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. Author manuscript; available in PMC: 2016 May 1.
Published in final edited form as: Integr Biol (Camb). 2015 Apr 24;7(5):569–579. doi: 10.1039/c5ib00060b

Fig. 3.

Fig. 3

An engineering analysis of diffusion reveals significant instability of the concentration gradient within a Transwell assay. (A) Schematic diagram of a Transwell assay with the sink above the membrane and the growth factor source below the membrane. (B) Concentration gradient profiles across a membrane pore are displayed as a percentage of the initial source concentration for times between 1 – 21600 s (i.e., 1 s – 6 h). (C) Finite element simulations of the concentration gradient across a membrane pore as a function of time. Red is 100% of the initial source concentration and dark blue is 0%.