Development of zwitterionic hydrogel thin film coatings of cochlear implant electrode arrays that reduce intracochlear inflammation and electrode impedance

Cochlear implants (CIs) have revolutionized the treatment of sensorineural hearing loss, yet patient outcomes remain highly variable due to biological responses within the cochlea. A critical challenge is the foreign body response (FBR) triggered by CI biomaterials, which can lead to inflammation, fibrosis, and increased electrode impedance, ultimately impairing auditory function. Zwitterionic hydrogels have been shown to provide a highly lubricious anti-fouling surface that minimizes protein and cell adsorption. This study evaluates a carboxybetaine methacrylate (CBMA) zwitterionic hydrogel coating to reduce the FBR to cochlear implants. Using a large animal (sheep) model, human CI electrode arrays were coated with a thin film CBMA hydrogel via one step UV photografting and photopolymerization with a custom mold. Electrophysiological measurements at the time of implantation demonstrate significantly reduced total impedance, polarization impedance, and access resistance in CBMA-coated CIs. Reductions in total impedance and access resistance were maintained after 4 weeks in vivo. High-resolution Xray Microscopy imaging confirmed intracochlear placement without translocation or tip fold-over and a trend to reduced neoossification in CBMA-coated implants. Histological analysis revealed significantly decreased cellular infiltration, macrophage infiltration, and fibrotic tissue deposition within the cochlea surrounding CBMA-coated implants compared to uncoated controls. This work highlights the potential of durable thin film zwitterionic coatings to enhance CI performance and preserve residual hearing by mitigating insertional trauma and attenuating chronic inflammation and fibrosis.