Biomedical applications, modified

Interest in dendritic polymers (dendrimers) has grown steadily over the past decade due to use of these molecules in numerous industrial and biomedical applications. One particular class of dendrimers, Starburst polyamidoamine (PAMAM) polymers, a new class of nanoscopic, spherical polymers that appears safe and nonimmunogenic for potential use in a variety of therapeutic applications for human diseases. This chapter will focus on investigations into PAMAM dendrimers for in vitro and in vivo nonviral gene delivery as these studies have progressed from initial discoveries to recent animal trials. In addition, we will review other applications of dendrimers where the polymers are surface modified. This allows the opportunity to target-deliver therapeutics or act as competitive inhibitors of viral or toxin attachment to cells. 

In recent years, CNTs have been receiving considerable attention because of their potential use in biomedical applications. Solubility of CNTs in aqueous media is a fundamental prerequisite to increase their biocompatibility. For this purpose several methods of dispersion and solubilisation have been developed leading to chemically modified CNTs (see Paragraph 2). The modification of carbon nanotubes also provides multiple sites for the attachment of several kinds of molecules, making functionalised CNTs a promising alternative for the delivery of therapeutic compounds. 

Mordehai, A., Lim, H. K., and Henion, J. D. (1995). Ion-spray liquid-chromatography mass-spectrometry and capillary electrophoresis mass-spectrometry on a modified benchtop ion-trap mass-spectrometer. In Practical Aspects of Ion-Trap Mass Spectrometry Chemical, Environmental and Biomedical Applications (R. E. March, and J. F. J. Todd, Eds), Vol. 3, pp. 215—237, CRC Press, Boca Raton, FL. 

We chose to modify the anhydride monomers with photopolymerizable methacrylate functionalities. Methacrylate-based polymers have a long history in biomedical applications, ranging from photocured dental composites [20] to thermally cured bone cements [21]. Furthermore, photopolymerizations provide many advantages for material handling and processing, including spatial and temporal control of the polymerization and rapid rates at ambient temperatures. Liquid or putty-like monomer/initiator... 

The most important xanthenes are the imino derivatives known as rhodamines, exemplified by rhodamine B (Cl Basic Violet 10) (3.23a), A. 543 nm and 552 nm and rhodamine 6G (Cl Basic Red 1) (3.23b), /L 530 and X 557 nm (Figure 3.11). These are intensively fluorescent dyes with quantum yields close to unity. Rhodamine 6G especially has found wide apphcation in dayhght fluorescent pigments (see section 3.5.2) and this ring structure has been much modified for use in many other outlets, especially as laser dyes (see section 3.5.3) and in biomedical applications (see section 3.5.6). 

Traditional applications for laiices arc adhesives, binders for libers and paniculate matter, protective and decorative coatings, dipped goods, loam, paper coatings, hackings for carpet and upholstery, modifiers for bitumens and concrele. thread, and textile modifiers. More recent applications include biomedical applications as protein immobilizers, visual detectors in immunoassays, as release agents, in electronic applications as photoresists for circuit boards, in batteries, conductive paint, copy machines, and as key components in molecular electronic devices. 

Secondary reactions of these types are widely used to produce polyphosphazenes that are required for biomedical applications or for polymer grafting reactions. They are also used to modify the surfaces of poly(organophosphazene), as discussed in the following section. 

Degradable materials with new mechanical properties and modified degradation profiles have been produced and characterized. The increasing demands of a larger number of biomedical applications have resulted in an increasing interest in producing macromolecules through controlled polymerization. 

Plasticised PVC sheets were surface modified by nucleophilic substitution of chlorine by azide in aqueous media under phase transfer conditions. The azidated PVC surface was then irradiated by UV light to crosslink the surface. It was found that considerable reduction in the migration of the plasticiser di-(2-ethylhexyl phthalate) could be achieved by this technique, depending on the extent of azidation of the PVC surface and the irradiation dose. After surface modification, there was around 30% reduction in the stress-strain properties of the PVC sheets but these values were still well above the minimum prescribed for PVC used in biomedical applications. 19 refs. 

A recent study has shown that membranes made of a modified polyetheretherketone (PEEK-WC) are interesting materials for biomedical applications [23,24]. The cytocompatibility of PEEK-WC membranes was evaluated by culturing hepatocytes isolated from rat liver (Figure 43.6). The properties of PEEK-WC membranes were compared to polyurethane membranes prepared using the same technique, and commercial membranes (made of Nylon, polyethersulphone, and polyester). The results have shown that PEEK-WC membranes promoted hepatocyte adhesion most effectively and metabolic activities of cells cultured on these membranes improved significantly. 

One can also envision applications involving the use of encapsulated or entrapped enzymes in bioreactors for therapeutic applications involving detoxification of deleterious substances or correction of metabolic deficiencies. In these applications, the enzymes could be contained within artificial cells [e.g., modified red blood cells (erythrocytes) or liposomes]. Liang, Li, and Yang have reviewed biomedical applications of immobilized enzyme bioreactors. 

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