Research Training Group 2154 - Materials for Brain

Project 4: Wiebke Reichstein

Controlling drug release by barrier layers

In this project a polymeric barrier layer is developed. This barrier is needed to tailor the drug release to be within the therapeutic window. We aim for a constant drug release over a long time up to one or two years in the best case. As a reservoir a porous polymer structure is used. This is coated in project P3 with drugs. Those drugs are oftentimes very sensitive to solvents or moisture in general. Therefore, a barrier material cannot be deposited via a wet chemical approach. Therefore, we use a deposition technique via the gas phase. This deposition technique is called initiated chemical vapor deposition (iCVD). iCVD has the advantage that it is an all-dry method. The substrate temperature remains at room temperature, which is advantageous due to the fact that most drugs are temperature sensitive.  Furthermore, iCVD is able to coat highly porous structures with a conformal polymer film. This is often not possible with wet chemical approaches. During the iCVD process a monomer gas and initiator gas are introduced into a vacuum chamber. The initiator is thermally cracked by heated filaments, creating free radicals. The monomer is not affected by the heat of the filaments and absorbs on the cooled (at room temperature) substrate surface. Now a free radical polymerization can occur at the surface by the absorption of initiator radicals. The release rate of the drug can be tailored by changing the overall thickness of the barrier polymer or by introducing a third reactant, a crosslinking molecule. The crosslinker reduces the meshsize of the polymer, which slows down the release rate of the drugs.