Development of Dry EEG Electrodes and Dry EEG Cap for Neuromonitoring

Abstract

Monitoring and recording of electroencephalogram (EEG) is a non-invasive procedure that is increasingly used in neuromonitoring. Patient management is assessed and tailored based on the acquired brain signals that indicates the neurological state of the patient. Conventional EEG systems are wet systems. EEG recording in itself is not painful, but scalp preparation for the electrode attachment and washing afterwards may be uncomfortable. In this paper, a soft flexible gel-free dry electroencephalogram (EEG) electrodes and dry EEG head cap is developed and proposed. The dry EEG electrodes is a hybrid packaging rigid metal snap connectors, soft and flexible polymer material, and Silver-Silver Chloride (Ag- AgCl) coating. The sensor body/ structure does not use conductive polymer and there is no peeling off of the structure that could lead to concern in signal degradation. The dry EEG head cap is a fully-adjustable one-piece stretchable material integrated with reference and ground electrodes. Impedance reading of wet system is <5 KOhms, mainly due to the use of electrolytic/ conductive paste with such system. The proposed dry electrodes have impedance readings measured at <65 KOhms, which is lower compared to commercially available dry EEG electrodes that have impedance readings between 100 KOhms and 2000 KOhms. Despite the difference in impedance readings between the conventional wet system and the proposed dry electrodes, the captured brain signals / brain wave patterns are comparable. These brain signals are important especially when utilized for brain computer interfaces (BCI) that power and drive limb orthotic for rehabilitation following a stroke. The dry electrodes passed biocompatibility tests, specifically cytotoxicity test per ISO-10993-5 and primary skin irritation tests per ISO- 10993-10.