Biorheology - Volume 57, issue 2-4

Authors: Sharma, Neha | Sastry, Sudeep | Sankovic, John M. | Kadambi, Jaikrishnan R. | Banerjee, Rupak K.

Article Type: Research Article

Abstract: BACKGROUND: Recirculation zones within the blood vessels are known to influence the initiation and progression of atherosclerotic lesions. Quantification of recirculation parameters with accuracy remains subjective due to uncertainties in measurement of velocity and derived wall shear stress (WSS). OBJECTIVE: The primary aim is to determine recirculation height and length from PIV experiments while validating with two different numerical methods: finite-element (FE) and -volume (FV). Secondary aim is to analyze how FE and FV compare within themselves. METHODS: PIV measurements were performed to obtain velocity profiles at eight cross sections downstream of stenosis at flow rate …of 200 ml/min. WSS was obtained by linear/quadratic interpolation of experimental velocity measurements close to wall. RESULTS: Recirculation length obtained from PIV technique was 1.47 cm and was within 2.2% of previously reported in-vitro measurements. Derived recirculation length from PIV agreed within 6.8% and 8.2% of the FE and FV calculations, respectively. For lower shear rate, linear interpolation with five data points results in least error. For higher shear rate either higher order (quadratic) interpolation with five data points or lower order (linear) with lesser (three) data points leads to better results. CONCLUSION: Accuracy of the recirculation parameters is dependent on number of near wall PIV data points and the type of interpolation algorithm used. Show more

Keywords: Recirculation length, recirculation height, wall shear stress, finite element, finite volume, stenosed carotid artery

DOI: 10.3233/BIR-201001

Citation: Biorheology, vol. 57, no. 2-4, pp. 53-76, 2021

Authors: Roberts, T.G. | Cox, S.J. | Lewis, A.L. | Jones, S.A.

Article Type: Research Article

Abstract: BACKGROUND: Foam sclerotherapy is the process of using an aqueous foam to deliver surfactant to a varicose vein to damage vein wall endothelial cells, causing the vein to spasm, collapse and ultimately be re-absorbed into the body. Aqueous foams are complex fluids that can exhibit a significant yield stress and high effective viscosity which depend on their composition, particularly the bubble size and liquid fraction. OBJECTIVE: To characterise the properties of foams used for varicose vein sclerotherapy and determine their effectiveness in the displacement of blood during sclerotherapy. METHODS: Foams are modelled as yield stress fluids …and their flow profiles in a model vein are predicted. Values of the yield stress are determined from experimental data for three different foams using the Sauter mean of the bubble size distribution. Along with the measured liquid fraction of the foams, this information is collected into a Bingham number which entirely characterises the process of sclerotherapy. RESULTS: Polydispersity in bubble size has a strong effect on the yield stress of a foam and the Sauter mean of the size distribution better captures the effects of a few large bubbles. Reducing the polydispersity increases the yield stress, and a higher yield stress results in a larger plug region moving along the vein, which is more effective in displacing blood. The width of the plug region is proportional to the Bingham number, which also has a quadratic dependence on the liquid fraction of the foam. Assuming typical values for the rate of injection of a foam, we predict that for a vein of diameter 5 mm, the most effective foams have low liquid fraction, a narrow size distribution, and a Bingham number B ≈ 4.5. CONCLUSIONS: The Sauter mean radius provides the most appropriate measure of the bubble size for sclerotherapy and the Bingham number then provides a simple measure of the efficacy of foam sclerotherapy in a vein of a given size, and explains the ability of different foams to remove varicose veins. Foams containing small bubbles, with a narrow size distribution, and a low liquid fraction are beneficial for sclerotherapy. Show more

Keywords: Foam, sclerotherapy, yield stress, varicose veins

DOI: 10.3233/BIR-201004

Citation: Biorheology, vol. 57, no. 2-4, pp. 77-85, 2021

Authors: Hinic, Stevan | Petrovic, Bojan | Kojic, Sanja | Omerovic, Nejra | Jevremov, Jovana | Jelenciakova, Nina | Stojanovic, Goran

Article Type: Research Article

Abstract: BACKGROUND: Numerous functions of saliva depend on its biophysical properties. Mouth rinses react with saliva and change both their own properties and properties of saliva. OBJECTIVE: The aim of this study was to define the level of mixing of artificial saliva and mouth rinses, and define their viscosity and its changes at room and body temperature. METHODS: Artificial saliva, fluoride solutions, chlorhexidine, zinc-hydroxyapatite solution and casein phosphopeptide amorphous calcium phosphate were used. To simulate their mixing, Y-channel PVC chips were used, in two different microfluidics systems. The experiments were recorded with a microscope, then the proportion …of mixing was calculated using Matlab. For viscosity measurements rotational viscometer was used. RESULTS: The results show partial mixing of all solutions with artificial saliva. Measurements with a viscometer indicate different viscosities of all used solutions. Viscosity of a mixture of solution and artificial saliva is always in the range of viscosity of the artificial saliva and the solution separately. Moreover, viscosity of all solutions, as well as mixture with artificial saliva, significantly decreases at higher temperature. CONCLUSION: Intraoral administration of mouth rinses results in change of biophysical properties of both saliva and mouth rinses. Those changes can affect preventive and therapeutic effect, and therefore oral health. Show more

Keywords: Dissolution, microfluidics, mouth rinses, saliva substitutes

DOI: 10.3233/BIR-201008

Citation: Biorheology, vol. 57, no. 2-4, pp. 87-100, 2021

Authors: Sugihara-Seki, Masako | Onozawa, Tenki | Takinouchi, Nozomi | Itano, Tomoaki | Seki, Junji

Article Type: Research Article

Abstract: BACKGROUND: In the blood flow through microvessels, platelets exhibit enhanced concentrations in the layer free of red blood cells (cell-free layer) adjacent to the vessel wall. The motion of platelets in the cell-free layer plays an essential role in their interaction with the vessel wall, and hence it affects their functions of hemostasis and thrombosis. OBJECTIVE: We aimed to estimate the diffusivity of platelet-sized particles in the transverse direction (the direction of vorticity) across the channel width in the cell-free layer by in vitro experiments for the microchannel flow of red blood cell (RBC) suspensions containing platelet-sized …particles. METHODS: Fluorescence microscope observations were performed to measure the transverse distribution of spherical particles immersed in RBC suspensions flowing through a Y-shaped bifurcating microchannel. We examined the development of the particle concentration profiles along the flow direction in the daughter channels, starting from asymmetric distributions with low concentrations on the inner side of the bifurcation at the inlet of the daughter channels. RESULTS: In daughter channels of 40 μm width, reconstruction of particle margination revealed that a symmetric concentration profile was attained in ∼30 mm from the bifurcation, independent of flow rate. CONCLUSIONS: We presented experimental evidence of particle margination developing in a bifurcating flow channel where the diffusivity of 2.9-μm diameter particles was estimated to be ∼40 μm2 /s at a shear rate of 1000 s−1 and hematocrit of 0.2. Show more

Keywords: Platelets, near-wall excess, cell-free layer, diffusivity

DOI: 10.3233/BIR-201010

Citation: Biorheology, vol. 57, no. 2-4, pp. 101-116, 2021