You are developing a controlled release drug delivery system to deliver growth factor to a diabetic skin lesion from a hydrogel based patch. To simulate the diffusion of drug through the hydrogel layer (layer1) and the top layer of scar tissue (layer 2), you designed an in vitro experiment.
In your experiment, the drug concentration outside the hydrogel layer is at constant concentration Co = 10 μM. At steady-state, you measure drug concentration under the scar tissue to be C3 = 1μM. Each layer is 200 μM thick. The diffusivity of drug in hydrogel is 10^-7 cm^2/s, and the diffusivity in scar tissue is 10^-9 cm^2/s.
a) If the partition coefficient between hydrogel and scar tissue is 1.0, then what is the concentration of drug at the boundary between the hydrogel and the scar tissue?