Conformational behavior of von Willebrand factor in response to regions of high shear and extension rates in converging or diverging pipes.

In this work, the conformational dynamics of the von Willebrand Factor (vWF) are investigated as it encounters localized regions of high shear and extensional forces in a converging/diverging channel. Using direct numerical simulations that employ two-way coupling between a lattice Boltzmann fluid solver and a Langevin dynamics-based bead-spring model for vWF, we study how flow-induced forces influence the spatiotemporal evolution of molecular unfolding. Unlike studies that rely on statistical models or averaged behavior, our approach captures transient and configuration-specific unfolding events that arise from the interplay between molecular conformation and flow-field structure. In the simulations, the vWF passes through a straight section of pipe with subcritical shear rates before entering a converging/diverging section where shear and extension rates exceed the known critical threshold for vWF unfolding. Streamwise extension and conformational states are analyzed over time. Results show that while vWF may unfurl in the converging/diverging sections, the likelihood of such events is significantly influenced by the vWF's initial conformation upon entering these regions. Notably, increasing the flow rate to elevate shear and extension rates does not necessarily enhance unfolding likelihood in the converging/diverging section due to its greatly reduced residence time.