Biomedical Engineering Reference
In-Depth Information
FIGURE 4.61
Electric PAN muscle apparatus showing gold-plated center rod as one elec-
trode and gold-plated spring as the circumferential electrode.
muscle, in close contact with the platinum wire, because of the change in the local
acidity will contract or expand depending on the polarity of the electric field. This
scheme will allow the experimenter to use a fixed flexible container of an electrolytic
solution whose local pH can be modulated by an imposed electric field while the
produced ions are trapped to stay in the neighborhood of a given electrode.
This method of artificial muscle activation has several advantages. First, the need
to use a large quantity of acidic or alkaline solutions is eliminated; second, the use
of a compact PAN muscular system is facilitated for applications in active muscu-
loskeletal structures. Third, the PAN muscles become electrically controllable and
therefore the use of such artificial muscles in robotic structures and applications
becomes more feasible (fig. 4.62). In this way, a muscle is designed such that it is
exposed to either Na
+
or Cl
-
ions effectively. In the following paragraphs, muscle
contraction or expansion characteristics under the effect of the applied electric field
are discussed.
As was discussed before, ionic polymeric gels are three-dimensional networks
of cross-linked macromolecular polyelectrolytes that swell or shrink in aqueous
solutions upon addition of alkali or acids, respectively. Reversible volumetric dilation
and contraction of the order of more than 800% for PAN fibers have been observed
in our laboratory. 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
gradient appears to be possible.
These gels possess an ionic structure in the sense that they are generally composed
of a number of fixed ions (polyions) pertaining 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. Electrically induced dynamic deformation of ionic polymeric
gels such as polyacrylic acid plus sodium acrylate cross-linked with bisacrylamide
(PAAM), poly (2-acrylamido-2-methyl-1-propanesulfonic acid), PAMPS, or various
