DATA: THE NEW CORPORATE RESOURCE - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 12

advantage offered by the use of self-assembling block copolymers is that
covalent modiication of CNTs' sidewalls, which introduces defects, reduces
the strength of the nanotubes and induces a perturbation of their electronic
structure, is not required. 32

1.5 STABILISATION OF AQUEOUS SUSPENSIONS OF CARBON
NANOTUBES BY CHITOSAN AND ITS DERIVATIVES

Covalent and non-covalent stabilisation of aqueous suspensions of CNTs has
recently been attempted by several research groups by using chitosan and its
derivatives. Chitosan is a biocompatible, safe, stable and biodegradable semi-
synthetic polymer obtained by alkaline deacetylation of chitin (Fig. 1.8), the
most abundant natural polysaccharide after cellulose. 33-35 Chitosan is a linear,
semi-rigid polysaccharide that presents a rigid crystalline structure through
inter- and intramolecular hydrogen bonding. 36 It is insoluble in water and
most organic solvents but soluble in aqueous diluted acids as the amine
groups of the polymer become protonated and result in a soluble, positively
charged polysaccharide that has a high charge density. 37
Chitosan exhibits a wide variety of activities; its immuno-stimulatory effect
has been investigated for applications in wound healing and regenerative
medicine, 38 and its antibacterial effect has also been studied for biomedical
and food industry applications. 39 Furthermore, chitosan has been found to
be a versatile carrier for biologically active species and drugs because of its

CH 2 O H

CH 2 O H

O

*

O O

*

n

O

n

NaOH

OH

OH

*

*

NH

NH 2

CO
CH 3

CHITIN CHITOSAN

Figure 1.8 Synthesis of chitosan by alkaline deacetylation of chitin.

properties as an absorption enhancer and mucoadhesive polymer, 40,41 and it
has also been extensively studied as a vaccine and gene therapy carrier. 42,43
The presence of functional groups such as primary and secondary hydroxyl
groups and amino groups along the polymeric backbone have allowed for
easy modiication of the polysaccharide and led to the synthesis of derivatives
with new and improved properties. 44-48 Owing to the variety of properties
and possible applications of chitosan and its derivatives, a lot of interest has
been raised in their use for the preparation of polymer-CNT composites.