Hydrogel coated and dexamethasone releasing cochlear implants: quantification of fibrosis in guinea pigs and evaluation of insertion forces in a human cochlea model.

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.