Biorheology - Volume 44, issue 4

Authors: Makino, Ayako | Shin, Hainsworth Y. | Komai, Yutaka | Fukuda, Shunichi | Coughlin, Mark | Sugihara-Seki, Masako | Schmid-Schönbein, Geert W.

Article Type: Research Article

Abstract: We review recent evidence which suggests that leukocytes in the circulation and in the tissue may readily respond to physiological levels of fluid shear stress in the range between about 1 and 10 dyn/cm2 , a range that is below the level to achieve a significant passive, viscoelastic response. The response of activated neutrophilic leukocytes to fluid shear consists of a rapid retraction of lamellipodia with membrane detachment from integrin binding sites. In contrast, a subgroup of non-activated neutrophils may project pseudopods after exposure to fluid shear stress. The evidence suggests that G-protein coupled receptor downregulation by fluid shear with …concomitant downregulation of Rac-related small GTPases and depolymerization of F-actin serves to retract the lamellipodia in conjunction with proteolytic cleavage of β2 integrin to facilitate membrane detachment. Furthermore, there exists a mechanism to up- and down-regulate the fluid shear-response, which involves nitric oxide and the second messenger cyclic guanosine monophosphate (cGMP). Many physiological activities of circulating leukocytes are under the influence of fluid shear stress, including transendothelial migration of lymphocytes. We describe a disease model with chronic hypertension that suffers from an attenuated fluid shear-response with far reaching implications for microvascular blood flow. Show more

Keywords: Shear stress, normal stress, neutrophils, monocytes, lymphocytes, actin, pseudopod, integrin, G-protein coupled receptor, cGMP, nitric oxide, migration, microcirculation, inflammation

Citation: Biorheology, vol. 44, no. 4, pp. 221-249, 2007

Authors: Craiem, Damian | Armentano, Ricardo L.

Article Type: Research Article

Abstract: Arterial viscoelasticity can be described with a complex modulus (E* ) in the frequency domain. In arteries, E* presents a power-law response with a plateau for higher frequencies. Constitutive models based on a combination of purely elastic and viscous elements can be represented with integer order differential equations but show several limitations. Recently, fractional derivative models with fewer parameters have proven to be efficient in describing rheological tissues. A new element, called “spring-pot”, that interpolates between springs and dashpots is incorporated. Starting with a Voigt model, we proposed two fractional alternative models with one and two spring-pots. The three …models were tested in an anesthetized sheep in a control state and during smooth muscle activation. A least squares method was used to fit E* . Local activation induced a vascular constriction with no pressure changes. The E* results confirmed the steep increase from static to dynamic values and a plateau in the range 2–30 Hz, coherent with fractional model predictions. Activation increased E* , affecting its real and imaginary parts separately. Only the model with two spring-pots correctly followed this behavior with the best performance in terms of least squares errors. In a context where activation separately modifies E* , this alternative model should be considered in describing arterial viscoelasticity in vivo. Show more

Keywords: Fractional calculus, complex modulus, constitutive models, arterial wall mechanics, viscoelasticity

Citation: Biorheology, vol. 44, no. 4, pp. 251-263, 2007

Authors: Kidane, Asmeret G. | Edirisinghe, Mohan J. | Bonhoeffer, Philipp | Seifalian, Alexander M.

Article Type: Research Article

Abstract: A non-biodegradable polyhedral oligomeric silsesquioxane (POSS) nanocomposite biopolymer has been developed for fabrication of medical devices and for tissue engineering human organs. The polymer in solution, containing 2 wt% of POSS, has been synthesized, characterized and investigated to determine its key rheological properties. Thus, the variation of shear stress and viscosity as a function of shear rate has been determined at ambient temperature to estimate yield stress and the index of pseudoplasticity, respectively. The temperature dependence of viscosity and the effect of ageing on the viscosity of the polymer have also been investigated. Results are compared with those of a …conventional polycarbonate urethane (PCU) polymer solution. The POSS-PCU polymer solution shows near-Newtonian behaviour in the shear rate range to 1000 s−1 , having an apparent viscosity of ~3000 mPa s and a pseudoplasticity index of 0.90, decreasing slightly as the polymer solution is aged over 9 months. The temperature dependence of viscosity of the POSS polymer is extremely low and does not change with ageing but the yield strength increases from 2.7 Pa to 8.3 Pa. Show more

Keywords: Biomaterial, biopolymer, solution, viscosity, flow behaviour, nanocomposite

Citation: Biorheology, vol. 44, no. 4, pp. 265-272, 2007

Authors: Ku, David N. | Flannery, Conor J.

Article Type: Research Article

Abstract: Occlusive thrombosis accounts for many heart attacks and strokes. These acute events are difficult to catch in patients and animal test methods may be misleading because anti-thrombotic therapeutics often do not cross-react with different species. This paper presents a new flow-through system that leads to rapid occlusive thrombosis in arterial flow conditions. Whole porcine blood is perfused through a tubular test section. The growing thrombus is visualized in real time from early platelet attachment, through accumulation, to occlusion. The progression of flow rate reduction provides a clear distinguishing parameter between thrombus formation and embolization. Thrombus growth rate is a linear …function of very high shear rate beyond 40,000 s−1 . The histology of the thrombus reveals predominantly platelet accumulation and growth as a rough surface with tendrils. This flow-through system may be useful for the economic testing of new anti-thrombosis therapies. Show more

Keywords: Occlusion, stenosis, high shear, thrombosis, platelet

Citation: Biorheology, vol. 44, no. 4, pp. 273-284, 2007

Authors: Mutrynowska, J. | Grzegorzewski, B.

Article Type: Research Article

Abstract: The red blood cell (RBC) sediment formation was studied using an optical method. The intensity of light transmitted through the blood sample was measured as a function of time and distance from the bottom of the sample. Blood was obtained from healthy donors and measurements were performed at initial hematocrits ranging from 30 to 50%. Sedimentation curves and time dependence of the intensity averaged along the height of the RBC suspension were determined to give a cumulative description of the process. Detailed analysis of the transmitted light intensity revealed a moving interface between sedimenting RBC aggregates and the forming of …a deposit of the cells. It was shown that although there is no discontinuity in the intensity an averaged interface can be found. A novel curve describing the sedimentation process called the deposit formation curve was found. Below this curve a formation of the RBC deposit occurs. Firstly, this curve represents the position of the interface between sedimenting RBC aggregates and a forming deposit, secondly this curve coincides with the last part of the sedimentation curve. Show more

Keywords: RBC sedimentation, RBC sediment formation, RBC aggregation

Citation: Biorheology, vol. 44, no. 4, pp. 285-297, 2007

Article Type: Other

Citation: Biorheology, vol. 44, no. 4, pp. 299-302, 2007