Biomedical Engineering Reference
In-Depth Information
In the next sections, the cases of electrically induced contraction of PAN muscles
are experimentally and theoretically described. Exact expressions are given relating
the deformation characteristics of the gel to the electric field strength or voltage
gradient, gel dimensions, and other physical parameters of the gel.
4.6
ELECTROCHEMOMECHANICAL ACTUATION
IN CONDUCTIVE POLYACRYLONITRILE (C-PAN)
FIBERS AND NANOFIBERS
4.6.1
I
NTRODUCTION
Electrical activation of contractile ionic polymeric fibers dates back to the pioneer-
ing works of Kuhn (1949), Katchalsky (1949), Kuhn et al. (1950), and Hamlen et
al. (1965). In recent years, Osada and Hasebe (1985), De Rossi et al. (1986),
Chiarelli and De Rossi (1988), Chiarelli et al. (1989), Caldwell and Taylor (1990),
Segalman et al. (1991), Umemoto et al. (1991), Shahinpoor et al. (1996, 1997a,
1997b), and Schreyer et al. (1999, 2000) have further contributed towards under-
standing of electrically controllable contractile ionic polymeric fibers. Figure 4.63
depicts a number of devices made in the early development of contractile fibrous
synthetic chemomechanical muscles.
Activated PAN fibers that are suitably annealed, cross-linked, and hydrolyzed
are known to contract and expand when ionically activated with cations and anions,
respectively. The change in length for these pH-activated fibers is typically greater
than 100%, but up to 200% contraction/expansion of PAN fibers has been observed
in our laboratories at AMRI. They are comparable in strength to human muscles
(~20 N/cm
2
) and have the potential of becoming medically implantable electroactive
contractile artificial muscle fibers.
Increasing the conductivity of PAN by making a composite with a conductive
medium such as a noble metal such as gold or platinum, or graphite, carbon nanotube,
or a conductive polymer such as polypyrrole or polyaniline (C-PAN) has allowed
for electrical activation of C-PAN artificial muscles when it is placed in an electro-
chemical cell. The electrolysis of water in such a cell produces hydrogen ions at a
C-PAN anode, thus locally decreasing the cation concentration and causing the C-
PAN muscle to contract. Reversing the electric field allows the C-PAN muscle to
Gripper
PAN-PPY
contractile fibers
Scale
Platinum wire
Platinum wire
Piston
Silicone urethra
Glass
support rod
PAN-PPY
contractile
elements
PVA-PAA
fiber
NaCl
solution
Chemical muscle
Hamlen et al., 1965
Artificial sphincter
Chiarelli et al., 1989
Gripper
Caldwell et al., 1989
FIGURE 4.63
A number of early contractile synthetic chemomechanical muscles.
