Chemical derivatization of chitosan provides a powerful means to promote new
biological activities and to modify its mechanical properties. The primary amino
groups on the molecule are reactive and provide a mechanism for side group
attachment using a variety of mild reaction conditions. The general effect of addition
of a side chain is to disrupt the crystal structure of the material and hence increase the
amorphous fraction. This modification generates a material with lower stiffness and
often altered solubility, but the precise nature of changes in chemical and biological
properties depends on the nature of the side groups. In addition, the characteristic
features of chitosan such as being cationic, hemostatic and insoluble at high pH, can
be completely reversed by a sulfation process that can render the molecule anionic
and water-soluble, and also introduce anticoagulant properties [7].
2.1.3 Biochemical Significance and Degradation of Chitin and Chitosan
Because both chitin and chitosan are biological materials and have excellent
biocompatibility, they have been developed as medical materials in recent years.
Some enzymes such as lysozyme and chitinase degrade chitin. Plants and insects
have chitinase but not mammals except cow, sheep and goat. Chitin and chitosan
are thought to be degraded mainly by lysozyme in mammals. Lysozyme in
mammalians is present in serum, saliva and other secretary fluids, including those
surrounding the cartilage. There are many kinds of glycosidase in the animal body
to hydrolyze chitin and its derivatives, including lysozyme. The 6-O-acyl, 6-Oalkyl and carboxymethyl chitin derivatives have similar enzymatic hydrolysis.
The rate of lysozymic hydrolysis of various chitosans are quite low compared
with those of other chitin derivatives, probably because of the poor binding ability
of chitosan to the active site of lysozyme.
2.1.4 Applications of Chitosan in Biomedical Technology
Biomedical applications relate to the impact of a material, device or procedure in a
medical or clinical situation on the health care of humans. The expected outcome
should be positive when properly utilized. The application can be a medical device
as simple as a syringe or a piece of gauze for cleaning wounds, or as complex as
pacemakers, orthopaedic implants and artificial heart valves. For the purpose of this
review, we take a focused view by considering the biomedical applications that
have been proposed for chitin and chitosan.
The name chitosan covers a large collection of preparations that all have nearly
the same natural composition but are different in their characteristics and applicability due to variations in source, charge, charge density, molecular weight and
crystallinity. For a specific application, this complicates the search for the most
useful form of chitosan, but it presents a large range of chitosan candidates that
might serve the specific purpose. Chitosans in diverse physical and chemical forms
have been introduced for a variety of applications in the sector of medical
Biopolymeric Micro- and Nanoparticles: Preparation, Characterization and. . .
275
biological activities and to modify its mechanical properties. The primary amino
groups on the molecule are reactive and provide a mechanism for side group
attachment using a variety of mild reaction conditions. The general effect of addition
of a side chain is to disrupt the crystal structure of the material and hence increase the
amorphous fraction. This modification generates a material with lower stiffness and
often altered solubility, but the precise nature of changes in chemical and biological
properties depends on the nature of the side groups. In addition, the characteristic
features of chitosan such as being cationic, hemostatic and insoluble at high pH, can
be completely reversed by a sulfation process that can render the molecule anionic
and water-soluble, and also introduce anticoagulant properties [7].
2.1.3 Biochemical Significance and Degradation of Chitin and Chitosan
Because both chitin and chitosan are biological materials and have excellent
biocompatibility, they have been developed as medical materials in recent years.
Some enzymes such as lysozyme and chitinase degrade chitin. Plants and insects
have chitinase but not mammals except cow, sheep and goat. Chitin and chitosan
are thought to be degraded mainly by lysozyme in mammals. Lysozyme in
mammalians is present in serum, saliva and other secretary fluids, including those
surrounding the cartilage. There are many kinds of glycosidase in the animal body
to hydrolyze chitin and its derivatives, including lysozyme. The 6-O-acyl, 6-Oalkyl and carboxymethyl chitin derivatives have similar enzymatic hydrolysis.
The rate of lysozymic hydrolysis of various chitosans are quite low compared
with those of other chitin derivatives, probably because of the poor binding ability
of chitosan to the active site of lysozyme.
2.1.4 Applications of Chitosan in Biomedical Technology
Biomedical applications relate to the impact of a material, device or procedure in a
medical or clinical situation on the health care of humans. The expected outcome
should be positive when properly utilized. The application can be a medical device
as simple as a syringe or a piece of gauze for cleaning wounds, or as complex as
pacemakers, orthopaedic implants and artificial heart valves. For the purpose of this
review, we take a focused view by considering the biomedical applications that
have been proposed for chitin and chitosan.
The name chitosan covers a large collection of preparations that all have nearly
the same natural composition but are different in their characteristics and applicability due to variations in source, charge, charge density, molecular weight and
crystallinity. For a specific application, this complicates the search for the most
useful form of chitosan, but it presents a large range of chitosan candidates that
might serve the specific purpose. Chitosans in diverse physical and chemical forms
have been introduced for a variety of applications in the sector of medical
Biopolymeric Micro- and Nanoparticles: Preparation, Characterization and. . .
275