Behaviour of the von Willebrand Factor in Blood Flow

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The von Willebrand factor (vWF), a large multimeric protein, is essential in hemostasis. Under normal conditions, vWF is present in blood as a globular polymer. However, in case of an injury, vWF is able to unwrap and bind to the vessel wall and to flowing platelets. Thus, platelets are significantly slowed down and can adhere to the wall and close the lesion. Nevertheless, it is still not clear how the unwrapping of the vWF is triggered. To better understand these complex processes, we employ a particle-based hydrodynamic simulation method to study the behaviour of vWF in blood flow. The vWF is modelled as a chain of beads (monomers) connected by springs. In addition, the monomers are subject to attractive interactions in order to represent characteristic properties of the vWF. The behaviour of vWF is investigated under different conditions including a freely-suspended polymer in shear flow and a polymer attached to a wall. We also examine the migration of vWF to a wall (margination) depending on shear rate and volume fraction of red blood cells (RBCs). Furthermore, the stretching of the vWF in flow direction depending on its radial position in a capillary is monitored. Our results show that attractive interactions between monomer beads increase margination efficiency and significantly affect the extension of vWF at different radial positions in blood vessels

Blood Flow in silico: From Single Cells to Blood Rheology

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Mesoscale hydrodynamics simulations of red blood cells under flow have provided much new insight into their shapes and dynamics in microchannel flow. The presented results range from the behavior of single cells in confinement and the shape changes in sedimentation, to the clustering and arrangement of many cells in microchannels and the viscosity of red blood cell suspensions under shear flow. The interaction of red blood cells with other particles and cells, such as white blood cells, platelets, and drug carriers, shows an essential role of red blood cells in the margination of other blood components

An Improved Coarse-Grained Model to Accurately Predict Red Blood Cell Morphology and Deformability

Accurate modelling of red blood cells (RBCs) has greater potential over experiments, as it can be more robust and significantly cheaper than equivalent experimental procedures to investigate the mechanical properties, rheology and dynamics of RBCs. The recent advances in numerical modelling techniques for RBC studies are reviewed in this study, and in particular, the discrete models for a triangulated surface to represent the in-plane stretching energy and out-of-plane bending energy of the RBC membrane are discussed. In addition, an improved RBC membrane model is presented based on coarse-grained (CG) technique that accurately and efficiently predicts the morphology and deformability of a RBC. The CG-RBC membrane model predicts the minimum energy configuration of the RBC from the competition between the in-plane stretching energy of the cytoskeleton and the out-of-plane bending energy of the lipid-bilayer under the given reference states of the cell surface area and volume. A quantitative evaluation of several cellular measurements including length, thickness and shape factor, is presented between the CG-RBC membrane model and three-dimensional (3D) confocal microscopy imaging generated RBC shapes at equivalent reference states. The CG-RBC membrane model predicts agreeable deformation characteristics of a healthy RBC with the analogous experimental observations corresponding to optical tweezers stretching deformations. The numerical approach presented here forms the foundation for investigations into RBC morphology and deformability under diverse shape-transforming scenarios, in vitro RBC storage, microvascular circulation and flow through microfluidic devices