Numerical model of bone remodeling sensitive to loading frequency through a poroelastic behavior and internal fluid movements

International audienceIn this article, a phenomenological numerical model of bone remodeling is proposed. This model is based on the poroelasticity theory in order to take into account the effects of fluid movements in bone adaptation. Moreover, the proposed remodeling law stands from the classical 'Stanford' law, enriched in order to take into account the loading frequency, through fluid movements. This coupling is materialized by a quadratic function of Darcy velocity. The numerical model is carried out, using a finite element method, and calibrated using experimental results at macroscopic level, from the literature. First results concern cyclic loadings on a mouse ulna, at different frequencies between 1 Hz and 30 Hz, for a force amplitude of 1.5 N and 2 N. Experimental results exhibit a sensitivity to the loading frequency, with privileged frequency for bone remodeling between 5 Hz and 10 Hz, for the force amplitude of 2 N. For the force amplitude of 1.5 N, no privileged frequencies for bone remodeling are highlighted. This tendency is reproduced by the proposed numerical computations. The model is identified on a single case (one frequency and one force amplitude) and validated on the other ones. The second experimental validation deals with a different loading regime: An internal fluid pressure at 20 Hz on a turkey ulna. The same framework is applied, and the numerical and experimental data are still matching in terms of gain in bone mass density

Elements Finis Espace-Temps 4D

Nous proposons une étude sur la résolution de problème de mécanique comprenant 3 dimensions d'espace et 1 de temps en utilisant la méthode des éléments finis espaces temps, qui consiste en une discrétisation de même nature sur l'espace et le temps. Il s'agit d'une extension de la méthode des éléments finis classiques. L'intérêt de cette méthode réside dans la facilité de remaillage, dans le temps ou dans l'espace. Elle a été appliqué en particulier pour résoudre des problèmes de contact frottant, avec maillage fin autour de la zone (mobile) de contact

In-vitro testing of stent retrievers for cerebral thrombi removal

International audienceRecent articles appeared in literature demonstrated that early mechanical thrombectomy offered to patients presenting with acute ischemic stroke is related to improved functional outcome. Stent retrievers (STR) are recognized as the most effective devices for intracranial thrombectomy. In the present study we experimentally analyzed devices mechanical properties, behavior during retrieval and their interaction with clots of different features. The aim of this study was to identify any device feature that was functional to the thrombus removal

Etude expérimentale et numérique de la diffusion de la chaleur dans la peau : influence de la circulation sanguine

Agir rapidement sur des brûlures corporelles, pour éviter la propagation des lésions due à la diffusion de la chaleur est un des objectifs à long terme de cette étude. L'article présente une expérimentation et propose un modèle numérique de la peau de l'avant-bras. L'évolution de la chaleur est mesurée avec une caméra infrarouge et les résultats ont montré une très nette influence de la circulation sanguine sur la diffusion de la température

A computational solution to automatically map metabolite libraries in the context of genome scale metabolic networks

This article describes a generic programmatic method for mapping chemical compound libraries on organism-specific metabolic networks from various databases (KEGG, BioCyc) and flat file formats (SBML and Matlab files). We show how this pipeline was successfully applied to decipher the coverage of chemical libraries set up by two metabolomics facilities MetaboHub (French National infrastructure for metabolomics and fluxomics) and Glasgow Polyomics (GP) on the metabolic networks available in the MetExplore web server. The present generic protocol is designed to formalize and reduce the volume of information transfer between the library and the network database. Matching of metabolites between libraries and metabolic networks is based on InChIs or InChIKeys and therefore requires that these identifiers are specified in both libraries and networks. In addition to providing covering statistics, this pipeline also allows the visualization of mapping results in the context of metabolic networks. In order to achieve this goal, we tackled issues on programmatic interaction between two servers, improvement of metabolite annotation in metabolic networks and automatic loading of a mapping in genome scale metabolic network analysis tool MetExplore. It is important to note that this mapping can also be performed on a single or a selection of organisms of interest and is thus not limited to large facilities

Intracranial aneurismal pulsatility as a new individual criterion for rupture risk evaluation: Biomechanical and numerical approach (IRRAs project).

International audienceThis study was designed to highlight by means of numerical simulations, the correlation between aneurism sac pulsatility and the risk of rupture through the mechanical properties of the wall. In accordance to previous work suggesting a correlation between the risk of rupture and the material properties of cerebral aneurysms, twelve fluid-structure interaction (FSI) computations were performed on 12 "patient-specific" cases, corresponding to typical shapes and locations of cerebral aneurysms. The variations of the aneurismal volume during the cardiac cycle (3V) are compared using wall material characteristics of either degraded and non-degraded tissues. Aneurysms were located on 7 different arteries: Middle Cerebral Artery (4), Anterior Cerebral Artery (3), Internal Carotid Artery (1), Vertebral Artery (1), Ophthalmic Artery (1) and Basilar Artery (1). Aneurysms presented different shapes (uniform or multi-lobulated) and diastolic volumes (from 18 to 392 mm3). The pulsatility (3V/V) was significantly larger for a soft aneurismal material (average of 26 %) than for a stiff material (average of 4 %). The difference between 3V, for each condition, was statistically significant: p = 0.005. The difference in aneurismal pulsatility as highlighted in this work might be a relevant patientspecific predictor of aneurysm risk of rupture

Challenges and perspectives for naming lipids in the context of lipidomics

Introduction: Lipids are key compounds in the study of metabolism and are increasingly studied in biology projects. It is a very broad family that encompasses many compounds, and the name of the same compound may vary depending on the community where they are studied. Objectives: In addition, their structures are varied and complex, which complicates their analysis. Indeed, the structural resolution does not always allow a complete level of annotation so the actual compound analysed will vary from study to study and should be clearly stated. For all these reasons the identification and naming of lipids is complicated and very variable from one study to another, it needs to be harmonized. Methods & Results: In this position paper we will present and discuss the different way to name lipids (with chemoinformatic and semantic identifiers) and their importance to share lipidomic results. Conclusion: Homogenising this identification and adopting the same rules is essential to be able to share data within the community and to map data on functional networks

A numerical model of wear taking account of multidirectional effects

Many work showed that the change of sliding direction is a factor worsening wear between two bodies in contact. The objective of this study is to propose a model of wear able to reply these observations. This model tries to show that part of the multidirectional effects is due to the variation of wear rate according to the number of cycles. The results presented in this paper come from numerical calculations. They show that using a wear coefficient depending on the sliding distance, one can obtain, for a rectangular motion pattern, a volumetric wear up to 2 times more important than for a rectilinear motion pattern

A numerical model for multidirectional wear

International audienceMany work showed that the change of sliding direction is a factor worsening wear between two bodies in contact. The objective of this study is to propose a model of wear able to reply these observations. This model tries to show that part of the multidirectional effects is due to the variation of wear rate according to the number of cycles. The results presented in this paper come from numerical calculations. They show that using a wear coefficient depending on the sliding distance, one can obtain, for a rectangular motion pattern, a volumetric wear up to 2 times more important than for a rectilinear motion pattern