A síntese de Fischer-Tropsch é um processo de conversão do gás de síntese (CO + H2) em hidrocarbonetos de cadeias longas. Os catalisadores clássicos para a hidrogenação do CO são, principalmente, o Fe e o Co suportados em diferentes óxidos. O desempenho catalítico do catalisador é influenciado pelo tamanho, dispersão e grau de redução das partículas metálicas. Estudos recentes mostram uma promissora aplicação de materiais à base de nanofibras de carbono na catálise heterogênea. Estes materiais apresentam algumas vantagens em relação aos suportes catalíticos tradicionais, tais como: uma baixa interação metal-suporte, elevada área superficial, ausência de poros fechados, alta condutividade térmica, elevada inércia química e hidrofobicidade. Neste trabalho foram fabricados suportes catalíticos macroscópicos à base de nanofibras de carbono, empregando o método de vapor deposição, a partir da decomposição do etano. Os catalisadores foram preparados pela impregnação incipiente do Co e de promotores na superfície do suporte. Foram empregados os metais nobres, Ir, Pt e Ru, como promotores catalíticos, com o objetivo de incrementar a redutibilidade e a atividade do catalisador. Todos os catalisadores foram caracterizados por Quimissorção de CO, Fisissorção de N2, Redução a Temperatura Programada (TPR), Espectroscopia Fotoeletrônica de Raios X (XPS) e Microscopia Eletrônica de Transmissão (MET). Os catalisadores foram, então, testados na síntese de Fischer-Tropsch, utilizando um reator de leito fixo e fluxo contínuo, com análise simultânea dos produtos gasosos e controle sistemático da temperatura, pressão e vazão dos reagentes. Finalmente, foram analisados os produtos líquidos obtidos na reação com objetivo de conhecer a influência dos promotores na seletividade dos hidrocarbonetos formados. / Fischer-Tropsch synthesis is a process of converting the syngas (CO + H2) to long-chain hydrocarbons. The traditional catalysts for the CO hydrogenation are Fe and Co supported on different oxides. Catalytic performance of the catalyst is influenced by size, dispersion and degree of reduction of metal particles. Recent studies show a promising application of materials based on carbon nanofibers in heterogeneous catalysis. These materials have some advantages compared to traditional catalyst supports, such as a low metal support interaction, high surface area, no closed pores, high thermal conductivity, high chemical resistance, and hydrophobicity. In this work, based on macroscopic carbon nanofiber catalyst supports have been manufactured by employing the method of chemical vapor deposition from ethane decomposition. Catalysts were prepared by incipient wetness impregnation of Co and promoters on the support surface. Noble metals, Ir, Pt and Ru were used as catalytic promoters, with the aim of increasing the reductibility and catalyst activity. All catalysts were characterized by CO Chemisorption, N2 Physisorption, Temperature Programmed Reduction (TPR), X-ray Photoelectron Spectroscopy (XPS), and Transmission Electron Microscopy (TEM). The catalysts were then tested in the Fischer-Tropsch synthesis using a fixed bed reactor, continuous flow, with simultaneous analysis of gaseous products and systematic temperature control, pressure, and flow rate of the reactants. Finally, the liquid products obtained in the reaction were analyzed in order to determine the influence of promoters on the selectivity of hydrocarbons formed.

Este trabalho demonstra o uso da fotopolimerização via absorção de dois fótons na produção de microestruturas dopadas com compostos orgânicos e nanopartículas de Au. A capacidade de produção de microestruturas com propriedades variadas é extremamente relevante, pois viabiliza o desenvolvimento de uma nova geração de dispositivos ópticos. Além disso, realizamos a conexão entre as microestruturas fabricadas e fontes de excitação, por meio de nanofibras de vidro. A integração entre essas estruturas, e destas com meios externos de excitação e detecção, é um passo essencial para o desenvolvimento de microcircuitos fotônicos, que podem representar uma nova revolução tecnológica, a exemplo do que foram os microcircuitos eletrônicos. Exploramos as possibilidades de dopagem da resina usando: (i) um composto fluorescente, (ii) um composto com birrefringência fotoinduzida e (iii) nanopartículas de ouro. Microestruturas contendo Rodamina B apresentaram boa integridade estrutural e fluorescência, tendo sido usadas para demonstrar a conexão dos microelementos com meios externos de excitação. Através de nanofibras e de micromanipuladores, comprovamos a capacidade de excitação seletiva de microestruturas através do guiamento da luz de um laser de Ar+. Estruturas birrefringentes foram obtidas pela dopagem com o azopolímero HEMA-DR13. Montamos um aparato que permite a observação da dinâmica de indução de birrefringência nas microestruturas, o qual representa um grande passo na caracterização deste tipo de microelementos. Com base nesse estudo, foi possível alcançar uma fração de birrefringência residual nas microestruturas de 35%. Por fim, propomos um método para a dopagem de microestruturas poliméricas com nanopartículas de ouro. Por se tratar de um método de dopagem indireta, ele evita interferências das nanopartículas no processo de microfabricação. Dessa forma, este trabalho abre possibilidades para a fabricação de microdispositivos funcionais com diversas propriedades especiais, bem como a integração desses microdispositivos em circuitos fotônicos. / This work demonstrates the use of two-photon photopolymerization in the fabrication of microstructures doped with organic compounds and gold nanoparticles. The ability to produce microstructures with different properties is extremely relevant, because it opens the possibility for the development of a new generation of optical devices. Besides, we have accomplished the connection between fabricated microstructures and excitation sources by means of silica nanowires. The connection among structures and with external means of detection and excitation is an essential step towards the development of new technological breakthrough in photonic microcircuits. We have explored the resin doping possibilities by using: (i) a fluorescent compound, (ii) a photoinduced birefringent compound and (iii) gold nanoparticles. Rhodamine B doped microstructures present good structural integrity and fluorescence, and were able to demonstrate the connection of microelements with external means of excitation. Through the use of nanofiber tapers and micromanipulators, we have shown the selective excitation capability of this method by guiding Ar+ laser light onto one single microstructure. Birefringent samples were obtained by doping the resin with the azopolymer HEMA-DR13. We have assembled an apparatus that allows observing the photoinduced birefringence dynamics, which represents a great step towards a better characterization of these kinds of microelements. Based on this study we were able to achieve a residual birefringence fraction of 35% in microscopic samples. Finally, we have proposed a new method for the doping of polymeric microstructures with gold nanoparticles. Because it is an indirect doping technique, it prevents gold nanoparticles from interfering with the microfabrication process. Thus, the work presented here paves the way for the fabrication of functional microdevices with a wide range of special properties, as well as for the connection of these microstructures for photonic microcircuit.

La fabrication de membranes nanofibreuses par un procédé d’électrospinning plus respectueux de l’environnement, ou plus « vert », est de nos jours un défi. L’électrospinning est un procédé qui permet, généralement à partir d’une solution de polymère, d’obtenir des membranes non-tissées dont le diamètre des fibres est compris entre 50 nm et quelques micromètres. Deux stratégies nouvelles ont été développées pour répondre à ce besoin croissant. La première consiste à fabriquer des membranes à partir de polymères bio- sourcés tandis que la deuxième vise à employer des solvants exclusivement aqueux. Cette deuxième stratégie permet de s’affranchir des vapeurs de solvants souvent toxiques utilisés au cours du procédé. Dans ce cadre, des membranes ont été fabriquées à partir de suspensions aqueuses de polymères non-hydrosolubles, d’une part, et à partir d’acide tannique, une molécule non-polymérique bio-sourcée en exploitant les interactions supramoléculaires. Ces stratégies plus « vertes » rendent moins dangereuse et moins couteuse l’utilisation d’émetteurs multi-jets et permettent, de ce fait, une meilleure industrialisation du procédé d’électrospinning. Les membranes développées ont été fabriquées pour des applications de microfiltration liquide. En effet, les membranes d’électrospinning peuvent allier des tailles de pores submicroniques à des porosités supérieures à 80% contrairement aux membranes de microfiltration commerciales (porosité < 40%). La fabrication de membranes de filtration par un procédé d’électrospinning multi-jet « vert » permet ainsi d’accroitre les débits de production et de filtration tout en respectant davantage l’environnement. / The fabrication of nanofibrous mats by an environmentally friendly, or in other words by a “green”, electrospinning process is nowadays a challenge. Electrospinning is a process allowing the fabrication, generally from a polymer solution, of nonwoven mats composed of fibers having diameters ranging between 50 nm and a few micrometers. Two new strategies have been developed to answer such a growing need. The first one consists in electrospinning bio-sourced polymers while the second one is based on the electrospinning of aqueous solutions exclusively. This second strategy allows avoiding toxic vapors coming from the evaporation of toxic solvents often used during the process. In this context, mats were electrospun from solutions composed of aqueous suspensions of water insoluble polymers, on one hand, and composed of tannic acid, a non-polymeric bio-based molecule exploiting supramolecular interactions. These new environmentally friendly strategies turn the electrospinning process in a less dangerous and less expensive one, and, as a result, ease the use of multi-jet setups and enable a better industrialization of the electrospinning process. Membranes have been developed for liquid microfiltration applications. As a matter of fact, electrospinning membranes can combine submicron pore sizes with porosities greater than 80% unlike commercial microfiltration membranes (porosity < 40%). The fabrication of liquid filtration membranes by a multi-jet "green" electrospinning process, thus, makes it possible to increase the production rates of electrospinning mats and filtration rates while respecting the environment.

O objetivo do presente estudo foi agregar valor a fibras de sisal, a dois dos componentes principais de fibras lignocelulósicas (celulose e lignina) e a PET reciclado, via produção de materiais com elevado valor agregado. Neste contexto, foram investigadas condições que levassem a mats constituídos por nanofibras/fibras ultrafinas, alinhadas (coletor rotativo) e não alinhadas (coletor estático), a partir da eletrofiação de soluções contendo essas matérias-primas, combinadas ou não [PET/sisal, PET/celulose e/ou lignina, PET/CNC (combinado ou não com OM)], em TFA. Parâmetros de solução, como razão PET/componente da biomassa e tempo de dissolução, foram diversificados, assim como parâmetros de processo (taxa de vazão da solução e velocidade de rotação do coletor utilizado, por exemplo). Os resultados de DMA indicaram a influência positiva do alinhamento das fibras nos superiores valores de E\' [tanto para os mats de PET/sisal, quanto para os mats de PET/celulose e/ou lignina e PET/CNC (combinado ou não com OM)] e também foi possível observar que não houve uma influência significativa desse alinhamento na Tg do PET nestes materiais. Como exemplo, o valor de E\' (a 30 &deg;C) para o mat de fibras alinhadas, com razão de sisal/PET = 0,40 (S/PET0,40 &#8211; A dir), caracterizado na direção preferencial de alinhamento das fibras, foi superior (765,0 MPa), em comparação ao valor apresentado pelo mat de fibras orientadas aleatoriamente, de composição correspondente, S/PET0,40 (E&rsquo; = 358,0 &plusmn; 1,5 MPa). A molhabilidade dos mats foi intrinsicamente dependente da razão fibra de sisal/PET e variou de altamente hidrofóbico (PETref, ACA de 134&deg;), a super hidrofílico (S/PET0,40, ACA de 0&deg;). Observou-se que, as principais influências da presença de lignina foram na morfologia achatada das fibras e no aumento do alongamento na ruptura dos materiais, de aproximadamente 90%, comparativamente a PETref. A presença da celulose resultou principalmente em um elevado diâmetro médio das fibras (valores de até 365,9 &plusmn; 139,7 nm) e módulo de Young dos materiais (com valores de até 360,4 &plusmn; 41,5 MPa), comparativamente ao apresentado pelos mats contendo PET e este polímero combinado com lignina. Os resultados mostraram que os CNCs exerceram uma ação efetiva como agentes de reforço, principalmente nos mats constituídos por fibras orientadas aleatoriamente de PET, considerando as propriedades mecânicas apresentadas por esses materiais (como resistência à ruptura de 4,6 &plusmn; 0,5 MPa), em comparação ao mat PETref (resistência à ruptura = 1,8 &plusmn; 0,2 MPa). O OM atuou como agente compatibilizante entre o PET reciclado e os CNCs, principalmente com relação ao superior valor de módulo de Young de PET/OM/CNC (354,2 &plusmn; 46,1 MPa), em comparação ao valor apresentado por PET/CNC (19,9 &plusmn; 3,9 MPa). Assim, os objetivos do presente trabalho foram atingidos com a preparação via eletrofiação, até onde se tem conhecimento, pela primeira vez, de mats de fibras alinhadas e não alinhadas baseadas em biomassa lignocelulósica nativa e dois de seus principais constituintes (celulose e lignina). Os materiais preparados apresentam uma vasta gama de possíveis aplicações, como sistemas de filtração de ar, por exemplo. / The aim of the present investigation was to add value to sisal fibers, to two of the major components of lignocellulosic fibers (cellulose and lignin) and recycled PET via preparation of materials with high added value. In this context, conditions that lead to mats of nanofibers and ultrathin fibers were investigated, aligned (rotating drum collector) and nonaligned (stationary collector), via electrospinning of solutions containing these raw materials, combined or not {PET/sisal fiber, PET/cellulose and/or lignin, PET/CNC [combined or not with castor oil (CO)]} in TFA. Solution parameters such as the ratio of PET/biomass component and dissolution times were diverse, as well as process parameters (e.g. solution flow rate and rotational speed of the collector). The DMA results indicated the positive influence of fiber alignment on the higher storage modulus &#8211; E&rsquo; [for mats of PET/sisal, PET/cellulose and/or lignin and PET/CNC (combined or not with CO)] and it was also possible to observe no significant influence of fiber alignment on the Tg of PET for these mats. The value of E&rsquo; (at 30 &deg;C) for the aligned fibers mat with sisal/PET ratio = 0.40 (S/PET0.40 - A dir), characterized in the preferred direction of fiber alignment, was higher (765.0 MPa) when compared to the value presented by the randomly oriented fibers mat of the corresponding composition, S/PET0.40 (E&rsquo; = 358.0 &plusmn; 1.5 MPa). The wettability of the mats was intrinsically dependent on the sisal/PET fiber ratio and ranged from highly hydrophobic (PETref, ACA of 134°) to super hydrophilic (S/PET0.40, ACA of 0°). It was observed that the main influences of the presence of lignin was on the flat fibers morphology and on the increase of the elongation-at-break of the materials of approximately 90% compared to PETref. The presence of cellulose resulted mainly in a high average fiber diameter (values up to 365.9 &plusmn; 139.7 nm) and elastic modulus of the materials (values up to 360.4 &plusmn; 41.5 MPa) compared to the ones presented by mats containing PET and by this polymer combined with lignin. The results showed that the CNCs were efficient as reinforcing agents, especially in the mats composed of randomly oriented fibers of PET, considering the mechanical properties presented by these materials (such as ultimate tensile strength of 4.6 &plusmn; 0.5 MPa) compared to PETref mat (ultimate tensile strength = 1.8 &plusmn; 0.2 MPa). CO acted as a compatibilizing agent between recycled PET and CNCs, mainly regarding the superior elastic modulus value of PET/OM/CNC (354.2 &plusmn; 46.1 MPa) compared to PET/CNC mat (19.9 &plusmn; 3.9 MPa). Therefore, the goals of the present study were reached for the first time with the preparation of aligned and nonaligned fiber mats based on native lignocellulosic biomass and two of its main constituents (cellulose and lignin), to the best of our knowledge. The prepared materials have a wide range of possible applications, such as air filtration systems, for example.

L'articulation temporo-mandibulaire (ATM) est une articulation formée entre l'os temporal et le condyle mandibulaire, et est fréquemment atteinte. Ces affections sont souvent si douloureuses lors d'activités orales fondamentales que les patients ont une qualité de vie diminuée. Les limites de la thérapeutique pour les atteintes des ATM, ont conduit à accroître l'intérêt pour les stratégies régénératives combinant les cellules souches, les "scaffolds" implantables et les molécules bioactives. Réussir dans la régénération fonctionnelle et structurelle de l'ATM constitue un véritable défi. Des stratégies innovantes et des biomatériaux sont absolument essentiels car l'ATM peut être considérée comme l'un des ensembles tissulaires les plus difficiles à régénérer, au vu de sa capacité de guérison limitée, de ses propriétés histologiques et structurelles uniques et de la nécessité de prévenir à long terme ses adhérences ossifiées ou fibreuses. Une première étude in vitro a été menée pour développer un implant nanostructuré pro-régénératif du cartilage portant des cellules souches mésenchymateuses humaines. Les nanoréservoirs de TGFβ3 au sein d’une matrice de collagène de type II de méduse ont montrés leur capacité chondrogénique. Ils ont permis une colonisation, puis une différenciation et une maturation matricielle favorable à la régénération cartilagineuse. Ces résultats sont encourageants vu la difficulté de mise en culture des chondrocytes et la nécessité d'une restauration rapide de la couche cartilagineuse des surfaces articulaires. Une deuxième étude in vivo a été menée pour développer un implant nanostructuré pro-régénératif anti-inflammatoire osseux. Des matrices biomimétiques nanofibreuses et microporeuses de polycaprolactone (PCL) ont été fonctionnalisées par des nanoréservoirs de BMP-2 et d’ibuprofène. Elles ont été implantées sur des modèles murins de lésions osseuses maxillaires. L’accélération de la régénération induite par ces implants nanofonctionnalisés a été mise en évidence sur des souris sauvages et sur des souris mutantes Tabby. Le bénéfice ainsi établi de fonctionnalisation des implants par la BMP-2 et l'ibuprofène revêt un intérêt particulier face aux fréquentes pathologies inflammatoires chroniques de l'ATM. Ces résultats prometteurs devront faire suite à des approches d'orchestration tridimensionnelle des différents tissus de l'ATM. / The temporomandibular joint (TMJ) is an articulation formed between the temporal bone and the mandibular condyle which is commonly affected. These affections are often so painful during fundamental oral activities that patients have lower quality of life. Limitations of therapeutics for severe TMJ diseases have led to increased interest in regenerative strategies combining stem cells, implantable scaffolds and well-targeting bioactive molecules. To succeed in functional and structural regeneration of TMJ is very challenging. Innovative strategies and biomaterials are absolutely crucial because TMJ can be considered as one of the most difficult tissues to regenerate due to its limited healing capacity, its unique histological and structural properties and the necessity for long-term prevention of its ossified or fibrous adhesions. A first in vitro study was conducted to develop a pro-regenerative nanostructured cartilage implant bearing human mesenchymal stem cells. The nanoreservoirs of TGFβ3 within a jellyfish type II collagen matrix showed their chondrogenic capacity. They allowed colonization, then differentiation and matrix maturation favorable to cartilaginous regeneration. These results are encouraging given the difficulty of culturing chondrocytes and the need for rapid restoration of the cartilaginous layer of articular surfaces. A second in vivo study was conducted to develop a nanostructured pro-regenerative anti-inflammatory bone implant. Nanofibrous and microporous biomimetic matrices of polycaprolactone (PCL) were functionalized by nanoreservoirs of BMP-2 and ibuprofen. They have been implanted in mouse models of maxillary bone lesions. The acceleration of regeneration induced by these nanofunctionalized implants has been demonstrated in wild-type mice and Tabby mutant mice. The benefit thus established of functionalization of implants by BMP-2 and ibuprofen is of particular interest in the frequent chronic inflammatory pathologies of TMJ. These promising results follow three-dimensional orchestration approaches for different TMJ tissues.

In this work we investigated fabrication of semiconductor nanomaterials and evaluated their potential for photo-chemical and photovoltaic applications. We investigated different II-VI semiconductor nanomaterial systems; (i) ZnO oriented nanowire arrays non-epitaxially grown from a substrate; and (ii) colloidal CdE (E=Te,Se,S) quantum structures synthesized by solution-based thermal decomposition of organo-metallic precursors. We have studied the synthesis of vertically aligned ZnO nanowire arrays (NWA), by a wet chemical process on various substrates. We have extended this method wherein nanofibers of poly-L-lactide act as a substrate for the radially oriented growth of ZnO nanowires. By combining the large surface area and the flexibility of the PLLA-ZnO hierarchical nanostructure we have shown the proof-of-principle demonstration of a ‘continuous-flow’ water treatment system to decompose known organic pollutants in water, as well as render common waterborne bacteria non-viable. We have studied synthesis of colloidal quantum dots (QD), and show size, morphology and composition tailored nanocrystals for CdE (E=S, Se, Te) compositions. We have studied the influence of crystal growth habits of the nanocrtsyals on the final morphology. Furthermore we have synthesized core-shell, CdSe-CdS QDs with spherical and tetrahedral morphologies by varying the reaction conditions. We show that these core-shell quantum dots show quasi-type II characteristics, and demonstrate with I-V measurements, the spatial localization of the charge carriers in these hetero-nanocrystals. For this purpose, we developed hybrid materials consisting of the core-shell quantum dots with electron acceptors (ZnO nanowires) and hole acceptors (polymeric P3HT nanofibers). In addition we have also compared the synthesis reaction when carried out with conventional heating and microwave-mediated heating. We find that the reaction is enhanced, and the yield is qualitatively better when using microwave induced heating. / QC 20120525

Replicating the multi-hierarchical self-assembly of collagen (peptide chain to triple helix to nanofiber and, finally, to a hydrogel) has long attracted scientists, both from the fundamental science perspective of supramolecular chemistry and for the potential biomedical applications perceived in tissue engineering. In terms of triple helical formation, collagen is the most abundant protein in the human body with at least 28 types, yet research involving collagen mimetic systems has only recently began to consider the innate ability of collagen to control helix composition and register. Collagen triple helices can be homotrimeric or heterotrimeric and while some types of natural collagen form only one specific composition of helix, others can form multiple. It is critical to fully understand and, if possible, reproduce the control that native collagen has on helix composition and register. In terms of nanofiber formation, many approaches to drive the self-assembly of synthetic systems through the same steps as natural collagen have been partially successful, but none have simultaneously demonstrated all levels of structural assembly. In this work, advancements in the ability to control helix composition and replicate the multi-hierarchical assembly of collagen are described. Both positive and negative design for the assembly of AAB type collagen heterotrimers were utilized by promoting heterotrimer formation though the use of charged amino acids to form intra-helix electrostatic interactions, while simultaneously discouraging homotrimers, resulting in the identification of multiple peptide systems with full control over the composition of the resulting triple helix. Similar salt-bridged hydrogen bonds between charged residues were incorporated into nanofiber forming peptides, one of which successfully assembled into sticky-ended triple helices, nanofibers with characteristic triple helical packing visible in the solution state, and strong hydrogels that are degraded by collagenase at a similar rate to natural collagen. Together, these results provide a better understanding of the self-assembly of collagenous sequences as well as a novel design scheme for synthetic extracellular matrix mimetics with potential applications in regenerative medicine and drug delivery.

The advancement of each component of aerospace vehicles is necessary as the continual demand for more aggressive missions are created. Improvements in propulsion and guidance system electronics are invaluable; however without material development to protect the vehicle from its environment those advances will not have a practical application. Thermal protection systems (TPS) are required in both external applications; for example on reentry vehicles, as well as in internal applications; to protect the casing of rockets and missiles. This dissertation focuses on a specific type of internal solid rocket motor TPS, ablatives. Ablatives have been used for decades on aerospace vehicles. To protect the motor from the hostile environment, these materials pyrolyze and char. Both of these mechanisms produce a boundary between the combustion gases and the motor as well as release the heat that the decomposed material has absorbed. These sacrificial materials are intended to protect the casing that it is attached to. With the development of polymer nanocomposites (PNCs) in the last couple of decades, it is of interest to see how these two fields can merge. Three different nanomaterials (carbon nanofibers, multiwall carbon nanotubes, and nanoclays) are examined to observe how each behaves in environments that simulate the motor firing conditions. These nanomaterials are individually added to a thermoplastic polyurethane elastomer (TPU) at different loadings, creating three distinct families of polymer nanocomposites. To describe a materials ablative performance, a number of material properties must be individually studied; such as thermal, density, porosity, char strength, and rheology. Different experiments are conducted to isolate specific ablative processes in order to identify how each nanomaterial affects the ablative performance. This dissertation first describes each material and the ablative processes which are characterized by each experiment. Then basic material properties of each family of materials are described. Degradation and flammability experiments then describe the degassing processes. Studies of the material char are then performed after full blown rocket experiments are done. These tests have shown that of the three nanomaterials, nanoclay enhances the TPU ablative performance the most while the CNF provides the least enhancement. / text

A biodegradable alternative to synthetic plastics was explored in this study through the extrusion of a soy-based protein/fiber composite film. Two fractions of fibers with different size distributions (nano- to micro-) were isolated from soy pods and stems using a chemi-mechanical method. Fibers through successive treatments were characterized via microscopy, x-ray diffraction, and Fourier Transform infrared analysis (FTIR). The continuous extrusion of homogenous SPI film (0.08 to 0.3 mm thick) was reported for the first time. Processing window was limited by protein sensitivity to moisture and heat. With the incorporation of extracted fibers, homogenous films were obtained with a concentration below 0.5% w/w fiber/SPI. Increasing fiber content resulted in the formation of aggregates. At the optimal concentration of 0.25% w/w fiber/SPI, films exhibited mild improvements in mechanical performance most noticeable at a high RH (84%). Film properties with and without fiber addition were negatively affected by relative humidity. Titanium dioxide addition suggested mild coupling effects for SPI and fiber. / Hannam Soy Foundation / Ontario Ministry of Agricultural, Food, and Rural Affairs (OMAFRA)

Organophosphates and carbamates are potent inhibitors of the neurotransmitter acetylcholinesterase. This inhibition results in the blocking of nerve signal transference into the post synaptic neuron leading to loss of muscle action and death. Because of the universal mechanisms of signal transduction in animals, these inhibitors have been widely used as agricultural pesticides as well as chemical warfare agents (nerve agents). Health issues associated with pesticide usage result from the fact that both the pesticides and their breakdown products often end up in water and food sources as well as in the soil. As a result, there has been an increase in the number of studies aimed at the detection of these pesticides in the environment. One popular research area is enzyme based biosensor construction. Some important criteria for consideration during the construction of biosensors are the importance of a suitable solid support as well as the enzyme immobilisation method. Recently, there has been increased interest in using nano-scale material e.g. using nanoparticles as enzyme support material. This is largely due to their advantages such as large surface area to volume ratio as well as reduced mass transfer resistance. Electrospinning is a straight forward and cost effective method for producing nanofibres from any soluble polymer(s). The applications of electrospun nanofibres have been reported in clinical studies, biofuel production as well as bioremediation. In this study two polymers were selected: nylon for its mechanical stability and chitosan for its biocompatibility and hydrophilicity, for the fabrication of electrospun nanofibres which would function as immobilisation support material for acetylcholinesterase. The first objective of this study was to electrospin nanofibres from a nylon-6 and chitosan blend solution. A binary solvent system consisting of formic acid and acetic acid (50:50) successfully dissolved and blended the polymers which were subsequently electrospun. Scanning electron microscopy characterisation of the nanofibres showed that (i) a nylon-6: chitosan ratio of 16%: 3% resulted in the formation of bead free nanofibres and (ii) the fibres were collected in non-woven mats characterised by different size nanofibres with average diameters of 250 nm for the main fibres and 40 nm for the smaller nanofibres. Fourier transform infra-red (FT-IR) analysis of the nanofibres indicated that a new product had been formed during the blending of the two polymers. The second aim of the study was to carry out a facile immobilisation of electric eel acetylcholinesterase via glutaraldehyde (GA) cross-linking. Glutaraldehyde solution 5% (v/v) resulted in the immobilisation of 0.334 mg/cm² of acetylcholinesterase onto the nanofibres. The immobilisation procedure was optimised with reference to acetylcholinestease and crosslinker concentrations, incubation time and the cross-linking method. A comparative investigation into the optimum pH and temperature conditions, pH and thermal stabilities, substrate and inhibition kinetics was then carried out on free and immobilised acetylcholinesterase. The final objective of this study was to determine the storage stabilities of the immobilised and free enzymes as well as the reusability characteristics of the immobilised acetylcholinesterase. Several conclusions were drawn from this study. Acetylcholinesterase was successfully immobilised onto the surface of nylon-6:chitosan nanofibres with retention of its activity. There was a shift in the pH optimum of the immobilised acetylcholineseterase by 0.5 units towards a neutral pH. Although both free and immobilised acetylcholinesterase exhibited the same optimum temperature, immobilised acetylcholinesterase showed enhanced thermal stability. In terms of pH stability, immobilised acetylcholinesterase showed greater stability at acidic pH whilst free acetylcholinesterase was more stable under alkaline pH conditions. Relative to free acetylcholinesterase, the immobilised enzyme showed considerable storage stability retaining ~50% of its activity when stored for 49 days at 4°C. Immobilised acetylcholinesterase also retained > 20% of its initial activity after 9 consecutive reuse cycles. When exposed to fixed concentrations of carbofuran or demeton-S-methyl sulfone, immobilised acetylcholinesterase showed similar inhibition characteristics to that of the free enzyme. The decrease in enzyme activity observed after immobilisation to the nanofibres may have been due to several reasons which include some enzyme molecules being immobilised in structural conformations which reduced substrate access to the catalytic site, participation of the catalytic residues in immobilisation and enzyme denaturation due to the reaction conditions used for acetylcholinesterase immobilisation. Similar observations have been widely reported in literature and this is one of the major drawbacks of enzyme immobilisation. In conclusion, nylon-6:chitosan electrospun nanofibres were shown to be suitable supports for facile acetylcholinesterase immobilisation and the immobilised enzyme has potential for use in pesticide detection. Future recommendations for this study include a comparative study of the GA cross-linking method for AChE immobilisation which will lead to more intensely bound enzyme molecules to prevent non-specific binding. An investigation into the effect of inhibitors on stored immobilised AChE, as well as reactivation and reuse studies, may also be useful for determining the cost-effectiveness of reusing immobilised AChE for pesticide detection in environmental water samples. Several models have been designed for the determination of the kinetic parameters for immobilised enzymes. These take into account the mass transfer resistance as well as the overall charge of the immobilisation matrix. The use of these models to analyse experimental data will give a clear understanding of the effects of immobilisation on enzyme activity