Rate of mixing controls rate and outcome of autocatalytic processes-theory and microfluidic experiments with chemical reactions and blood coagulation
Rebecca R. Pompano 1, Hung-Wing Li 1 and Rustem F. Ismagilov 1*
1 The University of Chicago
* To whom correspondence should be addressed. E-mail: r-ismagilov{at}uchicago.edu.
Submitted on January 15, 2008
Revised on February 18, 2008
Accepted on 1 April 2008
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Abstract |
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This paper demonstrates that the rate of mixing can regulate the rate and outcome of both biological and non-biological autocatalytic reaction systems that display a threshold response to the concentration of an activator. Plug-based microfluidics was used to control the timing of reactions, the rate of mixing, and surface chemistry in blood clotting and its chemical model. Initiation of clotting of human blood plasma required addition of a critical concentration of thrombin. Clotting could be prevented by rapid mixing when thrombin was added near the critical concentration, and mixing also affected the rate of clotting when thrombin was added at concentrations far above the critical concentration in two clinical clotting assays for human plasma. This phenomenon was modeled by a simple mechanism-local and global competition between the clotting reaction, which autocatalytically produces an activator, and mixing, which removes the activator. Numerical simulations showed that the Damköhler number, which describes this competition, predicts the effects of mixing. Many biological systems are controlled by thresholds, and these results shed light on the dynamics of these systems in the presence of spatial heterogeneities and provide simple guidelines for designing and interpreting experiments with such systems.
Key Words:
activated partial thromboplastin time, analytical accuracy, bistability, chlorite-thiosulfate reaction, hemostasis, prothrombin time
