Biology Reference
In-Depth Information
Chitosan is prepared by alkaline hydrolysis of acetamide groups of chitin.
High temperature (100
C) combined with strong aqueous alkali treatments
are used to deacetylate chitin (N-acetylation degree lower than 30%), in order
to obtain chitosan. Two different methods of preparing chitosan from chitin
with varying degrees of acetylation are known: heterogeneous deacetylation
of solid chitin and homogeneous deacetylation of preswollen chitin under
vacuum in an aqueous medium (
Aranaz et al., 2009; Muzzarelli, 1977
).
The main limitations in the use of chitosan in several applications are its
high viscosity and low solubility at neutral pH. Different experimental vari-
ables should be taken into account when working with chitosan solutions
such as the nature of the salt counterion, length of polymer chain, molecular
weight (Mw), pH, ionic strength, the addition of a nonaqueous solvent, and
the degree of N-acetylation (
Aranaz et al., 2009; Muzzarelli, 1977
). Their
different solubilities in dilute acids are commonly used to distinguish
between chitin and chitosan. Chitosan, the soluble form, can have a degree
of acetylation between 0% and about 60%, the upper limit depending on
parameters such as processing conditions, molar mass, and solvent character-
istics (
Aiba, 1992
). Thanks to the protonation of free amine groups present
along the chitosan chain; this macromolecule can be dissolved in diluted
aqueous acidic solvents, rendering the corresponding chitosan salt in
solution. Degradation rate can be tuned based on its degree of deacetylation
(DD), whereas fully deacetylated (DD
100%) chitosan is nondegradable
(
Freier, Koh, Kazazian, & Shoichet, 2005; Tomihata & Ikada, 1997
) and
partially deacetylated (DD
¼
¼
70%) chitosan is fully degradable (
Tomihata
& Ikada, 1997
).
Chitin and chitosan are interesting candidates for use in the medical and
pharmaceutical applications because they have positive properties such as
biocompatibility, biodegradability, and nontoxicity that make them suitable
in biomedical field (
Khor & Lim, 2003
). Moreover, other properties such as
analgesic effect, antitumor activity, hemostatic, anticholesterolemic, antimi-
crobial, permeation enhancing effect, and antioxidant properties have also
been reported (
Kumar, Muzzarelli, Muzzarelli, Sashiwa, & Domb, 2004
).
Several chitosan products have been approved by the Food and Drug
Administration. Furthermore, chitosan has been used to generate laser-
activated film surgical adhesive (SurgiLux) that can be very useful as an alter-
native to microsurgery for peripheral nerve reconstruction (
Foster &
Karsten, 2012
). SurgiLux has been tested
in vitro
and
in vivo
on different tis-
sues including nerve, intestine,
dura mater
, and cornea, demonstrating a good
biocompatibility (
Foster & Karsten, 2012
).
