Biorheology - Volume 43, issue 6

Authors: van Dam, Evelyne A. | Dams, Susanne D. | Peters, Gerrit W.M. | Rutten, Marcel C.M. | Schurink, Geert Willem H. | Buth, Jaap | van de Vosse, Frans N.

Article Type: Research Article

Abstract: The objective of this study is to determine whether the linear viscoelastic properties of an abdominal aortic aneurysm thrombus can be determined by rheometry. Although large strains occur in the in vivo situation, in this work only linear behavior is studied to show the applicability of the described methods. A thrombus exists of several layers that vary in composition, structure and mechanical properties. Two types of thrombus are described. In discrete transition thrombi the layers are not or at most weakly attached to each other and the structure of each layer is different. Continuous transition thrombi consist of strongly attached …layers whose structure changes gradually throughout the thickness of the thrombus. Shear experiments are performed on samples from both types of thrombus on a rotational rheometer using a parallel plate geometry. In the discrete type the storage modulus G′ cannot be assumed equal for the different layers. In the continuous thrombus, G′, changes gradually throughout the layered structure. In both types the loss modulus, G″, does not vary throughout the thrombus. Furthermore, it was found that Time–Temperature Superposition is applicable to thrombus tissue. Since results were reproducible it can be concluded that the method we used to determine the viscoelastic properties is applicable to thrombus tissue. Show more

Keywords: Mechanical properties, rheometry, intraluminal thrombus, Time–Temperature Superposition, storage modulus, loss modulus

Citation: Biorheology, vol. 43, no. 6, pp. 695-707, 2006

Authors: Fehrenbacher, Andreas | Steck, Eric | Roth, Wolfgang | Pahmeier, Andrea | Richter, Wiltrud

Article Type: Research Article

Abstract: One major problem in cartilage tissue engineering is the insufficient biochemical composition of the generated biocomposites. The aim of this study was to improve the collagen and proteoglycan deposition in tissue engineering constructs by application of long-term mechanical loading in culture. Chondrocyte-seeded chitosan biocomposites revealed a homogenous cell distribution, high viability (>95%) and maintenance of a rounded cell shape typical for chondrocytes over 3 weeks of load-free culture. Cyclic compression of chitosan biocomposites (0.1 Hz, amplitude 5–15%, 45 min on and 315 min off) was applied after two different preculture times (3, 21 days) for 3 weeks. At day 42 …this resulted in enhanced mRNA levels for aggrecan and a significantly higher specific proteoglycan (5-fold, p<0.0002) and collagen type II (2-fold, p<0.02) deposition compared to unloaded controls. In sum, the chitosan scaffold was highly attractive for cartilage tissue engineering approaches and mechanical loading allowed to further improve the biochemical composition of these biocomposites. Show more

Keywords: Cartilage tissue engineering, mechanical compression, chitosan scaffold, extracellular matrix

Citation: Biorheology, vol. 43, no. 6, pp. 709-720, 2006

Authors: Boudou, Thomas | Ohayon, Jacques | Picart, Catherine | Tracqui, Philippe

Article Type: Research Article

Abstract: Substrates with tunable mechanical properties are crucial for the study of cellular processes, and polyacrylamide gels (PAGs) are frequently used in this context. Several experimental techniques have been proposed to obtain the mechanical properties of PAGs. However, the range of the considered Poisson's ratio values remains quite large and no attempt has been made to propose an analytical relationship allowing the estimation of PAG Young's modulus when both bis-acrylamide and acrylamide concentrations are known. In order to complete the actual knowledge on the mechanical properties of PAGs, we took benefit of our original method based on the micropipette aspiration technique …(Boudou et al., J. Biomech. 2006) for characterizing gels made with concentrations in the range 0.02% ≤[Bis]≤0.20% and 3% ≤[Acry]≤10%. We found that the PAGs Young's modulus varies nonlinearly with the acrylamide amount. Moreover, our study validates the quasi-incompressibility hypothesis usually made in studies using PAGs (mean Poisson's ratio of 0.480±0.012). More generally, and in agreement with data published by other groups, we propose an original nonlinear mathematical relationship allowing the computation of Young's modulus of PAG for any given acrylamide and bis-acrylamide amounts taken in the range of values we considered. Show more

Keywords: Micropipette, incompressibility, cell substrate, linear elasticity

Citation: Biorheology, vol. 43, no. 6, pp. 721-728, 2006

Authors: Thurston, George B. | Henderson, Nancy M.

Article Type: Research Article

Abstract: The viscoelastic properties of blood are dominated by microstructures formed by red cells. The microstructures are of several types such as irregular aggregates, rouleaux, and layers of aligned cells. The dynamic deformability of the red cells, aggregation tendency, cell concentration, size of confining vessel and rate of flow are determining factors in the microstructure. Viscoelastic properties, viscosity and elasticity, relate to energy loss and storage in flowing blood while relaxation time and Weissenberg number play a role in assessing the importance of the elasticity relative to the viscosity. These effects are shown herein for flow in a large straight cylindrical …tube, a small tube, and a porous medium. These cases approximate the geometries of the arterial system: large vessels, small vessels and vessels with many branches and bifurcations. In each case the viscosity, elasticity, relaxation time and Weissenberg number for normal human blood as well as blood with enhanced cell aggregation tendency and diminished cell deformability are given. In the smaller spaces of the microtubes and porous media, the diminished viscosity shows the possible influence of the Fåhraeus–Lindqvist effect and at high shear rates, the viscoelasticity of blood shows dilatancy. This is true for normal, aggregation enhanced and hardened cells. Show more

Keywords: Viscosity, elasticity, relaxation time, sickle cell, aggregation, deformability

Citation: Biorheology, vol. 43, no. 6, pp. 729-746, 2006

Authors: Zhao, Rui | Antaki, James F. | Naik, Tikeswar | Bachman, Timothy N. | Kameneva, Marina V. | Wu, Zhongjun J.

Article Type: Research Article

Abstract: The understanding of erythrocyte deformation under conditions of high shear stress and short exposure time is central to the study of hemorheology and hemolysis within prosthetic blood contacting devices. A combined computational and experimental microscopic study was conducted to investigate the erythrocyte deformation and its relation to transient stress fields. A microfluidic channel system with small channels fabricated using polydimethylsiloxane on the order of 100 μm was designed to generate transient stress fields through which the erythrocytes were forced to flow. The shear stress fields were analyzed by three-dimensional computational fluid dynamics. Microscopic images of deforming erythrocytes were experimentally recorded …to obtain the changes in cell morphology over a wide range of fluid dynamic stresses. The erythrocyte elongation index (EI) increased from 0 to 0.54 with increasing shear stress up to 123 Pa. In this shear stress range, erythrocytes behaved like fluid droplets, and deformed and flowed following the surrounding fluid. Cells exposed to shear stress beyond 123 Pa (up to 5170 Pa) did not exhibit additional elongation beyond EI=0.54. Two-stage deformation of erythrocytes in response to shear stress was observed: an initial linear elongation with increasing shear stress and a plateau beyond a critical shear stress. Show more

Keywords: Red blood cell, blood damage, shear stress, elongation index

Citation: Biorheology, vol. 43, no. 6, pp. 747-765, 2006

Article Type: Other

Citation: Biorheology, vol. 43, no. 6, pp. 767-775, 2006