Modélisation numérique d'un fémur ostéoporotique: avant et après implantation d'une prothèse totale de hanche

International audienceNot availableLa résistance de l'os dépend de son état de minéralisation et de sa géométrie, qui eux même dépendent des sollicitations supportées. Ainsi l'os optimise sa masse et sa géométrie à travers le processus de remodelage et améliore sa portance. Ce phénomène peut être altéré par des déséquilibres métaboliques comme l'ostéoporose ou par des traumatismes. Il en résulte en général des fractures, dont les plus importantes sont celles qui touchent la partie proximale du fémur. La conséquence directe de ce type de fracture est le remplacement de l'articulation par une Prothèse Totale de Hanche (PTH). Le nombre d’implantations prothétiques ne cesse d’augmenter compte tenu de l’allongement de l’espérance de vie des patients. Dans la pathologie de l'ostéoporose, la résistance osseuse est essentiellement altérée par des mécanismes de dégradation de la structure. La résistance est ainsi altérée et conduit à une fracture. De même, la mise en place d'une PTH pour remplacer l'articulation, perturbe le régime des sollicitations physiologiques et mécaniques. Ainsi l'os est soumis à un nouvel environnement mécanique qui se traduit localement par des variations de champs de contraintes perturbants ainsi le remodelage osseux déjà touché par l'ostéoporose. L'objectif de ce travail est d'étudier la répartition des contraintes au sein du tissu osseux et l'influence de la perturbation des zones de sollicitations dans un fémur ostéoporotique

A topology optimization based model of bone adaptation

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Numerical modeling of an osteoporotic femur: comparison before and after total hip prosthesis implantation

International audienceABSTRACT: The bone strength depends on its mineralization and its geometry, which depend themselves on the supported solicitations. The bone optimizes its mass and geometry in order to improve its strength. The optimization process is called bone remodeling. This phenomenon can be deteriorated by metabolic diseases like osteoporosis. This disease weakens the bone structure and causes bone fractures. Among those fractures, femoral neck fractures (hip articulation) are the most recurrent and involve the replacement of the entire hip articulation by a mechanic articulation (Total Hip Arthroplasty). In this paper, finite element models were developed to evaluate, firstly, the stress distribution within osteoporotic human femur bone tissue and secondly, the influence of the perturbation of the stress distribution by Total Hip Arthroplasty on its first stability. The geometry of the femur and the prosthesis was obtained by helicoid scanner acquisition. The bone was considered as two separate types of tissue: cortical bone and cancellous bone. The cortical bone was separated from the trabecular bone by apparent density threshold. In the case of osteoporotic femur the results obtained from the simulations suggest that the mechanism of load transmission is pertubated by the bone remodelling. The degradation of trabecular architecture causes high stresses in the antero-inferior zone of the cortical bone. For the femur with hip prosthesis, the results showed that the implant has significant effects on the stress distribution within bone tissue. High stresses, due to the implant, weak the bone tissue in the lateral zone of the proximal dyaphisis and in the medial zone of the distal part at the end of the stem

Modèle de tenségrité viscoélastique pour l'étude de la réponse dynamique des cellules adhérentes

Un modèle de tenségrité viscoélastique est développé et caractérisé dans les domaines temporel et fréquentiel pour comprendre le rôle joué par la déformation structurale du cytosquelette dans la réponse cellulaire. Des tests de fluage et d oscillations imposées sont simulés, permettant d établir des dépendances entre les propriétés viscoélastiques globales du modèle et la déformation globale, des paramètres locaux à l état de référence et la fréquence. L augmentation de la tension induit des processus de rigidification et de solidification du modèle. De plus, l augmentation de la fréquence entraîne des processus de rigidification, de dilution et de solidification. Ces résultats sont en accord avec les résultats expérimentaux obtenus sur cellules alors que l effet d échelle est en accord avec les processus d assouplissement et de dilution. A l échelle cellulaire, le modèle prédit le rôle de la redistribution spatiale des filaments sur les propriétés mécaniques de la cellule.A viscoelastic tensegrity model is developed and characterized in both the time and the frequency domains to understand the role of the structural deformation of the cytoskeleton in the cellular response. Simulations of creep tests and forced oscillations are performed, allowing the close links between the global viscoelastic properties of the model and the global deformation, local parameters defined at reference state and the forced frequency. Increasing the tension produces stiffening and solidifying processes of the model. Moreover, increasing the frequency produces stiffening, watering and solidifying processes. These results are in agreement with the experimental results reported in living cells while the scale effect is in agreement with the softening and watering processes. At cellular scale, the model can predicts the role of the spatial reorganization of the cytoskeletal filaments on the mechanical properties of the cell.PARIS12-CRETEIL BU Multidisc. (940282102) / SudocSudocFranceF

Toward a generalized tensegrity model describing the mechanical behaviour of the cytoskeleton structure

The control of many cell functions including growth, migration and mechanotransduction, depends crucially on stress-induced mechanical changes in cell shape and cytoskeleton (CSK) structure. Quantitative studies have been carried out on 6-bar tensegrity models to analyse several mechanical parameters involved in the mechanical responses of adherent cells (i.e. strain hardening, internal stress and scale effects). In the present study, we attempt to generalize some characteristic mechanical laws governing spherical tensegrity structures, with a view of evaluating the mechanical behaviour of the hierarchical multi-modular CSK-structure. The numerical results obtained by studying four different tensegrity models are presented in terms of power laws and point to the existence of unique and constant relationships between the overall structural stiffness and the local properties (length, number and internal stress) of the constitutive components

Tensegrity behavior of cortical and cytosolic cytoskeletal components in twisted living adherent cells

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Interrelations between elastic energy and strain in a tensegrity modeL ; contribution to the analysis on the mechanical response i

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Divided medium-based model for analyzing the dynamic reorganization of the cytoskeleton during cell deformation

International audienceCell deformability and mechanical responses of living cells depend closely on the dynamic changes in the structural architecture of the cytoskeleton (CSK). To describe the dynamic reorganization and the heterogeneity of the prestressed multi-modular CSK, we developed a two-dimensional model for the CSK which was taken to be a system of tension and compression interactions between the nodes in a divided medium. The model gives the dynamic reorganization of the CSK consisting of fast changes in connectivity between nodes during medium deformation and the resulting mechanical behavior is consistent with the strain-hardening and prestress-induced stiffening observed in cells in vitro. In addition, the interaction force networks which occur and balance to each other in the model can serve to identify the main CSK substructures: cortex, stress fibers, intermediate filaments, microfilaments, microtubules and focal adhesions. Removing any of these substructures results in a loss of integrity in the model and a decrease in the prestress and stiffness, and suggests that the CSK substructures are highly interdependent. The present model may therefore provide a useful tool for understanding the cellular processes involving CSK reorganization, such as mechanotransduction, migration and adhesion processes