On the simultaneous motions of many blood cells.

Readers who have mentally juggled to compare models of thrombosis based on discrete concepts with those based on continuum representations will enjoy the article by Skorczewski et al. (1) because they bring first-principles methods to provide a fascinating description of the motions of red blood cells, platelets, and events in flows over a prototypical thrombotic mound. The temporal dynamics of the situation are captured over many scales in an exemplary two-dimensional situation as the red cells control most of the available space, block direct motions to the wall, and are less likely to be present near the wall. The size of the near-wall region is visibly changed when the hematocrit of the flow changes. And, the platelet dynamics, their individual behaviors in the flow field, is shown to differ for lower and higher hematocrits. The authors’ work sets a standard for careful depiction of the flow-driven events involving interactions among red cells and platelets, for computing local descriptions of platelet exposure, and for representing the totality of events for distinct values of the average hematocrit. Readers can be assured that proper methods were implemented for the computations used to uncover the applicable shear strain rates and shear (or other) stress distributions at all sites in the flow and that these events induced the gradients of concentration and effective diffusion coefficient. The movies that are a part of the article’s Supporting Material will help the reader appreciate the dynamism that is connected with exposure to biochemical agents and processes. As you enjoy the article, think of the steps that will come with increased computational power. This framework is sturdy enough for work in three dimensions and for including more of the applicable biochemistry and cellular biology. Recognizing the physiological and pathological importance of thrombotic events in flowing blood, many readers and contributors to Biophysical Journal work in or follow the field. Our New & Notable paper joins a group (2–5) that has addressed the larger multiscale problem. Each of them followed the precepts of the Biophysical Society, and the Biophysical Journal, by making effective use of mathematical depictions, models, and experimental data. These four works illustrate major aspects of thrombosis and hemostasis that are within our readers’ purviews; however, the list is too short to capture all the important contributions by the Biophysical Journal community on this general topic. Direct treatment of the total three-dimensional situation, with its nonlinearity and many elements, is still our dream. Yet strong attacks on specific aspects are possible when numerical means are combined with sound data. This is true especially when the numerical studies are based in sound mathematical science, the results are verified by their ability to capture the prior experimental findings, and the studies predict behaviors that can be sought in future experiments. Most importantly, the numerical means will permit workers to explore details that are extremely difficult or even impossible to capture experimentally, and thereby extend our understanding of the intrinsic processes.