低频振动下微织构电极与脑组织交互作用的特性机理研究

Corresponding to low targeting accuracy and severe brain injury due to lacking of interaction mechanisms between electrode and brain tissues for neurosurgeons, the technical idea of combining anti-frictional effect of low-frequency vibration and surface textures is firstly proposed to minimize brain tissue deformation and injury. Moreover, interaction mechanisms between micro-textured electrode and brain tissues during electrode insertion process with low-frequency vibration will be revealed. The main research thoughts are as follows: Mechanical properties of brain tissues on the implanting trajectory of sub-thalamic nucleus are investigated according to conditions of STN-DBS. Using electrode insertion tests and finite element analysis under different conditions, brain tissue responses to electrode insertion are obtained. Then, regularities of brain tissue deformation and inserting forces are inferred. The intracranial kinetic model of electrode is established and characteristics of intracranial motion are revealed. Micro-textured electrodes are designed and fabricated. The anti-frictional effects of low-frequency vibration and micro-textured electrode are researched by insertion tests with low-frequency vibrations. Theoretical model of contact interface between micro-textured electrode and brain tissues will be established. The Lagrangian stress function of brain tissues will also be established. The ultimate shear strength of brain tissues under the combination of low-frequency vibration and surface textures will be calculated. At last, interaction mechanisms between micro-textured electrode and brain tissues during electrode insertion process with low-frequency vibration will be proposed. The research work in this project is helpful to provide theoretical and technical guidance for deep brain stimulation.

针对脑深部刺激手术因神经外科医师对电极与脑组织交互作用机理认识不足而导致的靶点定位精度低及颅脑损伤大的问题，本项目提出将低频振动与表面微织构技术相结合的思路，利用二者对摩擦表面的减摩优点，降低穿刺过程中脑组织的变形及损伤程度，揭示低频振动下微织构电极与脑组织交互作用的特性机理。本项目的研究思想：结合手术条件研究穿刺涉及区域脑组织的材料力学属性；利用穿刺测试及有限元法，分析不同条件下脑组织对普通电极的穿刺反应，得出穿刺过程中脑组织变形及受力规律，建立电极的颅内动力学模型，揭示其颅内运动特性；设计并制备微织构电极，通过低频振动穿刺测试，验证低频振动下微织构电极的穿刺性能；建立微织构电极-脑组织接触界面的理论模型及脑组织受力的拉格朗日应力函数，计算低频振动与微织构组合作用下脑组织的剪切极限强度，揭示低频振动下微织构电极与脑组织交互作用的特性机理。本项目的研究可为脑深部刺激手术提供理论和技术指导。

针对神经外科医师对电极与脑组织交互作用机理认识不足而导致的定位精度低及颅脑损伤大的问题，本项目研究了电极与脑组织的交互作用机理，制备了多种微织构电极，测试了微织构电极的穿刺减摩效果，研究了低频振动下微织构电极对脑组织更好的减摩作用。. 分析了电极对完整脑组织的小截面压缩作用及对穿刺路径上脑组织的径向压痕-松弛作用，建立了穿刺力学模型及压痕-松弛遗传积分模型，测试得出了完整脑组织的弹性模量4.044 kPa，用剪切松弛模量对穿刺路径上6个区域脑组织的粘弹性分别进行了表征，求得了各区域的差异性。. 对脑组织进行了单次和二次穿刺测试，得出了脑组织变形影像及穿刺力曲线，发现脑组织变形及穿刺力集中在轴向，皮质表面随针尖位置规律的上下变动，不同穿刺阶段穿刺力呈不同规律变化，刺破深度和刺破力之间呈高度正相关，最优穿刺速度为2.5 mm/s；第二次进针时脑组织变形、穿刺力降低，同参数的二次进针将使靶点定位过深。通过电极对脑组织的有限元侵彻模型得出：脑组织变形最大位置在电极顶端；电极对脑组织的穿刺影响范围上半部分截面呈梯形，下半部分呈球形；电极下方的脑组织被径向压长和轴向压缩，电极周围的脑组织被切向拉长和径向压缩；脑组织应力最大位置在电极头部与针轴的过渡部分。. 设计并制备了形貌间距为0.1~0.4 mm的圆形、正方形凹坑微织构及直线型、直线交错型沟槽微织构电极，通过分析固体表面水滴润湿性及脑组织穿刺摩擦性能得出：间距为 0.1mm时，微织构的减摩效果最好；直线交错型微织构电极穿刺减摩效果最好；相对光滑电极，间距为0.1mm的直线交错型微织构电极的摩擦力增长率降低至少60%；. 利用直线交错型微织构电极进一步测试了低频振动下微织构电极对脑组织更优的穿刺减摩效果。以穿刺速度、振幅和频率为参数，以刺破力和摩擦力增长率为指标进行了正交实验，得到了最优参数组合V(2mm/s) A(4µm )f(50Hz)。此情况下摩擦力增长率仅为0.9，低于其他参数及光滑电极的无振动穿刺。. 以上结论可为脑深部刺激手术提供理论和技术指导。