A Polymer Cochlear Electrode Array: Atraumatic Deep Insertion, Tripolar Stimulation, and Long-Term Reliability

This book describes the design, fabrication and evaluation of a polymer-based neural interface for a cochlear electrode array, reviewed in terms of fabrication process, functionality, and reliability. Polymer-based devices have attracted attention in the neural prosthetic field due to their flexibility and compatibility with micro-fabrication process. A liquid crystal polymer (LCP) is an inert, highly water-resistant polymer suitable for the encapsulation of electronic components and as a substrate material for fabricating neural interfaces. The author has designed, fabricated, and evaluated an LCP-based cochlear electrode array for an improved polymer-based cochlear implant. The thesis deals with 3 key topics: atraumatic deep insertion, tripolar stimulation, and long-term reliability. Atraumatic insertion of the intracochlear electrode and resulting preservation of residual hearing have become essential in state-of-the-art cochlear implantation. A novel tapered design of an LCP-based cochlear electrode array is presented to meet such goals. For high-density and pitch-recognizable cochlear implant, channel interaction should be avoided. Local tripolar stimulation using multi-layered electrode sites are shown to achieve highly focused electrical stimulation. This thesis addresses another vital issue in the polymer-based neural implants: the long-term reliability issue. After suggesting a new method of forming mechanical interlocking to improve polymer-metal adhesion, the author performs accelerating aging tests to verify the method's efficacy. The aforementioned three topics have been thoroughly examined through various in vitro and in vivo studies. Verification foresees the development of LCP-based cochlear electrode array for an atraumatic deep insertion, advanced stimulation, and long-term clinical implant.

Autorentext

Dr. Tae Mok Gwon was a member of the NanoBio-electronics & Systems Laboratory, Department of Electrical and Computer Engineering, Seoul National University, Korea. He is currently a Senior engineer at Semiconductor R&D center, Samsung Electronics Co., Ltd..

Inhalt

Abstract. Contents. List of Figures. List of Tables. List of Abbreviations.

Chapter 1 Introduction. 1.1 Overview of Neural Prostheses and Cochlear Implants. 1.2 Review of Cochlear Electrode Arrays. 1.2.1 Conventional Cochlear Electrode Arrays. 1.2.2 Polymer-Based Cochlear Electrode Arrays. 1.3 Proposed Polymer Cochlear Electrode Array. 1.3.1 Electrode Arraysfor Atraumatic Deep Insertion. 1.3.2 Electrode Arraysfor Tripolar Stimulation. 1.4 Long-Term Reliability of Polymer-Based Neural Prostheses. 1.5 Objectives of the Dissertation.

Chapter 2 Materials and Methods. 2.1 Liquid Crystal Polymer (LCP). 2.1.1 Material Properties and Types of LCP. 2.1.2 MEMS Technologies compatible with LCP. 2.2 Cochlear Electrode Array for Atraumatic Deep Insertion. 2.2.1 Electrode Design. 2.2.2 Fabrication Process. 2.2.3 Experimental Setup and Protocol of In Vitro*and *In Vivo*Evaluation Tests. 2.2.3.1 Insertion and Extraction Force Measurements in Scala Tympani Model. 2.2.3.2 Human Temporal Bone Insertion Studies. 2.2.3.3 *In Vivo*Animal Study. 2.2.3.3.1 Acute Implantation and Electrically Evoked Auditory Brainstem Response (EABR) Recording. 2.2.3.3.2 Hearing Preservationand Histologic. Evaluation. 2.3 Polymer Electrode Array for Tripolar Stimulation. 2.3.1 Modeling and Simulation of Polymer-Based Cochlear Electrode Array for Tripolar Stimulation. 2.3.1.1 Simulation Tool and Modeling. 2.3.1.2 Electrode Designs. 2.3.2 Fabrication Process. 2.3.3 *In Vitro Measurements. 2.3.3.1 Test Board for Tripolar Stimulation. 2.3.3.2 Experimental Setup and Protocol. 2.4 Long-Term Reliability Analysis of LCP-Based Neural Implants. 2.4.1 Overview of the Long-Term Reliability. 2.4.1.1 Failure Mechanism. 2.4.1.2 Measurement Methods for Reliability Analysis. 2.4.2 Technical Strategiesto Improve Reliability of LCP-Based Implantable Device. 2.4.2.1 Mechanical Interlocking to Strengthen Metal-LCP. Adhesion. 2.4.2.1.1 Fabrication Process using Dual Lithography and Electroplating. 2.4.2.1.2 *In Vitro*Peel Testand Electrochemical Measurements. 2.4.2.1.3 *In Vitro*Accelerated Soak Test. 2.4.2.1.4 Visual Inspection and Statistical Analysis. 2.4.2.2 Fabrication using LCP and Dielectric Materials. 2.4.2.2.1 Role of Dielectric Materials. 2.4.2.2.2 Proposed Fabrication Process. 2.4.2.2.3 Preliminary Study.

Chapter 3 Results. 3.1 LCP-Based Cochlear Electrode Array for Atraumatic Deep Insertion. 3.1.1 Fabricated Electrode Array. 3.1.2 Insertion and Extraction Force Measurements. 3.1.3 Insertion Trauma in Human Temporal Bone Insertion Study. 3.1.4 Electrically Evoked Auditory Brainstem Response Recording. 3.1.5 Histological Change and Hearing Preservation. 3.2 Polymer Electrode Array for Tripolar Stimulation. 3.2.1 Simulation Results according to Electrode Site Design. 3.2.2 Fabricated Electrode Array. 3.2.3 In Vitro Measurements. 3.3 Long-Term Device Reliability. 3.3.1 LCP-Based Neural Electrode Array using Mechanical Interlocking at Metal-LCP Interface. 3.3.1.1 Fabricated Electrode Arrayand Metal-LCP Interface. 3.3.1.2 Adhesion Force and Electrochemical Measurements. 3.3.1.3 Accelerated Soak Test and Lifetime Estimation. 3.3.2 Fabrication Method using LCP and Dielectric Materials. 3.3.2.1 AdhesionStrength of Bonding between LCP and Dielectric Materials. 3.3.2.2 Lamination Result of the Proposed Fabrication. Method.

Chapter 4 Discussion. 4.1 LCP-Based Cochlear Electrode Arraysfor Atraumatic Deep Insertion. 4.1.1 Comparison of the Current Proposed Electrode Array to the Previous Electrode Array. 4.1.2 ImprovingElectrode Design Related toInsertion Depth and Trauma. 4.1.3 Aspectsto Improve in the Fabrication Process. 4.1.4 *In Vivo*Implantation. 4.2 Power Consumption and Stimulation Threshold of Tripolar Stimulation. 4.3 Technical Strategies to Improve Device Reliability. 4.3.1 Mechanical Interlocking at the Metal-Polymer Interface. 4.3.2 Hybrid Device Based on Polymer and DielectricMaterials. 4.4 Review of Long-Term Reliability of LCP-Based Devices.

Chapter 5 Conclusion.

References.