## 4 Discussion
Additionally, the fluctuated graph pattern at 0.1 mm/s indicates a constant change of adherence and sliding between the electrode array and scala typpani model lumen. Moreover, the first force peak (within 3-4 mm/s) recorded at each insertion speed is formed when the electrode array touches the lateral wall of the scala typpani model for the first time. The force peaks within 14-15 and 25-27 mm are due to the scala typmani model lumen shape. These force peaks corresponding to the distance where the model lumen turns. The detected negative forces are measurement artifacts based on the background noise (measurement range is 0.02 N-10 N). Notable, insertion distance is defined by test bench settings but terminated by the scala typmani model lumen length. Reasonably, the electrode array reached the end of the lumen before the total set insertion distance is attained. Therefore, the recorded insertion forces initially increase. Afterward, the electrode kinked, which causes the insertion forces to drop. Hence, mean values are more representative to compare than maximum forces. Due to the different materials used in the two test benches, different lubricants were used. While the porcine fascia together with artificial perilymph used in the friction test bench simulates closely the physiological conditions in the cochlea, the interaction between the scala typmani model (polyester) and the electrode (silicone) in the force test bench results in increased adhesion. Consequently, to better simulate the physiological conditions in force measurements (by decreasing adhesion) and improve the comparability to friction measurement, soap was used as a lubricant. Against expectations, despite different friction conditions, a high correlation coefficient of 0.9 between the insertion force and friction coefficient was calculated during measurements. This finding emphasizes the strong influence of applied speed. Moreover, the fact that no cluster formation was detected in the correlation plot at a speed of 0.1 mm/s might be attributed to the high statistical variance of the force values at a given speed. That the point 0.043 N/0.048 was defined as an outlier is due to the case that these values were recorded at the very beginning of the experiment and can be considered as not representative. However, the strong dependency between these biomedical properties suggests that the electrode insertion force depends not only on insertion speed but also on the friction conditions within the cochlear implantation. Matching results are reported by [PERSON] et al. (2017). They compared hydroxy-ethyl-cellulose-coated electrode carriers with uncoated electrode carriers and showed that insertion forces were markedly reduced during the insertion of coated carriers. Additionally, the insertion depth ([PERSON] et al., 2018) and consequently the electrode array length determine biomechanical properties. This correlates with the occasional clinical observations in 31.5 mm electrode arrays incomplete insertion into the human cochlear. These incomplete insertions can be attributed to the fact of a high friction contact between the electrode array and endocollear structures and causes the electrode array to stick. Accordingly, this contradicts the opinion in the literature where incomplete inserted electrodes are discussed to be due to variations in cochlear duct length ([PERSON] et al., 2018). To our knowledge, this is the first study investigating the impact of the insertion speed on friction conditions between the cochlear electrode array and endosteum lining mimicking tissue. The present study reveals high insertion speed causes increased electrode array friction properties with a non-linear dependence. Also, it is demonstrated that at defined insertion speeds, generated friction coefficients correlate with the insertion forces of the electrode array. Hence, the insertion speed and frictional conditions play a crucial role as a parameter to evaluate and reduce electrode insertion force and subsequently cochlear trauma.