Fig. 2 Simulations of RBC sickling with a mechanistic model. Simulations of RBC sickling with a mechanistic model. (A) Configuration of an HbS fiber bundle in a stretched RBC. Green particles, actin junctions; purple particles, spectrin filaments; black particles, glycophorin proteins; yellow particles, band-3 proteins; red particles, lipid bilayer. Yellow bar inside the RBC represents a chain of CG HbS particles with varying thickness, mimicking an HbS fiber bundle. (B) Bending stiffness of fiber bundles plotted as a function of the number of constituent fibers. Bending stiffness of fiber bundle dictates the variations in the ensuing fiber bundle and RBC shapes, as illustrated in the plot: (I) fiber buckled, (II) fiber buckled with one protrusion on the RBC, (III) fiber buckled with two protrusions on the RBC, (IV) nonbuckled with two protrusions on RBC. Fibers are plotted with an exaggerated thickness for clarity. In the insets, a part of the RBC membrane is not shown such that the HbS fiber configuration inside the RBC can be viewed. Lu Lu et al. Sci Adv 2019;5:eaax3905 Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).