LaRC-TPI, an aromatic thermoplastic polyimide, and Kapton®, a poly(pyromellitimide) were exposed to oxygen, argon and ammonia plasmas as pretreatments for adhesive bonding. Chemical changes which occurred in the surface as a result of the plasma treatments were investigated using x-ray photoelectron spectroscopy (XPS) and infrared reflection-absorption spectroscopy (IR-RAS). Water contact angle analysis was utilized to characterize the changes in surface wettability, and the ablative effects of the plasmas were monitored using ellipsometry and high resolution scanning electron microscopy (HR-SEM). Both XPS and IR-RAS results revealed the formation of polar functional groups at the surface. Contact angle analysis showed enhanced water wettability of the plasma-treated surfaces. As monitored by ellipsometry, oxygen and argon plasmas were seen to be highly ablative, whereas an ammonia plasma was only moderately so. HR-SEM micrographs revealed texturized surfaces in the case of oxygen and argon plasmas, but not in the case of ammonia plasma. Oxygen and argon plasmas appear to react with the polyimides via a fragmentation/oxidation mechanism, forming a loosely attached layer composed of low molecular weight polymer chains. The effect of ammonia plasma is postulated to be imide ring-opening resulting in the formation of amide functional groups. The 180° peel test was utilized to determine the receptability of the plasma-treated polyimide surfaces toward bonding with other polymeric materials. Adhesives used were a pressure sensitive acrylate and poly(ether sulfone). The pressure sensitive adhesive, although not representing a realistic bonding situation, does represent a system which presents the least disturbance to the plasma-modified layer, allowing the physical nature of the plasma-treated surface to be probed. The peel test values of the pressure sensitive adhesive/plasma-treated polyimide systems fell below the level of the non-treated controls, regardless of the plasma treatment used. Peel surface analysis revealed the presence of polyimide on the pressure sensitive adhesive failure surface, indicating failure in the plane of a weak boundary layer created by plasma. The removal of the weak boundary layer by solvent treatment restored the peel values to the level of the controls. Bonding of Kapton® films with poly(ether sulfone) showed an opposite trend; peel strengths of the plasma-treated samples all showed improvements versus the non plasma-treated control. Plasma treatments of LaRC-TPI which had been deliberately contaminated with mold release and high density polyethylene illustrated showed that plasma treatments are not always detrimental to adhesion. It was shown that the physical as well as the chemical nature of a polymer surface is critical to the level of adhesion which can be achieved. / Master of Science

Cordierite was adhered to molybdenum using various metallic interlayers of copper, nickel, and chromium. The development of a coating adhesion test methodology was required to choose between interface designs. An indentation method was chosen because of ease in testing and availability of fracture mechanics interpretations of test data. The interfacial fracture toughness was determined from indentation load vs. crack length data by examining the residual stress and critical buckling load of the ceramic coatings. The interfacial fracture toughness values obtained using a slightly different indentation analysis agree with those in the literature. Quantitative chemical analysis of the interface microstructure was used to explain differences in interfacial fracture toughness values for samples with different metallic interlayer designs. The best interface design for adhering cordierite glass-ceramic coatings to molybdenum was found to be molybdenum / 2 μm copper / 4 μm chromium / cordierite. / Master of Science

Blast neurotrauma represents a significant mode of traumatic injury to the brain. The incidence of blast neurotrauma is particularly high amongst military combat personnel and can be debilitating and endure clinically for years after injury is sustained. Mechanically, blast represents a unique and complex loading paradigm associated with compressive shock waves that propagate out from an explosive event and interact with the head and other organs through high-rate loading. When subjected to such insult, brain cells undergo characteristic injury responses which include neuroinflammation, oxidative stress, edema and persistent glial activation. These features of the injury have emerged as important mediators of the chronic brain damage that results from blast. Astrocytes have emerged as a potential therapeutic target because of their ubiquitous roles in brain homeostasis, tissue integrity and cognitive function. This glial subtype has a characteristic reactive response to mechanical trauma of various modes. In this work, custom in vitro injury devices were used to characterize functional models of astrocyte reactivity to high-rate insult to study mechano-stimulation mechanisms associated with the reactive phenotype. The working hypothesis was that high-rate overpressure exposure would cause metabolic aberrations, cell junction changes, and adhesion signal transduction activation, all of which would contribute to astrocyte response and reactivity. Astrocyte cultures were exposed to a 20 psi high-rate overpressure scheme using an underwater explosion-driven device. Astrocytes experienced dynamic energetic fluctuations in response to overpressure which were followed by the assumption of a classically defined reactive phenotype. Results indicated specific roles for cationic transduction, cell junction dynamics (gap junction and anchoring junctions) and downstream signal transduction mechanisms associated with adhesion alterations in onset of the astrocyte reactive phenotype. Investigation into adhesion signaling regulation by focal adhesion kinase in 2D and 3D cultures was also explored to better understand cellular reactivity as a function of extracellular environment. Additionally, another underwater in vitro device was built to study combination effects from overpressure and fluid shear associated with insult. Overall, the combined studies offer multiple mechanisms by which to explore molecular targets for harnessing astrocytes' potential for repair after traumatic injury to the brain. / PHD / Blast neurotrauma represents a significant mode of traumatic injury to the brain. The incidence of blast neurotrauma is particularly high amongst military combat personnel in which close to 80% of the injuries sustained in combat are attributed to explosive mechanisms. This injury, like other traumatic brain injuries, can be debilitating and result in altered quality of life for years after injury is sustained. There is a critical need to understand how brain cells are injured by and respond to blast loading in order to develop effective therapeutic strategies. The following work approaches this problem through the use of cellular models of blast-type insult. Custom injury devices were used to develop models of brain cell reactive response to high-rate insult based on experimental simulations of blast neurotrauma. In particular, a sub-type of brain cells called astrocytes were studied. Astrocytes have emerged as a potential therapeutic target because of their ubiquitous roles in brain homeostasis, tissue integrity and cognitive function. The working hypothesis was that high-rate overpressure exposure would cause metabolic aberrations, cell junction changes, and adhesion signal transduction activation, all of which would contribute to astrocyte response and reactivity. Astrocytes experienced dynamic energetic fluctuations in response to overpressure which were followed by the assumption of a classically defined reactive phenotype. Results indicated specific roles for cationic transduction, cell anchorage and downstream signaling mechanisms associated with adhesion alterations in onset of the astrocyte reactive phenotype. Investigation into adhesion signaling regulation by focal adhesion kinase in 2D and 3D cultures was also explored to better understand cellular reactivity as a function of extracellular environment. Additionally, another underwater cell injury device was built to study combination effects from overpressure and fluid shear associated with insult. Overall, the combined studies offer multiple mechanisms by which to explore molecular targets for harnessing astrocytes’ potential for repair after traumatic injury to the brain.

Polymeric methylenebis(phenylisocyanate) (pMDI) has increasingly been used in the wood particulate composite industry. Wood composites, especially oriented strand board (OSB) are made with many variations of wood species. Little research has been done to investigate how pMDI adhesion has been affected by species. The present is divided into two parts. First, mode I fracture mechanics and surface free energy analysis was performed to investigate differences in adhesion between southern yellow pine and yellow-poplar bonded with pMDI. Secondly, an improvement in the synthesis of 13C, 15N labeled pMDI is discussed. Mode I fracture results show that pMDI adhesion was affected differently by southern yellow pine compared yellow poplar. The shear energy release rate was significantly higher in pine/pMDI composites than in yellow poplar/pMDI composites. The total surface energy of southern yellow pine was shown to be significantly greater than yellow poplar. The free energy of adhesion (DG) of the pine/pMDI and the poplar/pMDI was investigated. The DG indicated that the pine/pMDI system would take more energy to separate compared to the poplar/pMDI system. Lastly, a double-labeled 13C, 15N pMDI adhesive was successfully synthesized to produce Solid-State NMR composites. / Master of Science

Master of Science / Glass has long been used in glazing applications because of its transparency, stiffness, hardness, resistance to corrosion, and recyclability. Despite these useful features, however, glass is a very brittle material, lacking the ability to usefully absorb energy. Multi-material laminates have been produced as an alternative for glazing applications to improve energy absorption and other functionality requirements. As the demand for these laminates has increased in the construction, automotive, and defense sectors, a need for a more durable system has become apparent. One such example is the laminated glass systems often used in automobiles where two sheets are bonded (laminated) together with a plastic interlayer. Several types of interlayers have been used for these laminated systems, with polyvinyl butyral (PVB) being the most prevalent. A more recently developed interlayer type is thermoplastic polyurethane (TPU), which has the ability to bond to substrates other than glass, making it useful for applications like ballistic-resistant glass laminates, which often involve sheets made of polycarbonate. This study aims to explore the durability of laminated polycarbonate systems by investigating the interaction of environment and TPU viscoelastic behavior on the time-dependent crack growth in these laminates. The main test utilized is the wedge test, where a wedge is inserted between two polycarbonate adherends bonded together with an interlayer. The wedge causes a debond (a crack) to form. This crack may then grow over time. The crack growth in wedge test specimens with different TPUs is evaluated at various temperature and humidity conditions. A separate test, referred to as dynamic mechanical analysis (DMA), is conducted to determine the thermomechanical properties of the TPUs. These properties are then used to analyze the results of the wedge tests. In addition to different TPU types, the effects of edge seals and surface treatment to improve bonding are compared. Models are used to analyze the resulting data to support the prediction of lifetimes of laminated polycarbonate systems employing the TPUs investigated.

Yes / For the first time a series of functional hydrogels based on semi-interpenetrating networks with both branched and crosslinked polymer components have been prepared and we show the successful use of these materials as substrates for cell culture. The materials consist of highly branched poly(N-isopropyl acrylamide)s with peptide functionalised end groups in a continuous phase of crosslinked poly(vinyl pyrrolidone). Functionalisation of the end groups of the branched polymer component with the GRGDS peptide produces a hydrogel that supports cell adhesion and proliferation. The materials provide a new synthetic functional biomaterial that has many of the features of extracellular matrix, and as such can be used to support tissue regeneration and cell culture. This class of high water content hydrogel material has important advantages over other functional hydrogels in its synthesis and does not require post-processing modifications nor are functional-monomers, which change the polymerisation process, required. Thus, the systems are amenable to large scale and bespoke manufacturing using conventional moulding or additive manufacturing techniques. Processing using additive manufacturing is exemplified by producing tubes using microstereolithography. / EPSRC

Environmental response as determined by the cell-polymer interaction stands as the greatest restriction to the implementation of new polymeric materials. Cell-polymer interactions are most influenced by substrate surface free energy, surface chemistry, topography, and rigidity[1]. Alteration of these properties through surface treatment has become a common approach to attain the desired cellular interaction. This study investigates Kr-F excimer laser(248 nm) surface modification of poly(methyl methacrylate), glycol-modified poly(ethylene terephthalate), and polytetrafluoroethylene and its effect on the adhesion of Escherichia Coli K-12 bacteria. These three polymers were chosen for their very different mechanisms of ablation as well as their range of surface free energies and bacterial responses[2-4]. Polymers were ablated using a pulsed Kr-F excimer laser with a dose of 3.3x 10-9 W/cm2 per pulse. This high level of UV radiation was sufficient to cause significant surface damage on both PMMA and PTFE. PETG showed some signs of wavering in the surface and material removal was confirmed through optical microscopy. Due to the extensive damage associated with ablation, a much lower-powered, continuous beam Kr-F laser was used for contact angle samples. It delivered a dose of 1.27 W/cm2. Contact angle measurements were then taken which showed dose-dependent surface free energy in all three polymers. Following ablation, bacterial adhesion to PETG was improved two-fold, while it decreased in both PTFE and PMMA. Surface chemistry analysis supported the idea that the ablation occurred through chain scission, since there were no new surface groups created. There were significan texture modifications observed in PTFE and PMMA whicle PETG demonstrated the rolling structure characteristic of polyesters following laser ablation described in Wefers et al [4] and Hopp et al [5]. Contact angle measurements showed a correlation between radiation dose and surface free energy of all three polymers. / Master of Science

The analysis of peeling tape or a bandage from skin is a challenging problem. Skin is a very complex material made of many layers with anisotropic material properties. Adhesives that bond tapes or patches to skin must attach to skin through moisture and skin movement, but then be removed with little skin trauma. A computer model of peeling from skin apparently has not been developed previously. With experiments and the application of mechanics, research was conducted to analyze adhesion to skin. Numerous peeling experiments were performed on human subject arms using 2.54-cm-wide pressure sensitive tape Durapore™ by 3M. Various rates, angles, and dwell times were tested. Testing machines recorded peel force and the displacement of the end of the tape. A range of maximum and average peeling force values were noted for human subjects, along with the influence of angle, rate, order of testing, dwell time, and subject. Also, rigid substrates were tested for comparison with human skin. Computer models were also developed to simulate peeling and skin behavior. Initial models dealt with peeling from a rigid surface, and intermediate models concerned plucking skin. The final model involved peeling a piece of tape from skin, the overall goal of this research. The skin and tape were modeled as they behave during peeling. With the final model, the peel angle, debonding moment, normal force on the skin, and net shear force tangential to the skin were analyzed. Results from the experiments and computer models of this research will increase knowledge of skin behavior and could contribute to improvements in the design of adhesives that contact the skin. / Master of Science

High glass transition (eg. 360 °C) melt processable thermoplastic polyimide homopolymers and poly(imide-siloxane) segmented copolymers were prepared from a number of diamines and dianhydrides via solution imidization, polydimethylsiloxane segment incorporation and molecular weight control with non-reactive phthalimide end-groups. The adhesive bond performance of these polyimides was investigated as a function of molecular weight, siloxane incorporation, residual solvent, test temperature, and polyimide structure via single lap shear samples prepared from treated Ti-6AI-4V alloy adherends and compression molded film adhesives or scrim cloth adhesives. The adhesive bond strengths increased greatly with siloxane segment incorporation at 10, 20 and 30 weight percent, and decreased slightly with total polymer molecular weight. As the test temperature was increased, adhesive bond strength increased, decreased or showed a maximum at some temperatures depending on the polyimide structure and siloxane content. The presence of residual solvent increased adhesive bond strength at ambient temperature but decreased the strength at the elevated temperatures. The variation of adhesive bond strength with residual solvent, siloxane and test temperature was attributed to the influence of these parameters on the brittle-ductile transition behavior of the polyimide system. This conclusion was supported by stress-strain measurements which indicated that tensile strength and modulus decreased with siloxane concentration and test temperature, demonstrating that there was an optimum combination of strength and strain for maximum adhesive bond strength. A model was developed to describe this behavior. The poly(imide-30%siloxane) segmented copolymer and a miscible poly(ether-imide) also demonstrated excellent adhesive bond strength with poly(arylene ether ketone) PEEK®-graphite composites. Oxygen or ammonia gas plasma treatment was very effective in further improving adhesive bond strength of melt laminated PEEK®-graphite composites. / Ph. D.

BACKGROUND:Transglutaminase-4 (TGase-4), also known as the Prostate Transglutaminase, is an enzyme found to be expressed predominately in the prostate gland. The protein has been recently reported to influence the migration and invasiveness of prostate cancer cells. The present study aimed to investigate the influence of TGase-4 on cell-matrix adhesion and search for the candidate active domains] within the protein.METHODS:Human prostate cancer cell lines and prostate tissues were used. Plasmids that encoded different domains and full length of TGase-4 were constructed and used to generate sublines that expressed different domains. The impact of TGase-4 on in vitro cell-matrix adhesion, cell migration, growth and in vivo growth were investigated. Interactions between TGase-4 and focal adhesion complex proteins were investigated using immunoprecipitation, immunofluorescence and phosphospecific antibodies.RESULTS:TGase-4 markedly increased cell-matrix adhesion and cellular migration, and resulted in a rapid growth of prostate tumours in vivo. This effect resided in the Core-domain of the TGase-4 protein. TGase-4 was found to co-precipitate and co-localise with focal adhesion kinase (FAK) and paxillin, in cells, human prostate tissues and tumour xenografts. FAK small inhibitor was able to block the action mediated by TGase-4 and TGase-4 core domain.CONCLUSION:TGase-4 is an important regulator of cell-matrix adhesion of prostate cancer cells. This effect is predominately mediated by its core domain and requires the participation of focal adhesion complex proteins.