Chitosan Composites for Biomedical Applications: An Overview - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 20

It has been reported that SF film has good oxygen permeability in its wet state
(Minoura et al., 1990), which suggests promising applications of SF as wound dress-
ing, artificial skin, surgical sutures, and biocompatible devices with controlled drug
release. However, SF in a dry state is very brittle and unsuitable for practical uses
(Freddi et al., 1995). To overcome this limitation, SF has been reported to blend with
other synthetic polymers, such as polyacrylamide (Freddi et al., 1999) and poly(vinyl
alcohol) (Yamaura et al., 1990), or natural polymers, such as cellulose (Freddi et al.,
1995) and sodium alginate (Liang and Hirabayashi, 1992), to improve its mechanical
and physical properties.
alginate
Alginate is a naturally occurring polysaccharide extracted from seaweed (Gombotz
and Wee, 1998). Alginates are well established as food additives and as encapsula-
tion agents in biotechnology. Commercial production from harvested brown seaweeds
commenced in the early 20th century. Brown seaweeds and only the two Gram-neg-
ative bacteria genera Azotobacter and Pseudomonas are capable of alginate produc-
tion. Alginates belong to exopolysaccharides and are non-repeating copolymers of b-
d-mannuronic acid (M) and a-l-guluronic acid (G) which are linked by 1-4 glycosidic
bonds. The comonomer composition and arrangement strongly impact on the alginate
material properties, which range in nature from slimy and viscous solutions to pseudo
plastic materials. Alginate has the unique ability to form gels and is an excellent mem-
brane material. It is also chemically very stable at pH values between 5 and 10. In ad-
dition, a chitosan-alginate polyelectrolyte complex has been used to prepare devices
used for the controlled release of drugs (Foldvari, 2000; Mi et al., 2002; Ribeiro et al.,
2005; Shu and Zhu, 2002).
Alginates well meet the entire requirement for their use in pharmaceutical and
biomedical applications. They have been largely used in wound dressings, dental im-
pression, and formulations for preventing gastric reflux. When alginate comes into
contact with wound exudates, ion exchange occurs between the calcium ions of the
alginate and the sodium ions in the exudates resulting in the formation of a gel on the
surface of the wound. This gel absorbs moisture and maintains an appropriately moist
environment that is considered to promote optimal wound healing. For these reasons,
SF/alginate-blended sponge is likely to be an effective material that can be used for
wound dressing and provide the necessary requirements for recovery. The SF and
alginate have been proved to be invaluable natural materials in the field of biomedical
engineering. It was revealed that SF/alginate-blended sponge treatment produced the
most prominent wound healing effect as compared with either SF or alginate sponge
treatment. It was found that the synergic effect of SF/alginate blended sponge is main-
ly involved in the promotion of re-epithelialization rather than collagen deposition.
Furthermore, chitosan and alginate are also well known for accelerating the heal-
ing of wounds in humans (Qin, 2008; Ueno et al., 2001; Wang et al., 2002). These
two kinds of polymer form complexes through chemical binding, after lyophilization,
which creates the porous structure, the sponge formed to act as a topical applications
matrix. Wound dressing based on alginic material is well known, in literature as well
as from commercial point of view, in wound management (Paul and Sharma, 2004).