Open Access
Numerical and experimental study of the fluid flow through a medical device
(Elsevier, 2015) Nicolás, M.; Palero, V. R.; Peña, Estefanía; Arroyo, M. P.; Malvè, Mauro; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
The purpose of this paper is to verify a commercial software based fluid–structure interaction scheme for the inferior vena cava. Vena cava deep thrombosis (TVP) is a potentially deathly disease consequent to pulmonary thromboembolism (TEP). TEP consist in the obstruction of the pulmonary artery due to a blood clot traveling in the cardiovascular system and is treated with anticoagulants and inferior vena cava filters. Flow fields along the vena cava and an antithrombus filter were studied and compared with a Particle Image Velocimetry (PIV) based model to validate the numerical model. The results show that the fluid–structure interaction (FSI) models are valid and can be used to study the deformations in the inferior vena cava wall using patient-specific geometries.
Open Access
Fluid-structure simulation of a general non-contact tonometry. A required complexity?
(Elsevier, 2018) Ariza Gracia, Miguel A.; Wu, Wei; Calvo, Begoña; Malvè, Mauro; Büchler, Philippe; Ingeniería; Ingeniaritza
Understanding corneal biomechanics is important for applications regarding refractive surgery prediction outcomes and the study of pathologies affecting the cornea itself. In this regard, non-contact tonometry (NCT) is gaining interest as a non-invasive diagnostic tool in ophthalmology, and is becoming an alternative method to characterize corneal biomechanics in vivo. In general, identification of material parameters of the cornea from a NCT test relies on the inverse finite element method, for which an accurate and reliable modelization of the test is required. This study explores four different modeling strategies ranging from pure structural analysis up to a fluid–structure interaction model considering the air–cornea and humor–cornea interactions. The four approaches have been compared using clinical biomarkers commonly used in ophthalmology. Results from the simulations indicate the importance of considering the humors as fluids and the deformation of the cornea when determining the pressure applied by the air-jet during the test. Ignoring this two elements in the modeling lead to an overestimation of corneal displacement and therefore an overestimation of corneal stiffness when using the inverse finite element method.
Open Access
CFD-based comparison study of a new flow diverting stent and commercially-available ones for the treatment of cerebral aneurysms
(MDPI, 2019) Catalán Echeverría, Borja; Kelly, Michael E.; Peeling, Lissa; Bergstrom, Donald; Chen, Xiongbiao; Malvè, Mauro; Ingeniería; Ingeniaritza
Flow-diverting stents (FDSs) show considerable promise for the treatment of cerebral aneurysms by diverting blood flow away from the aneurysmal sacs, however, post-treatment complications such as failure of occlusion and subarachnoid haemorrhaging remain and vary with the FDS used. Based on computational fluid dynamics (CFD), this study aimed to investigate the performance of a new biodegradable stent as compared to two metallic commercially available FDSs. CFD models were developed for an idealized cerebral artery with a sidewall aneurysmal sac treated by deploying the aforementioned stents of different porosities (90, 80, and 70%) respectively. By using these models, the simulation and analysis were performed, with a focus on comparing the local hemodynamics or the blood flow in the stented arteries as compared to the one without the stent deployment. For the comparison, we computed and compared the flow velocity, wall shear stress (WSS) and pressure distributions, as well as the WSS related indices, all of which are of important parameters for studying the occlusion and potential rupture of the aneurysm. Our results illustrate that the WSS decreases within the aneurysmal sac on the treated arteries, which is more significant for the stents with lower porosity or finer mesh. Our results also show that the maximum WSS near the aneurysmal neck increases regardless of the stents used. In addition, the WSS related indices including the time-average WSS, oscillatory shear index and relative residence time show different distributions, depending on the FDSs. Together, we found that the finer mesh stents provide more flow reduction and smaller region characterized by high oscillatory shear index, while the new stent has a higher relative residence time.
Open Access
In vitro comparison of Günther Tulip and Celect filters. Testing filtering efficiency and pressure drop
(Elsevier, 2015) Nicolás, M.; Malvè, Mauro; Peña, Estefanía; Martínez, Miguel Ángel; Leask, R.; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
In this study, the trapping ability of the Günther Tulip and Celect inferior vena cava filters was evaluated. Thrombus capture rates of the filters were tested in vitro in horizontal position with thrombus diameters of 3 and 6 mm and tube diameter of 19 mm. The filters were tested in centered and tilted positions. Sets of 30 clots were injected into the model and the same process was repeated 20 times for each different condition simulated. Pressure drop experienced along the system was also measured and the percentage of clots captured was recorded. The Günther Tulip filter showed superiority in all cases, trapping almost 100% of 6 mm clots both in an eccentric and tilted position and trapping 81.7% of the 3 mm clots in a centered position and 69.3% in a maximum tilted position. The efficiency of all filters tested decreased as the size of the embolus decreased and as the filter was tilted. The injection of 6 clots raised the pressure drop to 4.1 mmHg, which is a reasonable value that does not cause the obstruction of blood flow through the system.
Open Access
Modeling the flow and mass transport in a mechanically stimulated parametric porous scaffold under fluid-structure interaction approach
(Elsevier, 2018) Malvè, Mauro; Bergstrom, Donald; Chen, Xiongbiao; Ingeniería; Ingeniaritza
Tissue engineering scaffolds combined with bioreactors are used to cultivate cells with the aim of reproducing tissues and organs. The cultivating process is critical due to the delicate in-vitro environment in which the cells should reproduce. The distribu- tion of nutrients within the engineered construct depend on the scaffold morphology and the analysis of the fluid flow and transport phenomena under mechanical loading when the scaffold is coupled with a bioreactor is crucial for this scope. Unfortunately, due to the complicated microstructure of the scaffold, it is not possible to perform this analysis with experiments and numerical simulation can help in this sense. In this study we have computed the fluid flow and the mass transport of a parametrized scaffold in perfusion bioreactors analyzing the influence of the microstructure of the scaffold using the fluid-structure interaction approach. The latter allows considering the porous construct as compliant yet determining important structural parameters such as stresses and strains that could be sensed by the cells. The presented model considered flow perfusion that provided nutrients and mechanical compression. In particular, we have studied the effect of controllable parameters such as the diam- eter of the scaffold strand and the porosity on the mechanical stresses and strains, shear stress and mass transport. The results of this work will help to shed light on the necessary microenvironment surrounding the cultivated cells improving culturing scaffold fabrication.
Open Access
Influence of a commercial antithrombotic filter on the caval blood flow during neutra and valsalva maneuver
(ASME, 2017) Nicolás, M.; Lucea, B.; Laborda, A.; Peña, Estefanía; Malvè, Mauro; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
Anticoagulants are the treatment of choice for pulmonary embolism. When these fail or are contraindicated, vena cava filters are effective devices for preventing clots from the legs from migrating to the lung. Many uncertainties exist when a filter is inserted, especially during physiological activity such as normal breathing and the Valsalva maneuver. These activities are often connected with filter migration and vena cava damage due to the various related vein geometrical configurations. In this work, we analyzed the response of the vena cava during normal breathing and Valsalva maneuver, for a healthy vena cava and after insertion of a commercial Günther-Tulip® filter. Validated computational fluid dynamics (CFD) and patient specific data are used for analyzing blood flow inside the vena cava during these maneuvers. While during normal breathing, the vena cava flow can be considered almost stationary with a very low pressure gradient, during Valsalva the extravascular pressure compresses the vena cava resulting in a drastic reduction of the vein section, a global flow decrease through the cava but increasing the velocity magnitude. This change in the section is altered by the presence of the filter which forces the section of the vena cava before the renal veins to keep open. The effect of the presence of the filter is investigated during these maneuvers showing changes in wall shear stress and velocity patterns.
Open Access
A theoretical model of the endothelial cell morphology due to different waveforms
(Elsevier, 2015) Sáez, Pablo; Malvè, Mauro; Martínez, Miguel Ángel; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
Endothelial cells are key units in the regulatory biological process of blood vessels. They represent an interface to transmit variations on the fluid dynamic changes. They are able to adapt its cytoskeleton, by means of microtubules reorientation and F-actin reorganization, due to new mechanical environments. Moreover, they are responsible for initiating a huge cascade of biological processes, such as the release of endothelins (ET-1), in charge of the constriction of the vessel and growth factors such as TGF β and PDGF. Although a huge efforts have been made in the experimental characterization and description of these two issues the computational modeling has not gained such an attention. In this work we study the 3D remodeling of endothelial cells based on the main features of blood flow. In particular we study how different oscillatory shear index and the time average wall shear stresses modify the endothelial cell shape. We found our model fitted the experimental works presented before in in vitro studies. We also include our model within a computational fluid dynamics simulation of a carotid artery to evaluate endothelial cell shape index which is a key predictor of atheroma plaque formation. Moreover, our approach can be coupled with models of collagen and smooth muscle cell growth, where remodeling and the associated release of chemical substance are involved.
Open Access
Computational simulation of scleral buckling surgery for rhegmatogenous retinal detachment: on the effect of the band size on the myopization
(Hindawi, 2016) Lanchares, Elena; Buey, María A. del; Cristóbal, José A.; Calvo, Begoña; Ascaso, Francisco J.; Malvè, Mauro; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
A finite element model (FE) of the eye including cornea, sclera, crystalline lens, and ciliary body was created to analyze the influence of the silicone encircling bandwidth and the tightness degree on the myopia induced by scleral buckling (SB) procedure for rhegmatogenous retinal detachment. Intraocular pressure (IOP) was applied to the reference geometry of the FE model and then SB surgery was simulated with encircling bandwidths of 1, 2, and 2.5 mm. Different levels of tightening and three values of IOP were applied.The anterior segment resulted as unaffected by the surgery. The highest value of Cauchy stress appeared in the surroundings of the implant, whereas no increment of stress was observed either in anterior segment or in the optic nerve head. The initial IOP did not appear to play any role in the induced myopia.The wider the band, the greater the induced myopia: 0.44, 0.88, and 1.07 diopters (D) for the 1, 2, and 2.5mm bandwidth, respectively.Therefore, patients become more myopic with a wider encircling element. The proposed simulations allow determining the effect of the bandwidth or the tightness degree on the axial lengthening, thus predicting the myopic increment caused by the encircling surgery.
Open Access
On studying the interaction between different stent models and rabbit tracheal tissue: numerical, endoscopic and histological comparison
(Biomedical Engineering Society, 2016) Chaure, J.; Serrano, C.; Fernández-Parra, Rocío; Peña, Estefanía; Malvè, Mauro; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
Stenting technique is employed worldwide for treating atherosclerotic vessel and tracheal stenosis. Both diseases can be treated by means of metallic stents which present advantages but are affected by the main problem of restenosis of the stented area. In this study we have built a rabbit trachea numerical model and we have analyzed it before and after insertion and opening of two types of commercial stent: a Zilver® FlexTM Stent and a WallStentTM. In experimental parallel work, two types of stent were implanted in 30 New Zealand rabbits divided in two groups of 10 animals corresponding to each stent type and a third group made up of 10 animals without stent. The tracheal wall response was assessed by means of computerized tomography by endoscopy, macroscopic findings and histopathological study 90 days after stent deployment. Three idealized trachea models, one model for each group, were created in order to perform the computational study. The animal model was used to validate the numerical findings and to attempt to find qualitative correlations between numerical and experimental results. Experimental findings such as inflammation, granuloma and abnormal tissue growth, assessed from histomorphometric analyses were compared with derived numerical parameters such as wall shear stress (WSS) and maximum principal stress. The direct comparison of these parameters and the biological response supports the hypothesis that WSS and tensile stresses may lead to a greater tracheal epithelium response within the stented region, with the latter seeming to have the dominant role. This study may be helpful for improving stent design and demonstrates the feasibility offered by in-silico investigated tracheal structural and fluid dynamics.
Open Access
Experimental bench for hemodynamic study of coronary artery with serial stenoses: fractional flow reserve assessment
(Taylor & Francis, 2017) Coppel, R.; Gómez, A. L.; Finet, G.; Malvè, Mauro; Pettigrew, R. I.; Ingeniería Mecánica, Energética y de Materiales; Mekanika, Energetika eta Materialen Ingeniaritza
The aim of this study was to develop an experimental hemodynamic bench to elucidate the influences of such geometrical parameters on the FFR assessment. As a first approach, the present work was focused on the influence of the severity of S1 and S2.