Biomedical Engineering Reference
In-Depth Information
or organic solvent processing, and can be chemically modified to suit a wide range of
biomedical applications.
BiomediCal aPPliCatioNs oF BioPolymer aNd its ComPosites
Chitosan and its derivatives
Chitosan, poly-β-(1→4)-2-amino-2-deoxy-D-glucose, is an aminopolysaccharide de-
rived from the N-deacetylation of chitin, which is a structural element in the exoskel-
eton of crustaceans (crabs, shrimps, etc.) and cell wall of fungi and it is also classified
as a natural polymer because of the presence of a degradable enzyme, chitosanase.
This polymer possesses hydrogel like properties through a reaction with glutaralde-
hyde as cross-linking agent. It is known that cross-linked chitosan hydrogel can swell
extensively due to the positive charges on the network and in response to changes in
the pH of the medium. It has been shown (Nunthanid et al., 2004; Puttipipatkhachorn
et al., 2001) that the drug release behavior of chitosan is governed mainly by the swell-
ing property, the dissolution characteristic of the polymer films, the pKa of the drug,
and the drug
-
polymer interaction. Thus chitosan has been studied as a unique vehicle
for the sustained delivery of drugs. For example, it was investigated for the delivery
of drugs such as prednisolone (Kofuji et al., 2000) and diclofenac sodium (Gupta and
Ravi Kumar, 2000). Chitosan displays interesting properties such as biocompatibility,
biodegradability, and its degradation products are non-toxic, non-immunogenic, and
non-carcinogenic. Moreover, chitosan is metabolized by certain human enzymes, es-
pecially lysozyme, and is considered as biodegradable.
The physicochemical and biological properties of chitosan led to the recognition of
this polymer as a promising material for biomedical applications. One of these proper-
ties is the antimicrobial activity of chitosan which is suggested for use in a variety of
different formulations, for example tapes for wound dressing, tooth paste or artificial
tears (Felt et al., 2000; Kim et al., 1999). The interaction between positively charged
chitosan and negatively charged microbial cell wall will lead to the leakage of intra-
cellular constituents of the microorganism. The binding of chitosan with DNA and
inhibition of mRNA synthesis occurs via the penetration of chitosan into the nuclei of
the microorganisms and interfering with the synthesis of mRNA and proteins. Wound
healing, another major application, is a complex process that can be compromised by
a number of factors.
Chitosan has been investigated by many researchers for a long time as possible
wound healing accelerators (Muzzarelli et al., 1988; Nishimura et al., 1986; Zikakis,
1984). Chitosan-based wound dressing delivers substances, which are active in wound
healing; either by delivery of bioactive compounds or dressings are constructed from
materials having endogenous activity. Chitosan has been known as being able to ac-
celerate the healing of wound in human (Kojima et al., 1998). Kifune et al. (1988) re-
cently developed a new wound dressing material, Beschitin W, a commercial product
that is composed of chitin nonwoven fabric and that has been found to be beneficial
in clinical practice (Kifune et al., 1988). The ability of chitosan to promote neovas-
cularization has been demonstrated by implanting it in the cornea. It is also reported
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