Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, United States of America.
J Neural Eng. 2020 Apr 29;17(2):026037. doi: 10.1088/1741-2552/ab8343.
Carbon fiber electrodes may enable better long-term brain implants, minimizing the tissue response commonly seen with silicon-based electrodes. The small diameter fiber may enable high-channel count brain-machine interfaces capable of reproducing dexterous movements. Past carbon fiber electrodes exhibited both high fidelity single unit recordings and a healthy neuronal population immediately adjacent to the recording site. However, the recording yield of our carbon fiber arrays chronically implanted in the brain typically hovered around 30%, for previously unknown reasons. In this paper we investigated fabrication process modifications aimed at increasing recording yield and longevity.
We tested a new cutting method using a 532nm laser against traditional scissor methods for the creation of the electrode recording site. We verified the efficacy of improved recording sites with impedance measurements and in vivo array recording yield. Additionally, we tested potentially longer-lasting coating alternatives to PEDOT:pTS, including PtIr and oxygen plasma etching. New coatings were evaluated with accelerated soak testing and acute recording.
We found that the laser created a consistent, sustainable 257 ± 13.8 µm electrode with low 1 kHz impedance (19 ± 4 kΩ with PEDOT:pTS) and low fiber-to-fiber variability. The PEDOT:pTS coated laser cut fibers were found to have high recording yield in acute (97% > 100 µV , N = 34 fibers) and chronic (84% > 100 µV , day 7; 71% > 100 µV , day 63, N = 45 fibers) settings. The laser cut recording sites were good platforms for the PtIr coating and oxygen plasma etching, slowing the increase in 1 kHz impedance compared to PEDOT:pTS in an accelerated soak test.
We have found that laser cut carbon fibers have a high recording yield that can be maintained for over two months in vivo and that alternative coatings perform better than PEDOT:pTS in accelerated aging tests. This work provides evidence to support carbon fiber arrays as a viable approach to high-density, clinically-feasible brain-machine interfaces.
碳纤维电极可能实现更好的长期脑植入，最大限度地减少硅基电极常见的组织反应。小直径纤维可以实现高通道计数的脑机接口，能够复制灵巧的运动。过去的碳纤维电极表现出高保真的单个单元记录和记录部位附近健康的神经元群体。然而，我们的碳纤维阵列在大脑中的慢性植入的记录产率通常徘徊在 30%左右，原因尚不清楚。在本文中，我们研究了旨在提高记录产率和延长寿命的制造工艺改进。
我们测试了一种新的切割方法，使用 532nm 激光切割与传统剪刀切割方法相比，用于创建电极记录部位。我们通过阻抗测量和体内阵列记录产率验证了改进记录部位的效果。此外，我们测试了可能更持久的涂层替代物，包括 PtIr 和氧等离子体蚀刻。新涂层通过加速浸泡测试和急性记录进行评估。
我们发现激光创建了一致的、可持续的 257 ± 13.8 µm 电极，具有低 1 kHz 阻抗（19 ± 4 kΩ 与 PEDOT:pTS）和低纤维间可变性。发现用 PEDOT:pTS 涂层的激光切割纤维具有高急性记录产率（97% > 100 µV ，N = 34 根纤维）和慢性记录产率（84% > 100 µV ，第 7 天；71% > 100 µV ，第 63 天，N = 45 根纤维）。激光切割记录部位是 PtIr 涂层和氧等离子体蚀刻的良好平台，与 PEDOT:pTS 相比，在加速浸泡测试中，1 kHz 阻抗的增加速度较慢。
我们发现激光切割碳纤维具有高记录产率，在体内可维持超过两个月，替代涂层在加速老化测试中的性能优于 PEDOT:pTS。这项工作为碳纤维阵列作为一种可行的高密度、临床可行的脑机接口方法提供了证据。
