Strategies to improve electrode positioning and safety in cochlear implants

Abstract

An injection-molded internal supporting rib has been produced to control the flexibility of silicone rubber encapsulated electrodes designed to electrically stimulate the auditory nerve in human subjects with severe to profound hearing loss. The rib molding dies, and molds for silicone rubber encapsulation of the electrode, were designed and machined using AutoCad and MasterCam software packages in a PC environment. After molding, the prototype plastic ribs were iteratively modified based on observations of the performance of the rib/silicone composite insert in a clear plastic model of the human scala tympani cavity. The rib-based electrodes were reliably inserted farther into these models, required less insertion force and were positioned closer to the target auditory neural elements than currently available cochlear implant electrodes. With further design improvements the injection-molded rib may also function to accurately support metal stimulating contacts and wire leads during assembly to significantly increase the manufacturing efficiency of these devices. This method to reliably control the mechanical properties of miniature implantable devices with multiple electrical leads may be valuable in other areas of biomedical device design.

Force Application During Cochlear Implant Insertion: An Analysis for Improvement of Surgeon Technique

“…The data was used by Cochlear™ to form the cavity of the ST model, which is approximately 9 mm (from cochleostomy to Basal turn area) by 6 mm (diameter about modiolus), with a depth of 1.5 mm. In previous insertion studies, synthetic replicas have been created from human cadavers [4], [5], [7]. In this paper, the model used was machined from Polytetrafluoroethylene (Teflon).…”

“…Researchers have identified key elements that affected force output during electrode insertion, including implant design and insertion behavior [4], [5], restoration forces [4], carrier stiffness [4], [6], [8], contact pressure at the tip [6], as well as coefficient of friction between a lubricated model and silicone tip [5]. Synthetic models of the ST have been used for the purpose of insertion force measurement during cochlear implantation [4], [5], [7]. Existing studies have shown the importance of quantifying force components and the assessment of electrode trajectories for specific electrode designs, for the minimization of trauma [4], [5], [8]- [17], optimal electrode placement [1], [4], [9], [13], [14], [18]- [21], and to avoid damage to the electrode [8], [11], [12].…”

“…Synthetic models of the ST have been used for the purpose of insertion force measurement during cochlear implantation [4], [5], [7]. Existing studies have shown the importance of quantifying force components and the assessment of electrode trajectories for specific electrode designs, for the minimization of trauma [4], [5], [8]- [17], optimal electrode placement [1], [4], [9], [13], [14], [18]- [21], and to avoid damage to the electrode [8], [11], [12]. In this paper, we examine and compare 0018-9294/$25.00 © 2007 IEEE force delivery, electrode positions and surgical techniques for implants not previously considered: the Contour and Contour Advance electrodes.…”

“…Insertion studies have been performed to quantify force delivery [4], [5] and evaluate electrode trajectories [4]- [7] during simulated cochlear implantation. These were carried out to assess force administration for different electrode designs, including the Clarion (Advanced Bionics Corporation) [4], [5], the Combi C40+ electrode (Med-El) [7], new prototypes such as the Flex EAS [7] and reduced-element electrodes (silicone housing without individual electrodes or wires) [4], [5].…”

“…These were carried out to assess force administration for different electrode designs, including the Clarion (Advanced Bionics Corporation) [4], [5], the Combi C40+ electrode (Med-El) [7], new prototypes such as the Flex EAS [7] and reduced-element electrodes (silicone housing without individual electrodes or wires) [4], [5]. Researchers have identified key elements that affected force output during electrode insertion, including implant design and insertion behavior [4], [5], restoration forces [4], carrier stiffness [4], [6], [8], contact pressure at the tip [6], as well as coefficient of friction between a lubricated model and silicone tip [5]. Synthetic models of the ST have been used for the purpose of insertion force measurement during cochlear implantation [4], [5], [7].…”