Naturally biodegradable polymers

naturally biodegradable polymers that have been modified with additives and fillers. 

Naturally biodegradable polymers produced in nature are renewable. Some synthetic polymers are also renewable because they are made from renewable feedstocks, for example polylactic acid (PLA) is derived from agricultural feedstocks. 

Amylopectin, the water-soluble portion of starch, has a molecular weight of 5 x 10 to 4 x 10 [9]. Normal corn starch is composed of 20-30% -amylose and 70-80% amylopectin [10]. 

The main use of thermoplastic starch alone is in foam applications. Starch-based foams have been found to be an effective alternative to PS foam in loose-fill protective packaging. Starch-based foams offer the advantage that they are readily biodegradable if they escape into the environment. They also offer superior antistatic properties. Starch-based foam, however, has some disadvantages it is brittle and the density is higher than PS. Foamed, starch-based articles are prepared by heating starch in an extruder in the presence of water with subsequent extrusion. 

One of the most crucial properties in packaging applications is bulk density. A comparison of bulk densities of expanded polystyrene loose-fill with starch-based foams is given in Table 6.1. 

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Since the purpose of this book is to describe applications of biodegradable polymers to drug delivery systems, particularly from the perspective of the materials employed, the approach taken in this chapter has been to focus on the natural biodegradable polymers which have been used most extensively as matrices for the delivery of drugs. Consideration was also given to the fact that collagen has not been the subject of any recent reviews. 

Biodegradable polymers can be categorized into natural and synthetic polymers. The typical examples of natural biodegradable polymers are proteins,... 

Vorhies, J.S., and Nemunaitis, J.J. (2008) Synthetic vs. natural/biodegradable polymers for delivery of shRNA based cancer therapies, in Macromolecular drag delivery (Belting, M., ed.), Humana Press, pp. 11-29. 

Synthetic vs. Natural/Biodegradable Polymers for Delivery of shRNA-Based Cancer Therapies... 

Key Players in Two Categories of Polymeric Non-viral Delivery Vehicle Systems Synthetic Polymers and Natural/Biodegradable Polymers... 

Many excellent options exist for synthetic and natural polymer-mediated delivery of shRNA. At present, synthetic polymers are limited by safety concerns and natural, biodegradable polymers are limited by efficacy issues. Active research in the field is causing these limitations to become less meaningful, but at present the choice to use a synthetic or a natural polymer for shRNA delivery must be made by considering the nature and location of the tumor(s) to be treated as well as the type of transcript to be targeted in order to maximize safety and optimize effectiveness. 

Polysacharides such as starch are the most prevalent naturally biodegradable polymer in commercial use. Aliphatic polyesters such as polyhydroxyalkanoates (PHA) are also a family of easily biodegradable polymers found in nature that are beginning to find commercial use. 

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. 

PH A blends with natural biodegradable polymers such as starch [108], pullulan [109], dextran, amylose and alginate [110], have been reported. Furthermore, blends of bacterially synthesized fully-biodegradable P(3HB)... 

Some cellulose derivatives and P(3HB) and P(3HB-co-3HV) have been found to show good compatibility [114-116]. These are chemically modified natural and natural biodegradable polymer blend systems. Blends obtained by melts compounding P(3HB) with cellulose acetate butyrate (CAB, degrees of butyrate and acetate substitution are 2.50 and 0.18, respectively) have been found to be miscible over the whole composition range by DSC and dynamic mechanical spectroscopy [116]. 

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... 

The natural biodegradable polymers that are most frequently used are polysaccharides, of which starch and cellulose derivatives are preferred. Starch is an inexpensive product available, e.g., from corn. It is biodegradable in a variety of environments. 

Natural biodegradable polymers with tailor-made properties offer excellent opportunities for advanced functional materials, e.g., biodegradable conductive nanocomposites based on polypyrrole (Ppy)/dextrin or PANI/dextrin provide enhanced conductive and antibacterial activities. 

CRA Cravo, C., Duarte, A.R.C., and Duarte, C.M.M., Solubihty of carbon dioxide in a natural biodegradable polymer Determination of diffusion coefficients, J. Supercrit. Fluids, 40, 194, 2007. 

A potentially important industrial extension of the production of naturally biodegradable polymers from renewable resources is the utilisation of biological processes to synthesise biodegradable polymers. 

Sharma K., Singh V., Arora A. (2011). Natural biodegradable polymers as matrices in transdermal drug delivery. Int. J. Drug Dev. Res., 3,85-103. 

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... 

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