  Damage to the blood vessel triggers formation of a hemostatic plug, which is
meant to prevent bleeding, yet the same phenomenon may result in a total
blockade of a blood vessel by a thrombus, causing severe medical conditions.
Here, we show that the physical interplay between platelet adhesion and
hemodynamics in a microchannel manifests in a critical threshold behavior of a
growing thrombus. Depending on the size of injury, two distinct dynamic
pathways of thrombosis were found: the formation of a nonocclusive plug, if
injury length does not exceed the critical value, and the total occlusion of
the vessel by the thrombus otherwise. We develop a mathematical model that
demonstrates that switching between these regimes occurs as a result of a
saddle-node bifurcation. Our study reveals the mechanism of self-regulation of
thrombosis in blood microvessels and explains experimentally observed
distinctions between thrombi of different physical etiology. This also can be
useful for the design of platelet-aggregation-inspired engineering solutions.
