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The development of the layer-by-layer (LbL) technique has turned out to be an efficient way to physically modify the surface properties of different materials, for example to improve the adhesive interactions between fibers in paper. The main objective of the work described in this thesis was to obtain fundamental data concerning the adhesive properties of wood biopolymers and LbL films, including the mechanical properties of the thin films, in order to shed light on the molecular mechanisms responsible for the adhesion between these materials. LbLs constructed from poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA), starch containing LbL films, and LbL films containing nanofibrillated cellulose (NFC) were studied with respect to their adhesive and mechanical properties. The LbL formation was studied using a combination of stagnation point adsorption reflectometry (SPAR) and quartz crystal microbalance with dissipation (QCM-D) and the adhesive properties of the different LbL films were studied in water using atomic force microscopy (AFM) colloidal probe measurements and under ambient conditions using the Johnson-Kendall-Roberts (JKR) approach. Finally the mechanical properties were investigated by mechanical buckling and the recently developed SIEBIMM technique (strain-induced elastic buckling instability for mechanical measurements). From colloidal probe AFM measurements of the wet adhesive properties of surfaces treated with PAH/PAA it was concluded that the development of strong adhesive joints is very dependent on the mobility of the polyelectrolytes and interdiffusion across the interface between the LbL treated surfaces to allow for polymer entanglements. Starch is a renewable, cost-efficient biopolymer that is already widely used in papermaking which makes it an interesting candidate for the formation of LbL films in practical systems. It was shown, using SPAR and QCM-D, that LbL films can be successfully constructed from cationic and anionic starches on silicon dioxide and on polydimethylsiloxane (PDMS) substrates. Colloidal probe AFM measurements showed that starch LbL treatment have potential for increasing the adhesive interaction between solid substrates to levels beyond those that can be reached by a single layer of cationic starch. Furthermore, it was shown by SIEBIMM measurements that the elastic properties of starch-containing LbL films can be tailored using different nanoparticles in combination with starch. LbL films containing cellulose I nanofibrils were constructed using anionic NFC in combination with cationic NFC and poly(ethylene imine) (PEI) respectively. These NFC films were used as cellulose model surfaces and colloidal probe AFM was used to measure the adhesive interactions in water. Furthermore, PDMS caps were successfully coated by LbL films containing NFC which enabled the first known JKR adhesion measurements between cellulose/cellulose, cellulose/lignin and cellulose/glucomannan. The measured adhesion and adhesion hysteresis were similar for all three systems indicating that there are no profound differences in the interaction between different wood biopolymers. Finally, the elastic properties of PEI/NFC LbL films were investigated using SIEBIMM and it was shown that the stiffness of the films was highly dependent on the relative humidity. / <p>QC 20110923</p>

Surface-assisted directed assembly allows ultrasoft and replusive functional polymeric “colloids” to assemble into the organized supramolecular ultrathin films on a monomolecular level. This study aims at achieving a fundamental understanding of molecular morphology and responsive behavior of major classes of branched star-shaped polymers (star amphiphilic block copolymers and star polyelectrolytes) and their aggregation into precisely engineered functional ultrathin nanofilms. Thus, we focus on elucidating the role of molecular architecture, chemical composition, and intra/intermolecular interactions on the assembly behavior of highly-branched entities under variable environmental and confined interfacial conditions. The inherent molecular complexity of branched architectures facilitates rich molecular conformations and phase states from the combination of responsive dynamics of flexible polymer chains (amphiphilic, ionizable arms, multiple segments, and free chain ends) and extened molecular design parameters (number of arms, arm length, and segment composition/sequence). These marcromolecular building components can be affected by external conditions (pH, salinity, solvent polarity, concentration, surface pressure, and substrate nature) and transformed into a variety of complex nanostructures, such as two-dimensional circular micelles, core/shell unimicelles, nanogel particles, pancake & brush micelles, Janus-like nanoparticles, and highly nanoporous fractal networks. The fine balance between repulsive mulitarm interactions and surface energetic effects in the various confined surfaces and interfaces enables the ability to fabricate and tailor well-organized ultrathin nanofilms. The most critical findings in this study include: (1) densely packed circular unimicelle monolayers from amphiphilic and amphoteric multiblock stars controlled by arm number, end blocks, and pH/pressure induced aggregation, (2) monolayer polymer-metal nanocomposites by in-situ nanoparticle growth at confined interfaces, (3) on-demand control of exponentially or linearly grown heterogeneous stratified multilayers from self-diffusive pH-sensitive star polyelectrolyte nanogels, (4) core/shell umimicelle based microcapsules with a fractal nanoporous multidomain shell morphology, and (5) preferential binding and ordering of Janus-like unimicelles on chemically heterogeneous graphene oxide surfaces for biphasic hybrid assembly. The advanced branched molecular design coupled with stimuli responsive conformational and compositional behavior presents an opportunity to control the lateral diffusion and phase segregation of branched compact supermolecules on the surface resulting in the generation of well-controllable monolayers with tunable ordering and complex morphology, as well as to tailor their stratified layered nanostructures with switchable morphological heterogeneity and multicompartmental architectures. These surface-driven star polymer supramolecular assemblies and interfaces will enable the design of multifunctional nanofilms as hierarchical responsive polymer materials.

Novel, tailored titanium dioxide pigments with controllable nanoscale morphological features were shown to significantly enhance the optical and strength properties of paper. The opacifying power of synthesized polycrystalline TiO2 particles in a cellulose matrix was found experimentally to be superior to that of a commercial rutile pigment, depending on the crystal structure of the synthesized particles. High aspect ratio polycrystalline rutile pigments composed of a linear linkage of several individual rutile crystals gave 6% more opacity than the commercial rutile pigment. Theoretical light scattering calculations using the T-Matrix Method showed the light scattering efficiency of linearly arranged polycrystalline rutile particles to depend on number and size of crystals composing the particle and confirmed the higher efficiency of the synthesized polycrystalline rutile pigments over commercial rutile. The opacifying power of hollow polycrystalline rutile particles was found experimentally to be superior to that of a commercial rutile pigment in a highly pressed bleached fiber matrix, depending on cavity size, while the opacifying power of silica-rutile titania core-shell particles was found comparable to commercial rutile at constant titania loading. The light scattering efficiency of titania core-shell particles was shown to be dependant on the light scattering efficiency of the core material. The overall particle shape and aspect ratio of titania core-shell and hollow nanoparticles were shown to be tunable by choosing an appropriate template and coating thickness in layer-by-layer or sol-gel templating synthesis. Inorganic-cellulose core-shell and hollow cellulose nanoparticles were prepared by self-encapsulation with regenerated cellulose via precipitation of cellulose in a polyacrylic acid hydrogel layer surrounding inorganic particle templates in 4-Methylmorpholine N-oxide (NMMO) monohydrate solution. This discrete encapsulation of inorganic pigments with a thin, uniform cellulose shell was found to increase the bondability improvement between the particles and a polysaccharide substrate. The crystallinity of several carbohydrate polymers was shown to significantly affect the bondability of encapsulated core-shell particles.

Two designs of inorganic/organic hybrid micro-structures are discussed: (1) silver nanowire reinforced layer-by-layer (LbL) polyelectrolyte composite film and (2) bimetallic silver-gold core-shell nanoparticles. In this work, zero-dimensional spherical gold nanoparticles (AuNPs), one-dimensional silver nanowires (AgNWs), and two-dimensional silver nanoplates (AgNPls) represent the inorganic component. Three-arm star polymer and polyelectrolytes represent the organic component. In the first design, the one-dimensional AgNWs serves as a mechanical reinforcement for the fabrication of mechanically isotropic and anisotropic polyelectrolyte composite films. The composite film is mechanically isotropic when the AgNWs are randomly oriented, and it is anisotropic when the AgNWs are unidirectionally oriented within the LbL polyelectrolyte matrix. Furthermore, above the AgNWs percolation threshold, the AgNWs reinforced LbL composite film is electrically conductive. Therefore, it can find application in ultrathin LbL film-based sensor. In the second design, the zero-dmensional AuNPs were assembled onto one-dimensional AgNWs and two-dimensional AgNPls by means of star polymer linker, or alternatively using polyelectrolytes via electrostatics interaction. The unique feature of these bimetallic silver-gold core-shell nanoparticles is their ability to greatly enhance electric field, due to the silver-gold intra-particle interaction. This allows it to serve as a single-nanoparticle surface enhanced Raman scattering (SERS) substrate for chemical sensing.

Submitted by Milena Rubi (milenarubi@ufscar.br) on 2017-08-16T16:46:54Z No. of bitstreams: 1 ANUNCIACAO_Eduardo_2017.pdf: 22889091 bytes, checksum: eaec97b1dbf9de44c126b87bb16c49c5 (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2017-08-16T16:47:02Z (GMT) No. of bitstreams: 1 ANUNCIACAO_Eduardo_2017.pdf: 22889091 bytes, checksum: eaec97b1dbf9de44c126b87bb16c49c5 (MD5) / Approved for entry into archive by Milena Rubi (milenarubi@ufscar.br) on 2017-08-16T16:47:10Z (GMT) No. of bitstreams: 1 ANUNCIACAO_Eduardo_2017.pdf: 22889091 bytes, checksum: eaec97b1dbf9de44c126b87bb16c49c5 (MD5) / Made available in DSpace on 2017-08-16T16:47:17Z (GMT). No. of bitstreams: 1 ANUNCIACAO_Eduardo_2017.pdf: 22889091 bytes, checksum: eaec97b1dbf9de44c126b87bb16c49c5 (MD5) Previous issue date: 2017-03-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Uric acid is an endogenous substance produced from the metabolism of purines. The concentration of serum uric acid in the human body considered normal is between 0.24 - 0.52 mmol.L-1 . High levels of uric acid in the body lead to a condition known as hyperuricemia. Therefore, the monitoring of uric acid in the body is of great importance. In this work we present amperometric biosensors based on the association of the enzyme UOx with platinum nanoparticles to detect uric acid. The technique used to assemble the films that compose the biosensor was the Layer-by-Layer (LbL). Two techniques were used for the synthesis of nanoparticles for the construction of two different film architectures. In the first architecture, the nanoparticles were deposited in situ on a polyethyleneimine (PEI) and sodium polyvinyl sulfate (PVS) film - by reducing hexachloroplatinic acid hexahydrate with sodium borohydride. The bilayers composed of (PEI/UOx)n were deposited on a film containing platinum nanoparticles deposited in situ. In the second architecture, the nanoparticles were synthesized by mixing PEI solution with hexachloroplatinic acid solution and sodium borohydride solution. This solution was deposited alternating with enzymatic solution. The amperometric analyses were performed at +0.347 V potential, with successive additions of 2 mmol.L-1 of uric acid in an electrochemical cell containing phosphate buffered saline (PBS) pH 7.4. For the first architecture, the limit of detection found by the amperometric method was 5.17 µmol.L-1 with the linear detection range comprised in the range between 3.92 - 11.3 µmol.L-1 . For the second architecture, the limit of detection found by the amperometric method was 4.68 µmol.L-1 with a linear detection range between 14.18 - 55.56 µmol.L-1 . For the same architecture an using the differential pulse voltammetry method the values of limit of detection and linear detection range were 0.11 µmol.L-1 and particles / mL, respectively. The biosensors presented limits of detection close to the values found in the literature for other biosensor proving to be efficient for the detection of uric acid. / O ácido úrico é uma substância endógena produzida a partir do metabolismo das purinas. A concentração de ácido úrico sérico no organismo humano considerado normal é entre 0,24 - 0,52 mmol.L-1 . Altos níveis de ácido úrico no organismo levam a um quadro conhecido como hiperuricemia. Portanto, o monitoramento de ácido úrico no organismo é de grande importância. Neste trabalho apresentamos biossensores amperométricos baseados na associação da enzima UOx com nanopartículas de platina para detecção de ácido úrico. A técnica utilizada para a fabricação dos filmes que compõem o biossensor foi a Layer-by-Layer (LbL). Duas técnicas foram utilizadas para a síntese de nanopartículas para a construção de duas arquiteturas diferentes na construção dos filmes. Na primeira arquitetura, as nanopartículas foram depositadas in situ sobre um colchão de polieletrólitos – polietilenoimina (PEI) e polivinil sulfato de sódio (PVS) – pela redução do ácido hexacloroplatínico hexaidratado com boroidreto de sódio. As bicamadas compostas por (PEI/UOx)n foram depositadas sobre colchão contendo nanopartículas de platina depositadas in situ. Na segunda arquitetura, as nanopartículas foram sintetizadas misturando-se solução de PEI com solução de ácido hexacloroplatínico e solução de borohidreto de sódio. Esta solução foi depositada alternando-se com solução enzimática. As análises amperométricas foram realizadas em potencial +0,347 V, com adições sucessivas de ácido úrico de concentração 2 mmol.L-1 em uma célula eletroquímica contendo tampão fosfato salino (PBS) pH 7,4. Para a primeira arquitetura, o limite de detecção encontrado pelo método amperométrico foi de 5,17 µmol.L-1 com a faixa linear de detecção compreendido no intervalo entre 3,92 - 11,3 µmol.L-1 . Para a segunda arquitetura, o limite de detecção encontrado pelo método amperométrico foi de 4,68 µmol.L-1 com a faixa linear de detecção compreendido no intervalo entre 14,18 – 55,56 µmol.L-1 , e para o método DPV os valores de LD e faixa linear de detecção encontrados foram 0,11 µmol.L-1 e 1,8×10& ± 0,2×10& partículas/mL, respectivamente. Os biossensores apresentaram limites de detecção próximos aos valores encontrados na literatura, mostrando-se eficientes para detecção de ácido úrico.

Les nanocristaux de cellulose (NCC) sont des nanoparticules biosourcées en forme de bâtonnets produites par l’hydrolyse à l’acide sulfurique de fibres de cellulose. Les nombreux avantages des NCC (excellentes propriétés mécaniques, faible densité, grande surface spécifique, non toxicité, source abondante et renouvelable) en font des briques élémentaires particulièrement attractives pour l’élaboration de nanocomposites biosourcés et expliquent l’intérêt croissant des mondes industriels et académiques pour ces nanoparticules. Au cours des dix dernières années, les NCC ont été associés à différents types de polymère pour former, grâce à la méthode d’assemblage couche par couche, des films minces aux architectures modulables. Dans ce travail, nous avons exploré trois axes de recherche innovants dans le domaine des films multicouches à base de NCC. Dans un premier temps, les chaînes de polymère ont été remplacées par des nanoparticules inorganiques de forme hexagonale chargée positivement, les nanoplaquettes de gibbsite (GN), pour former des films minces hybrides entièrement constitués de nanoparticules. Nous avons montré que l’architecture des films (NCC/GN) pouvait être modulée sur une large gamme en ajustant les paramètres physico-chimiques comme le facteur de forme, la force ionique de la suspension de NCC ou le protocole de séchage. La caractérisation fine de la structure interne des films a été déterminée par l’utilisation de deux techniques de surface complémentaires, la microscopie à force atomique (AFM) et la réflectivité des neutrons (RN). Nous avons pu prouver que l’architecture interne des films était le résultat de différentes forces d’interaction dont la portée dépend des paramètres physico-chimiques utilisés. Dans un second temps, la résistance à l’humidité de films entièrement biosourcés a été étudiée en comparant des films dans lesquels les NCC étaient associés soit à des chaines de xyloglucane (XG) natives soit à des chaines de XG oxydées. Les résultats d’AFM et de RN révèlent que les cinétiques d’absorption d’eau et l’hydratation des films dépendent fortement de la possibilité de créer des liaisons hémiacétales intra- et intercouches générant ainsi un réseau covalent. Le troisième axe de recherche concerne la production de surfaces macroscopiques au sein desquelles les NCC seraient orientés dans des directions privilégiées pour élaborer des nanocomposites anisotropes. Un alignement prononcé a été obtenu par l’utilisation d’un flux laminaire de cisaillement.L’ajustement des paramètres structuraux confère aux films multicouches des propriétés physiques macroscopiques spécifiques. Les propriétés mécaniques des films ont donc été déterminées en utilisant la technique SIEBIMM (strain induced elastic buckling instability for mechanical measurements) et ont été reliées aux paramètres structuraux. Ces nanocomposites aux architectures et propriétés modulables pourraient permettre la conception de films minces ou de revêtements intéressants pour des domaines tels que les membranes de séparation ou les supports flexibles pour l’électronique. / CNCs are biobased nanorods that are attracting increasing attention from both the academic and industrial communities due to their numerous properties such as renewability, high specific surface area, excellent mechanical properties, light weight, or non-toxicity. CNCs are thus considered as highly promising blocks for the production of high performance biobased composites. In the last ten years, negatively charged CNCs have been associated with natural or synthetic polycations or neutral biopolymers within multilayered films built by the layer-by-layer assembly technique. In the present study, we have investigated three new research axes in the CNC-based multilayers field. In a first part, polymer chains have been replaced by positively charged inorganic Gibbsite nanoplatelets (GN) to form innovative hybrid nanoparticules-based thin films. We have shown that the architecture of (CNC/GN) films can be tuned over a wide range by adjusting the physico-chemical parameters such as the aspect ratio of the CNC, the ionic strength, or the drying protocol. The detailed internal structure of the multilayered films has been elucidated by the complementary use of AFM and neutron reflectivity (NR) and was attributed to a combination of different interaction forces. In a second part, the resistance to humidity of purely biobased films was investigated by comparing films where CNCs are associated either with neutral xyloglucan chains or with oxidized ones. AFM and NR reveal that the kinetics of water intake and hydration strongly depends on the possibility to form inter- and intra-layer hemiacetal bonds forming a covalent network. The third axis concerns the production of uniformly oriented macroscopic surfaces of CNCs to build anisotropic multilayered nanocomposites. Enhanced alignment was achieved by the use of laminar shear flow.The fine tuning of the structural features of all the multilayered systems studied gives rise to specific macroscopic physical properties. The mechanical properties of films of various architectures (Young’s modulus) have thus been measured using the strain induced elastic buckling instability for mechanical measurements (SIEBIMM) technique and tentatively related to the film’s structure. The tunable properties of such multilayered systems pave the way to the design of thin films and coatings for separation membranes or supports for flexible electronics.

L’Ingénierie tissulaire (IT) est un domaine interdisciplinaire qui applique les principes de l'ingénierie et des sciences de la vie au développement de substituts biologiques afin de restaurer, maintenir ou améliorer la fonction tissulaire. Sa première application consiste à remplacer les tissus endommagés par des produits cellulaires artificiels. Une autre application de l’IT est basée sur la production des modèles en 2 et 3 dimensions (2D et 3D) pour des études biologiques et pharmacologiques in vitro. Ces modèles ou remplacements de tissus peuvent être fabriqués en utilisant des différentes méthodes de médecine, biologie, chimie, physique, informatique et mécanique, fournissant un micro-environnement spécifique avec différents types de cellules, facteurs de croissance et matrice. L'un des principaux défis de l'IT la pénétration cellulaire limitée dans les parties internes des biomatériaux poreux. Une faible viabilité cellulaire au centre du produit d'IT est la conséquence de la diffusion limitée d'oxygène et de nutriments du fait d’un réseau vasculaire insuffisant dans l'ensemble de la construction 3D. Le BioAssembage couche-par-couche est une nouvelle approche basée sur l'assemblage de petites constructions cellularisées permettant une distribution cellulaire homogène et une vascularisation plus efficace dans des produits d’IT.Notre hypothèse est que l'approche couche-par-couche est plus adaptée à la régénération osseuse que l'approche conventionnelle de l'IT. L'objectif principal de cette thèse était d'évaluer les avantages de l'approche couche-par-couche en utilisant des membranes de polymères imprimées en 3D et ensemencées avec des cellules primaires humaines. Nous avons évalué l'efficacité de la formation du réseau vasculaire in vivo dans toute la construction 3D en utilisant cette approche et en la comparant à l'approche conventionnelle basée sur l'ensemencement des cellules sur la surface des scaffolds massives. Il n'y avait pas de différence significative dans le nombre de vaisseaux sanguins formés en 3D au niveau des parties externes des constructions implantées en site souscutanée chez des souris. Mais dans les parties internes des implants qui n'étaient pas en contact direct avec un tissu hôte, nous avons pu observer une formation des vaisseaux sanguins statistiquement plus efficace lorsque l'approche du bio-assemblage couche-par-couche a été utilisée. Cette formation de réseau vasculaire était plus importante dans le cas de co-cultures que de mono-cultures.Il y avait plusieurs objectifs secondaires dans ce travail. Le premier était de fabriquer des constructions 3D cellularisées pour l'IT en utilisant des membranes d'acide polylactique (PLA) et des cellules primaires humaines : des cellules de stroma de moelle osseuse humaine (HBMSCs) isolées de la moelle osseuse et des cellules progénitrices endothéliales (EPCs) isolées du sang du cordon ombilical. Ensuite, nous avons comparé différentes technologies de fabrication des scaffolds: impression 3D directe à partir de poudre de PLA et impression par fil fondu en utilisant une imprimante commerciale et une autre fabriquée sur mesure. L'imprimante sur mesure a permis le plus haut niveau de résolution d'impression spécialement adaptée à la forme et la taille des pores. Par ailleurs, nous avons évalué différents systèmes de stabilisation pour l'assemblage couche par couche : l’utilisation de clips en PLA imprimés en 3D a fourni une stabilisation plus efficace pour empiler les membranes PLA couche par couche. Un autre avantage de ce système de stabilisation est qu'il peut être implanté avec des implants. Ensuite, nous avons observé une prolifération et une différenciation cellulaire plus efficaces lorsque le système de co-culture était utilisé, en comparaison avec des mono-cultures.L'approche du bioassemblage couche-par-couche semble être une solution appropriée pour une vascularisation efficace dans des structures 3D entières d'ingénierie tissulaire. / Tissue Engineering (TE) is “an interdisciplinary field that applies principles of engineering and the life sciences toward development of biological substitutes that restore, maintain, or improve tissue function”. The First application of TE is to replace damaged tissues by artificial cell-materials products of tissue engineering (TE). Another TE application is to produce 2 or 3 dimensional (2D and 3D) models for biological and pharmacological in vitro studies. These models or tissue replacements can be fabricated using a combination of different interdisciplinary methods of medicine, biology, chemistry, physics, informatics and mechanics, providing specific micro-environment with different cell types, growth factors and matrix.One of the major challenges of tissue engineering is related to limited cell penetration in the inner parts of porous biomaterials. Poor cell viability in the center of engineered tissue is a consequence of limited oxygen and nutrients diffusion due to insufficient vascular network within the entire construct. Layer-by-layer (LBL) BioAssembly is a new approach based on assembly of small cellularized constructs that may lead to homogenous cell distribution and more efficient three dimensional vascularization of large tissue engineering constructs.Our hypothesis is that LBL Bioassembly approach is more suitable for bone regeneration than conventional tissue engineering approach. The primary objective of this thesis was to evaluate the advantages of LBL Bioassembly approach using 3D-printed polymer membranes seeded with human primary cells. We have evaluated the efficiency of vascular network formation in vivo within entire 3D tissue engineering construct using LBL bioassembly approach and comparing it to the conventional approach based on seeding of cells on the surface of massive 3D scaffolds. There was no significant difference in number of formed blood vessels in 3D at the outer parts of constructs implanted subcutaneously in mice 8 weeks post-implantation. But in the inner parts of implants which were not in direct contact with a host tissue, we could observe statistically more blood vessel formation when LBL bioassembly approach was used. This vascular network formation was more important in the case of co-cultures than mono-vultures of HBMSCs.There were several secondary objectives in this work. The first was to fabricate cellularized 3D constructs for bone tissue engineering using poly(lactic) acid (PLA) membranes and human primary cells: human bone marrow stroma cells (HBMSCs) isolated from the bone marrow, and endothelial progenitor cells (EPCs) isolated from the umbilical cord blood. Then, we have compared different Additive manufacturing technologies to fabricate scaffolds: direct 3D printing (3DP) starting from PLA powder dissolved in chloroform and fused deposition modelling (FDM) using a commercial or a custom-made printer with different resolutions.The custom-made printer equipped with 100 μm nozzle allowed the highest level of printing resolution concerning pores shape and size. In the meantime we evaluated different stabilization systems for layer-by-layer assembling of PLA membranes with human primary cells: the use of 3D printed PLA clips provided the most efficient stabilization to stack PLA membranes in 3D. Another advantage of this stabilization system is that it could be implanted together with LBL constructs. Then we investigated the most suitable cell culture system for such constructs and we observed more efficient cell proliferation and differentiation when co-culture system is used, comparing to mono-cultures.LBL bioassembly approach seems to be suitable solution for efficient vascularization within entire large 3D tissue engineering constructs especially when co-cultures of mesenchymal and endothelial cells are used.

Submitted by Maria de Lourdes Mariano (lmariano@ufscar.br) on 2017-01-06T15:30:57Z No. of bitstreams: 1 ALMEIDA_Tiago_2013.pdf: 11250021 bytes, checksum: 5affb78879d355e9d8f0a65f51ec2b78 (MD5) / Approved for entry into archive by Maria de Lourdes Mariano (lmariano@ufscar.br) on 2017-01-06T15:31:06Z (GMT) No. of bitstreams: 1 ALMEIDA_Tiago_2013.pdf: 11250021 bytes, checksum: 5affb78879d355e9d8f0a65f51ec2b78 (MD5) / Approved for entry into archive by Maria de Lourdes Mariano (lmariano@ufscar.br) on 2017-01-06T15:31:13Z (GMT) No. of bitstreams: 1 ALMEIDA_Tiago_2013.pdf: 11250021 bytes, checksum: 5affb78879d355e9d8f0a65f51ec2b78 (MD5) / Made available in DSpace on 2017-01-06T15:31:20Z (GMT). No. of bitstreams: 1 ALMEIDA_Tiago_2013.pdf: 11250021 bytes, checksum: 5affb78879d355e9d8f0a65f51ec2b78 (MD5) Previous issue date: 2013-03-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / The present work aimed the fabrication of layer-by-layer nanostructured films of poly (allylaminehydrochloride) (PAH) and poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) onto Nafion® 212 membranes. Nafion® is the most used polyelectrolyte in proton exchange membranes (PEM) fuel cells due to its high proton conduction and good chemical stability at ambient temperature. Therefore, this polyelectrolyte presents some disadvantages due to the high methanol permeability when applied in Direct Methanol Fuel Cells (DMFC), reducing drastically the performance of the device. We studied how ultrathin films of PAH/PEDOT:PSS influence the methanol permeability and proton conduction in the LbL modified membranes. Results indicated good adherence of the LbL films onto Nafion® 212 and also good action as a methanol barrier. Nonetheless, together with the methanol blocking there was also a reduction in the proton conductivity, which occurs due to the LbL dipping deposition on both sides of Nafion® 212, trapping water inside the Nafion membrane, and certainly affecting the proton conduction. Moreover, the LbL film deposition might use some important chemical groups present at the Nafion® surface, used to water permeation, also affecting the proton permeation throughout the membrane. / O presente trabalho visou a fabricação de filmes automontados nanoestruturados (LbL, do inglês layer-by-layer) de poli(alilaminahidroclorada) (PAH) e poli(3,4-etilenodioxitiofeno)poli(estirenossulfado)(PEDOT:PSS) sobre membranas de Nafion® 212. O Nafion® é o polieletrólito mais usado em células combustíveis do tipo PEM (do inglês Proton Exchange Membrane) devido a sua alta capacidade de condução protônica e boa estabilidade química em temperatura ambiente. Entretanto, este polieletrólito apresenta a desvantagem da alta permeação de metanol quando aplicado em células combustíveis a base de metanol direto (DMFC, do inglês Direct Methanol Fuel Cell), que reduz drasticamente o desempenho do dispositivo. Estudamos como filmes ultrafinos de PAH/PEDOT:PSS influenciam a permeabilidade do metanol e a condução protônica de membranas de Nafion® modificadas com filme LbL. Os resultados indicaram boa aderência dos filmes nanoestruturados sobre o Nafion® 212, e ainda boa atuação como barreira à passagem de metanol. No entanto, junto com o bloqueio à passagem de metanol houve redução na condução protônica, que ocorre pelo fato da técnica LbL por imersão depositar material em ambos os lados no Nafion® 212, aprisionando a água no interior da membrana, que certamente afeta a condução protônica. Adicionalmente, a deposição do filme LbL pode estar usando alguns agrupamentos químicos importantes na superfície do Nafion®, utilizados para permeação de água, também afetando a condução protônica através da membrana.

A imobilização de moléculas de interesse biológico em superfícies sólidas é essencial para uma série de aplicações biotecnológicas. Dentre as técnicas de imobilização, a automontagem camada por camada por adsorção física possui inúmeras vantagens, incluindo condições brandas e fisiológicas de preparação, capacidade de incorporar diferentes biomoléculas, e controle molecular. Nesta tese foram explorados filmes nanoestruturados de materiais de interesse biológico, bem como modelos de membranas, em que foram empregadas a técnica de automontagem e a preparação de lipossomos. Os lipossomos, que serviram como modelos de membrana, foram imobilizados em filmes automontados e sua integridade estrutural foi mantida. Também foram utilizados para incorporar e estabilizar melanina, e então imobilizados em filmes automontados, com preservação da propriedade fluorescente da melanina. A automontagem também foi utilizada para imobilização das enzimas uricase, fitase e colesterol oxidase, alternadas com camadas de polieletrólitos. Estes filmes mostraram bom desempenho como biossensores amperométricos para uricase e fitase, e como biossensores usando espectroscopia de impedância para a fitase e colesterol oxidase. Tais biossensores foram usados para detectar baixas quantidades de ácido úrico, ácido fítico e colesterol, respectivamente. Não houve efeitos de interferentes nos sensores amperométricos devido à utilização de eletrodos previamente modificados com azul da Prússia, que funcionou como mediador redox. A alta sensibilidade e seletividade dos biossensores foram atribuídas à natureza do filme ultrafino e à capacidade de reconhecimento das biomoléculas, respectivamente. Esta abordagem abre caminho para novas tecnologias de dispositivos para diagnósticos clínicos e análises de alimentos, bem como para entender mecanismos de interação da biomolécula com a membrana celular para o desenvolvimento de agentes terapêuticos. / The immobilization of molecules of biological interest on solid surfaces is essential for a number of biotechnological applications. Among the techniques for immobilization the layer-by-layer (LbL) method based on physical adsorption exhibits several advantages, including mild, physiological conditions for film preparation, ability to incorporate different biomolecules and molecular control. In this thesis, nanostructured films made with materials of biological interest were exploited as model membranes, where use was made of the LbL technique and liposomes. The latter, which served as membrane models, were immobilized in LbL films and had their structural integrity preserved. Liposomes were also used to incorporate and stabilize melanin, which were then deposited on LbL films with the fluorescence of melanin being preserved. The LbL method was also used to immobilize the enzymes uricase, phytase and cholesterol oxidase, alternated with layers of polyelectrolytes. These LbL films were employed in amperometric biosensors with uricase and phytase, and in biosensors based on impedance spectroscopy for phytase and cholesterol oxidase. Low amounts of uric acid, phytic acid and cholesterol were detected, respectively. There was no effect from interferents in the amperometric biosensors because the electrodes were previously modified with a layer of Prussian Blue, which acted as a redox mediator. The high sensitivity and selectivity were attributed to the ultrathin nature of the films and the ability of molecular recognition of the biomolecules, respectively. The approaches used here open the way for novel devices for clinical diagnostics and food quality control, in addition to understanding the interaction mechanisms between the biomolecules and the cell membranes, which is important for developing therapeutic agents.