This research presents a system for mechanically characterizing single cells using automated micropipette aspiration. Using vision-based control and position control, the system controls a micromanipulator, a motorized translation stage, and a custom-built pressure system to position a micropipette (4 $\mu$m opening) to approach a cell, form a seal, and aspirate the cell into the micropipette for quantifying the cell's elastic and viscoelastic parameters as well as viscosity. Image processing algorithms were developed to provide controllers with real-time visual feedback and to accurately measure cell deformation behavior on the fly. Experiments on both solid-like and liquid-like cells demonstrated that the system is capable of efficiently performing single-cell micropipette aspiration and has low operator skill requirements. Once the system was validated, it was used to study voided urine cells. In this study, the mechanical properties of bladder carcinoma cells were investigated.

This research presents a system for mechanically characterizing single cells using automated micropipette aspiration. Using vision-based control and position control, the system controls a micromanipulator, a motorized translation stage, and a custom-built pressure system to position a micropipette (4 $\mu$m opening) to approach a cell, form a seal, and aspirate the cell into the micropipette for quantifying the cell's elastic and viscoelastic parameters as well as viscosity. Image processing algorithms were developed to provide controllers with real-time visual feedback and to accurately measure cell deformation behavior on the fly. Experiments on both solid-like and liquid-like cells demonstrated that the system is capable of efficiently performing single-cell micropipette aspiration and has low operator skill requirements. Once the system was validated, it was used to study voided urine cells. In this study, the mechanical properties of bladder carcinoma cells were investigated.

This thesis presents the experimental work performed on the spectrin protein. The aim of the work was to study the direct interactions of spectrin, the cytoskeleton of RBCs, with membrane lipid to determine its effects on the mechanical properties of the lipid bilayer. Motivation for this work came from a lack of unanimity in the field of spectrin, and the hypothesized potential of the protein to perforate giant unilamellar vesicles. The work aimed to investigate and determine how spectrin-lipid interactions influence membrane mesoscopic morphology and biophysics in ways that could ultimately be important to cellular function. For this purpose, a protocol was implemented to take into account the different aspects of the binding. Direct visualisation of the spectrin-lipid interaction and distribution was achieved using confocal fluorescence microscopy. Changes in the mechanical properties of the membrane were investigated using the micropipette aspiration technique. Finally the thermodynamics of the interaction were considered with isothermal titration calorimetry experiments. This allowed evaluation of the protein-lipid interaction in a complete and coherent manner. Experiments were also performed on another elastic protein, alpha-elastin, for comparison. In addition to its similarities with spectrin (both possess hydrophobic domains and entropy elasticity), elastin is auto-fluorescent which makes it an attractive model protein. Elastin was also used as a sample model to implement new techniques using nonlinear optics microscopy.

It would be beneficial to incorporate transmembrane proteins (TMPs) into biosensors, because TMPs are important for cell function in healthy and diseased states. These devices would employ an artificial cell membrane to maintain TMP function since cell membranes, which are mostly lipids, are necessary for the TMPs to function. These artificial lipid membranes must be robust for sensor applications. The ruggedness of these artificial membranes can be increased by using polymerizable lipids. Some polymerized lipid membranes exhibit increased stability, while successfully incorporating TMPs.Some polymerized membranes do not support the activity of certain TMPs, while maintaining the function of others. It is believed the physical properties of the membranes are important for TMP function. Some important physical properties of polymerizable lipid membranes have not yet been measured. Here, fluidity and mechanical properties of polymerizable dienoylPC lipid membranes were investigated.Fluorescence Recovery After Photobleaching was used to measure the fluidity of polymerizable dienoylPC membranes. Unpolymerized, UV-polymerized, and redox-polymerized membranes were investigated. Three types of membranes were found: fluid, partially fluid, and immobile. Unpolymerized and some polymerized membranes were fluid, while only polymerized membranes were partially fluid or immobile. Polymer size is believed to cause the differences in fluidity. This study highlights how polymerization parameters can influence membrane fluidity.Micropipette Aspiration was used to measure the mechanical properties of Giant Unilamellar Vesicles (GUVs) composed of dienolyPC lipids. Unpolymerized and UV-polymerized GUVs were investigated. Strength measurements showed that denoylPC GUVs were stronger than sorbylPC GUVs. Area expansion moduli of denoylPCs and mono-SorbPC GUVs were slightly lower than SOPC GUVs, while bis-SorbPC GUVs were substantially easier to stretch. The bending moduli of all GUVs was similar. UV-polymerization had no significant effect on the parameters. The difference in strength between denoylPCs and sorbylPCs is hypothesized to be due to the porous nature of sorbylPCs. It is thought UV-polymerization of these GUVs created polymers too small to significantly alter mechanical properties.It was demonstrated that some stable membranes are also fluid, which is important for the function of certain TMPs. A correlation cannot be made between the bending and stretching moduli of polymerizable membranes and function of TMPs.

The objective of this work is to develop an innovative and quantitative method to study cell failure under fluidic pressure to understand cell membrane mechanical properties. Due to lack of experimental data related to cell failure property, the current research focuses on investigating the cell failure using a micro pipette aspiration experiment method to elaborate gradually increasing hydrostatic pressure to the cell causing the membrane to deform and eventually rupture. Based on our observation, the prostate cancer cells (PC-3) deformed into a deflated and flattened shape under higher hydrostatic pressure (249 Pa) while prostate epithelial cells (PrEC LH) cells generate a spherical and rounded shape. The stress along the cell membrane was estimated from the curvature data captured from the 2D microscopic images for each pressure magnitude to quantify the damage before rupture state. From the results, non-transformed prostate epithelial cells (PrEC LH) presented a stiffer and rupture resilient property compared to transformed prostate cancer cells (PC-3) which presented a softer and vulnerable property. Besides, the alteration of shape of the aspirated membrane directly affected the stress distribution over the membrane and as a result, provoked membrane failure. Multiple pieces of research have shown a higher stiffness of healthy cells compared to cancer cells including one of the previous studies done by our group which have also found that cancer cell tends to become stiffer after exposing to fluid shear stress. The discovery of this cellular behavior and novel numerical quantification method of cell failure could advance the study of cancer cell membrane failure, cellular matrix structure, response to mechanical loadings and potentially foundation in developing new treatment for cancer other than destructive chemical treatment.

In an effort to help understand the mechanical properties of human platelets, their deformations were measured using micropipette experiments over an aspiration pressure range of 1-5 cmH2O, in steps of 1 cmH2O. The experiments confirmed the previously reported linear relationship between deformation and pressure. The experimental results were used to determine the material constants of a thin-axisymmetric shell model based on a strain-energy constitutive relation to describe the platelet deformations under aspiration. The model was successful in capturing the experimental deformations. It also suggested that the mechanical properties of human platelets are not significantly influenced by their volumes, but do vary depending on the platelets’ undeformed shape ratios. In addition, the model suggested that platelet membrane ruptures due to micropipette aspiration may be strain-related. The limitations of the experimental methods arising from direct contact with reactive cells such as platelets are highlighted, prompting the need for developing new methods which will not require the use of inhibition agents that alter the platelets’ mechanical properties. Afin d’approfondir les connaissances des propriétés mécaniques des plaquettes humaines, leurs déformations ont été mesurées lors d’expériences avec des micropipettes pour des pressions d’aspiration de 1-5 cmH2O, par intervalles de 1 cmH2O. Les expériences ont confirmé la relation linéaire entre les déformations et la pression d’aspiration telle que précédemment publié. Les données expérimentales ont été utilisées pour déterminer les constantes matérielles d’un modèle de membrane mince axisymétrique basé sur une loi de comportement caractérisant l’énergie de déformation. Le modèle simule bien les déformations des plaquettes sous aspiration; il suggère également que les propriétés mécaniques des plaquettes humaines ne sont pas influencées significativement leur volume, mais varient en fonction de leurs formes avant déformation. De plus, le modèle suggère que les ruptures de la membrane des plaquettes sous aspiration seraient reliées aux déformations. Les limites des méthodes expérimentales utilisées, du fait du contact direct avec des cellules aussi réactives que les plaquettes sont soulignées, et mettent l’emphase sur le besoin de mettre au point de nouvelles méthodes ne requérant pas d’agents d’inhibitions qui altèrent les propriétés mécaniques des plaquettes.

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Calcific aortic valve disease (CAVD) is associated with significant cardiovascular morbidity. While late-stage valve disease is well-described, there remains an unmet scientific need to elucidate early pathobiological processes. In CAVD, pathological differentiation of valvular interstitial cells (VICs) and lesion formation occur focally in the fibrosa layer. This VIC pathological differentiation has been shown to be influenced by matrix stiffness in vitro. However, little is known about the focal layer specific mechanical properties of the aortic valve in health and disease and how these changes in matrix moduli may influence VIC pathological differentiation in vivo. In this thesis, micropipette aspiration (MA) was shown to be capable of measuring the mechanical properties of a single layer in multilayered biomaterial or tissue such as the aortic valve, if the pipette inner diameter was less than the top layer thickness. With MA, the fibrosa of normal porcine aortic valves was significantly stiffer than the ventricularis; stiffer locations found only within the fibrosa were comparable to stiffnesses shown in vitro to be permissive to VIC pathological differentiation. Early CAVD was induced in a porcine model, which developed human-like early CAVD lesion onlays. Extracellular matrix remodeling occurred in the absence of lipid deposition, macrophages, osteoblasts, or myofibroblasts, but with significant proteoglycan-rich onlays and chondrogenic cell presence. These early onlays were softer than the collagen-rich normal fibrosa, and their proteoglycan content was positively correlated with Sox9 chondrogenic expression, suggesting that soft proteoglycan-rich matrix may be permissive to chondrogenic VIC differentiation. The findings from this thesis shed new light on early disease pathogenesis and improve the fundamental understanding of aortic valve mechanics in health and disease.

Calcific aortic valve disease (CAVD) is associated with significant cardiovascular morbidity. While late-stage valve disease is well-described, there remains an unmet scientific need to elucidate early pathobiological processes. In CAVD, pathological differentiation of valvular interstitial cells (VICs) and lesion formation occur focally in the fibrosa layer. This VIC pathological differentiation has been shown to be influenced by matrix stiffness in vitro. However, little is known about the focal layer specific mechanical properties of the aortic valve in health and disease and how these changes in matrix moduli may influence VIC pathological differentiation in vivo. In this thesis, micropipette aspiration (MA) was shown to be capable of measuring the mechanical properties of a single layer in multilayered biomaterial or tissue such as the aortic valve, if the pipette inner diameter was less than the top layer thickness. With MA, the fibrosa of normal porcine aortic valves was significantly stiffer than the ventricularis; stiffer locations found only within the fibrosa were comparable to stiffnesses shown in vitro to be permissive to VIC pathological differentiation. Early CAVD was induced in a porcine model, which developed human-like early CAVD lesion onlays. Extracellular matrix remodeling occurred in the absence of lipid deposition, macrophages, osteoblasts, or myofibroblasts, but with significant proteoglycan-rich onlays and chondrogenic cell presence. These early onlays were softer than the collagen-rich normal fibrosa, and their proteoglycan content was positively correlated with Sox9 chondrogenic expression, suggesting that soft proteoglycan-rich matrix may be permissive to chondrogenic VIC differentiation. The findings from this thesis shed new light on early disease pathogenesis and improve the fundamental understanding of aortic valve mechanics in health and disease.