A fractal approach to the rheology of concentrated cell suspensions

Results on the rheological behavior of novel CHO cell suspensions in a large range of concentrations are reported. The concentration dependent yield stress and elastic plateau modulus are formalized in the context of fractal aggregates under shear, and quite different exponents are found as compared to the case of red blood cell suspensions. This is explained in terms of intrinsic microscopic parameters such as the cell-cell adhesion energy and cell elasticity but also the cell individual dynamic properties, found to correlate well with viscoelastic data at large concentrations (phi>0.5).Comment: 4 pages, 5 figure

Dynamics and rheology of a dilute suspension of vesicles: higher order theory

Vesicles under shear flow exhibit various dynamics: tank-treading ($tt$), tumbling ($tb$) and vacillating-breathing ($vb$). A consistent higher order theory reveals a direct bifurcation from $tt$ to $tb$ if $C_a\equiv \tau \dot\gamma$ is small enough ($\tau$= vesicle relaxation time towards equilibrium shape, $\dot\gamma$=shear rate). At larger $C_a$ the $tb$ is preceded by the $vb$ mode. For $C_a\gg 1$ we recover the leading order original calculation, where the $vb$ mode coexists with $tb$. The consistent calculation reveals several quantitative discrepancies with recent works, and points to new features. We analyse rheology and find that the effective viscosity exhibits a minimum at $tt-tb$ and $tt-vb$ bifurcation points.Comment: 4 pages, 5 figure

La construcción social de la fibromialgia como problema de salud a través de las políticas y la prensa en España

Antecedentes/Objetivos: La fibromialgia (FM) es una enfermedad crónica dolorosa recientemente reconocida que afecta principalmente a las mujeres. El objetivo de este estudio es analizar la emergencia y visibilidad de la FM como un problema de salud en las políticas sanitarias, iniciativas parlamentarias (IP) y noticias de prensa en España. Métodos: Este estudio está estructurado en tres análisis independientes pero relacionados entre sí, acerca de la visibilización de la FM como un problema de salud desde distintos enfoques metodológicos y fuentes de información. Para ello se realizaron búsquedas sistemáticas a través de Internet y análisis de contenido cualitativo de los planes de salud autonómicos, noticias de prensa (El País, El Mundo y ABC) e iniciativas parlamentarias (IP) en España hasta el año 2013. Resultados: Los planes de salud no incluyen la FM entre los problemas de salud que priorizan en sus estrategias. Las IP reflejan la desproporcionada prevalencia femenina de la FM y denuncian su difícil diagnóstico, la falta de recursos destinados a la investigación y a su tratamiento, así como la falta de reconocimiento social y de las incapacidades laborales. La prensa refleja el estereotipo de enferma de las pacientes, pasivas y resignadas, que por el contrario cobran fuerza en grupo mediante las asociaciones, representadas como activas y luchadoras, quienes han conseguido llegar al Parlamento y tener impacto en las políticas. Ambos análisis indican que el año 2002 supuso un punto de inflexión en el reconocimiento social de la enfermedad, debido a la popularización del caso de particular de la diputada del PSOE en Cataluña, Manuela de Madre, a quien se le diagnosticó FM. Conclusiones: La incipiente incorporación de la FM en la agenda parlamentaria española y su cobertura periodística tienen un impacto positivo, puesto que promueven el conocimiento y la sensibilización social sobre este problema de salud. Aún así, los resultados muestran que la construcción social de la FM como problema de salud se encuentra en fase de decrecimiento gradual de interés. Además, la falta de reconocimiento social de la enfermedad puede estar relacionada con que se construye socialmente como un problema de salud de mujeres, con estereotipos de género.Centro de Estudios sobre la Mujer (CEM), Universidad de Alicante

On the quasi-static effective behaviour of poroelastic media containing elastic inclusions

The aim of the present study is to derive the effective quasi-static behaviour of a composite medium, made of a poroelastic matrix containing elastic impervious inclusions. For this purpose, the asymptotic homogenisation method is used. On the local scale, the governing equations include Biot's model of poroelasticity in the porous matrix and Navier equations in the inclusions, with elastic properties of the same order of magnitude. Biot's diphasic model of poroelasticity is obtained on the macroscopic scale, but with effective parameters that are strongly impacted by the distribution of inclusions, even at low volume fraction. The impact on fluid flow is strictly geometrical, showing that the inclusions do not play the role of a porous network

3D cancer cell migration in collagen matrices

International audienceCell migration is a widely studied subject but often limited to 2D motion (Sheetz et al., 1999) on various substrates for it allows to simplify cell-substrate interactions. The important relevant parameters to 2D cell migration are substrate rigidity, adhesion, and the role of the cell cytoskeleton. More recently, new studies on 3D cell migration have been performed thanks to the development of new visualization tools such as reflectance confocal microscopy (Iordan et al. 2010, Wolf et al. 2013). In particular, it is possible to image cell and the extra-cellular matrix at the same time. This leads to interesting applications on cancer cell migration, and could possibly open new routes to the understanding of cancer development, like the mechanisms used by cancer cells to invade new tissues.Thus, the aim of this study is to study cancer migration in collagen matrices, as a model of soft tissue, to investigate their motility within the surrounding collagen matrix. Different collagen concentrations will be used and the ability of these cancer cells to move through such a complex structure will be addressed. To this aim, first results of cell migration velocity as well as the Mean Squared Displacement (MSD) will be analyzed

A biomechanical model for the transendothelial migration of cancer cells

We propose a biomechanical model for the extravasation of a tumor cell (TC) through the endothelium of a blood vessel. Based on prior in vitro observations, we assume that the TC extends a protrusion between adjacent endothelial cells (ECs) that adheres to the basement membrane via focal adhesions. As the protrusion grows in size and branches out, the actomyosin contraction along the stress fibers inside the protrusion pulls the relatively rigid nucleus through the endothelial opening. We model the chemo-mechanics of the stress fibers and the focal adhesions by following the kinetics of the active myosin motors and high-affinity integrins, subject to mechanical feedback. This is incorporated into a finite-element simulation of the extravasation process, with the contractile force pulling the nucleus of the tumor cell against elastic resistance of the ECs. To account for the interaction between the TC nucleus and the endothelium, we consider two scenarios: solid-solid contact and lubrication by cytosol. The former gives a lower bound for the required contractile force to realize transmigration, while the latter provides a more realistic representation of the process. Using physiologically reasonable 1 parameters, our model shows that the stress-fiber and focal-adhesion ensemble can produce a contractile force on the order of 70 nN, which is sufficient to deform the ECs and enable transmigration. Furthermore, we use an atomic force microscope to measure the resistant force on a human bladder cancer cell that is pushed through an endothelium cultured in vitro. The magnitude of the required force turns out to be in the range of 70-100 nN, comparable to the model predictions

Amélioration des performances d'un amplificateur de puissance pour un radar GPR

Cet article présente l'amélioration du fonctionnement d'un amplificateur de puissance inclus dans le module d'émission d'un radar GPR (ground penetrating RADAR) dont la finalité est d'analyser la constitution et la géométrie du sous-sol de la planète Mars. Cet amplificateur opérant en HF (2MHz) est capable de fournir une puissance de 10W sur une charge de 50Ω. Lorsque l'amplificateur est connecté à l'antenne réelle, la charge complexe présentée en modifie les performances. Une solution utilisant un correcteur proportionnel-intégral (PI) a été étudiée et testée expérimentalement afin d'améliorer les performances de l'amplificateur en régime impulsionnel

Atomic Force microscopy reveals a role for endothelial cell ICAM-1 expression in bladder cancer cell adherence

International audienceCancer metastasis is a complex process involving cell-cell interactions mediated by cell adhesive molecules. In this study we determine the adhesion strength between an endothelial cell monolayer and tumor cells of different metastatic potentials using Atomic Force Microscopy. We show that the rupture forces of receptor-ligand bonds increase with retraction speed and range between 20 and 70 pN. It is shown that the most invasive cell lines (T24, J82) form the strongest bonds with endothelial cells. Using ICAM-1 coated substrates and a monoclonal antibody specific for ICAM-1, we demonstrate that ICAM-1 serves as a key receptor on endothelial cells and that its interactions with ligands expressed by tumor cells are correlated with the rupture forces obtained with the most invasive cancer cells (T24, J82). For the less invasive cancer cells (RT112), endothelial ICAM-1 does not seem to play any role in the adhesion process. Moreover, a detailed analysis of the distribution of rupture forces suggests that ICAM-1 interacts preferentially with one ligand on T24 cancer cells and with two ligands on J82 cancer cells. Possible counter receptors for these interactions are CD43 and MUC1, two known ligands for ICAM-1 which are expressed by these cancer cells