*4.2. Materials*

The investigated silicone (Sil) and Pt-contact samples were provided by MED-EL (Innsbruck, Austria). All silicone samples used in this study contained 5 wt% DMS, which was added during the manufacturing process.

Poly-L-lactide (PLLA, L210) was purchased from Evonik (Schwerte, Germany). The crosslinker (3-glycidyloxypropyl)trimethoxysilane (GOPS) was purchased from Sigma-Aldrich (Taufkirchen, Germany) and PLLA-NH2 was provided by VWR (Dresden, Germany).

## *4.3. Preparation of Substances*

Dexamethasone (Sanofi, Paris, France) and diclofenac (Sigma-Aldrich) were dissolved in ethanol (Carl Roth, Karlsruhe, Germany) whereas enalapril (Selleckchem, Munich, Germany) was dissolved in DMSO (#A3672 AppliChem GmbH, Darmstadt, Germany) at concentrations of 10 mmol/L. The stock solutions were further diluted with complemented cell culture medium to reach a concentration twice as high as the intended test concentrations.

## *4.4. Spiral Ganglion Cell Culture*

Freshly isolated spiral ganglion cells were prepared from neonatal Sprague-Dawley rats (p3–5) following the protocol published by Schulze et al. [40]. In brief, after rapid decapitation, the cochleae were prepared from both halves of the skull and the bony shell of the cochleae was removed. After separating the spiral ganglia from the cochleae, these were enzymatically dissociated with HBSS containing 0.1% trypsin (Biochrom, Berlin, Germany) and 0.01% DNase I (Roche, Basel, Switzerland) for about 20 min followed by gentle trituration in 1 mL serum-free Panserin 401 (PAN Biotech, Aidenbach, Germany), supplemented with HEPES (23.4 μmol/mL, Invitrogen, Carlsbad, CA, USA), glucose (0.15%; Braun AG, Melsungen, Germany), penicillin (30 U/mL; Biochrom, Berlin, Germany), PBS (0.172 mg/mL; Gibco, Thermo Fisher Scientific, Waltham, MA, USA), N2-supplement (0.1%, Invitrogen, Carlsbad, CA, USA), and insulin (8.7 μg/mL; Biochrom, Berlin, Germany) until

a homogeneous solution was achieved. Viable cells were counted and seeded at a concentration of 1 × 10<sup>4</sup> cells per well in a 96-multiwell culture plate (TPP, Trasadingen, Switzerland), coated with 0.1 mg/mL poly-D/L-ornithine (Sigma-Aldrich) and 0.01 mg/mL laminin (natural from mouse, Life Technologies, Carlsbad, CA, USA). Cells were cultivated for 48 h in a mixture of complemented Panserin, supplemented with brain-derived neurotrophic factor (BDNF, Invitrogen, Carlsbad, CA, USA), and the different dilutions of the abovementioned substances. The final BDNF concentration was 50 ng/mL and for the test substances 2 × 10−<sup>4</sup> to 6.4 × 10−<sup>8</sup> mol/L. Each concentration was tested 6 times (*N* = 6) with three repetitions (*n* = 3) on each plate. After 48 h, the cells were fixed by addition of a 1:1 mixture of acetone (J. T. Baker, Deventer, Netherlands) and methanol (Carl Roth) for 10 min and washed three times with PBS.
