Experimental and computational data suggest that hemodynamics play a critical role in the development, growth, and rupture of cerebral aneurysms. The flow structure, especially in aneurysms with a large sac, is highly complex and three-dimensional. Therefore, volumetric and time-resolved measurements of the flow properties are crucial to fully characterize the hemodynamics. In this study, phase-contrast Magnetic Resonance Imaging is used to assess the fluid dynamics inside a 3D-printed replica of a giant intracranial aneurysm, whose hemodynamics was previously simulated by multiple research groups. The physiological inflow waveform is imposed in a flow circuit with realistic cardiovascular impedance. Measurements are acquired with sub-millimeter spatial resolution for 16 time steps over a cardiac cycle, allowing for the detailed reconstruction of the flow evolution. Moreover, the three-dimensional and time-resolved pressure distribution is calculated from the velocity field by integrating the fluid dynamics equations, and is validated against differential pressure measurements using precision transducers. The flow structure is characterized by vortical motions that persist within the aneurysm sac for most of the cardiac cycle. All the main flow statistics including velocity, vorticity, pressure, and wall shear stress suggest that the flow pattern is dictated by the aneurysm morphology and is largely independent of the pulsatility of the inflow, at least for the flow regimes investigated here. Comparisons are carried out with previous computational simulations that used the same geometry and inflow conditions, both in terms of cycle-averaged and systolic quantities.

This paper aims to review the State of the Art in metal self-expanding stents made from nitinol (NiTi), showing shape memory and superelastic behaviors, to identify the challenges and the opportunities for improving patient outcomes. A significant contribution of this paper is its extensive coverage of multidisciplinary aspects, including design, simulation, materials development, manufacturing, bio/hemocompatibility, biomechanics, biomimicry, patency, and testing methodologies. Additionally, the paper offers in-depth insights into the latest practices and emerging trends, with a special emphasis on the transformative potential of additive manufacturing techniques in the development of metal stents. By consolidating existing knowledge and highlighting areas for future innovation, this review provides a valuable roadmap for advancing nitinol stents.

In this study, we investigate the steady inhalation, steady exhalation, and oscillatory flow in a realistic airway geometry for physiologically relevant regimes ranging from quiet breathing to respiration under high frequency ventilation (HFV). We use magnetic resonance velocimetry to characterize and quantify three-dimensional (3D) velocity fields in 3D printed replicas of realistic bronchial trees. Expanding on previous studies [Jalal et al., Exp. Fluids 57, 148 (2016); Jalal et al., Phys. Rev. Fluids 3, 103101 (2018)] which focused on respiration in planar double bifurcation geometries, we compare levels of axial and lateral dispersion, and find that they exceed those found in the idealized models. Furthermore, we find that the secondary flows in realistic airways propagate deep in the bronchial tree and are stronger during exhalation as compared to inhalation, while the mean flow topology does not vary significantly between the two steady regimes. Under HFV, we note significant regions of flow reversal during the inhalation-exhalation and exhalation-inhalation transitions. This is found to be due to a difference in impedance (dominated by inertance) in the different regions of the lung and results in an asynchronous ventilation between the upper and lower lobes. This phenomenon, also known as pendulluft is demonstrated experimentally for the first time, using both Eulerian velocity fields and Lagrangian pathlines. Secondary flows are stronger in exhalation compared to inhalation and at the peak of the ventilation cycle, match the steady cases although the flow topology can be significantly different. Finally, the cycle-averaged drift velocity suggests that steady streaming, while not negligible, is not the main transport mechanism during high-frequency ventilation.

Background: The aorta, a central component of the cardiovascular system, plays a pivotal role in ensuring blood circulation. Despite its importance, there is a notable lack of idealized models for experimental and computational studies.Objective: This study aims to develop computer-aided design (CAD) models for the idealized human aorta, intended for studying hemodynamics or solid mechanics in both in vitro and in silico settings.Methods: Various parameters were extracted from comprehensive literature sources to evaluate major anatomical characteristics of the aorta in healthy adults, including variations in aortic arch branches and corresponding dimensions. The idealized models were generated based on averages weighted by the cohort size of each study for several morphological parameters collected and compiled from image-based or cadaveric studies, as well as data from four recruited subjects. The models were used for hemodynamics assessment using particle image velocimetry (PIV) measurements and computational fluid dynamics (CFD) simulations.Results: Two CAD models for the idealized human aorta were developed, focusing on the healthy population. The CFD simulations, which align closely with the PIV measurements, capture the main global flow features and wall shear stress patterns observed in patient-specific cases, demonstrating the capabilities of the designed models.Conclusions: The collected statistical data on the aorta and the two idealized aorta models, covering prevalent arch variants known as Normal and Bovine types, are shown to be useful for examining the hemodynamics of the aorta. They also hold promise for applications in designing medical devices where anatomical statistics are needed.