Delivery of drugs through skin has become a popular mechanism for delivering long term, controlled dosages of various compounds. A drug is mixed with an adhesive and cast into a patch, which is then applied to the skin.

The transport of the drug into the body, however, is not constant for single layered patches. An initial peak flux quickly occurs before the overall drug flux falls and stabilizes, as shown above right. Patch designers must carefully design their product to deliver the correct drug dosage in an acceptable time profile to avoid skin irritation while keeping a near constant dosage level and small form factor. Experimentation with different patch parameters involves expensive clinical trials and can take months to complete.

In this example, we modeled the transdermal drug delivery process for a dual-layer patch using a one dimensional continuum diffusion model. Each layer of skin has its own diffusion parameters, and the model tracks the depletion of drug within the applied patch. The model displays the drug flux into the body as a function of time. The two layer patch is able to maintain a more constant overall flux over the dosage life of the patch, as shown in the graph to the bottom right.