Biomedical Engineering Reference
In-Depth Information
the MWNT electrode. The calcium indicator Fluo-4 allowed for the detection
of action potentials by observation of intracellular Ca
2+
level change. Fluo-4
can be loaded into cells and exhibits a large increase in luorescence intensity
on binding free Ca
2+
. It was also demonstrated that the neurons could be
stimulated repeatedly with the MWNT electrode, thus highlighting the long-
term endurance of the MWNT electrode.
Recently, Hanein and coworkers investigated the neurite-CNT interactions
at the nanoscale and elucidated the nature of the interface between neurons
and CNTs.
42
Process entanglement was explained as a neuronal anchorage
mechanism to CNT-based surfaces.
In this study, isolated islands of pristine CNTs were fabricated and plated
with cells (mammalian cortex neurons from rats and insect ganglion cells
from locusts). The arrangement of neurons and glial cells on CNT-based
surfaces was characterised by high-resolution scanning electron microscopy
(HRSEM), immunostaining and confocal microscopy. The neurons and cells
were found to preferentially adhere to CNT islands and extend towards their
periphery. This is in agreement with previous reports that have demonstrated
preferential adhesion to rough surfaces.
39-41
The processes at the periphery
of the CNT islands were curled and entangled, thus leading to enhanced
interactions with the CNT surface that facilitated their anchorage. However,
the processes that appeared too thick to interact with CNTs had the tendency
to intertwine. Therefore, Hanein
et al.
pointed out that the roughness of the
surface must match the diameter of the neuronal processes to help them
anchor. The authors also suggested that adhesion of neuronal cells was in part
achieved through an entanglement process. This mechanical effect may thus
contribute to the mechanism by which neurons adhere to rough surfaces.
Recently, Hanein
et al.
also investigated the use of CNT MEAs as an
interface material for retinal recording and stimulation applications.
43
Electrodes were coated via CVD of CNTs, and electrical stimulation
of retinal cells was achieved. The signals obtained with the CNT-based
electrodes showed a remarkably high signal-to-noise ratio during recordings
in comparison with commercial TiN electrodes. This would be particularly
interesting for long-term
in vivo
implantation of electrodes. In addition, the
authors observed an increase of the signal amplitude over several hours of
recording. These results were indicative of an improved electrode-tissue
coupling of CNT-based electrodes compared with conventional commercial
electrodes. This is consistent with previous studies reported by Wang and
coworkers, who validated the effectiveness of CNT electrodes for stimulation
applications.
42
In summary, this work showed that CNT MEAs provide exceptional
electrochemical and adhesive properties. This demonstrates the great
potential of CNT-based electrodes for retinal implant applications.
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