This research program focuses on developing an attractive way to mitigate the adverse effects of high shear stress in cardiovascular hardware by investigating miniature, surface-integrated passive flow control elements (e.g., vortex generators, riblets, dimples, etc.). Blood damage caused by flow shear can cause thromboembolic complications that seriously limit the performance of a broad range of cardiovascular hardware including prosthetic valves, bypass pumps, and assist device. In particular, recent work with bileaflet mechanical heart valves has emphasized the significant risk of thromboembolic complications when blood elements are subjected to non-physiological hemodynamic shear stresses. Currently, patients with mechanical heart valves must undergo lifelong anti-coagulant therapy as a preventive measure against thromboembolic complications, but at an increased risk of hemorrhage and other secondary complications. An attractive way to mitigate the adverse effects of high shear stress in cardiovascular hardware is to use miniature, surface-integrated passive flow control elements (e.g., vortex generators, riblets, dimples, etc.) to alter the internal velocity distributions at known critical areas of high shear and thereby directly minimize these stresses. These passive flow control elements which in many cases have been bio-inspired, manipulate and manage secondary vorticity concentrations within the flow and thereby enhance cross stream mixing, momentum transfer, and alter local velocity and shear stress distributions. Although preliminary work demonstrates the viability of the approach, further exploration and optimization of various passive flow control configurations is necessary to take the technology to the next level. The broader impact of this research program is the development of a new design paradigm or technology, applicable to any cardiovascular hardware, based on the flow control principles developed here. The proposed work will focus on a simple cardiovascular test-bed system comprised of an idealized heart valve fitted with passive vortex generator arrays and other configurations. Different passive flow control configurations (rigid, flexible, geometries) will be explored and optimized. The effect of the secondary flow (streamwise vorticity) induced by the passive vortex generators on the momentary turbulent jet that forms when the leaflets close will be investigated in the pulsatile flow loop facility using highresolution, phase-locked particle image velocimetry (PIV). In addition to fluid mechanical evaluation, the pro-coagulant properties of optimized configurations of passive flow control configurations will be characterized and compared to a baseline flow in the absence of flow control. Similar to the recent preliminary blood investigations at Georgia Tech, the proposed blood studies will focus on measures of blood coagulation, platelet activation, and hemolysis. The study will directly involve participating Georgia Tech graduate and undergraduate students. Particular emphasis will be placed on collaboration and testing in configuration of practical interest.
This project is jointly funded by the Thermal Transport Processes (TTP) Program, the Biomedical Engineering (BME) Program, and the Fluid Dynamics (FD) Program, all of the Chemical, Bioengineering, Environmental, and Transport Systems (CBET) Division within the Directorate for Engineering (ENG).
It is well established that blood element damage and platelet activation that are caused by flow-induced shear stresses result in thrombus formation. These factors seriously limit the performance of a broad range of cardiovascular hardware including devices such as prosthetic valves, stents, bypass pumps and flow-assist device. In particular, recent work with bileaflet mechanical heart valves (MHVs) has emphasized the significant risk of thromboembolic complications when blood elements are subjected to artificial high level of shear stresses as it flows across these MHVs. Currently, patients with mechanical heart valves must undergo lifelong anti-coagulant therapy as a preventive measure against thromboembolic complications, but at an increased risk of hemorrhage and other secondary complications. An attractive way to mitigate the adverse effects of high shear stress in cardiovascular hardware is to use miniature, surface-integrated passive flow control elements (e.g., vortex generators, riblets, dimples, etc.) to alter the internal velocity distributions at known critical areas of high shear and thereby directly minimize these stresses. These passive flow control elements, which in many cases have been bio-inspired, manipulate and manage the flow patterns and thereby mitigating the blood damaging effects of these cardiovascular hardware.The overall hypothesis of this study is: Use of passive flow control methodologies in cardiovascular hardware to diminish the flow-induced stresses on blood elements significantly reduces blood damage and thromboembolic potential. It was proposed to address this hypothesis through three Specific Aims. Specific Aim 1: Develop and Optimize Surface-Mounted Passive Flow Control Elements for Reduced Shear. As part of this specific aim, passive flow control elements were designed, prototyped and tested. Both particle image velocimetry (PIV) and blood experiments involving freshly drawn human blood were used. The various flow control elements that were tested in a steady flow system before this grant period are being tested in the newly developed novel pulsatile system. Specific Aim 2: Explore Conformable Passive Flow Control Elements. Under this aim, it was proposed to investigate the effect of dynamic flexible flow control elements in reducing fluid energy loss, cavitation and structural stresses. Owing to a severe cut (50%) in the original proposed budget, Aim 2 was not included in the present work. Specific Aim 3: Quantify Pro-Coagulant Properties of Optimized Passive Flow Control Configurations. In this aim, a well-controlled physiologically accurate pulsatile test rig was built to test various flow control elements. Both PIV and blood damage experiments were carried out in parallel, to continuously refine and validate the design. Accomplishments Significant progress was made towards accomplishment of the grant goals despite the severe (50%) budget cut from the outset. Specifically, key accomplishments of the present work include: Design, construction, and validation of a low-volume biocompatible pulsatile flow facility that operates successfully under physiological flow and pressure conditions. Design of an optical system with the optical access necessary for high-resolution imaging and PIV measurements in the vicinity of the bi-leaflet valve. Realization of an integrated vortex generator design that enables radical changes in the induced flow through the valve and thereby mitigate the conditions that can lead to blood damage. Manuscripts Arjunon S., Saikrishnan N., Ardana Hidalgo P., Glezer A., Yoganathan A.P. "Design of low volume pulsatile tester to characterize thrombogenic potential of heart valves", in preparation for submission to ASME journal. Arjunon S., Saikrishnan N., Ardana Hidalgo P., Glezer A., Yoganathan A.P. "Reduction of blood damage in mechanical heart valves using flow control elements", in preparation for submission to ASME journal. Conference proceedings Wu J., Yun B.M., Fallon A.M., Simon H.A., Aidun C.K., Yoganathan A.P. "Numerical investigation of blood damage in the hinge area of bileaflet mechanical heart valves" (Oral Presentation) American Society of Mechanical Engineers: Summer Bioengineering Conference, Naples, FL. June 2010. Arjunon S., Saikrishnan N., Culp J., Dasi L.P., Vukasinovic J., Jones T., Bandari S., Glezer A., Yoganathan A.P., "Novel System to Quantify Thromboembolic Potential of Mechanical Heart Valves"; World Congress of Biomechanics, Singapore, August 2010. Yun B.M., Wu J., Simon H.A., Sotiropoulos F., Aidun C.K., Yoganathan A.P. "A numerical investigation of blood damage in the hinge area of bileaflet mechanical heart valves" (Oral Presentation) American Physical Society: Division of Fluid Dynamics, Long Beach, CA. November 2010. Zakharin B., Arjunon S., Saikrishnan N., Yoganathan A.P., Glezer A., "Mitigation of Shear-Induced Blood Damage by Mechanical Bileaflet Heart Valves"; 63rd Annual Meeting of the APS Division of Fluid Dynamics, Long Beach, November 2010.
