Biorheology - Volume 40, issue 1-3

Authors: Stamenović, Dimitrije | Mijailovich, Srboljub M. | Tolić‐Nørrelykke, Iva Marija | Wang, Ning

Article Type: Research Article

Abstract: The tensegrity model depicts the cytoskeleton (CSK) as a prestressed network of interconnected filaments. The prestress is generated by the CSK contractile apparatus and is partly balanced by traction at the cell–substrate interface and partly by CSK internal compression elements such as microtubules (MTs). A key feature of tensegrity is that the shear modulus (G) must increase in proportion with the prestress. Here we have tested that prediction as well as the idea that compression of MTs balance a portion of the cell prestress. Airway smooth muscle cells were studied. Traction microscopy was used to calculate traction. Because traction must …be balanced by the stress within the cell, the prestress could be computed. Cell G was measured by oscillatory magnetic cytometry. The prestress was modulated using graded concentrations of contracting (histamine) or relaxing (isoproterenol) agonists and by disrupting MTs by colchicine. It was found that G increased in proportion with the prestress and that compression of MTs balanced a significant, but a relatively small fraction of the prestress. Taken together, these results do not disprove other models of cell deformability, nor they prove tensegrity. However, they do support a priori predictions of tensegrity. As such, it may not be necessary to invoke more complex mechanisms to explain these central features of cell deformability. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 221-225, 2003

Authors: Li, LePing | Shirazi‐Adl, A. | Buschmann, M.D.

Article Type: Research Article

Abstract: The fibril reinforced poroelastic models have been found successful in describing some mechanical behaviors of articular cartilage in unconfined compression that were not understood previously, including the strong and nonlinear transient response, the strain‐magnitude and strain‐rate dependent cartilage stiffness and the depth‐varying stresses and strains. It has been demonstrated that a better description for the mechanical behavior of cartilage is obtained by introducing a fibrillar matrix into a poroelastic model, in addition to the nonfibrillar matrix and water. This paper reports the development of the nonlinear fibril reinforced homogeneous and nonhomogeneous models and further explores the potentials of the models …for investigation of cartilage mechanical response. Some comments are made in regard to further applications of the models and improved accuracy of the material representation. Show more

Keywords: Cartilage mechanics, fibril reinforcement, finite element, inhomogeneity, nonlinear biomechanics, poroelasticity

Citation: Biorheology, vol. 40, no. 1-3, pp. 227-233, 2003

Authors: Laurent, Valérie M. | Planus, Emmanuelle | Fodil, Redouane | Isabey, Daniel

Article Type: Research Article

Abstract: This study aims at quantifying the cellular mechanical properties based on a partitioning of the cytoskeleton in a cortical and a cytosolic compartments. The mechanical response of epithelial cells obtained by magnetocytometry – a micromanipulation technique which uses twisted ferromagnetic beads specifically linked to integrin receptors – was purposely analysed using a series of two Voigt bodies. Results showed that the cortical cytoskeleton has a faster response (∼1 s) than the cytosolic compartment (∼30 s). Moreover, the two cytoskeletal compartments have specific mechanical properties, i.e., the cortical (resp. cytosolic) cytoskeleton has a rigidity in the range: 49–85 Pa (resp.: 74–159 …Pa) and a viscosity in the range 5–14 Pa.s (resp.: 593–1534 Pa.s), depending on the level of applied stress. Depolymerising actin‐filaments strongly modified these values and especially those of the cytosolic compartment. The structural relevance of this two‐compartment partitioning was supported by images of F‐actin structure obtained on the same cells. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 235-240, 2003

Authors: Fodil, Redouane | Laurent, Valérie | Planus, Emmanuelle | Isabey, Daniel

Article Type: Research Article

Abstract: Evaluation of the cytoskeleton mechanical properties requires specific micromanipulation techniques such as the magnetic twisting cytometry technique, in which microbeads are specifically linked to the cytoskeleton via transmembrane receptors. The aim of the study was to assess the structural relationship between the bead and the cytoskeleton structure. The spatial arrangement of the CSK network was therefore studied in fixed cells probed by beads and stained for F‐actin by rhodamined phalloïdine. The spatial character of the actin CSK network, both in the bead neighborhood and at the cell scale, could then be studied for various degrees of fluorescent intensity from 3D‐images …of the actin structure, reconstructed from z‐stack views obtained by confocal microscopy. Results show the feasibility of the staining/reconstruction technique which allows to reveal the three‐dimensional organization of the cytoskeleton structure including an internal cytosolic structure with a high fluorescent F‐actin intensity, and a sub‐membranous cortical structure with a low fluorescent F‐actin intensity. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 241-245, 2003

Authors: Lenormand, G. | Hénon, S. | Richert, A. | Siméon, J. | Gallet, F.

Article Type: Research Article

Abstract: We have measured by optical tweezers micromanipulations the area expansion and the shear moduli of spectrin skeletons freshly extracted from human red blood cells, in different controlled salinity conditions. At medium osmolarity (150 mOsm/kg), we measure KC =9.7±3.4 μN/m, μC =5.7±2.3 μN/m, KC /μC =2.1±0.7. When decreasing the osmolarity, both KC and μC decrease, while KC /μC is nearly constant and equal to about 2. This result is consistent with the predictions made when modeling the spectrin skeleton by a two‐dimensional triangular lattice of springs. From the measured elastic moduli we estimate the persistence length of a …spectrin filament: ξ∼2.5 nm at 150 mOsm/kg. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 247-251, 2003

Authors: Dumas, D. | Grossin, L. | Cauchois, G. | Gentils, M. | Santus, R. | Stoltz, J.F.

Article Type: Research Article

Abstract: The increase in lateral and spatial resolutions is one of the major targets of research and development in the field of optical microscopies applied to living tissue. The optical geometry of Confocal Laser Scanning Microscopy (CLSM) demonstrates its undeniable advantage on conventional fluorescence microscopy by segregating the planes outside the focussing plane. The methodological and technological advances of the last five years have been fast evolving, especially with regard to the optimisation of CLSM and deconvolution process. The limited analysis in thick tissue have given rise to the development of other techniques, multi‐photon excitation microscopy in particular. In this …paper, we have applied these techniques on major biological applications in bioengineering (endothelial cell, chondrocyte in 3D‐culture, human cartilage) and discussed the technical limitations and perspectives. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 253-259, 2003

Authors: Even, P. | Chaubet, F. | Letourneur, D. | Viriot, M.L. | Carré, M.C.

Article Type: Research Article

Abstract: Polysaccharides are interesting and often essential macromolecules but are difficult to analyse due to their lack of convenient chromophores. We propose an efficient labelling procedure for polysaccharides such as functionalized dextrans with coumarin derivatives: the fluorescent tracers present inter alia properties of emission of fluorescence dependent on the molecular environment (polarity, viscosity, temperature, pH, etc.). Hence, with in mind the understanding of cell–polysaccharide interactions, the labelled polymers were studied by in vitro tests on a line of endothelial cells sensitive to the proliferative effect of these dextran polysaccharides. Using 3D fluorescence microscopy, the fixation and internalization of fluorescent functionalized dextrans …were observed in endothelial cells. Show more

Keywords: Fluorescence, polysaccharides, endothelial cells, coumarin

Citation: Biorheology, vol. 40, no. 1-3, pp. 261-263, 2003

Authors: Miyazaki, Hisako | Yamaguchi, Takami

Article Type: Research Article

Abstract: Thrombogenesis and thrombolysis processes were simulated using a computational mechanics method called the discrete element method (DEM) to model the mechanical interactions between blood flow, platelets, the vessel wall, and von Willebrand factor (vWf). The inclusion of vWf and a complex blood flow field in the DEM are new developments used in this study. A primary thrombus did not form in the simulations if only the axial fluid force was considered, even when vWf was activated to simulate an endothelial injury. When the radial fluid force was considered to include the exclusion effect of erythrocytes, the modeled platelets formed primary …thrombi at lesions where vWf was present. This suggests that activation of vWf is not sufficient to promote the formation of primary thrombi; a complex flow field that facilitates the transport of platelets towards the wall is also required. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 265-272, 2003

Authors: Brodland, G. Wayne

Article Type: Research Article

Abstract: In order to verify theories about the mechanics of cell sorting, tissue spreading and checkerboard pattern formation, it is necessary to measure certain cell properties such as surface tension and adhesiveness. The purpose of this work is to clarify the relationship between these two important properties and to use computer simulations and analytical calculations to extract additional information from parallel plate compression tests. This paper shows that compression tests can be used to determine not only the surface tension between the aggregate and the surrounding medium, but also the effective viscosity of the cell cytoplasm and the interfacial tension that …acts between the cells that make up the aggregate. The findings reported here also support a novel, differential interfacial tension‐based theory for cell sorting, tissue spreading and checkerboard pattern formation, and pose further challenges to current differential adhesion‐based models. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 273-277, 2003

Authors: Nerem, Robert M.

Article Type: Research Article

Abstract: There is a clinical need for the tissue engineering of a small diameter blood vessel substitute. Ideally such a vascular substitute should possess the functional attributes of the native vessel which it will replace. This means not only having the appropriate mechanical properties, but also being non‐thrombogenic and exhibiting vasoactivity. In each of these there is in some way a role of mechanics. For thrombogenicity, an “endothelial‐like” lining is required, one which is responsive to its mechanical environment in a manner similar to that of the normal vascular endothelium. If vasoactivity is exhibited, then this lining must also serve as …a signal transduction interface, communicating with the underlying smooth muscle cells which themselves must be of a contractile phenotype if they are to carry out the biomechanical function resulting in contraction and dilation. Having appropriate mechanical properties means not only exhibiting sufficient strength, but also a viscoelasticity which allows for a compliance that matches that of the vascular system into which the vascular substitute is to be placed. Finally, once implanted the biological responses which will occur at least in part are regulated by biomechanical factors. Thus, the proper incorporation of biomechanics into the design of a vascular substitute is critical to achieving success. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 281-287, 2003