Biomedical Engineering Reference
In-Depth Information
microelectrode sieve is inserted between the two cut ends of a nerve. 45,46 The
caveats to this design is the diculty in placing the sieve near Ranvier nodes,
which limits the selectivity of recording or stimulation and the crosstalk
between the electrodes of the sieve since they cannot be perfectly insulated from
each other. Despite apparent nerve regeneration, the force in the corresponding
muscle declines by 40%. This observation limits the application of such
interfaces. The problem is attributed to the size of the holes and morphological
changes at the insertion site due to long-term implantation.
To circumvent such diculties, cone-ingrowth electrodes were developed.
A gold wire is inserted in a hollow glass cone filled with nerve growth factor or
another neurotrophic factor. The devices can be implanted for long term in the
brain with remarkably stable activity. Furthermore, multielectrode contacts
can be implanted in the motor areas of the brain in order to control movement
or to develop real-time, electroencephalogram (EEG) based brain-computer
interfaces, which function on processing the event-related synchronization or
desynchronization of EEG wave patterns.
d n 4 t 3 n g | 7
3.7.2 Microfluidic Structures
In the design of neuronal experiments, a promising microfluidic structure is the
utilization of compartments with microscopic geometries for localized exposure
of neurons to specific and controlled environmental conditions. Examination of
certain neurodegenerative diseases such as multiple sclerosis (which causes injury
to the axon) exemplifies the physiological importance of localization of neurons
as opposed to whole neuron exposure, which is traditionally encountered in
neuronal cultures. In vitro targeted studies of neurons are important in further
understanding the molecular basis of neurodegenerative diseases.
Developing an optimized experimental platform is essential to conducting
neuronal experiments. Scaling the experimental platform to match the cell
geometry necessitates the use of miniaturized chemical stimulation and analysis
systems. Achieving this analysis and simulation in a microsystem has long been
an advertised promise of labs working with chips. As a result, there have been a
number of developments in the application of microfluidic systems for neuronal
experiments. 47,48
Strategies for the use of microfluidic devices range from seeding neurons in
reservoirs and growing axons into adjacent reservoirs (separated by microchannel
barriers) to achieving localization of neurites and their isolation from the cell
soma for targeted studies. Partially enclosed reservoirs separated by thin walls
incorporating microchannels underneath the barriers have also been successful in
providing isolation as well as improved access to the soma and axons. 49,50
Molded chambered and channels have been experimentally proven to
separate the soma with good adhesion between the poly(dimethylsiloxane)
(PDMS) cover and the glass substrate with no leakage between the two
reservoirs or between the channels (see Figure 3.12).
The development and spatial generation of the nervous system is highly
regulated by the spatio-temporal regulation of guidance molecules. The
n 3 .
 
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