a. A spherical capsule is used for long term, sustained drug release. A saturated solution containing
the drug (A) is encapsulated within a rigid gel-shell, and the saturated solution contains a lump
of solid A. A diffuses through the shell (gel B) to the surroundings where it is no longer
concentrated (i.e it is dilute). What is the purpose of the solid lump of solid A in the system?
i. A uniform liquid can't easily be encapsulated in a gel.
ii. It allows for the assumption of a dilute solution in order to simplify Fick's equation.
iii. It allows for the system to maintain steady state.
iv. The boundary condition at the sphere's surface can be assumed to be equal to 1, and at
infinity equal to 0.
