Biomedical Engineering Reference
In-Depth Information
5
PAMPS Gel Artificial
Muscles
5.1
INTRODUCTION
Ionic polymeric gels are three-dimensional networks of cross-linked macromolec-
ular polyelectrolytes that swell or shrink in aqueous solutions upon addition of
alkali or acids, respectively. Reversible dilation and contraction of the order of more
than 800% have been observed in our laboratory for polyacrylonitrile (PAN) gel
fibers. Furthermore, it has been experimentally observed that swelling and shrinking
of ionic gels can be induced electrically. Thus, direct computer control of large
expansions and contractions of ionic polymeric gels by means of a voltage controller
is possible.
Swelling and contraction of ionic polymeric gels by pH variations have been
historically discovered and reported by Kuhn et al. (1948) and Katchalsky (1949),
followed by a wealth of additional papers on pH activation of ionic gels by them
and their students to the late 1960s. Such investigation on pH response of ionic gels
is still going strong, as can witnessed by the recent works of Aluru and his coworkers
(De et al., 2002).
The first paper in connection with electrically controllable response of polymer
gels was that of Hamlen and coworkers on electrolytically active polymers published
in
in 1965. In modern times De Rossi et al. (1986) reported for the first time
on contractile behavior of electrically activated mechanochemical polymer actuators.
Segalman et al. (1991, 1992a, 1992b, 1992c) reported their investigation on electrically
controlled polymeric gels as active materials in adaptive structures. The first papers
on the use of electrically controllable ionic polymeric gel actuators and artificial
muscles in connection with swimming robotic structures were produced by Shahinpoor
(1991, 1992, 1993a). The first patent (U.S. patent 5,250,167) in the world on electrically
controllable polymeric gel actuators was reported in 1993 by Adolf et al.
These electrically controllable gel actuators possess an ionic structure in the
sense that they are generally composed of a number of fixed ions (polyions) per-
taining to sites of various polymer cross-links and segments and mobile ions
(counter-ions or unbound ions) due to the presence of an electrolytic solvent. Elec-
trically induced dynamic deformation of ionic polymeric gels, such as polyacrylic
acid plus sodium acrylate cross-linked with bisacrylamide (PAAM), or poly (2-
acrylamido-2-methylpropanesulfonic acid), or PAMPS, or various combinations of
chemically doped polyacrylic acid plus polyvinyl alcohol (PAA-PVA), can be easily
observed in the laboratory. Such deformations give rise to an internal molecular
network structure with bound ions (polyions) and unbound or mobile ions (counter-
ions) when submerged in an electrolytic liquid phase. In the presence of an electric
Nature
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