Toward a controlled intra-cochlear positioning change of an electrode array using a stepwise-activated shape memory effect

Introduction 

An electrode array (EA) of the cochlear implant (CI) with a perimodiolar positioning is assumed to be beneficial for stimulating the auditory nerve. To enable an intracochlear shape change from a straight to a spiral configuration, a thermal shape memory effect (SME) can be utilized. A common way to activate the SME is resistance heating. In order to prevent heating of the surrounding organ, a short current pulse was found to be favorable. However, this leads to a fast movement toward the modiolus, which might cause intracochlear trauma. By a better controlling of the position change, potential trauma due to the fast movement should be prevented.

Methods 

In order to provide a more controlled movement a stepwise activation of the shape memory effect was investigated using varied parameters for the current feed. Four sets of current pulses with increasing parameters were applied by a microcontroller. Therefore, a prototype EA was manufactured with embedded Nitinol wire (Ø 100 µm). To apply electric power, two copper wires (Ø 50 µm) were soldered to the Nitinol wire. An infrared camera recorded the shape change and temperature of the EA.

Results 

Controlling the intra-cochlear position shift by different parameters of the current feed was successfully applied resulting in a stepwise and therefore slow intracochlear position change. After each step, a small spring back effect of the EA was observed, but a stable perimodiolar position was reached with the last set of current pulses.

Discussion 

The presented method is suitable to control the deformation of an EA with SME. Consequently, using a greater number of sets with varied parameters for the current pulses, a quasi-constant intra-cochlear position change with adjustable speed of shape change is reachable.

German Research Foundation (DFG, RA 2751/1-1) and under Germany's Excellence Strategy – EXC 2177/1 – Project ID 390895286)

Publication History

Article published online:
24 May 2022