Poly-vinyl-alcohol (PVA) coating of cochlear implant electrode arrays: An in-vivo biosafety study

Objective: The tissue response and biosafety of poly-vinyl-alcohol (PVA) has been investigated to explore its potential use as an agent to straighten pre-curved cochlear implant electrode arrays for surgical insertion. Methods: Test arrays were implanted either subcutaneously or into the cochlea of guinea pigs for 3 months. The arrays were uncoated (Treatment 1) or coated with low molecular weight (MW) PVA (Treatment 2), high MW PVA (Treatment 3) or a 50:50 mixture of low and high MW PVA (Treatment 4). After explantation the tissues were examined histologically. Results: In both study groups, Treatment 2 dissolved completely and induced the least tissue reaction, while Treatments 3 and 4 not only dissolved incompletely, but also induced more fibrous tissue growth. Treatment 4 coated arrays induced severe insertion trauma in all the cochleas, most likely due to the thickness of the coat and the resulting rigidity of the array. Spiral ganglion cell density (SGCD) in the basal turn of the scala tympani was reduced for both Treatments 2 and 4. While the reduction in SGCD in the Treatment 4 group is likely to be a result of the insertion trauma caused and the subsequent loss of peripheral dendrites, it is unknown what caused the reduction of SGCD in the Treatment 2 group. Conclusion: Prior to the specific use of PVA as electrode array coating material, the ideal composition and its biosafety needs to be reassessed.