This thesis examines the dynamics of the formation of tethers, which are tubes of lipids 20 - 200 nm in diameter. In particular, this work investigates how the loading rate affects the observed threshold force at which a tether forms from a vesicle membrane. Tether dynamics are important to a myriad of biological processes such as signaling when white blood cells adhere to the walls of healthy and diseased blood vessels, or in the transport of intracellular material between neighboring cells. To understand the dynamics of tether formation in such systems more fully, the studies presented in this thesis focus on the dependence of the force needed to create a tether on the rate of force change. To conduct these experiments, I combined, for the first time, a microfabricated magnetic force transducer, or a microscale device that generates well-controlled and localized magnetic fields, and microaspiration, a technique to apply known tension to a lipid membrane. Using the combined global and local mechanical control of the joint system, I discovered a strong correlation between the threshold force of tether formation and the applied force ramp. An energy model, based upon that used to describe membrane rupture, characterized the observed dependencies and provided a mechanism to examine physically relevant quantities within the system. The usefulness of this combined approach was further substantiated by determining the influence of membrane modulators, including cholesterol, tension, adhesion site concentration, and phosphatidylserine, on the dependence seen between force threshold and force rates. Additionally, application of the experimental technique developed in this thesis led to the calculation of the inter-layer drag coefficient between membrane leaflets and to the first measurements of the thermal expansivity in aspirated 1-stearoy1-2-oleoyl- sn -glycero-3-phosphatidylcholine vesicles. This new tool for dynamic studies of membrane mechanics may further be extended to study how tethers form off of flowing cells or how phase regimes, induced by the presence of cholesterol, influence membrane dynamics.

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Persons with paraplegia who use a manual wheelchair for mobility are at high risk for overuse injuries in the upper extremities. Years of shoulder overuse performing transfers, wheelchair propulsion, dressing, bathing, and household chores, (activities of daily living or ADL) leads to an increased incidence of cumulative trauma to the shoulders. Few studies have addressed the stressful task of wheelchair transfers among SCI individuals. The goal of this pilot study is to develop valid and reliable measurement technologies to quantify shoulder musculoskeletal stressors during wheelchair transfers and pressure relief tasks among individuals with SCI. Using a standard wheelchair, 10 participants were asked to perform 3 typical pairs of independent transfer tasks: wheelchair to/from bed, wheelchair to/from commode, and wheelchair to/from vehicle. Also, two pressure relief tasks (P/R) were performed sitting in a wheelchair, one using the armrest and one using the wheels. By observation, the transfers in descending order from the most demanding to the least demanding were as follows: vehicle, commode, and bed. During a P/R using the wheels there is a 40% greater max shoulder force and a 47% greater mean shoulder force than when using the armrest. The max shoulder force of over 1000 N is generated at the initial push off, during a P/R using the wheels, then the force drops 45% to an average of 558 N. The max shoulder force of 722 N at the initial push off, during a P/R using the Armrest, drops 48% and then averages 378 N. During a P/R using the wheels there is a 104% greater max shoulder torque and a 17% greater mean shoulder torque than when using the armrest. As in the initial large amount of shoulder force there is also a large amount of shoulder torque that drops 77% during a P/R using the wheels. The shoulder torque decreases 62% during a P/R using the armrest. Because of the greater distance the body's Center of Mass (COM) travels during the P/R using the armrest, 24% more work is done.

The aim of this thesis is to investigate the potential of replacing the material 1.4418 (R87), currently used in ABB's PFCL201 load cells, with the material 1.402 (R03). Both materials possess desirable properties, including high strength, toughness and magnetoelastic characteristics, making them suitable for force transducer applications in strip tension systems. However, the scarcity and high cost of R87 necessitate exploring the feasibility of utilizing the more affordable and easily obtainable R03. The research methodology involved a combination of mechanical and thermal simulations, as well as the evaluation of prototype measurements made from R03. Mechanical simulations were conducted to identify a new load cell geometry that would facilitate the use of R03, while thermal simulations focused on comparing the thermal properties of R03 with real-life measurements. Furthermore, prototypes made from R03 were tested to investigate the transducer characteristics of the material. Lastly, a cost analysis was performed, comparing the manufacturing costs associated with R87 and R03. The study yielded promising results. R03 improves the manufacturing process and significantly reduces the costs related to it. A new load cell geometry was identified, which could be manufactured using existing resources at the factory. Thermal simulations demonstrated improvements in the thermal properties when employing R03. However, measurements of the PFCL201-20 kN load cell made from R03, indicated that to maintain the same accuracy class and commutation angle as the current R87 load cells, the nominal load would need to be adjusted to 12 kN instead of 20 kN. Nonetheless, with the identified geometric modifications, R03 load cells could still be utilized as 20 kN load cells. Alternatively, by changing either the accuracy class or commutation angle. This research provides valuable insights into the possibility of replacing the expensive and scarce R87 material with the more cost-effective and readily available R03 in ABB's PFCL201 load cells. The findings offer a foundation for future studies and potential business decisions regarding material selection and load cell design optimization.