Flexible and Fully Biocompatible Microneedle Array Dry Electrodes for Bio Potentials Measurement in Organic Electronic Wearable Healthcare Applications

Abstract

Dry electrodes are an important component of organic-electronic wearable devices for future healthcare and Internet of Humans applications; measuring brain, heart, and muscle bio potentials can allow an early diagnosis of diseases relating to these organs as well as prevention, treatment and therapy. In addition, they may provide a means to monitor an auxiliary brain-related information when used, for example, together with OLED-based photo biomodulation (PBM) devices that activate brain activity by light. Likewise, they may allow one to realize a wearable device combining both electrocardiogram (ECG) and photoplethysmography (PPG), the latter of which can be realized with OLEDs and organic photodiodes. If realized, such devices will provide continuously measured vital information beyond a simple heart-beating rate in a way that minimizes any disturbances on daily life. Current clinical-use electrodes have limited wearable and external use capabilities due to the use of gels, a long time to set up the electrodes, and lack of comfort. Dry electrodes have shown to improve on this issues, but still lack the recording quality of gel electrodes required for accurate and relevant measurements. Some research has been done on dry electrodes based on soft polymers with different structures on the surface, and covered by metallic layers and nanowires, as well as carbon nanotubes among other conductive materials; these approaches are successful measuring bio potentials but show high electrode-skin impedance compared to gel electrodes, this directs to a lower SNR of the signal.

In this study, we propose microneedle-array dry electrodes with decreased electrode-skin impedance compared with contact dry electrodes. The electrodes were fabricated using a biocompatible conductive-filled polymer on top of an also biocompatible flexible substrate, reducing skin irritation and increasing the comfort of the electrode. By constructing the electrode with a microneedle array structure, we provide a shallow penetration of the Stratum Corneum, the outermost layer of the skin, ensuring the reduction of the electrode-skin impedance while keeping the electrode comfortable to wear. The impedance of the electrodes are characterized using impedance spectrometry over typical bio potential frequencies; and the signal quality was characterized recording EEG and ECG, to later calculate the SNR of the signals. The characteristics are compared with clinical-use gel cup electrodes and discussed. We believe the proposed electrode can be used on wearable applications requiring long-term measurement, comfort and high performance, and can pave the road to future Internet of Humans applications.