Durability of photografted zwitterionic hydrogel coatings for reduction of the foreign body response to cochlear implants

ObjectiveDurability of photografted zwitterionic hydrogel coatings on cochlear implant biomaterials was examined to determine viability of these antifouling surfaces during insertion and long-term implant usage. Approach: Tribometry was used to determine the effect of zwitterionic coatings on lubricity of surfaces with varying hydration level, applied normal force, and timeframe. Additionally, flexural resistance was investigated using mandrel bending. Ex vivo durability was assessed by determining coefficient of friction between tissues and treated surfaces. Furthermore, cochlear implantation force was measured using cadaveric human cochleae. Main results: Hydrated zwitterionic hydrogel coatings reduced frictional resistance approximately 20-fold compared to uncoated PDMS, which importantly led to significantly lower mean force experienced by coated cochlear implants during insertion compared to uncoated systems. Under flexural force, zwitterionic films resisted failure for up to 60 minutes of desiccation. The large increase in lubricity was maintained for 20 hours under continual force while hydrated. For loosely crosslinked systems, films remained stable and lubricious even after rehydration following complete drying. All films remained hydrated and functional under frictional force for at least 30 minutes in ambient conditions while drying, with lower crosslink densities showing the greatest longevity. Moreover, photografted zwitterionic hydrogel samples showed no evidence of degradation and nearly identical lubricity before and after implantation. Significance: This work demonstrates that photografted zwitterionic hydrogel coatings are sufficiently durable to maintain viability before, during, and after implantation. Mechanical properties, including greatly increased lubricity, are preserved after complete drying and rehydration for various applied forces. Additionally, this significantly enhanced lubricity translates to significantly decreased force during insertion of implants which should result in less trauma and scarring.