The insertion of cochlear implants (CIs) often causes fibrous tissue growth around the electrode, which leads to attenuation of function of CIs. Inhibition of fibrosis in vivo using dexamethasone (Dex) released from the implant base material (polydimethylsiloxane [PDMS]) coated with a protein repelling hydrogel (star-shaped polyethylene glycol prepolymer, sPEG) was, therefore, the aim of the study. PDMS filaments with Dex or sPEG were implanted into guinea pigs. The hearing status after implantation did not differ significantly in the treated groups. Using confocal laser scanning microscopy in transparent whole mount preparations, Dex, Dex/sPEG, as well as sPEG showed a tendency toward reduced formation of connective tissue around the implant. To apply such coatings for glass fibers for optical stimulation of the inner ear, insertion forces were measured into a human scala tympani model using fibers with sPEG coating. The results show that the hydrogel did not reduce insertion forces compared to the uncoated samples. However, PDMS-embedded fibers provide comparable insertion forces and depth to those measured with conventional CI electrodes, demonstrating the suitability of laser fibers for a minimal traumatic cochlear implantation.

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The insertion of cochlear implants into the inner ear often causes inflammation and fibrosis inside the scala tympani and thus growth of fibrous tissue on the implant surface. This deposition leads to the loss of function in both electrical and laser-based implants. The design of this study was to realize fibroblast growth inhibition by dexamethasone (Dex) released from the base material of the implant [polydimethylsiloxane (PDMS)]. To prevent cell and protein adhesion, the PDMS was coated with a hydrogel layer [star-shaped polyethylene glycol prepolymer (sPEG)]. Drug release rates were studied over 3 months, and surface characterization was performed. It was observed that the hydrogel slightly smoothened the surface roughened by the Dex crystals. The hydrogel coating reduced and prolonged the release of the drug over several months. Unmodified, sPEG-coated, Dex-loaded, and Dex/sPEG-equipped PDMS filaments were cocultivated in vitro with fluorescent fibroblasts, analyzed by fluorescent microscopy, and quantified by cell counting. Compared to the unmodified PDMS, cell growth on all modified filaments was averagely 95% ±standard deviation (SD) less, while cell growth on the bottom of the culture dishes containing Dex-loaded filaments was reduced by 70% ±SD. Both, Dex and sPEG prevented direct cell growth on the filament surfaces, while drug delivery was maintained for the duration of several months.