Natural/biodegradable polymers chitosan

There are many kinds of natural biodegradable polymers. They are classified into three types according to their chemical structures, i.e., polysaccharides, polypeptides/proteins and polynucleotides/nucleic acids. Among them, polysaccharides, such as cellulose, chitin/chitosan, hyaluronic acid and starch, and proteins, such as silk, wool, poly( y-glutamic acid), and poly(e-lysin), are well known and particularly important industrial polymeric materials. 

There are several kinds of natural biodegradable polymers in addition to bacterial PHAs, such as proteins, nucleic acids and polysaccharides. Among them, particulary important polymers such as industrial materials are polysaccharides, such as starch, cellulose, chitin and chitosan. The solid-state structure and properties of starch and amylose [127], cellulose [128] and chitin... 

Chitosan. Chitosan (CH) is a natural biodegradable polymer. CH is a copolymer of glucosamine and N-aeetyl-u-glucosamine. It is derived by alkaline de-N-acetylation of chitin, whieh in turn is derived from... 

The naturally biodegradable polymers such as starch, chitosan and cellulose derived from natural sources have produced a number of interesting NR blends and IPNs. These blended systems have an advantage in that they create fewer waste disposal problems compared to the petroleum based polymeric materials. The use of stareh blends to enhance the biodegradability of conventional plastics has been reported by many researchers in order to reduce the environmental impaet of petroleum based plastic products and waste. The NR/maize stareh blends exhibited a decrease in their mechanical strength due to the speeifie properties of starch. However, the blended polymers showed a low interfaeial interaetion between the two phases due to the different polarity behaviour of the hydrophobic NR and the hydrophilic starch. 

Natural pol5miers are formed in nature during the growth cycles of all organisms. Natural biodegradable polymers are called biopolymers or renewable polymers. There are two main types of biopolymers those that come from renewable resources and those that need to be polymerized but come from renewable resources. Therefore, the first type includes potysaccharide (starch, chitosan), protein (keratin, soy protein, etc.) the second type includes potylactic acid (Tang et al., 2012). 

Biodegradable polymers, both synthetic and natural, have gained more attention as carriers because of their biocompatibility and biodegradability and therewith the low impact on the environment. Examples of biodegradable polymers are synthetic polymers, such as polyesters, poly(orfho-esters), polyanhydrides and polyphosphazenes, and natural polymers, like polysaccharides such as chitosan, hyaluronic acid and alginates. 

Chitosan Chitosan is a nontoxic, biodegradable polymer obtained by hydrolysis of chitin, a natural polysaccharide that is a chief component of the crustacean exoskeleton. Unmodified chitosan is soluble in acidic media and has significant muco-adhesive properties. 

Polysaccharide Containing Polymers. Chitosan (Table 7.3-1) is composed of 2-amino-2-deoxy p-D-glucan and is prepared from naturally occurring chitin via alkaline deacetylation. Unlike other cationic polymers chitosan is nontoxic and biodegradable, making it an ideal candidate for therapeutic applications. Although the density of positive charges of chitosan is lower than for other cationic polymers. 

Chitosan, a natural-based polymer obtained by alkaline deacetylation of chitin, is nontoxic, biocompatible, and biodegradable. These properties make chitosan a promising candidate for conventional and novel drug delivery systems. Because of the high affinity of chitosan for cell membranes, it has been used as a coating agent for liposome formulations [43-45]. 

Hyaluronic acid is a naturally occurring polysaccharide comprising monosaccharide sequences with carboxylic or acetamido side groups. Early production of hyaluronic acid, a biodegradable polymer similar to chitosan, was achieved through extraction of natural tissues, and the evolution of hyaluronic acid technology was made possible after its successful production in sufficient quantities as a fermentation product. The key evolution of... 

Overall, much effort has been made to develop biocompatible organic materials, which allows for the ultimate integration between the electronic device and biological system. The possibility of fabricating memory devices on biodegradable substrates, such as, rice paper and chitosan is also demonstrated. Biocompatible and flexible resistive switching memory devices are made on the basis of Ag-doped chitosan as the natural solid polymer electrolyte layer on the transparent and bendable substrate. Decomposable devices, where chitosan layer serves as the substrate while Mg as the electrode, have been also achieved (Hosseini and Lee, 2015). A comparison of the biocompatible material-based resistive switching memory devices is made in Table 3.2. 

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