*3.2. PLLA Coating*

In order to reach a local long-term release of DMS and DCF, the DMS should be incorporated in the silicone carrier and the DCF should be embedded in a coating for the initial release. Coating silicone carriers is still a challenge due to their inert surface properties [36]. A desired PLLA coating of DMS-containing silicone without crosslinking resulted in a nonsufficient adhesion (data not shown). By first contact with water, the coating immediately peeled off. Therefore, a coating using the covalent binding of GOPS to silicone via the silane group and intermolecular forces between the PLLA-NH2-moiety and the PLLA-bulk was generated, with the PLLA-NH2 providing additional stability of the coating. The contact angle measurements revealed the alteration of the surface hydrophilic properties after each step of the coating. In contrast to the literature, contact

angles after GOPS treatment remained quite high (80◦ vs. 57◦) [37]. This goes back to the modification step. While the processes used in the literature are wet chemical in nature, our modification is a plasma-chemical process. The surface density of the groups generated by the O2 plasma for binding GOPS is thus lower than in wet-chemical processes. As a result, the silicone surface is not completely masked by the GOPS modification and still contributes to the contact angle. The slight increase in the contact angle after the binding of PLLA-NH2 was expected, because of the resulting thin PLLA-layer that presents a more hydrophobic surface. The contact angle after PLLA-coating remains the same as in the NH2-PLLA modification step as the material at the surface before and after the coating process remains PLLA. Chemical changes of the surface composition after each reaction step could also be confirmed by IR measurements. IR spectra of the polymer-coated samples exhibit several characteristic bands of the pure polymer as well as bands that correspond to the pure silicone.
