Device-Oriented CFD Comparison of Rectangular and Circular Microchannels with Single and Double Asymmetric Stenoses Under Identical Operating Conditions

4D-FLOW MRI MAPPING OF REGIONAL AORTIC WALL SHEAR STRESS IMPLICATES HEMODYNAMICS IN HUMAN BICUSPID AORTOPATHY

Magnetic resonance imaging-based hemodynamic wall shear stress alters aortic wall tissue biomechanics in bicuspid aortic valve patients

The contribution of wall shear stress insult to the growth of small unruptured cerebral aneurysms in longitudinal 3D-TOF-MRA

A 3-D thin-wall model with fluid–structure interactions for blood flow in carotid arteries with symmetric and asymmetric stenoses

Endothelial cells (ECs) are believed to respond differentially to hemodynamic forces in the vascular tree. Once atherosclerotic plaque has formed in a vessel, the obstruction creates complex spatial gradients in wall shear stress (WSS). In vitro models have used mostly unrealistic and simplified geometries, which cannot reproduce accurately physiological conditions. The objective of this study was to expose ECs to the complex WSS pattern created by an asymmetric stenosis. Endothelial cells were grown and exposed for different times to physiological steady flows in straight dynamic controls and in idealized asymmetric stenosis models. Cell morphology was noticeably different in the regions with spatial WSS gradients, being more randomly oriented and of cobblestone shape. Inflammatory molecule expression was also altered by exposure to shear and endothelial nitric oxide synthase (eNOS) was upregulated by its presence. A regional response in terms of inflammation was observed through confocal microscopy. This work provides a more realistic model to study endothelial cell response to spatial and temporal WSS gradients that are present in vivo and is an important advancement towards a better understanding of the mechanisms involved in coronary artery disease.

An aneurysm's rupture is commonly associated with its maximum diameter, yet biomechanical studies emphasize the significant influence of mechanical wall shear stress (WSS) in this process. This study focuses on two models of aortic aneurysms: abdominal aortic aneurysm and descending thoracic aortic aneurysm. Five cases, comprising two for model 1 and three for model 2, are examined to explore both axisymmetric and asymmetric shapes, as patient geometry may manifest as either fusiform (axisymmetric) or saccular (asymmetric), while maintaining a consistent aneurysm diameter and adjusting the bulge shape factor to induce asymmetry. Hemodynamic factors, including WSS and wall shear stress gradient, are computed to evaluate thrombus formation and rupture risk within the aneurysms. Our results indicate the presence of recirculation zones in both the medial and transverse planes, generating vortices within the aneurysm. These vortices are more prominent in asymmetric cases compared to axisymmetric cases, leading to increased blood residence time within the aneurysm and a higher likelihood of thrombus formation. Thrombus formation can further impede blood flow, heightening the risk of embolism or ischemic events. Rupture occurs when the WSS surpasses tissue strength; thus, if the tissue strength of all aneurysms is same, our findings suggest that rupture risk varies according to asymmetry. In the transverse direction, our results demonstrate that in model 1, case 1 exhibits uniform WSS on both sides, while in case 2, WSS is higher at the posterior sides of the aneurysm sac. Conversely, in model 2, WSS is higher at the anterior side of the aneurysm. In the medial direction of the aneurysm, WSS is highest for case 5, followed by case 3, case 4, case 2, and case 1, respectively, indicating elevated WSS when the anterior bulge dominates over the posterior bulge for each model. Overall, a higher rupture risk is observed in model 2 compared to model 1 due to increased mechanical stresses.

Ultra-Low Von Willebrand Factor (VWF) Adsorption Under Shear with a Polymer Coating for Blood-Contacting Devices

Introduction: Intracranial arterial stenosis (IAS) is a significant cause of ischemic stroke worldwide. Prior studies have identified degree-of-stenosis, time from symptom onset, and gender as predictors of recurrent stroke. However, the role of wall shear stress (WSS), turbulent kinetic energy (TKE), flow velocity (FV), and pressure gradients have not been studied. We present a computational fluid dynamics (CFD) model of IAS extracted from diagnostic imaging with added anatomical details to further investigate these factors. Methods: The vascular anatomy was reconstructed from a semi-automatically delineated biplane angiogram to obtain the geometry of the internal carotid artery bifurcation, middle cerebral artery (MCA) and anterior cerebral artery (ACA). Lenticulostriate arteries (LSAs) and 0%, 70% and 90% stenoses were added. A volumetric mesh was generated with more than 2 million tetrahedral cells and used to evaluate the hemodynamic parameters of the models using the ANSYS: Simulation Technology package. The boundary conditions of the MCA and ACA outlets were adjusted based on an autoregulatory model of the distal vasculature. Results: In the 0% stenosis model, flow throughout the MCA was laminar observed through the LSAs. Pressure drop, FV, WSS, and TKE were unremarkable. At 70% stenosis, there was an elevated FV through the stenosis (5.4m/s), pressure drop across the stenosis (8.04kPa), distal TKE (0.39m^2/s^2), and WSS distal to the stenosis (25.3Pa) (Figure 1). The 90% stenosis model had high FV and pressure drop (4.2m/s, 10.3kPa), elevated WSS (32.2Pa), but a negligible TKE. Conclusions: A CFD model of the IAS based on patient images with added anatomical details can reproduce hemodynamic parameters associated with IAS. The addition of patient-specific flow patterns and arterial wall elasticity could provide further insight into IAS progression and patient outcomes.

Congenital heart malformations occur to substantial number of pregnancies. Studies showed that abnormal flow biomechanical environments could lead to malformations, making it important to understand the biomechanical environment of the developing heart. We performed 4D high-frequency ultrasound scans of chick embryonic hearts at HH25 to study the biomechanics of the whole heart (atria and ventricle). A novel and high-fidelity motion estimation technique, based on temporal motion model and non-rigid image registration algorithm, allowed automatic tracking of fluid-structure boundaries from scan images, and supported flow simulations. Results demonstrated that atrial appendages were the most contractile portion of the atria, having disproportionately high contribution to atrial blood pumping for its volume in the atria. However, the atria played a small role in blood pumping compared to the ventricle, as it had much lower ejection energy expenditure, and as the ventricle appeared to be able to draw inflow from the veins directly during late diastole. Spatially and temporally averaged wall shear stresses (WSS) for various cardiac structures were 0.062–0.068 Pa, but spatial-averaged WSS could be as high as 0.54 Pa in the RV. WSS was especially elevated at the atrial inlet, atrioventricular junction, regions near to the outflow tract, and at dividing lines between the left and right atrium and left and right side of the ventricle, where septation had begun and the lumen had narrowed. Elevated WSS could serve as biomechanics stimulation for proper growth and development.

The aim of the present study is to numerically evaluate the hemodynamic factors which affect the formation of atherosclerosis and plaque rupture in the human artery. An increase of atherosclerosis in the artery causes geometry changes, which results in hemodynamic changes such as flow separation, reattachment and adhesion of new cells (chemotactic) in the artery. Hence, geometry plays an important role in the determining the nature of hemodynamic patterns. Influence of stenosis in the non-bifurcating artery, under pulsatile flow condition has been studied on an idealized geometry. Analysis of flow through symmetric and asymmetric stenosis in the artery revealed the significance of oscillating shear index (OSI), flow separation, low wall shear stress (WSS) zones and secondary flow patterns on plaque formation. The observed characteristic of flow in the post-stenotic region highlight the importance of plaque eccentricity on the formation of secondary stenosis on the arterial wall.

Theoretical Study of Flow Phenomena in the Constricted Tubes

Two dimensional flow of a non-Newtonian fluid through an asymmetric stenosed artery is analysed under the influence of body acceleration with an external magnetic field on the flow field. The Casson fluid model is considered to characterize the non-Newtonian behaviour of the blood. The flow is assumed to be unsteady, laminar, two-dimensional, asymmetric and of pulsatile nature. The artery wall has been treated as an elastic (moving wall) cylindrical tube. The un- steady flow mechanics is influenced by externally imposed periodic body acceleration. An explicit finite difference scheme is applied to obtain the flow field. The effect of body acceleration, magnetic field on the flowing blood is ana- lyzed and these results are presented through graphs for the axial and radial velocities, flow rate and wall shear stress.

Numerical simulation of the blood flow through the coronary artery stenosis: Effects of varying eccentricity

Multidirectional WSS disturbances in stenotic turbulent flows: A pre- and post-intervention study in an aortic coarctation

Blood-contacting devices are vital in treating cardiovascular diseases but may trigger coagulation and thrombosis, requiring lifelong anticoagulation or repeated surgeries. Endothelial cells, which regulate vascular homeostasis, form a barrier between blood and tissue. Promoting stable endothelialization on device surfaces may reduce these risks. However, conventional devices often fail due to high wall shear stress (WSS), which damages the endothelium. This study numerically evaluates surface topographies to identify those that lower WSS and enhance cell stability. CFD simulations were used to estimate WSS on quadrangular and grooved patterns (10 × 4 mm) with depths of 1, 5, 12 mm, spaced 20 mm apart. Two flow conditions were considered: steady (0.4 m/s) and pulsatile with a sinusoidal profile. Blood was modeled as a Newtonian fluid (density: 1060 kg/m³, viscosity: 3.5·10⁻³ Pa·s). In-silico simulations assessed the impact of meso- and micro-topographies on WSS across various patterns. After an initial instability, WSS stabilized along the 10 mm section. The highest mean WSS (12 Pa) occurred at the shallowest depth, decreasing to 8 Pa and 2 Pa with greater depths. Notably, 8 Pa and 2 Pa fall within the physiological range favorable to cell survival. The comparison with grooved topographies, showed similar WSS at 1 and 5 mm depths, increasing to 5 Pa at 12 mm. Surface topography affects WSS and thereby endothelial growth. The square pattern best preserves tissue integrity by reducing WSS. Future work will explore additional patterns and flow conditions. Cellular experiments are planned to validate the numerical models.