The interest in chitin originates from the study of the behaviourand chemical characteristics of lysozyme, an enzyme present in the human bodyfluids. It dissolves certain bacteria by cleaving the chitinous material of thecell walls17. A wide variety of medical applications for chitin andchitin derivatives have been reported over the last three decades42,43.It has been suggested that chitosan may be used to inhibit fibroplasia in woundhealing and to promote tissue growth and differentiation in tissue culture44.
The synthesis of chitosan hydrogels was carried out by Qu .29 by direct graftingof lactic and/or glycolicacid onto chitosan in the absence of catalysts. They demonstrated that astronger interaction existed between water and chitosan chains after graftinglactic and/or glycolic acid. The side chains could aggregate and form physicalcrosslinking, which results in pH-sensitive chitosan hydrogels9,30-33.These hydrogels are considered potentially useful for biomedical applicationssuch as, wound dressings and drug delivery systems, since both polyester sidechains and chitosan are biocompatible and biodegradable34.
Antioxidant effect of chitin, chitosan, and their derivatives may be used as functional ingredients in food formulations to promote consumer health and to improve the shelf life of food products.
Commercial availability of high-purity forms of chitin, chitosan and the continuous appearance of new types of chitin / chitosan derivatives with more and more useful and specific properties have led to an unlimited R&D efforts on this most versatile amino polysaccharide, chitin to find new applications, which are necessary to realize its full potential.
This book is divided into following sections:* Production and derivatives of chitosan* Chitosan in the textile and food industries* Chitosan in biomedical applications* Chitosan in agriculture and water treatment The book is practical as readers will be able to see descriptions of chitosan production methods as well as techniques that can be used to estimate and modify their physical and chemical properties.
Chitin and chitosan are considerably versatile and promisingbiomaterials. The deacetylated chitin derivative, chitosan is more useful andinteresting bioactive polymer. Despite its biodegradability, it has manyreactive amino side groups, which offer possibilities of chemicalmodifications, formation of a large variety of useful derivatives that arecommercially available or can be made available via graft reactions and ionicinteractions. This study looks at the contemporary research in chitin andchitosan towards applications in various industrial and biomedical fields.
Chitin is the second most ubiquitous natural polysaccharideafter cellulose on earth and is composed of (14)-linked2-acetamido-2-deoxy--D-glucose1 (-acetylglucosamine) (Figure 1). It isoften considered as cellulose derivative, even though it does not occur inorganisms producing cellulose. It is structurally identical to cellulose, butit has acetamide groups (NHCOCH3) at the C-2 positions. Similarly theprinciple derivative of chitin, chitosan is a linear polymer of (14)-linked2-amino-2-deoxy---glucopyranose and is easily derivedby -deacetylation, to a varyingextent that is characterized by the degree of deacetylation, and isconsequently a copolymer of -acetylglucosamineand glucosamine (Figure 2). Chitin is estimated to be produced annually almostas much as cellulose. It has become of great interest not only as anunder-utilized resource but also as a new functional biomaterial of highpotential in various fields and the recent progress in chitin chemistry isquite significant.
109. Lu AH, Salabas EL, Schüth F. Magnetic nanoparticles: synthesis, protection, functionalization, and application. 2007;46:1222-44
Chitin and chitosan the naturally abundant and renewablepolymers have excellent properties such as, biodegradability,bio-compatibility, non-toxicity, and adsorption2. The reaction ofchitosan is considerably more versatile than cellulose due to the presence of-NH2 groups. Various efforts have been made to prepare functionalderivatives of chitosan by chemical modifications3, graft reactions,ionic interactions, and only few of them are found to dissolve in conventionalorganic solvents4. Chitosan is only soluble in aqueous solutions ofsome acids, and some selective -alkylidinations3,5and -acylation4,6 havealso been attempted. Although several water-soluble7 or highlyswelling2 derivatives are obtained, it is difficult to develop thesolubility in common organic solvents by these methods. Modification of thechemical structure of chitin and chitosan to improve the solubility inconventional organic solvents has been reviewed by many authors8-13.On the other hand, only a few reviews have been reported on biomedicalapplications of chitin/chitosan14-16, and no comprehensive reviewhas yet been published covering the entire range of applications. The presentreview covers the literature from 1993 to 2003 dealing with properties,processing, and applications in various industrial and biomedical fields.
Chitosan may be readily derivatized by utilizing thereactivity of the primary amino group and the primary and secondary hydroxylgroups. Glycol chitin, a partially -hydroxyethylatedchitin was the first derivative of practical importance4,23.
Derivatives of chitin may be classified into two categories;in each case, the -acetyl groups areremoved, and the exposed amino function then reacts either with acyl chloridesor anhydrides to give the group NHCOR or is modified by reductive amination toNHCH2COOH of greatest potential importance are derivatives of bothtypes formed by reaction with bi- or polyfunctional reagents, thus carryingsites for further chemical reaction24,25. In practice, suchreactions are carried out on native chitin or on incompletely deacetylatedchitin, chitosan, so that the resulting polymer contains three types ofmonomeric units.
These polyampholytes are particularly effective in removingmetal cations from dilute solutions. Chitosan itself chelates metal ions,especially those of transition metals, and also finds application as a matrixfor immobilization of enzymes26. Special attention has been given tothe chemical modification of chitin, since it has the greatest potential to befully exploited. Reactions with pure chitin have been carried out mostly in thesolid state owing to the lack of solubility in ordinary solvents. A 50 per centdeacetylated chitin has been found to be soluble in water1,17. Thiswater-soluble form of chitin is a useful starting material for its smoothmodifications, through various reactions in solution phase. Some of the veryrecently reported chitosan derivatives are enumerated as follows: