Biomedical Engineering Reference
In-Depth Information
[113, 114], in a rat stroke model in which carbon nanotubes were implanted
[115]. One hypothesis why carbon nanotubes induced neuronal cell differen-
tiation is the conductivity of carbon nanotubes and their ability to adsorb laminin
[113]. An in vitro brain circuit model has confirmed the relationship between
electrical signal transfer and synaptic stimulation of carbon nanotubes and
neurons [116]. According to the highly conductive and unique surface energy
properties of carbon nanotubes, a novel application of carbon nanotubes is to
improve electronic nerve interfaces.
An electronic nerve interface device is an `artificial nerve' usually employing
electrodes to connect with and stimulate host nerves to treat neurological
disorders (like chronic spinal cord injury) or improve life quality (like enhancing
visual ability or memory). Because electronic tissue interface devices send and
receive electrical signals from the nervous tissues via an array of electrodes
usually composed of platinum, silicon or silicon rubber, electrode arrays are
important to device functions. The lifetime of these devices depend on the
stability of the electrode array and the effect and signal quality of such devices
depends on the efficiency of single transfer between electrode arrays and host
nerves. Electrodes often fail to perform over time due to the accumulation and
growth of astrocytes (glial scar tissue forming cells) and neuronal cell death
around the electrodes or electrochemical reactions at the interface causing
toxicity [117]. A reliable electrode recording requires not only the stability of
the electrode itself (reduction of electrochemical degradation and dielectric layer
growth) but also favorable cell responses (such as the stimulation of neurons and
inhibition of glia) [118]. Again, nanotechnology can help to improve such
`artificial nerve' implant cytocompatibility and electrical functions. Because of
their chemical stability, low resistance and high charge capacitance, carbon
nanotubes are promising materials for electrodes or as electrode coatings
[119, 120]. A study has shown that carbon nanotubes possess excellent cyto-
compatibility properties and inhibit functions of astrocytes, which could increase
the lifetime of electrodes [121]. Nanotechnology also has numerous advantages
to allow engineers to design a miniature electrode array with thousands of tiny
electrodes to obtain better signal quality and transfer. BrainGate Technology has
tried to produce `tiny' electrode arrays (Fig. 9.16). It produced an electrode array
down to micrometer level which was placed on the primary motor surface cortex
and penetrated into the intermediate layers for a computer±brain interface to
control prosthetic limbs. A more recent report has made the electrode even
smaller (nanometer level) to control cell to cell interfaces, as shown in Fig. 9.17.
Although the activity recorded so far is only from single cells and only after
chemical stimulation (neither spontaneous activity nor signal propagation), it is
promising to explore the link between a single cell (even cellular features) and
an electrode for highly sensitive interfacing applications [122].
In summary, nanotechnology is able to improve drug delivery through the
blood±brain barrier, induce neuron differentiation and function and increase the
