Polymers with Hydrolyzable Backbones

A method for gelatin application to produce thin flexible artiflcial skin adherent to an open wound to protect it from infection and fluid loss has been developed. This material was obtained as a blend of commercial gelatin and polyglycerol, either natural or after its epoxidation with epichlorohydrin, formed into thin films by casting on trays covered with Teflon. The films were tough and spontaneously adhered to open wounds. The films can contain bioactive molecules such as growth factors or antibiotics that will be released for a couple of days. The skin substitute prepared in this way could be sterilized with y-rays or produced under sterile conditions [26]. 

Pofycaprolactone (PCL) has been thoroughly examined as a biodegradable medium and as a matrix in controlled drug-release systems. PCL is predominantly produced in the e-caprolactone polymerization process [32-35]. Tokiwa and Suzuki [36] studied the hydrolysis process and PCL biodegradation by fungi and showed that polycaprolactone can be broken down enzymatically. 

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A polymer is a very large, chain-like molecule made up of simple chemical units called monomers. It can be naturally occurring or synthetic. Polymers have a wide range of applications and can be classified into three major groups biopolymers, polymers with hydrolyzable backbones, and polymers with carbon backbones [9,10]. 

Synthetic polymers with hydrolyzable backbones have been found to be susceptible to biodegradation. In this group you can find polymers such as ... 

Polymers with hydrolyzable linkages in the backbone can also be used as degradable materials. So far, most of them are too expensive and do not have the desirable combination of mechanical and chemical properties. Well-known synthetic hydrolyzable polymers are polyesters [1], polycarbonates [2], polyanhydrides [2], polyamides [2] and poly(amino acids) [2]. Hydrolyzable natural polymers may be cheaper and are believed to be representative of the future development in degradable polymers. Many scientists today are looking for new possibilities using such traditional natural polymers as polysaccharides, proteins and lipids. Special interest is focused on poly(j8-hydroxybutyrate) and its copolymers [3,4]. Well-known natural products... 

Polyesters, such as microbially produced poly[(P)-3-hydroxybutyric acid] [poly(3HB)], other poly[(P)-hydroxyalkanoic acids] [poly(HA)] and related biosynthetic or chemosynthetic polyesters are a class of polymers that have potential applications as thermoplastic elastomers. In contrast to poly(ethylene) and similar polymers with saturated, non-functionalized carbon backbones, poly(HA) can be biodegraded to water, methane, and/or carbon dioxide. This review provides an overview of the microbiology, biochemistry and molecular biology of poly(HA) biodegradation. In particular, the properties of extracellular and intracellular poly(HA) hydrolyzing enzymes [poly(HA) depolymerases] are described. 

Poly( vinyl alcohol) is a versatile polymer with many industrial applications, and it may be the only polymer with an all carbon-carbon bond backbone that is truly biodegradable. The monomer is vinyl acetate, which is readily polymerized with free radical initiators to form poly(vinyl acetate), and the latter can be hydrolyzed either partially to prepare vinyl alcohol-vinyl acetate copolymers, or fully to prepare poly(vinyl alcohol). At high vinyl alcohol contents, the copolymers, and the vinyl alcohol homopolymer, are water soluble, and the aqueous solutions of these polymers find many applications for example, as adhesives or for coatings. The homopolymer and the very high vinyl alcohol copolymers are crystalline with melt transitions between 180 and 230 °C and glass transitions between 58 and 85 °C, depending on the vinyl alcohol content. The polymers can be melt processed to form molded plastics, fibers and films [36]. 

In these schemes only one of the positional isomers is shown, but analysis indicated that about 70% of the methyl ester is on the number 1 position and 30% on the number 2 position of the 1,2,4-benzenetricarboxylic acid monomer mixture. Therefore, in reality, the length of the straight backbone sections between bends is on average 30% longer than shown. The ester groups are then selectively hydrolyzed by treating the hot solutions of the polymers with Lil to produce the respective carboxy-decorated polyamides without any measurable reduction in chain length. 

Although polymers with the —P=N— backbone were produced as long ago as the 1890s by ring-scission polymerization of (NPCljls, moisture hydrolyzes the polymer to a brittle material. 

One of the most successful conjugate polymer systems was developed by Duncan and Kopecek (25). The polymer carrier used in their system is poly [N(2-hydroxypropyl) methacrylamide] a biocompatible polymer that was originally developed as a plasma extender. They have evaluated a number of polymer conjugated drugs for cancer chemotherapy with interesting results. The attachment of the drug is through a peptidyl spacer pendent to the polymer backbone. These peptides links are stable in aqueous media but are readily hydrolyzed intracellularly... 

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