L'excitabilité est une propriété bien connue des neurones biologiques. Il s'agit d'une réponse de type tout-ou-rien à une perturbation au delà d'un seuil caractéristique appelé seuil excitable. D'autres propriétés importantes existent dans les neurones comme les périodes réfractaires et la sommation temporelle ou spatiale de stimuli d'entrée.L'excitabilité a été étudiée dans certains composants actifs à semiconducteur et notamment les composants à semiconducteurs III-V. Leurs propriétés neuro-mimétiques pourraient permettre de traiter l'information de façon tout-optique avec une grande bande passante et une faible consommation.Grâce aux nouvelles techniques de micro-nano fabrication, il est devenu possible de fabriquer des micropiliers lasers à absorbant saturable. Ces micropiliers pourraient permettre la réalisation de réseaux de micropiliers couplés excitables analogues à des réseaux de neurones photoniques.Dans cette thèse j'ai étudié les propriétés neuro-mimétiques de micropiliers lasers à absorbant saturable intégré. Les principaux résultats de cette thèse sont les suivants : 1) la technique de fabrication des micropiliers a été améliorée conduisant à une augmentation de leur durée de vie et une diminution du seuil laser. 2) des propriétés de base des neurones biologiques, comme l'excitabilité, l'existence des périodes réfractaires, la sommation temporelle, ont été mises en évidence expérimentalement et analysées à l'aide du modèle de Yamada. 3) des effets de propagation d'excitations ont été démontrés dans des structures unidimensionnelles : des lasers ligne et des chaînes de micropiliers couplés.La démonstration des propriétés neuromimétiques de micropiliers lasers à absorbant saturable et la mise en évidence de la propagation d'excitations ouvrent la voie à la réalisation de réseaux de micropiliers couplés pour les traitements neuromimétiques des signaux qui pourront être exploités pour de la logique codée à l'aide de pics excitables ainsi que pour du stockage d'information dans des circuits mémoires tout-optiques. / Excitability is a well known property of biological neurons. In excitable systems, the response to a perturbation above the excitable threshold is of all-or-none type. Other properties exist in neurons such as the refractory periods and temporal or spatial summation of input stimuli.Excitability has been demonstrated in many III-V semiconductor material devices. Thanks to their nonlinear properties it could be possible to realize neuromimetic and all-optical signal processing with high speed and low energy consumption. Thanks to progress in fabrication techniques it is possible to fabricate high quality micropillar laser with saturable absorber. Thus, using micropillars it could be possible to realize neural photonic networks analog to neural networks.In this thesis work, I studied neuron-like properties of a micropillar laser with a saturable absorber. My main results are : 1) fabrication of micropillars has been improved leading to an increase of their robustness and a reduction of the laser threshold. 2) well known properties of biological neurons, such as excitability, existence of refractory periods, temporal summation, have been demonstrated experimentally and have been numerically analyzed with the Yamada model. 3) propagation effects of excitations have been demonstrated in one-dimensional structures : wire lasers and chains of coupled micropillars.The demonstration of neuromimetic properties in micropillar lasers with saturable absorber and the evidence of propagation of excitations pave the way to neuromorphic networks based on coupled micropillars for neuromimetic signal processing like information encoding with excitable pulses and realization of optical memories.

In this dissertation, an exosome capturing ciliary micropillar array microfluidics is introduced and applied to evaluate the response of resistant cancer cells under nanoparticle encapsulated chemotherapy. Cancer cells are able to develop different mechanisms to resist therapeutic treatment, frequently causing chemotherapy failure. Active drug expulsion is one of the usual resisting schemes to reduce intracellular drug accumulation to a non-effective level. Evidence has suggested a potential exosomal pathway is used by multi-drug resistant (MDR) cancer cells to expel drugs. Here I study the exosomes derived from MDR cancer cells treated by nanotherapeutics aiming to establish the correlation between nanotherapeutics and exosomal pathway for drug expulsion. The outcome would boost further understanding of cancer MDR, and in turn direct the development of pharmaceutical nanoparticles to overcome MDR cancer. To effectively isolate exosomes for drug expulsion evaluation, a ciliary micropillar structure is fabricated employing microelectromechanical systems (MEMS) and metal assisted chemical etching (MACE) techniques. The ciliary micropillar is fabricated in two major steps: deep silicon etch (DSE) for pillars followed by a MACE process to etch nanowires on the pillars. The concept of using MACE as an alternative to DSE is also explored to reduce fabrication cost. With optimized parameters, it shows a comparable result to DSE. COMSOL simulation revealed that ciliated micropillars exhibited a unique advantage as a unit structure for capturing small particles in fluid flow, according to particle filtration theory. A nanowire layer with high permittivity allows fluid streamlines to pass through, and increases interaction with particle carrying fluid to increase the probability of particle interception. Nanowires on the pillar can trap specific sized particles due to their characteristic dimension. Thanks to the weaker stability of porous silicon nanowires, trapped particles can then be released by dissolving these nanowires without damage to the particles themselves. A microfluidic chip is fabricated with an optimized circular micropillar arrangement for resistance reduction, and its particle filtration performance is demonstrated by processing model cell culture medium. The device is applied to study MDR cells’ response to micelle encapsulated paclitaxel treatment. Cell culture medium from sensitive and MDR variant of MDA-MB-231 cells treated with pure and capsulated drugs are processed through the device for exosome isolation. Drug volume in collected exosomes is determined after measurement. By measuring drug efflux through exosomes, it is determined that MDA-MB-231MDR cells do use an exosomal pathway to expel drugs, but other mechanisms are also at play. Nanoparticle encapsulation results in higher drug concentration in exosomes partly because the origin of exosomes and nanoparticle intake through endocytosis share some similar route. / text

The ability to control stem cell functions, particularly neuronal progenitors, has long since been believed to be the key to successful treatment of neurodegenerative disorders such as Alzheimer's, Parkinson's and accidents involving head trauma. The neurology field calls for many new solutions to address the controlled neural stem cell seeding and placement of cells for neural tissue regeneration. Self-assembled monolayers (SAM) from the alkanethiol group provide a straightforward applicable, reliable treatment for cell adhesion. An ODT/gold treatment was used to adhere the cells to patterned areas, due mainly to a high confluence of cells attracted to it, as well as the viable environment it produced for the cells. Arrays of micropillars, made of SU-8 photoresist, then covered with a thin film of gold and treated with the ODT, created scaffolding allowing manipulation of neural stem cells. Based on multiple trials of observing varying cross-sectional geometric parameters, metal layer thicknesses and the ODT/Gold treatment, this study explores seeding density control, base and circumferential cell population dependence on those parameters.

No description available.

Irradiation of metals with energetic particles causes heavy damage effects in microstructure and mechanical properties, which is closely associated with irradiation conditions, presence of impurities, and microstructural features. It has been proposed that the radiation tolerance of a certain material can be enhanced by introducing a high density of interfaces, acting as ‘sinks’ that can frequently involve in attracting, absorbing and annihilating defects. Nanostructured materials with large volume fraction of interfaces, therefore, are assumed to be more radiation tolerant than conventional materials. This thesis focuses on the radiation damage effects in nanostructured Cu via the methods of in-situ TEM (transmission electron microscope) radiation experiments, postirradiation TEM analyses, small-mechanical tests (nanoindentation and micro-pillar compression), and computer simulations (molecular dynamics and phase-field modeling). We design and fabricate nanostructured Cu using direct current (DC) magnetron sputtering deposition technique, a typica physical vapor deposition (PVD) method and a bottom-up way to construct various nanostructured metals. High-density twin boundaries (TBs) and nanovoids (NVs) are introduced into two distinct nanostructured Cu films, including nanovoid-nanotwinned (NVNT) Cu (111) and nanovoid (NV) Cu (110). The in-situ high-energy Kr⁺⁺ (1 MeV) and ex-situ low energy He⁺ (< 200 keV) irradiations are subsequently preformed on the as-deposited Cu samples. On the one hand, the in-situ TEM observations suggest that TBs and NVs can influence the formation, distribution and stability of radiation-induced defects. Meanwhile, the preexisting microstructures also undergo structural change through void shrinkage and twin boundary migration. On the other hand, the ex-situ micro-pillar compression tests reveal that the Heirradiated NV-NT Cu contains less defect clusters but experiences more radiation-induced hardening. The underlying mechanisms of void shrinkage, twin boundary migration, and radiationinduced hardening are fully discussed based on post-irradiation analyses and computer simulations.

Precise manipulation of heterogeneous droplets on an open droplet microfluidic platform could have numerous practical advantages in a broad range of applications, from proton exchange membrane (PEM) fuel cells and microreactors, to medical diagnostic platforms capable of assaying complex biological analytes. Toward the aim of developing electrically controllable micropost arrays for use in open droplet manipulation, custom-designed titanium dioxide (TiO2)- loaded poly(dimethylsiloxane) (PDMS) micropost arrays were developed in this work and indirectly mechanically actuated by applying an electric field. Initial experiments explored the bulk properties of TiO2-loaded PDMS films, with scanning electron microscopy (SEM) confirming a uniform TiO2 particle distribution in the PDMS, and tensile testing of bulk films showing an inverse relationship between TiO2 % (w/w) and Young’s Modulus with the Young’s Moduli quantified as 4.22 ± 0.51 MPa for unloaded PDMS, 2.27 ± 0.18 MPa for 10 % (w/w) TiO2, and 1.39 ± 0.20 MPa for 20 % (w/w) TiO2. Following bulk material evaluation, soft lithography methods were developed to fabricate TiO2- loaded PDMS micropost arrays. Mathematical predictions were applied to design microposts of varying shape, length, and gap spacing to yield super-hydrophobic surfaces actuatable by an electric field. Visual inspection and optical microscopy of the resulting arrays confirmed a non- collapsed micropost geometry. Overall, round microposts that were 100, 200, and 300 μm in length, 15 μm in diameter, and spaced 50 μm apart were produced largely free of defects, and used in contact angle measurements and micropost deflection experiments. Droplet contact angles measured on the arrays remained above 120° indicating the arrays successfully provided super- hydrophobic surfaces. Individual microposts deflected most notably above an electric field strength of 520 kV/m (12.5 kV nominal voltage). The ability to mechanically deflect customized microposts using an electric field demonstrated by this work is promising for translating this technology to precise droplet manipulation applications. Indirect actuation of droplets could enable the manipulation of liquids with varying electrical properties, which is a limitation of current micropumping technologies. Once optimized, electrically actuated micropost arrays could significantly contribute to the micro- handling of heterogeneous, highly ionic, and/or deionized fluids. / Thesis (Master, Chemical Engineering) -- Queen's University, 2013-03-03 17:25:49.785

The objective of this dissertation is to demonstrate the use of in situ TEM mechanical testing to find mechanical properties of as received, self-ion, and proton irradiated Fe-9%Cr ODS. The desire to work at small scale in the characterization of irradiated materials to reduce costs and improve throughput, require the development of novel methods to assess mechanical properties in volume-limited irradiation damage layers. Yet at these micrometer or nanometer scales, the mechanical properties can begin to be impacted by size effects. In this work micropillar compression, cantilever bending, lamellae indentation, and clamped beam fracture testing is conducted on ion-irradiated Fe-9%Cr ODS to find yield stress, elastic modulus, flow stress, and fracture toughness. Micropillars in compression allow us to define a minimum sample dimension, which approaches the obstacle spacing of the material, at which size effects are observed. This relationship between sample dimension and obstacle spacing defined through micropillar compression is extended to a new testing geometry, cantilever bending, and material property, flow stress. Lessons learned during the cantilever bending informed the clamped beam design for conducting fracture testing on a ductile engineering alloy at micrometer scales. Finally, lamellae indentation was conducted to link qualitative observations of the microstructure under load with literature strength of obstacle values. By combining an understanding of the microstructure of irradiated Fe-9%Cr ODS and the in situ TEM technique, one can find the bulk-like mechanical properties of ion irradiated Fe-9%Cr ODS.

<p><a>Aluminum (Al) alloys have been widely used in </a>industry as light-weight structural materials. However, the mechanical strength of the strongest Al alloys is still much lower than most high-strength steels. This thesis aims to investigate the fabrication and mechanical behaviors of nanotwinned high-strength Al alloys and multilayers.</p> <p>Twin boundaries are special grain boundaries with mirror symmetry. Twin boundaries can generate slip discontinuity and block the transmission of dislocations, and serve as dislocation sources to accommodate plasticity. However, twinning in Al is rare due to its high stacking fault energy and low unstable stacking fault energy. In this thesis, we used multiple methods to introduce high-density twins into Al and achieve outstanding mechanical properties and thermal stability. </p> <p>Certain type of solutes can greatly increase the twin density in Al by decreasing the stacking fault energy of Al and retarding the detwinning process. Nanotwinned Al-Ni and Al-Ti binary alloys fabricated by magnetron sputtering show high strength, good deformability, and unique deformation mechanisms. Furthermore, deformation and thermal stability of binary nanotwinned Al alloys can be enhanced by adding a third or fourth solute element. </p> <p>Interfaces can facilitate twin formation in Al as well. High-density twins and stacking faults were introduced into Al by using Al/Ti layer interfaces. Nanotwinned Al/Ti multilayers have ultra-high strength, superb deformability and thermal stability. This thesis provides promising pathways to fabricate Al alloys and composites with high strength and good thermal stability.</p>

Mechanical forces have been observed to affect various aspects of life, for example, cell differentiation, cell migration, locomotion and behavior of multicellular organisms etc. Such forces are generated either by external entities such as mechanical touch, fluid flow, electric and magnetic fields or by the living organisms themselves. Study of forces sensed and applied by living organisms is important to understand the interactions between organisms and their environment. Such studies may reveal molecular mechanisms involved in mechanosensation and locomotion. Several techniques have been successfully applied to measure forces exerted by single cells and cell monolayers. The earliest technique made use of functionalized soft surfaces and membranes as substrates on which cell monolayers were grown. The forces exerted by the cells could be measured by observing deformation of the substrates. Atomic Force Microscope (AFM) is another sensitive instrument that allows one to exert and measure forces in pico-Newton range. Advances in micromachining technology have enabled development of miniature force sensors and actuators. Latest techniques for mechanical force application and measurement use micromachined Silicon cantilevers in single as well as array form and micropillar arrays. Micropillar arrays fabricated using soft lithography enabled the use of biocompatible materials for force sensors. Together, these techniques provide access to a wide range of forces, from sub micro-Newton to milli-Newton. In the present work, types of forces experienced in biological systems and various force measurement and actuation techniques will be introduced. This will be followed by in depth description of the two major contributions of this thesis, 1) ―Colored polydimethylsiloxane micropillar arrays for high throughput measurements of forces applied by genetic model organisms‖. Biomicrofluidics, January 29, 2015. doi: 10.1063/1.4906905 2) ―Air microjet system for non-contact force application and the actuation of micro-structures‖. Journal of micromechanics and microengineering, December 15, 2015. doi: 10.1088/0960-1317/26/1/017001 Device developed for force measurement consists of an array of micropillars made of a biocompatible polymer Poly Dimethyl Siloxane (PDMS). Such devices have been used by researchers to measure traction forces exerted by single cells and also by nematode worm Caenorhabditis elegans (C. elegans). C. elegans is allowed to move in between the micropillars and the locomotion is video recorded. Deflection of the micropillar tips as the worm moves is converted into force exerted. Transparent appearance of C. elegans and PDMS poses difficulties in distinguishing micropillars from the worm, thus making it challenging to automate the analysis process. We address this problem by developing a technique to color the micropillars selectively. This enabled us to develop a semi-automated graphical user interface (GUI) for high throughput data extraction and analysis, reducing the analysis time for each worm to minutes. Moreover, increased contrast because of the color also delivered better images. Addition of color changed the Young‘s modulus of PDMS. Thus the dye-PDMS composite was characterized using hyper-elastic model. The micropillars were also calibrated using commercial force sensor. Analysis of forces exerted by wild type and mutant C. elegans moving on an agarose surface was performed. Wild type C. elegans exerted a total average force of 7.68 µN and an average force of ~1 µN on an individual pillar. We show that the middle of C. elegans exerts more force than its extremities. We find that C. elegans mutants with defective body wall muscles apply significantly lower force on individual pillars, while mutants defective in sensing externally applied mechanical forces still apply the same average force per pillar compared to wild type animals. Average forces applied per pillar are independent of the length, diameter, or cuticle stiffness of the animal. It was also observed that the motility of the worms with mechanosensation defects, lower cuticle stiffness, and body wall muscle defects was reduced with worms that have defective body wall muscle having the largest degree. Thus, we conclude that while reduced ability to apply forces affects the locomotion of the worm in the micropillar array, the reduced motility/locomotion may not indicate that the worm has reduced ability to apply forces on the micropillars. We also used the colored micropillar array for the first time to measure forces exerted by Drosophila larvae. Our device successfully captured the peristaltic rhythm of the body wall muscles of the larva and allowed us to measure the forces applied on each deflected pillar during this motion. Average force exerted by 1st instar wild type Drosophila larvae was measured to be ~ 1.5 µN per pillar. We demonstrated that a microjet of air can be used to apply forces in micro-Newton range. We developed a standalone system to generate a controlled air microjet. Microjet was generated using a controlled electromagnetic actuation of a diaphragm. With a nozzle diameter of 150 µm, the microjet diameter was maintained to a maximum of 1 mm at a distance of 5 mm from the nozzle. The force generated by the microjet was measured using a commercial force sensor to determine the velocity profile of the jet. Axial flow velocities of up to 25 m/s were obtained at distances as long as 6 mm. The microjet exerted a force up to 1 µN on a poly dimethyl siloxane (PDMS) micropillar (50 µm in diameter, 157 µm in height) and 415 µN on a PDMS membrane (3 mm in diameter, 28 µm thick). We also demonstrate that from a distance of 6 mm our microjet can exert a peak pressure of 187 Pa with a total force of about 84 µN on a flat surface with 8 V operating voltage. Next, we demonstrated that the response of C. elegans worms to the impinging air microjet is similar to the response evoked using a manual gentle touch. This contactless actuation tool avoids contamination and mechanical damage to the samples. Out of the cleanroom fabrication and robust design make this system cost effective and durable. Magnetic micropillars have been used as actuators. We fabricated magnetic micropillar arrays and designed actuation mechanisms using permanent magnet and a pulsed electromagnet. Force of about 19 µN was achievable using a permanent magnet actuation. In a pulsed electromagnetic field micropillar exerted a force of about 10 µN on a commercial force sensor. These techniques have promising applications when actuation needs to be controlled from long distances.