A spherical diffusion-controlled drug delivery device will be designed to limit drug release rate below a certain toxicity level. The inner radius of the spherical reservoir is ri and the outer shell thickness is t, as shown in the diagram below. r e The outer shell is made from a polymer membrane and the diffusion coefficient of the drug in the membrane is Dm = 3e 6 The initial drug dose in the reservoir is 750 mg and the ratio of membrane thickness to reservoir radius must be 1. ? s with more? AC A. Fick's 1st Law can be manipulated to become = -AD Convert the general expression Ar ac AC we learned in class to this one. What must you assume when exchanging ar B. Before getting started with the design calculations, what must you assume about the drug concentration in the reservoir? And what should you assume about the initial concentration of drug on the exterior of the membrane? C. Determine the outer diameter of the drug device to limit the initial drug release rate to 0.2 mg