COMSOL Exercise 3 Release of drug molecules from a drug patch and write report. Must have COMSOL software installed

Motion sickness is a common ailment afflicting travelers. A transdermal patch is available on the market which prevents motion sickness. The small circular patch is applied to the hairless area behind the ear and it gradually delivers the drug scopolamine over a three-day period. A schematic of the patch is shown in the figure. The objective is to model the diffusion of scopolamine through the patch into the skin and look at the efficacy of the patch.

The patch is circular in shape and we can use axisymmetric assumption to formulate the problem. We will consider the computational domain in the skin to a symmetric region around the patch so that the problem remains axisymmetric. The patch consists of three layers: drug reservoir, microporous membrane, and adhesive layers. Dimensions are given in the figure. The Governing equation for this problem is

∂c  1 ∂  ∂c  ∂ 2 c  = D  r  + ∂t   r ∂r  ∂r  ∂z 2

where c is the concentration of drug scopolamine. Diffusivity of the drug scopolamine in different layers of the patch and the skin are given in table below. Note the molar mass of scopolamine is 303 g/mol. You need to convert it to mol/m 3 for data entry to COMSOL.

Steps:

  1. Run the problem for 72 hours,
  2. Perform a mesh convergence analysis
  3. Plot the concentration profile in the domain after 72 hours
  4. Change the diffusivity in the micro-porous membrane to 1 x 10 -8 cm2 /sec and solve the problem again.

Compare the concentration profile obtained with the new diffusivity and discuss the differences.

Diffusivity

cm2 /sec

Reservoir

1 x 10-7

Microporous membrane

1 x 10-10

Adhesive

1 x 10-7

Epidermis

1.45 x 10-9

Dermis

5.8 x 10-7

Initial Drug concentration

mg/mm3

Reservoir

0.08

Microporous membrane

0

Adhesive

0.04