The observed multiscale phenomenon of rough surfaces, i.e. the smaller mountains mount on the bigger ones successively, renders the hierarchical structures which are described by the fractal geometry. In this situation, when two rough surfaces are loaded together with a higher load, the smaller asperities will undergo plastic flow and immerge into the bigger asperities below them. In other words, the higher load needs to be supported by the bigger asperities. However, when the GW model was proposed in 1966, its analytical method considered that the length-scale of asperities is fixed, which is independent of load (or surface separation). In such condition, the analytical results for a specific asperity length-scale can only suit the situation of a certain narrow range of load. In this research, a new model, called the multiscale GW model, has been developed, which takes into account the relationship between the load and the asperity length-scale. At first, based on the Nayak¡¦s model the multiscale asperity properties with different surface parameters have been derived, and based on the material yielding theory a criterion for determining the optimal asperity length-scale, which functions as supporting the load, is developed. Then both of the above are integrated into the GW model to build the multiscale GW model. The new model is compared with traditional one qualitatively and quantitatively and show their essential differences. The effects of surface parameters and material parameters are discussed in this model. Finally a comparison with the experiment is made, and reveal the good coincidence.

Surface plasmon microscopes are mostly built around the prism based Kretschmann configuration. In these systems, an image of a sample can be obtained in terms of an intensity map, where the intensity of the image is dependent on the coupling of the light into the surface plasmons. Unfortunately the lateral resolution of these systems relies on the ability of plasmons to propagate along the metallised layer and is usually limited to a few microns unless special measures are taken. The widefield surface plasmon microscope (WSPR), used here enables surface plasmon imaging at significantly higher lateral resolutions than prism based systems. In this study we demonstrate the functionality of the WSPR by imaging a sequence of binding events between micro-patterned extracellular matrix proteins and their specific antibodies. Using the WSPR system a change in contrast was observed with each binding event. Images produced via the WSPR system were analyzed and compared qualitatively and quantitatively. Consequently, we confirm that the WSPR microscope described here can be used to study sequential monomolecular layer binding events on a micron scale. These results have significant implications in the development of new micron scale bioassays.

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.

Cette thèse porte sur la dynamique, normale à l'interface, d'un contact sec en glissement stationnaire entre deux surfaces de topographies aléatoires, soumis à une faible charge normale. Dans ce contexte, le mouvement d'un patin sous son propre poids a été étudié expérimentalement. Des mesures par vibrométrie laser du déplacement et de la vitesse normale du patin ont confirmé que, lorsque la vitesse de glissement augmente, le patin transite entre un régime où le contact est permanent vers un régime dynamique où il subit décollements, chocs et rebonds.À basse vitesse, le mouvement normal résulte d'un filtrage géométrique des topographies. Les caractéristiques statistiques et spectrales de ce mouvement ont pu être décrites. Les influences de la rugosité, de la longueur de corrélation, de la largeur de bande du spectre de rugosité et de l'aire apparente de contact ont été identifiées et analysées. Ces résultats ont pu être reproduits par des modèles numériques, mais aussi analytiques en adaptant la théorie des valeurs extrêmes. Des modèles de type Bouncing Ball, dont l'excitation est supposée donnée par le processus de filtrage géométrique, ont également été mis en place. Ils reproduisent une large gamme d'observations en régime dynamique, de la transition aux vibro-impacts.Pour tester certaines hypothèses des modèles mis en place, un patin multi-voies original a été développé et a permis d'accéder à la localisation spatiale des micro-contacts transitoires entre surfaces antagonistes. On observe que les micro-contacts sont gouvernés par une longueur caractéristique à basse vitesse de glissement et par un temps caractéristique à haute vitesse. Les rotations du patin deviennent importantes à haute vitesse, modifiant la répartition des micro-contacts à la surface du patin. / This PhD thesis addresses the issue of the dynamics, normal to the interface, of a dry steady-sliding contact between two random topographies under weak normal load. In this context, the motion of a slider under its own weight has been studied experimentally. Measurements, using a laser vibrometer, of the normal displacement and velocity of the slider confirm the existence of a transition, as the sliding speed increases, from a regime of permanent contact to a regime of lift-offs, shocks and rebounds.At low speed, the normal motion is due to a geometrical filtering of the topographies, the statistical and spectral properties of which have been described. The roles of the roughness, including its spectral breadth and correlation length, and of the apparent contact area have been identified and analyzed. Those results have been reproduced not only using numerical models, but also using analytical ones based on the extreme value theory. Bouncing-Ball-like models, the excitation of which is assumed to be given by the geometrical filtering, have also been implemented and match with a broad range of experimental observations in dynamical regime, from the transition to vibro-impacts.To test some of the hypothesis of the models, a new experimental multi-channel slider has been designed and has enabled access to the spatial localization of the transient micro-contacts between the antagonists surfaces. It has been shown that micro-contacts are governed by a characteristic length at low sliding speed and by a characteristic time at high speed. The rotational motion of the slider also increases with sliding speed, changing the micro-contact distribution along the surface of the slider.

This thesis provides a compendium for the use of microcontact printing in fabricating electrical devices. Work has been undertaken to examine the use of soft lithographic techniques for employment in electronic manufacture. This thesis focusses on the use of high electric field generators as a means to producing electroluminescent devices. These devices provide a quantifiable output in the form of light. Analysis of the electrical performance of electrode structures can be determined by their success at producing light. A prospective reduction in driving voltage would deem these devices more efficient, longer lasting and an improvement on current specification. The work focussed on the viability of using relatively crude print techniques to create high resolution structures. This was carried out successfully and demonstrated that lighting structures of 75 μm and 25 μm have been produced. Microcontact printing has been established as a method for patterning gold surfaces with a functionalising self-assembled monolayer using alkanethiol molecules. This layer is then utilised as an etch resist layer to expose gold tracks for use as electric field generator electrode arrays. Through careful analysis of each step of the printing process, techniques were developed and reported to create a robust and repeatable print mechanism for reliability and accuracy. These techniques were employed to optimise the print process culminating in the development of each stage and final electrode structures mounted on a rigid backplate for use as electroluminescent devices for characterisation. These devices were then modelled for their electrical characteristics and investigated for being used in low voltage application. In this case for the development of electroluminescent applications, a driving voltage of 65 V was achieved and represents a significant advance to the field of printed electronics and Electroluminescence.

A non-crosslinking approach that covalently bonds nitroxide polymer brushes onto the ITO substrates via surface-initiated atom transfer radical polymerization (ATRP) was develpoed. Since the indium tin oxide (ITO)-silane covalent bonding providesvery strong chemical bonds to adsorb the nitroxide polymer brushes on ITO, it prevents polymers from dissolving into electrolyte solvent and thus improves its electrochemical properties. Moreover, micro-contact printing technology was used to pattern nitroxide polymer brushes on an ITO surface for the potential application in microbatteries. The morphology of electrodes was observed by atomic force microscopy.The electrochemical properties of the cathode were also studies.

Surface plasmon microscopes are mostly built around the prism based Kretschmann configuration. In these systems, an image of a sample can be obtained in terms of an intensity map, where the intensity of the image is dependent on the coupling of the light into the surface plasmons. Unfortunately the lateral resolution of these systems relies on the ability of plasmons to propagate along the metallised layer and is usually limited to a few microns unless special measures are taken. The widefield surface plasmon microscope (WSPR), used here enables surface plasmon imaging at significantly higher lateral resolutions than prism based systems. In this study we demonstrate the functionality of the WSPR by imaging a sequence of binding events between micro-patterned extracellular matrix proteins and their specific antibodies. Using the WSPR system a change in contrast was observed with each binding event. Images produced via the WSPR system were analyzed and compared qualitatively and quantitatively. Consequently, we confirm that the WSPR microscope described here can be used to study sequential monomolecular layer binding events on a micron scale. These results have significant implications in the development of new micron scale bioassays.

Yes / Cell behavior in terms of adhesion, orientation and guidance, on extracellular matrix (ECM) molecules including collagen, fibronectin and laminin can be examined using micro contact printing (MCP). These cell adhesion proteins can direct cellular adhesion, migration, differentiation and network formation in-vitro. This study investigates the effect of microcontact printed ECM protein, namely fibronectin, on alignment and morphology of HeLa cells cultured in-vitro. Fibronectin was stamped on plain glass cover slips to create patterns of 25μm, 50μm and 100μm width. However, HeLa cells seeded on 50μm induced the best alignment on fibronectin pattern (7.66° ±1.55SD). As a consequence of this, 50μm wide fibronectin pattern was used to see how fibronectin induced cell guidance of HeLa cells was influenced by 100μs and single pulse electric fields (PEF) of 1kV/cm. The results indicates that cells aligned more under pulse electric field exposure (2.33° ±1.52SD) on fibronectin pattern substrate. Thus, PEF usage on biological cells would appear to enhance cell surface attachment and cell guidance. Understanding this further may have applications in enhancing tissue graft generation and potentially wound repair. / Ministry of Higher Education Malaysia and UTHM Tier 1 Research Grant (U865)

Scaffold based tissue reconstruction inherently limits regenerative capacity due to inflammatory response and limited cell migration. In contrast, scaffold-free methods promise formation of functional tissues with both reduced adverse host reactions and enhanced integration. Cell-sheet engineering is a well-known bottom-up tissue engineering approach that allows the release of intact cell sheet from a temperature responsive polymer such as poly-N-isopropylacrylamide (pNIPAAm). pNIPAAm is an ideal template for culturing cell sheets because it undergoes a sharp volume-phase transition owing to the hydrophilic and hydrophobic interaction around its lower critical solution temperature (LCST) of 32°C, a temperature close to physiological temperature. Compared to enzymatic digestion via trypsinization, pNIPAAm provides a non-destructive approach for tissue harvest which retains its basal surface extracellular matrix and preserves cell-to-cell junctions thereby creating an intact monolayer of cell sheet suitable for tissue transplantation. The overall thrust of this dissertation is to gain a comprehensive understanding of how tissue precursors are formed, harvested and printed from interactions with shape-changing pNIPAAm hydrogel. A simple geometrical microbeam pattern of pNIPAAm structures covalently bound on glass substrates for culturing mouse embryonic fibroblast and skeletal myoblast cell lines is presented. In order to characterize the cell-surface interactions, three main investigations were conducted: 1) the mechanism of cell detachment; 2) the feasibility of micro-contact printing tissue precursors onto target surfaces; and 3) the assembly of these tissues into three-dimensional (3D) constructs. Detachment of cells from the shape-changing hydrogel was found to correlate with the lateral swelling of the microbeams, which is induced by thermal activation, hydration and shape distortion of the patterns. The mechanism of cell detachment was primarily driven by strain, which occurred almost instantaneously above a critical strain of 25%. This shape-changing pNIPAAm construct allows water penetration from the periphery and beneath the attached cells, providing rapid hydration and detachment within seconds. Cell cultured microbeams were used as stamps for micro-contact printing of tissue precursors and their viability, metabolic activity, local and global organization were evaluated after printing. The formation and printing of intact tissues from the shape-changing hydrogel suggests that the geometric patterning of pNIPAAm directs spatial organization through physical guidance cues while preserving cell functioning. Tissue precursors were sequentially assembled into parallel and perpendicular configurations to demonstrate the feasibility of constructing dense tissues with different organizations such as interconnected cell lines that could induce vascularization to solve perfusion issues in regenerative therapies. The novel approach presented in this dissertation establishes an efficient method for harvesting and printing of tissue precursors that may be applicable for the modular, bottom up construction of complex tissues for organ models and regenerative therapies.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.