Biomedical Engineering Reference
In-Depth Information
200
µ
m
50
µ
m
Raw PAN fibers with a small amount of
platinum deposited
Contracted PAN fibers
50
µ
m
Elongated PAN fibers
FIGURE 4.67
SEM micrographs that show raw fibers (top left), contracted (top right), and
elongated states (bottom right), respectively. It should be noted that SEM micrographs were
taken for the dry samples. The elongated PAN fibers show that they contain a salt (possibly
NaCl).
muscle near an electrode where the ions are generated or, if the conductivity of activated
PAN can be increased, the PAN muscle can serve as the electrode.
The study reported here takes the second approach, where platinum is deposited
on PAN fibers to increase conductivity so that the muscle can serve as the electrode
directly. This procedure of depositing Pt on the polymer and activating it in an
electrochemical cell was initially demonstrated a few years ago by Hamlen et al.
(1965) with a polyvinyl alcohol-polyacrylic acid copolymer. It resulted in about
a 5% decrease in length, with contraction and elongation each taking about 12
min. However, our recent improvements to an electroactive nanofibrous version
of PAN muscles or C-PAN-N have reduced the activation time to a few seconds,
with muscle strength approaching human muscles in the range of 20
N
/cm
2
of
muscle fiber cross-section.
In order to activate as-received PAN fibers (Mitsubishi), first, they were oxidized
in air at an elevated temperature range of 220-240
C. It is likely that the oxidation
process makes a linear-like structure of as-received PAN fibers to a cross-linked
structure of pyridine and cyano groups shown in figure 4.65. The preoxidized PAN
fibers show dark brown or black depending upon the level of crosslinking.
Second, they were saponified in an alkaline solution (2
N
NaOH for 20-30 min).
The elongation and contraction behavior of PAN fibers is interesting in the fact that
hysteresis exists, changing upon pH values. In an approximate pH range of 3-10,
°
