Les dispositifs de stimulation tactile sont des systèmes destinés à fournir un retour sensoriel à leurs utilisateurs. Ils enrichissent les interfaces homme-machine dans les applications de réalité virtuelle ou augmentée. Ce mémoire traite de l'apport des microsystèmes électromécaniques (MEMS) actionnés magnétiquement à la réalisation d'interfaces de stimulation tactile facilement intégrables.Un état de l'art des solutions d'actionnement mises en œuvre dans les dispositifs existants est proposé, ainsi qu'une définition des besoins pour les applications visées. Les solutions retenues sont basées sur l'actionnement magnétostatique.Les premiers prototypes d'interfaces de stimulation tactile se présentent sous la forme d'un réseau de 4x4 actionneurs élastomériques hybrides avec un pas de 2 mm, combinant microfabrication et techniques de fabrication conventionnelles. La conception et l'élaboration de ces micro-actionneurs est présentée en détail. L'actionnement impulsionnel permet d'atteindre des amplitudes de vibration importantes (jusqu'à 200 µm) et des forces élevées (32mN par actionneur). Des tests sensoriels confirment enfin leur efficacité. Des micro-bobines ont aussi été développées afin de répondre aux besoins des micro-actionneurs magnétiques, ainsi qu'au cahier des charges des interfaces de stimulation tactile. Diverses configurations de micro-bobines adaptées à l'actionnement de puissance sont proposées et réalisées par électrodéposition. Des micro-actionneurs basés sur ces bobines intégrées ont alors été réalisés, puis caractérisés. L'utilité des bobines pour les micro-actionneurs de puissance est alors discutée face aux solutions d'actionnement hybride

Dans ce mémoire, une étude des conditions de contrôles d'écoulements aérodynamiques par des réseaux de générateurs de tourbillons fluidiques pulsés est menée pour établir un cahier des charges des micro-actionneurs instrumentés de faible coût, indispensables à la réalisation de ce type de contrôle actif à l'échelle industrielle. Une discussion des problématiques rencontrées dans la mise en place de ces dispositifs permet de définir des solutions techniques pertinentes. Une micro-valve encapsulée, constituée d'un canal micro-fluidique en silicium dont l'ouverture est contrôlée par un résonateur annulaire en PDMS, actionnée par différents dispositifs macroscopiques magnétiques, est alors modélisée, fabriquée et caractérisée. Le dispositif permet de générer des jets d'air pulsés complètement contrôlés jusqu'à des vitesses de 150m/s sur la gamme de fréquence [0 ; 500 Hz]. Des réseaux de ces micro-actionneurs polyvalents sont ensuite utilisés en soufflerie pour démontrer sur différents profils aérodynamiques classiques l'intérêt du contrôle par jet pulsé. Le recollement du flux d'air décollé est obtenu sur chacune de ces maquettes pour des conditions réalistes et avec un rendement fluidique supérieur à celui des jets continus.Un débitmètre massique composé d'un capteur de température, d'un capteur de frottement pariétal et d'un capteur de pression de type Pirani, réalisés dans le même procédé de fabrication, est intégré au micro-actionneur. Il permet de caractériser in-situ les jets d'air produits.Enfin un prototype répondant complètement au cahier des charges industriel est obtenu. Sa taille est minimisée par l'optimisation de l'actionneur grâce à un algorithme génétique

L' Imagerie médicale par Résonance Magnétique (IRM) constitue un outil puissant pour le diagnostic et le suivi de pathologies dans le cadre des modèles développés sur petit animal en neurosciences. Cette application requiert une haute résolution spatiale et un Rapport Signal à Bruit(RSB) élevé, rendus possibles par l'utilisation d'un haut champ magnétique (7 T) et d'une antenne miniature à forte sensibilité, implantée à proximité de la zone d'intérêt. Le design monolithique de l'antenne, appelé Résonateur Multi-tours à Lignes de Transmission (RMLT), permet la miniaturisation en dessous du centimètre et sa réalisation par les technologies de microfabrication en salle blanche.Afin de réduire l'aspect invasif de l'implantation, l'antenne a été réalisée sur support souple :FEP Téflon® ou PDMS. Pour résoudre les problèmes d'adhérence liés à ces matériaux polymères, des traitements plasmas spécifiques ont été mis en œuvre pour le FEP Téflon® tandis qu'un procédé de transfert de motifs dédié au PDMS a été élaboré. Outre la fiabilité mécanique, l'épaisseur du revêtement PDMS assurant la bio compatibilité de l'antenne a été optimisée pour limiter le couplage diélectrique avec les tissus et ainsi conserver des caractéristiques électromagnétiques appropriées à l'IRM à 7 T lorsque l'antenne est implantée. L'ensemble de ces travaux a permis la réalisation des premières images du cerveau du rat acquises in vivo avec une micro-antenne souple implantée. Ces images ont démontré un RSB amélioré d'un facteur 5, comparées à celles acquises avec une antenne commerciale quadrature. D'autres applications et perspectives dans le domaine biomédical sont ouvertes par ces travaux comme des capteurs pour la détermination des propriétés diélectriques des tissus, et des microbobines et des capteurs de pression intégrés dans les canaux microfluidiques.

The objective of this work is to investigate the elastic modulus of gastrula-stage avian embryos and the effect of substrate stiffness on presumptive precardiac cell fate. Our overall hypothesis is that the mechanical microenvironment, specifically, tissue modulus and substrate stiffness, influences gastrulation and cardiac induction. Large-scale morphogenetic movements during early embryo development are driven by complex changes in biochemical and biophysical factors. Current models for amniote primitive streak morphogenesis and gastrulation take into account numerous genetic pathways but largely ignore the role of mechanical forces. Here, we used atomic force microscopy (AFM) to obtain for the first time precise biomechanical properties of the early avian embryo. Our data reveal that the primitive streak is significantly stiffer than neighboring regions of the epiblast, and that it is stiffer than the pre-primitive streak epiblast. To test our hypothesis that these changes in mechanical properties are due to a localized increase of actomyosin contractility, we inhibited actomyosin contractility via the Rho kinase (ROCK) pathway using the small-molecule inhibitor Y-27632. Our results using several different assays show the following: 1) primitive streak formation was blocked; 2) the time-dependent increase in primitive streak stiffness was abolished; and 3) convergence of epiblast cells to the midline was inhibited. Taken together, our data suggest that actomyosin contractility is necessary for primitive streak morphogenesis, and specifically, ROCK plays a critical role. To better understand the underlying mechanisms of this fundamental process, future models should account for the findings presented in this study. As presumptive cardiac cells traverse the course of differentiation into cardiac myocytes during cardiogenesis, the sequence, magnitude, and spatiotemporal map of biomechanical and biochemical signals has not been fully explored. There have been many studies detailing the induction of cardiogenesis on a variety of substrates and extracellular matrix (ECM) proteins, but none have completed a rigorous study of the effects of substrate stiffness on the induction of precardiac cells prior to the onset of cardiac gene expression (smooth muscle alpha actin [SMAA] at stage 5.) We investigate the effects of the mechanical environment on precardiac cell behaviors in an in vitro setting to elucidate the effect of substrate stiffness and inducing factors on precardiac tissue and the potential connection between them. The cells in the anterior portion of the primitive streak are fated to form the heart, and we show differing levels of SMAA expression on substrates of differing moduli, which suggests that substrate stiffness may play a role in cardiac differentiation. We cannot determine the physical mechanisms during morphogenesis without understanding the response of precardiac cells to changes in their mechanical environment.

Microfluidics is gaining in importance due to its wide ranging benefits and applicability in chemical and biological analysis. Although traditional microfluidic devices are created with glass or silicon based fabrication technologies, polymer based devices are gaining in popularity. Soft lithography and replica molding are techniques for the rapid prototyping of such devices, utilizing Polydimethylsiloxane (PDMS) as the dominant material. Other benefits include its low costs and ease of fabrication. Even though soft lithography is a well researched and developed fabrication process, new applications have been discovered in which the technology can be applied. Often, changes in the fabrication process are necessary for their application in other areas of research. This thesis will address several microfluidic applications using soft lithography. These areas of research include microfluidic thermometry, isoelectric focusing (IEF), and micromixers. In microfluidic thermometry, a novel thin film PDMS/Rhodamine B has been developed allowing whole-chip temperature measurements. In addition, compatibility problems between Rhodamine B and PDMS microfluidic devices were resolved. The thin film fabrication process, experimental results, and issues with its use are discussed. Future work and attempts at improving the thin film performance are also provided. IEF involves applications in which samples are separated according to its electrostatic charge. Two types of IEF applications are shown in which soft lithography has been shown to be beneficial to its development and performance. In isoelectric focusing with the use of thermally generated pH gradients, soft lithography allows for the rapid design, production and testing of different channel layouts. In general, due to PDMS insulation and overall low heat transfer rates, the temperatures detected are more gradual than those previously reported in literature. IEF using carrier ampholytes are also discussed, with preliminary results in which devices fabricated using soft lithography are compared to commercially available IEF cartridges. Its fabrication issues are discussed in detail. In micromixers, soft lithography fabrication issues and overall integration with flow mechanisms is discussed. In general it is difficult to perform mixing in the microscale due to the predominantly laminar flow and flow rate restrictions. Channel geometry is insignificant, as can be seen through numerical simulations.

Microfluidics is gaining in importance due to its wide ranging benefits and applicability in chemical and biological analysis. Although traditional microfluidic devices are created with glass or silicon based fabrication technologies, polymer based devices are gaining in popularity. Soft lithography and replica molding are techniques for the rapid prototyping of such devices, utilizing Polydimethylsiloxane (PDMS) as the dominant material. Other benefits include its low costs and ease of fabrication. Even though soft lithography is a well researched and developed fabrication process, new applications have been discovered in which the technology can be applied. Often, changes in the fabrication process are necessary for their application in other areas of research. This thesis will address several microfluidic applications using soft lithography. These areas of research include microfluidic thermometry, isoelectric focusing (IEF), and micromixers. In microfluidic thermometry, a novel thin film PDMS/Rhodamine B has been developed allowing whole-chip temperature measurements. In addition, compatibility problems between Rhodamine B and PDMS microfluidic devices were resolved. The thin film fabrication process, experimental results, and issues with its use are discussed. Future work and attempts at improving the thin film performance are also provided. IEF involves applications in which samples are separated according to its electrostatic charge. Two types of IEF applications are shown in which soft lithography has been shown to be beneficial to its development and performance. In isoelectric focusing with the use of thermally generated pH gradients, soft lithography allows for the rapid design, production and testing of different channel layouts. In general, due to PDMS insulation and overall low heat transfer rates, the temperatures detected are more gradual than those previously reported in literature. IEF using carrier ampholytes are also discussed, with preliminary results in which devices fabricated using soft lithography are compared to commercially available IEF cartridges. Its fabrication issues are discussed in detail. In micromixers, soft lithography fabrication issues and overall integration with flow mechanisms is discussed. In general it is difficult to perform mixing in the microscale due to the predominantly laminar flow and flow rate restrictions. Channel geometry is insignificant, as can be seen through numerical simulations.

Hybrid macrocycles, which chimerically integrate multiple chemical compositions and architectures, provide an effective way to impart new properties to polymers that are not found in their linear or homocyclic analogues. This dissertation addresses the incorporation of hydrophilic blocks into hydrophobic polymer, as either a poly(dimethyl siloxane)-block-poly(oxyethylene) (PDMS-POE) tadpole with a hydrophobic head and a hydrophilic tail or as a diblock poly(styrene)-block-diethylene glycol (PS-DEG) hydrophobic-hydrophilic macrocycle. The supramolecular association properties of both kinds of cycles were studied: the PDMS-POE tadpoles in forming micelles, and the PS-DEG macrocycles in threading with linear polymer to form polyrotaxanes. For the PDMS-POE macrocycle, linear alpha,omega-dihydroxy PDMS was cyclized under dilute conditions with dichloromethylhydrosilane as a linking group to produce hydrosilane-functionalized cyclic PDMS. This was joined to alpha-methoxy,omega-allyl POE via a free radical hydrosilylation reaction to produce the hybrid tadpole macrocycle, which was analyzed by GPC, DSC, and 1H, 13C, and 29Si NMR spectroscopy. Supramolecular aggregation consisting of the formation of micelles under both polar and nonpolar conditions was studied by surface tensiometry and quasielastic light scattering. For the PS-DEG macrocycle, linear alpha,omega-dihydroxy PS was prepared by ATRP polymerization of styrene, followed by reaction with KOH to give hydroxyl endgroups. The linear PS was then cyclized under dilute conditions with diethylene glycol ditosylate, and the product was analyzed by GPC, MALDI-TOF MS, DSC, and 1H, 13C and DOSY NMR spectroscopy. The macrocycle was then statistically threaded with linear PS to give the supramolecular structure poly(styrene)-rotaxa-cyclo[poly(styrene)-block-diethylene glycol]. Characterization was performed with DOSY NMR to verify that the product was threaded, and 1H NMR was collected to determine that the product was 13% macrocycle by weight. DSC showed only one Tg, indicating that the linear and cyclic species were present in the same phase.

Embryonic stem cells (ESCs) are pluripotent cells derived from the inner cell mass of the blastocyst that can give rise to cells of the ectoderm, endoderm and mesoderm lineages. Once isolated from the blastocyst, ESCs can be cultured indefinitely in vitro in an undifferentiated state or can be induced to differentiate. In the case of mouse ESCs (mESCs), the cytokine leukemia inhibitory factor (LIF) is added to culture media to maintain pluripotency and is removed to induce differentiation. Although it is known that extracellular matrix (ECM) components influence stem cell maintenance, proliferation and differentiation, the precise effects of ECM environments on embryonic stem cell behavior have not been systematically studied. The main purpose of this thesis project was to investigate the behavior of undifferentiated mESCs cultured in different 3D hydrogel matrices and to determine whether viscoelastic and biochemical variations in the matrices differentially affect the ability of stem cells to self-renew; that is, retain their pluripotency or undifferentiated phenotype. Their behavior in 3D environments was compared to mESC behavior in traditional 2D culture. In addition, a new method of casting hydrogels in polydimethylsiloxane (PDMS) molds was developed in order to efficiently cast multiple hydrogels of varying sizes and shapes. The findings of this thesis project will benefit both the scientific and engineering community as it encourages researchers to re-evaluate the quality of standard 2D embryonic stem cell culture methods versus potentially novel and advantageous 3D hydrogel culture methods.

In this study we use PDMS thin films to fabricate of multi-domain surface. PDMS gets the characteristic of good physical properties and chemical, not only low surface free energy, flexible, also has low toxicity, low cost and can protect our environment. We used the DI water that was dropped on the PDMS thin film surface and became stable to explore the wettability of the surface, and we had a discussion about when liquid crystal dropped on the PDMS thin film surface. Then we also observe the phenomenon that was liquid crystal will shift a little distance and we used the optical image to analyze our device.

In this study, the PDMS with microgroove structure was used controlling pretilt anlge of liquid crystal. Polydimethylsiloxane, also called PDMS, is one transparent, flexible, and stable material. It was usually fabricated the flexible display and so on. Based on Groove Theory, we can create the microgroove structure with the different groove depths and the width of the lines on PDMS by Replica Molding Method, in order to controlling the pretilt anlge of liquid crystal. We used the photoresist with different thickness to developing, and then the groove will get with different depth of groove. The PDMS was injected to the surface of groove with slow motion. When the liquid-like PDMS was curing, the PDMS can readily convert into solid elastomers by cross-linking. Finally, The microgrooved PDMS structure will obtain.