Cellulose and Cellulose Derivative
Cellulose is a polysaccharide that is the main constituent of all plant tissues and fibers. The name cellulose, from Latin cellula, was coined in 1838 by French chemist Anselme Payen. Special forms of cellulose fiber are found in most plants in the leaves and stalks, with cotton fiber (95% cellulose) [149]; wood (about 50%) being the principle industrial sources of cellulose [150]. Because of its ubiquity in the plant kingdom, cellulose is arguably the most abundant polymer on earth, with billions of tons produced annually through photosynthesis. The strong glucosidic bonds ensure the stability of the cellulose in various media. Cellulose is mostly insoluble and highly crystalline. Chemical reactions such as esterification are conducted on the free hydroxyl groups to improve its thermoplastic behavior. The main uses of cellulose are for paper, membranes, dietary fibers, explosives and textiles [151]. CellophaneTMis a blend of cellulose and diaphane [152]. A transparent paper-like product that is impervious to moisture and used to wrap candy, cigarettes, etc. The name was coined in 1912 by Swiss chemist Jacques Edwin Brandenberger, the invention of the material dates from 1908. Cellophane films are obtained by dissolution of cellulose in a sodium hydroxide and carbon disulphide solution (Xanthation) and then by recasting in a sulphuric acid bath. Degradation takes place after six weeks of composting. Cellophane films are mainly used in food packaging where they are valuable for their barrier properties against microorganisms, gases and smells. Cellulose acetate is mainly used in the synthesis of membranes for reverse osmosis.
Cellulose is the principle part of most plant cell walls, and is currently of interest because of processes for paper making, and as a major structural component of textile fibers such as (Gossypium spp.), ramie (Boehmeria nivea), jute (Corcorus capsularis), flax (Linum usitatissiumum) and sisal (Agare sisalana). Surgical cotton is actually made from wood. Cellulose used as biopolymer, biomaterial, drug delivery, bacterial microparticles [153, 154].
Bacterial cellulose is synthesized in a process whereby the polymer material is extruded from the bacterial cells. Most cellulose-producing bacteria (i.e., Acefobacter) extrude cellulose as a ribbon-like product from one fixed site on the cell surface. This results in a network of interlocking fibers forming. Bacterial cellulose is produced under conditions of agitated fermentation. Bacterial cellulose is a water-insoluble material that has a large surface area because of its large network of fibers; bacterial fibers have roughly 200 times the surface area of fibers from wood pulp. This, coupled with their ability to form hydrogen bonds, makes them unique when used as suspensions, they have pseudoplastic thickening properties. The bacterial cellulose is used for dressing chronic wounds [155], nanocomposites [156], cancer treatment [157], natural rubber latex formation [158], antimicrobial food packaging applications [77], biocomposite [159], gravity-driven oil/water separation [160] and many others.
2.4.3 Hemicellulose
Hemicelluloses are a group of substances which occur in association with cellulose, and are usually a mixture of xylans, xyloglucans, arabinogalactans, glucomannans and galactoglucomannans. Hemicellulose is one of the most abundant polysaccharides after cellulose. Hemicelluloses were used as feedstock for producing sugars. Hemicelluloses are mostly heteropolysaccharides classified according to the sugar residues present, namely xylans, mannans, arabinans and galactans, and they are either linear or branched polymers. Xyloglucan is used as a barrier film [161].
2.4.4 Chitin and Chitosan
Chitin was discovered in 1811 by Braconnot and was initially termed fungine because it was discovered in mushrooms [25], it is derived from shrimp, crab, Antarctic krill, and cultivated fungi. It was later in 1823 that Odier gave the name chitin to the same material discovered now in the elytrum of the cock chafer beetle based on the Greek term chitos, meaning coat. Chitin as a natural polysaccharide is a tough, semitransparent horny substance; the principal component of the exoskeletons of arthropods and the cell walls of certain fungi.
Chitosan is known as soluble chitin [162–167]. Chitosan is produced commercially by deacetylation of chitin. It has many uses: diluent, binder, drug carrier, drug release, site specific drug delivery, absorption, enhancer, carrier, anticancer, anticoagulant, antiviral, antioxidant, tissue engineering and food technology. Chitosan is soluble in water and in some organic solvents. The difference between chitin and chitosan is defined by their solubility in a dilute solution of weak acids. Chitosan dissolves in dilute acetic acid. It presents a unique combination of properties, brought about by its polysaccharide structure, large molecular weight, and cationic character. Chitin and chitosan are biocompatible and present antithrombogenic and hemostatic properties. These polymers can be extruded to make films for packaging applications. Chitosan is used in many applications including: hydrogel, tissue engineering, drug delivery, tissue repair.
Chitosan is the partially or fully deacetylated form of chitin. The chitosan deacetylation degree is usually in the range between 70% and 95%, and the molecular weight is also between 10 to 1000 kDa. Its application in the tissue engineering and drug delivery fields is wide ranging from cartilage, bone, vascular grafts and skin to substrates for cell culture. Biologically renewable, biocompatible, biodegradable, non-toxic and non-antigenic properties of chitosan make it a bio-functionally useful biomaterial. In addition, hydroxyl and amino groups of chitosan can be modified chemically to provide a high chemical diversity. It also has bio-adhesive properties. Chitosan exhibits different behaviors at various pH levels. It does not dissolve at high pH while it is soluble at lower pH ranges. This property makes chitosan a suitable tool for delivery applications. Chitosan, and their derivatives have found a number of pharmaceutical or biomedical applications. Although chitosan was mostly used as a diluent in tablet manufacturing, it was also proposed as a binder, lubricant, or potential disintegrating agent. The mucoadhesive properties of chitosan make it an attractive material for the local delivery of drugs in the oral cavity.
2.4.5 Xanthan
Xanthan gum, a complex copolymer produced by a bacterium, one of the first commercially successful bacterial polysaccharides to be produced by fermentation [168, 169]. In terms of production volume, xanthan gum is the most widely used microbial polysaccharide. Worldwide production is currently in the range of 10,000 to 20,000 tons. Xanthans have many applications such as in hydrogel, antibacterial and catalytic applications, in silver nano-particles, in medicinal and pharmaceutical applications [170]. It is used in drug release [171], wound healing [172], blended hydrogels for connective tissue regeneration [173], immobilized biocatalyst [174], edible coatings and many others. Xanthan gum is a HMW extracellular polysaccharide produced by the fermentation of the gram-negative bacterium Xanthomonas campestris. Companies such as ADM and Merck have recently announced the expansion of their xanthan production facilities. About 60% of the xanthan produced is used in foods, with the remaining 40% used in industrial applications. Food-grade xanthan costs about $8 to $10 per pound, while non-food grades sell for about $5 per pound. So far, only experimental samples of genetically modified xanthan have been produced.
2.4.6 Dextran
Dextran is the generic name of a large family of microbial polysaccharides that are assembled or polymerized outside the cell by enzymes called dextran sucrases. This class of polysaccharides is composed of building blocks (monomers) of the simple sugar glucose [169, 175–177]. It can be found as storage material in yeasts and bacteria. Dextrans are produced by enzymatic conversion of the feedstock sucrose. Most commercial dextran production uses the microorganism Leuconstoc mesenteroides. Cyclodextrins is used as a stabilizer and in edotoxin removal [178]. Dextran polymers have some medical applications. Dextrans were used for wound coverings, in surgical sutures, as blood volume expanders, to improve blood flow in capillaries in the treatment of vascular occlusion, and in the treatment of iron deficiency anemia in humans and animals.
Chemically modified dextrans such as dextran sulfate [179] have antiulcer and anticoagulant
