In this work, a numerical model that enables simulation of the deformation and flow behaviour of differently aged Red Blood Cells (RBCs) is developed. Such cells change shape and decrease in deformability as they age, thus impacting their ability to pass through the narrow capillaries in the body. While the body filters unviable cells from the blood naturally, cell aging poses key challenges for blood stored for transfusions. Therefore, understanding the influence RBC morphology and deformability have on their flow is vital. While several existing models represent young Discocyte RBC shapes well, a limited number of numerical models are developed to model aged RBC morphologies like Stomatocytes and Echinocytes. The existing models are also limited to shear and stretching simulations. Flow characteristics of these morphologies are yet to be investigated. This paper aims to develop a new membrane formulation for the numerical modelling of Stomatocyte, Discocytes and Echinocyte RBC morphologies to investigate their deformation and flow behaviour. The model used represents blood plasma using the Lattice Boltzmann Method (LBM) and the RBC membrane using the discrete element method (DEM). The membrane and the plasma are coupled by the Immersed Boundary Method (IBM). Previous LBM-IBM-DEM formulations represent RBC membrane response based on forces generated from changes in the local area, local length, local bending, and cell volume. In this new model, two new force terms are added: the local area difference force and the local curvature force, which are specially incorporated to model the flow and deformation behaviour of Stomatocytes and Echinocytes. To verify the developed model, the deformation behaviour of the three types of RBC morphologies are compared to well-characterised stretching and shear experiments. The flow modelling capabilities of the method are then demonstrated by modelling the flow of each cell through a narrow capillary. The developed model is found to be as accurate as benchmark Smoothed Particle Hydrodynamics (SPH) approaches while being significantly more computationally efficient.

Red blood cells (RBCs) are the main component of the blood and comprise about 45% of the total volume of blood. The key role of RBCs is to transfer oxygen from pulmonary capillaries to tissue capillaries, and transfer carbon dioxide from tissues to lungs. While some of these capillaries have uniform cross-sections, some non-uniform capillaries are also present. Often the diameters of these cross sections are smaller than the diameter of the RBCs. Yet because of the high deformability of its viscoelastic membrane, the RBCs are able to flow through these capillaries. The purpose of this analysis is therefore to investigate the flow activity of RBCs during their passage through a non-uniform capillary using the Lattice Boltzmann -Immersed Boundary (LB-IB) method.

Transfusions involving red blood cells (RBCs) are critical to modern health care. However, there is no effective clinical way to remove aged cells from stores to increase maximum shelf life and enhance transfusion safety. The spleen filters aged RBCs but the specific mechanisms are not well understood. In this study, an accurate and efficient new numerical model was developed for different RBC shapes and investigated their flow and deformation behaviour using the LBM-IBM-DEM method. Cell orientation, stiffness, morphology, interior viscosity of the cell, and flow velocity were found to be the major parameters that determine splenic cell filtration.