Abstract
The configuration of proteins is critical for their biochemical behavior. Mechanical stresses that act on them can affect their behavior leading to the development of decease. The von Willebrand factor (vWF) protein circulating with the blood loses its efficacy when it undergoes non-physiological hemodynamic stresses. While often overlooked, extensional stresses can affect the structure of vWF at much lower stress levels than shear stresses. The statistical distribution of extensional stress as it applies on models of the vWF molecule within turbulent flow was examined here. The stress on the molecules of the protein was calculated with computations that utilized a Lagrangian approach for the determination of the molecule trajectories in the flow filed. The history of the stresses on the proteins was also calculated. Two different flow fields were considered as models of typical flows in cardiovascular mechanical devises, one was a Poiseuille flow and the other was a Poiseuille–Couette flow field. The data showed that the distribution of stresses is important for the design of blood flow devices because the average stress can be below the critical value for protein damage, but tails of the distribution can be outside the critical stress regime.
Highlights
While there have been many papers focused on the effect of shear stress on von Willebrand Factor (vWF) damage and blood cell trauma, the extensional components of the viscous stress play a significant role in inducing cell damage[11,26]
The history of the particles was computed, allowing the calculation of the average value of the stresses, and of the statistical distribution of the stresses as a function of time and as a function of the location of vWF release, and of the history of the stresses as a function of time of exposure in the flow field. The contributions of this manuscript are (1) the development of a numerical methodology for obtaining the history of the stresses on vWF molecules as they move in a flow field; (2) the detailed calculation of extensional stress statistical distributions on the vWF molecules showcasing the importance of the tails of the distributions in addition to average values; and (3) the investigation of the importance of the flow field configuration and of the location of vWF injection on the distribution of stresses over time
One would expect that the extensional stress on vWF markers that are released in this flow field at Y0 < 25 would start increasing as the markers move to the regions of high extensional stress, and decrease, as the markers move farther away into the channel
Summary
While there have been many papers focused on the effect of shear stress on vWF damage and blood cell trauma, the extensional components of the viscous stress play a significant role in inducing cell damage[11,26]. The critical value of shear stress for vWF deformation is around 5 Pa16. Investigation of vWF in solution at shear stress of 6 Pa has showed that high shear stresses and long exposure times caused loss of high molecular weight multimers of vWF, resulting in poor binding to platelets and subendothelial c ollagen[29]. For blood cells, both the shear and the extensional stresses combine to act on the cell[11,14,26,30,31].
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