Biomedical Engineering Reference
In-Depth Information
50
m
µ
FIGURE 4.76
Conventional PAN fibers. The fiber diameter is 8-10
µ
m.
Acc_V
10.0 kV
Spot
5.4
Magn
5000
×
Det
SE
WD
10.4
Exp
1
5
µ
m
Hivac
pan2 3.0 kV 11.9 mm
×
15.0 k SE(U) 2/21/02
3.00 um
FIGURE 4.77
Spun PAN nanofibers. Average fiber diameter is approximately 300-600 nm.
In order to manufacture nano-PAN fibers, a technique called “electrospinning”
is employed. It typically produces fiber diameters in the tens or hundreds of nano-
meters, as shown in figure 4.77, and can offer new opportunities far beyond textiles
to numerous other industrial, biomedical, and consumer applications. In particular,
as discussed before, once these PAN nanofibers or strands are made conductive and
used in an electrochemical cell for chemomechanical linear contractile transduction,
they will be able to provide us with contraction response time comparable to bio-
logical muscles—that is, in the range of a few milliseconds.
Realizing that the response time of PAN artificial muscle is governed by the
diffusional processes of ion-solvent interaction, the use of PAN nanofibers or fibrils
is promising for fabricating fast-response PAN artificial muscles. The contrac-
tion/elongation behavior explanation is based upon the exchange of counter-ions and
solvent (in this case, water) into and out of activated PAN. Donnan equilibrium
theory may possibly describe the situation properly (figs. 4.78, 4.79, and 4.80).
If so, the swelling force may be identified by the net osmotic pressure difference
associated with relevant ions. Also, the columbic force could play a role. The
combination of such effects can describe the situation reasonably well. If we describe
the kinetics of PAN fibers by using the diffusion-controlled slab-type gels, then the
contraction of PAN-N fibers would be (Yoshida et al., 1996):
