Biomedical Engineering Reference
In-Depth Information
These findings clearly indicated that the short-time response of the gel to the
electric field is due to electrophoretic migration of unbound counter-ions in the gel
and to impingement of solvent ions on the surfaces of the gel samples. It is the
surplus or deficiency of such ions that determines the osmotic pressure and free
volume and, therefore, deformation of such gels. In the next section, the case of
electrically induced nonhomogeneous deformation of transparent PAMPS and
PAAM cylindrical lenses have been 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 param-
eters such as the resistance and the capacitance of the gel samples.
5.2
PAMPS GELS
This chapter briefly concentrates on and describes the characteristics and application
of poly2-acrylamido-2-methyl-1-propane sulfonic acid (PAMPS) gel as electroactive
artificial muscles. Although many experiments have been performed in the application
of this polyelectrolyte in swimming structures, emphasis is placed on other applications,
such as electrically controllable and active optical lenses. The reason is that, in simple
engineering actuation configuration such as swimming robotic structures in which
PAMPS gel actuators are used as caudal fin structure (Shahinpoor, 1991, 1992), there
is simply not enough structural strength in these materials in gel form. There exist a
number of papers on the applications of PAMPS to robotic structures and, in particular,
gel star fish by Osada et al. (1992); Shahinpoor (1992, 1993); Shiga et al. (1993); Osada,
Okuzaki, Gong, et al. (1994); Gong et al. (1994); Okuzaki and Osada (1994b); Ueoka
et al. (1997); Narita et al. (1998); and Otake et al. (2000, 2001, 2002).
These papers basically deal with weakly cross-linked PAMPS gel. The principle
of this behavior is based upon an electrokinetic molecular assembly reaction of
surfactant molecules on the polymer gel caused by electrostatic and hydrophobic
interactions. Under an electric field, PAMPS gel undergoes significant and quick
bending and the response could be controlled effectively by changing the alkyl chain
length of the surfactant molecule, the salt concentration, and the current applied.
The results allow us to consider that cooperative complex formation between
PAMPS gel and CnPyCl is responsible for this effective chemomechanical behavior.
This copolymer is clear in color when synthesized and, similarly to other polyelec-
trolyte gels, it swelled in water several times its original volume. When placed in an
electric field, strips of the PAMPS bent within a few seconds. Depending on the
thickness of the gel synthesized, the response time for bending actuation varied. Thinner
and smaller actuators had faster response, whereas thicker samples were slower.
5.3
GEL PREPARATION
Here we present a very simple procedure to prepare an electroactive version of
PAMPS gels. Electrically active PAMPS gels can be prepared by free radical copo-
lymerization. A 15 wt% aqueous solution (deionized [DI] water) of a reaction mixture
with a desired molar ratio of a common monomer and a cross-linker density of about
