Biomedical use

The phenomenon of acoustic cavitation results in an enormous concentration of energy. If one considers the energy density in an acoustic field that produces cavitation and that in the coUapsed cavitation bubble, there is an amplification factor of over eleven orders of magnitude. The enormous local temperatures and pressures so created result in phenomena such as sonochemistry and sonoluminescence and provide a unique means for fundamental studies of chemistry and physics under extreme conditions. A diverse set of apphcations of ultrasound to enhancing chemical reactivity has been explored, with important apphcations in mixed-phase synthesis, materials chemistry, and biomedical uses. 

Biomedical Uses. The molybdate ion is added to total parenteral nutrition protocols and appears to alleviate toxicity of some of the amino acid components in these preparations (see Mineral NUTRIENTS) (97). Molybdenum supplements have been shown to reduce iiitrosarnine-induced mammary carcinomas in rats (50). A number of studies have shown that certain heteropolymolybdates (98) and organometaUic molybdenum compounds (99) have antiviral, including anti-AIDS, and antitumor activity (see Antiviral agents Chemotherapeutics, anticancer). 

Numerous barriers remain to be overcome before the promise of biomedically-useful peptoids can be more completely fulfilled. The following sections detail some examples. 

The purpose of this chapter is to introduce a new class of polymers for both types of biomedical uses a polymer system in which the hydrolytic stability or instability is determined not by changes in the backbone structure, but by changes in the side groups attached to an unconventional macromolecular backbone. These polymers are polyphosphazenes, with the general molecular structure shown in structure 1. 

The biomedical uses of polyphosphazenes mentioned earlier involve chemistry that could in principle be carried out on a classical petrochemical-based polymer. However, in their bioerosion reactions, polyphosphazenes display a uniqueness that sets them apart. This uniqueness stems from the presence of the inorganic backbone, which in the presence of appropriate side groups is capable of undergoing facile hydrolysis to phosphate and ammonia. Phosphate can be metabolized, and ammonia is excreted. If the side groups released in this process are also metabolizable or excretable, the polymer can be eroded under hydrolytic conditions without the danger of a toxic response. Thus, poljnners of this tjT are candidates for use as erodible biostructural materials or sutures, or as matrices for the controlled delivery of drugs. Four examples will be given to illustrate the opportunities that exist. 

Birch, N. Biomedical Uses of Lithium Farrell, N., Ed. The Royal Society of Chemistry Cambridge, 1999, pp 11-21. 

PGA was one of the very first degradable polymers ever investigated for biomedical use. PGA found favor as a degradable suture, and has been actively used since 1970 [45 -7]. Because PGA is poorly soluble in many common solvents, limited research has been conducted with PGA-based drug delivery devices. Instead, most recent research has focused on short-term tissue engineering scaffolds. PGA is often fabricated into a mesh network and has been used as a scaffold for bone [48-51], cartilage [52-54], tendon [55, 56], and tooth [57]. 

Molybdenum co-factor (Moco), 77 33 Molybdenum complexes, 26 927-929, 949 Molybdenum(III) complexes, 17 26-27 Molybdenum compounds, 17 19-43 in advanced structural and heating materials, 17 38-39 in anticorrosion agents, 17 39 biological aspects of, 17 31-34 biological uses for, 17 39-40 biomedical uses for, 17 40 catalytic applications of, 17 38 chemistry of, 17 29-31... 

Qu L, Cao W, Xing G, Zhang J, Yuan H, Tang J, Cheng Y, Zhang B, Zhao Y, Lei H (2006) Study of rare earth encapsulated carbon nanomolecules for biomedical uses. J. Alloys Compd. 408-412 400 104. 

Despite the highly versatile application prohles of polymers with adjunct sucrose (or other sugar) residues—their major asset is enhanced hydrophUicity as compared to their hydrophobic petroleum-derived counterparts—interest appears to be restricted to biomedical uses. Currently none is produced commercially, as the generation of vinyl-sucroses and their often capricious polymerization have made their use as commodity plastics uneconomical. Another reason is their limited biodegradability only the sugar portion is biodegradable, with a polymeric carbon chain left over. Because biodegradability is a major issue today, " these polyvinylsaccharides are unlikely to become petrochemical substitution options in the near future. 

Bacterial resistance to conventional antibiotics has become a serious problem in infection control, and has led to intensive research efforts to develop an effective novel antimicrobial agent. Antimicrobial peptides have already played a crucial role in pharmaceutical research as biomedically useful agents or as lead compounds for drug development. More specifically, cyclic peptides have shown some potential as a possible new class of... 

S. Guzy, Enzymic reactors for biomedical uses engineering aspects, D.Sc. thesis, Technion (Israel Institute of Technology), Haifa, Israel, 1989. 

Artificial materials designed for the biomedical use should be biocompatible, i.e. free of adverse effects on cells and tissues, such as cytotoxicity, immimogenicity, mutagenicity and carcinogenicity. Biocompatible materials can be constructed as bioinert, i.e. not allowing adsorption of proteins and adhesion of... 

Brief reminder of basic properties of perfluorocarbons relevant to biomedical uses... 

M.P. Krafft, J.G. Riess, Perfluorocarbons, life sciences and biomedical uses, J. Polym. Sci. Part A Polym. Chem. 45 (2007) 1185-1198. 

E. P. Goldberg and A. Nakajima, Biomedical Polymen- Polymeric Materials and Pharmaceuticals for Biomedical Use, Academic Press, New York 1980). 

A final biomedical use for polyphosphazenes is as components in microspheres, vesicles, and micelles for use in drug-delivery applications. Microspheres are pseudo-spherical constructs that range in size from 1 to 600 microns. Vesicles (lipozomes) are hollow, water-filled bilayer spheres with diameters that range from 0.03 tolO microns. Micelles typically have diameters near 1 micron (100 nanometers). Idealized representations of these three structures are shown in Figure 3.23, together with the location of trapped drug molecules. 

S. Abouhilale, J. Greiner, and J. G. Riess, One-step preparation of 6-perfluoroalkylalkanoates of trehalose and sucrose for biomedical uses, Carbohydr. Res., 212 (1991) 55-64. 

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