Date Published: April 19, 2019
Publisher: Public Library of Science
Author(s): Nadeeshani Maheshika Geekiyanage, Marie Anne Balanant, Emilie Sauret, Suvash Saha, Robert Flower, Chwee Teck Lim, YuanTong Gu, Krishna Garikipati.
An improved red blood cell (RBC) membrane model is developed based on the bilayer coupling model (BCM) to accurately predict the complete sequence of stomatocyte-discocyte-echinocyte (SDE) transformation of a RBC. The coarse-grained (CG)–RBC membrane model is proposed to predict the minimum energy configuration of the RBC from the competition between lipid-bilayer bending resistance and cytoskeletal shear resistance under given reference constraints. In addition to the conventional membrane surface area, cell volume and bilayer-leaflet-area-difference constraints, a new constraint: total-membrane-curvature is proposed in the model to better predict RBC shapes in agreement with experimental observations. A quantitative evaluation of several cellular measurements including length, thickness and shape factor, is performed for the first time, between CG-RBC model predicted and three-dimensional (3D) confocal microscopy imaging generated RBC shapes at equivalent reference constraints. The validated CG-RBC membrane model is then employed to investigate the effect of reduced cell volume and elastic length scale on SDE transformation, to evaluate the RBC deformability during SDE transformation, and to identify the most probable RBC cytoskeletal reference state. The CG-RBC membrane model can predict the SDE shape behaviour under diverse shape-transforming scenarios, in-vitro RBC storage, microvascular circulation and flow through microfluidic devices.
Red blood cell (RBC) is a unique cell without any nucleus or mitochondria [1–3] and is remarkably simple in its structure. The most important function of RBC is the transfer of oxygen to body tissues and RBC is adapted with many features to maximize its performance as a gas carrier. It is extremely deformable and elastic to sustain its passage through narrow capillaries of the microvasculature [3, 4]. RBC holds ~ 40% excess surface area as compared to a sphere with the same volume [2, 5], and the higher surface area allows an increased gas transfer across its surface . The structural integrity and the stability of the RBC is due to its membrane which is comprised of three main components; the phospholipid bilayer, transmembrane proteins and the cytoskeleton [4, 7]. The cytoskeleton is mainly composed of spectrin tetramers connected at actin junctional complexes in a triangular network form [7, 8], and is the major contributor to the highly elastic nature of the RBC, whereas the lipid bilayer contributes to the viscosity and area preserving nature of the RBC [9, 10].
The RBC membrane is the primary contributor for its mechanical nature since a RBC does not possess any internal structure. The lipid-bilayer contributes to its out-of-plane bending resistance and surface area incompressibility while the cytoskeletal spectrin network contributes to the in-plane shear deformation , and its cytoplasm contributes to the volume incompressibility of the RBC. The Helmholtz free energy of the RBC membrane is the collective contribution of out-of-plane membrane bending energy, in-plane shear energy and the energy penalty due to cell surface area and volume constraints relative to the specified reference membrane configuration. The equilibrium RBC shape is determined at the minimum free energy state of the RBC membrane.
A CG-RBC membrane model was developed in this study to improve the understanding of the stomatocyte-discocyte-echinocyte (SDE) transformation of RBC. In contrast to the existing ADE-based numerical simulation methodologies, a bilayer coupling model (BCM)-based membrane bending energy was employed in combination with a new additional constraint: the total-membrane-surface-curvature, in order to predict each stage of stomatocyte IV–echinocyte IV RBC shapes.