Description
Flowing blood through microfluidic devices has numerous applications, such as blood-plasma separation or isolation of circulating tumour cells [1]. In order to optimise those devices, an understanding of the mechanisms changing the cross-sectional distribution (CSD) of red blood cell suspensions is necessary. In this work, we numerically investigate how two different geometrical structures, a narrowing of the channel and a bifurcation, alter the CSD of the red blood cell suspension, and the conditions for the suspension to recover its pre geometrical disturbance distribution [2, 3].
We model blood as a suspension of deformable particles in a continuous fluid [1]. We simulate the continuous fluid with the lattice-Boltzmann method, and we model the red blood cells with an isotropic and hyperelastic model (Skalak’s model). The fluid-structure interaction between the red blood cells and the fluid is resolved using the immersed boundary method. This method has previously been shown to reproduce the physics of red blood cell suspensions.
Our results show that by flowing the suspension through a geometric narrowing, the width of the CSD is narrowed in a haematocrit (concentration of red blood cell) dependant way, while the centre of mass of the CSD is unchanged. On the other hand, when the suspension reaches a bifurcation, the centre of mass of the CSD is shifted towards the inner side of the bifurcation, while the width of the CSD is less affected. The mechanisms to recover from those changes in CSD differ as well. On the one hand, when the CSD of the red blood cells is narrowed through the geometric constriction, the pre disturbance distribution is recovered through cell-cell interaction, making the length scale of the recovery haematocrit dependant [4]. On the other hand, when the suspension reaches a bifurcation and the centre of mass of the distribution is changed, the recovery mechanism is due to the lift force driving red blood cells away from the channel wall, and is largely independent of haematocrit, with a fixed length scale of 25 channel diameters [5].
In this work, we model red blood cells as a suspension of deformable red blood cells and flow them through geometric disturbances (a narrowing of the channel and a bifurcation) to investigate how the cross-sectional distribution of the suspension changes. Our results show that one can modulate the centre of mass or the width of their CSD separately, and we investigate the length scale and mechanisms for the recovery of the CSD. This work shows different ways that one can modulate red blood cell suspensions in microchannel to manipulate blood in microfluidic devices.
References
1. Owen et al., Advances in physics: X, 2023
2. Enjalbert et al., PNAS, 2020
3. Bernabeu et al., PNAS, 2021
4. Grandchamp et al., Phys. Rev. Lett., 2013
5. Katanov et al., Microvascular research, 2015