Biology Reference
In-Depth Information
more axons from different fascicles. The reduced size of the wings would
make the SELINE less prone to produce fibrotic encapsulation and electrical
insulation.
Multielectrode arrays
(MEAs) (
Fig. 2.1
E) are electrodes composed of a base
made of silicon, ceramic, polyimide, or glass, and tens of needles with elec-
trode tips made of carbon, gold, platinum, or iridium oxide (
Nordhausen,
Maynard, & Normann, 1996; Zhang, Peng, Qi, Gao, & Zhang, 2009
).
MEAs are inserted transversely into the nervous system thus providing mul-
tisite recording and stimulation. On the other hand, the high number of
electrical contacts may generate some neural damage produced not only
by the rigid structure of the electrodes in contact with the nervous tissue
but also by tethering forces during movements by lead wires. Over the past
decade, these electrodes have been mainly used as CNS microinterfaces to
selectively record or stimulate the brain cortex, allowing communication of
paralyzed patients to control computers and robotic assistive devices during
years after implantation (
Hochberg et al., 2012, 2006; Velliste, Perel,
Spalding, Whitford, & Schwartz, 2008
). However, MEAs have also been
used in peripheral nerves in experimental works with cats (
Branner &
Normann, 2000
) and also in human volunteers (
Warwick et al., 2003
).
A modified version of the MEA (named Utah Slanted Electrode Array,
USEA) has been developed. The array is composed of electrodes of different
length in order to reduce the number of redundant electrodes. Therefore,
access to more fascicles within the nerve is provided, allowing low-current
highly selective stimulation of motor fibers (
Branner, Stein, Fernandez,
Aoyagi, & Normann, 2004; Branner, Stein, & Normann, 2001
) and selec-
tive recording of single-unit responses (
Clark, Ledbetter, Warren, &
Harrison, 2011
) during several months after nerve implantation. Neverthe-
less, chronic studies reported poor stability of recorded signals over time
(
Branner et al., 2004; Warwick et al., 2003
). Promising results have been
obtained both
in vitro
and
in vivo
with newly developed flexible and stretch-
able MEAs. These electrodes are polyimide- or silicone based and they can
deform in 3D along with the nerve, thus diminishing traumatic injuries pro-
duced by mechanical tension in the nerve interface (
Lacour et al., 2010
).
3.3. Regenerative electrodes
Regenerative electrodes represent a different approach to interface the PNS
and are probably the most invasive electrodes but also the ones that might
offer the highest level of selectivity. These electrodes are not thought to be
