Fabrication of Bendable Microneedle-Array Electrode by Magnetorheological Drawing Lithography for Electroencephalogram Recording

Continuous electroencephalogram (EEG) recording is vital for brain science research, monitoring pathological and physiological conditions, and the diagnosis of brain disease. Conventional wet electrodes require skin preparation and a gel electrolyte to reduce electrode-skin interface impedance (EII), which limits its further application in long-term EEG signal recording. Microneedle-array electrodes (MAEs) have been employed in EEG recording, as they can be used directly without skin preparation or the gel electrolyte. However, most microneedles used in MAE are rigid and have a high aspect ratio; thus, they can break easily. Hence, we developed a novel bendable MAE for EEG recording. It is made of a flexible polydimethylsiloxane (PDMS) pillar array with rigid microneedle tips. The PDMS pillar array could help the MAE pass through hair and enable the microneedle tips to penetrate a stratum corneum layer into a scalp, thus reducing the EII. Moreover, the PDMS pillar array is bendable, which prevents the microneedles tips from breaking. The MAE can record EEG signals well in a BIOPAC system and an Emotiv EPOC+ device. The bendable MAE may be an alternative electrode for long-term EEG recording.