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    3D Modeling of Self-Expandable Valves for PPVI in Distinct RVOT Morphologies
    (Springer, 2026) Odemis, Ender; Aka, Ibrahim Basar; Kizilkaya, Mete Han
    Tetralogy of Fallot often requires transannular patch repair, leading to pulmonary insufficiency. Percutaneous pulmonary valve implantation (PPVI) with self-expandable valves offers a promising alternative, especially for enlarged right ventricular Queryoutflow tracts (RVOT). Five RVOT types identified in patients with Tetralogy of Fallot reflect anatomical variations due to disease and prior surgeries. This study assesses the Pulsta THV (R) valve's in vitro hemodynamic performance across these RVOT morphologies using 3D-printed models. Five RVOT morphologies were recreated as 3D models from patient-specific imaging data. The Pulsta THV (R) valves, available in 28, 30, and 32 mm sizes, were evaluated using the ViVitro Pulse Duplicator System at three cardiac outputs (2, 3.5, and 5 L/min). Hemodynamic performance was assessed by measuring regurgitation rates and pressure gradients in the left and right pulmonary arteries. The Pulsta THV (R) performed optimally in RVOT Types 1 and 2, demonstrating lower regurgitation rates and pressure gradients, particularly with larger valve sizes. Conversely, RVOT Types 3 and 5 showed increased pressure gradients and hemodynamic variability, indicating less favorable outcomes. The results highlighted the critical role of precise anatomical compatibility, with larger valve sizes proving more effective in enlarged RVOT geometry. Valve sizes tailored to specific RVOT morphologies can enhance PPVI outcomes. Types 1 and 2 are ideal for PPVI, while Types 3 and 5 present challenges due to hemodynamic variability. This study supports 3D modeling and in vitro testing for pre-procedural planning to reduce complications, with future research exploring dynamic imaging and materials mimicking tissue properties.
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    A complete LPM-CFD Coupling on a Dummy Aortic Model
    (IEEE, 2022) Aka, Ibrahim Basar; Yildirim, Canberk
    Computational fluid dynamics (CFD) has become a widely used method for solving complex fluid problems. However, it is still evolving in the field of biomedical engineering. The reason why the CFD method in the biomedical field lags behind other engineering fields is the complex structure of the flows in the human body. Apart from CFD analyses, using lumped parameter models (LPM), flows and pressures in the human circulation can be simulated in a computer environment by mimicking electrical analog circuits. The flows and geometries in the relevant cardiovascular structures have been solved in the CFD environment by adding LPM codes as the boundary conditions (BC). The areas where this technique has been used in the last decade can be listed as congenital heart diseases, heart failure, ventricular function, aortic diseases and modeling of diseases in the brain vessels. However, studies that analyze a full and comprehensive human circulation, are based on simplified models and are very limited in the applications of this still developing multidimensional model (LPM-CFD) technique. Therefore, this study demonstrates a complete two-way LPM-CFD coupling with a dummy aortic segment solved in CFD. This solution is coupled with a traditional LPM exchanging data at every time step of solution. Results demonstrate a good agreement with the traditional CFD technique. The methodology provides a basis for the development of many new cardiovascular devices.
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    An AI-Accelerated CFD Application on a Benchmark Device: FDA Nozzle
    (IEEE, 2022) Aka, Ibrahim Basar; Iscan, Mehmet
    In this study, we suggest a procedure for speeding CFD (computational fluid dynamics) analysis up by combining a conventional opensource CFD solver with a traditional AI module. The studied case is the FDA benchmark nozzle with various Reynolds numbers. The considered CFD simulations belong to a group of steady-state simulations and utilize the laminar flow solver SimpleFoam in the OpenFOAM toolbox. The proposed module is implemented as a Feed-Forward Neural Network (FFNN) supervised learning procedure. Our method distributes the data by creating a combined AI model for each quantity of the simulated phenomenon for various Reynolds numbers. The model can then be combined after the initial iteration phase to decrease the execution time or to lower memory requirements. We analyze the performance of the proposed method depending on the estimation accuracy of the data of interest, velocity, and pressure. For test data, we achieve time-to-solution discounts of nearly a factor of 10. Comparing simulation results based on the FFNN test results and 3D visualization shows the average accuracy for all the parameters over 99% for the velocity and the pressure.
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    Development of an Ex Vivo Mitral Valve Evaluation Model Using a Pulsatile Flow Simulator
    (Journal of Visualized Experiments, 2025) Albrahimi, Ergida; Aka, Ibrahim Basar; Ali, Mhd Homam Alhaj; Korun, Oktay; Odemis, Ender; Ipek, Gokhan
    Surgical mitral valve repair remains a challenging procedure. Although several repair techniques have been defined, data comparing their hemodynamic effects are lacking. The commercially available pulse duplicators are commonly used to simulate blood circulation through mechanical or 3D printed cardiac valves. However, due to the specific structure and working mechanism of the mitral valve, the experiments on surgical techniques require the use of biological tissues. Ex vivo lamb mitral valves are suitable for such experiments, but the methods for mounting these valves to the pulse duplicator system (PDS) are not well defined. To address this, we modified the system by 3D printing and silicone molding as a mitral valve holder. We excised the mitral valve from a lamb heart for each experiment, including its annulus and subvalvar apparatus. We implanted this into the atrioventricular (mitral) valve area of the test machine using the silicone holder. Papillary muscle tension was simulated by tying sutures around the chordae-papillary junctions and passing these sutures through the release hole at the bottom of the ventricular chamber. Initial testing of the valve competence was conducted at a heart rate of 120 beats per minute and a cardiac output of 2 L/min. Valve regurgitation and the pressure gradient between the atrial and ventricular chambers were measured using pulse duplicator electromagnetic flowmeters and validated with echocardiography. Baseline hemodynamic testing demonstrated consistent valve function across five experiments, with a mean regurgitation fraction of 21.1% and echo-derived transmitral gradients ranging from 5.15 to 8.13 mmHg. Stroke volumes and peak flow rates varied among specimens, reflecting physiological variability within the pediatric model.
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    Evaluation of the total hydrodynamic energy loss using 4D flow MRI in a case with Fontan failure
    (Cell Press, 2024) Odemis, Ender; Gumus, Terman; Aka, Ibrahim Basar; Ozkok, Sercin; Pekkan, Kerem
    Fontan Failure (FF) is a common problem for single-ventricle patients as they reach adulthood. Although several mechanisms may cause FF, an optimized blood flow stream through the surgical conduits is essential to avoid excessive energy loss (EL). Recent clinical studies showed EL is related to the quality of life, exercise capacity, and hepatic function since the single-ventricle feeds pulmonary and systemic circulation serially. 4D flow MRI effectively estimates EL in Fontan circulation and allows clinicians to compare the effectiveness of the treatment strategy concerning pre-intervention. Here, we present 26-year-old women with FF who had normal cardiac catheterization findings and were treated according to high EL definitions that are measured through 4D flow MRI.
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    Hemodynamic Effects on Acute Mesenteric Ischemia of Superior Mesenteric Artery
    (Institute of Electrical and Electronics Engineers Inc., 2025) Azazi, Hazal; Kamburoglu, Burak; Dikicier, Enis; Aka, Ibrahim Basar
    This study evaluates the role of superior mesenteric artery (SMA) geometry and hemodynamic parameters in diagnosing acute mesenteric ischemia (AMI) using patient-specific computational fluid dynamics (CFD) simulations. SMA models reconstructed from CT scans of five AMI patients and five controls were analyzed to quantify aortomesenteric (AOM) angle and distance, while transient pulsatile CFD simulations provided wall shear stress, oscillatory shear index, relative residence time (RRT), endothelial cell activation potential, and energy loss values. Results showed that AMI patients exhibited larger mean AOM angles and distances than controls, and reduced angles/distances correlated with increased energy loss. At end systole, RRT values were significantly higher in the AMI group, indicating its potential as a key discriminative marker. These findings highlight the promise of a non-invasive computational approach to complement imaging techniques for improved AMI diagnosis. © 2025 IEEE.
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    Novel small-sized ePTFE valves for neonatal RVOT reconstruction: an in-vitro investigation
    (Elsevier Sci Ltd, 2025) Aka, Ibrahim Basar; Altin, Husnu Firat; Aka, Bahaeddin Umur; Turkoz, Riza; Pekkan, Kerem
    Small-sized right ventricle to pulmonary artery conduits are hindered by calcification, degeneration, or infective endocarditis and face limited availability. Valved conduits of expanded polytetrafluoroethylene leaflets offer a promising path toward enhanced longevity and performance. This in-vitro study introduces innovative expanded polytetrafluoroethylene valve designs for small-sized conduits.Three bicuspid and three tricuspid expanded polytetrafluoroethylene leaflets designed for size 12 mm were tested using an in-vitro pediatric right-heart mockup loop and compared with our baseline leaflet design. Polyvinylchloride was used to create a transparent tube for visual access. Regurgitation rates, pressure gradients, effective orifice area under 0.5-3 L/min cardiac outputs, and 100-150beats/min heart rates are measured. Mechanical differences between expanded polytetrafluoroethylene and polyvinylchloride are investigated through biaxial strain tests. In newborn hemodynamic conditions, 0.5-1 L/min cardiac output, bileaflet valves demonstrated regurgitation rates below 20%, and two tricuspid models maintained regurgitation rates below 15% with gradients below 25 mmHg. In infant conditions, 1-3 L/min output, the regurgitation rates of trileaflet models were below 20%, with gradients consistently below 35 mmHg. The fully coapting bileaflet model showed a regurgitation rate of less than 15% and a gradient below 30 mmHg across newborn and infant conditions. A circumferential difference of less than 0.12 mm was detected between expanded polytetrafluoroethylene and polyvinylchloride. Both the fully coapting bileaflet and redundant trileaflet configurations can be integrated in the small conduits. Polyvinylchloride can be an alternative to expanded polytetrafluoroethylene tube graft in in-vitro studies, allowing visual access to assess leaflet kinematics.
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    Numerical investigation of volute tongue design on hemodynamic characteristics and hemolysis of the centrifugal blood pump
    (Springer Int Publ Ag, 2021) Aka, Ibrahim Basar; Ozturk, Caglar; Lazoglu, Ismail
    In the design of rotary blood pumps, the optimization of design parameters plays an essential role in enhancing the hydrodynamic performance and hemocompatibility. This study investigates the influence of the volute tongue angle as a volute geometric parameter on the hemodynamic characteristics of a blood pump. A numerical investigation on five different versions of volute designs is carried out by utilizing a computational fluid dynamics (CFD) software ANSYS-FLUENT. The effect of volute tongue angle is evaluated regarding the hydrodynamic performance, circumferential pressure distribution, the radial force, and the blood damage potential. A series of volute configurations are constructed with a fixed radial gap (5%), but varying tongue angles ranging from 10 to 50 degrees. The relative hemolysis is assessed with the Eulerian based empirical power-law blood damage model. The pressure-flow rate characteristics of the volute designs at a range of rotational speeds are obtained from the experimental measurements by using the blood analog fluid. The results indicate an inverse relationship between hydraulic performance and the tongue angle; at higher tongue angles, a decrease in performance was observed. However, a higher tongue angle improves the net radial force acting on the impeller. The pump achieves the optimized performance at 20 degrees of the tongue angle with the relatively high hydrodynamic performance and minor blood damage risk.