CHITIN AND CHITOSAN FOR TISSUE ENGINEERING APPLICATION - Intelligent Scaffolds for Tissue Engineering and Regenerative Medicine - page 438

is insoluble even in dilute aqueous acidic solutions. 11 It is from
resultsofX-raydiffractionpatternsofthetwochitosansthatthefor-
mer chitosan is a random copolymer of N -acetyl-glucosamine and
N -glucosamine units and the latter chitosan is a block copolymer. 14
The solubility of chitosan depends on the distribution of free amino
and N -acetyl groups. The free amino groups are ionized in a dilute
aqueousacidicsolutionofaroundpH6orless,andthenthechitosan
becomes soluble. 2 The solubility of chitosan can be varied depend-
ing on itsmolecular weight andchemical structure.
Several studies have examined the host tissue response
to chitosan-based implants, because the chemical structure of
chitosan is very similar to that of glycosaminoglycans (GAG) exist-
ing in living tissue. 15 In the results of the studies, chitosan is non-
toxic, biodegradable, and biocompatible with living tissues 13 and
degrades by lysozyme, the primary enzyme in body fluid, through
hydrolysis of acetylated residues in vivo . The degradation rate of
chitosan is inversely related to the degree of crystallinity and
depends on the degree of deacetylation. 16 , 17 Chitosan also has a
free amine group of a cationic charge and is responsible for electro-
static interactions with anionic GAG, proteoglycans, and other neg-
atively charged molecules. 2 Chitosan can be combined with vari-
ous materials such as alginate, collagen, hydroxyapatite, hyaluronic
acid, polymethylmethacrylate, calcium phosphate, poly-L-lactic acid
(PLLA), poly(D,L-lactic-co-glycolic acid) (PLGA), and growth factors
for potential applications. 1 , 18 - 24
Chitosan has a wide range of applications since it can be for-
mulated into a variety of forms, including powders, gels, and films,
and can also provide controlled release of growth factors and
ECM components. 20 - 22 In the recent studies, chitosan has good
characteristics for the attachment, proliferation, and viability of
mesenchymal stem cells (MSCs). 23 , 24 On the other hand, a hemosta-
sis bandage from chitosan was developed and commercialized
by HemCon Medical Technologies, Inc., and was approved by the
Food and Drug Administration (FDA). Chitosan attracts red blood
cells, which have a negative charge, because chitosan has a posi-
tive charge. The red blood cells create a seal over the wound as
they are drawn into the bandage, forming a very tight, coherent
seal. 25 With these promising features, chitosan is considered a very