Search

Efflux pumps confer multidrug resistance to bacteria by exporting drugs and preventing them from reaching their target. The most abundant and best studied efflux pump in Salmonella Typhimurium is AcrB. The biological function of AcrB was unexplored. Therefore, the impact of loss of AcrB-mediated efflux was studied in S. Typhimurium, using an AcrB D408A mutant, which expressed an inactive form of AcrB. Transcriptomics studies revealed significant differences between the AcrB D408A mutant and previously constructed ΔacrB and acrB::aph mutants, which did not express AcrB. The acrB::aph mutant differed in the motility phenotype from the other two mutants. However, all three mutants were multidrug hypersusceptible and were attenuated when compared against their parental wild-type strain. AcrB-mediated efflux also had a role in quorum sensing, persister formation and maintenance of the overall metabolic state of Salmonella. Analysis of the effluxome of AcrB in S. Typhimurium and E. coli revealed that fatty acids/alcohols are a common substrate of AcrB in both species and acylcarnitines were exclusive to S. Typhimurium. This study presents a novel model to analyse the physiological role of RND efflux pumps and demonstrates that AcrB is more than just a mechanism of antibiotic resistance.

Volume CT (VCT) scan is being used in various industrial and medical applications. One example of such is the inspection of turbine blades in jet engines. Even with the complete 3D data, it can be difficult to directly inspect potential anomaly regions (e.g. drilled holes) in the internal of the blade. The aim of this thesis is to design methods to help manual visual inspection and automatic detection of anomalies in turbine blade VCT data.In the first part, an unwrapping method inspired by medical research was designed and tested on the dataset. The method applies thresholding methods to the CT scans and extracts the skeleton of the major internal cavities. The skeleton branches are then used to perform unwrapping on the VCT data to transform it into a flattened 3D representation. The result reveals the internal of the blade and allows much more convenient visual inspection.The second part then explores deep learning techniques to automate anomaly detection. This chapter begins with an introduction to fundamental ideas of deep learning and popular frameworks, followed by a discussion of dataset composition and training/validation/testing set partitioning strategies. Finally, four Convolutional Neural Networks (CNN) were designed and trained to identify a specific type of anomaly. The result shows that an optimal combination of set partitioning strategy and network design allows the system to reach high accuracy in automatic anomaly detection. In conclusion, the thesis demonstrated a novel view to inspect VCT data and investigated the application of deep learning techniques to capture 3D features in the industrial environment. Both demonstrate great practical value and may inspire and stimulate more discussions and researches in this area.

Good processability is often required for applications of conducting materials like polyaniline (PANI), carbon nanotubes (CNTs) and graphene. This can be achieved by either physical stabilization or chemical functionalization. Functionalization usually expands the possible applications for the conducting materials depending on the properties of the functional groups. Processable conducting materials can also be combined with other co-dissolving materials to prepare composites with desired chemical and physical properties.Polyanilines (PANI) doped with dodecylbenzenesulfonic acid (DBSA) are soluble in many organic solvents such as chloroform and toluene. Single wall carbon nanotubes (SWCNTs) can be dispersed into PANI/DBSA to form homogeneous solutions. PANI/DBSA functions as a conducting surfactant for SWCNTs. The mixture can beiicombined with two-parts polyurethanes that co-dissolve in the organic solvent to produce conducting polymer composites. The composite mixtures can be applied onto various substrates by simple spray-on methods to obtain transparent and conducting coatings.Graphene, a single layer of graphite, has drawn intense interest for its unique properties. Processable graphene has been produced in N-methyl-2-pyrrolidone (NMP) by a one-step solvothermal reduction of graphite oxide without the aid of any reducing reagent and/or surfactant. The as-synthesized graphene disperses well in a variety of organic solvents such as dimethylsulfoxide (DMSO), ethanol and tetrahydrogenfuran (THF). The conductivity of solvothermal reduced graphite oxide is comparable to hydrazine reduced graphite oxide.Attempts were made to create intrinsically conducting glue comparable to mussel adhesive protiens using polyaniline and graphene. Mussels can attach to a variety of substrates under water. Catechol residue in 3,4-dihydroxyphenylalanine (L-DOPA) is the key to the wet adhesion. Tyrosine and phosphoserine with primary alkyl amine groups also participate in adhesion. A novel water soluble synthetic mussel adhesive containing both catechol and amine groups are synthesized in a simple approach. A polyallylamine backbone is used to take the place of the polyamide chain. Catechol is appended to the backbone as the key cross-linking group. Compared to polyallyamine, poly[N-(3,4- dihydroxybenzylidene)allylamine] exhibits good adhesion under alkaline water due to moderate cross-linking. When exposed to cross-linkers, this synthetic mussel adhesive can form a hydrogel at a very low concentration.iiiVarious methods were tried to attach catechol group onto polyaniline and graphene to make synthetic conductive mussel adhesive. Although the chemistry proved to be successful, the material doesn't show great adhesion to selected substrates probably due the nature of the backbone and difficulties associated with its processability.

This dissertation presents material design strategies to investigate cell-biomaterial interactions on specific biocompatible polymers and polymer blends by using mouse pre-osteoblastic MC3T3 cells aiming for potential applications in bone tissue engineering. Chapter 1 reviews some related background knowledge including polymeric biomaterials for tissue engineering, cell-biomaterial interaction, synthetic photo-crosslinkable and degradable polymers, and the effect of surface features on osteoblast cell responses. Chapter 2 presents photo-crosslinkable composites of poly(propylene fumarate) (PPF), an injectable and biodegradable polyester, and methacryl-polyhedral oligomeric silsesquioxane (mPOSS), which has eight methacryl groups tethered with a cage-like hybrid inorganic-organic nanostructure, for bone tissue engineering applications. Blending mPOSS with PPF was found to decrease the viscosity of PPF, expedite photo-crosslinking process, increase tensile modulus and accelerate hydrolytic degradation of crosslinked PPF/mPOSS while it did not significantly alter surface wettability, protein adsorption, and cell response. Chapter 3 demonstrates a polymer blend composed of amorphous PPF and semicrystalline poly(ε-caprolactone) (PCL), a widely used biocompatible and biodegradable polymer, in both uncrosslinked and photo-crosslinked forms. Thermal, rheological, mechanical properties as well as surface hydrophilicity and morphology can be well controlled by crosslinking density and crystallinity. Distinct cell attachment, spreading, and proliferation have been found to PPF/PCL blends in the presence or absence of cross-links. Chapter 4 and 5 describe the crystallization induced banded spherulitic morphologies in PPF/PCL blends and PCL homo-blends and their preliminary biological evaluation. Thermal properties, crystallization kinetics, and surface morphology of these blends can be regulated by isothermal crystallization temperature and composition. Surface roughness has been found to play an important role in influencing protein adsorption and cell response. Chapter 6 introduces a newly synthesized biodegradable elastomer, poly(ε-caprolactone) triacrylate (PCLTA), with two different molecular weights resulting in distinct mechanical properties at physiological temperature. Using replica molding from silicon wafers, photo-crosslinked PCLTA substrates with concentric micro-grooves have been successfully fabricated. MC3T3 cell attachment, proliferation, and differentiation could be better supported by stiffer substrates while not significantly influenced by micro-groove dimensions. Cell orientation, nuclei shape and localization, mineralization, and gene expression level of osteocalcin have been found to be more significant on narrower micro-grooves when groove depth was 10 μm.

Iridium(I)-catalyzed olefin isomerization in bis(allyl) ethers is integrated into a generally applicable strategy for affecting highly stereoselective Claisen rearrangements. Catalyzed alkene isomerization affords allyl vinyl ethers from easily prepared di(allyl) ethers; direct thermolysis of these reaction mixtures leads to highly diastereoselective [3,3] sigmatropic rearrangements affording syn-2,3-dialkyl-4-pentenal derivatives. An easily executed strategy for realizing asymmetric variants of the isomerization-Claisen rearrangement (ICR) reactions is also described.Merging the catalytic asymmetric synthesis of di(allyl) ethers with ensuing olefin isomerization-Claisen rearrangement (ICR) reactions provides a convenient, two-step route to asymmetric aliphatic Claisen rearrangements from easily obtained starting materials. These reactions deliver the 2,3-disubstituted 4-pentenal derivatives characteristic of aliphatic Claisen rearrangements with excellent relative and absolute stereocontrol. A catalytic enantioselective synthesis of the (+)-calopin dimethyl ether demonstrates the utility of this reaction technology in asymmetric synthesis enterprises.Stereoselective quaternary all-carbon stereocenter construction is often not easily achieved from methodologies developed primarily for accessing less substituted stereogenic carbons. Olefin isomerization-Claisen rearrangement (ICR) reactions offer a strategy for recruiting the venerable Claisen rearrangement for asymmetric quaternary carbon construction. Several complementary strategies for enantioselective quaternary carbon synthesis derive directly from the ICR reaction design.