Zhang Wenguang, Ma Yakun, Li Zhengwei
State Key Laboratory of Mechanical System and Vibration, Shanghai Jiao Tong University, Shanghai 200240, China.
Med Phys. 2016 Jan;43(1):505. doi: 10.1118/1.4938064.
The application of neural probes in clinic has been challenged by probes' short lifetime when implanted into brain tissue. The primary goal is to develop an evaluation system for testing brain tissue injury induced by neural probe's insertion using microscope based digital image correlation method.
A brain tissue phantom made of silicone rubber with speckle pattern on its surface was fabricated. To obtain the optimal speckle pattern, mean intensity gradient parameter was used for quality assessment. The designed testing system consists of three modules: (a) load module for simulating neural electrode implantation process; (b) data acquisition module to capture micrographs of speckle pattern and to obtain reactive forces during the insertion of the probe; (c) postprocessing module for extracting tissue deformation information from the captured speckle patterns. On the basis of the evaluation system, the effects of probe wedge angle, insertion speed, and probe streamline on insertion induced tissue injury were investigated.
The optimal quality speckle pattern can be attained by the following fabrication parameters: spin coating rate-1000 r/min, silicone rubber component A: silicone rubber component B: softener: graphite = 5 ml: 5 ml: 2 ml: 0.6 g. The probe wedge angle has a significant effect on tissue injury. Compared to wedge angle 40° and 20°, maximum principal strain of 60° wedge angle was increased by 40.3% and 87.5%, respectively; compared with a relatively higher speed (500 μm/s), the maximum principle strain within the tissue induced by slow insertion speed (100 μm/s) was increased by 14.3%; insertion force required by probe with convex streamline was smaller than the force of traditional probe. Based on the experimental results, a novel neural probe that has a rounded tip covered by a biodegradable silk protein coating with convex streamline was proposed, which has both lower insertion and micromotion induced tissue injury.
The established evaluation system has provided a simulation environment for testing brain tissue injury produced by various insertion conditions. At the same time, it eliminates the adverse effect of biological factors on tissue deformation during the experiment, improving the repeatability of measurement results. As a result, the evaluation system will provide support on novel neural probe design that can reduce the acute tissue injury during the implantation of the probe.
神经探针植入脑组织后寿命较短，这对其在临床中的应用构成了挑战。主要目标是开发一种评估系统，使用基于显微镜的数字图像相关方法来测试神经探针插入引起的脑组织损伤。
制作了一种表面带有散斑图案的硅橡胶脑组织模型。为获得最佳散斑图案，使用平均强度梯度参数进行质量评估。设计的测试系统由三个模块组成：（a）用于模拟神经电极植入过程的加载模块；（b）用于捕获散斑图案显微图像并获取探针插入过程中反作用力的数据采集模块；（c）用于从捕获的散斑图案中提取组织变形信息的后处理模块。基于该评估系统，研究了探针楔角、插入速度和探针流线型对插入引起的组织损伤的影响。
通过以下制作参数可获得质量最佳的散斑图案：旋涂速率-1000转/分钟，硅橡胶组分A：硅橡胶组分B：软化剂：石墨=5毫升：5毫升：2毫升：0.6克。探针楔角对组织损伤有显著影响。与40°和20°楔角相比，60°楔角的最大主应变分别增加了40.3%和87.5%；与相对较高的速度（500微米/秒）相比，缓慢插入速度（100微米/秒）引起的组织内最大主应变增加了14.3%；具有凸形流线型的探针所需的插入力小于传统探针。基于实验结果，提出了一种新型神经探针，其圆形尖端覆盖有可生物降解的丝蛋白涂层且具有凸形流线型，具有较低的插入和微动引起的组织损伤。
所建立的评估系统为测试各种插入条件下产生的脑组织损伤提供了模拟环境。同时，它消除了实验过程中生物因素对组织变形的不利影响，提高了测量结果的可重复性。因此，该评估系统将为新型神经探针的设计提供支持，以减少探针植入过程中的急性组织损伤。
