基于硅基电极的脑组织微动损伤仿真

Silicon microelectrode-based simulation of brain tissue micromotion-induced injury

目的:为预测脑组织微动损伤和解决植入电极的长期寿命问题,本研究基于硅基微电极进行建模,并对神经电极-脑组织有限元模型进行数值仿真。方法:采用超黏弹性模型描述脑组织材料,研究不同微动模式(纵向和横向)、不同物理耦合度下电极附近脑组织应变分布。结果:纵向载荷分析显示当摩擦系数μ增加时,脑组织最大von Mises应变呈降低趋势,并且电极尖端附近的组织应变最大,这表明电极与脑组织之间的物理耦合度对脑组织微动损伤有较大影响。增强电极和脑组织间的黏附程度,可以有效减小脑组织损伤。电极尖端的形状也极大地影响着组织的应变大小。横向载荷分析显示X轴方向的载荷产生的脑组织损伤区域大约为60μm,这表明电极之间的间距应大于60μm,否则不同电极产生的组织应变会发生重叠,这对于电极之间理想间距的设计和防止重叠应变形成多余的细胞鞘有着重要的意义。结论:数值仿真模型可以为电极-脑组织界面参数和电极间距设计参数提供参考,从而减少组织损伤,提高电极工作寿命,满足临床应用。

Objective To predict the injuries induced by brain tissue micromotions and improve the long-term stability of brain implanted electrode by developing finite element models of brain tissues based on silicon microelectrode and conducting a series of numerical simulations of the neural probe-finite element model.Methods The material of brain tissue was described by a hyperviscoelastic constitutive equation.Strain fields around the electrode were analyzed in varying micromotion models（longitudinal and transverse） and different degrees of physical coupling between the electrode and the brain tissues.Results The analysis of longitudinal loading showed that the maximum von Mises strain around the electrode decreased with increasing friction coefficients,and that strain peaked at the electrode tip,which indicated that physical coupling degree between the electrode and the brain tissues had significant effects on the injuries induced by brain tissue micromotions.Enhancing the attachment between the electrode and the brain tissues was proved to effectively decrease brain tissue injury.The design of the electrode tip also greatly affected the strain of the brain tissues.The analysis of transverse loading revealed that the brain injury region due to the X-axis direction micromotions was approximately 60 μm.Given this result,when a multi-probe array was implanted into the brain,the strains induced by individual probes may overlap if the distance between probes was shorter than the affected range（60 μm）.Those findings were of great significant for deciding an ideal spacing between electrodes and preventing excess cellular sheath formation due to overlapping strain.Conclusion The established numerical model can provide references for the parameters of the electrode-brain tissue interface and the design of neural probe,which will be helpful to reduce tissue injuries and improve the working life of implanted electrode,achieving the long-term clinical application.