Biomedical Engineering Reference
In-Depth Information
For instance, Ozkan
et al.
demonstrated the formation of directed neurite
growth on patterned, vertically aligned MWNTs.
35
Different substrate
geometries and nanotube heights were investigated for their ability to induce
guided neuronal growth. Vertical MWNT arrays were functionalised with
growth adherents that promote neuron adhesion and viability. In particular,
the MWNTs were coated with a growth adherent, poly--lysine (PLL), which
is known to enhance adhesion of neurons by altering surface charges on the
culture substrate.
36
Hippocampal rat cells were cultured on patterns of short
(500 nm high) and long (10 μm high) vertical MWNTs. Preferential directed
growth of neurons was observed over the long MWNT array, but not over the
short MWNT array. Indeed, in the latter case, neurons were seen to grow both
on the short MWNT pattern and on the silicon chip, with no selection of one
of the two types of substrate. On the contrary, in the former case, neurons
showed preferential growth along the MWNT array, although the substrate
was covered with PLL. The authors pointed out that the difference observed
in terms of scaffolding capability between the short and long MWNT arrays
could stem from the lexibility of the CNTs, which depends on the nanotube
length. Indeed, to allow proliferation of neurites, the long MWNTs were found
to undergo deformation, as observed by SEM. This deformation resulted from
the extending neurite that interacted with the edges of the MWNT patterns.
The neuronal cell networks were found to be viable after they were stained
with Fluo-3 calcium. This luorescent dye binds to the intracellular free
calcium ions, which in principle are in high concentration in the cytoplasm
of viable neuronal cells. The results of this study highlight the potential
applications of long MWNT array substrates for the development of three-
dimensional scaffolds suitable for implants.
Hanein and coworkers published a review on the development of CNT-
based MEAs for neuronal interfacing and network engineering applications.
37
They also described the use of CNT patterns as substrate for neuronal
growth.
38
The CNT templates on which neurons adhered and assembled were
fabricated by photolithography and microcontact printing. The deposition of
iron nanoparticles on hydrophilic silicon dioxide or quartz substrates was
controlled to allow the growth of regular arrays of CNT islands using CVD.
During this process, long CNTs (on the order of 100 μm) can thermally fluctuate
and may bind to other nanotubes to form a three-dimensional, entangled
network. Neurons and glial cells were then deposited on the patterned
quartz substrates. After four days' incubation, neurons were seen to adhere
to and grow on the region of the substrate containing CNTs. Interconnections
between neighbouring islands were also observed because of the formation
of axons and dendrites. The electrical viability of the neuronal networks was
then tested and the action potential, generated by electrical stimulations,
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