A novel mechanical aortic valve prosthesis design, mechanical analysis and prototype production

Today, although there are many different types of mechanical or biological aortic valve prosthesis, the lack of a model that can be considered ideal and suitable for every patient is the main motivation of this thesis study. In addition, computational fluid dynamics analysis for the analysis of mechanical design systems can only address one cardiac cycle by fluid-solid interaction simulation. A complete cardiac cycle was not established in any mechanical analysis with fatigue analyses for designs currently in development. Therefore, obtaining fatigue information for a design system requires performance of a bench-top physical tests. It is thought that the knowledge in the field and the current technology can be re-evaluated from a different perspective to contribute to this field of study. In line with the motivation of the study, the existing aortic prosthesis types were examined first and a new design that can be developed in a patient-specific and a practical way with today's technology was aimed. The proposed design, which is thought to be original, consists of two subsystems. The first is called Sub-System-1, which has a mechanism that allows the leaflets to open and close around a single pivot axis. The SubSystem-2 design was developed based on the images of a healthy person, the design method was developed such that it could be adapted to patients with aortic constriction or congenital bicuspid aortic valve. Therefore, the entire design and the design method was presented to Akdeniz University Technology Transfer Office, Patent Office under the title of "Novel Aortic Prosthesis Design and Patient-Specific Design Method" with an up-to-date invention notification form. In the mechanical analysis part of the study, the prosthesis problem was considered in as linear intervals as possible, it has been shown that the analysis of the system was possible for a complete cardiac cycle in the ANSYS Workbench program. The fixed support from the boundary conditions required for the analysis was defined in the Modal Analysis, then the load vectors affecting the prosthesis from the annulus and aorta sections were applied in the Transient Analysis. Particularly, by starting from the expanded Bernoulli work-energy equation, the equations were derived while calculating the load conditions, the problem conditions were presented step by step. Today, it is known that the left ventricle acts as a pulsatile pump and the blood flow is turbulent, especially during the systole phase. Therefore, to be able to calculate the dynamic pressure difference, the difference coefficient was thought to be directly proportional to the Reynolds number and inversely proportional to the Womersley number. Hence, the friction factor, ƒ in the pressure difference equation for loss, was taken as the difference coefficient, where that was called as the dynamic pressure difference equation in this study. Additionally, the hydrostatic pressures were estimated by the modified Bernoulli equation and the summation of the dynamic and static pressures was used separately for the aortic and annular positions. In this study, the preliminary prototype production was carried out by selecting the existing technology and materials that could be analysed, since the design was intended to be produced by three-dimensional printing. For this reason, the materials used in the prosthesis design were chosen as titanium alloy (Ti6Al4V, annealed) for the Subsystem-1 parts (leaflets, ring, axle) and rubber, silicone for the Subsystem-2 (aortic root) model. According to transient analysis results, the directional deformation for leaflets of 9 mm radius, were maximum 7.46 mm in -y direction and 2.95 mm in +y direction, during systole. In the diastole phase, the leaflets were in closed position, in contact with the inner surface of the aortic root model. The fatigue analyses were obtained according to Equivalent von-Mises stress values for 1 cardiac cycle was set as 1sec and the result of the life analysis was found to be 10^8 cardiac cycles which has suggests that the results of the study are confirmative. Therefore, this design might be considered in the future projects to perform fluid-solid interaction simulations and accompanying invitro tests to compare flow and mechanical analysis results. Subsequently, in-vivo tests might be foreseen by following patient-specific designs and analysis methodology.