Biomedical Engineering Reference
In-Depth Information
looked at chitosan gels and, incorporating
different elements into the gel, to improve
them for desired properties such as mechani-
cal or binding properties. Chitosan polyethylene
glycol forms a semi-interpenetration polymer
network that increases the mechanical
properties and pH-dependent swelling prop-
erties of the gel. For an excellent article on
supramolecular interactions in chitosan gels,
see Kato and Schneider
[41]
.
The chitosan ionomers are useful in many dif-
ferent applications in a variety of fields. From cut-
ting edge biomedical applications to agricultural
applications, these gels are an essential asset for
the future. One of the main advantages of these
ionomers is their ability to contain and release
various substances. They have also been recently
developed as cationic membranes for fuel cell
application to replace Nafion®
®
[42-44]
. Interest-
ingly, Nafion®
®
as a perfluorinated sulfoinc mem-
brane is one of the basic materials used to
manufacture IPMCs by a redox operation. Thus,
it appears quite feasible to combine chitosan and
Nafion®
®
to manufacture chitosan/IPMC artificial
muscles with healing and diagnostic capabilities.
evaporating the solvent (isopropyl alcohol)
out of the solution, recast ionic polymer can
be obtained
[45]
. As a biopolymer is used,
the IPMC is called an ionic biopolymer-metal
nanocomposite (IBMC).
6.3 CHITOSAN/NAFION
®
COMPOSITE 3-D
MA
NUFACTURING PROCEDU
RE
The general procedure in manufacturing cat-
ionic chitosan is to first obtain a chitosan from
a vendor, say, Sigma-Aldrich, with a medium
molecular weight for ease of acetylation. Ace-
tic acid (HCl),
3
COOH), hydrochloric acid (HCl),
nitric acid (HNO
3
), sodium hydroxide (NaOH),
sodium tripolyphosphate (Na
5
P
3
O
10
) and
sodium sulfite (Na
2
SO
3
), 10% Nafion®
®
solution
and (DMSO) dimethyl sulfoxide (CH
3
)
2
SO),
sodium or lithium borohydrides (NaBH
4
,
LiBH
4),
tetra-amine platinum chlorides hydrate
([Pt(NH
3
)
4
]Cl
2
and [Pt(NH
3
)
6
]Cl
4
), dichlorophen-
anthrolinegold (III) chloride (Au(phen) Cl
2
]Cl),
and ammonium tetrachloroaurate (III) hydrate
(NH
4
AuCl
4
·
XH
2
O) in solution are also needed.
All chemicals used should be of reagent grade.
The chitosan should be dissolved in 0.1 M ace-
tic acid to prepare a 2% (by volume) chitosan
solution. This solution should then be mixed
thoroughly with a 10% Nafion®
®
solution at room
temperature. Subsequently, a solution of DMSO
should be added to the mixture to act as a solvent.
The resulting chitosan/Nafion®
®
should be thor-
oughly mixed with acetic acid to make a Nafion®/
®
/
chitosan composite that should then be sonicated
for about 15 min in a bath sonicator to remove
surface contaminants and impurities and then be
vigorously stirred for 5 h. The chitosan/Nafion®
®
mixture should then be poured into a glass petri
dish to be cured for 13 h in an oven at 114 °C. The
resulting membrane should be soaked in DI
water at 85 °C for 2 h. The resulting chitosan/
Nafion®
®
membrane should further be hydrolyzed
in 1M HCl for 2 h at 85 °C to protonate it.
6.2 THREE-DIMENSIONAL
FABRICATION OF BIOPOLYMER
N
ANOCOMPOSITES (IBMCs
)
The fundamental procedure here is to manu-
facture chitosan membranes from chitin and
then hydrolyze the chitosan membranes to
give them ion-exchange capability, then boil
them in an acid to protonate them for quick
ion exchange with a noble metal such as plati-
num, gold, or palladium. The membrane form
of these biopolymers has a typical thickness
in the range of approximately 300-400
μ
m.
Shahinpoor's group
[25, 45]
has devised a fab-
rication method that can scale up or down the
IPMC artificial muscles in a strip size of micro-
to-centimeter thickness, using a liquid form of
perfluorinated ionic polymers. By meticulously
