Biology Reference
In-Depth Information
Tesfayesus & Durand, 2006
), have been developed. The reduced size and
thickness of thin-film polymer cuffs make feasible the implantation of several
small cuffs around different fascicles or branches of a peripheral nerve, con-
sequently achieving selective stimulation of a higher number of targets
(
Stieglitz, 2007
). Cuff electrodes have a long record of use in FES systems
for human applications, such as in devices to correct foot-drop, allow hand
grasping, and control of micturition, with successful outcomes over years
of use (
Brindley, 1994; Lyons, Sinkjær, Burridge, & Wilcox, 2002;
Waters, McNeal, Faloon, & Clifford, 1985
).
Flat interface nerve electrode
(FINE,
Fig. 2.1
B) is a design variation of the
cuff electrode developed by Durand and coworkers (
Leventhal &
Durand, 2003; Tyler & Durand, 2002
). The FINE applies a small pressure
to the nerve to enlarge its cross-section and thus increases the nerve surface
area. Such flattening of the nerve displaces the axons from the center to the
surface and closer to the electrode active sites. Studies in laboratory animals
with FINEs implanted over 1-3 months showed that electrodes applying
moderate and small forces did not cause detectable nerve damage, but high
reshaping forces induced nerve lesion (
Tyler & Durand, 2003
). Studies in
humans have revealed that FINEs placed on the femoral nerve trunk can
selectively and independently activate the different muscles innervated by
the femoral nerve (
Schiefer, Polasek, Triolo, Pinault, & Tyler, 2010
).
3.2. Intraneural electrodes
Intraneural electrodes are implanted within nerve fascicles. They show a bet-
ter selectivity than extraneural electrodes as they may have closer contact
with different fascicles in both superficial and deep-nerve locations. There-
fore, the threshold to stimulate the axons is reduced, and both the selectivity
and the signal-to-noise are improved (
Badia, Boretius, Andreu, et al., 2011
).
On the other hand, their invasiveness is higher than the extraneural elec-
trodes as the implantation itself may cause more damage to the nerve. An
important issue limiting the usability of intraneural electrodes is the long-
term stability of the contact between the probe and the nerve fibers. Shape
memory alloys applied as smart actuators in the electrode and development
of biological methods to reduce the fibrotic reaction around the electrode
are promising methods to improve the performance for long-term applica-
tion (
Bossi et al., 2007
).
Longitudinal intrafascicular electrodes
(LIFEs) (
Fig. 2.1
C) are constructed
from thin, insulated conducting wires (such as Pt-Ir or metalized polymers)
