Polymers natural, biodegradable

Natural biodegradable polymers (unmodified natural polymers). 

Modified, natural biodegradable polymers (natural biodegradable polymers modified with additives and fillers). 

Natural biodegradable polymers are produced in nature, thus are always renewable. Some synthetic biodegradable polymers are also renewable when produced from renewable feedstocks one example is polylactic acid (PLA), derived from agricultural sources. Modified natural biodegradable polymers can be totally or partially renewable, depending on the modifying agent used. 

Starch was added as filler to various resin systems to make films that were impermeable to water but permeable to water vapour. Starch as a biodegradable filler in LDPE was reported (Griffin, 1973 Griffin and Turner, 1978) and disposable polyvinyl chloride (Westhoff et al, 1974). There have been contrasting reports on the mechanical properties on starch/PLA composites (Kim et al, 1998 Willett, 1998). However, a recent report confirms that the 

Streptomyces genus (Berrocal et al, 1997). Even though hgnin biodegradation is aeeepted as an aerobic process, some audiors have reported that anaerobic microorganisms in the rumen may alter, if not partially degrade, portions of lignified plant cells (Akin, 1980). 

Albertsson A C and Ranby B (1976). In Sharpley J M and Kaplan A M (eds), Proc. 3rd Int. Biodegradation Symp., Applied Science Publishers, London, 743. 

Alexander M (1977). Introduction to Soil Microbiology (2nd edn), Wiley, New York. 

Allen N S Edge M Mohammadian M and Jones K (1994). Polym. Degrad. Stab., 43, 229. 

Enz5mie-catalyzed chain growth potymerization reactions of activated monomers are general involved in the synthesis of natural polymers, which are usualty formed within cells by complex metabolic process. 

The starch polymer consists of two important functional groups -OH group, which undergoes substitution reaction, and C-O-C bond, which undergoes breakage of chain. The hydroxyl group is nucleophilic and is modified for various properties. For example, reaction with silane improves its dispersion in 

By trans-esterification, the degree of acetylation can be easily controlled allowing polymers to form with a wide range of hydrophobicity. Starch acetate can be prepared by the acetylation of starch with pyridine acetic anhydride mixtures and cast into films from 90% solutions of formic acid. The wet strength of the film is maintained in the aqueous solution with sufficient acetyl content when exposed to buffered amylase solution. But the acetyl content permits degradation by a mixture of a- and /5-amylase in 1 h. These films can be useful as membranes for bioreactors, which are degraded by enzyme addition. 

Proteins are naturally occurring polymers in animals, plants, bugs, fungi, and other living organisms. These are made up of long-chain amino acids. A polymer protein with an amide group as the backbone is called polyamide, and artificial polyamides are known as nylon. 

---

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. 

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

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... 

---