BIOMEDICAL APPLICATIONS V: INFLUENCE OF CARBON NANOTUBES IN NEURONAL LIVING NETWORKS - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 156

MWNTs were irst oxidised using a mixture of sulphuric acid and nitric
acid. Diaminoalkyl compounds were then introduced on the resulting MWNT-
COOH via amidation. Neurotrophin was covalently bound to the resulting
amino-modiied MWNTs using a carbodiimide reagent. The inluence of
neurotrophin-functionalised MWNTs on the neurite outgrowth of embryonic
chick dorsal root ganglion neurons was then examined. These MWNTs were
found to promote the neurite outgrowth of dissociated neurons, in a similar
manner to soluble NGF and BDNF, while the amino-terminated MWNTs did
not promote neurite outgrowth.
Romero and coworkers reported the preparation of strong and highly
electrically conducting semi-transparent sheets and yarns from pristine
MWNTs. 23
The CNT sheets were fabricated by drawing the CNTs from a sidewall of an
MWNT forest produced by chemical vapour deposition (CVD). The thickness
of the CNT sheet was approximately 50 nm. The CNT yarn was then prepared
by spinning the sheet. 24 The authors demonstrated that the CNT sheets were
permissive substrates for primary central and peripheral neuronal culture.
Indeed, the results indicated that the CNT substrates were able to promote cell
attachment and differentiation of a variety of cell types, including cerebellar
and sensory dorsal root ganglion neurons, and to support their long-term
growth at a similar level to that achieved on PLO-coated glass substrates used
in this study for comparison. The neuronal phenotype was demonstrated by
immunoluorescence using β -tubulin, 25 which is a speciic neuronal marker.
In addition, the extension of neuronal axon growth cones was enhanced.
Neurons from murine cerebellum and cerebral cortex, which are usually more
sensitive to the substrate and the environment for survival and growth, were
used too. Also in this case, the neurons were able to dissociate and extend
their neurites onto the CNT sheets, as they did similarly onto PLO-coated
glass substrates. 26 Thus, contrary to previous studies reporting that axonal
growth is limited on pristine CNTs, 5,11 neurons were shown here to grow on
pristine CNT sheets and to extend their neurites with similar characteristics
(number and length) than those grown on PLO-treated glass substrates.
Furthermore, the authors demonstrated that the neuronal growth could
be directed by CNT yarns. Neonatal dorsal root ganglion neuron explants
were prepared by wrapping a single CNT yarn around the ganglia, where
the free end suspended in culture media. The sensory neurons adhered and
extended along the CNT yarn by intimately following the surface topography
of the CNT substrate.
In summary, directionally oriented pristine CNTs conigured as sheets or
yarns were demonstrated to be viable substrates for neuronal growth.
Lu et al. recently reported that thin-film scaffolds constituted of a
biocompatible polymer grafted on CNTs can promote neuron differentiation
from human embryonic stem cells (hESCs). 27