Biorheology - Volume 50, issue 3-4

Authors: Chien, Shu

Article Type: Other

DOI: 10.3233/BIR-130639

Citation: Biorheology, vol. 50, no. 3-4, pp. 95-97, 2013

Authors: Wang, Weixiong | Graziano, Francesca | Russo, Vittorio | Ulm, Arthur J. | De Kee, Daniel | Khismatullin, Damir B.

Article Type: Research Article

Abstract: The endovascular treatment of intracranial aneurysms remains a challenge, especially when the aneurysm is large in size and has irregular, non-spherical geometry. In this paper, we use computational fluid dynamics to simulate blood flow in a vertebro-basilar junction giant aneurysm for the following three cases: (1) an empty aneurysm, (2) an aneurysm filled with platinum coils, and (3) an aneurysm filled with a yield stress fluid material. In the computational model, blood and the coil-filled region are treated as a non-Newtonian fluid and an isotropic porous medium, respectively. The results show that yield stress fluids can be used for aneurysm …embolization provided the yield stress value is 20 Pa or higher. Specifically, flow recirculation in the aneurysm and the size of the inflow jet impingement zone on the aneurysm wall are substantially reduced by yield stress fluid treatment. Overall, this study opens up the possibility of using yield stress fluids for effective embolization of large-volume intracranial aneurysms. Show more

Keywords: Intracranial aneurysm, vertebro-basilar junction, endovascular treatment, embolic agent, yield stress fluid, computational fluid dynamics

DOI: 10.3233/BIR-130630

Citation: Biorheology, vol. 50, no. 3-4, pp. 99-114, 2013

Authors: Wex, C. | Stoll, A. | Fröhlich, M. | Arndt, S. | Lippert, H.

Article Type: Research Article

Abstract: The preservation time of a liver graft is one of the crucial factors for the success of a liver transplantation. Grafts are kept in a preservation solution to delay cell destruction and cellular edema and to maximize organ function after transplantation. However, longer preservation times are not always avoidable. In this paper we focus on the mechanical changes of porcine liver with increasing preservation time, in order to establish an indicator for the quality of a liver graft dependent on preservation time. A time interval of 26 h was covered and the rheological properties of liver tissue studied using a …stress-controlled rheometer. For samples of 1 h preservation time 0.8% strain was found as the limit of linear viscoelasticity. With increasing preservation time a decrease in the complex shear modulus as an indicator for stiffness was observed for the frequency range from 0.1 to 10 Hz. A simple fractional derivative representation of the Kelvin Voigt model was applied to gain further information about the changes of the mechanical properties of liver with increasing preservation time. Within the small shear rate interval of 0.0001–0.01 s−1 the liver showed Newtonian-like flow behavior. Show more

Keywords: Soft tissue mechanics, shear rheology, liver transplantation, stiffness

DOI: 10.3233/BIR-130632

Citation: Biorheology, vol. 50, no. 3-4, pp. 115-131, 2013

Authors: Hatami-Marbini, Hamed | Etebu, Ebitimi

Article Type: Research Article

Abstract: The corneal stroma is a highly ordered extracellular matrix and mainly responsible for the mechanical strength of the cornea. The rate dependent mechanical and rheological properties of the cornea are not completely understood and there is large variation in the reported estimates. In this work, the rate dependent mechanical behavior of the corneal stroma was investigated using experimental studies and theoretical models. Unconfined compression stress-relaxation experiments at different displacement rates and compressive strains were conducted. The unconfined compression material parameters, i.e. corneal out-of-plane modulus, in-plane modulus and permeability coefficient were determined from curve-fitting the experimental data with a transversely isotropic …biphasic model. It was found that the maximum force reached during the step loading increased with both increasing magnitude and rate of the compressive strain. It was also observed that at all loading rates the in-plane Young's modulus increased with increasing strain, while the permeability coefficient decayed with increasing compressive strain. At a constant compressive strain, both the in-plane Young's modulus and the permeability coefficient increased with increasing the loading rate. Regardless of loading rates and compressive strains, a range of corneal out-of-plane modulus of 0.6 kPa to 13.8 kPa, in-plane modulus of 0.5 MPa to 4.8 MPa, and permeability coefficient of 1×10−14 m4 /N·s to 7×10−14 m4 /N·s was found. Show more

Keywords: Soft tissue mechanics, stress relaxation experiments, transversely isotropic biphasic model, rate dependent compressive behavior

DOI: 10.3233/BIR-130634

Citation: Biorheology, vol. 50, no. 3-4, pp. 133-147, 2013

Authors: Makino, Masato | Sugihara-Seki, Masako

Article Type: Research Article

Abstract: In channel flow of multicomponent suspensions, segregation behavior of suspended components perpendicular to the flow direction is often observed, which is considered to be caused by the differential properties of the lateral migration depending on their shape, size, flexibility, and other characteristics. In the present study, we investigate the effect of size differences between suspended components on the segregation behavior, by a two-dimensional numerical simulation for binary dispersed suspensions of fluid droplets of two different sizes subjected to a plane Poiseuille channel flow. The small and large droplets are assumed to have equal surface tensions and equal viscosity ratios of …internal to external fluids. The time evolutions of the lateral positions of large and small droplets relative to the channel centerline were computed by changing the area fraction of the small droplets in a mixture with a constant total area fraction. The large droplets are found to migrate closer to the channel centerline and the small droplets are found to migrate closer to the channel wall compared to the corresponding lateral positions in mono-dispersed suspensions at the same area fractions, although the mean lateral positions of the large and small droplets in mono-dispersed suspension are comparable. This segregation behavior as well as the margination of small droplets are enhanced when the size difference between large and small droplets is increased and the area fraction of large droplets is increased. These results may arise from higher tendencies for the large droplets to approach the channel centerline compared to the small droplets, which consequently expel small droplets from the central region toward the channel walls. Show more

Keywords: Droplets dispersion, margination

DOI: 10.3233/BIR-130638

Citation: Biorheology, vol. 50, no. 3-4, pp. 149-163, 2013

Authors: Meram, Ece | Yilmaz, Bahar D. | Bas, Ceren | Atac, Nazlı | Yalcin, O. | Meiselman, Herbert J. | Baskurt, Oguz K.

Article Type: Research Article

Abstract: Classically, it is known that red blood cell (RBC) deformability is determined by the geometric and material properties of these cells. Experimental evidence accumulated during the last decade has introduced the concept of active regulation of RBC deformability. This regulation is mainly related to altered associations between membrane skeletal proteins and integral proteins, with the latter serving to anchor the skeleton to the lipid matrix. It has been hypothesized that shear stress induces alterations of RBC deformability: the current study investigated the dynamics of the transient improvement in deformability induced by shear stress at physiologically-relevant levels. RBC were exposed to …various levels of shear stress (SS) in a Couette type shearing system that is part of an ektacytometer, thus permitting the changes in RBC deformability during the application of SS to be monitored. Initial studies showed that there is an increase in deformability of the RBC subjected to SS in the range of 5–20 Pa, with kinetics characterized by time constants of a few seconds. Such improvement in deformability, expressed by an elongation index (EI), was faster with higher levels of SS and hence yielded shorter time constants: absolute values of EI increased by 3–8% of the starting level. Upon the removal of the shear stress, this response by RBC was reversible with a slower time course compared to the increase in EI during application of SS. Increased calcium concentration in the RBC suspending medium prevented the improvement of deformability. It is suggested that the improvement of RBC deformability by shear forces may have significant effects on blood flow dynamics, at least in tissues supplied by blood vessels with impaired vasomotor reserve, and may therefore serve as a compensating mechanism for the maintenance of adequate microcirculatory perfusion. Show more

Keywords: Erythrocyte deformability, regulation, shear stress, ektacytometry, calcium

DOI: 10.3233/BIR-130637

Citation: Biorheology, vol. 50, no. 3-4, pp. 165-176, 2013

Authors: Walker, Andrew M. | Xiao, Yao | Johnston, Clifton R. | Rival, David E.

Article Type: Research Article

Abstract: Although information pertaining to the viscous characterization of HES 130/0.4 Voluven® and HES 260/0.45 Pentaspan® is available, quantification is limited to 100% concentrations. We focus here on the quantification of their viscous behavior along with HES 130/0.4 Volulyte® in a shear thinning non-Newtonian blood analog of aqueous xanthan gum and glycerol. Dynamic viscosities of multiple batches of HES fluids were measured through capillary viscometry. The viscous behavior of 100%, 25% and 12.5% concentrations were then measured through a closed flow loop across physiologically relevant flow rates. Measured viscosities were 2.57 millipascal second (mPa·s) 6.52 mPa·s and 2.48 …mPa·s for HES 130/0.4 Voluven® , HES 260/0.45 and HES 130/0.4 Volulyte® , respectively. Pipe flow analysis found that all HES fluids displayed Newtonian behavior at 100% concentrations. 25% concentrations of both HES 130/0.4 fluids decreased analog viscosity 23%–29% at a flow rate of 1.0 ml/s and 16%–21% at a flow rate of 22.5 ml/s. At a flow rate of 22.5 ml/s, 25% and 12.5% concentrations of HES 260/0.45 resulted in analog viscosity changes of 3.9%–4.5%. Capillary viscosity reductions of approximately 7% and 14.5% in HES 130/0.4 Voluven® and HES 260/0.45 suggest changes in molecular composition to batches previously measured. Maintenance of analog viscosity suggests that HES 260/0.45 would be suitable as a high viscosity plasma expander in extreme hemodilution through preservation of microcirculatory function and wall shear stress (WSS). Show more

Keywords: HES fluids, hemodilution, microcirculation, shear thinning, non-Newtonian fluids

DOI: 10.3233/BIR-130635

Citation: Biorheology, vol. 50, no. 3-4, pp. 177-190, 2013

Authors: Chaudhry, Hans | Bukiet, Bruce | Roman, Max | Stecco, Antonio | Findley, Thomas

Article Type: Research Article

Abstract: In this paper, we computed fluid pressure and force on fascia sheets during manual therapy treatments using Squeeze Film Lubrication theory for non-Newtonian fluids. For this purpose, we developed a model valid for three dimensional fluid flow of a non-Newtonian liquid. Previous models considered only one-dimensional flows in two dimensions. We applied this model to compare the one-dimensional flow of HA, considered as a lubricating fluid, around or within the fascia during sliding, vibration, and back-and-forth sliding manipulation treatment techniques. The fluid pressure of HA increases dramatically as fascia is deformed during manual therapies. The fluid force increases more during …vertical vibratory manipulation treatment than in constant sliding, and back and forth motion. The variation of fluid pressure/force causes HA to flow near the edges of the fascial area under manipulation in sliding and back and forth motion which may result in greater lubrication. The fluid pressure generated in manual therapy techniques may improve sliding and permit muscles to work more efficiently. Show more

Keywords: Hyaluronic acid, fascia, manual manipulation, massage therapy

DOI: 10.3233/BIR-130631

Citation: Biorheology, vol. 50, no. 3-4, pp. 191-202, 2013

Authors: Yamamoto, Takehiro | Ueda, Shuya

Article Type: Research Article

Abstract: Biofilm is a slime-like complex aggregate of microorganisms and their products, extracellular polymer substances, that grows on a solid surface. The growth phenomenon of biofilm is relevant to the corrosion and clogging of water pipes, the chemical processes in a bioreactor, and bioremediation. In these phenomena, the behavior of the biofilm under flow has an important role. Therefore, controlling the biofilm behavior in each process is important. To provide a computational tool for analyzing biofilm growth, the present study proposes a computational model for the simulation of biofilm growth in flows. This model accounts for the growth, decay, detachment and …adhesion of biofilms. The proposed model couples the computation of the surrounding fluid flow, using the finite volume method, with the simulation of biofilm growth, using the cellular automaton approach, a relatively low-computational-cost method. Furthermore, a stochastic approach for considering the adhesion process is proposed. Numerical simulations for the biofilm growth on a planar wall and that in an L-shaped rectangular channel were carried out. A variety of biofilm structures were observed depending on the strength of the flow. Moreover, the importance of the detachment and adhesion processes was confirmed. Show more

Keywords: Biofilm, numerical simulation, cellular automaton method, detachment, adhesion, macro flow

DOI: 10.3233/BIR-130636

Citation: Biorheology, vol. 50, no. 3-4, pp. 203-216, 2013