基于ANSYS/LS-DYNA的神经电极植入脑组织过程数值仿真

目的建立神经电极-脑组织数值仿真模型,研究神经电极在植入过程中对脑组织产生的植入损伤。方法采用超黏弹性模型描述脑组织材料,基于单元删除法和最大主应变失效准则模拟组织破坏与分离,并通过平均等效应变量化组织植入损伤,考察神经电极楔形角、植入速度以及电极刚度对脑组织急性损伤的影响规律。结果150°楔角所产生应变值较90°增加37.1%;100μm/s慢速植入时电极植入路径上组织应变值较大(57%),500μm/s较高速植入时植入路径上组织应变明显变小(25%);而电极刚度对组织损伤影响不明显,电极刚度从165 GPa下降至5 k Pa时,组织应变仅增加1%~2%。结论数值仿真模型可为神经电极与植入参数设计提供参考,从而减少组织植入损伤,提高电极工作寿命,满足长期临床应用。     

基于ANSYS/LS-DYNA的神经电极植入脑组织过程数值仿真

目的 建立神经电极-脑组织数值仿真模型,研究神经电极在植入过程中对脑组织产生的植入损伤。方法 采用超黏弹性模型描述脑组织材料,基于单元删除法和最大主应变失效准则模拟组织破坏与分离,并通过平均等效应变量化组织植入损伤,考察神经电极楔形角、植入速度以及电极刚度对脑组织急性损伤的影响规律。结果 150°楔角所产生应变值较90°增加37.1%;100 μm/s慢速植入时电极植入路径上组织应变值较大（>57%）,500 μm/s较高速植入时植入路径上组织应变明显变小（<25%）;而电极刚度对组织损伤影响不明显,电极刚度从165 GPa下降至5 kPa时,组织应变仅增加1%~2%。结论 数值仿真模型可为神经电极与植入参数设计提供参考,从而减少组织植入损伤,提高电极工作寿命,满足长期临床应用。     

基于ANSYS/LS-DYNA的神经电极植入脑组织过程数值仿真

目的 建立神经电极-脑组织数值仿真模型，研究神经电极在植入过程中对脑组织产生的植入损伤。方法 采用超黏弹性模型描述脑组织材料，基于单元删除法和最大主应变失效准则模拟组织破坏与分离，并通过平均等效应变量化组织植入损伤，考察神经电极楔形角、植入速度以及电极刚度对脑组织急性损伤的影响规律。结果 150°楔角所产生应变值较90°增加37.1%；100 μm/s慢速植入时电极植入路径上组织应变值较大（>57%），500 μm/s较高速植入时植入路径上组织应变明显变小（<25%）；而电极刚度对组织损伤影响不明显，电极刚度从165 GPa下降至5 kPa时，组织应变仅增加1%~2%。结论 数值仿真模型可为神经电极与植入参数设计提供参考，从而减少组织植入损伤，提高电极工作寿命，满足长期临床应用。     

涂层修饰的柔性神经电极力学综合性能评估

目的对带有涂层修饰的柔性神经电极进行力学综合性能的评估,为电极及涂层参数的优化设计提供依据。方法对接触、植入以及微动阶段建立简化力学模型,以聚酰亚胺为电极材料,PEG为涂层材料,PDMS模具注塑法为涂层涂覆方法,设置40、80、120、160、200μm涂层厚度梯度,对3个因素(临界载荷、最大形变、脑组织最大应变)进行综合对比评估。结果厚度增加会引起临界载荷增大、最大形变减小以及脑组织最大应变减小,同时也会导致脑组织应变区域增大。均衡3个因素考虑,选择200μm作为涂层最佳厚度,在该厚度下,临界载荷为17.9 m N,最大形变为10.1μm,脑组织最大应变为0.011 4。结论涂层厚度对神经电极的力学性能有较大影响,在具体情况下可通过设置多个力学性能因素的影响因子选择最优参数。涂层的最优参数选择可提高电极的性能,对神经电极的临床应用具有重要意义。     

基于动态拉伸试验数据的脑组织粘性–超弹性材料模型参数求解

本研究旨在确定能够有效模拟冲击载荷作用下脑组织力学特性的粘性–超弹性本构方程。本文运用有限元仿真与优化算法相结合的方法,开展了脑组织粘性–超弹性材料模型参数求解。首先,基于脑组织动态单轴拉伸试验数据,建立最大拉伸率为1.3、应变率分别为30 s–1和90 s–1的脑组织动态拉伸有限元仿真模型。然后,以仿真预测的工程应力–应变曲线与参考试验测量结果均值曲线的拟合误差最小化作为优化设计的目标函数,利用多目标遗传算法进行材料模型参数求解。结果显示,运用本文所确定的本构方程的脑组织有限元模型能够准确地预测不同加载速率下的脑组织动态拉伸力学特性。应用本文获取的脑组织粘性–超弹性本构方程于颅脑有限元模型,将有利于提高模型在动态冲击载荷下的生物逼真度。     

矩形微缺损关节软骨在压缩载荷损伤演化的数值分析

目的 研究软骨在压缩载荷作用下的损伤扩展行为和演变机制。方法 采用有限元方法建立微缺损的纤维增强多孔弹性的软骨模型,对压缩载荷作用下损伤演化过程进行模拟和参数研究,获得不同损伤扩展阶段软骨基体和纤维的应力、应变分布规律。结果 软骨损伤表层和损伤前沿的应变随压缩量的增大而显著增大,两者呈明显的正相关性;在软骨演化过程中同时存在向深层和左右两侧扩展的趋势;软骨中的裂纹和损伤优先沿着纤维切线方向延伸,随着损伤的加剧,软骨横向扩展度明显快于纵向扩展速度。结论 软骨损伤演化过程与纤维的分布有着密切的关系,基质和纤维的损伤相互促进,骨演化速度和程度在不同层区和不同阶段存在变化。研究结果可为软骨创伤性退变的预测及修复提供定性的参考,为临床解释损伤退变病理现象和治疗提供理论依据。     

矩形微缺损关节软骨在压缩载荷下损伤演化的数值分析

目的研究软骨在压缩载荷作用下的损伤扩展行为和演变机制。方法采用有限元方法建立微缺损的纤维增强多孔弹性的软骨模型,对压缩载荷作用下损伤演化过程进行模拟和参数研究,获得不同损伤扩展阶段软骨基体和纤维的应力、应变分布规律。结果软骨损伤表层和损伤前沿的应变随压缩量的增大而显著增大,两者呈明显的正相关性;在软骨演化过程中同时存在向深层和左右两侧扩展的趋势;软骨中的裂纹和损伤优先沿着纤维切线方向延伸,随着损伤的加剧,软骨横向扩展度明显快于纵向扩展速度。结论软骨损伤演化过程与纤维的分布有着密切的关系,基质和纤维的损伤相互促进,骨演化速度和程度在不同层区和不同阶段存在变化。研究结果可为软骨创伤性退变的预测及修复提供定性的参考,为临床解释损伤退变病理现象和治疗提供理论依据。     

神经电极的水凝胶涂层及楔形角对组织损伤的影响

目的研究水凝胶涂层的厚度以及电极楔形角对植入损伤的影响。方法基于植入损伤评估系统,进行模拟神经电极植入过程的实验,评估电极植入造成的组织损伤。用浸涂次数(分别为0、1、2、3)控制水凝胶涂层的厚度,选用30°、40°、50°、60°为电极楔形角的变量。以最大组织应变和最大植入力为组织损伤的衡量标准。结果水凝胶涂层越厚,电极植入损伤越大。楔形角越小,植入损伤也越小。同时,减小针尖的楔形角可以减小涂层对组织损伤的影响程度。3次浸涂时,楔形角为30°时,最大组织应变与最大植入力分别增加3.4%和3.8%,而楔形角为60°时,两者分别增加11.3%和18.1%。结论神经电极的水凝胶涂层将增大植入电极对生物组织的损伤,然而减小电极尖端楔形角的方法可以降低水凝胶涂层厚度对植入损伤的影响程度。     

压缩载荷下不同应变判定皮质骨断裂准确性分析

目的 寻找适合压缩断裂工况下的应变判据。方法 基于连续损伤力学理论进行皮质骨在压缩载荷下的断裂模拟。分别将等效应变与主应变设置为有限元模型单元损伤与失效判据进行断裂模拟,通过对比两种预测结果与动物实验数据,探究应用两种应变判据进行断裂模拟的准确性。结果 应用等效应变判据模拟的断裂时间晚于应用主应变模拟;相比等效应变,应用主应变进行仿真所得结果与动物实验结果更为接近。结论 压缩载荷下,应用主应变判定皮质骨单元力学状态进行断裂模拟较为准确。通过对比分析找到准确模拟皮质骨在压缩载荷下断裂的数值方法,能够为临床中提高骨折预测精度提供理论基础。     

经颅直流电刺激中阴极参数对电场分布的影响

经颅直流电刺激是一种非介入式的刺激方法。为了解电刺激中阴极电极数与位置对头脑模型中空间电场分布的影响,基于人体头部解剖结构,通过COMSOL仿真软件,建立3层同心球体有限元头模型,通过数值计算方法,研究不同偏转角度下阴极电极数对头脑组织电场分布的影响,并得到头脑模型中不同偏转角度下电极个数与电场强度的关系曲线。结果表明:阴极个数及偏转角度对头脑组织中电场分布的影响趋势不同;阴极偏转角度的增加,使电场更易分布在较深的脑组织中;放置2个或3个阴极可使大脑皮层获得更为良好的刺激效果。在实际应用中,需根据刺激靶点的位置及刺激强度的要求,综合选择合理的电极数及阴极偏转角度。     

The surface immobilization of the neural adhesion molecule L1 on neural probes and its effect on neuronal density and gliosis at the probe/tissue interface

Brain tissue inflammatory responses, including neuronal loss and gliosis at the neural electrode/tissue interface, limit the recording stability and longevity of neural probes. The neural adhesion molecule L1 specifically promotes neurite outgrowth and neuronal survival. In this study, we covalently immobilized L1 on the surface of silicon-based neural probes and compared the tissue response between L1 modified and non-modified probes implanted in the rat cortex after 1, 4, and 8 weeks. The effect of L1 on neuronal health and survival, and glial cell reactions were evaluated with immunohistochemistry and quantitative image analysis. Similar to previous findings, persistent glial activation and significant decreases of neuronal and axonal densities were found at the vicinity of the non-modified probes. In contrast, the immediate area (100 μm) around the L1 modified probe showed no loss of neuronal bodies and a significantly increased axonal density relative to background. In this same region, immunohistochemistry analyses show a significantly lower activation of microglia and reaction of astrocytes around the L1 modified probes when compared to the control probes. These improvements in tissue reaction induced by the L1 coating are likely to lead to improved functionality of the implanted neural electrodes during chronic recordings.     

Development of a Finite Element Model for Blast Brain Injury and the Effects of CSF Cavitation

Blast-related traumatic brain injury is the most prevalent injury for combat personnel seen in the current conflicts in Iraq and Afghanistan, yet as a research community,we still do not fully understand the detailed etiology and pathology of this injury. Finite element (FE) modeling is well suited for studying the mechanical response of the head and brain to blast loading. This paper details the development of a FE head and brain model for blast simulation by examining both the dilatational and deviatoric response of the brain as potential injury mechanisms. The levels of blast exposure simulated ranged from 50 to 1000 kPa peak incident overpressure and 1–8 ms in positive-phase duration, and were comparable to real-world blast events. The frontal portion of the brain had the highest pressures corresponding to the location of initial impact, and peak pressure attenuated by 40–60% as the wave propagated from the frontal to the occipital lobe. Predicted brain pressures were primarily dependent on the peak overpressure of the impinging blast wave, and the highest predicted brain pressures were 30%less than the reflected pressure at the surface of blast impact. Predicted shear strain was highest at the interface between the brain and the CSF. Strain magnitude was largely dependent on the impulse of the blast, and primarily caused by the radial coupling between the brain and deforming skull.The largest predicted strains were generally less than 10%,and occurred after the shock wave passed through the head.For blasts with high impulses, CSF cavitation had a large role in increasing strain levels in the cerebral cortex and periventricular tissues by decoupling the brain from the skull. Relating the results of this study with recent experimental blast testing suggest that a rate-dependent strain-based tissue injury mechanism is the source primary blast TBI.     

A novel neural electrode with micro-motion-attenuation capability based on compliant mechanisms—physical design concepts and evaluations

In order to solve the problem of the short lifespan of the neural electrode caused by micro motion, this study designed a novel neural electrode based on lumped compliance compliant mechanism to control different modes of micro-motion in a more effective way. According to the mathematical modeling of the novel neural electrode, the equivalent bending stiffness and equivalent tensile (compression) stiffness were calculated. The results of the finite element analysis based on the mathematical modeling revealed that the novel neural electrode showed excellent micro-motion-attenuation capability. The static analysis results showed that the novel design dramatically reduced the maximum displacement of the brain in 51% and the maximum stress in 41% under longitudinal micro-motion environment. It also effectively reduced the 5.1% maximum stress while maintaining the maximum displacement under lateral micro-motion environment. The experimental results based on the tissue injury evaluation system also confirmed that the novel electrode is more effective in micro-motion attenuation than the reference one. In detail, the strain of the brain tissue caused by the implantation of the neural electrode was decreased by 1.26 to 27.84% at the insertion depth of 3 mm, and 0.522 to 17.24% at the insertion depth of 4.5 mm, which has convinced the effectiveness of the design.

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Graphical abstract The schematic of the novel neural electrode and evaluationsystem of tissue injury

     

Mechanical failure modes of chronically implanted planar silicon-based neural probes for laminar recording

Penetrating intracortical electrode arrays that record brain activity longitudinally are powerful tools for basic neuroscience research and emerging clinical applications. However, regardless of the technology used, signals recorded by these electrodes degrade over time. The failure mechanisms of these electrodes are understood to be a complex combination of the biological reactive tissue response and material failure of the device over time. While mechanical mismatch between the brain tissue and implanted neural electrodes have been studied as a source of chronic inflammation and performance degradation, the electrode failure caused by mechanical mismatch between different material properties and different structural components within a device have remained poorly characterized. Using Finite Element Model (FEM) we simulate the mechanical strain on a planar silicon electrode. The results presented here demonstrate that mechanical mismatch between iridium and silicon leads to concentrated strain along the border of the two materials. This strain is further focused on small protrusions such as the electrical traces in planar silicon electrodes. These findings are confirmed with chronic in vivo data (133–189 days) in mice by correlating a combination of single-unit electrophysiology, evoked multi-unit recordings, electrochemical impedance spectroscopy, and scanning electron microscopy from traces and electrode sites with our modeling data. Several modes of mechanical failure of chronically implanted planar silicon electrodes are found that result in degradation and/or loss of recording. These findings highlight the importance of strains and material properties of various subcomponents within an electrode array.     

Hibernation, a model of neuroprotection

Hibernation, a natural model of tolerance to cerebral ischemia, represents a state of pronounced fluctuation in cerebral blood flow where no brain damage occurs. Numerous neuroprotective aspects may contribute in concert to such tolerance. The purpose of this study was to determine whether hibernating brain tissue is tolerant to penetrating brain injury modeled by insertion of microdialysis probes. Guide cannulae were surgically implanted in striatum of Arctic ground squirrels before any of the animals began to hibernate. Microdialysis probes were then inserted in some animals after they entered hibernation and in others while they remained euthermic. The brain tissue from hibernating and euthermic animals was examined 3 days after implantation of microdialysis probes. Tissue response, indicated by examination of hematoxylin and eosin-stained tissue sections and immunocytochemical identification of activated microglia, astrocytes, and hemeoxygenase-1 immunoreactivity, was dramatically attenuated around probe tracks in hibernating animals compared to euthermic controls. No difference in tissue response around guide cannulae was observed between groups. Further study of the mechanisms underlying neuroprotective aspects of hibernation may lead to novel therapeutic strategies for stroke and traumatic brain injury.     

坐姿下不同组织压力性损伤生物力学研究

目的 探讨坐姿下臀部压力性损伤易发部位以及不同软组织的生物力学响应,为有效预防深层组织压力性损伤提供参考。 方法 基于臀部 CT 扫描数据,建立坐位臀部有限元模型,包括骨骼、肌肉、脂肪和皮肤组织及坐垫模型,利用生死单元模拟组织损伤。 对比实验坐垫界面压力测量数据与有限元模拟结果,验证模型有效性。 模拟坐位力学状态,研究软组织的应力、应变情况,分析不同软组织中的压应力及超出极限值后可能造成的损伤情况。结果 通过对比坐垫模型仿真结果与实验界面压力测量结果,证明模型有效。 坐位时坐骨结节下方软组织区域出现应力集中现象。 其中,臀大肌组织中的横向压应力峰值约为 38 kPa,剪切应力峰值约为 3. 4 MPa;而脂肪组织中的最大压应力与剪切应力峰值分别为 22 kPa 与 4. 5 MPa,均未出现在坐骨结节正下方。 结论 软组织受到一定时间和大小的压力载荷作用,可能出现深层组织损伤。 当保持坐姿一定时间后,应及时变换体位,以降低压力性损伤出现的概率。 研究结果为预防压力性损伤提供生物力学依据,具有重要的临床研究价值。     

Neural tracts injuries in patients with hypoxic ischemic brain injury: Diffusion tensor imaging study

Many studies have reported on vulnerable areas of the brain in hypoxic ischemic brain injury (HI-BI). However, little is known about the involvement of neural tracts following HI-BI. We investigated neural tract injuries in adult patients with HI-BI, using diffusion tensor tractography (DTT). Twelve consecutive patients with HI-BI and 12 control subjects were recruited for this study. We classified the patients into two subgroups according to the preservation of alertness: subgroup A-5 patients who had intact alertness and subgroup B-7 patients who had impaired alertness. DTI-Studio software was used for evaluation of seven neural tracts: corticospinal, cingulum, fornix, superior longitudinal fasciculus, inferior longitudinal fasciculus, inferior fronto-occipital fasciculus, and optic radiation. We measured the DTT parameters (fractional anisotropy, apparent diffusion coefficient and voxel number) of each neural tract. In the individual analysis, all 12 patients showed injuries in all 24 neural tracts in terms of both DTT parameters and integrity, except for the corticospinal tract (75.0% injury). In the group analysis, the patient group showed neural injuries in all 24 neural tracts. In comparison of subgroups A and B, subgroup B showed more severe injuries: subgroup B showed a higher rate of disruption (39.8%) than subgroup A (12.9%) on individual DTTs and subgroup B had more severe injuries in both the cingulum and superior longitudinal fasciculus. In conclusion, we found that extensive injuries in the neural tracts were accompanied by HI-BI. Patients with impaired alertness appeared to show more severe injuries of neural tracts.     

A three-dimensional finite element model of the cervical spine: an investigation of whiplash injury

Very few finite element models of the cervical spine have been developed to investigate internal stress on the soft tissues under whiplash loading situation. In the present work, an approach was used to generate a finite element model of the head (C0), the vertebrae (C1–T1) and their soft tissues. The global acceleration and displacement, the neck injury criterion (NIC), segmental angulations and stress of soft tissues from the model were investigated and compared with published data under whiplash loading. The calculated acceleration and displacement agreed well with the volunteer experimental data. The peak NIC was lower than the proposed threshold. The cervical S- and C-shaped curves were predicted based on the rotational angles. The highest segmental angle and maximum stress of discs mainly occurred at C7–T1. Greater stress was located in the anterior and posterior regions of the discs. For the ligaments, peak stress was at anterior longitudinal ligaments. Each level of soft tissues experienced the greatest stress at the time of cervical S- and C-shaped curves. The cervical spine was likely at risk of hyperextension injuries during whiplash loading. The model included more anatomical details compared to previous studies and provided an understanding of whiplash injuries.     

Finite Element Analysis of the Current-Density and Electric Field Generated by Metal Microelectrodes

Electrical stimulation via implanted microelectrodes permits excitation of small, highly localized populations of neurons, and allows access to features of neuronal organization that are not accessible with larger electrodes implanted on the surface of the brain or spinal cord. As a result there are a wide range of potential applications for the use of microelectrodes in neural engineering. However, little is known about the current-density and electric field generated by microelectrodes. The objectives of this project were to answer three fundamental questions regarding electrical stimulation with metal microelectrodes using geometrically and electrically accurate finite elements models. First, what is the spatial distribution of the current density over the surface of the electrode? Second, how do alterations in the electrode geometry effect neural excitation? Third, under what conditions can an electrode of finite size be modeled as a point source? Analysis of the models showed that the current density was concentrated at the tip of the microelectrode and at the electrode–insulation interface. Changing the surface area of the electrode, radius of curvature of the electrode tip, or applying a resistive coating to the electrode surface altered the current-density distribution on the surface of the electrode. Changes in the electrode geometry had little effect on neural excitation patterns, and modeling the electric field generated by sharply tipped microelectrodes using a theoretical point source was valid for distances >～ 50μm from the electrode tip. The results of this study suggest that a nearly uniform current-density distribution along the surface of the electrode can be achieved using a relatively large surface area electrode μ00--1000μm²), with a relatively blunt tip (3–6 μm radius of curvature), in combination with～mμ～ 1μm) moderately resistive ～( ～ 50Ωm). © 2001 Biomedical Engineering Society. PAC01: 8719Nn, 0270Dh, 8780-y, 8710+e