E-gels

The power-law variation of the dynamic moduli at the gel point has led to theories suggesting that the cross-linking clusters at the gel point are self-similar or fractal in nature (22). Percolation models have predicted that at the percolation threshold, where a cluster expands through the whole sample (i.e. gel point), this infinite cluster is self-similar (22). The cluster is characterized by a fractal dimension, df, which relates the molecular weight of the polymer to its spatial size R, such that... 

Successful application of chromatographic techniques relies on resolution, or the resolving power of the particular technique used. Resolution is defined by the relation of selectivity and efficiency of the chromatographic gel media (i). Selectivity is a function of the mode of separation of the gel (i.e., gel filtration, ion exchange, etc.) and efficiency is a function of the support matrix (Le., particle shape, size distribution, mechanical stability, density of interactive chemical groups, etc.). Each of the various modes of chromatographic separation have unique advantages that dictate where and when in a purification process these techniques should be used. 

Nicolas has also considered batch and tubular reactors and a cascade of stirred vessels he finds, in agreement with other workers, that a batch process produces narrower distributions than perfectly-stirred continuous reactors, but he finds that tubular reactors (assuming no axial or radial mixing) always produce material of infinite Pw, i.e. gel. 

Fig. 3. Effect of varied crosslink density on swelling of HPMC-E gels. Increased crosslinking decreases swelling below the transition temperature but has little effect on gel transition temperature, sharpness of transition, or degree of swelling above the transition. Lines added are to guide the eye. Reprinted from the Journal of Controlled Release (1991) 17 175 by permission of the publishers, Elsevier Science Publishers BV [52]...

This technique was applied for a description of the scattering behavior of branched fibrils from fibrin in the molecular weight region, where first only a rod growth was observed, up to the point of clotting, i.e. gel formation. Since electron microscopic pictures (EM) showed only single branching points, the AB2-domains appeared to consist of one unit only. This implies... 

On the other hand, in the Erdos-Renyi process, the size of a typical largest component in a system comprising N units has been proved to be proportional to log N up to the gel point. Beyond the gel point it (i.e., gel molecule) has a size proportional to N itself [20,34]. 

Very recently, Shibayama et al. (1991) reported that cross-linked (a(3)A (chP)aXL isolated by our procedure (i.e., gel filtration in the presence of 1 M MgCl2 followed by ion-exchange chromatography) was found to be contaminated with about 20% of an electrophoret-ically silent impurity that shows higher 02 affinity. They developed a purification technique to separate the desired cross-linked Hb A from the impurity. They found that their purified (aP)A(aP)AXL in the absence of organic phosphate has the same 02 affinity, cooper-ativity, and alkaline Bohr effect as native Hb A. 

Bardella F, Eritja R, Pedroso E, Giralt E, Gel-phase 31P-NMR. A new analytical tool to evaluate solid phase oligonucleoside synthesis, Bioorg. Med. Chem. Lett., 3 2793-2796, 1993. 

When fine inorganic materials (e.g., bentonite, oxides) are added to water containing suspended particles, the dispersion becomes thixotropic and the inorganic materials form a three-dimensional network (i.e., gel) structure in the medium. The gel network has sufficient elastic properties. It entraps the particles and prevents settling and cake formation. The network structure is broken down upon shaking, thus facilitating pouring. However, the gel structure is influenced by pH and electrolyte concentration. 

Gums. Gums are hydrophobic or hydrophilic polysaccharides derived from plants or microorganisms that upon dispersing in either hot or cold water produce viscous mixtures or solutions (i.e., gels (1)). As used in the modern sense, the term gum includes any water-soluble or water-swellable polysaccharide or its derivative. This includes starch and dextrins and various derivatives of cellulose. The latter, however, are considered separately. 

In Figure 1 are shown experimental conversion histories from bulk polymerization of styrene, methyl methacrylate, and vinyl acetate. It appears that with any of these monomers the rate of polymerization increases substantially during reaction, i.e. gel-effect is important in bulk polymerization of these monomers. The effect is particularly pronoimced with methyl methacrylate. 

Penn, L.E. Gel dosage forms theory, formulation, and processing. In Topical Drug Delivery Eormulations Osborne, D.W., Amann, A.H., Eds. Marcel Dekker, Inc. New York, 1990 381-338. 

Fig[ure 5.4 Non-exchange electrolyte sorption of NaCl and HCl by styrenk anion and cation exchange resins respectively against external concentration [m = internal molality A = macroporous SB A (low capacity) B = macroporous SBA (conventional) C = isoporous SBA (gel) D = macroporous SAC E = gel SAC]... 

Fig. 5. The helicase high-throughput assay can detect both DNA and RNA unwinding activity and gives similar results to the traditional gel-based helicase assay. (A-E) Gel-based assay showing unwinding of RNA and DNA heteroduplex and homoduplex substrates by action of 5-120 fmol of HCV NS3/4A enzyme. The positions of the dsNA and ssNA are labeled.

Fig. 16 a-e In vitro release profiles for dextran-HTC released from a-CD-PEO-PHB-PEO hydrogels with different compositions in comparison with a-CD-PEO hydrogel a Gel-1 b Gel-2 c Gel-3 d Gel-4 e Gel-5 [71]. The compositions of the hydrogels are listed in Table 4... 

Figure 21-5 A, Poiyacrylam id e-gel electrophoresis of bone and liver alkaline phosphatases in human serum. Left, Mixture of two sera containing, respectively, entirely bone phosphatase and entirely liver phosphatase. Right, Mixture of the same two sera after each has been treated with neuraminidase for 0 minutes at 37 C.The anodai direction is downward.The more anodal zone is liver phosphatase. B, Densltometric scans of electrophoretic patterns shown in A. Broken line, Scan of mixture of untreated sera solid line, scan of mixture of sera treated briefly with neuraminidase. The anode is to the left. (From Moss DW, Edwords RK. In proved electrophoretic resolution of bone and liver alkaline phosphatases resulting from partial digestion, with neuraminidose. Clin Chim Acta 1984 143 i 77-82.) ...

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