Long-term patency of a polymer vein valve

Chronic Venous Insufficiency (CVI) is a condition in present in almost 27% of adults in which an insufficient amount of blood is pumped back to the heart due to damaged or poorly apposed one-way valves in the leg veins. During forward flow, vein valves allow blood to return to the heart while posing very little resistance to the flow. During gravity-driven reverse flow, normal valves close and prevent blood from flowing backward through the valve. Incompetent, or damaged, vein valves cannot prevent this reverse flow and lead to a pooling of blood at the feet. CVI is a painful disease presents itself in various ways, including varicose veins, ulcerations of the lower extremities, and severe swelling. Current therapies and treatments include compressive stockings, destruction or removal of affected veins, valve repair, and valve transplants. The implantation of prosthetic vein valves is a future treatment option that does not require an invasive surgery, human donor, or lengthy hospital stay. While no prosthetic vein valves are currently commercially available, this thesis describes the design, verification, and validation of a novel prosthetic vein valve. Verification tests include CFD simulations, functional tests, mechanical tests, and in vitro thromogenicity tests. The validation of the device was done through an animal study in sheep external jugular veins. CFD analysis verified that shear rates within the valve support its lower thrombogenicity as compared to a previous vein valve. Benchtop tests demonstrate superiority in short-term patency over a previous polymer valve. In a sheep study, patency was shown at 6 weeks, surpassing many autograft valves and showing great potential to meet the goal of 3 month patency in sheep.M.S.Committee Chair: Ku, David; Committee Member: Gleason, Rudolph; Committee Member: Milner, Ros

A parametric investigation of transcatheter aortic valve replacement performance

While transcatheter aortic valve replacement (TAVR) has many advantages over surgical replacement, it is a young technology with little evidence of long-term effectiveness. As such, there is an ever-growing need to understand factors which can lead to poor patient outcomes. Two such scenarios where there are gaps in knowledge are valve-in-valve (VIV) procedures (a failing surgical bioprosthesis replaced by a transcatheter heart valve (THV)) and THV leaflet thrombosis. While VIV may restore function to a failing bioprosthesis, adverse events such as elevated pressure pressure gradients, device malpositioning, coronary obstruction, and valve thrombosis are not uncommon. Changes in local hemodynamics around the valve have been implicated in THV thrombosis, however there is currently no understanding of how anatomical, hemodynamic, and deployment factors affect thrombosis presence and severity in TAVR. The work presented in this dissertation aims to clarify which surgical and transcatheter prosthesis type, size, and deployment position will yield the most favorable performance while minimizing adverse events. In addition, this study provides possible mechanistic explanations for the presence of TAVR leaflet thrombosis. These phenomena are investigated through novel analyses of clinical data and innovative in vitro experimental techniques. Understanding the complex interplay between anatomical, deployment, and hemodynamic conditions in such complex scenarios will help inform clinical practice and guide the development of improved next-generation valve replacements.Ph.D

Mechanical Advantage of a Compliant Mechanism and Significant Factors Affecting IT, Using the Pseudo-Rigid-Body Model Approach

Although work related to mechanical advantage of compliant mechanisms has been presented almost two decades ago, unlike many rigid-body mechanism systems, this performance measure has seldom been used. In great part, the reasons are attributed to, one, the relatively recent development of and a lack of familiarity with this technology and, two, the complexity of the understanding and evaluation of mechanical advantage of compliant systems. In an effort to simplify the evaluation, this work uses the pseudo-rigid-body model (PRBM) of a compliant mechanism, along with traditional notions of power conservation and angular velocity ratios using instant centers. As a first step, the inherent compliance in the mechanism is neglected in determining its mechanical advantage, followed by considerations to optimize its structural configuration for enhancing its mechanical advantage. The PRBM methodology, which offers us a way to estimate the characteristic compliance of the mechanism, now enables its inclusion in determining the mechanical advantage of the compliant mechanism. Two significant factors affecting it are i) the structural configuration of the PRBM, and ii) the energy stored in compliant elements of the mechanism. Several case studies are presented, which suggest that minimizing the latter contribution relative to that of an optimized structural configuration may improve the mechanical advantage of a compliant mechanism. Nonetheless, its effect on the mechanical advantage cannot be neglected

Cold extruded rods : residual stresses and mechanical properties

Cold extruded rods : residual stresses and mechanical propertie

Computer simulation of morphology and packing behaviour of irregular particles, for predicting apparent powder densities

This paper describes a methodology for prediction of powder packing densities which employs a new approach, designated as random sphere construction (RSC), for modelling the shape of irregular particles such as those produced by water atomization of iron. The approach involves modelling an irregular particle as a sphere which incorporates smaller corner spheres located randomly at its surface. The RSC modelling technique has been combined with a previously developed particle packing algorithm (the random build algorithm), to provide a computer simulation of irregular particle packings. Analysis of the simulation output data has allowed relationships to be established between the particle modelling parameters employed by the RSC algorithm, and the density of the simulated packings. One such parameter is η, which is the number of corner spheres per particle. A relationship was established between η (which was found to have a profound influence on packing density), and the fractional density of the packing, fd. Vision system techniques were used to measure the irregularity of the simulated particles, and this was also related to η. These two relationships were then combined to provide a plot of fractional density for a simulated packing against irregularity of the simulated particles. A comparison was made of these simulated packing densities and observed particle packing densities for irregular particles, and a correlation coefficient of 0.96 was obtained. This relatively good correlation indicates that the models developed are able to realistically simulate packing densities for irregular particles. There are a considerable number of potential applications for such a model in powder metallurgy (PM), process control. In combination with on-line particle image analysis, the model could be used to automatically predict powder densities from particle morphology

Exploring the Use of Functional Models in Biomimetic Conceptual Design

The biological world provides numerous cases for analogy and inspiration. From simple cases such as hook and latch attachments to articulated-wing flying vehicles, nature provides many sources for ideas. Though biological systems provide a wealth of elegant and ingenious approaches to problem solving, there are challenges that prevent designers from leveraging the full insight of the biological world into the designed world. This paper describes how those challenges can be overcome through functional analogy. Through the creation of a function-based repository, designers can find biomimetic solutions by searching the function for which a solution is needed. A biomimetic function-based repository enables learning, practicing, and researching designers to fully leverage the elegance and insight of the biological world. In this paper, we present the initial efforts of functional modeling biological systems and then transferring the principles of the biological system to an engineered system. Four case studies are presented in this paper. These case studies include a biological solution to a problem found in nature and engineered solutions corresponding to the high-level functionality of the biological solution, i.e., a housefly\u27s winged flight and a flapping wing aircraft. The case studies show that unique creative engineered solutions can be generated through functional analogy with nature

Exploring the Use of Functional Models as a Foundation for Biomimetic Conceptual Design

The natural world provides numerous cases for analogy and inspiration. From simple cases such as hook and latch attachments to articulated-wing flying vehicles, nature provides many sources for ideas. Though biological systems provide a wealth of elegant and ingenious approaches to problem solving, there are challenges that prevent designers from leveraging the full insight of the biological world into the designed world. This paper describes how those challenges can be overcome through functional analogy. Through the creation of a function-based repository, designers can find biomimetic solutions by searching the function for which a solution is needed. A biomimetic function-based repository enables learning, practicing and researching designers to fully leverage the elegance and insight of the natural world. In this paper, we present the initial efforts of functional modeling natural systems and then transferring the principles of the natural system to an engineered system. Four case studies are presented in this paper. These case studies include a biological solution to a problem found in nature and engineered solutions corresponding to the high level functionality of the biological solution, i.e., a fly\u27s winged flight and a flapping wing aircraft. The case studies show that unique, creative engineered solutions can be generated through functional analogy with nature

Exploring the Use of Functional Models in Biomimetic Conceptual Design

The biological world provides numerous cases for analogy and inspiration. Fro