Anisotropic Hydrogel Microelectrodes for Intraspinal Neural Recordings in vivo

Creating durable, motion-compliant neural interfaces is crucial for accessing dynamic tissues under in vivo conditions and linking neural activity with behaviors. Utilizing the self-alignment of nano-fillers in a polymeric matrix under repetitive tension, here, we introduce conductive carbon nanotubes with high aspect ratios into semi-crystalline polyvinyl alcohol hydrogels and create electrically anisotropic percolation pathways through cyclic stretching. The resulting anisotropic hydrogel fibers (diameter of 187 ± 13 µm) exhibit fatigue resistance (up to 20,000 cycles at 20% strain) with a stretchability of 64.5 ± 7.9%, and low electrochemical impedance (33.20 ± 9.27 kΩ @ 1 kHz in 1 cm length). We observe the reconstructed nanofillers’ axial alignment and a corresponding anisotropic impedance decrease along the direction of cyclic stretching. We fabricate fiber-shaped hydrogels into bioelectronic devices and implant them into wild-type and transgenic Thy1::ChR2-EYFP mice to record electromyographic signals from muscles in anesthetized and freely moving conditions. These hydrogel fibers effectively enable the simultaneous recording of electrical signals from ventral spinal cord neurons and the tibialis anterior muscles during optogenetic stimulation. Importantly, the devices maintain functionality in intraspinal electrophysiology recordings over eight months after implantation, demonstrating their durability and potential for long-term monitoring in neurophysiological studies.

创建耐用且顺应运动的神经接口（neural interfaces）对于在体内条件下获取动态组织信息、关联神经活动与行为具有关键意义。本研究利用重复张力下聚合物基质（polymeric matrix）中纳米填料（nano-fillers）的自对齐特性，将高长径比的导电碳纳米管（conductive carbon nanotubes）引入半结晶聚乙烯醇水凝胶（semi-crystalline polyvinyl alcohol hydrogels），并通过循环拉伸构建电各向异性渗流路径（electrically anisotropic percolation pathways）。所得各向异性水凝胶纤维（anisotropic hydrogel fibers）直径为187±13 µm，具有优异的抗疲劳性（20%应变下可承受20,000次循环）、64.5±7.9%的拉伸性及低电化学阻抗（1 cm长度下1 kHz时为33.20±9.27 kΩ）。我们观察到，重构后的纳米填料呈轴向排列（axial alignment），且沿循环拉伸方向的阻抗相应呈各向异性降低。将纤维状水凝胶制备为生物电子器件（bioelectronic devices）后，植入野生型及转基因Thy1::ChR2-EYFP小鼠体内，以记录麻醉及自由活动状态下肌肉的肌电信号（electromyographic signals）。这些水凝胶纤维可有效实现光遗传刺激（optogenetic stimulation）期间脊髓腹侧神经元与胫骨前肌电信号的同步记录。重要的是，该器件在植入后八个月内仍能维持脊髓内电生理记录（intraspinal electrophysiology recordings）功能，彰显其耐用性及在神经生理学研究中长期监测的潜力。