Conception et développement d'un banc d'essai afin d'évaluer les différentes techniques de réparation de la valve mitrale

L'insuffisance mitrale (IM), définie comme le reflux de sang du ventricule gauche vers l'oreillette gauche en phase de systole ventriculaire, est une affection fréquente, touchant env. 2% de la population européenne [1-2]. A terme, celle-ci peut se compliquer de problèmes respiratoires tels qu'un oedème pulmonaire ou de troubles du rythme tels qu'une fibrillation auriculaire, affectant la survie des patients. Si elle n'est pas traitée, l'IM est une maladie de mauvais pronostic avec une mortalité estimée à 5% par an et plus de 70% à 8 ans [3]. Deux options curatrices sont aujourd'hui proposées aux patients en fonction de leur état de santé et de la gravité de leur maladie : i) le traitement endovasculaire, dont l'avantage principal est son caractère peu invasif et ii) le traitement chirurgical, plus invasif mais qui demeure la méthode de référence [4-6]. L'indication opératoire est posée grâce à différents critères cliniques et radiologiques [7-8] permettant d'offrir aux patients les meilleures conditions de traitement et de sélectionner l'intervention la plus adaptée. Toutefois, à l'heure actuelle, aucun système ex-vivo ne permet d'évaluer l'efficacité de nouvelles techniques chirurgicales, ceci obligeant les chercheurs à recourir à des méthodes invasives et coûteuses, tant chez l'animal que chez l'être humain. Nous avons donc décidé de concevoir et de construire un banc d'essai ex-vivo tentant de palier à ce problème. Il s'agit d'un modèle constitué d'un coeur de porc, suspendu grâce à un tube introduit dans l'aorte, dépourvu (volontairement) de sa valve aortique et sur lequel nous avons découpé l'oreillette gauche afin de voir la valve mitrale. Quinze coeurs ont été nécessaires à l'élaboration de ce banc d'essai. Une fois finalisé, celui-ci nous a permis de tester l'efficacité de l'annuloplastie de De Vega, une technique de réparation utilisée normalement sur la valve tricuspide. Cette méthode s'est révélée être efficace en corrigeant totalement l'insuffisance mitrale préalablement induite. De plus, bien qu'utilisée sur la valve tricuspide en pratique clinique, la technique de De Vega semble également adaptée à la réparation mitrale, du moins avec ce banc d'essai. En conclusion, le modèle que nous avons conçu et construit peut servir de point de départ pour un banc d'essai plus complexe et performant permettant de tester rapidement et à bas prix de nouvelles techniques chirurgicales de réparation mitrale

Light Weight Alloys: Processing, Properties and Their Applications

There is growing interest in light metallic alloys for a wide number of applications owing to their processing efficiency, processability, long service life, and environmental sustainability. Aluminum, magnesium, and titanium alloys are addressed in this Special Issue, however, the predominant role played by aluminum. The collection of papers published here covers a wide range of topics that generally characterize the performance of the alloys after manufacturing by conventional and innovative processing routes

Market-consistent valuation: a step towards calculation stability

In this paper we address some of the stability issues raised by the European life insurance regulation valuation scheme. Via an in-depth study of the so-called economic valuation framework, shaped through the market-consistency contract we first point out the practical interest of one of the El Karoui, Loisel, Prigent & Vedani (2017) propositions to enforce the stability of the cutoff dates used as inputs to calibrate actuarial models. This led us to delegitimize the argument of the no-arbitrage opportunity as a regulatory criteria to frame the valuation, and as an opposition to the previously presented approach. Then we display tools to improve the convergence of the economic value estimations be it the V IF or the SCR, using usual variance reduction methods and a specific work on the simulation seeds. Through various implementations on a specific portfolio and valuation model we decrease the variance of the estimators by over 16 times

Microstructural, texture, plastic anisotropy and superplasticity development of ZK60 alloy during equal channel angular extrusion processing

In this study, equal channel angular pressing (ECAP) was exploited to refine the grain size of a ZK60 magnesium alloy in multi-processing steps, namely at temperatures of 250˚C, 200˚C and 150˚C, producing an ultrafine-grained (UFG) structure. The microstructural development and texture evolution during ECAP were systemically investigated by electron backscattered diffraction (EBSD) analysis. The microstructure of the ECAP processed alloy was remarkably refined to an average grain size of 600 nm. During ECAP process the original fiber texture of the as-extruded alloy was gradually weakened and eventually replaced by a stronger texture component coinciding with ECAP shear plane. The ECAP processed material showed a proper balance of tensile as well as compression strength and tensile ductility at room temperature. Yield strength of 273 and 253 MPa in tension and compression, respectively, ultimate tensile strength of 298 MPa and fracture elongation of about 30% were obtained in the UFG alloy. A transition from ductile–brittle to ductile fracture consisting of very fine and equiaxed dimples was also found in the ECAP processed material. Compared to the as-received alloy, a combination of grain refinement and texture development in the UFG alloy gave rise to a notable reduction in mechanical asymmetric behavior at room temperature. The superplastic behavior of the as-extruded and ECAP processed alloy was also investigated at 200˚C with strain rate of 1.0×10-3 s-1. The concurrent effect of grain boundary sliding and favorable basal texture in the UFG alloy led to an achievement of elongation value of about 300% while, under similar testing conditions, the elongation of about 140% was obtained in the as-extruded alloy

Effect of annealing temperature on microstructure and high-temperature tensile behaviour of Ti-6242S alloy produced by Laser Powder Bed Fusion

This work is focussed at investigating the properties of additive manufactured Ti-6242S, a Ti alloy with excellent mechanical strength and stability up to 550 °C. Special attention is given to the effect of different heat treatment routes on microstructure and high-temperature mechanical behaviour of the Ti-6242S alloy produced by Laser Powder Bed Fusion. Annealing was performed in the α/β field (at 940 °C, 960 °C, 980 °C) or above the β transus (at 1050 °C). Annealing step was followed by Ar gas cooling and ageing at 595 °C. The as-built material exhibits high strength and anisotropic behaviour, showing lower fracture elongation in the direction parallel to the build platform. Heat treatments are responsible for a reduction of material strength but an increase in fracture elongation. Tensile tests at high temperature show that the best heat treatment for applications up to 300 °C is the annealing at 940 °C followed by Ar cooling and ageing. For applications at higher temperatures (namely 550 °C, 750 °C) the annealing step should be performed above the β transus temperature, at 1050 °C, to achieve the best tensile properties

Market inconsistencies of the market-consistent European life insurance economic valuations: pitfalls and practical solutions

International audienceThe Solvency II directive has introduced a specific so-called risk-neutral framework to valuate economic accounting quantities throughout European life insurance companies. The adaptation of this theoretical notion for regulatory purposes requires the addition of a specific criterion, namely the market-consistency, in order to objectify the choice of the valuation probability measure. This paper aims at pointing out and fixing some of the major risk sources embedded in the current regulatory life insurance valuation scheme. We compare actuarial and financial valuation schemes. We then address first operational issues and potential market manipulation sources in life insurance, induced by both theoretical and regulatory pitfalls. For example, we show that calibrating the interest rate model in October 2014 instead of December 31 st 2014 generates a 140%-increase in the economic own funds of a representative French life insurance company. We propose various adaptations of the current implementations, including product-specific valuation scheme, to limit the impact of these market-inconsistencies

VirtualToxLab – in silico Prediction of the Endocrine-Disrupting Potential of Drugs and Chemicals

In the last decade, we have developed and validated an in silico concept based on multidimensional QSAR (mQSAR) for the prediction of the toxic potential of drugs and environmental chemicals. Presently, the VirtualToxLab includes eleven so-called virtual test kits for estrogen (?/?), androgen, thyroid (?/?), glucocorticoid, aryl hydrocarbon, mineralocorticoid and peroxisome proliferator-activated receptor ? as well as for the enzymes cytochrome P450 3A4 and 2A13. The surrogates have been tested against a total of 824 compounds and are able to predict the binding affinity close to the experimental uncertainty with only six of the 194 test compounds giving calculated results more than a factor of 10 off the experimental binding affinity and the maximal individual deviation not exceeding a factor of 15. These results suggest that our approach is suited for the in silico identification of endocrine-disrupting effects triggered by drugs and environmental chemicals. Most recently, the technology has been made available through the Internet for academic laboratories, hospitals and environmental organizations

Binder jetting additive manufacturing of biodegradable Zn

Biodegradable materials avoid second surgeries and long-term associated risks of conventional inert implants. Zn arose as a potential candidate for bioresorbable implants due to its proper degradation behaviour and biocompatibility [1]. However, its low melting point induces uncontrolled porosity in LPBF, promoting the future cracking of the implant. Therefore, new fabrication techniques need to be explored. In this work, binder jetting 3d printing (BJ3P) was studied for Zn powders. The samples were printed and sintered under different conditions. It is concluded that, the increase the temperature almost up to melting point leads to higher densification, at the same time, the rise of temperature provokes the formation and growth of oxidized layer on the surface of the powders