Biomedical Engineering Reference
In-Depth Information
1 mol% (of total monomers) should be bubbled with nitrogen for about 20 min to
remove any oxygen in the reaction mixture. Then 35
L of a 10 wt% ammonium
persulfate (APS) solution should be added to the mixture. The final solutions should
be filtered through a fine filter.
One portion of the resulting gels should be washed in deionized water to remove
the unreacted monomers and should be titrated with aqueous sodium hydroxide
solution to determine the composition of the copolymer. Another portion of the gels
should be washed in a large amount of dilute sodium hydroxide solution for 20 days
in order to neutralize the poly(methacrylic acid) and to remove the unreacted mono-
mers. The dilute sodium hydroxide solution should be changed every two days, and
the final pH value should be kept above the neutral pH of 7.
Specifically, in order to make an electroactive PAMPS gel, make two mixtures
and mix them quickly to form the gel. First, mix 0.5 g of tannish sodium acrylate
powder with 2.13 g of whitish acrylamide powder in the presence of 0.08 g of a
cross-linker N,N
µ
-methylene-bisacrylamide [(H2C = CHCONH)2CH2] in 30 mL of
DI water reaction mixture. Then, mix 0.156 g of N,N,N
′
-tetramethyl-ethylene-
diamine (TMEDA) [(CH2)2NCH2CH2N(CH3)2] with 0.02 g of APS. Put these two
into 20 mL of DI water, shake well, and then add to the 30-mL reaction mixture
immediately within few seconds. Otherwise, APS decomposes and never forms a
gel of PAMPS. The mixture will take a few minutes to gel up. The resulting PAMPS
gel is then highly electroactive.
′
,N
′
5.4
PAMPS GEL APPLICATION
Since PAMPS gel appears colorless and is soft and compliant, there are many areas
of adaptive smart materials into which it can be incorporated. The following sections
describe one application of PAMPS ionic gels that was investigated in our Artificial
Muscle Research Institute. This particular hydrophilic gel has also been investigated
extensively for use in drug delivery systems (DDS) by Osada et al. (1985, 1989,
1991, 1992, 1993, 1994, 1995, 2005). For example, Okuzaki and Osada (1994) have
described the electro-driven chemomechanical polymer gel as an intelligent soft
material. In their work, weakly cross-linked PAMPS gel was synthesized and the
chemomechanical behaviors in the presence of N-alkylpyridinium chloride (CnPyCl
n = 4, 12, 16) were studied.
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 underwent 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.
5.4.1
A
O
L
DAPTIVE
PTICAL
ENSES
Reversible change in optical properties of ionic polymeric gels, PAMPS, under the
effect of an electric field is reported. The shape of a cylindrical piece of the gel,
