Porous Microneedle Array Electrode Using Interstitial Fluid as Conductive Fillers for Biosafe and Long-Term Biopotential Monitoring

The microneedle array electrodes (MNAEs) can record high-quality biopotentials comparable to wet electrodes while effectively addressing durability and comfort issues caused by electrolytic gel. However, current MNAEs rely on the use of conductive materials, such as metals, which typically exhibit insufficient biosafety and raise concerns due to the risk of functional coating shedding or microneedles (MNs) fracturing and remaining in the body. Here, a biosafe porous-MNAE using interstitial fluid (ISF) as conductive fillers is proposed. Its porous-MNs can penetrate the high-impedance stratum corneum (SC) and automatically absorb ISF through capillary action for electric conduction. This allows the preparation of porous-MNs using totally biodegradable and biocompatible materials, such as polyglycolic acid (PGA) and polylactic acid (PLA) used in this work, without compromising electrode impedance. The results show that the proposed porous-MNAE possesses adequate mechanical property, hygroscopicity, biodegradability, and wearability for practical applications. Meanwhile, it demonstrates a competitive normalized electrode-skin interface impedance (EII) of $1.94~\pm ~0.09$ k $\Omega \cdot $ cm2 at 10 Hz on pig ear skin and exhibits priority in continuous 6-h EII measurement. In brief, these results reveal the promising potential of porous-MNAE for biosafe and long-term biopotential monitoring.