Microbeads

As we explore the use of these microbeads and the resulhng consequences, we ll examine data pertaining to three kinds of products. 

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Technologies to purify cells from white cell concentrates are in the research stage. Principles used include antibodies covalently bound to a surface, antibody-coated microbeads in a column, magnetic microparticles that have been coated with antibodies, and hoUow fibers that have been coated with antibodies. 

In the 1990s, carbon microbeads have been produced by a proprietary process using phenoHc resin. Potential appHcations are lubricants, adhesives, and conductive fillers for plastics, mbbers, and coatings (97). 

Coals mesophase pitch coal chars coal tar pitch carbon mesocarbon microbeads, carbon fibers semi-coke, calcined coke activated carbons premium cokes, carbon fibers, binder and matrix... 

Polymers mesophase pitch polyacrylonitrile carbons" mesocarbon microbeads, carbon fibers PAN-based carbon fibers ... 

Yamada, Y., Imamura, T., Kakiyama, H., Honda, H., Oi, S., and Fukuda, K., Characteristics of meso-carbon microbeads separated from pitch. Carbon, 1974, 12, 307 319. 

It has been reported that tertiary aromatic amines can be encapsulated in formaldehyde-crosslinked microbeads, and used in an adhesive [54]. These microbeads burst when the joint is mated, and cure is accelerated. 

Beaded polymeric support, whether polystyrene-divinylbenzene, polymethacrylate, or polyvinyl alcohol, is conventionally produced by different variations of a two-phase suspension polymerization process, in which liquid microdroplets are converted to the corresponding solid microbeads (1). 

Microspherical polymer beads are widely used as packing materials for chromatography and a variety of other applications. Size exclusion chromatography is based on pore size and pore-size distribution of microbeads to separate... 

Beaded polymeric supports are produced by a two-phase suspension polymerization in which microdrops of a monomer solution are directly converted to the corresponding microbeads. The size of a microdroplet is usually determined by a number of interrelated manufacturing parameters, which include the reactor design, the rate of stirring, the ratio of the monomer phase to water, the viscosity of both phases, and the type and concentration of the droplet stabilizer. 

The pore size, the pore-size distribution, and the surface area of organic polymeric supports can be controlled easily during production by precipitation processes that take place during the conversion of liquid microdroplets to solid microbeads. For example, polystyrene beads produced without cross-linked agents or diluent are nonporous or contain very small pores. However, by using bigb divinylbenzene (DVB) concentrations and monomer diluents, polymer beads with wide porosities and pore sizes can be produced, depending on the proportion of DVB and monomer diluent. Control of porosity by means of monomer diluent has been extensively studied for polystyrene (3-6) and polymethacrylate (7-10). 

The synthetic methods of macromolecules having an active pendant group include (1) the transformation reactions of polymer and copolymers, and (2) polymerization and copolymerization of functional monomers having active pendant groups. The macromolecules, either in the shape of film or microbeads, can be used as the substrate. As we have mentioned previously, the rate of polymerization initiated with the Ce(IV) ion redox system is much faster than that initiated by Ce(l V) ion alone, as expressed in / r 1. Therefore, the graft... 

Apart from manifold structures, carbons can have various shapes, forms, and textures, including powders with different particle size distributions, foams, whiskers, foils, felts, papers, fibers [76, 77], spherical particles [76] such as mesocarbon microbeads (MCMB s) [78], etc. Comprehensive overviews are given, for example in [67, 71, 72], Further information on the synthesis and structures of carbonaceous materials can be found in [67, 70, 72, 75, 79]. Details of the surface composition and surface chemistry of carbons are reviewed in Chapter II, Sec. 8, and in Chapter III, Sec. 6, of this handbook. Some aspects of surface chemistry of lithiated carbons will also be discussed in Sec. 5.2.2.3. 

Figure 2. Irradiation of uranyl glass microspheres (A) and FITC-labeled microbeads (B) demonstrate photobleaching and stability of both materials.

Schwartz, A. Quantitative Fluorescein Microbead Standards Flow Cytometry Standards Corporation Research Triangle Park, NC 27709, [1985] technical brochure. 

Insulin (molecular weight 7000) has been formulated in controlled release microbeads and pellets (135,136). A solvent evaporation micro-encapsulation procedure was used to produce microspheres with up to 20% by weight insulin. Solvent-casting techniques were used to prepare pellets. The investigations demonstrated that the PLA... 

In practice the terms microspheres. nanoparticles. and microbeads are often used synonymously. 

The stationary phase matrices used in classic column chromatography are spongy materials whose compress-ibihty hmits flow of the mobile phase. High-pressure liquid chromatography (HPLC) employs incompressible silica or alumina microbeads as the stationary phase and pressures of up to a few thousand psi. Incompressible matrices permit both high flow rates and enhanced resolution. HPLC can resolve complex mixtures of Upids or peptides whose properties differ only slightly. Reversed-phase HPLC exploits a hydrophobic stationary phase of... 

Cadexomer-H is an iodophor similar to povidone-iodine. It is a 2-hydroxymethylene crosslinked (1-4) a-D-glucan carboxymethyl ether containing iodine. The compound is used especially for its absorbent and antiseptic properties in the management of leg ulcers and pressure sores where it is applied in the form of microbeads containing 0.9% iodine. 

Figure 7. Gold NPs directly deposited on PVC microbeads by deposition-reduction method.

We have recently deposited directly onto activated carbons and polymer microbeads by deposition-reduction method and have found that gold NPs on pol5mers exhibit remarkably high catalytic activity, which may exceed those of Au/activated carbons and Au/ fine Ce02. The type of polymers and their functional groups are critical to the catalytic activity. 

Hacroreticular resins are prepared by suspension polymerization of, for example, styrene-divinylbenzene copolymers in the presence of a substance which is a good solvent for the sononer but a poor swelling agent for the polymer [178-180]. Each resin bead is formed from many microbeads joined together during the polymerization process to create a network of holes and 7 channels. This results in greater mechanical stability,... 

Pancreatic enzyme replacement is the mainstay of gastrointestinal therapy. Most enzyme products are formulated as capsules containing enteric-coated microspheres or microtablets to avoid inactivation of enzymes in the acidic stomach instead, they dissolve in the more alkaline environment of the duodenum. Capsules may be opened and the microbeads swallowed with food, as long as they are not chewed. A powder form is available for patients unable to swallow the capsules or microbeads, but bioavailability is poor. While products may contain similar enzyme ratios, they are not bioequivalent and cannot be substituted. Generic enzyme products generally display poor dissolution and should not be used.5 Table 13-3 lists commonly used enzyme replacement products. 

Brenner S et al. Gene expression analysis by massively parallel signature sequencing (MPSS) on microbead arrays. Nature Biotechnol 2000 18 630-634. 

Mesocarbon microbeads (MCMB) particles, obtained from Osaka Gas Co., which are round graphite particles. They are also far from having a smooth morphology and have crevices on their surface. 

Synthetic carbonaceous materials are widely used in these applications. Several types of synthetic materials (e.g. graphitized mesophase carbon microbeads (MCMB), graphitized milled carbon fiber, and even, initially, hard carbons) became the materials of choice at the time of commercialization of first successful lithium-ion batteries in late 1980s. New trends, mainly driven by cost reduction and need for improved performance, currently shift focus towards application of natural graphite. 

Given the complex process to produce mesophase carbon (graphitized microbeads and fibers), natural graphite can be very competitive in terms of its manufacturing costs [18]. The physical characteristics of certain SLC type materials are extremely close to the characteristics of state-of-the-art MCMB grades. 

With these principles in mind, we refer the reader to valuable recent reviews, original reports, and discussions [65-68] of probes consisting of proteins, organic dyes, and nanoparticles such as quantum dots (QDs, [2, 68-77]) and other intriguing particles plastic microspheres and nanoparticles [78], multifunctional encoded particles [79], nanodisk codes [80], nano-flares [81], E-PEBBLES [82], C-dots [83], nanocrystal (NC)-encoded microbeads... 

Sukhanova, A and Nabiev, I. (2008). Fluorescent nanocrystal-encoded microbeads for multiplexed cancer imaging and diagnosis. Crit. Rev. Oncol. Hematol DOI 10.1016/j.critrevonc.2008.05.006. 

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