Biorheology - Volume 40, issue 1-3

Article Type: Research Article

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

Article Type: Research Article

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

Authors: McCormick, Susan M. | Frye, Stacie R. | Eskin, Suzanne G. | Teng, Christina L. | Lu, Chiung‐Mei | Russell, Christopher G. | Chittur, Krishnan K. | McIntire, Larry V.

Article Type: Research Article

Abstract: The cDNA microarray is an extremely beneficial tool for study of differential gene expression in the cardiovascular system. This technique is used in many different applications including drug discovery, environmental science, and the effects of mechanical forces on vascular cell phenotype. The paper reviews work by others, and describes our study on effects of shear stress on vascular endothelial cells. These microarray studies verified earlier findings using Northern and polymerase chain reaction (PCR) analyses in this area; and also found previously unidentified differentially expressed genes, leading to new hypotheses regarding how cells and tissues respond to biochemical and mechanical stimuli.

Citation: Biorheology, vol. 40, no. 1-3, pp. 5-11, 2003

Authors: Born, Gustav V.R. | Medina, R. | Shafi, Shahida | Cardona‐Sanclemente, L.E.

Article Type: Research Article

Citation: Biorheology, vol. 40, no. 1-3, pp. 13-22, 2003

Authors: Yao, X. | Kwan, H.Y. | Dora, K.A. | Garland, C.J. | Huang, Y.

Article Type: Research Article

Abstract: Ca2+ is an important intracellular second messenger in signal transduction of endothelial cells. It has long been recognized that a mechanosensitive Ca2+ ‐permeable channel is present in vascular endothelial cells. The activity of this channel may increase intracellular Ca2+ level in endothelial cells. A recent finding is that the activity of this channel may be regulated by cGMP through a protein kinase G‐dependent pathway. Inhibition of the channel by cGMP abolishes the Ca2+ influx elicited by flow. Several inhibitors of the cation channel including Gd3+ , Ni2+ , and SK&F‐96365 also inhibit the Ca2+ influx due …to flow stimulation. These data suggest that a mechanosensitive cation channel is the primary pathway mediating the flow‐induced Ca2+ entry in vascular endothelial cells. Another important finding is that the opening of this mechanosensitive channel by KT5823 leads to endothelium‐dependent vascular dilation. Therefore, it appears that this channel may play a crucial role in the regulation of vascular tone. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 23-30, 2003

Authors: Sun, R.J. | Muller, S. | Zhuang, F.Y. | Stoltz, J.F. | Wang, X.

Article Type: Research Article

Abstract: Caveolin‐1 is a principal component of caveolae and is involved in signaling transduction in a number of cells. A hypothesis was proposed in this work that mechanical forces due to flow induce caveolin‐1 translocation. So the changes of caveolin‐1 expression and distribution in cultured endothelial cells (HUVECs) exposed to a steady laminar flow were studied. For comparing with the influence of cytokine, caveolin‐1 in the cells stimulated by TNF‐α was also investigated. Indirect immunofluorescence and double fluorescence labeling showed that in control cells, caveolin‐1 was primarily localized on the cell surface, which corresponded to the peripheral distribution of F‐actin, and …presented some local concentrations. In the cells exposed to a laminar flow (1.0 Pa), caveolin‐1 distribution showed a time‐dependent variation. After 24 h of shear, the local concentration of caveolin‐1 was found, in the most cells, at upstream side of cell body. Also more caveolin‐1 molecules were observed in the cells. In contrast, TNF‐α induced a decrease of caveolin‐1 in cells. The redistribution of caveolin‐1 seems to be correlated to F‐actin organization. Show more

Keywords: Caveolin‐1, shear stress, endothelial cell, TNF‐α, F‐actin, signal transduction

Citation: Biorheology, vol. 40, no. 1-3, pp. 31-39, 2003

Authors: Gomes, N. | Berard, M. | Vassy, J. | Peyri, N. | Legrand, C. | Fauvel‐Lafeve, F.

Article Type: Research Article

Abstract: The adhesion of breast adenocarcinoma cells (MDA‐MB‐231) to human umbilical vein endothelial cells (HUVEC) was studied in whole blood and under varying flow conditions. This study was done on HUVEC either kept under static conditions or pre‐conditioned in flow for 2 hours at a shear stress of 5 or 13 dyn/cm2 . Coverslips coated by HUVEC were placed in a parallel plate perfusion chamber and perfused at a shear rate of 300 or 1500 sec−1 with heparin‐anticoagulated blood containing 111 In labelled MDA‐MB‐231 cells. We report here the optimal conditions for studying the adhesion of MDA‐MB‐231 to endothelial cells …under shear constraints corresponding to those observed into small and medium sized arteries. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 41-45, 2003

Authors: Labrador, Vénus | Chen, Kuang‐Den | Li, Yi‐Shuan | Muller, Sylvaine | Stoltz, Jean‐François | Chien, Shu

Article Type: Research Article

Abstract: Integrins may serve as mechanosensors in endothelial cells (ECs): shear stress causes integrin–Shc association, assembly of the signaling complex and then leads to JNK activation. Flow also mediates selective and cell‐specific alterations in vascular cell G‐protein expression that correlate with changes in cell‐signalling, G‐protein functionality and modulate Ca2+ concentration. In this study, we explored the cross‐talks between EC membrane mechanosensors, such as integrins, ion channels, and G‐proteins in shear stress‐induced signal transduction by their specific inhibition. Confluent monolayer of bovine aortic endothelial cells (BAECs) were incubated with or without specific inhibitors prior to shearing experiments. Our results showed an …attenuation of integrin–Shc association under shear stress with RGD, and with PTX, but not with BAPTA/AM. The inhibitions of shear‐activated JNK are similar for RGD and PTX. However, unlike for integrin association, the chelation of calcium reduced JNK activation. These results provide several lines of evidence of the interactions between different mechanosensors in ECs. First, integrin–Shc association required cell attachment and G‐protein activity, but not intracellular calcium. Second, shear‐induced JNK activation is regulated by multiple mechano‐sensing mechanisms such as integrin, G‐protein and calcium concentration. Show more

Keywords: Endothelial cells, shear stress, integrin, G‐proteins, mechanotransduction pathways

Citation: Biorheology, vol. 40, no. 1-3, pp. 47-52, 2003

Authors: Chen, Huaiqing | Wu, Lizhi | Liu, Xiaoheng | Chen, Youqin | Wang, Boyao

Article Type: Research Article

Abstract: In order to demonstrate that IL‐8 mRNA expression in endothelial cells is not only regulated by chemical factors, but also by mechanical factors, in this article, after pretreating cultured human umbilical vein endothelial cells (HUVECs) with shear stress for different time, we employed both RT‐PCR to assay IL‐8 mRNA expression and immunocytochemical staining to detect NF‐κB activation in HUVECs. We found that: (i) IL‐8 mRNA expressed little in HUVECs untreated or pretreated with low laminar shear stress for 0.5 hour; IL‐8 mRNA expression was increased when HUVECs were pretreated with low laminar shear stress for 1 hour, and increased further …when pretreated for 2 hours; (ii) the immunoreactivity of NF‐κB p65 in the nuclei of HUVECs untreated or pretreated with low laminar shear stress for 0.5 hour was negative, while it became weak positive in the nuclei of HUVECs pretreated with shear stress for 1 hour and positive in the nuclei of HUVECs pretreated for 2 hours. The results imply that low laminar shear stress was capable of inducing IL‐8 gene expression and activating NF‐κB, which were both time‐dependent. The induction of IL‐8 gene expression by laminar shear stress is probably due to the activation of NF‐κB. We suggest that IL‐8 mRNA expression in endothelial cells induced by low shear stress may play a key role in the pathogenesis and development of both inflammation and arterioatherosclerosis. Show more

Keywords: Endothelial cells, interleukin‐8, mRNA, RT‐PCR, NF‐κB, shear stress

Citation: Biorheology, vol. 40, no. 1-3, pp. 53-58, 2003

Article Type: Research Article

Citation: Biorheology, vol. 40, no. 1-3, pp. 59-59, 2003

Authors: Hung, Clark T. | LeRoux, Michelle A. | Palmer, Glyn D. | Chao, P.‐H. Grace | Lo, Sansan | Valhmu, Wilmot B.

Article Type: Research Article

Abstract: The effects of hypotonic (180 mOsm) and hypertonic (580 mOsm) medium loading on chondrocyte aggrecan gene expression in 2D monolayer and 3D hydrogel culture (agarose or alginate) were studied. Aggrecan promoter activity was monitored using a luciferase reporter gene assay and transient transfection. Osmotic loading was observed to differentially affect promoter activity, with hypotonic loading generally producing at least a 40% elevation in promoter activity, except for the case of alginate where a 50% suppression was observed. Hypertonic loading produced at least a 35% decrease in activity for all cultures. Similar osmolality‐induced changes to aggrecan mRNA levels were observed in …monolayer cells using qPCR. Deletion of exon 1 blocked the sensitivity of monolayer cells to hypertonic but not hypotonic medium changes. Confocal microscopy measurements suggested that the degree of hypotonic swelling in cells encapsulated in 3D matrix was restricted compared to monolayer cells whereas the degree of hypertonic shrinking was similar under both culture conditions. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 61-72, 2003

Authors: Hopewell, Bethan | Urban, Jill P.G.

Article Type: Research Article

Abstract: Articular chondrocytes are exposed to a unique osmotic environment, which varies throughout the depth of cartilage, and in response to mechanical loading or pathological conditions. In light of such osmotic variations we investigated the response of chondrocytes cultured in alginate beads to long term hypo‐ and hyperosmotic challenge. Following pre‐incubation at 380 mOsmol, exposure to hyperosmotic conditions (550 mOsmol) initially decreased 35 S‐sulphate incorporation, but after 24 hours of culture, rates had recovered and surpassed their original levels. MAP kinase inhibitors abrogated this response suggesting their involvement in the adaptation mechanism. Hypo‐osmotic challenge caused a decrease in 35 S‐sulphate incorporation …throughout the culture period. These results suggest that osmolality is a powerful regulator of macromolecular synthesis, and that perturbations in the osmotic environment may alter the set point for turnover. Show more

Keywords: Cartilage, MAP kinase, proteoglycan, glycosaminoglycan

Citation: Biorheology, vol. 40, no. 1-3, pp. 73-77, 2003

Authors: Toyoda, Takashi | Seedhom, Bahaa B. | Kirkham, Jennifer | Bonass, William A.

Article Type: Research Article

Abstract: The aim of this study was to investigate the effect of hydrostatic pressure on the expression of messenger ribonucleic acid (mRNA) for specific extracellular matrix proteins in chondrocytes. Chondrocytes obtained from bovine metatarsophalangeal joints were embedded in cylindrical 2% agarose gels. A novel experimental system was used to apply 5 MPa of static hydrostatic pressure to these chondrocytes for 4 hours. The application of hydrostatic pressure caused a significant increase in the level of aggrecan mRNA by almost four fold (p<0.01) as well as a 50% increase in the level of type II collagen mRNA (p<0.05). However, there was no …significant change in the level of TIMP‐1 mRNA. It was suggested that the application of hydrostatic pressure, in the absence of cell deformation, can bring about changes in the matrix components which may play an important role in the homeostasis and mechanical properties of articular cartilage. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 79-85, 2003

Authors: Kaarniranta, Kai | Elo, Mika A. | Sironen, Reijo K. | Karjalainen, Hannu M. | Helminen, Heikki J. | Lammi, Mikko J.

Article Type: Research Article

Abstract: High hydrostatic pressure causes stress response in many types of mammalian cells. We have previously shown that an accumulation of heat shock protein 70 (Hsp70) in a chondrocytic cell line occurred without an activation of the gene itself. Stabilization of the hsp70 mRNA was shown to be the reason for the Hsp70 stress response in the pressurized cells. Since accumulation of Hsp70 in pressurized cells indicated that high hydrostatic pressure induces a stress response without heat shock transcription factor activation, we decided to investigate the activation of two other stress‐associated transcription factors, activator protein‐1 (AP‐1) and nuclear factor‐κB (NF‐κB). Induction …of Hsp70 in immortalized and primary chondrocytes, murine Neuro‐2a neuroblastoma and HeLa cervical carcinoma cell lines was investigated at both mRNA and protein levels. In immortalized chondrocytes and HeLa cells, hsp70 mRNA levels were clearly elevated after 6 hours of the onset of 30 MPa continuous hydrostatic pressure, while in primary chondrocytes and Neuro‐2a cells (the cells known to be stress‐sensitive) no induction was observed. Surprisingly, neither heat shock nor high hydrostatic pressure could induce the hsp70 mRNA in Neuro‐2a cells, although an activation of heat shock transcription factor could be observed in heat‐shocked cells. No activation of the AP‐1 and NF‐κB binding to their target DNA sequences could be shown in the immortalized chondrocytes. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 87-92, 2003

Authors: Karjalainen, Hannu M. | Sironen, Reijo K. | Elo, Mika A. | Kaarniranta, Kai | Takigawa, Masaharu | Helminen, Heikki J. | Lammi, Mikko J.

Article Type: Research Article

Abstract: Mechanical forces have a profound effect on cartilage tissue and chondrocyte metabolism. Strenuous loading inhibits the cellular metabolism, while optimal level of loading at correct frequency raises an anabolic response in chondrocytes. In this study, we used Atlas Human Cancer cDNA array to investigate mRNA expression profiles in human chondrosarcoma cells stretched 8% for 6 hours at a frequency of 0.5 Hz. In addition, cultures were exposed to continuous and cyclic (0.5 Hz) 5 MPa hydrostatic pressure. Cyclic stretch had a more profound effect on the gene expression profiles than 5 MPa hydrostatic pressure. Several genes involved with the regulation …of cell cycle were increased in stretched cells, as well as mRNAs for PDGF‐B, glucose‐1‐phosphate uridylyltransferase, Tiam1, cdc37 homolog, Gem, integrin α6 , and matrix metalloproteinase‐3. Among down‐regulated genes were plakoglobin, TGF‐α, retinoic acid receptor‐α and Wnt8b. A smaller number of changes was detected after pressure treatments. Plakoglobin was increased under cyclic and continuous 5 MPa hydrostatic pressure, while mitogen‐activated protein kinase‐9, proliferating cell nuclear antigen, Rad6, CD9 antigen, integrins αE and β8 , and vimentin were decreased. Cyclic and continuous pressurization induces a number of specific changes. In conclusion, a different set of genes were affected by three different types of mechanical stimuli applied on chondrosarcoma cells. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 93-100, 2003

Authors: Giannoni, Paolo | Siegrist, Mark | Hunziker, Ernst B. | Wong, Marcy

Article Type: Research Article

Abstract: Physical forces are known to influence the synthesis, assembly and degradation of the cartilage extracellular matrix. The expression of cartilage oligomeric matrix protein (COMP) was found to be sensitive to long term cyclic compression. Explants of calf articular cartilage as well as cylindrical alginate/chondrocyte constructs were subjected to uniaxial unconfined dynamic compression for 18 hours after which total mRNA was extracted from samples. COMP expression was assessed by means of semi‐quantitative RT–PCR and Northern blot techniques. The COMP transcript was found to be significantly enriched upon compression in both experimental systems. Incubation with anti‐β1 integrin blocking antibodies abolished the mechanosensitivity …of COMP expression. In addition, the presence of a fully developed pericellular matrix was shown to be a prerequisite for enhanced COMP expression with cyclic loading. Cell/matrix interactions are therefore one of the key events in mechanotransduction in chondrocytes. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 101-109, 2003

Authors: Blain, Emma J. | Mason, Deborah J. | Duance, Victor C.

Article Type: Research Article

Abstract: Osteoarthritis (OA) develops as a consequence of articular cartilage degeneration possibly initiated by excessive or abnormal loading of the joint, and potentially mediated through a proteinase/proteinase inhibitor imbalance. We have shown previously that physiological loads (0.5 MPa, 1 Hz, 3 hour) elicit increased expression and activation of the matrix metalloproteinases (MMPs) in articular cartilage explants in vitro. The objective of this study was to identify mechanically‐regulated genes involved in the observed induction of MMP expression and enhanced activation. Differential RNA Display (DRD) was used to identify mechanically‐regulated genes by comparing DRD products derived from loaded and unloaded cartilage. One gene …up‐regulated in cartilage after 10, 30 and 60 minute loading revealed 83% homology with Mus musculus thymosin β4 which is known to induce MMP gene expression. The identification of mechanically regulated genes will greatly enhance our understanding of matrix turnover providing an exciting future in elucidating the role of mechanically‐regulated genes in the development of OA. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 111-117, 2003

Authors: Romanello, Milena | Veronesi, Valentina | D'Andrea, Paola

Article Type: Research Article

Abstract: Mechanically induced intercellular Ca2+ signalling was investigated in differentiated HOBIT osteoblastic cells. HOBIT cells express connexin43 clustered at the cell‐to‐cell boundary and display functional intercellular coupling assessed by intercellular transfer of Lucifer yellow. Mechanical stimulation of single cells, besides leading to an intracellular Ca2+ rise, induced a wave of increased Ca2+ that was radially propagated to surrounding cells. Treatment of cells with thapsigargin blocked mechanically induced signal propagation. Intercellular Ca2+ spreading was inhibited by 18α‐glycyrrhetinic acid, demonstrating the involvement of gap junctions in signal propagation. Suramin and apyrase decreased the extent of wave propagation, suggesting that …ATP‐mediated paracrine stimulation contribute to cell‐to‐cell signalling. The functional expression of gap‐junctional hemichannels was evidenced in experiments of Mn2+ quenching, extracellular dye uptake and intracellular Ca2+ release, activated by uptake of inositol 1,4,5‐trisphosphate from the external medium. Gap‐junctional hemichannels were activated by low extracellular Ca2+ concentrations and inhibited by 18α‐glycyrrhetinic acid. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 119-121, 2003

Authors: Frijns, A.J.H. | Huyghe, J.M. | Kaasschieter, E.F. | Wijlaars, M.W.

Article Type: Research Article

Abstract: Cartilage exhibits a swelling and shrinking behaviour that influences the function of the cells inside the tissue. This behaviour is caused by mechanical, chemical and electrical loads. It is described by the electrochemomechanical mixture theory, in which the tissue is represented by four components: a charged porous solid, a fluid, cations and anions. By distinguishing between the cations and anions, electrical phenomena can be modelled. This mixture theory is verified by fitting the deformations and the electrical potentials in a uniaxial confined swelling and compression experiment to a mixed finite element simulation. The fitted stiffness, permeability, diffusion coefficients, and osmotic …coefficients are in the same range as reported in literature. Show more

Keywords: Mixture theory, streaming potential, cartilage, hydrogel, mixed finite element method

Citation: Biorheology, vol. 40, no. 1-3, pp. 123-131, 2003

Authors: Laasanen, M.S. | Töyräs, J. | Korhonen, R.K. | Rieppo, J. | Saarakkala, S. | Nieminen, M.T. | Hirvonen, J. | Jurvelin, J.S.

Article Type: Research Article

Abstract: Structure and properties of knee articular cartilage are adapted to stresses exposed on it during physiological activities. In this study, we describe site‐ and depth‐dependence of the biomechanical properties of bovine knee articular cartilage. We also investigate the effects of tissue structure and composition on the biomechanical parameters as well as characterize experimentally and numerically the compression–tension nonlinearity of the cartilage matrix. In vitro mechano‐optical measurements of articular cartilage in unconfined compression geometry are conducted to obtain material parameters, such as thickness, Young's and aggregate modulus or Poisson's ratio of the tissue. The experimental results revealed significant site‐ and depth‐dependent …variations in recorded parameters. After enzymatic modification of matrix collagen or proteoglycans our results show that collagen primarily controls the dynamic tissue response while proteoglycans affect more the static properties. Experimental measurements in compression and tension suggest a nonlinear compression–tension behavior of articular cartilage in the direction perpendicular to articular surface. Fibril reinforced poroelastic finite element model was used to capture the experimentally found compression–tension nonlinearity of articular cartilage. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 133-140, 2003

Authors: Elo, Mika A. | Sironen, Reijo K. | Karjalainen, Hannu M. | Kaarniranta, Kai | Helminen, Heikki J. | Lammi, Mikko J.

Article Type: Research Article

Abstract: In chondrocytes, a low‐amplitude intermittent hydrostatic pressure induces production of extracellular matrix molecules, while high hydrostatic pressure inhibits it. High pressure increases cellular heat shock protein 70 level in a number of cell types on account of increased stabilisation of the heat shock protein 70 mRNA. In our experiments, only bovine primary chondrocytes, but not an immortalized chondrocytic cell line, could resist the induction of the stress response in the presence of continuous 30 MPa hydrostatic pressure. We have recently shown that protein synthesis is required for the stabilization. According to two‐dimensional gel electrophoresis the synthesis of heat shock protein …90 was also increased in a chondrocytic cell line and in HeLa cells, and mass spectrometric analysis suggested that the induction was rather due to increase in heat shock protein 90β than in heat shock protein 90α. The stress response was rather intense in HeLa cells, therefore, we investigated the effect of continuous 30 MPa hydrostatic pressure on the expression of the two heat shock protein 90 genes in HeLa cells using Northern and Western blot analyses. Heat shock protein 90β mRNA level increased within 6 hours of exposure to 30 MPa hydrostatic pressure, while hsp90α level remained stable. At protein level there was a clear increase in the heat shock protein 90β/heat shock protein 90α ratio, too. These results show a specific regulation of stress proteins in cells exposed to high hydrostatic pressure. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 141-146, 2003

Authors: Hemmerlé, J. | Picart, C. | Gergely, C. | Schaaf, P. | Stoltz, J.‐F. | Voegel, J.‐C. | Senger, B.

Article Type: Research Article

Abstract: This article deals with the modeling of the detachment of a molecule initially adsorbed on a surface and submitted to an external force whose strength increases with time. By means of an atomic force microscope (AFM), it is possible to measure the force when the molecule separates from the substrate. However, it is known that this force depends to a large extend on the rate at which the pulling force is applied (“Bell–Evans effect”). Two models are described to illustrate this behavior. First, a random walk approach is suggested to reveal the fundamental principle of the escape over a time‐dependent …energy barrier. Second, a multi bead‐and‐spring model is proposed to mimic the AFM experiment and numerical simulations, based on Brownian dynamics, are performed. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 149-160, 2003

Authors: Riha, P. | Dumas, D. | Latger, V. | Muller, S. | Stoltz, J.F.

Article Type: Research Article

Abstract: The role of clustered of L‐selectin receptors on the leukocyte surface is discussed in connection with the postulated velocity‐dependent formation of selectin–ligand tether bonds to interpret the mechanism of leukocyte tethering to, and rolling along, the vascular endothelium. The distinct feature of this step‐wise process is a weak dependence of leukocyte rolling velocity on the hydrodynamic forces of ambient flow due to the increased number of selectin bonds with increasing flow shear rate and also their clustering. The contact zones on the leukocyte surface are separated by distances with distribution which corresponds to the distribution of distances of the observed …L‐selectin clusters. It suggests that the localization of L‐selectin receptors to clusters and the way of their approach to the ligand molecules creates such conditions for binding of L‐selectin and ligand molecules that resulting number of bonds stabilizes rolling velocity. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 161-166, 2003

Authors: Latger‐Cannard, Véronique | Dumas, Dominique | Bensoussan, Danièle | Stoltz, Jean‐François

Article Type: Research Article

Abstract: Receptors such as CD62L and CD11b/CD18, are transmembrane glycoproteins which regulate leukocyte adhesive phenotype. Flow cytometry (FCM) makes it possible to assess a characterization of the cell activation level by receptor quantifying, but that technique does not integrate other factors of adherence regulation, such as spatial distribution and molecular conformation. Our study consisted in exploring the main adherence receptors on Polymorphonuclear Neutrophils (PMN) that were simultaneously analyzed by FCM and Conventional Optical Scanning Microscopy (COSM). FCM analysis showed that TNFα induce a decrease in CD62L expression and an increase in β2 integrins. COSM analysis distinguished three stages of cellular …distribution of CD11b/CD18 within resting PMN: most of them (about 80%) had homogeneous distribution (heterogeneous spots distributed over the entire cell surface), for 10–15% of the cells, there was a crown distribution around the widest cell diameter and in less that 10% of them receptor distribution was polarized. CD62L was in the form of heterogeneous spots distributed in a circle on the surface on non‐stimulated PMN. PMN stimulation by TNFα was associated to a randomized clustering involving both selectin and β2 integrin. Three‐dimensional analysis elicited data not shown by quantitative cytometry. For a single averaged value of the density determined by FMC, various spatial distributions of adherence receptors are found on the surface of non‐stimulated PMN. The characterization of the leukocyte adhesive phenotype has to integrate adherence receptors density as well as their spatial distribution. Show more

Keywords: 3D microscopy, polymorphonuclear neutrophil, adherence receptors

Citation: Biorheology, vol. 40, no. 1-3, pp. 167-172, 2003

Authors: Renard, M. | Heutte, F. | Boutherin‐Falson, O. | Finet, M. | Boisseau, M.R.

Article Type: Research Article

Abstract: Background: Rolling of leukocytes at the surface of the vascular endothelium is a prerequisite for a subsequent firm adhesion, particularly the slow rolling appearing on ELAM CD62E. Therefore, it may be considered that increasing the rolling velocities should be a precise therapeutic target in clinical situations where leukocytes accumulate, mainly venous and arterial ischaemia. Methods: Human neutrophils were allowed to flow on endothelial HUVECs, with and without 4 hours interleukin‐1α activation, the cells having or not been incubated with INO5042 anti‐inflammatory drug. Under a mean shear‐stress of 2 dyn/cm2 , rollers and stickers were identified and quantified, using a …video‐camera and picture analysing software. Results: When the drug had been added to endothelial cells a shift of velocities was observed towards fast speeds (from 3–5 to 7–11 μm/sec). The same results was significantly found when neutrophils, alone or along with endothelium, had been submitted to the drug, the number of stickers and rollers beeing reduced as well. Finally, such a precise pharmacological method proved efficient to detect the exact mechanism of INO5042 on white cell adhesion. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 173-178, 2003

Authors: Zhao, Hong | Zhuang, Fengyuan | Stoltz, Jean François | Wang, Xiong

Article Type: Research Article

Abstract: Interaction of lymphocyte function‐associated antigen‐1 (LFA‐1) with intercellular adhesive molecule‐1 (ICAM‐1) is important in a number of cellular events, including inflammation, adhesion, transendothelial migration. The aim of this work was to study comparatively the adhesive interaction between LFA‐1 and ICAM‐1 by a micropipette technique and a flow chamber method, and also to explore the effects of tumor necrosis factor (TNF‐α), phytohemagglutinin (PHA), and tetramethylpyrazine (TMP) on this interaction. The adhesion probability (Pa) between a lymphocyte cell line SKW‐3 expressing LFA‐1 and a red blood cell (RBC) coated with soluble ICAM‐1 was approached by the micropipette technique, while the flow chamber …allowed to observe the firm adhesion of SKW‐3 on human umbilical vein endothelial cells (HUVECs). Experimental results show that PHA stimulation of lymphocytes resulted in significant increases in the adhesion probability (Pa) and in number of firmly adhered lymphocytes to HUVECs, but TMP treatment could significantly inhibit such increases. Show more

Keywords: Cell adhesion, LFA‐1, ICAM‐1, micropipette, flow chamber

Citation: Biorheology, vol. 40, no. 1-3, pp. 179-187, 2003

Authors: Gigant, C. | Latger‐Cannard, V. | Bensoussan, D. | Fawzi, S. | Feugier, P. | Bordigoni, P. | Stoltz, J.F.

Article Type: Research Article

Abstract: To investigate the function of the main adhesion receptors (CD62L, CD49d, CD49e, CD11b and CD18) on CD34+ cells during homing, their expression was quantified by flow cytometry using calibration beads. CD34+ cells were isolated from bone‐marrow (BM), cord blood (CB) or peripheral blood (PB) from patients with myeloma. As this process might mimic the mature leukocyte migration, we also observed the effect of exposing endothelial cells to shear stress (7 dyn/cm2 ) on the adhesion of CB CD34+ cells. The proportion of CD34+/CD62L+ cells was greater in PB than in BM (p<0.05). Likewise, we found a significantly greater expression …of CD62L receptor on PB cells compared to BM cells (p<0.05) and on BM cells compared to CB cells (p<0.05). The proportions of CD34+/CD49d+ cells and CD34+/CD49e+ cells were significantly higher in the BM and CB than in PB. However, no significant difference in CD49d or CD49e antigen densities was observed. The β2 integrins (CD11b and CD18) receptors are also implicated in CD34+ cells homing to BM. No significant variation in CD34+/CD11b+ and CD34+/CD18+ cells frequency was noted. However quantitative analysis revealed that CD18 was more strongly expressed on BM cells than on PB and CB cells. The adhesion assay showed that fluid flow may favour a firm adhesion of CB CD34+ cells to endothelial cells whereas static conditions just allowed CD34+ cells sedimentation. In conclusion, quantitative expression of the main receptors on CD34+ cells indicates that the three main sources of CD34+ cells currently used for transplantation have neither the same phenotype nor the same number of antigenic sites for a receptor. So, we hypothesize that migrational capacity of these cells might be different. Moreover, it seems that shear stress could favor adhesion of CD34+ cells to endothelial cells. Show more

Keywords: Adhesion molecules, CD34+ cells, endothelial cells, hematopoietic stem cell transplantation, quantitative expression, shear flow

Citation: Biorheology, vol. 40, no. 1-3, pp. 189-195, 2003

Authors: Rasia, R.J. | de Isla, N. | Altube, L. | Muller, S. | Valverde, J. | Stoltz, J.F.

Article Type: Research Article

Abstract: A problem in immunohematology is to define the antibody quality which is related to its affinity expressed by the equilibrium constant. The activity of an antibody can be measured by the strength of its interaction, related to the adhesive energy exchanged during RBC agglutination which depends on the antigen–antibody liaison strength. To estimate this adhesive energy, two methods are used in this paper. Firstly, the dissociation behaviour of suspended RBC agglutinates was analysed by laser backscattering intensity (r) in a Couette flow. Backscattered intensity issued from shear‐induced mechanical dissociation is recorded and submitted to a numerical process to obtain the …energy parameter (ED ). Secondly, a modification of this technique is proposed for measuring specific binding energy. Samples were exposed to increasing shear stress, and backscattered intensity was recorded. A constant increase of this intensity with raising shear stress was observed, pointed to a progressive dissociation of RBC agglutinates into smaller ones. Considering that complete dissociation of agglutinates is only approached asymptotically it is assumed that the final break‐up of doublets (two‐cell agglutinates) is produced at a critical shear stress (τC ) reflecting the work done to breaking‐up the molecular bridges between both adjacent cells. This shear stress is defined by the extrapolation of the linear part of the curves [r–log τ] to the backscattered signal (r0 ) corresponding to the complete dispersion of RBCs. These approaches permit to define the specific surface adhesive energy (Γ) by using the Derjaguin relation and to assess the functional characterization of specific immunoglobulins. In conclusion, two parameters characterizing monoclonal antibody agglutination properties, ED and Γ, were estimated by laser backscattering methods, which could be very useful for antibodies quality control. Show more

Keywords: Blood group antigens, monoclonal antibodies, rheooptical method, laser backscattering

Citation: Biorheology, vol. 40, no. 1-3, pp. 197-203, 2003

Authors: Miyazaki, Hiroshi | Hayashi, Kozaburo | Hasegawa, Yoshitaka

Article Type: Research Article

Abstract: Tensile properties of fibroblasts (FBs) and vascular smooth muscle cells (VSMCs) of synthetic and contractile phenotypes were studied using a newly developed micro‐tensile tester. FBs were obtained from the rabbit patellar tendon. Synthetic and contractile VSMCs were isolated from the rabbit thoracic aorta with an explant and an enzymatic digestion method, respectively. Each cell was attached to the fine tips of a pair of micropipettes with a cell adhesive and, then, stretched at the speed of 6 μm/sec. Load and length were obtained using a cantilever‐type load cell and a VDA, respectively. FBs were broken at the load of …0.9 μN and the elongation to failure of 86 μm, and had the stiffness of 0.02 N/m. VSMCs were not broken even at 2.4 μN. The stiffness of synthetic and contractile VSMCs were 0.09 and 0.17 N/m, respectively. Such large different tensile properties among the three cells are attributable to the differences in components and cytoskeletal structures. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 207-212, 2003

Authors: Volokh, K.Yu.

Article Type: Research Article

Abstract: Conventional continuum mechanics models considering living cells as viscous fluid balloons are unable to explain some recent experimental observations. In contrast, new microstructural models provide the desirable explanations. These models emphasize the role of the cell cytoskeleton built of struts‐microtubules and cables‐microfilaments. A specific architectural model of the cytoskeletal framework called “tensegrity” deserved wide attention recently. Tensegrity models particularly account for the phenomenon of linear stiffening of living cells. These models are discussed from the structural mechanics perspective. Classification of structural assemblies is given and the meaning of “tensegrity” is pinpointed. Possible sources of non‐linearity leading to cell stiffening are …emphasized. The role of local buckling of microtubules and overall stability of the cytoskeleton is stressed. Computational studies play a central role in the development of the microstructural theoretical framework allowing for the prediction of the cell behavior from “first principles”. Algorithms of computer analysis of the cytoskeleton that consider unilateral response of microfilaments and deep postbuckling of microtubules are addressed. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 213-220, 2003

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

Authors: Mattart, Mélanie | Mazzolai, Lucia | Chambaz, Céline | Hayoz, Daniel | Brunner, Hans R. | Silacci, Paolo

Article Type: Research Article

Abstract: Both plaque‐free and plaque‐prone hemodynamic environments induce an increase in the oxidative state of endothelial cells (ECs), whereas differential gene expression regulation was described in cells exposed to these conditions. In order to investigate the role of the increased oxidative state in flow‐regulation of gene expression, we first exposed EC to non‐pulsed unidirectional shear stress. These conditions only slightly increases ECs oxidative state and endothelin‐1 (ET‐1) mRNA expression, whereas endothelial nitric oxide synthase (NOS III) mRNA level were significantly up‐regulated. On the contrary, both ET‐1 and NOS III gene expression were significantly induced in EC exposed to pulsed‐unidirectional flow (plaque‐free). …Only ET‐1 gene expression was up‐regulated by oscillatory flow (plaque‐prone). Moreover, use of an antioxidant only partially inhibited NOS III gene up‐regulation by unidirectional flow, whereas it completely abrogated ET‐1 gene up‐regulation by unidirectional and oscillatory flows. Thus suggesting that mechanical forces regulate gene expression in ECs both via oxidative stress‐dependent and ‐independent mechanisms. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 289-297, 2003

Authors: Botchwey, Edward A. | Pollack, Solomon R. | El‐Amin, Saadiq | Levine, Elliot M. | Tuan, Rocky S. | Laurencin, Cato T.

Article Type: Research Article

Abstract: In a previous study, we showed that the combination of appropriately designed three‐dimensional (3D) microcarrier scaffolds and fluid flow through and around the scaffolds during high aspect ratio vessel (HARV) rotation enhances the elaboration of mineralized bone matrix by osteoblast‐like cells. In this study, we describe the ongoing characterization of our 3D culture system, including the investigation of interior fluid flow within the scaffolds and early stage integrin expression during hydrodynamic culture. Using theoretical and experimental methods, we have estimated that cells cultured on the interior of microcarrier scaffolds experience an interior nutrient flow velocity between 1×10−3 and 1×10−2 …cm/s and maximum shear stress of 0.03 N/m2 . Under these conditions, osteoblast‐like cells grew extensively in the interior regions of the scaffold and retained their osteoblastic phenotype as measured by alkaline phosphatase. In addition, flow cytometric analysis of the overall cell population showed that cells constitutively expressed integrin α3 β1 during 3D hydrodynamic culture. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 299-306, 2003

Authors: Nakayama, Koichi | Obara, Kazuo | Tanabe, Yoshiyuki | Saito, Maki | Ishikawa, Tomohisa | Nishizawa, Shigeru

Article Type: Research Article

Abstract: Blood vessels are always subjected to hemodynamic stresses including blood pressure and blood flow. The cerebral artery is particularly sensitive to hemodynamic stresses such as pressure and stretch, and shows contractions that are myogenic in nature; i.e., the mechanical response is generated by the vascular smooth muscle itself. The artery constricts in response to an increase in intraluminal pressure, and dilates in response to a decrease in the intraluminal pressure. We provide herein some insights into the mechanotransduction of vascular tissue; i.e., we discuss how the tissue is receptive to mechanical force and how the latter induces the specific signals …leading to myogenic contraction in terms of mechanosensor action and subsequent intracellular signaling. The interactive role of tyrosine kinase, protein kinase C, and Rho/Rho‐kinase systems in the mechanotransduction process is discussed, which systems also seem to play an important role in the development of experimental cerebral vasospasm. The study of the mechanotransduction in vascular tissue may aid in clarifying the mechanisms underlying vasospastic episodes and pathologic remodeling in cardiovascular diseases, and may potentially have therapeutic consequences. Show more

Keywords: Mechanotransduction, stretch‐induced contraction, cerebrovascular contraction, cerebral vasospasm, tyrosine kinase, protein kinase C isoforms, Rho/Rho‐kinase, myosin light‐chain phosphorylation, tyrosine phosphorylation

Citation: Biorheology, vol. 40, no. 1-3, pp. 307-314, 2003

Authors: Ruimerman, Ronald | van Rietbergen, Bert | Hilbers, Peter | Huiskes, Rik

Article Type: Research Article

Abstract: Mechanical loading of trabecular bone affects the bone architecture. Bone mass is correlated to the magnitude of the external load and trabeculae are aligned to the loading direction. Physical exercise increases bone mass while disuse or microgravity decreases it. In previous work we have presented a mathematical model of bone metabolism that could explain the emergence, maintenance and adaptation of trabecular bone under influence of the load imposed, using a 2‐dimensional computer model (Huiskes et al., Nature 404 (2000), 704–706). This model was based on hypothetical mathematical descriptions of bone formation by osteoblastic cells, and resorption by osteoclastic cells, both …as governed by mechanical stimuli. In order to quantitatively compare the behavior of the proposed regulation mechanism to real trabecular bone metabolism we present a 3‐dimensional computer simulation model. The first 3‐dimensional simulation results show that the regulatory rules proposed earlier mimic trabecular bone metabolism in a robust way. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 315-320, 2003

Authors: Martin, J.A. | Mehr, D. | Pardubsky, P.D. | Buckwalter, J.A.

Article Type: Research Article

Abstract: Although most tendon regions are subjected primarily to high tensile loads, selected regions, primarily those that directly contact bones that change the direction of the tendon, must withstand high compressive loads as well. Compressed tendon regions differ from regions subjected to primarily tensile loads: they have a fibrocartilaginous structure with spherical cells surrounded by a matrix containing aggrecan and collagen types I and II, in contrast regions not exposed to compression have a fibrous structure with spindle shaped fibroblasts surrounded by a matrix of dense, longitudinally oriented type I collagen fibrils. The spherical shape of cells in fibrocartilagenous regions indicates …these cells are more loosely attached to the matrix than their spindle‐shaped counterparts in fibrous regions, a feature that may help to minimize cell deformation during tendon compression. We hypothesized that expression of tenascin‐C, an anti‐adhesive protein, is part of the adaptation of tendon cells to compression that helps establish and maintain fibrocartilaginous regions. To test this hypothesis we compared tenascin‐C content and expression in compressed (distal) versus uncompressed (proximal) segments of bovine flexor tendons. Immunohistochemistry and immunoblot analyses showed that tenascin‐C content was increased in the distal tendon where it co‐distributed with type II collagen and aggrecan. Tendon cells from the distal segments expressed more tenascin‐C than did cells from the proximal segments for up to four days in cell culture, indicating that increased tenascin‐C expression is a relatively stable feature of the distal cells. These observations support the hypothesis that tenascin‐C expression is a cellular adaptation to compression that helps establish and maintain fibrocartilagenous regions of tendons. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 321-329, 2003

Authors: Démarteau, O. | Jakob, M. | Schäfer, D. | Heberer, M. | Martin, I.

Article Type: Research Article

Abstract: A bioreactor has been developed to apply different regimes of physical stimulation to tissue specimens under highly controlled conditions. The computer‐controlled device exposes specimens to compressive deformation at various strains and frequencies, measures the load applied to each sample and allows simultaneous medium stirring at different velocities. Validation tests confirmed the accuracy of the system in (i) its displacement (errors averaged 0.072±0.051 μm), and in (ii) setting the contact with the samples utilizing micrometer screws coupled to plungers (errors averaged 1.74±0.36% for samples of 1.60–3.18 mm thickness), thus ensuring accurate compressive deformation. The developed bioreactor, which represents an advance in …the technology for physical stimulation of tissue specimens, is currently used to apply compressive deformation and hydrodynamic forces to human chondrocytes cultured in biodegradable polymer scaffolds, with the goals of (i) engineering functional grafts for the repair of cartilage defects (ii). Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 331-336, 2003

Authors: Berry, C.C. | Cacou, C. | Lee, D.A. | Bader, D.L. | Shelton, J.C.

Article Type: Research Article

Abstract: Fibroblasts within tissues are exposed to a dynamic mechanical environment, which influences the structural integrity of both healthy and healing soft tissues. Various systems have been proposed to subject such cells to mechanical stimulation in culture. However the diverse nature of the studies, in terms of the strain profiles and the cell types, makes direct comparisons almost impossible. The present study addresses this issue by examining the metabolic response of two cell types subjected to three well defined strain profiles. A young fibroblast cell population, represented by HuFFs, showed both greater cell proliferation and collagen production than adult dermal …fibroblasts under unstrained conditions. The three strain profiles produced differing effects on both cell types. Uniaxial strains enhanced [3 H]‐thymidine incorporation for both cell types, whilst biaxial strains either inhibited or had no effect on its incorporation. In contrast, [3 H]‐proline incorporation was inhibited under biaxial and uniaxial strains for the adult fibroblasts, whilst the HuFF cells showed a small increase in proline incorporation under non‐uniform and uniaxial strains. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 337-345, 2003

Authors: Petrov, Nikola | Pollack, Solomon R.

Article Type: Research Article

Abstract: Marker migration experiments suggest that cyclic mechanical loading of cortical bone in vivo increases marker penetration into bone. Is this a result of stress induced fluid flow or of stress stimulation of active transport processes? Active lacunar–canalicular transport of nutrients was suggested by Ham in 1979 on the basis of the presence of actin filaments in osteocyte processes and their suspected role in cell motility. In addition, Tanaka in 1984 observed active transport of microperoxidase in bone and Tanaka‐Kamioka et al. in 1998 observed experimentally that osteocyte processes are able to actively change their form. In this study we …performed parametric and comparative analyses of the transport efficiencies of diffusion and stress generated fluid flow of (glucose) nutrients in lacunar–canalicular systems in cortical bone. The result obtained is that neither diffusion nor stress induced fluid flow is capable of sustaining osteocyte viability. It is possible that cyclic stress stimulates an active nutrient transport mechanism to supplement stress flows. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 347-353, 2003

Authors: Chotard‐Ghodsnia, R. | Drochon, A. | Faucheux, N. | Nagel, M.‐D. | Grebe, R.

Article Type: Research Article

Abstract: Biomaterials used in some biomedical devices are exposed to flow of physiological fluids. The flow‐induced forces may influence the morphological and the biochemical responses of adhering cells. The objective of this work is to examine the capacity of a mechanical stress to cause changes in cell/substratum and cell/cell interactions via the second messenger cAMP pathway (cyclic Adenosine Monophosphate). Cyclic AMP is known to modulate cell shape, cell adhesion and intercellular communication in static conditions. A specially designed flow chamber was used to analyze the responses of mouse 3T3 fibroblasts spread on biocompatible substrata and submitted to controlled shear stresses. A …1.1‐Pa shear stress induced: cell rounding, disruption of vitronectin receptors clusters and clustering of connexins 43 at cell–cell apposition points. These cell responses were cAMP‐dependent. These investigations should help provide a better understanding of the early biochemical events triggered by mechanical forces. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 355-360, 2003

Authors: Screen, H.R.C. | Lee, D.A. | Bader, D.L. | Shelton, J.C.

Article Type: Research Article

Abstract: Tenocytes detect mechanical stimuli in vivo, and respond through mechanotransduction pathways to initiate matrix remodelling in tendons. Due to the crimped nature of tendon fascicles, the strain field throughout is non‐homogeneous. The present study has developed a means to quantify the local strain fields within a fascicle by monitoring the relative movement and deformation of fluorescently labelled tenocyte nuclei. A stage mounted test rig was designed to apply tensile strain to fascicles. Rat tail and bovine extensor tendons were harvested for analysis, and the cell nuclei stained and visualised using an inverted confocal microscope. As the fascicles were subjected to …gross strains of up to 5%, the movement of selected tenocyte nuclei were recorded. Results from a series of cell nuclei from both tendon sources revealed that local strains were significantly less than the applied strain. The nuclei length to width ratio, an indicator of cell deformation, also increased with applied strain, most significantly between 2 and 3% applied strain. Show more

Citation: Biorheology, vol. 40, no. 1-3, pp. 361-368, 2003