**5. Conclusions**

After proving cytocompatibility of DCF for application in the inner ear and developing a coating strategy for drug-loaded medical-grade silicone, an approach to realize a dual drug release from cochlear implants was presented that combines a short-term release from a polymeric coating with a long-lasting release from the silicone body of the electrode array. The effect of the coating on electrode contact impedances was characterized and a strategy to overcome the insulation of the contacts was presented. The developed dual drug release for cochlear implant electrode arrays can now be investigated in vivo.

**Supplementary Materials:** The following supporting information can be downloaded online. Figure S1: Silicone sample as used for impedance measurements; (**a**): uncoated sample with three Pt-contacts and the connector; (**b**): Enlargement of one contact—coated version. Figure S2: Water contact angle ΘW ± standard deviation (SD) on silicone surfaces after each reaction step for sessile drop method (*N* = 5). \*\*\* *p* < 0.001. Figure S3: Fourier transform infrared spectra of investigated Sil-GOPS in comparison with pure GOPS in the range of 3500–500 cm<sup>−</sup>1; (**1**) prominent band at 1254 cm<sup>−</sup><sup>1</sup> depicts Si-CH2 bond from the GOPS structure (**2**) prominent band around 1254 cm<sup>−</sup><sup>1</sup> represents oxirane group from the GOPS structure. Figure S4: Fourier transform infrared spectra of investigated Sil-PLLA-NH2 in comparison with pure PLLA-NH2 in the range of 4000–500 cm<sup>−</sup>1; prominent band at 1751 cm<sup>−</sup><sup>1</sup> corresponds to the C=O stretching vibration from the PLLA structure. Figure S5: Fourier transform infrared spectra of investigated Sil-PLLA in comparison with pure PLLA in the range of 4000–500 cm<sup>−</sup>1; prominent band at 1751 cm<sup>−</sup><sup>1</sup> corresponds to the C=O stretching vibration from the PLLA structure. Figure S6: Microscopic image of stained spiral ganglion neurons (dark cell bodies) with 5 traced neurites (red). Treatment: 3.2 × 10−<sup>7</sup> mol/L DCF. Scale bar: 50 μm.

**Author Contributions:** Conceptualization, T.L., N.G., methodology, S.R., M.T., T.E., G.P.; validation, T.E.; formal analysis, K.W., M.G., investigation, K.W., M.G.; writing—original draft preparation, K.W., M.G.; writing—review and editing, T.E., G.P.; supervision, G.P.; project administration, resources, funding acquisition, T.L., N.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was supported by German Ministry for Education and Research (BMBF) as part of RESPONSE-partnership for innovation in implant technology, FKZ: 03ZZ0914D (Hannover), 03ZZ0914A (Rostock), and 03ZZ0914K (MED-EL).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** All the data that support the findings of this study are available on request from the corresponding author.

**Acknowledgments:** The authors would like to thank Dalibor Bajer, Andrea Rohde, Caroline Dudda, Katja Hahn, Jasmin Bohlmann and Babette Hummel for the technical assistance.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

**Sample Availability:** Samples of the compounds used during the current study are available from the corresponding author on reasonable request.
