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.

PLE presents an alternative or complementary probe-based tool to DPN, PPL, and NFL. Unlike most scanning probe techniques, where patterning by deposition is usually employed, PLE is unique because it is capable of deposition and removal in one or multiple steps. Therefore, PLE allows rectification of patterning errors, and it can be employed for both additive and subtractive patterning through molecular deposition and chemical and electrochemical etching, respectively. PLE is a technique that exploits the intrinsic porosity of hydrogels like agarose and polyacrylamide. The probes are made by polymerizing a liquid mixture of agarose or acrylamide monomers in a conical or pyramidal master. The polymeric probe is hydrated in deionized water or ink of interest after polymerization. For deposition, PLE has shown promising results in the selective deposition of fluorescent inks on bare or functionalized glass substrates. Erasing via PLE has been done in two ways: the first method involves selectively erasing the fluorescent molecules using a probe loaded with deionized water by bringing the probe in contact with the area of interest. Thus, solvation and transportation of the molecules into the polymeric probes render selective removal of materials (fluorescent inks) from a substrate. On the other hand, erasing or removal of metals deposited on a substrate was demonstrated using redox reactions. Here, the probe is loaded with an etchant, which is selectively delivered onto the substrate by bringing the probe close to or in contact with the surface. Thus, the etchant molecules passively diffuse from the probe to the substrate through a meniscus formed at the probe-substrate interface. Removal of molecules occurs after the redox reaction between the ink, and the substrate is completed. Many in-length microscale complex patterns can be easily made by translocating the probe over the substrate while the probe’s tip is in contact with the surface. Since the probes used in PLE are made of polymers, the probe-substrate contacting area can be easily modulated, and damage to the substrate by the probe is minimum. Moreover, it has been shown that the probes can be used multiple times, a hurdle frequently faced by probes made of hard materials such as silicon-based probes. We explored the capabilities of a polymeric probe made of PAAM to selectively deliver and remove (erase) material deposited on a surface. PLE, pioneered by our group, takes advantage of the hydrophilic and porous nature of polyacrylamide. In addition, the conformability of PAAM hydrogels was exploited to make patterns of various sizes and to the pattern on non-planar surfaces. The main advantage of PLE is removing materials from various substrates. Additionally, selective delivery of material to planar and non-planar substrates was demonstrated. Whereas DPN and sister techniques require multiple steps for patterning through the etching process, PLE can perform etching in one step. Therefore, using PLE, microscale patterning on surfaces can save considerable time, labor, and cost. Further, chemical and supplies waste are minima in PLE. Notably, the deposition and etching at the microscale level can be simultaneously achieved in one single step, providing an extremely high throughput patterning rate (on the order of 1000 mm2/s). The PLE patterning rate is two to three orders larger than DPN-based patterning. However, PLE inherently deposits and removes materials with features much larger (microscale) than that can be achieved with DPN (sub-nanoscale). Therefore, PLE is an alternative to DPN, PPL, and related probe-based deposition and erasing techniques, and in some cases, PLE provides enhanced capabilities than its contemporary techniques. In this dissertation, I intend to demonstrate the potential of PLE for fabricating working devices at a lower cost as an alternative to contemporary fabrication. Chapter 2 involves the fabrication of micro-electrodes on rigid and flexible substrates by selectively removing copper and ITO from a glass and a PET substrate. As proof of concept, substrates coated with the PLE patterned surfaces were used to fabricate a photodetector, and LEDs were assembled on the electrodes made on ITO-PET substrates. Chapter 3 describes a series of experiments involving the evaluation of ink withholding capacity, large area patterning, and the effect of modification of substrate surface energy on PLE patterning. These experiments an increased understanding of processes involved in PLE editing and microscale patterning. A potential pitfall of PLE-based etching was also observed in these experiments, where a thin layer of material was left behind after subtractive editing with a PLE probe. EDS analysis indicated that the material was composed of iron, chlorine, and copper ─ components of the etchant solution and the copper film. The ring structure was attributed to the coffee-ring effect pinning the water meniscus to the substrate. By understanding the potential causes of the formation of the coffee-ring possible solutions to this problem were formulated. Chapter 4 describes the physical and mechanical properties of the hydrogel PAAM probes at the nanoscale. ESEM and AFM were employed to investigate the structural and mechanical properties of the probes after impregnation with metal etchants of various concentrations. The effect of local RH on PLE patterns was also investigated. More importantly, these experiments show critical structural differences of PAAM hydrogels composed of various monomer and crosslinker concentrations. ESEM showed the significant influence exerted by RH on meniscus size and its interaction with the substrate. The behavior of the water meniscus observed in ESEM shows that large RH promotes water spreading on the substrate generating larger patterning features. Chapter 5 describes the capability of PLE to selectively deliver metallic inks on a non-linear curved substrate to fabricate a microscale battery. PLE was used to deposit silver nitrate onto a non-planar flexible substrate which was used to grow a thin electrically conductive copper film via copper electroless deposition. Electrodeposition of zinc on the copper substrate was accomplished. By coupling a zinc electrode to a manganese oxide-graphite composite cathode, we demonstrated a working Zn-MnO2 aqueous microscale battery.

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.