La bioélectronique utilise des signaux électriques pour interagir avec des systèmes biologiques. Les capteurs qui permettent la lecture électrique de marqueurs de maladies importantes et les implants/stimulateurs utilisés pour la détection et le traitement d'activité cellulaire pathologique ne sont que quelques exemples de ce que cette technologie peut offrir. Du fait de leurs propriétés électro-actives et mécaniques fascinantes, l'électronique organique ou les matériaux conjugués π ont été largement exploités dans le domaine de la bioélectronique. Le mélange intéressant entre conductivité électronique et ionique de ces polymères conducteurs permet le couplage entre les charges électroniques présentent dans le volume des films organiques avec les flux ioniques du milieu biologique. Le matériau prototypique de la bioélectronique organique est le polymère conducteur poly(3,4-éthylènedioxythiophène) (PEDOT) dopé avec du polystyrène sulfonate (PSS). Dans ce rapport, nous étudierons une approche pour moduler les propriétés mécaniques, électriques et électrochimiques du PEDOT: PSS et étudier leur impact sur la performance des transistors électrochimiques organiques. Par ailleurs, nous évaluerons l'effet de la micro-structuration et du nano-patterning sur l'impédance électrochimique des électrodes en or recouvertes de PEDOT: PSS utiles pour de futurs enregistrements et stimulations neurales. Enfin, nous démontrerons l'utilisation du PEDOT:PSS à micro-motifs pour l'adhésion et la migration de cellules. / Bioelectronics uses electrical signals to interact with biological systems. Sensors that allow for electrical read-out of important disease markers, and implants/stimulators used for the detection and treatment of pathological cellular activity are only a few examples of what this technology can offer. Due to their intriguing electroactive and mechanical properties, organic electronics or π-conjugated materials have been extensively explored regarding their use in bioelectronics applications. The attractive mixed electronic/ionic conductivity feature of conducting polymers enables coupling between the electronic charges in the bulk of the organic films with ion fluxes in biological medium. The prototypical material of organic bioelectronics is the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonate (PSS). PEDOT:PSS is commercially available, water-dispersible conjugated polymer complex that can be cast into films of high hole and cation conductivity, good charge storage capacity, biocompatibility, and chemical stability. In the present work we investigate an approach to tailor the mechanical, electrical, and electrochemical properties of PEDOT:PSS and study their impact on the performance of organic electrochemical transistors. In addition, we study the effect of micro-structuring and nano-patterning on the electrochemical impedance of PEDOT:PSS- coated gold electrodes for future neural recordings and stimulation. Moreover we demonstrate the use of micro-patterned PEDOT:PSS in cell adhesion and migration.

Oxide materials display a wide range of physical properties. Recently, doped complex oxides have drawn considerable attention for various applications including thermoelectrics. Doped complex oxide materials have high Seebeck coefficients (S) and electrical conductivities (o) comparable to other doped semiconductors but low thermoelectric figure of merit ZT values due to their poor thermal conductivities. For example, niobium doped strontium titanate (SrNbxTi_1-xO₃ or simply Nb:STO) has a power factor comparable to that of bismuth telluride. Semiconductor nanostructures have demonstrated a decrease in thermal conductivity (κ) resulting in an increase in the thermoelectric figure of merit (ZT). Nanostructures of doped oxides like niobium doped strontium titanate, may also lead to decreased κ and a corresponding increase in ZT. The major impediment to nanostructured oxide thermoelectric materials is the lack of suitable fabrication techniques for testing and eventual use. Electron Beam Lithography (EBL) was used to pattern poly-methyl-methacrylate (PMMA) resists on undoped single crystalline SrTiO₃ (STO) substrates which were then filled with Nb:STO using Pulsed Laser Deposition (PLD) at room temperature. This technique produced nanowires and nanodots with critical dimensions below 100 nm, and a yield of approximately 95%. In addition to scanning electron microscopy and atomic force microscopy morphological studies of the patterned oxide, thin film analogues were used to study composition, crystallinity and electrical conductivity of the material in response to a post deposition heat treatment. Since the thin films were grown under similar experimental parameters as the oxide nanostructres, the patterned oxides are believed to be stoichiometric and highly crystalline. The study found that using a combination of EBL and PLD, it is possible to produce highly crystalline, doped complex oxide nanostructures with excellent control over morphology. Furthermore, the technique is applicable to nearly all materials and provides the capability of patterning doped oxide materials without the requirement of etching or multiple lithography steps makes this approach especially interesting for future fundamental materials research and novel device fabrication. / Master of Science

Durant les dernières décennies, de plus en plus de types de cellules se sont révélées capables de sonder leur environnement mécanique par l'application de forces. Ce phénomène appelé «Mecanosensing» est lié à l'adhésion et la mécanique cellulaire, et est souvent étudié grâce à l'interaction des cellules avec des substrats artificiels. Dans des études distinctes, des surfaces chimiquement structurées avec une répartition des ligands spécifiques ont montré une forte influence sur l’adhésion et la mécanique cellulaire. Cependant, la relation entre les deux phénomènes n'a pas été beaucoup explorée, en partie parce que la fonctionnalisation de substrats mous s’est révélée être un défi technique.Pour résoudre ce problème, nous avons développé une technique simple et rentable nommée «reverse contact printing», afin de fabriquer des plots de protéines sub-microniques sur un élastomère d'élasticité contrôlée, le polydiméthylsiloxane (PDMS). Mon travail de thèse a focalisé sur la standardisation et la compréhension du procédé de transfert. A l’aide de mesures de forces réalisées par AFM nous avons mesuré l’élasticité du PDMS, ainsi que les forces de cohésion et d'adhésion effectives impliquées dans le processus. Nous avons également étudié l'adhésion cellulaire avec des lymphocytes-T sur des surfaces de PDMS d'élasticité variable. Nous avons montré que contrairement à la plupart des autres types de cellules, les cellules-T s'étalent davantage sur substrat mou que sur dur. Finalement nous avons réalisé des expériences pilotes d'adhésion cellulaire sur PDMS structuré. / In the past decade, more and more types of cells have been shown to be capable of probing the mechanics of their environment by application of forces. The stiffness of the environment strongly influences a host of cellular parameters including cell adhesion and mechanics. In separate studies, the spatial distribution of ligands, modulated by chemical patterning of a target surface, has been shown to strongly influence cell adhesion and mechanics. However, the cross-talk between the two phenomena has not been much explored, partly because patterned functionalization of soft substrates is an engineering challenge. To address this issue, we have developed a simple and technique named "reverse contact printing" for fabrication of nanometric protein patches on PDMS (polydimethylsiloxane) elastomer. My PhD work consisted of deciphering the molecular mechanisms that underlie this technique. We realized that the rate of transfer crucially depended on the molecular groups on the protein and on the nature of the PDMS surface. We used atomic force microscopy (AFM) force measurements to measure PDMS elasticity as well as protein-substrate interactions to understand the molecular mechanism governing the transfer. We have identified that a successful reverse transfer is facilitated by the grafting of appropriate chemical groups on the protein, and depends on the PDMS surface treatment and elasticity. We also studied adhesion and mechanics of T lymphocytes on PDMS. We found that surprisingly T lymphocytes spread more on softer than on harder PDMS. In on-going pilot experiments, cells on patterned soft PDMS seem to exhibit different behavior as compared to cells on patterned glass.

Real-time coherent Grazing-Incidence Small-Angle X-ray Scattering was used to investigate the average kinetics and the fluctuation dynamics during self-organized ion beam nano-patterning of two semiconductor surfaces: silicon at room temperature and germanium heated above its recrystallation temperature. For silicon nano-patterning, initially flat samples at room temperature were bombarded by a broad collimated beam of 1keV Ar+ and Kr+ ions at 65° polar angle, leading to the amorphization of the ion-irradiated surfaces and the spontaneous formation of nanoscale ripples. The temporal evolution of the average X-ray scattering intensity shows the evolution of average kinetics, while the fluctuation dynamics can be investigated by correlation of X-ray speckles. The surface behavior at early times can be explained within a linear theory framework. The transition away from the linear theory behavior is observed in the dynamics since the intensity correlation function quickly evolves into a compressed exponential decay on length scales corresponding to the peak wavelength and a stretched exponential decay on shorter length scales. The correlation times for silicon nano-patterning are maximum at the ripple wavelengths while they are smaller at other wavelengths. This has notable similarities and differences with the phenomenon of de Gennes narrowing. Overall, this dynamics behavior is found to be consistent with the simulations of a nonlinear growth model by Harrison et al. Following the formation of self-organized nano-ripples, they move across the surface. Homodyne X-ray alone cannot detect the motion, but because of the gradient of ion flux across the sample, we were able to measure in-situ the corresponding ripple velocity gradient by cross-correlating speckles and tracking their movements. For germanium nano-patterning at an elevated temperature, flat germanium samples kept at 300°C were bombarded by 1keV Ar+ ions at normal incidence. Unlike the case when surfaces are amorphizated during room temperature bombardment, the crystalline nano-pattern formation occurs mainly due to a surface instability caused by the Ehrlich-Schwoebel barrier. By using a linear theory analysis on the X-ray scattering intensities in the early times, we measured the contribution of the Ehrlich-Schwoebel barrier to the crystalline nano-patterning kinetics.

In this work the development of a Self-Powered System-On-Chip is explored by examining two components of process development in different perspectives. On one side, an energy component is approached from a biochemical standpoint where a Microbial Fuel Cell (MFC) is built with standard microfabrication techniques, displaying a novel electrode based on Carbon Nanotubes (CNTs). The fabrication process involves the formation of a micrometric chamber that hosts an enhanced CNT-based anode. Preliminary results are promising, showing a high current density (113.6mA/m2) compared with other similar cells. Nevertheless many improvements can be done to the main design and further characterization of the anode will give a more complete understanding and bring the device closer to a practical implementation. On a second point of view, nano-patterning through silicon nitride spacer width control is developed, aimed at producing alternative sub-100nm device fabrication with the potential of further scaling thanks to nanowire based structures. These nanostructures are formed from a nano-pattern template, by using a bottom-up fabrication scheme. Uniformity and scalability of the process are demonstrated and its potential described. An estimated area of 0.120μm2 for a 6T-SRAM (Static Random Access Memory) bitcell (6 devices) can be achieved. In summary, by using a novel sustainable energy component and scalable nano-patterning for logic and computing module, this work has successfully collected the essential base knowledge and joined two different elements that synergistically will contribute for the future implementation of a Self-Powered System-on-Chip.

Le cytosquelette de microtubule (MT) est essentiel dans de nombreux processus cellulaire. Il est notamment impliqué dans le trafic intracellulaire, la division cellulaire, la modification et le maintien de la forme de la cellule. En fonction du type cellulaire ou de son état de différenciation, les réseaux de MTs vont adopter des architectures différentes. Ces organisations sont définies par des contraintes géométriques intracellulaires et l'activité moléculaire de nombreuses protéines associées aux MTs (MAPs). Parmi ces protéines, des membres de la famille des MAP65s ont été identifiés. In vitro, elles forment des ponts entre les MTs pour les organiser en faisceaux. Le but de mon travail de thèse a été d'étudier in vitro le rôle de MAP65s dans l'auto-organisation d'un réseau de faisceaux de MTs. Dans un premier temps, j'ai mis au point un système biomimétique utilisant la technique de « micro-patterning » qui imposent une géométrie d'assemblage pour les MTs dans des limites qui se rapprochent de celles observées dans les cellules. Cette méthode permet de contrôler précisément l'assemblage des MTs à partir de zones dont les formes, la taille et la distribution des unes par rapport aux autres sont définies. Pour valider cette technique, j'ai reconstitué des réseaux qui miment des architectures cellulaires (i.e modules du fuseau mitotique). Dans un deuxième temps j'ai étudié le rôle de MAP65s dans l'auto-organisation de réseaux de faisceaux de MTs, et plus particulièrement l'étape de co-alignement entre MTs dynamiques et dispersés. J'ai montré que MAP65-1 de plante et son orthologue chez la levure, Ase1, diminuent fortement la longueur de persistance de MTs isolés ou organisés en faisceaux. Cet assouplissement leur permet de se déformer et donc de se co-aligner pour former des faisceaux lorsqu'ils se rencontrent à des angles de rencontre élevés. L'augmentation de flexibilité est du à l'interaction du domaine de liaison de MAP65-1/Ase1 avec la lattice des MTs. Ces résultats suggèrent que la diminution de la rigidité des MTs contrôle dans les cellules l'issue des évènements des rencontres entre MTs. De façon plus générale, la modulation des propriétés mécaniques des MTs par des MAPs représente un nouveau mécanisme pour réguler la plasticité des réseaux de MTs dans les cellules eucaryotes. / The microtubule (MT) cytoskeleton is essential for many cell processes, such as the intracellular trafficking, the cell division, and the cell morphogenesis. Depending on the cell type or on its differentiation state, the MT networks will adopt different architectures. These organizations are defined by intracellular geometric constraints and the regulation of the acticity of many MT associated proteins (MAPs). Among these proteins, we get a particular interest in MAP65s family that crosslink MTs to organize them into bundles. The aim of my thesis was to study in vitro the role of MAP65s in the self-organization of MT bundles in particular networks. As a first step, I developed a biomimetic system using the micro-patterning procedure which imposes a MT assembly geometry within limits close to those observed in cells. This method allows to precisely control the MT assembly from micro-patterns with define shape, size and spatial distribution. In order to validate this technic, I reconstituted MT networks which mimic cellular architecture (i.e mitotic spindle modules). In a second time, I studied the role of major MT cross-linkers that are members of the MAP65 family in the formation of MT bundles, particularly the step of MT co-aligment after encountering of dynamic growing MTs. I found that plant MAP65-1 and its yeast ortholog, Ase1, lower the global rigidity of single MTs and MT bundles. This increase in MT flexibility is directly caused by interactions between the MAP65 MT-binding domain and the MT lattice. These data suggest that MT softening by MAP65 controls the issue of MT encounters, so that self-organized ordered MT bundles are formed in living cells. In a more general way, the modulation of MT mechanical propreties by MAPs represent a new mecanism to regulate MT networks plasticity in eukaryote cells.

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