Synthetic microspheres

Figure 2 Release of BDNF from synthetic microspheres. Microspheres composed of poly-(D,L-lactic-co-glycolide) were engineered to release BDNF over a sustained period. The release of total protein was measured by protein assay and ELISA. There is an initial burst of release over the first 48 hours, followed by sustained release of nanogram quantities for up to 28 days. Abbreviations . BDNF, brain derived neurotrophic factor ELISA, enzyme linked immunosorbent assay.

The most important role of UO3 is in the production of UF4 [10049-14-6] and UF [7783-81-5], which are used in the isotopic enrichment of uranium for use in nuclear fuels (119—121). The trioxide also plays a part in the production of UO2 for fuel peUets (122). In addition to these important synthetic appHcations, microspheres of UO3 can themselves be used as nuclear fuel. Fabrication of UO3 microspheres has been accompHshed using sol-gel or internal gelation processes (19,123—125). FinaHy, UO3 is also a support for destmctive oxidation catalysts of organics (126,127). 

Truly porous, synthetic ion exchangers are also available. These materials retain their porosity even after removal of the solvent and have measurable surface areas and pore size. The term macroreticular is commonly used for resins prepared from a phase separation technique, where the polymer matrix is prepared with the addition of a hq-uid that is a good solvent for the monomers, but in which the polymer is insoluble. Matrices prepared in this way usually have the appearance of a conglomerate of gel-type microspheres held together to... 

Lactide/glycoUde polymers have been investigated for delivery of several other macromolecules. Synthetic double-stranded RNA, poly-isosinic acid/polycytidylic acid, a potent inducer of interferon, was formulated in a 53 47 copolymer of DL-lactide-co-glycoUde. The microspheres were evaluated in mice challenged with Right Valley fever virus. More than 16 days protection was afforded versus only 3 days for controls (137). 

Bakhtiar 114 adsorbed toluene and iso-octane vapours from a vapour-laden air stream on to the surface of synthetic alumina microspheres and followed the change of concentration of the outlet gas with time, using a sonic gas analyser. It was found that equilibrium was attained between outlet gas and solids in all cases, and therefore transfer coefficients could not be calculated. The progress of the adsorption process was still followed, however. 

The coprecipitation technique was based on the dropwise addition of a synthetic polymer solution, in a solvent mixture, into an aqueous protein solution under magnetic stirring. The progressive interaction between the water insoluble polymer and the protein gave rise to the microsphere formation. The glycolipid was then added as an aqueous dispersion to the nanoparticle suspension. No sedimentation was observed after several weeks of storage at room temperature. 

We varied the gel-forming parameters, the content of Kaolin clay, the crystal size, and the thickness-to-diameter ratio in a series of experiments. A dual structure began to appear at about 35-40% Kaolin. If the clay content was increased to too high a level, the microspheres became too weak and began to have poor attrition resistance. The cost of the various grades also affected our choice. Figure 9 shows a comparison of pore volume distribution for a typical synthetic versus a clay modified catalyst. 

Microsphere with short single strands of synthetic DNA... 

Bioadhesive formulations and microsphere delivery systems in particular have attracted much attention. As drug formulations are usually rapidly removed from the site of deposition by the mucociliary clearance, increasing the retention time of drug in the nasal cavity via bioadhesion can increase bioavailability [28], Bioadhesion may be defined as the ability of a material (synthetic or biological) to adhere to a biological tissue for an extended period of time. When applied to a mucous membrane, a bioadhesive polymer may adhere primarily to the mucus layer or epithelial cell surface in a phenomenon known as mucoadhesion [29,30]. The bioadhesive properties of a wide range of materials have been evaluated over the last decade. 

Polyphosphazenes are a relatively new class of biodegradable polymers. Their 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. Synthetic flexibility and versatile adaptability of polyphosphazenes make them unique for drug delivery applications. For example, Veronese et al.18 prepared polyphos-phazene microspheres with phenylalanine ethyl ester as a phosphorous substituent and loaded it with succinylsulphathiazole or naproxen. The kinetics of release from these matrices were very convenient in yielding local concentrations of the two drugs that are useful per se or when mixed with hydroxyapatite for better bone formation. Polyphosphazene matrices are also considered as potential vehicles for the delivery of proteins and vaccines.19... 

The catalyst, which may be an activated natural or synthetic material, is employed in bead, pellet or microspherical form and can be used as a fixed bed, moving-bed, or fluid-bed configurations. Moving bed units often employ catalysts in the form of beads or cylinders (1/8 to 1/4-inch diameter). Fluid bed units usually employ the catalyst in much smaller form where particle sizes may be of the order of 50 pm (50 X 10 4 cm). 

The literature of metabolism in proteinoids and proteinoid microspheres is reviewed and criticized from a biochemical and experimental point of view. Closely related literature is also reviewed in order to understand the function of proteinoids and proteinoid microspheres. Proteinoids or proteinoid microspheres have many activities. Esterolysis, decarboxylation, animation, deamination, and oxido-reduction are catabolic enzyme activities. The formation of ATP, peptides or oligonucleotides is synthetic enzyme activities. Additional activities are hormonal and inhibitory. Selective formation of peptides is an activity of nucleoproteinoid microspheres these are a model for ribosomes. Mechanisms of peptide and oligonucleotide syntheses from amino acids and nucleotide triphosphate by proteinoid microspheres are tentatively proposed as an integrative consequence of reviewing the literature. 

Catabolic and Synthetic Enzyme Activities of Proteinoids and Proteinoid Microspheres... 

The catalytic, synthetic, hormonal, and inhibitory activities that have been found in proteinoids or proteinoid microspheres are listed in Table 2. The possibility that metabolic activities found were due to contamination by micro-organisms is denied by experiments under aseptic condition or by the several experimental observations. The activities of proteinoids are generally weak. In some cases, proteinoids act several orders of magnitude more slowly than do modern enzymes or organisms, but free amino acids or Leuchs polypeptides usually have no activity or less than the proteinoid composed of the same amino acids. In general, activities of proteinoids increase approximately in proportion to its molecular weight. One or more of the proteinoids has been found to meet the salient requirements of enzymes such as Michaelis-Menten kinetics, pH-activity curves, etc. 

The inactivity of acidic proteinoid (A) synthesize peptides in solution of pH 7.2 is in contrast to the activity of the lysine-rich proteinoid (B), when A and B form microspheres. The activity of the complex is several times as large as that of lysine-rich proteinoid alone 28). Physical surface and interior providing suitable environment for dehydration may be responsible. It may also be that the closed molecules of both proteinoids may be opened by the interaction, consequently buried active sites of proteinoids become effective. Neutral amino acids contained in each proteinoid may prevent the entire neutralization of acidic and basic residues. In the synthetic pathways of peptides and oligonucleotides by proteinoid microspheres, proteinoid nucleotide complex is proposed in this article as a main intermediate of the reactions. Oligo-... 

Substantial enzymic and synthetic activities of proteinoid microspheres have been found, in spite of a requirement for a narrowed range of condition and materials for the experiments. These findings are evidence to support the evolutionary theory for proteinoid microspheres. 

Emulsions and suspensions are colloidal dispersions of two or more immiscible phases in which one phase (disperse or internal phase) is dispersed as droplets or particles into another phase (continuous or dispersant phase). Therefore, various types of colloidal systems can be obtained. For example, oil/water and water /oil single emulsions can be prepared, as well as so-called multiple emulsions, which involve the preliminary emulsification of two phases (e.g., w/o or o/w), followed by secondary emulsification into a third phase leading to a three-phase mixture, such as w/o/w or o/w/o. Suspensions where a solid phase is dispersed into a liquid phase can also be obtained. In this case, solid particles can be (i) microspheres, for example, spherical particles composed of various natural and synthetic materials with diameters in the micrometer range solid lipid microspheres, albumin microspheres, polymer microspheres and (ii) capsules, for example, small, coated particles loaded with a solid, a liquid, a solid-liquid dispersion or solid-gas dispersion. Aerosols, where the internal phase is constituted by a solid or a liquid phase dispersed in air as a continuous phase, represent another type of colloidal system. 

The present article is intended to discuss the state-of-the-art of the design and characterization of the branched polymers obtained by the macromonomer technique, with particular stress on the characterization and the properties of the brush polymers obtained by the homopolymerization of macromonomer. The synthetic aspects of the macromonomer technique, including preparation of various kinds of macromonomers, have been recently reviewed by one of the authors [1]. Therefore, we intend here to outline briefly the macromonomer technique and describe only the very recent important developments in syntheses. Preparation and characterization of the polymeric microspheres by use of macromonomers as reactive (copolymerizable) emulsifiers or dispersants will be described in some detail to represent one of their unique applications. 

Synthetic silica microspheres (Figure 2.29) can easily be obtained by using the Stobe-Fink-Bohn (SFB) method [154-157], as explained in Section 3.2.3. 

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