The development of highly selective and very sensitive methods to detect peptides and proteins of interest in complex mixtures remains an important goal in proteomics applications. This dissertation focuses on the use of reverse-micelle forming amphiphilic homopolymers as part of liquid-liquid extraction to selectively extract and concentrate peptides from an aqueous solution into an immiscible organic phase. After extraction, the polymer-peptide mixtures are amenable to direct analysis by matrix assisted laser desorption ionization mass spectrometry (MALDI-MS). The charged interiors of the reverse micelles enable oppositely charged peptides to be selectively extracted into the aggregate’s cores via coulombic attraction. Reverse micelles formed by negatively charged carboxylic acid or positively charged quaternary amine groups can be used alone or in sequence to selectively extract and fractionate peptides according to their isoelectric points (pIs). Furthermore, the pI cutoff can be readily tuned by adjusting the extraction pH. The coalescence of polymer-peptide conjugates into hotspots on the MALDI target plate during MALDI-MS analysis results in significant signal enhancement for the enriched peptides, enabling reproducible ion signals at concentrations as low as 10 fM. Interestingly, reverse micelles formed by positively charged polymers with quaternary amine substituents can selectively enrich acidic peptides that are undetectable during regular MALDI-MS analysis. The extraction protocol along with MALDI-MS can also be used for the selective enrichment and detection of low abundance peptide/protein biomarkers in human serum at physiologically relevant concentrations. Overall, the results described in this dissertation reveal that this selective extraction protocol along with MALDI-MS analysis might have a significant impact on protein identification and early stage screening of biomarkers.

This thesis explores the effects of bilayer mechanics on the adhesion of biomimetic membranes and vesicles, establishing copolymer lamellae as versatile model membranes that more widely vary membrane mechanics and chemical functionalization than can be achieved using phospholipids. This new biomimetic system provides fundamental insight into cell adhesion, and motivates new design strategies for vesicles in applications such as targeted delivery.^ This study focused on the dynamic adhesion kinetics and spreading of vesicle pairs held in micropipettes at moderate tensions. The program employed two copolymers of different membrane stiffnesses, a graft copolymer of poly(dimethyl siloxane)-poly(ethylene oxide) [PDMS-PEO] and a diblock copolymer of poly(butadiene)-PEO [PBD-PEO]. The depletion-driven adhesion between pairs of these vesicles was studied, as was the avidin-biotin-driven adhesion between functionalized vesicles. This experimental grid therefore varied the membrane stiffness, adhesion strength, and point-wise versus laterally uniform application of adhesive forces.^ This study systematically demonstrated, for the first time, the activated nature of vesicle adhesion and spreading, with the bending cost of kink formation at the spreading front comprising a line tension that destabilizes adhesion nuclei. Despite modest differences between the bending moduli of phospholipid and stiffer copolymer vesicles, the effect was often sufficiently strong to prevent spreading, or at least produce a lag time prior to the onset of spreading. For instance, flexible membranes subject to depletion forces as small as 0.008 erg/cm2 responded instantaneous to changes in membrane tension, achieving the equilibrium contact angle in less than a second. Stiff vesicles, however, never spread over a substrate vesicle or displayed an equilibrium contact angle, even when depletion forces were increased to 0.35 erg/cm 2. Avidin-biotin functionalized flexible vesicles displayed a lag time prior to spreading while fully functionalized stiff vesicles never spread over substrate vesicles. Of note, in cases where spreading did not, or had not yet occurred, there was evidence for adhesion in a contact nucleus. For instance, avidin-biotin functionalized vesicles could not be separated, and unfunctionalized vesicles subject to depletion forces deformed momentarily upon separation.^ Estimates of the activation energy associated with spreading for depletion-driven adhesion were consistent with experimental observations, while a semi-quantitative treatment of avidin-biotin binding kinetics predicted the form of the concentration-dependence of the pre-spreading lag time. Once initiated, spreading kinetics were rapid and independent of membrane tension.^ These results find significance in the areas of fundamental membrane physics and in biology. As micropipette manipulation is becoming an increasingly popular tool for membrane characterization, the current thesis demonstrates that the approach to equilibrium, as measured through the contact angle, may be impeded by bending mechanics, rendering the Young's analysis of adhesion strength meaningless. The findings also suggest that in cell adhesion and processes involving sharp membrane curvature, such as endocytosis, membrane mechanics likely plays an important role in the dynamic mechanism.^

The applications of stimuli responsive materials have tremendously increased over the past decade. In particular, these materials can potentially be used for improving the selectivity and efficiency of delivering a payload (drug) in drug delivery applications. This thesis discusses the design and synthesis of amphiphilic polymers which can respond to chemical, physical, and biological stimuli. We have synthesized a novel amphiphilic block copolymer which can form micellar assemblies in aqueous medium and respond to multiple stimuli; viz physical (temperarure) and chemical (pH, DTT and gluthathione). This amphiphilic block copolymer is sensitive not only to a single stimulus, but also to the simultaneous presence of multiple stimuli. This system provides a unique opportunity to fine tune the release kinetics of the encapsulated hydrophobic guest molecules. Besides designing polymeric systems responsive to chemical and physical stimuli, we were also interested in systems responsive to biological stimuli, since they can directly respond to the primary imbalances in biological functions instead of a secondary change such as pH, or redox potential characteristics. Amphiphilic polymers designed earlier in the group with –COOH as the hydrophilic group are known to provide micellar assemblies in water. The charged exterior (-COO-) of the micellar assemblies was used to disrupt protein-protein interaction. To further investigate if these polymeric micelles can be made responsive to proteins, we have studied the binding event of a ligand (pendant on the polymer chain) with the protein. Block copolymers and random copolymers functionalized with specific ligands were used as model systems to understand the interaction of polymers with proteins. We established that block copolymers provide better binding with proteins compared to random copolymers, possibly due to the higher effective molarity of ligands present in the former than the latter. Amphiphilic biaryl dendrimers decorated with ligands at different locations were also studied. We established that ligands present in at any layer of the dendron are equally available for binding with protein. Amphiphilic homopolymer and amphiphilic biaryl dendrimer were found to be the potential candidates for drug delivery applications by using proteins as the trigger to disassemble the micelles.

abstract: Delamination of solar module interfaces often occurs in field-tested solar modules after decades of service due to environmental stressors such as humidity. In the presence of water, the interfaces between the encapsulant and the cell, glass, and backsheet all experience losses of adhesion, exposing the module to accelerated degradation. Understanding the relation between interfacial adhesion and water content inside photovoltaic modules can help mitigate detrimental power losses. Water content measurements via water reflectometry detection combined with 180° peel tests were used to study adhesion of module materials exposed to damp heat and dry heat conditions. The effect of temperature, cumulative water dose, and water content on interfacial adhesion between ethylene vinyl acetate and (1) glass, (2) front of the cell, and (3) backsheet was studied. Temperature and time decreased adhesion at all these interfaces. Water content in the sample during the measurement showed significant decreases in adhesion for the Backsheet/Ethylene vinyl acetate interface. Water dose showed little effect for the Glass/ Ethylene vinyl acetate and Backsheet/ Ethylene vinyl acetate interfaces, but there was significant adhesion loss with water dose at the front cell busbar/encapsulant interface. Initial tensile test results to monitor the effects of the mechanical properties ethylene vinyl acetate and backsheet showed water content increasing the strength of ethylene vinyl acetate during plastic deformation but no change in the strength of the backsheet properties. This mechanical property change is likely inducing variation along the peel interface to possibly convolute the adhesion measurements conducted or to explain the variation seen for the water saturated and dried peel test sample types. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2020

Epoxy resins are used in a number of different industries and therefore have application-specific material requirements, from satellites that require materials that operate in space, to paints and coatings that require high scratch resistance and mechanical durability, to medical devices, designed to be in continuous contact with biological fluids. Commercial epoxy products come with manufacturer’s information explaining the epoxy properties and recommended preparation processing conditions, which may include epoxy resin to curing agent mix ratio (Part A : Part B), cure time, and cure temperature, for example. Due to proprietary reasons, it can be difficult to understand why these values are provided, and more importantly, the consequences when deviating from the prescribed recommendations. When manufacturing bioprocessing products for the medical field, a company is under a limited capacity to change materials of construct. Determining how to modify the processing conditions in order to control the material properties of an epoxy would benefit bioprocessing product manufacturers as it would allow them to use the same epoxy that meets the different application-specific requirements of different products. Five different epoxy systems that were designed for medical applications were characterized to determine how variations in preparation and processing conditions, such as mix ratio (by weight) and cure conditions, affect the final properties of the cured epoxy, including: glass transition temperature, chemical resistance, and coefficient of thermal expansion. For each system, it was found that one mix ratio would produce a material with a maximum glass transition temperature, while changing the mix ratio with either excess Part A epoxy resin or excess Part B amine curing agent would result in a decrease in the glass transition temperature. A higher glass transition temperature indicates higher crosslink density, as a more tightly crosslinked network requires more thermal energy to reach the “rubbery” phase. This mix ratio did not always coincide with the manufacturer’s specifications, suggesting that these recommendations are potentially application specific. While variations in the curing agent’s chemical composition impacted the final material properties of epoxy, as expected, it was also found that varying the mix ratio and annealing conditions resulted in changes in epoxy material properties. A wide range of experiments provided critical data that supported the idea that a single epoxy formulation can be used to produce epoxy materials with varied performance properties through modifications in the preparation and processing conditions, while still remaining usable to manufacture products.

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<p>QC 20150323</p>

Atom transfer radical polymerization (ATRP) has proven to be a powerful technique to obtain polymers with narrow polydispersities and controlled molecular weight. It also offers control over chain-ends. The technique is the most studied and utilized of thecontrolled/”living” radical polymerization techniques since a large number of monomerscan be polymerized under simple conditions. ATRP can be used to obtain polymer graftsfrom multifunctional substrates. The substrates can be either soluble (i. e. based ondendritic molecules) or insoluble (such as gold or silicon surfaces). The large number ofgrowing chains from the multifunctional substrates increases the probability of inter-and intramolecular reactions. In order to control these kinds of polymerizing systems, andsuppress side-reactions such as termination, the concentration of propagating radicalsmust be kept low. To elaborate such a system a soluble multifunctional substrate, based on 3-ethyl-3-(hydroxymethyl)oxetane, was synthesized. It was used as a macroinitiatorfor the atom transfer radical polymerisation of methyl acrylate (MA) mediated byCu(I)Br and tris(2-(dimethylamino)ethyl)amine (Me6-TREN) in ethyl acetate at room temperature. This yielded a co-polymer with a dendritic-linear architecture. Since mostsolid substrates are sensitive to the temperatures at which most ATRP polymerisations are performed, lowering the polymerization temperatures are preferred. ATRP at ambienttemperature is always more desirable since it also suppresses the formation of thermally formed polymer. The macroinitiator contained approximately 25 initiating sites, which well mimicked the conditions on a solid substrate. The polymers had low polydispersity and conversions as high as 65% were reached without loss of control. The solid substrateof choice was cellulose fibers that prior to this study not had been grafted through ATRP.As cellulose fibers a filter paper, Whatman 1, was used due to its high cellulose content.The hydroxyl groups on the surface was first reacted with 2-bromoisobutyryl bromidefollowed by grafting of MA. Essentially the same reaction conditions were used that hadbeen elaborated from the soluble substrate. The grafting yielded fibers that were very hydrophobic (contact angles&gt;100°). By altering the sacrificial initiator-to-monomer ratiothe amount of polymer that was attached to the surface could be tailor. PMA with degreesof polymerization (DP’s) of 100, 200 and 300 were aimed. In order to control that thepolymerizations from the surface was indeed “living” a second layer of a hydrophilicmonomer, 2-hydroxymethyl methacrylate (HEMA), was grafted onto the surface. Thisdramatically changed the hydrophobic behavior of the fibers. / QC 20100524

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No description available.