Non-invasive brain stimulation (NIBS) is currently considered as one of the promised therapeutic solutions for neurological disorders. The most common approach of NIBS is transcranial direct current stimulation (tDCS), which applies a small electric current over scalp for modulating cortical excitability and facilitating treatment outcomes. High-definition tDCS (HD-tDCS) is a focal approach of conventional tDCS, which is proposed to increase the electric current delivered to a specific region of the brain. Instead of using large sponge electrodes, a high-definition montage with multi-electrodes is used in HD-tDCS. However, the usage of conventional electrodes includes sponge or dry electrode combining with conductive gel bring inconveniences in preparation and error-prone steps. In order to improve the contact and signal transmission of electrodes with scalp, a novel solid-gel with low resistivity was developed by Plastics Industry Development Center (PIDC, Taiwan). In this study, we evaluated and validated the performance of novel solid-gel with HD-electrodes in performance-based in vitro and in vivo experiments. The tests included biocompatibility and gel-electrodes performance evaluation. Our results showed that the solid-gel electrodes met the ISO 10993 biocompatibility requirements. Our solid-gel has shown a better performance than several commercial electrodes with low resistance (165 ± 5 Ohm in single state), high moisture (95% after 24 hours) and stable structure (80%). In addition, our HD-tDCS stimulation experiment using solid-gel can operate smoothly for more than 40 minutes and maintain at low level (lower than 2k Ohm). In this study, we evaluated the performance of a novel solid-gel and demonstrated superior performance for potential use in HD-tDCS. Out design of solid-gel could help to reduce the preparation time and enhance the effectiveness of HD-tDCS. Further studies can be carried out in different conditions for more subjects in order to fully validate potentials of solid-gel.

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