode was
constituted of individual MWNTs having a diameter in the 30-50 nm range
and separated by a distance of the order of tens of nanometres. The CNT
electrode was 40 μm tall and was made more hydrophilic by coating with
an amphiphilic PEG-lipid conjugate. Non-covalent binding of the PEG-lipid
conjugate allowed for the preservation of the electronic properties of the CNTs.
The MWNT MEA was coated with poly--lysine to favour cell adhesion to the
nanotube substrates. Embryonic rat hippocampal neurons were deposited
on the MWNT microelectrode and were shown to grow and differentiate.
The viability and neurite outgrowth were comparable to those of cultures on
plastic Petri dish controls. The neurons were then electrically stimulated by