Beyond the virtual intracranial stenting challenge 2007: non-Newtonian and flow pulsatility effects

The attached article is a post print version of the final published version which may be accessed at the link below. Crown Copyright (c) 2010 Published by Elsevier Ltd. All rights reserved.The Virtual Intracranial Stenting Challenge 2007 (VISC’07) is becoming a standard test case in computational minimally invasive cerebrovascular intervention. Following views expressed in the literature and consistent with the recommendations of a report, the effects of non-Newtonian viscosity and pulsatile flow are reported. Three models of stented cerebral aneurysms, originating from VISC’07 are meshed and the flow characteristics simulated using commercial computational fluid dynamics (CFD) software. We conclude that non-Newtonian and pulsatile effects are important to include in order to discriminate more effectively between stent designs

Vascular device interaction with the endothelium

Copyright @ 2008 Elsevier. This is the post-print version of the article.Cerebral stents and Intra Aortic Balloon Pumps (IABP) are examples of mechanical devices that are inserted into arteries to restore flows to clinically healthy states. The stent and the IABP ‘correct’ the arterial flow by static dilation and by cyclical occlusion respectively. As this presentation shows, these functions are effectively modelled by current engineering practice. As interventions however, by their very nature they involve physical contact between a non-biological structure and the sensitive endothelial surface. The possible damage to the endothelium is not currently well addressed and we also consider this issue. Cerebral stents generally have two primary clinical objectives: to mechanically dilate a stenosed artery and to have minimal detrimental impact upon local blood flow characteristics. These objectives are well served at the arterial scale as these devices are evidently effective in opening up diseased arteries and restoring vital flows. However, at the near-wall micro-scale the picture is less satisfactory, as thin stent wires apply stresses to the endothelium and glycocalyx and the local flow is disturbed rather than being ideally streamlined. This causes further interaction with this endothelium topography. Wall Shear Stress (WSS) is the measure commonly used to indicate the interaction between fluid and wall but it is a broad brush approach that loses fidelity close to the wall. We will present simulation results of blood flow through a stented cerebral saccular aneurysm under these limitations of WSS. The Intra Aortic Balloon Pump (IABP) is a widely used temporary cardiac assist device. The balloon is usually inserted from the iliac artery, advanced in the aorta until it reaches the desired position; with its base just above the renal bifurcation and the tip approximately 10cm away from the aortic valve. The balloon is inflated and deflated every- (1:1), every other- (1:2) or every second (1:3) cardiac cycle. Balloon inflation, which takes place during early diastole, causes an increase in the pressure of the aortic root which leads to an increase in coronary flow. Balloon deflation which takes place during late diastole achieves one of the main IABP therapeutic effects by reducing left ventricular afterload. Unavoidably, the balloon contacts the inner wall of the aorta with every inflation/deflation cycle. This repeated event and possible contact with atherosclerotic plaque have been reported to be responsible for balloon rupture. However, there has not been a methodical study to investigate the mechanical effects of balloon-wall interaction. For example, during inflation the balloon approaches the endothelium as it displaces a volume of blood proximally and distally. This squeezing process generates shear stresses, which hasn't yet been quantified. Similarly, when the balloon moves away from the endothelium during deflation, it generates micro pressure differences that may impose stretching (pulling) stresses on the endothelium cells. Both of the above cases indicate that a very high spatial resolution is required in order to fully understand the process of interaction between device and endothelium, and to interpret the effects at the cellular level

Actin and microtubules differently contribute to vacuolar targeting specificity during the export from the er

Plants rely on both actin and microtubule cytoskeletons to fine-tune sorting and spatial targeting of membranes during cell growth and stress adaptation. Considerable advances have been made in recent years in the comprehension of the relationship between the trans-Golgi network/early endosome (TGN/EE) and cytoskeletons, but studies have mainly focused on the transport to and from the plasma membrane. We address here the relationship of the cytoskeleton with different endoplasmic reticulum (ER) export mechanisms toward vacuoles. These emergent features of the plant endomembrane traffic are explored with an in vivo approach, providing clues on the traffic regulation at different levels beyond known proteins’ functions and interactions. We show how traffic of vacuolar markers, characterized by different vacuolar sorting determinants, diverges at the export from the ER, clearly involving different components of the cytoskeleton

An integrated approach for the analysis and modeling of road tunnel ventilation. Part I: Continuous measurement of the longitudinal airflow profile

The knowledge of the flow field inside road tunnels under normal operation, let alone fire conditions, is only approximate and partial. The reason is that while the full three-dimensional, unsteady problem is out of reach of numerical methods, on the other hand accurate measurement of the airflow in road and railway tunnels constitutes an extremely demanding task. The present work, structured as a twofold study, takes up the challenge and proposes an original integrated experimental and numerical approach for the analysis and modeling of flow inside a road tunnel and its ventilation systems, aiming at defining a methodology for the creation of “digital twins” of the system itself, on which advanced ventilation and smoke control strategies can be tested and fine-tuned. In this first part, an innovative experimental facility for the continuous acquisition of the longitudinal velocity profile along the whole length of a road tunnel has been designed and built. The facility consists of a survey rake with five bidirectional vane anemometers, which is mounted on a small electric vehicle that can travel through the tunnel at constant speed. This paper reports the design procedure of the measurement facility, with particular focus on the conception and realization of the vehicle carrying the survey rake. Results of the first experimental campaign carried out under the 11611 meters long Mont Blanc road tunnel are presented to corroborate the validity of the approach adopted and the accuracy of the measurement chain

New Insights on Plant Cell Elongation: A Role for Acetylcholine

We investigated the effect of auxin and acetylcholine on the expression of the tomato expansin gene LeEXPA2, a specific expansin gene expressed in elongating tomato hypocotyl segments. Since auxin interferes with clathrin-mediated endocytosis, in order to regulate cellular and developmental responses we produced protoplasts from tomato elongating hypocotyls and followed the endocytotic marker, FM4-64, internalization in response to treatments. Tomato protoplasts were observed during auxin and acetylcholine treatments after transient expression of chimerical markers of volume-control related compartments such as vacuoles. Here we describe the contribution of auxin and acetylcholine to LeEXPA2 expression regulation and we support the hypothesis that a possible subcellular target of acetylcholine signal is the vesicular transport, shedding some light on the characterization of this small molecule as local mediator in the plant physiological response

Non-Newtonian and flow pulsatility effects in simulation models of a stented intracranial aneurysm

Permission to redistribute provided by publishers.Three models of different stent designs implanted in a cerebral aneurysm, originating from the Virtual Intracranial Stenting Challenge'07, are meshed and the flow characteristics simulated using commercial computational fluid dynamics (CFD) software in order to investigate the effects of non-Newtonian viscosity and pulsatile flow. Conventional mass inflow and wall shear stress (WSS) output are used as a means of comparing the cfd simulations. In addition, a WSS distribution is presented, which clearly discriminates in favour of the stent design identified by other groups. It is concluded that non-Newtonian and pulsatile effects are important to include in order to avoid underestimating wss, to understand dynamic flow effects, and to discriminate more effectively between stent designs. © Authors 2011

Compositional changes by SIMS and XPS analyses on fresh and aged Roman-like glass

This study reports important analytical evidence of an unusual non-uniform element distribution in the superficial layers of glass matrices (from few nm up to 1 µm). The unforeseen observation was made on silica-soda-lime glass mock-ups before and after their artificial ageing, using secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) surface analysis techniques. The analyses showed a marked non-homogeneous element distribution at the glass surface. The results indicated a very low concentration of Na at the surface up to a depth of around 500 nm below the surface, where its concentration increases reaching a plateau. In addition, the profile distribution of H in the first 200 nm of the pristine glass surface indicated a diffusion of hydrogen from the surrounding environment to the glass network. Additional modifications during the glass ageing process related to external factors (such as temperature and humidity) were also identified in relation to sodium atoms, with atoms on the glass surface showing a different chemical state from those in the bulk. This study confirms that glass composition as well as glass alteration are non-homogeneous locally supporting the importance of studying glass surface as region of interaction with surrounding environment

Specific modulation of airway epithelial tight junctions by apical application of an occludin peptide

Tight junctions are directly involved in regulating the passage of ions and macromolecules (gate functions) in epithelial and endothelial cells. The modulation of these gate functions to transiently regulate the paracellular permeability of large solutes and ions could increase the delivery of pharmacological agents or gene transfer vectors. To reduce the inflammatory responses caused by tight junction-regulating agents, alternative strategies directly targeting specific tight junction proteins could prove to be less toxic to airway epithelia. The apical delivery of peptides corresponding to the first extracellular loop of occludin to transiently modulate apical paracellular flux has been demonstrated in intestinal epithelia. We hypothesized that apical application of these occludin peptides could similarly modulate tight junction permeability in airway epithelia. Thus, we investigated the effects of apically applied occludin peptide on the paracellular permeability of molecular tracers and viral vectors in well differentiated human airway epithelial cells. The effects of occludin peptide on cellular toxicity, tight junction protein expression and localization, and membrane integrity were also assessed. Our data showed that apically applied occludin peptide significantly reduced transepithelial resistance in airway epithelia and altered tight junction permeability in a concentration-dependent manner. These alterations enhanced the paracellular flux of dextrans as well as gene transfer vectors. The occludin peptide redistributed occludin but did not alter the expression or distribution of ZO-1, claudin-1, or claudin-4. These data suggest that specific targeting of occludin could be a better-suited alternative strategy for tight junction modulation in airway epithelial cells compared with current agents that modulate tight junctions

Advantages of the recursive operability analysis in updating the risk assessment

With the introduction of new regulations and sustainable technologies, revamping and upgrading already existing chemical plants is nowadays an important element in the framework of process engineering. Such important modifications must come along in parallel improvement of process safety. In this sense, risk assessment is a tool that should be versatile and easy to update by definition. However, even the most common methods currently used for accidental scenarios identification and risk assessment estimation (such as HazOp) may prove to be very time-consuming when discussing about safety from process modifications. The availability of a reliable and easy-to-update tool for safety engineering is crucial for process industries. In this work, we compare a risk analysis on a chemical plant subject of modifications performed with two different tools: HazOp and FTA vs Recursive Operability Analysis (ROA) and FTA. Both techniques have been applied to a tank dedicated to dust mixing that was subject of process modifications. Both methods come to the same conclusions, highlighting new failures and process criticalities, associated with the introduction of flow alarms and interlocks in case of excessive depressurizing. It is shown that the Recursive Operability Analysis, with its cause-consequence structure tied with process variable interactions, is much more effective in a risk assessment update