Biocompatible polymers, molecular

Protein drugs have been formulated with excipients intended to stabilize the protein in the milieu of the pharmaceutical product. It has long been known that a variety of low molecular weight compounds have the effect of preserving the activity of proteins and enzymes in solution. These include simple salts, buffer salts and polyhydroxylated compounds such as glycerol, mannitol, sucrose and polyethylene glycols. Certain biocompatible polymers have also been applied for this purpose such as polysaccharides and synthetic polymers such as polyvinyl pyrrolidone and even nonionic surfactants. 

Fig. 3 Hydrolyzable, acid-sensitive and reducible bonds. Efficient and biocompatible high molecular weight polymers are created by reversible linkage of small molecular weight compounds. Thus, programmed biodegradation due to, for example, hydrolyzable ester bonds [92] (a), acid-sensitive ketal (b) or acetal linkages (c) [98] is possible. The reducing cytosolic environment can also be taken advantage of in order to create biodegradable polymers by introduction of disulfide bonds as shown in (d) [105, 106]...

As a silicone mbber membrane is not permeable to hydrophilic or high molecular weight compounds, concerted efforts were made to develop other biocompatible polymers for use in implantable devices. Such polymers include poly(ethylene-co-vinyl acetate), poly (ethylene), poly(propylene), poly(hydroxymethyl methacrylate), poly(lactide-co-glycolide), poly (anhydrides) and poly(ortho esters). The characteristics and applications of each important polymer family will be discussed later in this chapter. 

Among all reported polymers used as soluble support, poly(ethyleneg-lycol) (PEG) is the most popular. Such material is relatively polydisperse with average molecular weights around 2000,3400, or 5000. Water-soluble PEG of lower molecular weights (<1000 mass units) are widely used as biocompatible polymers. Indeed, the solubility in water increases with decreasing molecular weight. In the frame of liquid-phase syntheses, two... 

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