Biorheology - Volume 43, issue 1

Authors: Lenormand, Guillaume | Fredberg, Jeffrey J.

Article Type: Research Article

Abstract: A trail of evidence has led to an unexpected intersection of topical issues in condensed matter physics and cytoskeletal biology. On the one hand, the glass transition and the jammed state are two outstanding unsolved problems; such systems are out-of-equilibrium, disordered, and their transitions between solid-like and liquid-like states are not understood. On the other hand, cellular systems are increasingly being considered as interconnected maps of protein interactions that are highly specific and tightly regulated but, even when such comprehensive maps become available, they may be insufficient to define biological function at the integrative level because they do not encompass …principles that govern dynamics at intermediate (meso) scales of organization. It is interesting, therefore, that the cytoskeleton of the living cell shows physical properties and remodeling dynamics with all the same signatures as soft inert condensed systems, although with important differences as well. Data reviewed here suggest that trapping, intermittency, and approach to kinetic arrest represent mesoscale features of collective protein–protein interactions linking underlying molecular events to integrative cellular functions such as crawling, contraction and remodeling. Because these are crucial cell functions, this synthesis may offer new perspectives on a variety of disorders including infectious disease, cardiovascular disease, asthma and cancer. Show more

Keywords: Airway, smooth muscle, latch, magnetic twisting cytometry, noise temperature, glass, soft glassy rheology, jamming

Citation: Biorheology, vol. 43, no. 1, pp. 1-30, 2006

Authors: Matharu, Nick M. | Rainger, G. Ed | Vohra, Rajiv | Nash, Gerard B.

Article Type: Research Article

Abstract: Numerous studies have shown that intracellular signalling, transcription factor activation and gene expression in endothelial cells are modulated by the magnitude and patterns of shear stress to which they are exposed. Although these responses suggest that the haemodynamic environment will consequently modulate the ability of the endothelial cells to support leukocyte recruitment as part of an inflammatory response, direct evidence is quite sparse. It seems that disturbances of flow (such as local spatial or temporal variation or sudden cessation) are likely to be pathogenic co-factors, combined with mediators such as cytokines, oxidised lipids or hypoxia, in conditions such as atherosclerosis, …post-surgical intimal hyperplasia and ischaemia/reperfusion injury. In fact there have been few experimental investigations of these scenarios that include measurement of leukocyte adhesion and migration. We recently demonstrated that the level of steady shear to which EC are exposed has a powerful effect on their ability to support cytokine-induced leukocyte adhesion and migration. However, more combined studies of flow and agonist-mediated responses, with functional readouts, appear necessary if we are to develop a better understanding of the mechanisms pre-disposing to vascular inflammatory responses and pathology. Show more

Citation: Biorheology, vol. 43, no. 1, pp. 31-44, 2006

Authors: Daxini, Sachin C. | Nichol, Jason W. | Sieminski, Alisha L. | Smith, Geoffrey | Gooch, Keith J. | Shastri, V. Prasad

Article Type: Research Article

Abstract: The use of synthetic polymeric vascular grafts is limited by the thrombogenecity of most biomaterials. Efforts to reduce thrombogenicity by seeding grafts with endothelial cells, the natural non-thrombogenic lining of blood vessels, have been thwarted by flow-induced cell detachment. We hypothesized that by creating well-defined micro-textured patterns on a surface, fluid flow at the surface can be altered to create discrete regions of low shear stress. We further hypothesized that, due to reduced shear stress, these regions will serve as sanctuaries for endothelial cells and promote their retention. To test these hypotheses, well-defined micro-textured polyurethane (PU) surfaces consisting of arrays …of parallel 95-micron wide and 32-micron deep channels were created using an etched silicon template and solvent casting techniques. Based on computational fluid dynamics, under identical bulk flow conditions, the average local shear stress in the channels (46 dyn/cm2 ) was 28% lower than unpatterned surfaces (60 dyn/cm2 ). When PU surfaces pre-seeded with endothelial cells (EC) were exposed to the same bulk flow rate, EC retention was significantly improved on the micropatterned surfaces relative to un-patterned surfaces (92% vs. 58% retention). Show more

Keywords: Endothelial cells, microfabrication, retention, computational fluid dynamics, vascular grafts, tissue engineering

Citation: Biorheology, vol. 43, no. 1, pp. 45-55, 2006

Authors: Castellini, Michael | Elsner, Robert | Baskurt, Oguz K. | Wenby, Rosalinda B. | Meiselman, Herbert J.

Article Type: Research Article

Abstract: Red blood cell (RBC) aggregation and blood viscosity are important determinants of in vivo blood flow dynamics and, in marine mammals, these parameters may impact diving physiology by altering blood oxygen delivery during the diving response. Weddell seals are superb divers and exhibit age-related patterns in blood oxygen chemistry and diving ability. By contrast, bowhead whales are not long duration divers, and little is known of their blood properties relative to diving. The present study was designed to compare rheological characteristics of blood from Weddell seal pups, Weddell seal adults, and from adult bowhead whales: blood viscosity and RBC aggregation …in plasma and in polymer solutions (i.e., RBC “aggregability”) were measured. Salient findings included: (1) significant 4- to 8-fold greater aggregation in blood from adult seals compared with pups and human subjects; (2) 2-to 8-fold greater aggregation in bowhead whale blood compared with human blood; (3) compared to human red cells, enhanced RBC aggregability of RBC from adult seals and whales as determined by their greater aggregation in polymer solutions; (4) increasing RBC aggregation and aggregability of seal pup blood over a seven day period following birth; (5) significantly greater blood viscosity for adult seals compared with pups at both native and standardized hematocrits. These results indicate that, for both species, hemorheological parameters differ markedly from those of humans, and suggest progressive changes with seal age; the physiological implications of these differences have yet to be fully defined. Show more

Keywords: Aggregation, blood viscosity, bowhead whale, red blood cell, Weddell seal

Citation: Biorheology, vol. 43, no. 1, pp. 57-69, 2006

Authors: Chakravorty, Srabasti J. | McGettrick, Helen M. | Butler, Lynn M. | Buckley, Christopher D. | Rainger, G. Ed | Nash, Gerard B.

Article Type: Research Article

Abstract: To model the later stages of neutrophil migration into tissue, we developed an assay in which human umbilical vein endothelial cells (HUVEC) were cultured on porous filters, treated with the inflammatory cytokine tumour necrosis factor-α (TNF), and then incorporated in a flow chamber. Video-microscopic observations were made of neutrophils as they were perfused over the HUVEC. When 3 μm pore filters were used (as opposed to 0.4 μm pore filters), neutrophils could be observed to migrate not only through the endothelial monolayer but also through the filter within minutes. The proportion of adherent neutrophils migrating through the endothelial monolayer and …velocity of migration underneath it, were similar on the different filters, and also when neutrophils were perfused over cultures in glass capillaries, or settled on HUVEC cultured in standard plastic dishes. However, neutrophils migrated through HUVEC/filter constructs more rapidly in the flow chamber than in a standard, static, Transwell system, even though the velocities of migration under HUVEC were similar when directly observed under flow or static conditions. A function-blocking antibody against CD31 did not alter movement through the endothelial monolayer or the filter in the new flow system, but did reduce the migration velocity of neutrophils underneath the HUVEC (by 24%). Thus, we have developed a method for following each stage of neutrophil migration, including exit from the sub-endothelial space, and shown how they may be modified by applied fluid shear stress and blockade of a regulatory adhesion molecule. Show more

Keywords: Endothelium, flow chamber, transwell filter

Citation: Biorheology, vol. 43, no. 1, pp. 71-82, 2006

Authors: Sánchez, Julio C. | Powell, Trevor | Staines, Henry M. | Wilkins, Robert J.

Article Type: Research Article

Abstract: Altered fluxes of Ca2+ across the chondrocyte membrane have been proposed as one pathway by which mechanical load can modulate cartilage turnover. In many cells, Na+ /Ca2+ exchange (NCX) plays a key role in Ca2+ homeostasis, and recent studies have suggested it is operative in articular chondrocytes. In this study, an electrophysiological characterisation of NCX in articular bovine chondrocytes has been performed, using the whole-cell patch clamp technique, and the effects of inhibitors and the transmembrane electrochemical gradients of Na+ and Ca2+ on NCX function have been assessed. A Ni2+ -sensitive current (INCX ) which …exhibited outward rectification, was elicited by a voltage ramp protocol. The current was also attenuated by the NCX inhibitors benzamil and KBR7943, without significant differences between the effect of these two compounds upon outward and inward currents. The Ni2+ -sensitive current was modulated by changes in extracellular and pipette Na+ and Ca2+ in a manner characteristic of \[$I\tsub{NCX}$ . Measured values for the reversal potential differed significantly from those predicted for an exchanger stoichiometry of 3Na+  : 1Ca2+ , implying that accumulation of intracellular Ca2+ (from influx or release from stores) or more than one transport mode is occurring. These results demonstrate the operation of NCX in articular chondrocytes and suggest that changes in its turnover rate, as might occur in response to mechanical load, may modify cell composition and thereby dictate cartilage turnover. Show more

Keywords: Chondrocyte, Na$^{+}$–Ca$^{2+}$ exchange, patch clamp

Citation: Biorheology, vol. 43, no. 1, pp. 83-94, 2006