Yes / Corneal ulcers, a leading cause of blindness in the developing world are treated inappropriately without prior microbiology assessment because of issues related to availability or cost of accessing these services. In this work we aimed to develop a device for identifying the presence of Gram-positive or Gram-negative bacteria or fungi that can be used by someone without the need for a microbiology laboratory. Working with branched poly (N-isopropyl acrylamide) (PNIPAM) tagged with Vancomycin, Polymyxin B, or Amphotericin B to bind Gram-positive bacteria, Gram-negative bacteria and fungi respectively, grafted onto a single hydrogel we demonstrated specific binding of the organisms. The limit of detection of the microbes by these polymers was between 10 and 4 organisms per high power field (100X) for bacteria and fungi binding polymers respectively. Using ex vivo and animal cornea infection models infected with bacteria, fungi or both we than demonstrated that the triple functionalised hydrogel could pick up all 3 organisms after being in place for 30 min. To confirm the presence of bacteria and fungi we used conventional microbiology techniques and fluorescently labelled ligands or dyes. While we need to develop an easy-to-use either a colorimetric or an imaging system to detect the fluorescent signals, this study presents for the first time a simple to use hydrogel system, which can be applied to infected eyes and specifically binds different classes of infecting agents within a short space of time. Ultimately this diagnostic system will not require trained microbiologists for its use and will be used at the point-of-care. / We gratefully acknowledge support for this research by the Well- come Trust which provided funding for Shivshetty, Swift and Pinnock (Grant 0998800/B/12/Z).

No description available.

Ce travail est consacré à l'étude d'origine et signatures de la dépendance en concentration $\phi$ du paramètre de Flory $\chi _(eff)$ pour les polymères neutres solubles dans l'eau. Les trois versions du modèle à deux états qui ont été proposés pour expliquer le comportement de phase de Poly(oxyéthylène) dans l'eau mènent à $\chi _(eff)(\phi) $. Cette dépendance peut servir à tester la qualité des modèles: elle permet de distinguer entre les différents modèles et juger de la pertinence des paramètres impliqués. L'apparition de $\chi _(eff)(\phi)$ à partir des modèles alternatifs à un seul état est aussi discutée. Les signatures macroscopiques de $\chi _(eff)(\phi)$ sont illustrées avec l'exemple du gonflement des chaînes isolées et des brosses planes. La dépendance de $\chi _(eff)$ avec $\phi$ dans les systèmes à concentration uniforme a deux conséquences principales: entraînement du déplacement du croisement entre les régimes Gaussien et auto-évitant, et la possibilité d'une transition de phase du premier ordre pour les chaînes flexibles isolées. $\chi _(eff)(\phi)$ peut provoquer une séparation verticale de phase dans des brosses polymères qui implique la coexistence de deux phases de concentration finie. Cette approche est appliquée à l'interprétation d'un ensemble des résultats expérimentaux qui suggère que cet effet pourrait exister avec les brosses de Poly(N-isopropylacrylamide).

abstract: Polymer-gold composite particles are of tremendous research interests. Contributed by their unique structures, these particles demonstrate superior properties for optical, catalytic and electrical applications. Moreover, the incorporation of “smart” polymers into polymer-gold composite particles enables the composite particles synergistically respond to environment-stimuli like temperature, pH and light with promising applications in multiple areas. A novel Pickering emulsion polymerization route is found for synthesis of core-shell structured polymer-gold composite particles. It is found that the surface coverage of gold nanoparticles (AuNP) on a polystyrene core is influenced by gold nanoparticle concentration and hydrophobicity. More importantly, the absorption wavelength of polystyrene-gold composite particles is tunable by adjusting AuNP interparticle distance. Further, core-shell structured polystyrene-gold composite particles demonstrate excellent catalyst recyclability. Asymmetric polystyrene-gold composite particles are successfully synthesized via seeded emulsion polymerization, where AuNPs serve as seeds, allowing the growth of styrene monomers/oligomers on them. These particles also demonstrate excellent catalyst recyclability. Further, monomers of “smart” polymers, poly (N-isopropylacrylamide) (PNIPAm), are successfully copolymerized into asymmetric composite particles, enabling these particles’ thermo-responsiveness with significant size variation around lower critical solution temperature (LCST) of 31°C. The significant size variation gives rise to switchable scattering intensity property, demonstrating potential applications in intensity-based optical sensing. Multipetal and dumbbell structured gold-polystyrene composite particles are also successfully synthesized via seeded emulsion polymerization. It is intriguing to observe that by controlling reaction time and AuNP size, tetrapetal-structured, tripetal-structured and dumbbell-structured gold-polystyrene are obtained. Further, “smart” PNIPAm polymers are successfully copolymerized into dumbbell-shaped particles, showing significant size variation around LCST. Self-modulated catalytic activity around LCST is achieved for these particles. It is hypothesized that above LCST, the significant shrinkage of particles limits diffusion of reaction molecules to the surface of AuNPs, giving a reduced catalytic activity. Finally, carbon black (CB) particles are successfully employed for synthesis of core- shell PNIPAm/polystyrene-CB particles. The thermo-responsive absorption characteristics of PNIPAm/polystyrene-CB particles enable them potentially suitable to serve as “smart” nanofluids with self-controlled temperature. Compared to AuNPs, CB particles provide desirable performance here, because they show no plasmon resonance in visible wavelength range, whereas AuNPs’ absorption in the visible wavelength range is undesirable. / Dissertation/Thesis / Doctoral Dissertation Chemical Engineering 2015

Composite materials formed from two or more functionally different materials offer a versatile avenue to create a tailored material with well defined traits. Within this dissertation research, multi-functional composites were synthesized based on organic and inorganic materials. The functionally of these composites was experimentally tested and a semi-empirical model describing the sedimentation behavior of these particles was developed. This first objective involved the fabrication of microcomposites consisting of titanium dioxide (TiO2) nanoparticles confined within porous, microgels of a thermo-responsive polymer for use in the photocatalytic treatment of wastewater. TiO2 has been shown to be an excellent photocatalyst with potential applications in advanced oxidative processes such as wastewater remediation. Upon UV irradiation, short-lived electron-hole pairs are generated, which produce oxidative species that degrade simple organic contaminants. The rapid sedimentation of these microcomposites provided an easy gravimetric separation after remediation. Methyl orange was used as a model organic contaminant to investigate the kinetics of photodegradation under a range of concentrations and pH conditions. Although after prolonged periods of UV irradiation (~8-13 hrs), the titania-microgels also degrade, regeneration of the microcomposites was straightforward via the addition of polymer microgels with no loss in photocatalytic activity of the reformed microcomposites. The second objective within this dissertation involved the systematic development of abrasive microcomposite particles containing well dispersed nanoparticles of ceria in an organic/inorganic hybrid polymeric particle for use in chemical mechanical polishing/planarization (CMP). A challenge in IC fabrication involves the defect-free planarization of silicon oxide films for successful multi-layer deposition. Planarization studies conducted with the microcomposites prepared in this research, yield very smooth, planar surfaces with removal rates that rival those of inorganic oxides slurries typically used in industry. The density and size of these ceria-microgel particles could be controlled by varying the temperature or composition during synthesis, leading to softer or harder polishing when desired.

In the first part of this work, silica nanoparticles and alternative or additional filler phases were incorporated into hydrogels based on the temperature-sensitive poly(N- isopropylacrylamide) (PNIPAm). Nano-SiO2-filled porous PNIPAm hydrogels with an enhanced force response (up to 100 g) to temperature stimuli were obtained by increasing several times the pore wall thickness, which was achieved via reducing the solvent (porogen) content during the gels' cryo-synthesis. A similar optimization of the force response was also carried out for analogous gels reinforced by nano-TiO2, in which the reinforcing effect of the filler is weaker. Partial intercalation of amylopectin starch into divinyl-crosslinked bulk as well as porous PNIPAm gels several times improved their extensibility. In case of starch-rich bulk gels, a very fast and extensive one-way deswelling in response to increased temperature was achieved (re-swelling upon cooling is much slower), which is attributed to specific properties of the starch-PNIPAm interface. In doubly-filled bulk PNIPAm/nano-SiO2/starch gels, a very strong synergic reinforcing effect of both fillers is observed, due to specific hydrogen bridging between the three phases. Highly porous cryogels based on PNIPAm/nano- SiO2/starch displayed a highly improved extensibility...

Stimuli-responsive (stimuli-sensitive, intelligent, or smart) polymers are polymer materials which, after small external stimuli, evidently change their physical or chemical properties. Smart polymers can be classified according stimuli they respond to such as: temperature changes, mechanical stress, light irradiation, ultrasonic treatment, application of external magnetic as well as electric field, changes of pH, ionic strength, addition of the chemical agents and presence of biomolecules and bioactive molecules. Stimuli-responsive synthetic polymer systems has attracted considerable attention due to wide range of applications, i.e. controlled drug delivery and release systems, diagnostics, tissue engineering and 'smart' optical systems, as well as biosensors, microelectromechanical systems, coatings, and textiles. Among the types of stimuli for this dissertation temperature, pH and reactive oxygen species (ROS) responsive polymer systems were studied. In case of thermoresponsive polymers, when polymer chains are molecularly dissolved in a good solvent, changes (increasing or decreasing) of temperature result in insolubility (globular nanoparticles formation) of polymer chains, called temperature induced phase-separation. pH responsive polymers change properties such as: solubility, volume (gels),...

Poly-N-isopropylacrylamide (PNIPAM) gels grafted to redox-active metal monomers undergo sudden expansion-contraction activity in response to change in environmental conditions, such as temperature, pH, ion concentration, and oxidation states of the metal. The relevance of these conditions to biological systems has garnered attention for PNIPAM-based polymer as potential biomedical materials. Candidate transition metal monomers containing ruthenium and nickel cores were designed and synthesized for copolymerization with NIPAM and cross-linker methylene-bis-acrylamide in order to attain metallopolymer microspheres with a high percentage of metal incorporation. Synthesis of 4-vinyl-4'-methyl-2,2'-bipyridine (vmbpy) was optimized from literature procedures for usage in the metal-containing monomers. Metal-containing monomers were then synthesized, purified, and characterized using electrospray ionization mass spectrometry (ESI-MS), proton nuclear magnetic resonance ( 1 H-NMR), X-ray diffraction, Ultraviolet-Visible light (UV-Vis) spectroscopy, and spectrofluorometry. While the Ru complex was pure and exhibited interesting photochemical properties, lability of the ligands on the Ni monomers resulted in complication of their synthesis. Polymer microspheres of poly(NIPAM-co-vmbpy), the cross-linked copolymer constructed from NIPAM and vmbpy monomers, were synthesized from modified emulsion polymerization procedures. Experimental setup parameters and conditions—such as the methods of injection of initiator and stirring, the time duration for incubating the emulsion, and the initiation temperature—were varied to assess their influences on the material properties of the final product. The polymers were tested for size and morphological uniformity by dynamic light scattering (DLS) and scanning electron microscopy (SEM). While varying the method of initiator injection had no measurable effect on the product, strong mechanical stirring and incubation of the polymer emulsion for 15-25 minutes at 71 °C procured similar polymer products. Consistent properties ensured the polymers' suitability for further material development. Preliminary morphological and spectroscopic characterization was conducted of metallopolymers made from Ru and Ni grafted to PNIPAM. Metallopolymers containing polypyridyl Ru cores exhibited desirable spectroscopic properties and spherical morphology.

No description available.

It is well known that ions affect polymers in specific ways not solely based on electric charge, usually referred to as the Hoffmeister effect or ion specific effects. Poly(N-isopropylacrylamid) (PNIPAM) is a thermosensitive polymer with a LCST at 32℃. PNIPAM is a well studied polymer due to its similarities with denaturation of proteins in aqueous solutions. Utilizing diffusion NMR this report studied the effect different Hoffmeister anion concentrations have on the configuration of pre-transitional PNIPAM. A fractionation process was developed for PNIPAM, yielding a product of about 87 000 g/mol, used for diffusion measurements. Diffusion coefficients for PNIPAM in saline solutions ranging from 0 to 800 mM were measured for NaCl, NaClO4, NaSCN and NaI. Diffusion coefficients for PNIPAM were also measured at some concentrations of NaF, Na2SO4 and Na2CO3. Hydrodynamic radius was calculated from the diffusion coefficients. The report found a pre-transitional chain collapse of PNIPAM which increased with ionic concentrations of NaCl, NaClO4, NaSCN, NaF and Na2CO3, but not for NaI and Na2SO4. At 800 mM the hydrodynamic radius decreased with 9% for NaCl, 13% for NaClO4 and 5% for NaSCN. The hydrodynamic radius decreased with 19% at 300 mM Na2CO3 and with 10% at 400 mM NaF. There was a significant decrease in hydrodynamic radius for high concentrations of NaCl and NaClO4 but exact decrease needs to be replicated to validate the findings due to an unexpected large decrease in hydrodynamic radius already at 50 mM. Values for NaF and Na2CO3 should be replicated with internal standard to accomodate for possible precipitation of the longer polymer chains within the fraction.