Page 89 - Handbook of Biomechatronics

84 Jeff Christenson

complications of communication and charging. Research still progresses in
the further development of IMES.
Due to sweat, a poor fitting socket, and changes in the muscle structure,
the surface EMG system you installed for Jacob was unreliable and caused
more problems than they solved. You consult with Jacob and he agrees
to undergo a minor, but experimental, surgery to have IMES implanted
in his residual limb. You implement the same algorithm as with the surface
EMG, and find the IMES system to be more reliable.

5.4 Nerve Cuff

The next step up in the nervous system is to access signals from the nerve
bundle before it enters the muscles. To do this, a sensor called the nerve cuff
has been developed (Fig. 28)(Weir et al., 2009). A nerve cuff consists of
biologically inert wrap which has small electrodes embedded into the wrap.
The nerve cuff is surgically inserted into the body.
During surgery, first the desired nerve branch is discovered. Then, the
nerve cuff is wrapped around the nerve bundle and a suture is used to
sow the cuff together, being careful not to pierce the nerve cuff membrane
(to prevent scaring). The fine wires attached to the electrodes are brought
out and a junction point is created on the skin. After the patient has healed,
the nerve cuff is ready to be used (Weir et al., 2009).
Since a nerve bundle is just that, a bundle of nerves, the nerve cuff must
be calibrated. By either stimulating the electrodes individually and recording
what part of the body the patient feels is like being touched, or by asking the
patient to think about moving a certain limb or joint and recording what
electrodes are activated, a map can be developed of which electrode corre-
sponds to which nerve or nerves. This system is currently being used to
attempt to restore sensation and is still experimental (Tyler and
Durand, 2002).

Fig. 28 Nerve cuff electrode.