Biorheology - Volume 45, issue 5

Authors: Duraiswamy, Nandini | Cesar, Jose M. | Schoephoerster, Richard T. | Moore Jr., James E.

Article Type: Research Article

Abstract: Platelet deposition has been shown previously to depend on convective transport patterns, visualized by the instantaneous streamlines. Previous attempts to quantify hemodynamic studies of platelet deposition have been limited to 2D geometries. This study provides a physiologic assessment of the effects of stent geometry on platelet deposition by using actual 3D stents. Human blood with fluorescently labeled platelets was circulated through an in vitro system producing physiologic pulsatile flow in a compliant tube in which Bx Velocity, Wallstent and Aurora stents were implanted. Computational fluid dynamic models of the stents provided flow data to aid in explaining localized platelet deposition. …Regions of constant flow separation proximal and distal to the strut exhibited very low platelet deposition. Platelet deposition was highest just downstream of flow stagnation regions due to convection towards the wall, then decreased with axial distance from the strut as flow streamlines became locally parallel to the wall. The nearly helically recirculating regions near the Bx Velocity stent connectors exhibited complex fluid dynamics with more platelet deposition, than the smaller separation regions. Localized platelet deposition was heavily dependent on flow convection, suggesting that arterial reaction to stents can be modulated in part by altering the hemodynamics associated with stent design. Show more

Keywords: Hemodynamics, fluorescent platelet labeling, computational fluid dynamics, flow convection, restenosis

DOI: 10.3233/BIR-2008-0497

Citation: Biorheology, vol. 45, no. 5, pp. 547-561, 2008

Authors: Le Maitre, Christine Lyn | Frain, Jennie | Fotheringham, Andrew P. | Freemont, Anthony J. | Hoyland, Judith Alison

Article Type: Research Article

Abstract: The intervertebral disc (IVD) is one of the body's most important load-bearing structures with the major mechanical force experienced in the nucleus pulposus (NP) being hydrostatic pressure (HP). Physiological levels of HP have an anabolic effect on IVD matrix metabolism in cells derived from non-degenerate animal and herniated IVD while excessive HP has a catabolic effect. However, no studies have investigated the response of non-degenerate and degenerate human disc cells derived from non-herniated discs to HP. Here we investigate the effect of physiological HP on such cells using a novel loading rig. Human IVD cells (both NP and AF) cultured …in alginate were subjected to dynamic HP (0.8–1.7 MPa 0.5 Hz) for 2 h. Cell viability was assessed, RNA extracted and qRT-PCR for 18 s, c-fos, Sox-9, collagen type II, aggrecan and MMP-3 performed. Cell viability was unaffected by the loading regime. In non-degenerate NP cells, HP increased c-fos, aggrecan, Sox-9 and collagen type II (significantly so in the case of c-fos and aggrecan), but not MMP-3 gene expression. In contrast, application of HP to AF or degenerate NP cells had no effect on target gene expression. Our data shows that cells obtained from the healthy NP respond to dynamic HP by up-regulating genes indicative of healthy matrix homeostasis. However, responses differed in degenerate NP cells suggesting that an altered mechanotransduction pathway may be operational. Show more

Keywords: Loading, degeneration, gene expression

DOI: 10.3233/BIR-2008-0498

Citation: Biorheology, vol. 45, no. 5, pp. 563-575, 2008

Authors: Williams, Lakiesha N. | Elder, Steven H. | Bouvard, J.L. | Horstemeyer, M.F.

Article Type: Research Article

Abstract: In this study, we examine the transverse and longitudinal compressive mechanical behavior of the rabbit patellar tendon. The anisotropic compressive properties are of interest, because compression occurs where the tendon attaches to bone and where the tendon wraps around bone leading to the development of fibro-cartilaginous matrices. We quantified the time dependent viscoelastic and anisotropic behavior of the tendon under compression. For both orientations, sections of patellar tendon were drawn from mature male white New Zealand rabbits in preparation for testing. The tendons were sequentially compressed to 40% strain at strain rates of 0.1, 1 and 10% strain(s) using a …computer-controlled stepper motor driven device under physiological conditions. Following monotonic loading, the tendons were subjected to stress relaxation. The tendon equilibrium compressive modulus was quantified to be 19.49±11.46 kPa for the transverse direction and 1.11±0.57 kPa for the longitudinal direction. The compressive modulus at applied strain rates of 0.1, 1 and 10% strain(s) in the transverse orientation were 13.48±2.31, 18.24±4.58 and 20.90±8.60 kPa, respectively. The compressive modulus at applied strain rates of 0.1, 1 and 10% strain/s in the longitudinal orientation were 0.19±0.11, 1.27±1.38 and 3.26±3.49 kPa, respectively. The modulus values were almost significantly different for the examination of the effect of orientation on the equilibrium modulus (p=0.054). Monotonic loading of the tendon showed visual differences of the strain rate dependency; however, no significant difference was shown in the statistical analysis of the effect of strain rate on compressive modulus. The statistical analysis of the effect of orientation on compressive modulus showed a significant difference. The difference shown in the orientation analysis validated the anisotropic nature of the tendon. Show more

Keywords: Unconfined compression, soft tissue, mechanics, biomechanics

DOI: 10.3233/BIR-2008-0509

Citation: Biorheology, vol. 45, no. 5, pp. 577-586, 2008

Authors: Wang, Xian-Wei | Hu, Lin | Zeng, Zhu | Yao, Wei-Juan | Han, Jing-Yan | Zhang, Ying-Yu | Xu, Xiao-Feng | Liu, Yu-Ying | Ka, Wei-Bo | Sun, Da-Gong | Wen, Zong-Yao | Chien, Shu

Article Type: Research Article

Abstract: There is evidence that hyperlipidemia can induce hemorheological and microcirculatory disturbances. Myakuryu, a Chinese traditional medicine is efficacious in promoting lipid metabolism and protecting oxidative stress, but whether this drug can ameliorate rheologic disturbances caused by hyperlipidemia is still unknown. The present study was conducted to investigate the effects of myakuryu on hemorheological and microcirculatory disturbances induced by hyperlipidemia. Wistar rats were divided into a group on control diet (n=8) and a group on high-fat diet (HFD, n=44). Eight weeks later, plasma triglyceride (TG) and total cholesterol (TC) were determined. Sixteen animals with the highest levels of hyperlipidemia from the …HFD group were randomly divided into two sub-groups: the untreated hyperlipidemia group (n=8) and the group treated with myakuryu (n=8). At the end of the sixteenth week, rheological and microcirculatory parameters were measured. Chemical analysis showed that myakuryu treatment caused significant reductions of plasma TG and TC levels (P<0.01), and the cholesterol/phospholipid ratio in the erythrocyte membrane (P<0.05). Rheological and microcirculatory measurements showed that myakuryu treatment led to a significant decrease in the erythrocyte aggregation index, plasma viscosity and blood viscosity at shear rates of 50, 100 and 150 s−1 and in adherent leukocytes in mesenteric venules. There was a significant increase in erythrocyte deformation, electrophoretic mobility, membrane fluidity and F-actin content in the erythrocyte membrane as well as in red cell velocity in mesenteric venules. Our findings suggest that myakuryu treatment can improve blood flow and reduce adherent leukocytes in the venules of rats fed with HFD by ameliorating blood viscosity, erythrocyte deformability and aggregation, and other hemorheological characteristics. Show more

Keywords: Myakuryu, hyperlipidemia, hemorheological characteristics

DOI: 10.3233/BIR-2008-0502

Citation: Biorheology, vol. 45, no. 5, pp. 587-598, 2008

Authors: Marhefka, Joie N. | Velankar, Sachin S. | Chapman, Toby M. | Kameneva, Marina V.

Article Type: Research Article

Abstract: Natural and synthetic soluble drag reducing polymers (DRP) have been shown to produce beneficial effects on blood circulation in various animal models and may represent a novel bioengineering way to treat cardiovascular disorders. These polymers are known to degrade when subjected to high shear stresses which could be a part of the process of their elimination from the vascular system. However, the relative rate of their degradation was not known especially in the presence of blood cells or particles. The hydrodynamic tests in this study demonstrated that DRP mechanical degradation was significantly increased by the presence of red blood cells …(RBC) and even more so by the presence of rigid particles of similar size. Degradation rates increased with an increase in RBC or particle concentration. The natural DRP (derived from aloe) was shown to be much more resistant to flow-induced degradation than polyethylene oxide in the presence or absence of RBC. Show more

Keywords: Drag reducing polymers, mechanical degradation, blood circulation, red blood cells, particles

DOI: 10.3233/BIR-2008-0511

Citation: Biorheology, vol. 45, no. 5, pp. 599-609, 2008

Authors: Ali, N. | Wang, Y. | Hayat, T. | Oberlack, M.

Article Type: Research Article

Abstract: An analysis is carried out to study the peristaltic motion of an incompressible Oldroyd 4-constant fluid in a planar channel. The flow modeling is first developed in dimensionless form and the governing problem is then simplified by adopting a long wavelength assumption. It is found that unlike Oldroyd 3-constant fluid, the governing problem of an Oldroyd 4-constant fluid under a long wavelength approximation contains the rheological parameters. The resulting non-linear problem has been solved numerically using a combination of the finite difference scheme and the iterative method. In addition, an analytical solution is presented for the domain near the channel …center. The effect of material parameters on the pumping and trapping is discussed. A comparison with the corresponding results for a viscous Newtonian fluid is also made. Show more

Keywords: Peristalsis, Oldroyd 4-constant fluid, channel flow, analytical solution, pumping, trapping

DOI: 10.3233/BIR-2008-0510

Citation: Biorheology, vol. 45, no. 5, pp. 611-628, 2008