Francisco Castro

The Liebau effect refers to the generation of unidirectional net fluid flow induced by periodic compression and release actions on a compliant tube within systems comprising tubes with varying elastic properties. This study introduces a semi-empirical model that elucidates Liebau pumping in scenarios involving impedance pumping, asymmetric pumping, or a combination thereof. The authors have established a Liebau pump configuration, previously employed in their experimental and numerical investigations. Experiments were conducted to validate the model in a facility designed to replicate the model configuration. A parametric analysis was performed using this model, emphasizing the most critical parameters influencing the pump operation and their interrelations. Furthermore, a dimensionless formulation is proposed, which not only aids in parametric analysis but also provides practical guidelines for optimizing the pump performance. This work extends previous models by incorporating the impedance pumping mechanism and examining the impact of the mechanical properties of the compliant tube.

Extracorporeal Membrane Oxygenation (ECMO) is a modality of extracorporeal life support which allows temporary support in cases of cardiopulmonary failure and cardiogenic shock. This study presents a valveless pump that works by the Liebau effect as a possible pumping system in ECMO circuits, replacing the current roller and centrifugal pumps. For this purpose, a mock circulatory loop emulating the haemodynamic of the right part of the heart has been constructed. A veno-venous ECMO circuit with the integrated Liebau pump has been incorporated to analyse its performance. The Liebau pump in the ECMO circuit showed a flow assistance in the range of paediatric ECMO and low blood flow range for adults. In addition, experimental tests conducted demonstrated the advantage of the Liebau pump over currently used pumps as the ability to generate a pulsatile flow, which has many advantages in biomedical applications.

Impedance pumping and asymmetric pumping are the main mechanisms of the Liebau effect, a type of valveless pumping. The primary objective of this study is to enhance the current understanding of the mechanics and functionality of a Liebau pump. To achieve this, a prototype pump is constructed, incorporating several novel features: a pinch frequency control system to optimize pump performance, a planar actuator developed using soft robotic technology, and a compliant chamber designed to mitigate flow fluctuations and prevent reverse flow, a common feature of this pumping method. Experimental tests conducted with this prototype demonstrate that the Liebau pump holds potential as a viable technology for fluid pumping in biomedical applications, especially when pulsatile flow is essential or when hemolysis needs to be minimized.

Asymmetric pumping can be achieved by periodically compressing a flexible tube in its plane of symmetry using an actuator, as long as the rigid pipes connected to its ends are asymmetric. This mechanism, together with impedance pumping, composes the Liebau effect. While there have been numerous studies on impedance pumping, there is a lack of available research on asymmetric pumping. The aim of this study is to examine the influence of key parameters on the performance of this type of pump. In addition, this study implements an actuator based on soft robotics technology in asymmetric valveless pumping for the first time. The pump developed in this study can be applied in different areas involving the pumping of special fluids, including biomedical applications.

Objective: Bioresorbable materials represent a promising technology for the treatment of coronary disease. Among the different materials employed, magnesium stents display favourable mechanical properties. One of the main uncertainties regarding use is their behaviour when deployed on coronary bifurcations, especially when their retardant coating has been damaged during the implantation process. This paper analyses the temporal evolution of the degradation of a damaged magnesium stent inserted into a coronary bifurcation. Methods: The rate of erosioncorrosion and the effect of the flow configuration on the mass transfer coefficient were estimated on the basis of previous experimental studies and numerical simulations. This coefficient has been employed to reproduce the conditions that can appear in real stent configurations, and computational fluid dynamics simulations were performed. Results: The diffusion coefficient for this particular case has been calculated from the mass transfer coefficient and the Sherwood number. The results of the simulation show how the presence of the inner artery wall has a positive effect, preventing a premature degradation of the stent, and how the distal strut is protected by the presence of the proximal struts. Conclusions: This study demonstrates the usefulness of the proposed methodology to evaluate the temporal evolution of the degradation of struts made of magnesium alloys. In addition, this methodology can be applied to a study of different materials and geometric configurations. Significance: The proposed technique can contribute to expanding existing knowledge concerning bioresorbable stent flow-corrosion, thus improving their design and implantation.

The most common type of cardiac arrhythmia is atrial fibrillation (AF), which is characterised by irregular and ineffective atrial contraction. This behaviour results into the formation of thrombi, mainly in the left atrial appendage (LAA), responsible for thromboembolic events. Very different approaches are considered as therapy for AF patients. Therefore, it is necessary to yield insight into the flow physics of thrombi formation to determine which is the most appropriate strategy in each case. Computational Fluid Dynamics (CFD) has proven successful in getting a better understanding of the thrombosis phenomenon, but it still requires validation by means of accurate flow field in vivo atrial measurements. As an alternative, in this paper it is proposed an in vitro flow validation, consisting in an idealised model that captures the main flow features observed in the human LA which, once combined with Particle Image Velocimetry (PIV) measurements, provides readily accessible, easy to emulate, detailed velocity fields. These results have been used to validate our laminar and Large Eddy Simulation (LES) simulations. Besides, we have run a parametric study of different boundary conditions sets previously employed in the literature. These data can be used as a benchmark for further development of LA CFD models.

DISPERSION ANALYSIS OF BULK ACOUSTIC WAVES IN PIEZOELECTRIC MEDIA DISCRETIZED BY ENERGY-ORTHOGONAL FINITE ELEMENTS - 8th International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering - 28-30 June 2021, Streamed from Athens, Greece