Biomedical Engineering Reference
In-Depth Information
characteristics of mammalian nerve cells. After long-term incubation (up to
10 days) the cells grew and proliferated on the surface of the SWNT ilms. The
neuronal cells were viable, as illustrated by their continuous intracellular
esterase activity, which is determined by the enzymatic conversion of the
non-luorescent cell-permeant calcein dye. The neuronal outgrowth of the
NG108-15 cells on the surface of the SWNT ilms was compared with that
of the cells on a control culture dish. Neurons were observed by SEM, and
their morphology was assessed by cell labelling with the neuronal lipophilic
tracer dialkylcarbocyanine. This dye has the capacity to diffuse through the
membrane of cells and to trace along their neurites in order to monitor the
surface morphology and growth of neurons. On the substrate comprising
SWNTs, many elongated neuronal processes were observed with extension
of neurites. Many secondary neurites and elaborated branches were grown
from these neurites. Interestingly, many processes were seen to start from
the neurites and to terminate at the surface of the SWNT ilm.
Free-standing SWNT membranes were then prepared in order to be used
as scaffold for neuronal growth and differentiation. The preparation involved
the etching of an SWNT ilm from the surface of a glass substrate using HF
and the subsequent rolling into a small elongated thread-like sample. The
free-standing ilms showed a tensile strength that was suficient for soft
neural implants. It is noteworthy that the ionic conductivity of these free-
standing ilms is brought about by its polyelectrolyte nature. This is essential
for the interaction with ionic luxes through neuron membrane. Adhesion
and differentiation of NG108-15 cells were seen to be similar to those of
SWNT ilms on solid supports. The neurite extension closely followed the
morphological shape and curvature of the surface of the free-standing ilms.
In summary, SWNT composite thin ilms prepared by LBL and resulting
free-standing ilms can support growth, viability and differentiation of
NG108-15 neuroblastoma/glioma hybrid cells. The free-standing SWNT/
polymer composite thin ilm membranes were found to guide the outgrowth
of neurites. The combination of different properties, including lexibility,
inertness, non-biodegradability and durability, allows us to envisage some
applications. For instance, the free-standing ilms could potentially be
integrated into extracellular implants for cell stimulation and pain control
and into neuroprosthetic devices for neuronal injuries.
Kotov and coworkers also reported the stimulation of the neurophysiological
activity of NG108-15 cells grown on LBL-assembled SWNT-polymer composite
ilms. 47 The LBL SWNT conductive ilms were prepared from positively charged
SWNTs coated with a copolymer, poly(acrylic acid), and were made of 30
multilayers. The NG108-15 cells differentiated and extended long neurites on
the surface of the SWNT ilms. The neurites developed into many secondary
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