Layer-by-layer (LbL) assembly has proven to be a powerful technique for assembling thin films with a variety of properties including electrochromic, molecular sensing, oxygen barrier, and antimicrobial. LbL involves the deposition of alternating cationic and anionic ingredients from solution, utilizing the electrostatic charges to develop multilayer films. The present work incorporates cationic antimicrobial agents into the positively-charged layers of LbL assemblies. When these thin films are exposed to a humid environment, the antimicrobial molecules readily diffuse out and prevent bacterial growth. The influence of exposure time, testing temperature, secondary ingredients and number of bilayers on antimicrobial efficacy is evaluated here. Additionally, film growth and microstructure are analyzed to better understand the behavior of these films. The antimicrobial used here is a positively-charged quaternary ammonium molecule (e.g. cetyltrimethylammonium bromide [CTAB]) that allow assemblies to be made with or without an additional polycation like polydiallyldimethylamine. While films without this additional polymer are effective, they do not have the longevity or uniformity of films prepared with its addition. All of the recipes studied show linear growth as a function of the number of bilayers deposited and this growth is relatively thick (i.e. > 100 nm per bilayer). In general, 10-bilayer films prepared with CTAB and poly(acrylic acid) are able to achieve a 2.3 mm zone of inhibition against S. aureus bacteria and 1.3 mm against E. coli when test are conducted at body temperature (i.e. 37oC). Fewer bilayers reduces efficacy, but lower test temperatures improve zones of inhibition. As long as they are stored in a dry atmosphere, antimicrobial efficacy was found to persist even when films were used four weeks after being prepared. The best films remain effective (i.e. antimicrobially active) for 4-6 days of constant exposure to bacteria-swabbed plates. This technology holds promise for use in transparent wound bandages and temporary surface sterilization.

An amperometric glucose biosensor was fabricated using electospun polyaniline fibers. Polyaniline was reacted with camphorsulfonic acid to produce a salt, which was then dissolved in chloroform containing polystyrene. Using this solution, fibers were formed and collected by electrospinning. Glucose oxidase was immobilized onto these fibers using an electrostatic layer-by-layer adsorption technique. In this method, poly(diallyldimethylammonium chloride) was used as the counter ion source. The level of adsorption was examined and evidence of layer-by-layer adsorption was obtained using a quartz crystal microbalance technique. A biosensor was fabricated from these fibers as a working electrode, and used to measure the glucose concentration accurately.

Microgels are solvent swollen, cross-linked polymer macromolecules of micro or nanoscale dimensions. In this work, microgels are used as versatile building blocks in layer-by-layer assemblies to form thin coatings. While conceptually simple materials, these microgel-based films actually possess extremely complex behavior as evidenced by two particular areas. First, microgel films have self-healing properties, allowing them to rapidly recover from damage in the presence of solvent. The healing step requires rearrangement of film components, demonstrating the dynamic and mobile nature of the films. Second, fibroblasts display complex behavior on microgel films arising from the properties of the coating. A chemical crosslinking treatment of the film affects the film network structure in a concentration-dependent manner. These network changes result in altered mechanical properties that are the primary controlling factor in determining cell behavior at the interface. These data suggest that fibroblasts are not solely controlled by the film elasticity, but rather by the viscoelasticity, and there is a viscoelastic range that results in maximal cell spreading.

No description available.

The problems and high medical costs associated with chronic wounds necessitate an economical bioactive wound dressing. A new strategy was investigated to inhibit MMP-9 proteases and to release epidermal growth factor (EGF) to enhance healing. Doxycycline (DOX) and EGF were encapsulated on polyacrylic acid modified polyurethane film (PAA-PU) using Layer-by-Layer (LbL) assembly. The number of bilayers tuned the concentration of DOX and EGF released over time with over 94% bioactivity of EGF retained over 4 days. A simple wound model in which MMP-9 proteases were added to cell culture containing fibroblast cells demonstrated that DOX inhibited the proteases providing a protective environment for the released EGF to stimulate cell migration and proliferation at a faster healing rate. In the presence of DOX, only small amounts of the highly bioactive EGF are sufficient to close the wound. Results show that this is new and promising bioactive dressing for effective wound management.

The problems and high medical costs associated with chronic wounds necessitate an economical bioactive wound dressing. A new strategy was investigated to inhibit MMP-9 proteases and to release epidermal growth factor (EGF) to enhance healing. Doxycycline (DOX) and EGF were encapsulated on polyacrylic acid modified polyurethane film (PAA-PU) using Layer-by-Layer (LbL) assembly. The number of bilayers tuned the concentration of DOX and EGF released over time with over 94% bioactivity of EGF retained over 4 days. A simple wound model in which MMP-9 proteases were added to cell culture containing fibroblast cells demonstrated that DOX inhibited the proteases providing a protective environment for the released EGF to stimulate cell migration and proliferation at a faster healing rate. In the presence of DOX, only small amounts of the highly bioactive EGF are sufficient to close the wound. Results show that this is new and promising bioactive dressing for effective wound management.

In the research described in this thesis, two molecular layers were successfully anchored on carbon surfaces (pyrolyzed photoresist films, PPFs) sequentially through two independent approaches. The first molecular layer, styrene, was covalently bonded on PPF surfaces via the method of reduction of in situ generated diazonium ions. The resulting molecular films were characterized by AFM measurements, and catechol and ferrocyanide voltammetry. The second molecular layer, ferrocene-thiol, was anchored on top of the first molecular layer through the method of thiol-ene reaction, which is an effective method for building up multilayers through layer-by-layer assembly. As ferrocene is an electrochemically active species, quantitative surface coverage was calculated according to the amount of surface-bound ferrocene through electrochemical measurements. Finally, molecular junctions were fabricated by depositing metal top contacts based on the molecular layers through electron-beam evaporation and the electronic characteristics of these molecular junctions were investigated.

Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, Sept. 2004. / Thesis advisor(s): Timothy P. Stanton. Includes bibliographical references (p. 95-99). Also available online.

Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 134-137). Also available on the World Wide Web.

Orientador: Marystela Ferreira / Resumo: Neste trabalho foram desenvolvidos diferentes tipos de filmes Layer-by-Layer (LbL) sensíveis a variação de pH, temperatura, exposição a luz e presença de carboidratos, com o objetivo de criar sistemas com resposta a estímulos que podem ser aplicados na área médica e ambiental para a entrega modificada de fármacos e pesticidas. O trabalho foi dividido em três partes, sendo o primeiro focado na liberação da emodina. Foram fabricados filmes com a emodina imobilizada diretamente e outra em que o fármaco foi encapsulado nos lipossomos formados por dipalmitoil fosfatidil glicerol (DPPG) e palmitoil fosfatidil glicerol (POPG) e então intercalado com polieletrólitos. Ambos os filmes foram expostos a condições fisiológicas e liberaram a emodina por um período prolongado em função da mudança de pH e temperatura. A segunda parte do trabalho é focado na construção de filmes com um polímero baseado em espiropirano (poli(SP-R)), um composto que quando recebe luz UV é convertido para a forma aniônica merocianina (poli(MC-R)) mudando sua cor e carga superficial. O filme foi composto pelo policátion poli(alilamina hidroclorada) (PAH) formando o (PAH/poli(SP-R))n que se desprendeu do substrato pelo processo disassembly após longo tempo de exposição à luz branca. Na terceita parte do trabalho foram desenvolvidos filmes com o polímero baseado em ácido fenil borônico (PBA), que tem a capacidade de se ligar covalentemente à açucares. Foram fabricados intercalado com PVS resultando no filme (PEI/PV... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this work, we developed some types of Layer-by-Layer (LbL) films sensible to pH and temperature changes, light exposition and carbohydrates solutions, with the aim of to create stimuli responsive system that can be applied to medical and environmental area to drug and pesticide modulated delivery. The work was divided in three parts, the first one is based on delivery emodin. One film was fabricated with emodin immobilized directly and other the drug was encapsulated on liposomes formed by dipalmitoyl phosphatidyl glycerol (DPPG) e palmitoyl phosphatidyl glycerol (POPG) and the carrier was intercalated with polyelectrolytes. Both systems were exposed to physiologic conditions and released the emodin for prolonged time in function of pH and temperature changes. On second part of this work it was focused on construction of film with spyropiran (SP) based polymer (poli(SP-R)). The UV irradiation over (poli(SP-R)) causes the conversion to anionic and purple merocyanine molecule (poli(MC-R)) changing the color and surface charge. The film were composed by poly(allylamine hydrochloride) (PAH) and poly(SP-R) forming the (PAH/poli(SP-R))n LbL film which disassemble after long time exposed to white light. On third part of work, films were developed with phenyl borônico acid (PBA) based polymer that has the capacity to bind covalently on sugars. The films were intercalated with PVS creating the coating (PEI/PVS)2(PBAp/PVS)n. It were prepared also a film with the pyranine (PYR), the ... (Complete abstract click electronic access below) / Doutor