Biomedical Engineering Reference
In-Depth Information
processes, branching in many directions on the surface. The SWNT ilms
exhibited a suficiently high electrical conductivity to electrically stimulate
signiicant ion conductance in excitable neuronal cells that were electrically
coupled to the SWNTs. The direction of the electrophysiological response
suggested that cells were stimulated by the inlux of cations in the cells.
Kotov
et al.
described that mouse cortical neural stem cells (NSCs) can
differentiate to neurons, astrocytes and oligodendrocytes with formation
of neurites on SWNT-based composite thin ilms.
48
Note that NSCs are well
known for their sensitivity to the environment.
The SWNT-polymer composite thin ilms were prepared by LBL assembly
of six bilayers of SWNT-PEI [(PEI/SWNT)
6
]. SWNTs were irst dispersed in
a 1 wt% poly(sodium 4-styrene-sulphonate) solution and then assembled
using LBL technique with PEI as polyelectrolyte. Mouse embryonic 14-day
neurospheres (i.e., spherical clonal structures of NSCs) from the cortex
were seen to attach to the SWNT-polyelectrolyte ilm substrates and to
differentiate, in a similar manner to poly--ornithine (PLO)-coated substrates
used as control. PLO is a standard substrate widely used for NSC cultures
as it is known to alter the surface charge, thus providing a more suitable
substrate for the negatively charged neurons.
27
The viability of neurospheres
determined using the MTT assay was found to be similar on (PEI/SWNT)
6
-
and PLO-coated substrates. In addition, both types of substrates supported
differentiation of neurospheres into the three primary neural cell types:
neurons, astrocytes and oligodendrocytes, according to immunostaining
experiments. Indeed, to analyse the differentiated phenotypes, neurospheres
were immunostained with antinestin-, antimicrotubule-associated protein
2 (anti-MAP2), antiglial ibrillary acidic protein (anti-GFAP) and anti-
oligodendrocyte marker O4 (anti-O4). Thus, NSCs grown on LBL-assembled
SWNT-polyelectrolyte composite ilms behaved similarly to NSCs cultured on
PLO substrates in terms of biocompatility, neurite outgrowth and expression
of neuronal markers.
In summary, this study is the irst demonstration of the differentiation
of environment-sensitive NSCs on a CNT-composite thin ilm. The results
are promising for further development of CNTs for neural interfaces as
the CNT-based substrate is able to promote cell viability and to induce the
development of neuronal processes, as well as the appearance and progression
of neural markers.
Further studies were conducted by Kotov and coworkers on the electrical
stimulation of NSCs by the SWNT composite constituted of laminin.
49
LBL ilms (up to 30 bilayers) were prepared from SWNTs wrapped
with poly(styrene-4-sulphonate) and laminin, a glycoprotein which is an
important protein in the basement membrane. Laminin is commonly used to
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