Universiẗat, Diss., 2003--Würzburg.

Techn. Universiẗat, Diss., 2001--Darmstadt.

No description available.

The effect of pH, temperature, and ionic strength on the molecular conformation of five industrial polyacrylamide-based flocculants was investigated by determining intrinsic viscosities on dilute flocculant solutions. The Fedors equation was found to be most suitable for all flocculants for determining the intrinsic viscosity. The results indicated that the flocculants are fully extended in distilled water at natural pH and at 25°C as evidenced by the high intrinsic viscosities. The data pointed to the strong dependence of the intrinsic viscosity on the presence of salts as a result of the shielding of negatively charged carboxylate groups by the counterions. At a constant ionic strength of 0.01M NaCl, the flocculants assumed a coiled conformation, and further coiling was observed in the presence of small quantities of calcium chloride. CaC1₂ (0.001 mo1/L) There was a decrease in intrinsic viscosities at high pH (~8.5 and 10.5) that was merely attributed to an increase in ionic strength with the increase in concentration of Na⁺ at high pH. Intrinsic viscosity measurements at higher temperatures (35°C and 50°C) showed a small effect of temperature on the conformation of the flocculants. Higher temperature, however, seemed to accelerate the aging of the flocculant solutions. The degrees of anionicity of the flocculants were found to be in the range 1.5% to 50%, as determined through chemical analysis. It was established that determination of total organic carbon content and sodium assays is an accurate way of obtaining the degrees of anionicity of industrial flocculants. The solution stability of the flocculants in distilled water and in 0.01M NaCl was investigated over a period of three days. The reduced viscosities of the anionic flocculant in distilled water steadily decreased. The decrease was more dramatic at high temperature (50°C) than at room temperature, but no viscosity loss was observed in the presence of NaCl. The viscosity of the nonionic flocculant was stable in both distilled water and NaCl. The viscosity loss with time in the case of the anionic flocculant can be correlated with the hydrolysis of the weakly acidic carboxylate (C00⁻) groups to release OH⁻ ions and simultaneous association into uncharged carboxylic (C00H) groups that promote coiling of polyacrylamide. This effect is therefore very similar to the earlier-mentioned effect of sodium chloride. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

Regulatory T cells (Tregs) provide an essential tolerance mechanism to suppress the immune response. Under normal conditions, Tregs reduce reaction to self-antigens, and conversely, lack of Treg function leads to autoimmune diseases. Reengineering of the immune system with regards to Tregs, such as through adoptive immunotherapy, holds great therapeutic promise for treating a range of diseases. These approaches require production of Tregs, which can be induced from conventional, reactive T cells. This thesis is driven by the concept that changing the mechanical stiffness of biomaterials can be used to direct and optimize this induction process. It is known that T cells sense their extracellular environment, and that T cell activation can be modulated by mechanical cues. However, it is still unclear whether or not human Treg induction is sensitive to material stiffness. We studied this phenomenon by replacing the stiff plastic supports commonly used for T cell activation with planar, elastic substrates — specifically polyacrylamide (PA) gels and polydimethylsiloxane (PDMS) elastomer. Treg induction, as measured by expression of FOXP3, a master transcription factor, was sensitive to stiffness for both materials. Substrate stiffness also modulated the suppressive function and epigenetic profiles of these cells, demonstrating that substrate rigidity can direct Treg induction, complementing the use of chemical and genetic tools. Delving deeper into the mechanisms of T cell mechanosensing, single-cell transcriptomic analysis revealed that substrate rigidity modulates the trajectory of Treg induction from conventional T cells, altering a host of functions including metabolic profile. Together, these studies introduce the use of substrate stiffness and T cell mechanosensing towards directing and optimizing regulatory T cell production. Further development of cell culture systems around this discovery is critical for emerging T cell-based therapies, targeting cancer but also a broad range of diseases.

No description available.

Chloroplast and cytoplasmic ribosomes have been isolated from a number of species of the angiosperm genus Nicotiana. Ribosomal subunit and monosome proteins were separated by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Resultant two-dimensional electrophoretic patterns of chloroplast and cytoplasmic ribosomal proteins were processed by a computer algorithm, developed to formally compare different electrophoretic patterns by the construction of two-dimensional, conformal average electrophoretic mobility maps. The chloroplast ribosomal subunit of N. tabacum contains 22-24 distinct basic polypeptides (pI > 5) and 2-3 acidic proteins (pI < 5). The 50S chloroplast ribosomal subunit possesses at least 1 acidic and 33-35 basic proteins. 40S and 60S cytoplasmic ribosomal subunits of the same species have 26-30 and 47-50 basic polypeptides, respectively. Molecular weights of chloroplast ribosomal proteins (ChRP) and cytoplasmic ribosomal proteins (CyRP) were estimated. There was little similarity between the 2D electrophoretic patterns of ChRP and CyRP of N. tabacum. However, 2D-PAGE patterns of N. tabacum ChRP and CyRP were qualitatively isomorphous with homologous patterns of Chlamydomonas reinhardi, pea and spinach. In terms of molecular weight and electrophoretic pattern N. tabacum ChRP were found to be more closely affiliated with prokaryotic ribosomal proteins than with CyRP from the same species. ChRP were isolated from N. gossei (an Australian species) and its reciprocol interspecies hybrids with N. tabacum (denoted by: T x G and G x T). Interspecies polymorphisms between homologous N. tabacum and N. gossei ChRP were delineated by computerized mobility mapping and co-electrophoresis of radiolabeled N. tabacum ChRP with a large molar excess of N. gossei ChRP. The inheritance mode (Mendelian vs. maternal) of a number of well-defined interspecies ChRP polymorphisms was determined by co-electrophoresis of radioiodinated N. tabacum ChRP with T x G and G x T hybrid ChRP. Results indicate that at least 4 30S ChRP and 3 50S ChRP are encoded by nuclear genes. 30S ChRP from an N. tabacum line carrying a maternally-inherited streptomycin-resistance mutation (SR-1) were compared to N. tabacum 30S ChRP by mobility mapping. Two differences were established between the SR-1 and wild-type 30S ChRP average mobility maps. These findings correlate with the reduced affinity of SR-1 30S chloroplast ribosomal subunits for ('3)H-dihydrostreptomycin, and show that at least one 30S ChRP is encoded by chloroplast DNA. Preparative 2D-PAGE and reverse high performance liquid chromatography (RPHPLC) separation techniques for complex ribosomal protein mixtures were developed. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI

Li, Yuefang. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 46-48). / Abstracts in English and Chinese. / Abstract --- p.i / 摘要 --- p.ii / Acknowledgement --- p.iii / Table of contents --- p.iv / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Introduction to protein crystallization --- p.1 / Chapter 1.1.1 --- Principles of protein crystallization --- p.2 / Chapter 1.1.2 --- Classical methods to crystallize protein --- p.4 / Chapter 1.2 --- Crystal growth in unique environments: the pursuit of better crystals --- p.6 / Chapter 1.2.1 --- Protein crystallization in space --- p.6 / Chapter 1.2.2 --- Crystallization in gel and capillary --- p.7 / Chapter 1.3 --- Microfluidic methods for protein crystallization: high through-put screenings --- p.9 / Chapter 1.3.1 --- Valve-controlled methods --- p.10 / Chapter 1.3.2 --- Droplet-based methods --- p.11 / Chapter 1.3.3 --- Microwell-based methods --- p.11 / Chapter 1.4 --- Objective of the project --- p.13 / Chapter Chapter 2 --- Rehydratable hydrogel in nanoliter microwells --- p.15 / Chapter 2.1 --- Introduction --- p.15 / Chapter 2.2 --- Experimental --- p.17 / Chapter 2.2.1 --- Fabrication of SU-8 mould --- p.17 / Chapter 2.2.2 --- Fabrication of the PDMS device --- p.19 / Chapter 2.2.3 --- Liquid dispensing in PDMS device --- p.20 / Chapter 2.2.4 --- Polymerization of PA gel --- p.21 / Chapter 2.2.5 --- Drying and Rehydration of PA gel --- p.22 / Chapter 2.3 --- Results and discussions --- p.23 / Chapter 2.3.1 --- Preparation of PA gel in PDMS device --- p.23 / Chapter 2.3.2 --- Immobilization of PA gel in microwells --- p.25 / Chapter 2.3.3 --- Dehydration and Rehydration of PA gel --- p.25 / Chapter 2.3.4 --- Liquid dispensing in the gel-preloaded microwells --- p.29 / Chapter 2.4 --- Conclusion --- p.31 / Chapter Chapter 3 --- Protein crystallization by gel-based FID --- p.32 / Chapter 3.1 --- Introduction --- p.32 / Chapter 3.2 --- Experimental --- p.34 / Chapter 3.2.1 --- Conditions used for crystallize proteins --- p.34 / Chapter 3.2.2 --- Protein crystallization by microbatch method --- p.34 / Chapter 3.2.3 --- Protein crystallization in microchip --- p.35 / Chapter 3.3 --- Results and discussions --- p.35 / Chapter 3.3.1 --- Crystallization in microplate --- p.36 / Chapter 3.3.2 --- Crystallization in microwells --- p.38 / Chapter 3.4 --- Conclusion --- p.41 / Chapter Chapter 4 --- Conclusions --- p.43 / Chapter 4.1 --- Summary of the work --- p.43 / Chapter 4.2 --- Future perspectives --- p.44 / Reference --- p.46

Les hydrogels de Polyacrylamide (PAAM) hydrolysés sont des matériaux électroactifs biocompatibles non biodégradables. Ils possèdent des propriétés très proches de celles du muscle naturel et leur mode opérationnel basé sur la diffusion d'ions est similaire à celui existant dans les tissus musculaires naturels. Compte tenu de ces caractéristiques, ces hydrogels sont de bons candidats pour la conception de nouveaux muscles artificiels. Le problème qui limite leur utilisation réside dans leur temps de réponse qui reste encore inférieur à celui du système de fibres musculaires naturelles. Leur fonction actuatrice est limitée par le phénomène de diffusion en raison de leur structure massique qui est à l'origine de cycles de fonctionnement relativement lents. Dans le but de développer un nouveau système artificiel mimant le comportement du muscle squelettique naturel cette étude se divise en deux grandes étapes. La première étape vise le développement d'une étude de la synthèse de l'hydrogel de PAAM et de son mode de fonctionnement. Dans cette étude les effets des paramètres gouvernant la polymérisation sur les propriétés des hydrogels sont évalués. Les propriétés électrochimiques et le mécanisme d'activation des actuateurs soumis à une excitation électrique sont étudiés et le mode de fonctionnement des actuateurs est caractérisé et expliqué. La seconde étape est la proposition et le développement d'une nouvelle architecture de muscle artificiel à base de PAAM. Cette architecture consiste en une structure fibreuse du gel encapsulée par une couche en gel conducteur jouant le rôle d'électrodes. La structure fibreuse permet au système d'exhiber une réponse rapide et la couche en gel améliore ses propriétés mécaniques. Comme un premier pas dans la réalisation du modèle nous avons mis en place un nouveau procédé basé sur la technique d'électrofilage qui permet la génération de fibres linéairement disposées. En utilisant ce processus nous avons réussi à fabriquer des microfibres de PAAM réticulées, électroactives montrant des réponses rapides.

Nanoporous polymer hydrogels offer a desirable combination of mechanical, optical, and transport characteristics that have placed them at the core of a variety of biomedical technologies including engineered tissue scaffolds, substrates for controlled release of pharmaceutical compounds, and sieving matrices for electrophoretic separation of DNA and proteins. Ultimately, we would like to obtain a detailed picture of the nanoscale pore morphology and understand how it can be manipulated so that we can rationally identify gel formulations best suited for a specific application. But this goal has proven elusive because the most fundamental descriptors of the pore network architecture (e.g., the average pore size and its polydispersity) are particularly difficult to measure in polymer hydrogels. Here we introduce an approach that enables both the mean pore size and the pore size distribution to be quantitatively determined without prior knowledge of any physical material parameters A novel technique to prepare TEM samples was developed so that the nanoscale hydrogel pore size, pore shape and distribution are clearly visualized and quantitatively studied for the first time. The pore sizes of the hydrogel are also estimated with rheology. A new fixture is used in the rheometer and the whole polymerization process can be directly studied using an in-situ rheology experiment. A series of thermoporometry experiments are also conducted, and suitable methods and equations to study hydrogel pore size and distribution are chosen. The pore size derived from TEM, rheology, DSC is compared and their values are self-consistent. These techniques help us understand how the nanoporous morphology of crosslinked polyacrylamide hydrogels is influenced by their chemical composition and polymerization conditions. It is interesting to find hydrogels with similar pore size but different distribution. For two hydrogels with similar pore size, the broader the distribution, the faster the release rate and the higher the accumulated release percentage. So we can control the release of trapped molecules by simply varying the hydrogel pore size distribution. This discovery would have a very promising potential in the application of pharmaceuticals.