Characterization of the threshold response of initiation of blood clotting to stimulus patch size.

This article demonstrates that the threshold response of initiation of blood clotting to the size of a patch of stimulus is a robust phenomenon under a wide range of conditions and follows a simple scaling relationship based on the Damköhler number. Human blood and plasma were exposed to surfaces patterned with patches presenting clotting stimuli using microfluidics. Perturbations of the complex network of hemostasis, including temperature, variations in the concentration of stimulus (tissue factor), and the absence or inhibition of individual components of the network (factor IIa, factor V, factor VIII, and thrombomodulin), did not affect the existence of this response. A scaling relationship between the threshold patch size and the timescale of reaction for clotting was supported in numerical simulations, a simple chemical model system, and experiments with human blood plasma. These results may be useful for understanding the spatiotemporal dynamics of other autocatalytic systems and emphasize the relevance of clustering of proteins and lipids in the regulation of signaling processes.