神经电刺激器作为一种新兴的治疗方式，已使数百万患者从中受益。植入导线是其重要组成部件，起到输出电刺激至合适治疗靶点的作用。在人体内数年乃至数十年的使用过程中，导线面临着各种弯曲、扭转和拉伸等交变载荷，疲劳环境严峻。植入导线一旦发生断裂，将导致设备失效，引起患者的二次手术伤害，此类情形在临床应用中时有报道。针对植入导线的重大应用需求，本文以研制国内第一个脑起搏器植入导线工作为背景，以其疲劳特性为切入点，兼顾植入小型化要求，研究当前普遍应用的金属导线疲劳特性，分析并阐明螺旋线存在的问题，进而提出基于碳纳米管线制备截面直径小、疲劳性能优异的植入导线的思路，并进行深入研究。首先，搭建本课题的试验平台，为研究开展提供硬件基础。设计、制造了用于研究导线疲劳性能的弯曲疲劳试验机、用于制备大直径碳纳米管线的绞线装置和用于监测疲劳过程中电阻变化的自动电阻测量系统。其次，对金属螺旋线和金属绞线的疲劳性能进行试验研究和理论分析。实验测量金属绞线和螺旋线的疲劳寿命；分析导线弯曲的应力分布；推导螺旋线弯曲时最大米泽斯应力与其结构之间的关系，并进行有限元计算验证。结果表明：螺旋线抗疲劳性能远优于绞线；螺旋线的疲劳寿命高度依赖于螺旋结构，一旦螺旋结构发生变化，导线疲劳寿命大受影响；螺旋线截面直径的减小也会大幅降低导线的疲劳寿命，进而阻碍植入导线的小型化。再而，开展弯曲疲劳、磨损疲劳、阻抗检测及断口形貌分析系列实验，综合研究碳纳米管线的疲劳性能。结果表明碳纳米管具有优异的弯曲疲劳性能，但易出现磨损疲劳。实际应用时，需要对其进行特别保护，可采用实时的阻抗测量以监测磨损状况。而不同的断口形貌特征，可以为碳纳米管线的断裂失效分析提供依据。最后，提出绞线法制备大直径、高性能的碳纳米管线，构建微观碳纳米管性能研究到宏观实用的桥梁。实验研究制备参数（单线上张力、绞距）对绞线性能的影响；成功将细直径碳纳米管线的高性能扩展到大直径绞线上；并制备出银丝复合碳纳米管绞线，兼具抗拉强度高、电导率高和疲劳寿命高的优点。
Electrical nerve stimulation, which is a new medical therapy, has brought benefit to thousands of patients. Implanted connecting wire is one of the most important components in the electrical nerve stimulation system. The wires transmit the electrical stimulation pulses to therapeutic targets. During the implanted duration, years or even decades, the connecting wire is always undertaking a variety of bending, twisting and stretching alternating loads, facing a serious fatigue situation. Once the fatigue fracture occurs, equipment failure will be caused, resulting in the second operation or severe damages for the patient. These cases have been reported in some clinical reports. Based on the experience of design and fabrication the connecting wire for the first deep brain stimulation device in China and understanding the requirements of the implanted connecting wires, this study took fatigue performance of implantable wires as a starting point, and also took the requirement of miniaturization into account. This work studied the fatigue properties of metal wires widely used currently, and analyzed and clarified the problems existing in the helical coils, and then proposed wires made of carbon nanotubes with small cross-section diameter.Firstly, a test platform was built for this program, providing hardware foundation for carrying out the study. In this platform, a bending fatigue testing machine for studying the fatigue properties, a wire twisting machine for producing carbon nanotube wires with large diameter, and resistance measurement equipment for automatically monitoring the resistance variation during the fatigue process, were designed and built. Secondly, this dissertation did theoretical analysis and experimental research to study the fatigue properties of the metal helical coils and metal strands. The fatigue life of the helical coils and strands were measured. The stress distribution of bending coils and strands were analyzed. The relationship between the coil structure and the maximum Mises stress was calculated, and verified through finite element simulation. The results showed that the anti-fatigue performance of the coils is far better than that of the strands. The fatigue life of the coils highly depends on the helical structure. Once the structure changes, the fatigue life of the coils would be greatly affected. Reduced cross-section diameter of the helical coils would substantially reduce the fatigue life of the coils, and hinder the miniaturization of the connecting wires.And then, a series of experiments including bending fatigue, wear fatigue, resistance measurement and fracture morphology analyzing were carried out, forming a comprehensive study the fatigue performance of the carbon nanotube wires. The results showed that carbon nanotube wires have excellent bending fatigue performance, but easy to suffer from wear fatigue. In the practical application, it needs special protection. Real-time resistance measurement can be taken to monitor the extent of the wear damage. The features of fracture morphology for four kinds of carbon nanotube wires failure were characterized, which are helpful to the failure analysis of carbon nanotube wires.Thereafter, twisting method was proposed to manufacture the carbon nanotube wires with large diameter and high-performance, building a bridge from the properties of microscopic carbon nanotubes to the application in macro world. Experiments were carried out to study the influence of the process parameters (wire tension, twist pitch) on the performance of the stranded wires. The high performance of single carbon nanotubes in small diameter was extended to the large-diameter stranded wires successfully. Composite silver- carbon nanotubes strands was developed creatively, which combines merits of high tensile strength, high conductivity and long fatigue life.
