Contribution of computational model for assessment of heart tissue local stress caused by suture in LVAD implantation

Study: Implantation of a Left Ventricular Assist Device (LVAD) may produce both excessive local tissue stress and resulting strain-induced tissue rupture that are potential iatrogenic factors influencing the success of the surgical attachment of the LVAD into the myocardium. By using a computational simulation compared to mechanical tests, we sought to investigate the characteristics of stress-induced suture material on porcine myocardium. Methods: Tensile strength experiments (n = 8) were performed on bulk left myocardium to establish a hyperelastic reduced polynomial constitutive law. Simultaneously, suture strength tests on left myocardium (n = 6) were performed with a standard tensile test setup. Experiments were made on bulk ventricular wall with a single U-suture (polypropylene 3–0) and a PTFE pledget. Then, a Finite Element simulation of a LVAD suture case was performed. Strength versus displacement behavior was compared between mechanical and numerical experiments. Local stress fields in the model were thus analyzed. Results: A strong correlation between the experimental and the numerical responses was observed, validating the relevance of the numerical model. A secure damage limit of 100 kPa on heart tissue was defined from mechanical suture testing and used to describe numerical results. The impact of suture on heart tissue could be accurately determined through new parameters of numerical data (stress diffusion, triaxiality stress). Finally, an ideal spacing between sutures of 2 mm was proposed. Conclusion: Our computational model showed a reliable ability to provide and predict various local tissue stresses created by suture penetration into the myocardium. In addition, this model contributed to providing valuable information useful to design less traumatic sutures for LVAD implantation. Therefore, our computational model is a promising tool to predict and optimize LVAD myocardial suture

Développement d’un dispositif médical implantable d’assistance ventriculaire par compression cardiaque directe : l’exosquelette cardiaque

Ventricular assistance is a promising therapeutic pathway for terminal chronic heart failure. Notwithstanding the progress made for the development of aorto-ventricular shunt pump among other things, the difficulties relatives to footprint, power supply and/or blood-device interactions are somehow limiting their clinical applications. Recently, direct cardiac compression (DCC) was suggested as a promising lead to overcome the difficulties mentioned above. In this work, we focused on the design and the feasibility of an implantable and mechanical Direct Cardiac Compression device called: The Cardiac Exosqueleton. Our experimental work used Computer Assisted Design (CAD) and numerical modeling to optimize and predict (i) tissue-device interactions and (ii) pressure generation inside ventricular cavities. Then, a functional prototype was realized by additive manufacturing (titanium, polymer) with the help of modeling data and with respect to the anatomical, mechanical and energetical limitations. Finally, we conducted an evaluation of the ability of our device on both in vitro setup and ex vivo heart. We were able to conceive and validate a numerical model based on finite element techniques. This simple yet robust model allowed us to study (i) the impact of suture fixation of a device at the apex of the heart, (ii) the influence of the direct cardiac compression on intracardiac pressures and (iii) overall and local tissue stress in the myocardium. Our prototype showed promising results concerning (i) the restoration of physiological intraventricular pressures, (ii) a low energy consumption and (iii) a shape that is compatible with the thoracic anatomical constraints. All of these results allow us to envision a total implantation of the cardiac exoskeleton into the patient.L’assistance ventriculaire constitue une voie thérapeutique prometteuse de l’insuffisance cardiaque terminale. En dépit des progrès, notamment dans le développement des assistances de type shunt ventriculo-aortique, les écueils relatifs à l’encombrement, à l’alimentation et/ou aux interactions avec le sang de ces dispositifs limitent leur application clinique. Récemment, le concept de Compression Cardiaque Directe (DCC) apparaît comme une piste prometteuse en palliant les difficultés sus-citées. Dans ce travail de thèse, nous avons mis l’accent sur la conception et le test de faisabilité d’une solution de Compression Cardiaque Directe de type mécanique et entièrement implantable appelée l’Exosquelette Cardiaque. Notre travail expérimental a porté, dans un premier temps, sur la conception assistée par ordinateur et sur la modélisation numérique permettant ainsi d’optimiser et de prédire (i) les interactions tissus myocardiques/dispositifs et (ii) les pressions ventriculaires générées. Ensuite, un prototype fonctionnel a été réalisé par fabrication additive (titane, polymères) en s’appuyant sur les données issues de la modélisation et en respectant les contraintes énergétiques, mécaniques et architecturales anatomiques. Enfin, nous avons conduit une phase d’évaluation du potentiel de ce dispositif original sur un modèle de cœur ex vivo. Nous avons pu concevoir et valider un modèle numérique fondé sur le principe des éléments finis. Ce modèle à la fois simple et robuste, a permis de simuler (i) l’impact des points de fixation du dispositif sur le tissu cardiaque, (ii) l’efficacité de la compression externe sur la genèse des pressions intraventriculaires et (iii) l’influence de la compression mécanique externe sur le tissu cardiaque. Le prototype issu de ce travail de thèse a pu produire des résultats prometteurs concernant (i) la restauration physiologique de la pression intraventriculaire, (ii) la consommation énergétique suffisamment basse et (iii) le design compatible avec les contraintes anatomiques thoracique. L’ensemble de ces résultats esquissent la possibilité d’une implantation totale de l’Exosquelette Cardiaque chez le patient

Finish machining of Ti6Al4V produced by selective laser melting: Influence on the surface intergity

International audienc

Influence of Finish Machining on the Surface Integrity of Ti6Al4V Produced by Selective Laser Melting

International audienc

Estimating changes in effective values of surface detention, depression storage and friction factor at the interrill scale, using a cheap and fast method to mold the soil surface micro-topography

Surface detention and depression storage constitute the two conceptual storages of water at the soil surface and depend on the spatial configuration of the micro-topography. To be able to measure directly those storages and investigate how they evolve with time and precipitation, it is necessary to isolate the impact of the micro-topography from the infiltration. Therefore we developed a fast and cheap in-situ molding method (+/−85 €/m2) that combines alginate, plaster and lacquer. It allows creating stable and impermeable artificial micro-topographies that reproduce real field situations and that can be submitted to various laboratory runoff simulations. Both the surface of a specific soil and its artificial reproduction were measured with a laser scanner in order to assess the quality of the molding method. This method is shown to be precise with a standard deviation of 0.55 mm, which is also the spatial resolution of the laser scanner method. This novel molding method was applied to get ten footprints of the micro-topography of a loamy bare soil, at different levels of cumulative rainfall erosivity value (R), starting with a tilled soil, and letting it evolve with natural rain events. We studied the evolution of the bulk values of depression storage and surface detention at the interrill scale, considering that these bulk values may provide useful input to hillslope models for which the size of the single grid cell corresponds to the size of our entire molds. We related the hydraulic properties to R, assuming that R would help explain the change in hydraulic parameters of micro-topographies over time. We found a general decrease of maximum depression storage and steady state surface detention with R. We finally parametrized surface detention by an effective friction factor, using a classical equation for an equivalent laminar sheet flow. A simple model to compute the surface detention as a function of the discharge per unit width and the cumulative rainfall erosivity was proposed

Thermal study during milling of Ti6Al4V produced by Electron Beam Melting (EBM) process

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Extensive exploration of a novel rat model of Parkinson's disease using partial 6-hydroxydopamine lesion of dopaminergic neurons suggests new therapeutic approaches

International audienceParkinson's disease (PD) is characterized by the degeneration of dopaminergic (DA) neurons constituting the nigrostriatal pathway. Neuroinflammation, related to microglial activation, plays an important role in this process. Exploration of animal models of PD using neuroimaging modalities allows to better understand the pathophysiology of the disease. Here, we fully explored a moderate lesion model in the rat in which 6-Synaps