面向脑-机接口：基于超大孔水凝胶的半干脑电电极研究

Modern applications of brain-computer interfaces (BCIs) based on electroencephalography rely heavily on the wet electrodes. Therefore, it is urgent to develop more convenient and reliable gel-free EEG electrodes. Since semi-dry electrodes have shown to be capable of recording reliable EEG signals without conductive gels or pastes, semi-dry electrodes have become the latest development direction of EEG electrodes which are suit for real-world BCIs. Although semi-dry electrodes have demonstrate several merits over dry electrodes, they still need to improve user convenience because of the need to supplement of electrolyte manually. This study aims to develop novel superporous hydrogel-based semi-dry electrodes using superporous hydrogel as interface materials, which are expected to realize automatic absorb or release of electrolyte. The principle of automatic absorb or release of electrolyte is mainly based on the rapid swelling behavior and macroporous structure of superporous hydrogels. The semi-dry electrodes will be optimized according theirs swelling rate in electrolyte solution and electrode-skin impedance. A set of evaluation methods of the semi-dry electrodes will be improved, and then the electrode performances (including electrochemical performance, signal quality, stability, and user experience) of the proposed semi-dry electrodes will be evaluated systematically. Further, the electrochemical impedance spectroscopy of three typical electrodes (wet electrodes, semi-dry electrodes, and dry electrodes) will be fitted by establishing their equivalent circuit models. Overall, the study will towards real-world BCIs, and provide new theories and technologies for development of gel-fee EEG electrodes.

目前基于脑电的脑-机接口严重依赖湿电极技术，亟需发展使用方便、信号可靠的无胶脑电电极技术。半干电极具有无胶、信号可靠等突出优点，是应用于脑-机接口电极的最新发展方向。尽管相对干电极优势明显，但需手动补充电解质，方便性仍有待提高。本项目拟发展一种基于超大孔水凝胶的半干脑电电极，利用超大孔水凝胶的溶胀速率快和大孔结构特性，有望实现电解质“自充放”，旨在解决半干电极存在的不方便问题。以溶胀速率、电极-皮肤阻抗作为筛选指标，筛选出电解质“自充放”性能最优的半干电极。紧密围绕脑-机接口应用，从电化学性能、信号质量、稳定性、用户体验角度进行系统评价，改善半干电极的评价方法。此外，还建立了3种典型电极（湿电极、半干电极、干电极）的等效电路模型，进一步通过阻抗谱拟合方法系统研究电极-皮肤阻抗特性。本项目面向现实生活场景的脑-机接口应用，为无胶电极开发提供了理论和技术支持，具有广泛的产业应用前景。

本项目创新构造了一种基于聚丙烯酰胺/聚乙烯醇超大孔水凝胶（PVA/PAM SPH）的新型半干脑电电极，证实了 “充放电”电解质概念可行。在中空电极腔中原位聚合形成的PVA/PAM SPH起动态“电解液库”的作用。超大孔水凝胶可以在短短几秒钟内完全充满盐水等电解质溶液，而且可通过电极端面的微柱以所需的速率“释放”到头皮。通过这种方式，在电极-皮肤接触部位实现了局部皮肤水合作用，形成生物电信号有效传输通路并显著降低了电极-皮肤阻抗。而且，有效地避免了短路和使用不便等问题。超大孔水凝胶半干电极具有低而稳定的接触阻抗和低的电位漂移值。半干电极和湿电极间的平均时域相关系数为0.941，说明半干电极的EEG信号质量高。超大孔水凝胶半干脑电电极具有快速安装、信号可靠和用户友好性等突出优势，在现实生活中EEG新应用中显示出了巨大的潜力。同时建立系统评价半干脑电电极性能的方法，为半干脑电电极的开发提供了方法学基础。本项目首次建立了湿电极、半干电极和干电极的等效电路模型，系统研究三种电极的电极-皮肤阻抗特性。半干电极与湿电极两种电极的面积归一化阻抗接近，充分说明半干电极概念是可行的。在压力或皮肤磨砂条件下，半干电极和干电极面积归一化阻抗差异都体现在皮肤电阻（Rs）和界面接触电阻（Res），而这两个参数都与电极/皮肤界面的电解质的量相关。这些电极-皮肤界面特性研究发现为半干脑电电极的设计提供了理论支撑。