A stent is used to prop up a clogged artery to allow blood to pass through it.

A €œstent€ is used to €œprop up€ a clogged artery to allow blood to pass through it. But stents can also be loaded with drugs to facilitate the timed release of the drug into the body, especially if the drug is not very soluble in body fluids. Consider the very simple stent design shown in the figure (above right). The pole of the stent, which is 0.20 cm in diameter and 1.0 cm in length, is coated with the anticancer drug Taxol. The thickness of the coating is 0.010 cm, and 5.0 mg total Taxol is loaded. Blood flows through the 1.0 cm diameter cylindrical blood vessel at a volumetric flow rate of 10.0 cm³/s. Taxol is not very soluble in aqueous environments; the maximum solubility of Taxol in blood is 2.5 × 10^-4 mg/cm³. The viscosity of blood is 0.040 g/cm · s, and its density is 1.05 g/cm³. Blood is a complex fluid, but you may assume that its average molecular weight is close to that of liquid water (18 g/gmole). The molecular diffusion coefficient of Taxol (A) in blood fluid (B) is D_AB = 1.0 × 10^-6 cm²/s. 

a. What is the convective mass-transfer coefficient (k_L) around the outer surface of the cylindrical portion of the stent, for the solute Taxol? State all assumptions. 

b. What is the minimum time will it take for all of the Taxol to be completely discharged from the stent? State all assumptions.

Transcribed Image Text:

Stent () -- V, = 10 cm3 /sec %3D 1.0 cm Blood vessel Stent detail Di Support ring Drug (Taxol) loaded on surface 1.0 cm of stent D = 0.2 cm