Animal polymeric materials

The remainder of this chapter will deal with natural polymers. These are large molecules, produced by plants and animals, that carry out the many life-sustaining processes in a living cell. The cell membranes of plants and the woody structure of trees are composed in large part of cellulose, a polymeric carbohydrate. We will look at the structures of a variety of different carbohydrates in Section 23.3. Another class of natural polymers are the proteins. Section 23.4 deals with these polymeric materials that make up our tissues, bone, blood, and even hair. ... 

Of these the last one has been most widely used, since heparin-modified polymeric materials exhibit the highest and by today unsurpassed effects of thromboresistance enhancement. Many of these materials have not only proved to be potent in trials on animals, but have already found clinical application. These achievements have stimulated continuous interest in heparin-containing polymers (HCP) which is best manifested by listing the investigations performed in the field in recent years and still under way. They involve the new procedures for the synthesis of HCP providing minimal loss of activity of bound heparin, the studies of interactions of HCP with blood and its individual components, as well as on the mechanism of enhanced thromboresistance of HCP, and the search for new tasks for HCP. 

In nature, thread-like polymeric material fulfils an essential structural role. Plant life is built mainly from cellulose fibres. Animal life is built from linear protein material such as collagen in skin, sinew and bone, myosin in muscle and keratin in nails and hair. The coiled polypeptide chains of the so-called globular proteins which circulate in the body fluids are folded up to give corpuscular particles. 

Today all available evidence suggests that dimethylsiloxane is one of the most acceptable polymeric materials known from the standpoint of health and environmental impact. But not all silicon based compounds are inert. For instance, families of physiologically active silicon-based materials are well known today and several very active research programs focus on the discovery of effective silicon based pharmaceuticals [16, 17]. All evidence today suggests that there is a natural silicon cycle which incorporates varying amounts of silicon into all life forms, plant or animal [18]. So a major challenge is to educate the public that all silicon-based materials are not the same and certainly all of them are not inert ... 

Sometimes, according to a broad definition, biodegradable polymers also include biomedically useful polymeric materials which degrade and are absorbed into the animal body and again contribute to polymer waste reduction. 

In the beginning, spheronization had been primarily used in the pharmaceutical industry as a final forming method for formulations with high active loading. A spherical particle was needed for coating with a thin polymeric material for controlled release (see also Section 10.1). Today, spheronization is also applied for animal medicines, herbicides, enzymes, specialty fertilizers, advanced ceramics, and many more. 

Tubular blood-contacting polymeric materials were modified by plasma polymerization and evaluated in animals (baboons) with respect to th r c iadty to induce acute and chronic arterial thrombosis. Nine plasma polymers based on tetrafluoro-ethylene, hexafluoroethane, hexafluwoethane/H, and methane, when deposited on silicone rubber, consumed platetets at rates ranging from l.l-5.6x 10 platelets/on day. Since these values are close to the lower detection limit for this test system, tl plasma polymers were considered relatively nonthrombogenk. Thus, artificial blood tube made of polyesters, having the inner side coated with plasma-pcrfymerized tetra-fluoroethylene, is now commercially available. 

A particular polymeric material is being evaluated for use in prosthetic devices. Initial in vitro tests showed the material to cause no apparent problems of blood compatibility. Long-term animal tests, however, resulted in the formation of dangerous blood clots in the region of the implant. Suggest an explanation for the observed results. 

The main actors involved in oleochemistry are located in Asia, because of the climatic suitability for such agricultural activity Malaysia, Indonesia and the Philippines being the main producers. Fats from animal biomass are produced mostly in the US and Europe. The respective production of fats and oils for the four main continents, Asia, North America, Europe and South America, is 44,16,15 and 14 per cent. The present chapter deals exclusively with the use of vegetable oils as sources of polymeric materials, because the structures of fats do not lend themselves meaningfully to that application. 

Most of the European sugar production is based on the exploitation of sugar beet (SB) and the corresponding industrial process generates enormous amounts of pulp as a by-product. This rather intractable fibrous solid, mostly made up of polysaccharides and pectin, has found some uses as fatilizer and animal feed, but the possibility of converting it into a source of polymeric materials had eluded researchers until it was shown that this remarkably inert natural product could in fact be readily converted into a viscous liquid polyol by a simple bulk oxypropylation treatment [8, 9]. 

A number of PTMC-based terpolymers have also been studied. Asplund et al. (2006) reported a three-armed P(TMC-co-CL)-PLLA terpolymer as potential stent cover. Random chain scission and homogenous hydrolysis resulted in a loss in mass and molar mass. After 6 weeks of in vitro hydrolysis the molar mass decreased by 54% and the elongation at break dropped from more than 300 to 90%. A medium free cell seeding study showed that endothelial cells adhered well to the polymeric material. Animal study showed very low levels of inflammation, but pronounced neointimal thickening was observed probably due to the premature failure of the material. 

There are several standards that medical polymers must adhere to. One of the most common standards observed for polymeric materials is published by the United States Pharmacopeia (USP), which necessitates using animal models (in vivo) to test toxicity of elastomers, plastics, and other polymeric materials, prior to clinical use. The standard and forms of testing it outlines is considered in the medical industry as the minimum requirement for a polymeric material before it is considered for use in healthcare applications. According to the standard the biological response of the test animals are measured and determined via three main techniques (1) Systemic toxicity test Evaluates the effects of leachables of intravenously or intraperitoneally injected materials on systems such as the nervous or immune system (2) Intracutaneous test Evaluates local response to materials injected under the skin (3) Implantation test Both local tissue microscopic and macroscopic parameters evaluated at material implant sites. 

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