Medical applications polymers

Every attempt has been made to include modem topics not covered in a convenient handbook format elsewhere, such as scaling and fractal dimensions, computational parameters, rotational isomeric state models, liquid-crystalline polymers, medical applications, biodegradability, surface and interfacial properties, microUthography, supercritical fluids, pyrolyzabil-ity, electrical conductivity, nonlinear optical properties, and electroluminescence. 

Rayleigh instability see axisymmetric varicose instability rayon, 4,6,18,20 recombinant silk fibres, 315-6 Recothrom, 581 relative density, 197 Relay devices, 661-2 resorbable biotextile, 94 resorbable polymers medical applications, 91-109 elastomeric properties of fibreforming copolymers, 97-101 elastomeric resorbable polymers, 101-8... 

Overviews on environmentally degradable plastics have recently appeared for the nonspecialist (1-4) as well as more technical symposia proceedings (5-13). Several extensive Web sites are maintained (14,15) and a commercial market report has been available (16) (see Biodegradable Polymers, Medical Applications). 

Green plastics comprise only a very small part (less than 1%) of today s plastics. They do, however, make up a significant part of some specialty, niche markets starch-based loose-fill packaging now constitutes 30% of the loose-fill packaging market. The plastics described here are those currently commercially available, and are limited mainly to those available in the United States. Manufacturers are named only for illustrative purposes the list is not intended to be comprehensive. The plastics materials are described generically, with respect to the major polymer constituent(s) for each generic type there are likely to be many specific formulations. Brief mention is made, at the end, of some materials that have been studied in the laboratory. Biomedical applications are described separately (see Biodegradable Polymers, Medical Applications). 

PHAs are biocompatible as well as biodegradable and PHBV is used in biomedical applications (see Biodegradable Polymers, Medical Applications). One of its degradation products, butyric acid, is a mammalian metabolite found in low concentrations in humans. 

N. Kumar, A. Ezra, T. Ehrenfroind, M. Y. Krasko, A. J. Domb, Biodegradable polymers, medical applications, in H. F. Mark (Ed.), Encyclopedia of Polymer Science Technology, 3rd edition, Wiley, Hoboken, NJ, 2003, Chapter 5, pp. 263-285. 

Polymers of this type find application in toys and housewares and are of interest for medical applications and a wide variety of miscellaneous industrial uses. 

Whilst approximately twice the raw material cost of TPO- and S-B-S-type polymers, thermoplastic polyurethane elastomers find applications where abrasion resistance and toughness are particular requirements. Uses include gears, timing and drive belts, footwear (including ski boots) and tyre chains. Polyether-based materials have also achieved a number of significant medical applications. There is also some minor use as hot melt adhesives, particularly for the footwear industry. 

An idea of the range of materials and applications for polymers in medicine can be gained from the information in Table 10.1. As can be seen from this table a number of polymers are used in medical applications. One particular such polymer is poly (methyl methacrylate), PMMA. Early on it was used as the material for fabricating dentures later other biomedical applications developed. For example, PMMA is now used as the cement in the majority of hip replacement operations worldwide. 

Report 127 Polymers in Medical Applications, B.J. Lambert and F.-W. Tang, Guidant Corp., and W.J. Rogers, Consultant. Report 128 Solid State NMR of Polymers, PA. Mirau,... 

As a preeminent biomaterial, silicones have been the most thoroughly studied polymer over the last half century. From lubrication for syringes to replacements for soft tissue, silicones have set the standard for excellent blood compatibility, low toxicity durability, and bioinertness. Many medical applications would not have been possible without this unique polymer. 

Hron P. Hydrophilisation of silicone rubber for medical applications. Polym Int, 2003, 52, 1531-1539. Tcholakian RK and Raad. Durability of anti-infective effect of long term silicone sheath catheters impregnated with antimicrobial agents. Antimicrob Agents Chemother, 2001, 45(7), 1990-1993. 

Ikada Y. Surface modification of polymers for medical application. Biomaterials, 1994, 15, 725-736. James SJ, Pogribna M, Miller BJ, Bolon B, and Muskhelishvili L. Characterization of cellular response to silicone implants in rats Implications for foreign-body carcinogenesis. Biomaterials, 1997, 18, 667-675. 

Polylactic acid (PLA) has been produced for many years as a high-value material for use in medical applications such as dissolvable stitches and controlled release devices, because of the high production costs. The very low toxicity and biodegradability within the body made PLA the polymer of choice for such applications. In theory PLA should be relatively simple to produce by simple condensation polymerization of lactic acid. Unfortunately, in practice, a competing depolymerization process takes place to produce the cyclic lactide (Scheme 6.10). As the degree of polymerization increases the rate slows down until the rates of depolymerization and polymerization are the same. This equilibrium is achieved before commercially useful molecular weights of PLA have been formed. 

In polyester synthesis via ring-opening polymerizations, metal catalysts are often used. For medical applications of polyesters, however, there has been concern about harmful effects of the metallic residues. Enzymatic synthesis of a metal-free polyester was demonstrated by the polymerization of l,4-dioxan-2-one using Candida antarctica lipase (lipase CA). Under appropriate reaction conditions, the high molecular weight polymer (molecular weight = 4.1 x 10" ) was obtained. 

Pulapura, S. and Kohn, J. Tyrosine Derived Polycarbonates New Polymers for Medical Applications, manuscript in preparation. 

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