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Article

Advanced Constitutive Modeling of the Thixotropic Elasto-Visco-Plastic Behavior of Blood: Steady-State Blood Flow in Microtubes

1
Laboratory of Fluid Mechanics and Rheology, Department of Chemical Engineering, University of Patras, 26504 Patras, Greece
2
Department of Mechanical and Materials Engineering, Cyprus University of Technology, Limassol 3036, Cyprus
*
Author to whom correspondence should be addressed.
Academic Editor: Norbert Willenbacher
Materials 2021, 14(2), 367; https://doi.org/10.3390/ma14020367
Received: 1 December 2020 / Revised: 2 January 2021 / Accepted: 9 January 2021 / Published: 13 January 2021
(This article belongs to the Special Issue Rheology of Advanced Complex Fluids)
The present work focuses on the in-silico investigation of the steady-state blood flow in straight microtubes, incorporating advanced constitutive modeling for human blood and blood plasma. The blood constitutive model accounts for the interplay between thixotropy and elasto-visco-plasticity via a scalar variable that describes the level of the local blood structure at any instance. The constitutive model is enhanced by the non-Newtonian modeling of the plasma phase, which features bulk viscoelasticity. Incorporating microcirculation phenomena such as the cell-free layer (CFL) formation or the Fåhraeus and the Fåhraeus-Lindqvist effects is an indispensable part of the blood flow investigation. The coupling between them and the momentum balance is achieved through correlations based on experimental observations. Notably, we propose a new simplified form for the dependence of the apparent viscosity on the hematocrit that predicts the CFL thickness correctly. Our investigation focuses on the impact of the microtube diameter and the pressure-gradient on velocity profiles, normal and shear viscoelastic stresses, and thixotropic properties. We demonstrate the microstructural configuration of blood in steady-state conditions, revealing that blood is highly aggregated in narrow tubes, promoting a flat velocity profile. Additionally, the proper accounting of the CFL thickness shows that for narrow microtubes, the reduction of discharged hematocrit is significant, which in some cases is up to 70%. At high pressure-gradients, the plasmatic proteins in both regions are extended in the flow direction, developing large axial normal stresses, which are more significant in the core region. We also provide normal stress predictions at both the blood/plasma interface (INS) and the tube wall (WNS), which are difficult to measure experimentally. Both decrease with the tube radius; however, they exhibit significant differences in magnitude and type of variation. INS varies linearly from 4.5 to 2 Pa, while WNS exhibits an exponential decrease taking values from 50 mPa to zero. View Full-Text
Keywords: blood flow; blood thixotropy; blood viscoelasticity; aggregation; rouleaux; hemodynamics; microtubes; relaxation time; CFL; Fåhraeus effect; plasma viscoelasticity; wall shear & normal stresses; interfacial shear & normal stresses; personalized hemorheology blood flow; blood thixotropy; blood viscoelasticity; aggregation; rouleaux; hemodynamics; microtubes; relaxation time; CFL; Fåhraeus effect; plasma viscoelasticity; wall shear & normal stresses; interfacial shear & normal stresses; personalized hemorheology
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MDPI and ACS Style

Giannokostas, K.; Dimakopoulos, Y.; Anayiotos, A.; Tsamopoulos, J. Advanced Constitutive Modeling of the Thixotropic Elasto-Visco-Plastic Behavior of Blood: Steady-State Blood Flow in Microtubes. Materials 2021, 14, 367. https://doi.org/10.3390/ma14020367

AMA Style

Giannokostas K, Dimakopoulos Y, Anayiotos A, Tsamopoulos J. Advanced Constitutive Modeling of the Thixotropic Elasto-Visco-Plastic Behavior of Blood: Steady-State Blood Flow in Microtubes. Materials. 2021; 14(2):367. https://doi.org/10.3390/ma14020367

Chicago/Turabian Style

Giannokostas, Konstantinos, Yannis Dimakopoulos, Andreas Anayiotos, and John Tsamopoulos. 2021. "Advanced Constitutive Modeling of the Thixotropic Elasto-Visco-Plastic Behavior of Blood: Steady-State Blood Flow in Microtubes" Materials 14, no. 2: 367. https://doi.org/10.3390/ma14020367

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