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How to assign a rate constant that will change through time into SimBiology model?

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I have a set of drug releaseing data, and I would like to apply its drug release kinetic into my model. The data and the regression equation is attached below. The equation used for the data set is a exponential plateau formula defined as y = ym-(ym-yo)*exp(-k*x). y is drug release percentage, ym,yo and k are constant and x reprecents time. How could I assign this durg release kinetic into my simbiology model? The derivative of this drug releaseing profile is the rate. However, the rate change through time, and the simbiology don't allow me to use time into my equation. Is there any way I could solve this kind of problem? Thank you.

Accepted Answer

Sietse Braakman
Sietse Braakman on 12 Jan 2021
Hi Jesse,
You can do this using a repeated assignment and the reserved keyword 'time'. E.g.:
  • Add a species 'drug_release' to your model
  • Add the necessary parameters ym, yo, k to your model
  • Add a repeated assignment to your model where the rule reads: 'drug_release = ym-(ym-yo)*exp(-k*time)'
Make sure your time units are consistent between the 'time' in your repeated assignment and the rest of your model.
Let me know if that works for you.
  1 Comment
Jesse Chao
Jesse Chao on 18 Jan 2021
Hello Sietse,
Thank you very much for your very detail suggestions. I have successfully applied the equation into my model by following your steps. I am very appreciated your help. Thank you.
Have a nice day.

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