Claude Verdier

Characterization of wheat flour–water doughs. Part I: Rheometry and microstructure

Abstract The results presented in this paper concern doughs prepared from an industrial soft wheat flour mixed with water using the traditional Brabender farinograph. These doughs are characterized using dynamic rheometrical measurements. In parallel, an innovative microscopy study, the Environmental Scanning Electron Microscope (ESEM) is investigated and found to be very well-suited for the observation of such doughs. A change in the slope of the curve giving the maximum of consistency is observed at a typical water content, due to the presence of excess free water. The main rheometrical characteristics |η*| and tan δ are exhibited for this kind of dough. Their adequacy to differentiate between various doughs is emphasized. Parameters such as mixing time, water content and rest time are shown to influence both the rheometrical properties and the microscopic structure of doughs. Changes generated by mixing are interpreted at the molecular level. It is shown that the study of the microstructure is essential to compare the evolution of different doughs.

Characterization of wheat-flour-water doughs: a new method using ultrasound.

In this paper, an original method of evaluating the physical properties of wheat-flour-water systems using high-frequency low-power ultrasound is presented. Most of the experiments were performed with a reflectance technique measuring the acoustic impedance of doughs. The velocity of propagation, attenuation and viscoelastic moduli have been evaluated for both compressional and shear ultrasonic waves in the interval 2-10 MHz for doughs of different hydrations. The 53% water content was found to be critical with respect to the presence of free water. The influence of the mixing and rest times on the longitudinal ultrasonic parameters is also studied.

An elasto-visco-plastic model of cell aggregates

Concentrated cell suspensions exhibit different mechanical behavior depending on the mechanical stress or deformation they undergo. They have a mixed rheological nature: cells behave elastically or viscoelastically, they can adhere to each other whereas the carrying fluid is usually Newtonian. We report here on a new elasto-visco-plastic model which is able to describe the mechanical properties of a concentrated cell suspension or aggregate. It is based on the idea that the rearrangement of adhesion bonds during the deformation of the aggregate is related to the existence of a yield stress in the macroscopic constitutive equation. We compare the predictions of this new model with five experimental tests: steady shear rate, oscillatory shearing tests, stress relaxation, elastic recovery after steady prescribed deformation, and uniaxial compression tests. All of the predictions of the model are shown to agree with these experiments.

Cell Mechanics. From single scale-based models to multiscale modeling

From Subcellular to Cellular Properties Microrheology of Living Cells at Different Time and Length Scales, Atef Asnacios, Sylvie Henon, Julien Browaeys, and Francois Gallet Actin-Based Propulsion: Intriguing Interplay between Material Properties and Growth Processes, Karin John, Denis Caillerie, Philippe Peyla, Mourad Ismail, Annie Raoult, Jacques Prost, and Chaouqi Misbah Cancer: Cell Motility and Tumor Suppressor Genes, Remy Pedeux, Damien Ythier, and Alain Duperray Single Cell Migration Modeling Coupling of Cytoplasm and Adhesion Dynamics Determines Cell Polarization and Locomotion, Wolfgang Alt, Martin Bock, and Christoph Mohl How Do Cells Move? Mathematical Modeling of Cytoskeleton Dynamics and Cell Migration, Dietmar Olz and Christian Schmeiser Computational Framework Integrating Cytoskeletal and Adhesion Dynamics for Modeling Cell Motility, Angelique Stephanou Mechanical Effects of Environment on Cell Behavior History Dependence of Microbead Adhesion under Varying Shear Rate, Sylvain Reboux, Giles Richardson, and Oliver E. Jensen Understanding Adhesion Sites as Mechanosensitive Cellular Elements, Sophie Fereol, Redouane Fodil, Gabriel Pelle, Bruno Louis, Valerie M. Laurent, Emmanuelle Planus, and Daniel Isabey Cancer Cell Migration on 2-D Deformable Substrates, Valentina Peschetola, Claude Verdier, Alain Duperray, and Davide Ambrosi Single Cell Imaging of Calcium Dynamics in Response to Mechanical Stimulation, Tae-Jin Kim and Yingxiao Wang From Cellular to Multicellular Models Mathematical Framework to Model Migration of Cell Population in Extracellular Matrix, Arnaud Chauviere and Luigi Preziosi Mathematical Modeling of Cell Adhesion and Its Applications to Developmental Biology and Cancer Invasion, Alf Gerisch and Kevin J. Painter Bridging Cell and Tissue Behavior in Embryo Development, Alexandre J. Kabla, Guy B. Blanchard, Richard J. Adams, and L. Mahadevan Modeling Steps from Benign Tumor to Invasive Cancer: Examples of Intrinsically Multiscale Problems, Dirk Drasdo, Nick Jagiella, Ignacio Ramis-Conde, Irene E. Vignon-Clementel, and William Weens Delaunay Object Dynamics for Tissues Involving Highly Motile Cells, Tilo Beyer and Michael Meyer-Hermann Index

Complex Interactions between Human Myoblasts and the Surrounding 3D Fibrin-Based Matrix

Anchorage of muscle cells to the extracellular matrix is crucial for a range of fundamental biological processes including migration, survival and differentiation. Three-dimensional (3D) culture has been proposed to provide a more physiological in vitro model of muscle growth and differentiation than routine 2D cultures. However, muscle cell adhesion and cell-matrix interplay of engineered muscle tissue remain to be determined. We have characterized cell-matrix interactions in 3D muscle culture and analyzed their consequences on cell differentiation. Human myoblasts were embedded in a fibrin matrix cast between two posts, cultured until confluence, and then induced to differentiate. Myoblasts in 3D aligned along the longitudinal axis of the gel. They displayed actin stress fibers evenly distributed around the nucleus and a cortical mesh of thin actin filaments. Adhesion sites in 3D were smaller in size than in rigid 2D culture but expression of adhesion site proteins, including α5 integrin and vinculin, was higher in 3D compared with 2D (p<0.05). Myoblasts and myotubes in 3D exhibited thicker and ellipsoid nuclei instead of the thin disk-like shape of the nuclei in 2D (p<0.001). Differentiation kinetics were faster in 3D as demonstrated by higher mRNA concentrations of α-actinin and myosin. More important, the elastic modulus of engineered muscle tissues increased significantly from 3.5±0.8 to 7.4±4.7 kPa during proliferation (p<0.05) and reached 12.2±6.0 kPa during differentiation (p<0.05), thus attesting the increase of matrix stiffness during proliferation and differentiation of the myocytes. In conclusion, we reported modulations of the adhesion complexes, the actin cytoskeleton and nuclear shape in 3D compared with routine 2D muscle culture. These findings point to complex interactions between muscle cells and the surrounding matrix with dynamic regulation of the cell-matrix stiffness.

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). The VB mode consists in a motion where the long axis of the vesicle oscillates about the flow direction, while the shape undergoes a breathing dynamics. We extend here the original small deformation theory [C. Misbah, Phys. Rev. Lett. 96, 028104 (2006)] to the next order in a consistent manner. The consistent higher order theory reveals a direct bifurcation from TT to TB if Ca identical with taugamma is small enough-typically below 0.5, but this value is sensitive to the available excess area from a sphere (tau=vesicle relaxation time towards equilibrium shape, gamma=shear rate). At larger Ca the TB is preceded by the VB mode. For Ca1 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 briefly analyze rheology and find that the effective viscosity exhibits a minimum in the vicinity of the TT-TB and TT-VB bifurcation points. At small Ca the minimum corresponds to a cusp singularity and is at the TT-TB threshold, while at high enough Ca the cusp is smeared out, and is located in the vicinity of the VB mode but in the TT regime.

TRACTION PATTERNS OF TUMOR CELLS

The traction exerted by a cell on a planar deformable substrate can be indirectly obtained on the basis of the displacement field of the underlying layer. The usual methodology used to address this inverse problem is based on the exploitation of the Green tensor of the linear elasticity problem in a half space (Boussinesq problem), coupled with a minimization algorithm under force penalization. A possible alternative strategy is to exploit an adjoint equation, obtained on the basis of a suitable minimization requirement. The resulting system of coupled elliptic partial differential equations is applied here to determine the force field per unit surface generated by T24 tumor cells on a polyacrylamide substrate. The shear stress obtained by numerical integration provides quantitative insight of the traction field and is a promising tool to investigate the spatial pattern of force per unit surface generated in cell motion, particularly in the case of such cancer cells.

Dynamic shear rheology of high molecular weight polydimethylsiloxanes : comparison of rheometry and ultrasound

Abstract The viscoelastic properties of three linear polydimethylsiloxanes (PDMS) of high molecular weights are investigated using rheometrical as well as ultrasonic tests over a large range of temperatures. Classical shear rheometrical measurements are carried out in the low frequency range from 10−1 to 102 rad s−1 between −50 and +20°C. The frequency range is enlarged using the time–temperature superposition principle, allowing coverage of about 6–7 decades of pulsation. Ultrasonic tests use an inclined incidence wave reflection technique to measure the complex shear mechanical impedance from 1.5 to 25 MHz, between −10 and +50°C. Rheometrical and ultrasonic experiments are then combined for the three PDMSs at the same reference temperature. They give the reduced shear elastic and loss moduli for reduced frequencies covering 10 decades. A discrete relaxation time spectrum is first deduced from the master curve in each case. More accurate predictions may be obtained using a molecular weight distribution and BSW (Baumgaertel–Schausberger–Winter) model for polydisperse systems.

Tumor cell/endothelial cell tight contact upregulates endothelial adhesion molecule expression mediated by NFκB: Differential role of the shear stress

Cancer metastasis is a multistep process involving cell-cell interactions, but little is known about the adhesive interactions and signaling events during extravasation of tumor cells (TCs). In this study, cell adhesion molecule (CAM) expression was investigated using an in vitro assay, in which TCs were seeded onto an endothelial cell (ECs) monolayer and cocultured during 5 h. Flow cytometry, confocal microscopy as well as western blot analysis indicated that endothelial ICAM-1 (Inter Cellular Adhesion Molecule-1), VCAM-1 (Vascular Adhesion Molecule-1) and E-selectin were up-regulated after TC-EC coculture, whereas no change was observed for CAMs expression in tumor cells. This increased CAMs expression required tight contact between TCs and ECs. Incubation of ECs with the pyrrolidine-dithiocarbamate NFkappaB inhibitor prior to coculture, fully prevented coculture-induced expression of endothelial CAMs. Using specific blocking antibodies we showed an implication of ICAM-1 and VCAM-1 for TCs extravasation and VCAM-1 for adhesion. Moreover, fluid flow experiments revealed that high shear stress totally abolished coculture-induced as well as TNFalpha-induced CAMs over-expression. This study suggests that TCs could act as a potent inflammatory stimulus on ECs by inducing CAMs expression via NFkappaB activation, and that this action can be modulated by shear stress.

The Mechanisms of Peeling of Uncross-Linked Pressure Sensitive Adhesives

Abstract We analyze the peeling properties of an uncross-linked pressure sensitive adhesive. 90° peeling master curves on PyrexTM and PMMA (polymethylmetacrylate) are constructed The shift coefficients aT are compared with the ones obtained from rheometrical shear tests. With our machine, the peeling front is kept fixed, enabling us to observe the mechanisms of deformation of the adhesive. We count four different mechanisms of peeling in cohesive failure, and three in interfacial peeling (the last being unstable); they correspond to various slopes that we identify. The flow patterns at slow reduced velocities are two-dimensional. Then they undergo transitions to three-dimensional periodic complex flows, due to instabilities in the flow of thin adhesives. Interpretation of these peeling master curves are discussed in terms of rheology and physico-chemistry. It appears necessary to take into account the elongational properties of the adhesive, as well as the surface energy properties, to predict adhesion.