On inverse analysis and robustness evaluation for biological structure behaviour in FE simulation. Application to the liver

To prevent abdominal organs traumas, the definition of efficient safety devices should be based on a detailed knowledge of injury mechanisms and related injury criteria. In this sense, FE simulation coupled to experiment could be a valuable tool to provide a better understanding of internal organs behaviour under crash conditions. This work proposes a methodology based on inverse analysis which combines exploration process optimisation and robustness study to obtain mechanical behaviour of the complex structure of the liver through FE simulation. The liver characterisation was build on Mooney Rivlin hyperelastic behaviour law considering whole liver structure under uniform quasi-static compression. With the global method used, the model fits experimental data. The variability induced by modelling parameters is quantified within a reasonable time. Liver compression, FE simulation, inverse analysis, robustness analysis

The deep-sea macrobenthos on the continental slope of the northwestern Mediterranean Sea: a quantitative approach

As part of the ECOMARGE operation (J.G.O.F.S. France), macrobenthic assemblages in the Toulon Canyon were described and quantified on the basis of sampling carried out between 250 and 2000 m depth on the Mediterranean continental slope. Results show that Mediterranean bathyal assemblages are made up mainly of continental shelf eurybathic species. The qualitative and quantitative composition of populations varies with depth on the slope and also varies with station position at equivalent depth, whether on the flanks or in the canyon channel. Various analyses have provided evidence on the factors responsible for this population distribution pattern. No single factor emerges as predominant, but rather a group of factors, which are related to the nature and origin of sediments and more particularly their grain size distribution, geochemical composition and mode of transportation and sedimentation (benthic nepheloid or originating from the water column), act in conjunction to determine the pattern. Comparison with ocean continental slopes shows that in the Mediterranean Sea the absence of tidal current modifies the trophic structure of the macrobenthic assemblages, which are characterized by a dominance of surface and subsurface deposit feeders as compared to a dominance of suspension feeders and carnivores in the upper and median part of the slope in the ocean. Surface dumping of dredge spoil at the canyon head and channelling of waste induces an increase of organic matter and pollutant concentrations in sediment from the upper part of the canyon channel but does not give rise to any marked population degradation

Neck Braces and Driving Posture Affect Neck Mobility on Powered Two-Wheelers

Cervical spine injuries are a major concern for motorcyclists in traffic accidents and racing competitions. Neck braces aim to prevent cervical spine injuries during accidents by reducing the neck range of motion, and keeping it under physiological limits. This work aims to evaluate the ability of neck braces to reduce neck mobility for two driving postures associated with PTW configurations. The neck mobility of twelve volunteer subjects testing four neck braces on two powered two-wheelers (scooter and racing motorbike) is measured using an optoelectronic motion capture system. With the tested neck braces worn, neck mobility is significantly reduced as compared to the physiological range of motion in all degrees of freedom. However, only flexion/extension is reduced by all neck braces tested. This suggests that these brace designs do not provide protection against all the cervical spine loading directions that may occur in a trauma. Furthermore, specific type of each powered two-wheeler considered significantly affects the neck mobility in axial rotation, as well as the postero-anterior and caudo-cranial translations, thus underscoring the need to consider the driving posture when evaluating neck brace devices

Method to geometrically personalize a detailed finite element model of the spine

To date, developing geometrically personalized and detailed solid finite element models of the spine remains a challenge, notably due to multiple articulations and complex geometries. To answer this problem, a methodology based on a free form deformation technique (kriging) was developed to deform a detailed reference finite element mesh of the spine (including discs and ligaments) to the patient-specific geometry of 10 and 82-year old asymptomatic spines. Different kriging configurations were tested: with or without smoothing, and control points on or surrounding the entire mesh. Based on the results, it is recommended to use surrounding control points and smoothing. The mean node to surface distance between the deformed and target geometries was 0.3 mm ± 1.1. Most elements met the mesh quality criteria (95%) after deformation, without interference at the articular facets. The method’s novelty lies in the deformation of the entire spine at once, as opposed to deforming each vertebra separately, with surrounding control points and smoothing. This enables the transformation of reference vertebrae and soft tissues to obtain complete and personalized FEMs of the spine with minimal post-processing to optimize the mesh. Biomechanics

The discovery, distribution, and evolution of viruses associated with drosophila melanogaster

Drosophila melanogaster is a valuable invertebrate model for viral infection and antiviral immunity, and is a focus for studies of insect-virus coevolution. Here we use a metagenomic approach to identify more than 20 previously undetected RNA viruses and a DNA virus associated with wild D. melanogaster. These viruses not only include distant relatives of known insect pathogens, but also novel groups of insect-infecting viruses. By sequencing virus-derived small RNAs we show that the viruses represent active infections of Drosophila. We find that the RNA viruses differ in the number and properties of their small RNAs, and we detect both siRNAs and a novel miRNA from the DNA virus. Analysis of small RNAs also allows us to identify putative viral sequences that lack detectable sequence similarity to known viruses. By surveying >2000 individually collected wild adult Drosophila we show that more than 30% of D. melanogaster carry a detectable virus, and more than 6% carry multiple viruses. However, despite a high prevalence of the Wolbachia endosymbiont—which is known to be protective against virus infections in Drosophila—we were unable to detect any relationship between the presence of Wolbachia and the presence of any virus. Using publicly available RNA-seq datasets we show that the community of viruses in Drosophila laboratories is very different from that seen in the wild, but that some of the newly discovered viruses are nevertheless widespread in laboratory lines and are ubiquitous in cell culture. By sequencing viruses from individual wild-collected flies we show that some viruses are shared between D. melanogaster and D. simulans. Our results provide an essential evolutionary and ecological context for host-virus interaction in Drosophila, and the newly reported viral sequences will help develop D. melanogaster further as a model for molecular and evolutionary virus research

Modélisation des ligaments des membres antérieurs. A propos des ligaments des genoux

Université de la Méditerranée - Aix-Marseille IIQue ce soit en accidentologie ou en traumatologie sportive, le genou est exposé à de très fortes sollicitations se traduisant par de l'endommagement et de la rupture des structures ligamentaires. Ce travail s'inscrit dans ce contexte et porte sur l'identification des lois de comportement des quatre ligaments du genou, dans un cadre de sollicitations dynamiques, c'est-à-dire lorsqu'ils sont soumis à des situations de chocs, entraînant de l'endommagement et de la rupture dans le matériau. Il s'articule autour de tois axes de recherche: - un axe expérimental où un dispositif de traction dynamique des ligaments du genou a été conçu. Les résultats obtenus (pour des vitesse de sollicitation de 2m/s) ont servi de support à l'identification des lois de comportement et ont pu mettre en évidence les caractéristiques de la rupture des ligaments du genou sollicités dans l'axe des fibres (modes, faciès, localisation). - un axe mécanique, qui consiste à identifier les lois de comportement des ligaments du genou au travers de deux types de formulation: une formulation thermodermique où un modèle viscoélastique endommageable est proposé et une formulation structurelle permettant, à partir d'un modèle éléments finis de la fibrille de collagène, de suivre les mécanismes de décohésions des fibres entres-elles. - un axe modélisation base sur la méthode des éléments finis, a permis de poser les bases d'un modèle 3D de l'articulation du genou. En intégrant les lois de comportement développées ci-dessus, ce modèle permet la simulation numérique de chocs sur l'articulation du genou

Séquences thérapeutiques dans la correction de l'effondrement occlusal postérieur

L'effondrement occlusal postérieur secondaire à la maladie parodontale peut se traduire par des diastèmes antérieurs, une perte de dimension verticale et un proglissement de la mandibule. L'orthodontie doit alors s'insérer dans le plan de traitement, conçu selon une thérapeutique bien définie

Expérimentation et modélisation détaillée de la colonne vertébrale pour étudier le rôle des facteurs anatomiques et biomécaniques sur les traumatismes rachidiens

L objectif de la thèse était d étudier l influence de facteurs anatomiques et biomécaniques tels que la présence d ostéophytes vertébraux, le taux de chargement et le profil sagittal rachidien (défini par l orientation et la forme de la colonne vertébrale dans le plan sagittal) sur les traumatismes de la colonne vertébrale thoracique et lombaire. Pour ce faire, des essais expérimentaux sur spécimens cadavériques rachidiens ont été réalisés et un modèle biomécanique détaillé du rachis T1-sacrum a été raffiné, validé expérimentalement et exploité. Les résultats ont démontré que les segments ostéophytiques présentaient des fractures de moindre sévérité localisées au niveau de la vertèbre proximale, contrairement aux segments sans ostéophytes, qui présentaient des fractures sévères (souvent comminutives) au niveau de la vertèbre médiane. Ils ont également confirmé que le taux de déformation jouait un rôle-clé dans l initiation du traumatisme et que le profil sagittal avait une influence significative sur les caractéristiques des fractures osseuses lors d accidents impliquant un mécanisme principalement en compression. En revanche, le profil sagittal n exercerait qu une influence limitée sur la nature des traumatismes lors d un accident impliquant un mécanisme de flexion-distraction.The objective of this thesis was to study the influence of anatomical and biomechanical factors such as the presence of vertebral osteophytes, the loading rate and the sagittal profile of the spine (defined by the orientation and shape of the spine in the sagittal plane) on spinal injuries at the thoracic and lumbar levels. To fulfill this objective, experiments on human cadaveric spines were performed and a detailed biomechanical model of the spine was refined, validated against experimental data, and exploited. Results showed that the presence of large osteophytes significantly influenced the location, pattern and type of fracture, and provided to the underlying vertebra a protective mechanism against severe compression fractures (e.g. burst fractures). They also showed that the loading rate played a key-role on the onset of spinal trauma and that the sagittal profile of the spine had a significant influence on the bone fracture in accidents that involve compression mechanisms. On the other hand, the sagittal profile of the spine had a limited influence on the nature of spinal injuries in accidents that involved flexion-distraction mechanisms.AIX-MARSEILLE2-Bib.electronique (130559901) / SudocSudocFranceF

A Visco-hyperelastic Model With Damage for the Knee Ligaments Under Dynamic Constraints

International audienceThe aim of this study was to identify the behaviour laws governing the knee ligaments, accounting for the damage incurred by the structure under dynamic constraints. The model is developed using a thermodynamic formulation based on the coupling between a viscoelastic model and a damage model. Identification is carried out using the results of dynamic traction tests performed on a bone ligament/bone complex to which traction velocities of around 1.98 m/s were applied. The results show the ability of the model to account for the brittle and ductile failure processes occurring in the cruciate and lateral ligaments, respectively