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

Objective Durability of photografted zwitterionic hydrogel coatings on cochlear implants was examined to determine viability of these anti-fouling surfaces during insertion and long-term implant usage. Approach Tribometry was used to determine the effect of zwitterionic coatings on lubricity of surfaces, varying hydration level, applied normal force, and timeframe. Additionally, flexural resistance was investigated using mandrel bending. Ex vivo durability was assessed by determination of friction between tissues and treated surfaces, as well as cochlear implantation force measurements using cadaveric human cochleae. Main results Hydrated zwitterionic hydrogel coatings maintained decreased friction for 20 hours under normal force. For loosely crosslinked systems, films remained stable and retained lubricity after complete drying. All films were able to remain hydrated and functional for at least 30 minutes under normal force, with lower crosslink densities showing the greatest longevity. Under flexural force, zwitterionic films underwent dehydration for up to 60 minutes before failure. Furthermore, photografted zwitterionic hydrogel samples showed nearly identical lubricity before and after implantation. Importantly, zwitterion-coated cochlear implants experienced a significantly lower mean force during insertion than uncoated implants. 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, the results show retention of up to 90% increase in lubricity relative to uncoated samples which translates to decreased force and overall less trauma during insertion of implants. ### Competing Interest Statement The authors have declared no competing interest.