Cell adhesion to extracellular matrix (ECM) is critical to various cellular processes like cell spreading, migration, growth and apoptosis. At the tissue level, cell adhesion is important in the pathological and physiological processes that regulate the tissue morphogenesis. Cell adhesion to the ECM is primarily mediated by the integrin family of receptors. The receptors that are recruited to the surface are reinforced by structural and signaling proteins at the adhesive sites forming focal adhesions that connect the cytoskeleton to further stabilize the adhesions. The functional roles of these focal adhesions extend beyond stabilizing adhesions and transduce mechanical signals at the cell-ECM interface in various signaling events. The objective of this research is to analyze the role of the spatial distribution of the focal adhesions in stabilizing the cell adhesion to the ECM in relation to cell's internal force balance. The central hypothesis was that peripheral focal adhesions stabilize cell adhesion to ECM by providing for maximum mechanical advantage for resisting detachment as explained by the membrane peeling mechanism. Micropatterning techniques combined with robust hydrodynamic shear assay were employed to test our hypothesis. However, technical difficulties in microcontact printing stamps with small and sparse features made it challenging to analyze the role of peripheral focal adhesions in stabilizing cell adhesion. To overcome this limitation, the roof collapse phenomenon in stamps with small and sparse features (low fill factor stamps) that was detrimental to the reproduction of the adhesive geometries required to test the hypothesis was analyzed. This analysis lead to the valuable insight that the non-uniform pressure distribution during initial contact caused by parallelism error during manual microcontact printing prevented accurate replication of features on the substrate. To this end, the template of the stamp was modified so that it included an annular column around the pattern zone that acted as a collapse barrier and prevented roof collapse propagation into the pattern zone. Employing this modified stamp, the required geometries for the cell adhesion analysis were successfully reproduced on the substrates with high throughput. Adhesive areas were engineered with circular and annular patterns to discern the contribution of peripheral focal adhesions towards cell adhesion strength. The patterns were engineered such that two distinct geometries with either constant adhesive area or constant spreading area were obtained. The significance of annular patterns is that for the same total adhesive area as the circular pattern, the annular pattern provided for greater cell spreading thereby increasing the distance of the focal adhesions from the cell's center. The adhesion strength analysis was accomplished by utilizing hydrodynamic shear flow in a spinning disk device that was previously developed. The results indicate that for a constant total adhesive area, the annular patterns provide for greater adhesion strength by enhancing cell spreading area and providing for greater moment arm in resisting detachment due to shear. The next examination was the effect of the cell's internal force balance in stabilizing the cell adhesion. The working hypothesis was that microtubules provide the necessary forces to resist the tensile forces expressed by the cell contractile machinery, thereby stabilizing cell adhesion. Since microtubule disruption is known to enhance cell contractility, its effect on the cell adhesion strength was examined. Moreover, the force balance in cells was altered by engineering adhesive areas so that the cells were either spherical or completely spread and then disrupted microtubules to understand the significance of the force balance in modulating the cell adhesion strength. The results indicated that disruption of microtubules in cells on adhesive islands resulted in a 10 fold decrease in adhesion strength compared to untreated controls whereas no significant change was observed in completely spread cells between treated and untreated controls. This is in surprising contrast to the previous contractility inhibition studies which indicate a less pronounced regulation of adhesion strength for both micropatterned and spread cells. Taken together, these findings suggest that the internal force balance regulated by cell shape strongly modulates the adhesion strength though the microtubule network. In summary, this project elucidates the role of peripheral focal adhesions in regulating the cell adhesion strength. Furthermore, this study also establishes the importance of the internal force balance towards stabilizing the cell adhesion to the ECM through the microtubule network.

This research project has investigated the mechanical properties and behaviour of third generation synthetic turf surfaces used for football and rugby, with a focus on the traction behaviour produced at the shoe-surface interface. The physical characteristics and mechanical properties of the component materials used in the construction of third generation surfaces were examined. The bulk density of the rubber infill material was found to be a key variable. This was shown to be influenced by compaction and the resulting compression of the rubber infill material under an applied load. Increasing the compactive effort and/or compression under loading increased the bulk density. Shear strength of the rubber infill material was shown to be influenced by bulk density, increasing with a higher bulk density. The composite surface system behaviour of third generation synthetic turf surfaces was investigated. Several surface variables were measured including; shockpad thickness, synthetic turf carpet construction, infill thickness, infill bulk density and infill material type. Shockpad thickness, rubber infill thickness and bulk density were found to influence the impact behaviour, with a thicker rubber layer (shockpad and/or rubber infill layer) reducing the hardness of a surface system. Increasing the bulk density of the rubber infill with compactive effort increased the surface system hardness. Traction behaviour of composite surface systems was explored using three traction test methods to measure both rotational and translational traction. Rubber infill bulk density was shown to be a primary influencing variable from the playing surface variables investigated. Several further traction variables were explored to provide a fuller understanding of the mechanisms involved in the production of traction at the shoe-surface interface including; vertical stress, stud configuration, stud dimension, stud penetration, water and temperature. Vertical stress and stud configuration were found to be primary variables influencing traction development. A traction framework has been developed identifying the factors affecting the production of traction at the shoe-surface interface. It is intended that the traction framework can be used by the sports surface industry, sports governing bodies and academia to aid in the decisions and judgements made during the design, construction and maintenance of these surfaces to obtain desired characteristics and optimise performance and safety.

Die vorliegende Arbeit verfolgt als Ziel Algorithmen zur anwendungsbezogenen Komponen-tenauswahl und Antriebskonfiguration dieselelektrischer Schienenfahrzeuge zu entwickeln und umzusetzen. Aus modellierten Einzelkomponenten werden automatisiert virtuelle Antriebsstränge generiert, anhand einer vorgebbaren Transportaufgabe simulationstechnisch bewertet und miteinander verglichen. Aus den Berechnungsergebnissen kann die für die vorgegebenen Randbedingungen am besten geeignete Antriebskonfiguration ermittelt werden. Zum Verifizieren der Ergebnisse wurden messtechnische Untersuchungen durch-geführt.

Cell migration is a fundamental biological process involved in tissue development, wound repair, and diseases such as cancer metastasis. It is a biomechanical process involving the adhesion of a cell to a substratum, usually an elastic extracellular matrix, as well as the physical contraction of the cell driven by intracellular actomyosin network. In the migration of cells as a group, known as collective migration, the cells are also physically linked to one another through cell-cell adhesions. How mechanical interactions with cell substratum and with neighboring cells regulate movements during collective migration, nevertheless, is poorly understood. To address this question, the effects of substrate stiffness on sheet migration of MCF10A epithelial cells were systematically analyzed. Speed, persistence, directionality and coordination of individual cells within the migrating sheet were all found to increase with substrate stiffening. Substrate stiffening also enhanced the propagation of coordinated movement from the sheet edge into the monolayer, which correlated with an upregulation of myosin-II activity in sheet edge cells. This mechano-response was dependent on cadherin-mediated cell-cell adhesions, which are required for the transmission of directional cue. Importantly, myosin-II contractility modulated cadherin- dependent cell-cell coordination, suggesting that contractile forces at cadherin adhesions regulate collective migration. To measure forces transmitted through cell-cell adhesions, a quantitative approach was developed in which cell-cell forces were deduced from cell-substrate traction forces, based on force balance principles and simple cell mechanics modeling. This method enabled the analysis of cell-cell mechanical interactions in small cell clusters of complex topology. The dynamic fluctuations of cell-cell forces over time revealed that force transmission between non-adjacent cells is typically limited, but is enhanced when the cell across which forces are being transmitted has reduced myosin-IIA or talin-1. This suggests that cells in a group may differentially regulate their levels of myosin-II contractility and cell-matrix mechanotransduction to promote longer-range force transmission during collective migration. Together, the results in this dissertation led to a working model of collective cell migration as regulated by cell-matrix mechanical properties and cell-cell mechanical interactions. This model, as well as the quantitative techniques developed here, will drive future studies on the mechanisms underlying collective migration.

No description available.

Electric mobility scooters are increasing in popularity and are used extensively by individuals with mobility impairments to conduct activities of daily living. Scientific literature on the safety and efficacy of scooters in winter conditions is sparse and the current technical standards for scooters do not mandate testing in these conditions. This study paves the way for more rigorous standard testing by: 1) Describing a novel, motion-capture based method to quantify the tractive performance of scooters; 2) Describing methods to create a wide variety of simulated winter conditions; 3) Presenting pilot-test results of a scooter driven in these winter conditions. The outcomes of this study are significant because it is the first study to evaluate the performance of a scooter in winter conditions. Furthermore, it constitutes the first phase of a broader initiative to develop a rigorous, new winter test method for scooters and drive improvements in safety, performance and design.

Electric mobility scooters are increasing in popularity and are used extensively by individuals with mobility impairments to conduct activities of daily living. Scientific literature on the safety and efficacy of scooters in winter conditions is sparse and the current technical standards for scooters do not mandate testing in these conditions. This study paves the way for more rigorous standard testing by: 1) Describing a novel, motion-capture based method to quantify the tractive performance of scooters; 2) Describing methods to create a wide variety of simulated winter conditions; 3) Presenting pilot-test results of a scooter driven in these winter conditions. The outcomes of this study are significant because it is the first study to evaluate the performance of a scooter in winter conditions. Furthermore, it constitutes the first phase of a broader initiative to develop a rigorous, new winter test method for scooters and drive improvements in safety, performance and design.

Le processus de migration est un processus moléculaire intégré qui contribue in vivo à de nombreux processus physiologiques de motilité, comme le développement, la surveillance immunitaire et les métastases du cancer. Pour comprendre la migration cellulaire, il est nécessaire de considérer l'environnement de la cellule, le type de cellules et la morphologie ainsi que l'organisation interne, i.e. son cytosquelette et ses adhérences focales. Ce travail se concentre sur l'étude de la migration de cellules cancéreuses de la vessie sur des supports déformables. L'analyse de trois lignées cellulaires de capacité métastatique différente est présentée. La capacité des cellules cancéreuses à réagir à leur environnement est analysée et le processus de migration est décrit en termes de contraintes de traction. La réorganisation interne de la structure des cellules est étudiée par l'observation microscopique des filaments d'actine, des moteurs de myosine et des sites de transmission de force, i.e. les adhésions focales. On s'intéresse à la relation de complémentarité entre les différentes capacités invasives des cellules cancéreuses, les forces de traction ainsi que les forces exercées sur le lamellipode et les structures internes des cellules. Il est constaté que plusieurs paramètres peuvent être utilisés pour discriminer la capacité métastatique, comme le type de migration, les forces de traction, les zones focales d'adhésion, ainsi que l'indice de diffusivité de migration. Cette étude constitue donc une première tentative pour différencier diverses cellules invasives en utilisant la migration sur des substrats mous.

Living organisms are made up of a multitude of individual cells that are surrounded by biomolecules and fluids. It is well known that cells are highly regulated by biochemical signals; however it is now becoming clear that cells are also influenced by the mechanical forces and mechanical properties of the local microenvironment. Extracellular forces causing cellular deformation can originate from many sources, such as fluid shear stresses arising from interstitial or blood flow, mechanical stretching during breathing or compression during muscle contraction. Cells are able to sense variations in the mechanical properties (elasticity) of their microenvironment by actively probing their surroundings by utilizing specialized proteins that are involved in sensing and transmitting mechanical information. The actin cytoskeleton and myosin-II motor proteins form a contractile (actomyosin) network inside the cell that is connected to the extracellular microenvironment through focal adhesion and integrin sites. The transmission of internal actomyosin strain to the microenvironment via focal adhesion sites generates mechanical traction forces. Importantly, cells generate traction forces in response to extracellular forces and also to actively probe the elasticity of the microenvironment. Many studies have demonstrated that extracellular forces can lead to rapid cytoskeletal remodeling, focal adhesion regulation, and intracellular signalling which can alter traction force dynamics. As well, cell migration, proliferation and stem cell fate are regulated by the ability of cells to sense the elasticity of their microenvironment through the generation of traction forces. In vitro studies have largely explored the influence of substrate elasticity and extracellular forces in isolation, however, in vivo cells are exposed to both mechanical cues simultaneously and their combined effect remains largely unexplored. Therefore, a series of experiments were performed in which cells were subjected to controlled extracellular forces as on substrates of increasing elasticity. The cellular response was quantified by measuring the resulting traction force magnitude dynamics. Two cell types were shown to increase their traction forces in response to extracellular forces only on substrates of specific elasticities. Therefore, cellular traction forces are regulated by an ability to sense and integrate at least two pieces of mechanical information - elasticity and deformation. Finally, this ability is shown to be dependent on the microtubule network and regulators of myosin-II activity.

No description available.