## 1 Introduction  
Cochlear implants (CIs) are the treatment of choice for the rehabilitation of severe to profound sensorineural hearing loss. Trending upwards, over 324,000 patients worldwide have received cochlear implants [1]. In a CI, an electrode array is inserted into the scala tympani (the lower tubular cochlear space) and electrically stimulates cochlear spiral ganglion cells. Unfortunately, implant insertion in such a sensitive area causes trauma to fragile endocochlear structures due to mechanical irritation [2, 3, 4, 5, 6].  
Various researchers have tried to investigate the factors contributing to cochlear structures' trauma [7, 8, 9, 10] and have reported a dependence on insertion depth and consequently to the electrode array length. It is shown that insertion trauma increased with deep insertions [10] combined with electrode kinking [11]. Furthermore, it was reported that cochlear trauma is determined by electrode insertion force [12, 13]. Some papers describe the relationship between cochlear anatomy and basilar membrane trauma. [PERSON] et al., [12] have shown that forces of only 0.029 to 0.039 N were required to rupture the cochlear basilar membrane. However, identification of the parameters determining this insertion force has not been performed so far.  
A crucial parameter that determines the extent of insertion trauma is the speed of implant insertion [14; 15]. It was reported that high insertion speeds of Nucleus 24 contour electrode arrays cause a significant increase in insertion force [14].  
During implantation, the electrode array has large sliding contact to the inner cochlear wall, which is covered with thin endosteum. This suggests that the friction between the electrode array and the thin endosteum lining strongly dictates the electrode sliding behavior and the insertion force. While several studies focused on frictional behavior between joint implants [16] or contact lenses to standard solid material [17], [PERSON] et al. [18] have shown frictional behavior of Nucleus standard straight and contour cochlear electrode array to endosteum lining. They reported decreased friction properties when applying glycerin as a lubricant in a slippage model. Additionally, [PERSON] and [PERSON] et al. [19] revealed that insertion forces of the Nucleus 24 contour electrode array are reduced following the application of glycerine if compared to water.  
However, neither the friction behavior of a 31.5 mm standard cochlear electrode array to endosteum lining under the impact of speed nor a correlation between the electrode friction and the insertion force has been investigated yet. This study aimed to examine the friction forces between the electrode array and endosteum lining mimicking tissue under the influence of different pulling speeds using a custom-made pulling device system. Friction coefficient calculation and comparison are also reported. Additionally, the electrode array was inserted in a scala typnani model and insertion forces were investigated, depending on different insertion speeds. Based on this data, we calculated a correlation between the friction coefficient and the insertion force to obtain the correlation coefficient.