Introduction

A lubricant coating of the cochlear implant (CI) electrode might be a useful tool to improve implantation procedure. The implantation can cause trauma of the inner ear tissue leading to e.g. loss of spiral ganglion neurons (SGN) or residual hearing. A coating with hydrogel could cover the electrode with a hydrophilic, smooth, and flexible layer that softens implantation and reduces trauma. Ultra-high viscosity (UHV) alginate and its barium chloride (BaCl2)-crosslinking are generally described as long-term stable and biocompatible. In previous studies, we showed the overall feasibility of an alginate-coating of the CI but detailed studies for toxicity of BaCl2 on inner ear tissue are lacking. Therefore, safety of BaCl2 and BaCl2-cross-linked alginate (Ba-Alg) was tested in vitro.

Material/Methods

UHV-alginate (Alginatec®) is gelled in a 20mM BaCl2 bath for CI-coating. Hence, dilution series ranging from 20mM to 2µM BaCl2 in medium and co-culture of 10µl beads of Ba-Alg were tested on dissociated SGN (neurotoxicity) and cochlear whole mounts (ototoxicity) of rats for 48h (BaCl2) and 7 days (Ba-Alg). Subsequently, surviving neurons and inner and outer hair cells were counted and compared to a control without BaCl2 or Ba-Alg.

Results

20mM and 2mM BaCl2 were neurotoxic and 20mM BaCl2 ototoxic, while Ba-Alg beads in co-culture had no effect on the inner ear tissue.

Discussion

Ba-Alg-CI-coating can reduce insertion forces and by this the inner ear trauma to protect residual hearing in patients. The results indicate that a limit of 200µM BaCl2 has to be considered for safe use. However, co-culture with Ba-Alg beads had no toxic effect and, in purely mathematical terms, the amount of BaCl2 in a CI-coating is far below the detected toxic concentration.

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