A constitutive hemorheological model addressing the aggregation of red blood cells at low hematocrit values
Date Issued
May 2026
Author(s)
Μιχαήλ, Μαριάννα
Cyprus University of Technology
Advisor
Abstract
Blood is a complex fluid whose behavior is governed by RBCs (red blood cells), who
bear the ability to deform and aggregate into coin-like structures known as rouleaux. From
a rheological point of view RBCs are cells suspended in a Newtonian fluid the plasma,
but overall, blood is considered a non-Newtonian fluid because it displays a shear
thinning-behavior.
In this work, a constitutive hemorheological model considering three structural
parameters is introduced at low hematocrit values. The three structural variables
considered are: a determinant conserved tensor accounting for the deformability of RBCs,
a trace conserved tensor accounting for the orientation of rouleaux, which in this present
work are taken to be rigid, and lastly the average rouleaux size hypnotized to follow a
discrete Poissonian distribution. Both transient and steady-state conditions were
analyzed. Numerical simulations were performed in MATLAB to simulate both these
conditions and to examine the influence on the distribution of key parameters and intrinsic
properties of the system, including variations in the shear rate (Ca), the average rouleaux
size at equilibrium (Neq), and intrinsic dimensionless parameters like ε, ξ and β.
The findings predict that intrinsic parameters play the most significant role in the system’s
resistance to flow- induced breakage specifically parameter ε, while β seems to mostly
influence the speed with which a certain steady-state is reached, but not the steady-state
itself. Parameter ξ was kept at near zero values to avoid unexpected complexity in results,
and the model predicted that systems with higher Neq, are more susceptible to
disaggregation.
bear the ability to deform and aggregate into coin-like structures known as rouleaux. From
a rheological point of view RBCs are cells suspended in a Newtonian fluid the plasma,
but overall, blood is considered a non-Newtonian fluid because it displays a shear
thinning-behavior.
In this work, a constitutive hemorheological model considering three structural
parameters is introduced at low hematocrit values. The three structural variables
considered are: a determinant conserved tensor accounting for the deformability of RBCs,
a trace conserved tensor accounting for the orientation of rouleaux, which in this present
work are taken to be rigid, and lastly the average rouleaux size hypnotized to follow a
discrete Poissonian distribution. Both transient and steady-state conditions were
analyzed. Numerical simulations were performed in MATLAB to simulate both these
conditions and to examine the influence on the distribution of key parameters and intrinsic
properties of the system, including variations in the shear rate (Ca), the average rouleaux
size at equilibrium (Neq), and intrinsic dimensionless parameters like ε, ξ and β.
The findings predict that intrinsic parameters play the most significant role in the system’s
resistance to flow- induced breakage specifically parameter ε, while β seems to mostly
influence the speed with which a certain steady-state is reached, but not the steady-state
itself. Parameter ξ was kept at near zero values to avoid unexpected complexity in results,
and the model predicted that systems with higher Neq, are more susceptible to
disaggregation.
Affiliation
Cyprus University of Technology
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