Temporary tattoo electrodes are the most recent development in the field of cutaneous sensors. They have successfully demonstrated their performances in the monitoring of various electrophysiological signals on the skin. These epidermal electronic devices offer a conformal and imperceptible contact with the wearer while enabling good quality recordings over time. Evaluations of brain activity in clinical practice face multiple limitations, where such electrodes can provide realistic technological solutions and increase diagnostics efficiency. Here we present the performance of inkjet-printed conducting polymer tattoo electrodes in clinical electroencephalography and their compatibility with magnetoencephalography. The working mechanism of these dry sensors is investigated through the modeling of the skin/electrode impedance for better understanding of the biosignals transduction at this interface. Furthermore, a custom-made skin phantom platform demonstrates the feasibility of high-density recordings, which are essential in localizing neuropathological activities. These evaluations provide valuable input for the successful application of these ultrathin electronic tattoos sensors in multimodal brain monitoring and diagnosis.

Conducting polymer electrodes based on poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) present many advantages for biological signal recording over traditional metal electrodes and are being steadily evaluated in health monitoring applications. A main requirement for wearable electrodes based on PEDOT:PSS is that selected additives, such as crosslinking agents, avoid the redispersion of the polymer or its postprocess delamination. In this work, a novel approach is presented to fabricate water stable conducting free‐standing films and textile electrodes by using a divinyl sulfone (DVS) crosslinker. As opposed to pristine and glycidoxypropyltrimethoxysilane (GOPS)‐crosslinked formulations, the stability of the conducting PEDOT:PSS/DVS is achieved without reducing its conductivity or an extreme stiffening of its mechanical properties. PEDOT:PSS/DVS formulation is easily processed on any substrate and forms low surface resistance free‐standing or textiles electrodes. Electrochemical and stretchable properties of the PEDOT:PSS/DVS in air and in an aqueous environment are demonstrated and its performance in recordings of electrophysiological signals such as electrocardiography is evaluated. This three‐component material shows great potential for making wearable and humidity stable devices in healthcare applications. Furthermore, it can also be highly attractive for the development of washable electroactive textiles.

In recent years, gels based on ionic liquids incorporated into polymer matrices, namely iongels, have emerged as long-term contact media for cutaneous electrophysiology. Iongels possess high ionic conductivity and negligible vapor pressure and can be designed on demand. In spite of the extensive efforts devoted to the preparation of biodegradable ionic liquids, the investigations related to the preparation of iongels based on biodegradable polymers remain scarce. In this work, biodegradable polycarbonate-based iongels are prepared by ring-opening polymerization of N-substituted eight ring membered cyclic carbonate monomers in the presence of imidazolium lactate ionic liquid. Our iongels are able to take up 10–30 wt % of ionic liquid and become softer materials by increasing the amount of free ionic liquid. Rheological measurements showed that the cross-over point between the storage modulus G′ and loss modulus G″ occurs at lower angular frequencies when the loading of free ionic liquid increases. These gels are able to take up to 30 wt % of the ionic liquid and the ionic conductivity of these gels increased up to 5 × 10−4 S·cm−1 at 25 °C as the amount of free ionic liquid increased. Additionally, we assess the biodegradation studies of the iongels by immersing them in water. The iongels decrease the impedance with the human skin to levels that are similar to commercial Ag/AgCl electrodes, allowing an accurate physiologic signals recording. The low toxicity and biodegradability of polycarbonate-based iongels make these materials highly attractive for cutaneous electrophysiology applications.

Tattoo electronics is one of the emerging technologies in skin compliant biosensing. The growing interest in their large application in health monitoring raises several interrogations on how these sensors interface with the skin. In this paper, the bioimpedance at the interface of the skin and ultra‐conformable tattoo electrodes made of conducting polymers are focused on. The electrochemical characteristics of these electrodes differ from traditional gelled Ag/AgCl electrodes. The modeling of equivalent circuits in different skin‐electrode configurations proposes the explanation of the biopotentials transduction mechanism. The strong agreement between the circuit model and experimental values reveals the capacitive coupling of conducting polymer tattoo electrodes where circuit's values reflect the electrodes’ and skin physical characteristics. Additional studies underline an enhanced signal stability in inter/intra‐subject evaluations using dry tattoos beneficial for broad long‐term recordings. This study provides a comprehensive explanation of the skin/tattoo electrode interface model. The understanding of this interface is essential when designing next generation wearable biomonitoring devices using imperceptible interfaces.

Today, wearable electronics devices combine a large variety of functional, stretchable, and flexible technologies. However, in many cases, these devices cannot be worn under everyday conditions. Therefore, textiles are commonly considered the best substrate to accommodate electronic devices in wearable use. In this paper, we describe how to selectively pattern organic electroactive materials on textiles from a solution in an easy and scalable manner. This versatile deposition technique enables the fabrication of wearable organic electronic devices on clothes.