Ultraconformable Temporary Tattoo Electrodes for broad surface Electrophysiology

Vital parameters can be recorded from the skin, by means of electrodes that transduce the biological signal, for the monitoring of personal health conditions. This is the objective of surface electrophysiology (sEP). Aim of this study was to develop and test novel skin-contact “temporary tattoo” sensors for broad application in sEP. Temporary tattoo paper based sensors are the avant-garde in skin contact applications. In this study the use of appropriate fabrication techniques and materials allowed the development of ultraconformable Temporary Tattoo Electrodes (TTEs), which are imperceptible for the user. Conformal adhesion of TTEs to the skin is due to their ultralow thickness (~1 µm). TTEs are readily fabricated by inkjet printing of a conductive polymer (PEDOT:PSS) onto commercially available temporary tattoo paper, allowing for large-area and low-cost production. The fabrication process provides tailorability in the electrode’s design, the integration of stable interconnections and wiring to external measurement/analysis devices, while preserving a reliable seamless interface with the skin. The capability of TTEs to faithfully record biosignals in various sEP techniques has been verified and their performance has been compared with state-of-the-art (SoA) Ag/AgCl electrodes. Ag/AgCl electrodes are in use in clinical practice since many decades, because they show excellent signal quality. However, they suffer from several drawbacks, mainly related to their poor wearability, due to their cumbersome nature, and to limited time stability (allowing just short-term recordings), due to their wet interface with the skin which dries up in some hours. Such drawbacks, among others, are limiting sEP capabilities in diagnosis and monitoring. A detailed investigation of TTE performance in various sEP applications has been carried out to prove that they can be considered as valid alternative to SoA electrodes. TTEs long-term recording capability has been assessed; these dry conformable electrodes were found to be able to record bioimpedance signal over more than 48h. TTE’s interface with the skin has been modelled, giving an innovative understanding of their peculiar signal transduction mechanism,. Electrocardiography (ECG) and electromyography (EMG) signals were successfully recorded with TTEs on multiple anatomical districts, including limbs and face, through single and multielectrodes arrays. Moreover, for the first time, a novel concept of perforable electrodes has been demonstrated with hairs growing through the tattoo electrode and not impairing its functioning. This permitted to envision long-term applications on areas with high hair density, as the scalp. We indeed performed electroencephalography (EEG) recordings. For the first time, we demonstrated the use and characterised TTEs in a clinical EEG monitoring. Moreover TTEs compatibility with magnetoencephalography (MEG) sensors has been successfully verified; they are thus the first example of MEG-compatible dry electrodes. Finally, a new phantom platform for electrodes evaluation has been developed and employed to prove the feasibility of high-density EEG. The successful assessment of TTEs in broad sEP paves the way for the exploitation of imperceptible interfaces in vital parameters monitoring. TTE is a cutting-edge technology that can open for new perspectives in clinical practice and provide great contribution for the development of next-generation wearables.