Etude de la réorganisation macroscopique de la peau de souris lors d'une sollicitation bi-axiale

La peau est composée en majorité de collagène et présente une microstructure très hiérarchisée qui influe sur son comportement mécanique aux différentes échelles. Pour caractériser l'influence de la microstructure sur les propriétés mécaniques, un test de traction bi-axiale couplé à une mesure macroscopique (corrélation d'images numériques) et microscopique (génération de second harmonique) a été développé . A terme, ce travail permettra de corréler les propriétés macroscopiques à la microstructures. Cette étude présente les résultats de la mesure effectuée par corrélation d'images

Molecular phylogeny and origin of polyploid gorses (Ulex, Fabaceae)

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Molecular phylogeny and origin of polyploid gorses (Ulex, Fabaceae)

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Improving the experimental protocol for a more accurate identification of a given mechanical behavior in a single assay: application to skin

International audienceMechanical properties of the skin, the external organ of the human body, are important for many applications such as surgery or cosmetics. Due to the highly hierarchical structure of the tissue, it is interesting to develop microstructural models which have a better predictability and should reduce the consequences of the sample variability. However, these models generally include a quite large number of mechanical parameters. Therefore, complex assays are required to achieve a proper identification of the microstructural models. We investigated here the best experimental protocol to identify a non-linear, anisotropic, model of skin behavior, namely the Holzapfel's law, using displacement field and force measurements. This was done through a sensitivity analysis of the different parameters. We determined first the 1 optimal assay, which appears to be a biaxial test with an alternated loading: first a stretch in one direction, then in the perpendicular one, and so on. To further improve the quality of the assay, we also determined the optimal geometry. Interestingly, slightly asymmetric geometries are more adequate than symmetric ones, while being easier to realize

Molecular phylogenetic evidence support an allopolyploid origin of the invasive european gorse, Ulex europaeus subsp. Europaeus (Fabaceae)

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Molecular phylogenetic evidence support an allopolyploid origin of the invasive european gorse, Ulex europaeus subsp. Europaeus (Fabaceae)

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Molecular phylogenetics shed light on polyploid speciation in gorses (Ulex, Fabaceae: Genisteae) and on the origin of the invasive Ulex europaeus

International audienceHybridization and polyploidy are key evolutionary forces in plant diversification, and their co-occurrence in the context of allopolyploid speciation is often associated with increased ability to colonize new environments and invasiveness. In the genus Ulex (Fabaceae), the European gorse (Ulex europaeus subsp. europaeus) is the only invasive and the only polyploid that has recently spread in different eco-geographical regions across the world. Understanding what confers such ecological advantages to this species, compared to its diploid and polyploid congeners, first requires clarification of the ecogeographical and evolutionary context of its formation. To achieve this, the geographical distributions of all Ulex spp. were estimated from species occurrence records, and phylogenetic analyses including all Ulex spp. were performed based on four nuclear (ITS and ETS nrDNA) and plastid (rps12 intron and trnK-matK) regions. The resulting trees were dated using a secondary calibration. Patterns of DNA sequence variation and dated phylogenetic trees were then interpreted in light of previous knowledge of chromosome numbers in Ulex to infer past events of polyploid speciation in the genus. We show that: (1) most current Ulex spp. radiated in the Iberian Peninsula during the past 1-2 Myr; (2) the history of Ulex was punctuated by multiple whole-genome duplication events; and (3) U. europaeus subsp. europaeus is the only gorse taxon that was formed by hybridization of two well-differentiated lineages (which separated c. 5 Mya) with wide climatic ranges (currently represented by Ulex minor and Ulex europaeus subsp. latebracteatus), possibly contributing to the invasive nature and wider climatic range of U. europaeus subsp. europaeus. These findings provide a much-needed evolutionary framework in which to explore the adaptive consequences of genome mergers and duplication in Ulex

Corrélation des propriétés mécaniques et micro-structurelles de la peau de souris à partir d'une sollicitation bi-axiale

International audienceLe derme, composant principal de la peau, est composée en majorité de collagène et présente une micro-structure très hiérarchisée qui influe sur son comportement mécanique aux différentes échelles. La prédiction de son comportement nécessite de caractériser l’influence de la micro-structure sur les propriétés mécaniques. Aussi, un test de traction bi-axiale couplé indépendamment à une mesure macroscopique et à une mesure microscopique a été développé. Ce travail a finalement permis d’identifier les paramètres d’une loi hyper-élastique anisotrope et de tester l’hypothèse de transformation affine sous-jacent au comportement adopté