用于长期神经电生理记录的自伸展电极阵列

Self-spreadable Octopus-like Electrode Arrays for Long-term Neural Recordings

由于能够实现高时空分辨的神经环路功能解析,微电极阵列已经成为了神经科学研究中的重要工具。然而,目前在自由活动动物中实施长期稳定的电生理记录仍然极具挑战。为此,我们研发了一种可自伸展的多通道电极阵列,并探讨了其应用于长期神经电生理记录的可行性和潜在优势。当电极植入后,其表面的水凝胶包裹层会迅速溶胀并溶解,随后电极阵列的记录通道会在脑组织中自行展开。由于分散的记录通道的直径较小,电极在长期植入后的组织反应显著减轻。得益于此,与传统的四电极(tetrode)相比,这种自伸展电极在长期植入后的界面阻抗显著降低,电生理信号质量更好。上述特性将受益于活体水平的神经环路机制研究。

Neural electrodes have been extensively utilized for the investigation of neural functions and the understanding of neuronal circuits because of their high spatial and temporal resolution.However,long-term effective electrophysiological recordings in free-behaving animals still constitute a challenging task,which hinders longitudinal studies on complex brain-processing mechanisms at a functional level.Herein,we demonstrate the feasibility and advantages of using a selfspreadable octopus-like electrode(octrode)array for long-term recordings.The octrode array was fabricated by enwrapping a bundle of eight formvar-coated nickel-chromium microwires with a layer of polyethylene glycol in a custom-made mold.After the electrodeposition of platinum nanoparticles,the microwires at the electrode tip were gathered together and then re-enwrapped with a thin layer of gelatin to maintain their structure and mechanical strength for implantation.Shortly after implantation(within 20 min),the biocompatible gelatin encapsulation swelled and dissolved,causing the self-spreading of the recording channels of the octrode array in the brain.The electrochemical characteristics of the electrode/neural tissue interface were investigated by electrochemical impedance spectroscopy(EIS).Four weeks after implantation,the average impedance of the octrodes(1.26 MΩat 1 kHz)was significantly lower than that of the conventional tetrodes(1.50 MΩat 1 kHz,p<0.05,t-test).Additionally,the octrodes exhibited a better pseudo-capacitive characteristic and a considerably faster ion transfer rate at the electrode interface than the tetrodes.Spontaneous action potentials and local field potentials(LFPs)were also recorded in vivo to investigate the electrophysiological performance of the octrodes.The peak-to-peak spike amplitudes recorded for the octrodes were remarkably larger than those recorded for the tetrodes.The signal quality remained at approximately the same level for the four-week period,while the peak-to-peak spike amplitudes recorded for the tetrodes decreased abruptly.Moreover,the voltage amplitudes recorded by the octrodes at 1–200 Hz were notably larger than those by the tetrodes,suggesting a higher sensitivity in the recording of electrophysiological events.Furthermore,we performed immunochemical analyses on the brain tissues at post-implantation to evaluate the histocompatibility of the electrodes.Tissue responses of the octrodes were alleviated considerably,evidenced by the reduced astroglial intensity and increased neuron density around the implant site as compared to the tetrodes,which may be due to the relatively small size of each decentralized recording channel after self-spreading in vivo.Generally,the fabricated octrodes exhibited a lower electrochemical impedance value at the octrode/neural tissue interface and an increased signal quality during the long-term electrophysiological recording in freely moving mice as compared to the conventional tetrodes.All of these are desirable characteristics in neural circuit dissections in vivo.