Diss. (sammanfattning) Uppsala : Univ., 2003. / Härtill 4 uppsatser.

Thesis (Ph. D.)--University of Washington, 1992. / Vita. Includes bibliographical references (leaves [210]-240).

This dissertation studies physical properties and technological applications of engineered heterogenous polymer gels. Such gels are synthesized based on modulation of gel chemical nature in space. The shape memory gels have been developed in this study by using the modulated gel technology. At room temperature, they form a straight line. As the temperature is increased, they spontaneously bend or curl into a predetermined shape such as a letter of the alphabet, a numerical number, a spiral, a square, or a fish. The shape changes are reversible. The heterogenous structures have been also obtained on the gel surface. The central idea is to cover a dehydrated gel surface with a patterned mask, then to sputter-deposit a gold film onto it. After removing the mask, a gold pattern is left on the gel surface. Periodical surface array can serve as gratings to diffract light. The grating constant can be continuously changed by the external environmental stimuli such as temperature and electric field. Several applications of gels with periodic surface arrays as sensors for measuring gel swelling ratio, internal strain under an uniaxial stress, and shear modulus have been demonstrated. The porous NIPA gels have been synthesized by suspension technique. Microstructures of newly synthesized gels are characterized by both SEM and capillary test and are related to their swelling and mechanical properties. The heterogenous porous NIPA gel shrink about 35,000 times faster than its counterpart--the homogeneous NIPA gel. Development of such fast responsive gels can result in sensors and devices applications. A new gel system with built-in anisotropy is studied. This gel system consists of interpenetrated polymer network (IPN) gels of polyacrylamide (PAAM) and N-isopropylacrylamide (NIPA). The swelling property of the anisotropy IPN gels along the pre-stressing direction is different from that along other directions, in contrast to conventional gels which swell isotropically. It is found that the ratio (L/D) of length (L) and diameter (D) of IPN samples has step-wise changes as the samples are heated from below the volume phase transition temperature to the above. A theoretical model is proposed and is in good agreement with the experimental results.

Soft materials are ubiquitous in every aspect of our daily life. These materials composed of a wide range of subfields including surfactants, foams, emulsions, pastes, slurries, polymers, gels, and colloidal suspensions. In recent years, there has been a great interest focusing on the understanding of the macroscopic properties of various types of soft materials as a function of their microstructures. For example, the structure-property relationship of physically-associating triblock copolymer gels can be controlled by selecting different types of solvents and changing the temperature. In these systems, gelation occurs due to the significant changes in the solubility of one or more of the blocks with temperature compared to the other blocks. Therefore, changing the temperature can lead to the structural transitions and macroscopic properties. The other strategy that can be used to modify the macroscopic performance of polymer gels is through the incorporation of nanoparticles, such as graphene nanoplatelets and nanotubes. The addition of nanoparticles can also affect the mechanical properties of concentrated suspensions in which, understanding the structure/flow properties is vital for processing and manufacturing of a product. Despite significant advances in the field of soft materials, our understanding in linking the structure-property relationships of polymer gels and concentrated suspensions is incomplete. With this perspective, in this dissertation, shear-rheometry and scattering techniques were used to understand the structural changes of the self-assembled triblock copolymer gels over a wide length-scale and broad temperature-range. Graphene nanoplatelets have been incorporated into this system to investigate the self-assembly behavior and mechanical properties as a function of graphene concentration. On the other hand, in concentrated suspensions of functionalized nanoparticles in a low-molecular- weight polymeric media, the effect of nanoparticles on the rheological properties were investigated. The present work provides a better understanding of the nanoparticles’contributions on microstructure and mechanical behavior of soft materials.

Molecular simulations are computer experiments that allow us to investigate thermodynamic and transport properties of complex chemical systems. Here, we have investigated self-assembly of organogelators and analysed the diffusion characteristics of small molecules in the nanopores of zeolites. Molecular gels are attractive soft-materials with viscoelastic properties with applications in drug delivery, tissue engineering, sensing, etc. Small organic amphiphilic gelators act as a building block of complex 3-dimensional network in molecular gels. Due to time and length scale differences, the understanding and characterization of early stage aggregation of gelators is difficult using experimental techniques. Classical and quantum mechanical approaches have been used to understand the self-assembly of gelator molecules and to rationalize the gelation. We have used density functional theory (DFT) to derive new quantity namely, pseudo-cohesive energy density to rationalize the gelation of di-Fmoc-L-lysine. Molecular dynamics is used to probe the self-assembly and conformation of gelators in DMSO-water. We have also studied the self-assembly of 12-hydroxyoctadecanamide in octane. We used DFT to calculate the dimer energy in the vacuum and meta-dynamics simulation to calculate potential of mean force in the condensed phase. Interestingly, we found that, dimer energetics was not sufficient to elucidate bulk aggregation behavior, such as, probability distribution of different dimers in aggregation. We also observed different types of branched and mesh-like networks in the aggregation, which are analogous to the network found through experimental imaging techniques. Zeolites are crystalline materials with well defined nanoporous channels and act as molecular sieves. They are attractive for catalytic applications due to their tunable Bronsted and Lewis acidity. A wide array of zeolite polymorph offers versatile micro and meso-porous channels to accommodate small molecules like glucose to big and complex lignocellulose molecules for undergoing chemical transformations. In this current study, we present the transport properties of -glucose into Faujisite zeolite framework. We have investigated the trajectory of the glucose molecule into porous material and found that, the diffusivity of glucose inside zeolite pore is two order of magnitude smaller than that of bulk solutions. We have also observed the variable loading rate of glucose molecule inside pore at different temperatures.

No description available.

No / We report on a supramolecular self-assembly system that displays coupled light switching, biocatalytic condensation/hydrolysis and gelation. The equilibrium state of this system can be regulated by light, favouring in situ formation, by protease catalysed peptide synthesis, of self-assembling trans-Azo-YF-NH2 in ambient light; however, irradiation with UV light gives rise to the cis-isomer, which readily hydrolyzes to its amino acid derivatives (cis-Azo-Y + F-NH2) with consequent gel dissolution.

No / Coupling of peptide self-assembly to dynamic sequence exchange provides a useful approach for the discovery of self-assembling materials. In here, we demonstrate the discovery and optimization of aqueous, gel-phase nanostructures based on dynamically exchanging peptide sequences that self-select to maximize charge transfer of n-type semiconducting naphthalenediimide (NDI)-dipeptide bioconjugates with various π-electron-rich donors (dialkoxy/hydroxy/amino-naphthalene or pyrene derivatives). These gel-phase peptide libraries are characterized by spectroscopy (UV–vis and fluorescence), microscopy (TEM), HPLC, and oscillatory rheology and it is found that, of the various peptide sequences explored (tyrosine Y-NDI with tyrosine Y, phenylalanine F, leucine L, valine V, alanine A or glycine G-NH2), the optimum sequence is tyrosine-phenylalanine in each case; however, both its absolute and relative yield amplification is dictated by the properties of the donor component, indicating cooperativity of peptide sequence and donor/acceptor pairs in assembly. The methodology provides an in situ discovery tool for nanostructures that enable dynamic interfacing of supramolecular electronics with aqueous (biological) systems.

Les gels sont des solides mous constitués d'un réseau de molécules emprisonnant une phase liquide. Certains gels constitués de polymères biologiques sont appelés biogels. Biocompatibles, biorésorbables et déformables, ils possèdent une structure similaire à la matrice extracellulaire. De plus, la phase aqueuse d'un gel représente 95% de sa masse. Il est donc possible d'inclure des molécules au sein du réseau gélifié et de les faire diffuser vers l'extérieur. Ces qualités confèrent aux biogels de grandes potentialités en tant que biomatériaux innovants et systèmes de délivrance thérapeutique.Durant cette thèse, nous avons étudié la diffusion des molécules à partir de différents gels de gélatine.Dans un premier temps la diffusion à partir d'un gel chimique à été caractérisée grâce à l'utilisation de différentes molécules modèles. Elles balaient une large gamme de poids moléculaire et de charge ionique. Il a été montré que la diffusion depuis ces gels dépend de la nature du réseau de gélatine et de la nature des molécules diffusantes.Dans un second temps, les gels chimiques de gélatine ont été modifiés afin de contrôler et stimuler la libération moléculaire. Cinq nouvelles matrices gélifiées ont donc été synthétisées puis testés en diffusion. La phase sol du gel a tout d'abord été modifiée à l'aide d'un polymère viscosigène : l'alginate. Celui-ci limite la diffusion de certaines molécules. De plus son hydrolyse progressive induit la libération graduelle de molécules piégées. Le réseau de gélatine a ensuite été modifié. La synthèse d'un deuxième réseau au sein du gel de gélatine augmente ses capacités de rétention. Enfin l'utilisation de la technologie enzgel permettant la resolubilisation enzymatique contrôlée et programmée du gel de gélatine permet la libération massive et totale des molécules.Dans un troisième temps, l'ensemble des résultats de diffusion a permis la mise au point d'un unique modèle mathématique de diffusion pour l'ensemble des matrices. Ce modèle repose sur la deuxième loi de Fick et prend en compte l'encombrement stérique au sein du réseau de gélatine. Ainsi, il est possible de prévoir la diffusion en fonction de la nature du réseau et de la molécule diffusante.Enfin les résultats ont été utilisés dans le but de développer un pansement actif permettant de stimuler la cicatrisation des plaies chroniques. / Gels are soft matter composed of a liquid phase entrapped in a polymer network. Biopolymers can form gels, and then called biogels. Biocompatible, bioresorbable, these structures are really closed to extracellular matrix. Furthermore, aqueous phase represents 95% of the whole gel. Its possible to include molecules inside this liquid phase. Molecules are then released from the gel to the external environment.During this PhD project, we have studied the molecular release from different gelatin matrices.First, the release of a large range of molecules from chemical gelatin gel was studied. Different molecular weights and ionic charges were compared. The results show that the release depend on both the network structure and the include molecule characteristics. Moreover, the simultaneous release of two different compounds is possible.In the second part of the manuscript, gelatin gel was modified in order to control or stimulate the release. Five matrices were synthesised and tested. At first, alginate, a viscous polymer was introduced into the aqueous phase. Alginate is able to limit diffusion and its hydrolysis stimulates molecular release. Then, the gelatin network itself was modified. The synthesis of a second network within gelatin gel increases the entrapment of molecules. On the contrary, the use of ephemeral gels, where gelatin network hydrolysis is programmed and timed-controlled, leads to stimulate the molecular release.Then, a simple model elaborated from Fick's second law was constructed to describe these different delivery systems. The originality of the model resides in the consideration of the steric hindrance inside the gel. This unique model is able to predict correctly the release kinetics of small and large molecules, with or without interaction with the solid network, the concomitant release of two molecules and the release from ephemeral gels.Finally, all results were used in order to develop a new wound dressing able to deliver drugs and stimulate chronics wound healing.

Les nucléolipides sont des molécules hybrides amphiphiles de faible poids moléculaire composées de deux parties liées de façon covalente : la première est un acide nucléique, un nucléotide, un nucléoside ou une nucléobase et la seconde un lipide. En combinant les propriétés physicochimiques de deux des biomolécules parmi les plus représentées dans le vivant, les nucléolipides présentent la capacité à former des auto-assemblages supramoléculaires d’intérêt pour la conception de biomatériaux. L'étude des capacités d’auto-assemblage des GlycoNucléoLipides, qui possèdent un lien aromatique de type triazole, a démontré que la nature du lien covalent qui unit les deux parties du nucléolipide a un effet déterminant sur l’assemblage. Ce travail a porté sur l'utilisation et le développement d'une réaction de Stetter, organocatalysée par des carbènes N-hétérocycliques et bioinspirée, pour obtenir un lien de type dicétone-1,4 entre la thymidine et différents lipides. Ce motif, précurseur de cycles hétéroaromatiques, a notamment conduit à la formation de liens de type pyrrole par une réaction de type Paal-Knorr. Les propriétés gélatrices de ces nucléolipides originaux ont été comparées à celles de ceux portant un motif triazole. Parmi les nucléolipides obtenus, un composé particulièrement lipophile, porteur du lien 1,4- dicétone, a montré la capacité de former un gel dans des huiles (soit un oléogel). Une étude structurepropriétés a été effectuée pour comprendre le rôle de chaque partie de la molécule. Ce type de formulation présentant un intérêt tout particulier pour le développement de systèmes de délivrance contrôlée de substances actives lipophiles, les propriétés physicochimiques de cet oléogel ont par ailleurs été étudiées. La réaction de Stetter présentant la plupart des caractéristiques d'une réaction dite de "chimie click", des conditions de réaction plus éco-compatibles et adaptées à la fonctionnalisation d’autres biomolécules ont ensuite été développées en milieu aqueux. / Nucleolipids are hybrid amphiphilic low molecular weight molecules composed of two parts covalently linked: the first one being a nucleic acid, a nucleotide, a nucleoside or a nucleobase and the second a lipid. Combining the physico-chemical properties of two of the most widespread biomolecules, nucleolipids are capable of self-assemble as supramolecular structures of interest for application in the field of biomaterials. The study of the self-assembling properties of GlycoNucleoLipids, bearing a triazole moiety as a linker, demonstrated the crucial influence of the nature of the covalent linker bringing together the two parts of the nucleolipid onto the self-assembly. In this work, the synthesis of nucleolipids bearing a 1,4-diketone linker between thymidine and various lipids via the bioinspired and N-Heterocyclic Carbene organocatalyzed Stetter reaction is described. As an heteroaromatic cycle precursor, this moiety led to the formation of pyrrole skeletons via the classical Paal-Knorr reaction. The gelating properties of these original nucleolipids were evaluated and compared with the ones bearing a triazole link. Among these original synthetic nucleolipids, a lipophilic compound bearing a 1,4-diketone link exhibited the ability to form gels in oils (i.e. oleogels). A structure-properties study was realized to understand the role of each part of the molecule. This type of formulation being of particular interest for the development of lipophilic drug delivery systems, the physico-chemical properties of the oleogel were also extensively studied. The Stetter reaction exhibiting most of the « click chemistry » characteristics, eco-friendly reaction conditions were developed in aqueous media and applied to other biomolecules conjugation.