Chitin and chitosan

Native chitin is highly crystalline and, depending on its origin, it occurs in three forms identified as a-, P-, and y-chitin, which can be differentiated by infrared and solid-state NMR spectroscopy together with X-ray diffraction (XRD). From a detailed analysis, it seems that the latter is just a variant of the a form [70]. In both 

Chitin has been known to form microfibrillar arrangements embedded in a protein matrix, and these microfibrils have diameters ranging from 2.5 to 2.8 nm [81]. Crustacean cuticles possess chitin microfibrils with diameters as large as 25 nm [82, 83]. Although it has never been specifically measured, the stiffness of chitin nanocrystals thought to be at least 150 GPa, based on the observation that cellulose is about 130 GPa and the extra bonding in chitin crystallites is going to stiffen it further [84]. 

Similar to conventional composites, the role of the matrix is to support and protect their nanoreinforcements, which are the stronger and stiffer components held together by the matrix. The matrix then transmits and distributes applied load to the nanoreinforcements [11, 12, 18, 19], Because the range of particle sizes is in the nanoscale, the surface area of the reinforcement is much higher, so the role of the particle/matrix interfacial region is even more important. 

Matrix molecules can be anchored to the reinforcement surface by chemical reactions or adsorption, which determines the strength of interfacial adhesion. In certain cases, the interface may be composed of an additional constituent such as a bonding agent or an interlayer between the two components of the composite. The choice of a matrix depends on several factors like application, compatibility between the components, technique of processing, and costs. 

1) polymers from biomass such as polymers from agricultural resources such as starch and cellulose  

Direct phosphorylation of chitin and chitosan has been reported but the degree of phosphorylation is uncertain. Such products are polyelectrolytes and may have medical or cosmetic applications. 

A variety of phosphorylated chitin, whose structure is unknown, is reported to be a strong absorber of metallic cations. It will absorb large amounts of uranium cations from dilute aqueous solution and has potential use as an extractant [39]. 

Chitosan and some of its derivatives, which are cationic polyelectrolytes, when mixed with alkali polyphosphates (anionic polyelectrolytes) will produce insoluble or gel-like macromolecular complexes. These are reported to be of use in microcapsules and in biotechnology. The structures of these materials are not known, but they presumably involve cross-linking between the chitosan and polyphosphate chains (10.32). 

Chitin/calcium phosphate complexes can form the basis of artificial bone and dental materials [40] and phosphated chitosan derivatives have been patented as detergent builders [41]. A protonconducting biopolymer has been obtained from chitin phosphate and imidazole [42]. 

Chitin is a polysaccharide constituted of N -acctylglucosamine, which forms a hard, semitransparent biomaterial found throughout the natural world. Chitin is the main component of the exoskeletons of crabs, lobsters and shrimps. Chitin is also found also in insects (e.g. ants, beetles and butterflies), and cephalopods (e.g. squids and octopuses) and even in fungi. Nevertheless, the industrial source of chitin is mainly crustaceans. 

Because of its similarity to the cellulose structure, chitin may be described as cellulose with one hydroxyl group on each monomer replaced by an acetylamine group. This allows for increased hydrogen bonding between adjacent polymers, giving the polymer increased strength. 

Chitin s properties as a tough and strong material make it favourable as surgical thread. Additionally, its biodegradibility means it wears away with time as the wound heals. Moreover, chitin has some unusual properties that accelerate healing of wounds in humans. Chitin has even been used as a stand-alone wound-healing agent. 

Industrial separation membranes and ion-exchange resins can be made from chitin, especially for water purification. Chitin is also used industrially as an additive to thicken and stabilize foods and pharmaceuticals. Since it can be shaped into fibres, the textile industry has used chitin, especially for socks, as it is claimed that chitin fabrics are naturally antibacterial and antiodour (www.solstitch.net). Chitin also acts as a binder in dyes, fabrics and adhesives. Some processes to size and strengthen paper employ chitin. 

The amino group in chitosan has a pKa value of about 6.5. Therefore, chitosan is positively charged and soluble in acidic to neutral solutions with a charge density dependent on pH and the deacetylation extent. In other words, chitosan readily binds to negatively charged surfaces such as mucosal membranes. Chitosan enhances the transport of polar drugs across epithelial surfaces, and is biocompatible 

Chitin is the second most abundant agro-polymer produced in nature after cellulose. It appears in nature as ordered crystalline microfibrils forming structural components in the exoskeleton of arthropods or in the cell walls of fungi and yeasts [Rinaudo, 2006]. It is an acetylated polysaccharide composed of N-acetyl-D-glucosamine. 

Chitosan is obtained from the deacetylation of chitin, which is found in marine environments. Because it is insoluble in water, chitosan is dissolved in acidic solutions before being incorporated into biodegradable polymer films. It can also be plasticized with glycerol to obtain a kind of thermoplastic material like, for instance, plasticized starch (Epure, 2011]. 

Pectin is a linear macromolecule composed of D-galacturonic acid. This monomer unit could be partially replaced by L-rhamnose leading to a new structure named rhamnogalacturonan I. A third pectin structural type is rhamnogalacturonan II, which is a less frequent, but complex and highly branched polysaccharide (Thakur, 1997 Averous and Pollet, 2012]. 

Proteins are agro-polymers. They are an Important renewable resources produced by animals, plants, and bacteria. The term protein comes from the Greek, proteios, for primary, first and foremost. A certain number of proteins have received much attention as biodegradable polymers but few have led to actual industrial scale-up due to the high production cost and the low 

Reprinted from [a.212] with permission from Elsevier  

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The subject of fiber production from chitin and chitosan has been reviewed considering the interest in the exploitation of chitin as a textile material [246-251]. The production of fibers, however, is a challenging and difficult task. 

Peculiar characteristics of chitins and chitosans are hemostatic action, anti-inflammatory effect, biodegradability, biocompatibihty, besides antimicrobial activity, retention of growth factors, release of glucosamine and M-acetylglucosamine monomers and oligomers, and stimulation of cellular activities [11,12,295-297]. 

Many years ago chitin was seen as a scarcely appeahng natural polymer due to the variety of origins, isolation treatments and impurities, but the works of several analytical chemists and the endeavor of an increasing number of companies have qualified chitins and chitosans for sophisticated applications in the biosciences. Chemistry today offers a range of finely characterized modified chitosans for use in the biomedical sciences. Moreover, surprising roles of these polysaccharides and related enzymes are being unexpectedly discovered [351]. 

UrbanczykGW (1997) In Goosen MFA (ed) Applications of Chitin and Chitosan. Technomic, Basel, p. 281... 

Numerous substituted derivatives of chitin and chitosan are known [67] some important examples are shown in Scheme 10.9. The possibility of forming either anionic (5,7,8,11) or cationic (9,12) derivatives should be noted. The O-carboxymethyl (5) and N-carboxymethyl (11) polymers are of particular interest as they have stronger complex-forming capabilities with metal ions than either unsubstituted chitosan or EDTA [65]. In practice, derivatives formed by substitution via the 2-amino group of chitosan are more common than those substituted via the 6-hydroxy position of the glucopyranose grouping [65]. 

Chitin and chitosan, Ed. G Skjak-Brack, T Anthonsen and P A Sandford (London Elsevier Applied Science, 1989). 

Christiansen, M.E. 1986. Effect of diflubenzuron on the cuticle of crab larvae. Pages 175-181 in International Conference on Chitin and Chitosan. Plenum Press, New York. 

Gupta V., Agarwal J., Sharma S. Adsorption Analysis of Mn(VII) from Aqueous Medium by Natural Polymer Chitin and Chitosan, Asian J. of Chem., 20(8), 6195-98 (2008)... 

Chitin and Chitosan Sources, Chemistry, Biochemistry, Biochemistry, Physical Properties and Applications Skjak-Braek, G. Anthousen, T. Sanford, P., Eds. Elsevier Applied Science New York, NY, 1989 835 pp. 

Hirano, S. Tokura, S. Chitin and Chitosan Japanese Society of Chitin and Chitosan Tottori, 1982. 

Chitin and chitosan derivatives have also been studied as blood compatible materials both in vivo and in vitro [520], Anticoagulant activity was greatest with O sulfated N acetyl chitosan, followed by N,0 sulfated chitosan, heparin, and finally sulfated N acetyl chitosan. The lipolytic activity was greatest for N,0 sulfated chitosan followed by heparin. The generally poor performance of chitosan was attributed to polyelectrolyte complexes with free amino groups present on the membrane surface. The O sulfate or acidic group at the 6 position in the hexosamine moiety was identified as the main active site for anticoagulant activity. 

Usami, Y., Okamoto, Y., Takayama, T., Shigemasa, Y., and Minami, S. (1998). Chitin and chitosan stimulate canine polymorphonuclear cells to release leukotriene B4 and prostaglandin E2.. Biomed. Mater. Res. 42,517-522. 

Anandan, R., Mathew, S., and Viswanathan, N. P. G. (2004). Antiulcerogenic effects of chitin and chitosan on mucosal antioxidant defense system in HCl-ethanol induced ulcer in rats. ]. Pharm. Pharmacol. 56, 265-269. 

Imonek, J. and Bartonova, H. (2005). Effect of dietary chitin and chitosan on cholesterolemia of rats. Acta Vet. Brno 74,491-499. 

Kurita, K. (2006). Chitin and chitosan Functional biopolymers from marine crustaceans. Mar. Biotechnol. 8,203-226. 

Sugano, M., Yoshida, K., Hashimoto, H., Enomoto, K., and Hirano, S. (1992). Hypocholesterolemic activity of partially hydrolyzed chitosan in rats. In "Advances in Chitin and Chitosan", (C. J. Brine, P. A. Sanford, and J. P. Zikakis, Eds), pp. 472-478. Elsevier Applied Science, London and New York. 

Uchida, Y., Izume, M., and Ohtakara, A. (1989). Preparation of chitosan oligomers with purified chitosanase and its application. In "Chitin and Chitosan", (G. Skjak-Braek,... 

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