Microvascular networks are highly complex structures comprised of the smallest blood vessels. Some of their major utilities include gas and nutrient exchange to surrounding tissues, and regulation of blood flow in individual organs. Blood cells squeeze and deform as they flow through the vessels that comprise them, an ability that is critical to the healthy functioning of the circulatory system. While much is known about the average behavior of blood cells flowing within these networks, little is known about the individual cellular-scale events giving rise to this average behavior. What is going on at the cellular-scale as the actual blood cells flow through such torturous geometries? To better understand this, we use a recently developed state-of-the-art simulation tool to model nearly one second in the life of red blood cells as they squeeze, twist, and tumble through physiologically realistic microvascular networks. The results are indeed surprising!
An image based on one such simulation is presented on the cover of the December 19 issue of the Biophysical Journal. Specifically shown is a snapshot of red blood cells flowing and deforming through a microvascular network. This network was designed following in vivo images and data, and was constructed by digitally rendering the geometry using a standard CAD software. The 3D vascular surfaces were then imported into our simulation tool, and using this we captured the 3D flow field as well as the large deformation and dynamics of each individual blood cell. The blood cells shown are suspended in plasma, which conveys them through the network. The cells are modeled using the finite element method, with each cell surface discretized by about 5000 elements. During the nearly one second simulated, thousands of cellular-scale events occur. The statistics associated with the resulting hemodynamic quantities in vessels are utilized to better understand microvascular network blood flow.
The inspiration behind the simulation shown on the cover is our desire to mimic what actually occurs in physiology as closely as possible. That is, we wanted to capture the realistic features of the geometries through which cells flow without sacrificing the particulate nature of blood, and vice versa. In doing so, we uncover new and interesting features associated with the cellular-scale dynamics. Furthermore, we reveal some surprising counter-intuitive behavior that can only be captured by considering the time-dependent 3D deformation and dynamics of each individual cell.
– Peter Balogh, Prosenjit Bagchi