Thesis (MEng) - Industrial Research Institute Swinburne, Swinburne University of Technology, 2003. / Thesis submitted for the degree of Master of Engineering by Research, Industrial Research Institute Swinburne, Swinburne University of Technology, 2003. Typescript. Includes bibliographical references (p. 159-169).

Thesis (Ph. D.)--Michigan State University. Dept. of Electrical and Computer Engineering, 2008. / Title from PDF t.p. (viewed on July 22, 2009) Includes bibliographical references (p. 294-312). Also issued in print.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2010. / Committee Co-Chair: Ajit Yoganathan; Committee Co-Chair: Ari Glezer; Committee Member: Rudy Gleason. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph.D.)--University of Iowa, 2006. / Includes separate files for thesis supplements. Supervisor: H.S. Udaykumar. Includes bibliographical references (leaves 182-195).

One of the major achievements in cardiac surgery over the past 30 years has been the ability to replace severely diseased heart valves with prosthetic ones. The option of using prosthetic heart valves for the treatment of valvular diseases has improved and prolonged many lives. This is reflected in around 120,000 heart valve replacement operations carried out every year in North America alone to correct the cardiovascular problems of stenosis, insufficiency, regurgitation, etc. The development of artificial heart valves depends on reliable knowledge of the hemodynamic performance and physiology of the cardiovascular system in addition to a sound understanding, at the fundamental level, of the associated fluid mechanics. It is evident from the literature review that noninvasive measurements in a confined area of complex transient geometry, providing critical information relating to valve performance, are indeed scarce. This thesis presents results of an extensive test program aimed at measuring turbulence stresses, steady and transient velocity profiles and their decay downstream of the mitral valve. Three mechanical tilting disc-type heart valves (Björk-Shiley convexo- concave, Björk-Shiley monostrut, and Bicer-Val) and two biological tissue valves (Hancock II and Carpentier-Edwards supraannular) are studied. The investigation was carried out using a sophisticated and versatile cardiac simulator in conjunction with a highly sensitive, noninvasive, two-component three-beam laser doppler anemometer system. The study covers both the steady (valve fully open) and pulsatile (resting heart rate) flow conditions. The continuous monitoring of the parametric time histories revealed useful details of the complex flow as well as helped establish location and timing of the peak parameter values. In addition, orientation experiments are conducted on the mechanical valves in an attempt to reduce stresses by altering the position of the major orifice. The experiments suggest correlation between high stresses and orientation. Based on the the data, the following general conclusions can be made: (i) Hemodynamic test results should be presented in nondimensional form to render them independent of test facilities, flow velocities, size of models, etc. This would facilitate comparison of results by different investigators, using different facilities and test conditions. (ii) The valves tested showed very disturbed flow fields which generated high turbulent stresses presenting a possibility of thromboembolism and, perhaps, haemolysis. (iii) Implantation orientation of the valve significantly affect the mechanical prostheses flow field. The single vortex formation in the posterior orientation results in a reduction in stresses compared to the anterior configuration. (iv) The present results together with the earlier information on pressure drop and regurgitation provide a comprehensive and organized picture of the valve performance. (v) The information is fundamental to the improvement in valve design, and development of guidelines for test methodology and acceptable performance criteria for marketing of the valves. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Graphene is a 2D material well known for its high intrinsic strength of 100 GPa and Young’s modulus of 1 TPa. Because of its 2D nature, the most promising avenues to utilize graphene as a mechanical material include incorporating it as reinforcement in a nanocomposite and creating free-standing foams and aerogels. However, the current techniques are not well-controlled – the reinforcing graphene particles are often discontinuous and randomly dispersed – making it difficult to accurately model and predict the resulting material properties. Here we aim to develop a framework for a new class of nanocomposites reinforced not by discrete nanoparticles, but by a continuous 3D graphene network. These 3D graphene networks were formed by chemical vapor deposition of graphene on periodic metallic microlattices, thereby providing mechanical reinforcement for the lattices. To assist in the lattice design, analytical models were derived for the mechanical properties of core/shell composite lattices and experimentally validated through compression testing of polymer lattices coated with electroless Ni-P. The models and experiments showed good agreement at lower shell thicknesses, while there was divergence at higher thicknesses, likely due to fabrication imperfections. The analytical models were also applied to hollow metallic lattices coated with graphene and compared to experimental data. The results showed that the models are plausible and suggest that graphene has a significant strengthening effect on the microlattices. These studies represent a paradigm shift in the design and fabrication of nanocomposites as one may now precisely prescribe the placement of the reinforcing nanomaterials. On a broader scale, this work also lays the framework for using a 2D material to span 3D space, enabling further exploration of 2D material properties and applications. One potential application area for a graphene-reinforced polymer composite is in prosthetic heart valves. The tissue of a human heart valve leaflet is heavily reinforced with networks of collagen and elastin fibers. One could similarly incorporate a graphene network as reinforcement within the polymeric leaflets of a prosthetic valve. One promising application of polymeric valves is in growth-accommodating implants for pediatric patients. Here we aim to develop a polymeric valved conduit that can be expanded by transcatheter balloon dilation to match a child’s growth. We designed the valve, characterized and selected materials, fabricated the devices and performed benchtop in vitro testing. The first generation of an expandable biostable valved conduit displayed excellent hydrodynamic performance before and after permanent balloon dilation from 22 to 25 mm. The second generation has shown the potential for a greater dilation from 12 to 24 mm. These results demonstrate concept feasibility and motivate further development of a polymeric balloon-expandable device to replace valves in children and avoid reoperations.

Diss. (sammanfattning) Stockholm : Karol. inst., 2002. / Härtill 6 uppsatser.

A Tissue Engineering (TE) approach to heart valve replacement has the aim of producing an implant that is identical to healthy tissue in morphology, function and immune recognition. The aim is to harvest tissue from a patient, establish cells in culture from this tissue and then use these cells to grow a new tissue in a desired shape for the implant. The scaffold material that supports the growth of cells into a desired shape may be composed of a biodegradable polymer that degrades over time, so that the final engineered implant is composed entirely of living tissue. The approach used at Swinburne University was to induce the desired mechanical and functional properties of tissue and is to be developed in an environment subjected to flow stresses that mimicked the haemodynamic forces that natural tissue experiences. The full attainment of natural biomechanical and morphological properties of a TE structure has not as yet been demonstrated. In this thesis a review of Tissue Engineering of Heart Valves (TEHVs) is presented followed by an assessment of biocompatible materials currently used for TEHVs. The thrust of the work was the design and development of a Bioreactor (BR) system, capable of simulating the corresponding haemodynamic forces in vitro so that long-term cultivation of TEHVs and/or other structures can be mimicked. A full description of the developed BR and the verification of its functionality under various physiological conditions using Laser Doppler Anemometry (LDA) are given. An analysis of the fluid flow and shear stress forces in and around a heart valve scaffold is also provided. Finally, preliminary results related to a fabricated aortic TEHV-scaffold and the developed cell culture systems are presented and discussed. Attempts to establish viable cell lines from ovine cardiac tissue are also reported.

Thesis (M.S.)--Chemical Engineering, Georgia Institute of Technology, 2003. / Sambanis Athanassios, Committee Member ; Sotiropoulos Fotis, Committee Member ; Yoganathan Ajit, Committee Chair. Includes bibliographical references (leaves 239-243).

Thesis (M.S.)--Chemical Engineering, Georgia Institute of Technology, 2004. / Sambanis Athanassios, Committee Member ; Sotiropoulos Fotis, Committee Member ; Yoganathan Ajit, Committee Chair. Includes bibliographical references (leaves 239-243).