Biomedical Engineering Reference
In-Depth Information
Sarcomere
Z
M
Z
FIGURE 4.64
A possible configuration for the electroactive C-PAN-N artificial muscle in
an antagonist configuration to provide biceps and triceps (left) similar to the action of a
sarcomere (right).
elongate. Typically close to 100% change in C-PAN muscle length in a few minutes
is observed when it is placed as an electrode in a 10-m
M
NaCl electrolyte solution
and connected to a 20-V power supply. Nanofibrous versions of C-PAN or C-PAN-N
obtained recently by electrospinning have allowed the response time to be reduced
to a few seconds. These results indicate the potential in developing electrically
activated C-PAN-N artificial nanomuscles and linear nanoactuators. Furthermore,
these results present a great potential for using electroactive fiber bundles of C-
PAN-N as artificial sarcomeres and artificial muscles for linear actuation as depicted
in figure 4.64.
Activated C-PAN contracts when exposed to protons, H
+
, in an aqueous medium
and elongates when exposed to hydroxyl ion, OH
-
, in a strong alkaline medium. The
length of activated PAN fibers can potentially more than double when going from
short to long. A possible explanation for the contraction and elongation of activated
C-PAN is the effect carboxylic acid groups (COO
-
and H
+
) have on the molecular
geometry. At high cationic concentration, all acid groups are protonated, potentially
collapsing the network and contracting the polymer.
On the other hand, the presence of hydroxyl ions causes the protons to detach
from the carboxylic groups and form water. The negatively charged carboxylic
groups would then cause the cross-linked polymer network to expand by coulombic
repulsion and attract the water molecules into the expanded network. These under-
lying mechanisms of expansion and contraction are considered later for the modeling
of activated PAN fibers in an electrochemical cell in the presence of an imposed
electric field.
4.6.2
P
REPARATION
OF
I
ONICALLY
A
CTIVE
PAN
Raw PAN fibers, which are composed of roughly 2,000 individual strands of PAN
(each about 10
C for 2 h. The fibers can
be bundled together at this point to form a PAN muscle. The PAN is then placed in
a boiling solution of 1
N
LiOH for 30 min, after which the PAN fibers become
hyperelastic like a rubber band.
At this point the PAN can be ionically activated. Flooding the activated PAN
with a high concentration of cations such as H
+
induces contraction while the
µ
m in diameter), are first annealed at 220
°
