"We looked at incorporating an anti-cancer drug initially, both as a proof of concept, but also as a potential application. For example, the drug patch could be implanted after the removal of tumours that have poorly defined margins or have high incidents of reoccurrence at the site of excision," Erik Pierstorff, a member of Northwestern University's nanoscale biotic-abotic systems engineering laboratory (N-BASE) told nanotechweb.org. "However, our technology is not limited to cancer treatments and could be used as a platform for delivering many different types of therapeutics at sites that require a prolonged, localized release."

Parylene C has been used in medical applications for more than two decades, which makes it an ideal choice from a regulatory perspective. Structurally, the material has multiple benefits.

"The stable architecture of parylene creates a durable matrix where drug release is maintained at its defined rate," explained Pierstorff. "In other words, wear and tear from the body's environment is unlikely to alter the release kinetics of the device."

Taking a closer look
For a long time, researchers believed that vapour deposited parylene films provided a uniform coating that blocks the transport of small molecules. Then recently, scientists identified "pinholes" within the film when the layer thickness was restricted to a few microns.

AFM images taken by the group show that the peak roughness of the parylene C top coat increases from 8 to 20 nm as more of the material is deposited using a SCS coatings tool (model number PDS 2010). The researchers used 0.2, 0.4 and 0.6 g of parylene C to prepare the controlled release layer, which corresponds to a film thickness of 20–30, 150 and 200 nm.

Next steps
Under the direction of team leader Dean Ho, the group is now evaluating other drugs and materials for use in its platform as well as exploring the technology's commercial potential.

One of the key challenges is controlling the interplay between the drug and the solvent. "For some drugs, there would be no difference in the release profile in different solvents, while for others there is a huge change," said Pierstorff. "It is a very important consideration when testing in vitro release kinetics and suggesting potential systems for in vivo studies."

The researchers presented their results in Nanotechnology.