Biomedical Engineering Reference
In-Depth Information
An upsurge of interest in chitin/chitosan and their derivatives has swept the globe, and
thus many countries are putting more efforts into relevant research and development.
Since 2000, the number of research papers on chitin/chitosan has been increasing linearly.
These usually concentrate on the application of chitin/chitosan and their composites in
biomedical fields such as tissue engineering, gene vectors, and drug carriers, which indi-
cates that chitin/chitosan and their derivatives are important in the research and applica-
tion of biomaterial in the twenty-first century.
Now, in industrial preparation, chitin is formed by removing calcium carbonates and
proteins from waste shrimp shells and crab shells from aquatic product factories by steep-
ing them in acid and alkali solutions. This technique has many inherent shortcomings; for
instance, the raw materials are hard to collect, preserve, and transport owing to limitations
of location and season; resources of raw material are very different; the quality of products
can hardly be controlled; and large amounts of calcium carbonate in the shells make extrac-
tion of chitin difficult, which increases cost and generates plenty of wastewater [10].
Therefore, new chitin resources have drawn a lot of attention: for example, various insects
that are abundant in nature such as pine moth [11], myiasis [12], silkworm chrysalis [13],
and cicada slough [14].
1.2 Deacetylation
Chitosan can be harvested by removing acetyls from chitin, but to eliminate all acetyls is
not easy. Chitosan can be made by a chemical method or an enzyme method. Chitosans
available in the market are formed by removing acetyls from chitin through strong base
hydrolysis. The equation is shown in Figure 1.2.
1.2.1 Chemical Method
The chemical method for preparing chitosan includes the alkali fusion method, the con-
centrated alkali solution method, the alkali catalysis method, and the hydrazine hydrate
method. The main performance indexes of chitosan are DD and relative molecular weight
or viscosity. To date, quite a few researchers have studied chitosan preparation and have
made significant achievements [15,16]. Research findings on the extraction process of chi-
tosan from shrimp and crab shells are shown in Figure 1.3.
The alkali fusion method is used in the early period, comprising the following steps:
fusing chitin and solid potassium hydroxide directly in a nickel crucible, melting them at
CH 2 OH
CH 2 OH
O
O
NaOH, N 2
O
O
OH
OH
*
*
*
*
NH 2
NHCOCH 3
n
n
Figure 1.2
Preparation of chitosan by base hydrolysis of chitin.
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