Biomedical Engineering Reference
In-Depth Information
Anode
Cathode
O
2
+ 4H
+
+ 4e
−
2H
2
O
2H
2
O + 4e
−
H
2
+ 2OH
−
FIGURE 4.68
Experimental setup for electrical activation of C-PAN artificial sarcomeres
and muscles. It describes the operating principle of the C-PAN.
the elongation process stays below the contraction process. This means that the
equilibrium length of PAN fibers during contraction is larger than that of PAN fibers
during elongation.
Based upon the Donnan theory of ionic equilibrium
(Flory, 1953b), we believe
that important forces arise from (1) induced osmotic pressure of free ions between
activated PAN fibers and their environment; (2) ionic interaction of fixed ionic
groups; and (3) the network itself. Among them, the induced osmotic pressure of
free ionic groups could be the dominating force. Much study is needed to clarify
this discussion.
Electrical activation of PAN fibers is performed in an electrochemical cell, shown
in figure 4.68. PAN fibers can be activated electrically by providing a conductive
medium in contact with or within the PAN fibers. Such electrical activation can be
made to have low overvoltage for hydrogen and oxygen evolution. At the anode,
oxygen evolves via 2H
2
O
⇒
O
2
+ 4H
+
+ 4
e
+
and the counter reaction at the cathode
is 2H
2
O + 2
e
-
H
2
+ 2OH
-
+ 4
e
+
.
Upon being hydrogenated in the vicinity of the PAN anode, the decreased pH
causes the PAN fibers to contract by the same effect as chemical activation. Also,
reversing the polarity of DC, elongation of PAN fibers is simply obtained.
⇒
4.6.3
D
IRECT
M
ETAL
D
EPOSITION
T
ECHNIQUE
As a first trial, conductivity of PAN was increased by means of chemical deposition
of platinum on PAN fibers. Raw PAN fibers were immersed in a tetraamineplatinum
chloride monohydrate solution. The PAN fibers were then transferred to a reducing
solution containing sodium borohydride. The solution was slowly heated to about
50-60
C with agitation at 100 rpm along with periodic additions of 5% NaBH
4
solution to reduce Pt metal. This process was repeated several times to seed the PAN
°
