BIOMEDICAL APPLICATIONS V: INFLUENCE OF CARBON NANOTUBES IN NEURONAL LIVING NETWORKS - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 151

was not inluenced by MWNTs. Scanning electron microscopy (SEM) was used
to identify the morphological changes of the neurons grown on the MWNT
substrate. Neurons were seen to be attached to the pristine MWNTs while
extending one or two neurites. Interestingly, when neurites grew across the
MWNTs and then on the glass coverslips coated with PEI, the neurites formed
branches on the coverslips but not on the MWNTs. Therefore, the pristine
MWNTs did not promote neurite branching, indicating a relatively weak
adhesion of growth cones to the surface of non-functionalised nanotubes.
This observation suggested that pristine MWNTs were not a suitable support
for branch formation. Nevertheless, MWNTs coated with 4-HNE had more
and longer neurites (Fig. 6.2). Both neurite outgrowth and branching were
enhanced in this case.
Figure 6.2 SEM images of neurons grown for three days on CNTs coated with 4-HNE.
The right image is a high magniication of the neurite designated by the black arrow
in the left image. Scale bars: left image, 5 μm; right image, 100 nm. Reproduced from
Mattson et al . 5 with permission.
The authors pointed out that the enhanced adhesion of growth cones to
the MWNTs could be favoured by the presence of 4-HNE that could possibly
induce changes in intracellular Ca 2+ levels. Indeed, Ca 2+ inlux can regulate
growth cone motility and neurite elongation. 10
Further studies were conducted by Haddon et al. , and they used MWNTs
functionalised with molecules bearing different electrostatic charges to
study neuronal growth. 11 The results showed that the neurite outgrowth was
controlled by the surface charge of MWNTs.
Three types of functionalised MWNTs were designed to carry negative,
neutral or positive charges at physiological pH. The approach relied on