Polysaccharides as Nanomaterials for Therapeutics - Harnessing Biomaterials in Nanomedicine: Preparation, Toxicity, and Applications - page 125

stability, low cost, hydrophilic nature, and availability of reactive sites
for chemical modification. In addition, many polysaccharides possess
bioadhesive properties, especially for mucosal surfaces, which have
been used for both targeting and prolonging drug residence time. All
of these qualities have led to the growing use of polysaccharides in
drug delivery systems.
The properties of common polysaccharides used for the
preparation of drug delivery systems are detailed below.
5.2.1 Chitosan
Chitosan is a linear polysaccharide composed of β-(1,4)-linked
D-glucosamine and N -acetyl-D-glucomasine (Figure 5.1). Chitosan
is obtained by deacetylation from chitin, a highly abundant
polysaccharide, which is the main component of crustaceans
exoskeleton [5]. Chitosan and its derivates are currently the most
widely used polysaccharides in newly developed drug delivery
systems. Chitosan-based delivery systems have been described for
nasal, ocular, oral, parenternal, and transdermal drug delivery [6-9].
Among the many advantages of chitosan are its low cytotoxicity and
biocompatibility [10, 11]. In addition, chitosan is positively charged
and therefore can interact with negatively charged molecules such
as negatively charged polysaccharides, polyanions, nucleic acid
and negatively charged proteins. Its positive charge also facilitates
adherence to mucosal surfaces, which are mostly negatively charged
[12, 13]. In addition, the ability of chitosan to open tight junctions
between epithelial cells and therefore increase the permeation
of macromolecular drugs across the mucosal epithelia has been
demonstrated [14, 15]. In spite of these advantages, chitosan is
inherently insoluble in aqueous solutions above pH 6.5 [16, 17].
High degree of deacetylation, low molecular weight, and chemical
modification can facilitate water solubility of chitosan. These factors
also aff ect particle properties such as size, surface charge, drug
entrapment efficiency, and stability [18].
5.2.2 Alginate
Alginate is a linear anionic polysaccharide composed of alternating
blocks of 1,4-linked β-D-mannuronic acid (M) and α-l-guluronic acid
(G) residues (Figure 5.1). The monomer composition of alginate is