Comparison of Brownian dynamics models for VWF. (A) Parameter space of the simulation as a function of bead diameter and LJ interaction strength. Comparison with the size of spheres representing monomers of the different models. Sizes of spheres are on the same scale as panel B. Blue space represents collapsed polymers, with yellow being uncollapsed polymers. Dotted line represents the ϴ-point, in which the attractive and repulsive forces cancel out. (B) Electron microscopy images of VWF adapted from Fowler et al.⁴⁹ (C) Comparison between Brownian dynamics simulation and experimental steady state extension for surface-tethered polymers under shear flow. The 3 models are the original LJ model (◇), the revised LJ model (Δ), and the uncollapsed polymer model (□). Simulations compared with experimental data from previous surface stretching experiments of 2- to 3.5-μm VWF molecules from the study by Fu et al (ο, 156 molecules measured).⁶ For each model and shear stress, the equilibrium extension of 5 independent simulations were averaged together at each shear stress. Extension is normalized by maximum extension and plotted on a semi–log plot. Shaded area shows standard deviation of the 5 simulations. (D) Comparison of Brownian dynamics simulation and experimental mean extension for free-in-flow VWF, with applied shear flow as measured by PULSIS, plotted on a semi–log plot. Because the contour length of the experimental data is unknown, simulations and data are not normalized. Polymer simulation extensions were averaged over a time window and independent runs. (LJ original runs = 3, revised LJ runs = 3, and uncollapsed polymer runs = 10). Absolute contour length of all simulations was ∼3 μm.