Cochlear implants are well established to treat severe hearing impairments. Despite many different approaches to reduce the formation of connective tissue after electrode insertion and to keep electrical impedances low, results are not yet satisfying. Therefore, the aim of the current study was to combine the incorporation of 5% dexamethasone in the silicone body of the electrode array with an additional polymeric coating releasing diclofenac or the immunophilin inhibitor MM284, some anti-inflammatory substances not yet tested in the inner ear. Guinea pigs were implanted for four weeks and hearing thresholds were determined before implantation and after the observation time. Impedances were monitored over time and, finally, connective tissue and the survival of spiral ganglion neurons (SGNs) were quantified. Impedances increased in all groups to a similar extent but this increase was delayed in the groups with an additional release of diclofenac or MM284. Using Poly-L-lactide (PLLA)-coated electrodes, the damage caused during insertion was much higher than without the coating. Only in these groups, connective tissue could extend to the apex of the cochlea. Despite this, numbers of SGNs were only reduced in PLLA and PLLA plus diclofenac groups. Even though the polymeric coating was not flexible enough, MM284 seems to especially have potential for further evaluation in connection with cochlear implantation.

Um ein endocochleäres Insertionstrauma zu verhindern, rückt die Entwicklung von wirkstofffreisetzenden Beschichtungen im Feld der CI-Elektroden zunehmend in den Fokus der Forschung. Der Einfluss eines mit Poly-L-Milchsäure (PLLA) beschichteten Elektrodenträgers auf die beiden mechanischen Parameter „Insertionsdruck“ und „Insertionsreibung“ ist bis jetzt noch nicht ausreichend untersucht worden. Ziel der Studie ist (I) die Messung des Insertionsdrucks und (II) die Erfassung des Reibungskoeffizienten eines, 31,5 mm langen, PLLA-beschichteten Elektrodenträgers. Bei verschiedenen Insertionsgeschwindigkeiten (0,1, 0,5, 1,0 1,5 und 2,0 mm/s) wird der Insertionsdruck in einem linearen Cochlea-Modell gemessen; der Reibungskoeffizient wird zwischen Elektrodenträger und porciner Faszie ermittelt, die die endocochleäre Auskleidung simuliert. Als Vergleichsgruppe dienen unbeschichtete Elektrodenträger. Es konnte gezeigt werden, dass sowohl der im linearen Modell erzeugte maximale Insertionsdruck als auch der Reibungskoeffizient einer PLLA-beschichteten Elektrode nicht von der Insertionsgeschwindigkeit abhängt. Darüber hinaus zeigte sich, dass ab höheren Insertionsgeschwindigkeiten (1,0 mm/s und höher) der Insertionsdruck (1,268±0,032 mmHg) und der Reibungskoeffizient (0,40±0,15) eines beschichteten Elektrodenträgers dem eines unbeschichteten gleicht (1,252±0,034 mmHg und 0,36±0,15). PLLA als Beschichtung nimmt folglich keinen signifikanten Einfluss auf den Insertionsdruck und die Insertionsreibung eines CI-Elektrodenträgers, wenn höhere Insertionsgeschwindigkeiten genutzt werden. Daher ist PLLA ein geeigneter Werkstoff für die Beschichtung von CI- Elektrodenträgern und kommt als potenzielles Material für ein wirkstofffreisetzendes System in Betracht.

To prevent endocochlear insertion trauma, the development of drug delivery coatings in the field of CI electrodes has become an increasing focus of research. However, so far, the effect of a polymer coating of PLLA on the mechanical properties, such as the insertion pressure and friction of an electrode array, has not been investigated. In this study, the insertion pressure of a PLLA-coated, 31.5-mm long standard electrode array was examined during placement in a linear cochlear model. Additionally, the friction coefficients between a PLLA-coated electrode array and a tissue simulating the endocochlear lining were acquired. All data were obtained at different insertion speeds (0.1, 0.5, 1.0, 1.5, and 2.0 mm/s) and compared with those of an uncoated electrode array. It was shown that both the maximum insertion pressure generated in the linear model and the friction coefficient of the PLLA-coated electrode did not depend on the insertion speed. At higher insertion speeds above 1.0 mm/s, the insertion pressure (1.268 ± 0.032 mmHg) and the friction coefficient (0.40 ± 0.15) of the coated electrode array were similar to those of an uncoated array (1.252 ± 0.034 mmHg and 0.36 ± 0.15). The present study reveals that a PLLA coating on cochlear electrode arrays has a negligible effect on the electrode array insertion pressure and the friction when higher insertion speeds are used compared with an uncoated electrode array. Therefore, PLLA is a suitable material to be used as a coating for CI electrode arrays and can be considered for a potential drug delivery system.

Background: During cochlear implantation, the electrode array has significant friction with the sensitive endocochlear lining and causes mutual mechanical trauma while the array is being inserted. Both, the impact of insertion speed on electrode friction and the relationship of electrode insertion force and friction have not been adequately investigated to date. Methods: In this study, friction coefficients between a CI electrode array (31.5 mm) and a tissue simulating the endocochlear lining have been acquired, depending on different insertion speeds (0.1, 0.5, 1.0, 1.5, and 2.0 mm/s). Additionally, the electrode insertion forces during the placing into a scala tympani model were recorded and correlated with the friction coefficient. Results: It was shown that the friction coefficient reached the lowest value at an insertion speed of 0.1 mm/s (0.24 ± 0.13), a maximum occurred at 1.5 mm/s (0.59 ± 0.12), and dropped again at 2 mm/s (0.45 ± 0.11). Similar patterns were observed for the insertion forces. Consequently, a high correlation coefficient (0.9) was obtained between the insertion forces and friction coefficients. Conclusion: The present study reveals a non-linear increase in electrode array friction, when insertion speed raises and reports a high correlation between friction coefficient and electrode insertion force. This dependence is a relevant future parameter to evaluate and reduce cochlear implant insertion trauma. Significance statement: Here, we demonstrated a dependence between cochlear electrode insertion speed and its friction behavior and a high correlation to insertion force. Our study provides valuable information for the evaluation and prevention of cochlear implant insertion trauma and supports the optimization of cochlear electrode arrays regarding friction characteristics.