Microneedle electrodes for collecting bioelectrical signals: From a materials science perspective

Microneedle electrodes acquire bioelectrical signals by measuring the potential difference generated through active cells. The common bioelectrical signals include electroencephalographic, electromyographic, and electrocardiographic signals, which have been extensively utilized across medical, neuroscience, and bioengineering domains. Microneedle electrodes, as invasive dry electrodes minimal penetrating the stratum corneum without reaching the dermis, effectively mitigate the impedance of the electrode-skin interface without requiring conductive gel, thus accommodating the requirements of long-term and high-precision measurements. This review provides a comprehensive summary of the electrode materials, fabrication methods, performance evaluation, and applications of microneedle electrodes for bioelectrical signal acquisition. Special emphasis is placed on the development of materials used in the fabrication of microneedle electrodes. Additionally, we discuss the challenges related to material selection and performance testing, offering insights into future trends in this field.