Biomedical Engineering Reference
In-Depth Information
are well suited for rapid, inexpensive, and quantitative screening of toxicants under well-
defined and controlled experimental conditions. The key to effective in vitro models is the
ability to capture physiologically relevant activity. In the case of neuronal systems, elec-
trophysiological activity is paramount relative to physiological function and behavior. A
major component of such activity, the suprathreshold action potential dynamics, can now
be captured from many neurons comprising the network and processed in real time. If cul-
tured on glass plates with transparent thin film indium-tin oxide (ITO) conductors, high-
power microscopy and associated fluorescence techniques can be applied in parallel with
electrophysiological monitoring (as shown in Figure 6.1). The latter includes discrimi-
nated action potential data where waveshape changes can be used to study pharmacolog-
ical effects on voltage-gated channels.
Neuronal network biosensors (NNBS), as described in this chapter, are positioned
between cell-based and tissue-based biosensors. The NNBS systems consist of functional,
spontaneously active networks that are formed on substrate-integrated microelectrode
arrays (MEAs). This approach provides extensive multisite electrophysiological data in
terms of action potential patterns and waveshapes, as well as simultaneous cytological
information through high-power microscopy and fluorescence. The dissociation and seed-
ing of embryonic neural tissue on appropriately prepared surfaces of MEAs produces an
intimate cellular contact with that surface, resulting in strong cell-surface and cell-
electrode coupling if the ratio of cell mass to adhesion area is small (see Figure 6.2). Such
coupling provides long-term morphological stability and excellent signal-to-noise ratios
(SNRs). In fact, the NNBS has the capacity to provide long-term electrophysiological data
over periods ranging from weeks to months, which constitutes a far greater performance
window than virtually any other in vitro electrophysiological assay.
The Center for Network Neuroscience has placed value in generating cultures that con-
tain all cell types present in the parent tissue in approximately the same ratios. Although
the developing embryonic circuitry is disrupted during the cell dissociation process, the
FIGURE 6.1
Neuronal network on the 1 mm
2
recording matrix of an MEA. Indium-tin oxide conductors connect this area
with amplifier contacts at the edges of a 5
5 cm glass plate. The electrode array is insulated with 2 µm of poly-
siloxane resin perforated with laser shots at the end of the conductors. Bodian stain with fixation 96 days after
seeding. Bar: 50 µm.
