Name: conformable wearable electrodes: from fabrication to electrophysiological assessment
Uploaded: 2022-07-22T13:00:00
Description: Watch this Scientific Journal Video about Conformable Wearable Electrodes: From Fabrication to Electrophysiological Assessment at JoVE.com

This work was supported by the French National Research Agency through the ANR JCJC OrgTex project (ANR-17-CE19-0010). It has also received funding from the European Union&#39;s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement no. 813863. E.I. wishes to thank the CMP cleanroom staff at the Centre Microelectronics in Provence for their technical support during the development of the project.

NOTE: Experiments involving human subjects did not involve the collection of identifiable private information related to the individual&#39;s health status and are only used here for technological demonstration. Data were averaged over three different subjects. The electrophysiological recordings were extracted from previously published data6,21.
1. Inkjet-printed PEDOT:PSS electrode fabrication
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<ol>
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This paper describes an easy and scalable process to fabricate wearable electrodes and demonstrates a method for recording electrophysiological biosignals. It uses three examples of wearable substrates, such as tattoo, textile, and thin films. It introduces how to build a sensor on these substrates and characterize its performance prior to its application. To make the electrodes here, we employed PEDOT:PSS, a conductive polymer that stands out from metal-based conductors due to its cost-effectiveness, versatile processab...

Noninvasive biopotential recording is performed through skin-contact electrodes, providing a vast amount of data on the physiological status of the human body in fitness and healthcare1. Novel types of wearable biomonitoring devices have been developed from the latest technological advances in electronics through the downscaling of integrated controlling and communicating components to portable dimensions. Smart monitoring devices pervade the market daily, offering multiple monitoring capabilities with the ultimate goal of providing sufficient physiological content to enable medical diagnostics2. Therefore, safe, reliable, and robust interfaces with the human body present critical challenges in the development of legitimate wearable technologies for healthcare. Tattoo and textile electrodes have recently appeared as reliable and stable interfaces perceived as innovative, comfortable devices for wearable biosensing3,4,5.
Tattoo sensors are dry and thin interfaces that, owing to their low thickness (~1 &#181;m), ensure adhesive-free, conformable skin contact. They are based on a commercially available tattoo paper kit composed of a layered structure, which allows the release of an ultrathin polymeric layer on the skin6. The layered structure also allows for easy handling of the thin polymeric layer during the sensor&#39;s fabrication process and its transfer to the skin. The final electrode is fully conformable and almost imperceptible to the wearer. Textile sensors are electronic devices obtained from fabric functionalization with electroactive materials7. They are mainly integrated or simply sewed into clothes to ensure the user&#39;s comfort due to their softness, breathability, and evident affinity with garments. For almost a decade, textile and tattoo electrodes have been assessed in surface electrophysiological recordings3,8,9, showing good results both in wearability and signal quality recordings and reporting high signal-to-noise ratio (SNR) in short- and long-term evaluations. They are also conceived as a potential platform for wearable biochemical sweat analysis1,10.
The growing interest in tattoo, textile, and, in general, flexible thin film technologies (e.g., those made of plastic foils such as parylene or different elastomers) is mainly promoted by the compatibility with low-cost and scalable fabrication methods. Screen printing, inkjet printing, direct patterning, dip coating, and stamp transfer have been successfully adopted to produce such kinds of electronic interfaces11. Among these, inkjet printing is the most advanced digital and fast prototyping technique. It is mainly applied to the patterning of conductive inks in a non-contact, additive fashion under ambient conditions and on a large variety of substrates12. Although multiple wearable sensors have been fabricated through noble metal ink patterning13, metal films are brittle and undergo cracking when mechanically stressed. Different research groups have adopted different strategies to endow metals with the property of mechanical compatibility with skin. These strategies include reducing the film thickness and using serpentine designs or wrinkled and prestretched substrates14,15,16. Soft and intrinsically flexible conductive materials, such as conductive polymers, found their application in flexible bioelectronic devices. Their polymeric flexibility is combined with electric and ionic conductivity. PEDOT:PSS is the most used conductive polymer in bioelectronics. It is characterized by softness, biocompatibility, sustainability, and printing processability17, which make it compatible with the widespread production of biomedical devices.
Devices, such as planar electrodes connected to an acquisition system, allow the recording of biopotentials in health monitoring. Human body biopotentials are electrical signals generated by electrogenic cells that propagate through the body up to the skin surface. According to where the electrodes are placed, it is possible to acquire data related to the electrical activity of the brain (EEG), muscles (EMG), heart (ECG), and skin conductivity (e.g., bioimpedance or electrodermal activity, EDA). The quality of the data is then assessed to evaluate the usability of the electrodes in clinical applications. A high SNR defines their performance18, which is typically compared with state-of-the-art Ag/AgCl electrode recordings. Although the Ag/AgCl electrodes also have high SNR, they lack long-term operationality and conformable wearability. High-quality biosignal recordings provide insights into human health status related to a particular organ&#39;s function. Thus, these benefits of comfortable tattoo or textile interfaces indicate their promise for long-term applications that can enable real-life mobile health monitoring and pave the way for the development of telemedicine19.
This paper reports how to fabricate and assess tattoo and textile electrodes in health biomonitoring. After its fabrication, a novel electrode must be characterized. Typically, electrochemical impedance spectroscopy (EIS) is adopted to study the electrical performance of the electrode with respect to a target interface (e.g., skin) in terms of the transfer function. EIS is used to compare the impedance characteristics of multiple electrodes and perform tests under different conditions (e.g., varying the electrode design or studying long-term responses). This paper shows the recording of surface biosignals through an easy setup and reports a user-friendly method to record different types of biosignals applicable to any novel fabricated electrode that needs to be validated for cutaneous biopotential recordings.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Biosignalplux - Plux wireless device for electrophysiological recordings</td>
			<td>PLUX Wireless Biosignals S.A</td>
			<td></td>
			<td>EEG, ECG, EMG, EDA sensors</td>
		</tr>
		<tr>
			<td>Covidien Kendal Disposable electrodes, medical grade disposable electrodes (Pregelled, 24 mm)</td>
			<td>Covidien / Kendal (formally Tyco) ARBO electrodes</td>
			<td>H124SG</td>
			<td>Commercial Ag/AgCl electrodes for electrophysiology</td>
		</tr>
		<tr>
			<td>Dimatix inkjet printer</td>
			<td>Fujifilm</td>
			<td>DMP 2800</td>
			<td>Inkjet printer</td>
		</tr>
		<tr>
			<td>Laser Cutter</td>
			<td>Universal Laser Systems</td>
			<td>VLS 3.50, 50 W</td>
			<td>Laser cutter to cut the glue sheet for tattoo electrodes fabrication</td>
		</tr>
		<tr>
			<td>NOVA</td>
			<td>Metrohm Autolab</td>
			<td>NOVA 2.1</td>
			<td>Electrochemistry software to control Autolab instruments</td>
		</tr>
		<tr>
			<td>OpenSignals</td>
			<td>2020 PLUX wireless biosignals, S.A.</td>
			<td></td>
			<td>Software suite for real-time biosignals visualisation, capable of direct interaction with PLUX devices</td>
		</tr>
		<tr>
			<td>PEDOT:PSS inkjet printable ink</td>
			<td>Heraeus Deutschland GmbH &#38; Co. KG</td>
			<td>CLEVIOS Pjet 700</td>
			<td></td>
		</tr>
		<tr>
			<td>Polyethylene naphthalene (PEN) foil</td>
			<td>&#160;Goodfellow</td>
			<td>thickness 1.3 &#956;m</td>
			<td>Used for tattoo electrodes interconnection fabrication</td>
		</tr>
		<tr>
			<td>Polyimide tape</td>
			<td>3M</td>
			<td>Kapton tape by 3 M, thickness 50 &#956;m</td>
			<td>Used for tattoo electrodes interconnection fabrication</td>
		</tr>
		<tr>
			<td>Potentiostat</td>
			<td>Metrohm Autolab</td>
			<td>Autolab potentiostat B.V.</td>
			<td>Used for EIS measurements</td>
		</tr>
		<tr>
			<td>Silhouette temporary tattoo paper kit</td>
			<td>Silhouette Americ, Inc, US</td>
			<td></td>
			<td>Substrate for tattoo-based electrodes</td>
		</tr>
		<tr>
			<td>Wowen textile 100% cotton and commercially available pantyhose</td>
			<td></td>
			<td></td>
			<td>Substrate for textile-based electrodes</td>
		</tr>
	</tbody>
</table>

conformable wearable electrodes: from fabrication to electrophysiological assessment

Wearable electronic devices are becoming key players in monitoring the body signals predominantly altered during physical activity tracking. Considering the growing interest in telemedicine and personalized care driven by the rise of the Internet of Things era, wearable sensors have expanded their field of application into healthcare. To ensure the collection of clinically relevant data, these devices need to establish conformable interfaces with the human body to provide high-signal-quality recordings and long-term operation. To this end, this paper presents a method to easily fabricate conformable thin tattoo- and soft textile-based sensors for their application as wearable organic electronic devices in a broad spectrum of surface electrophysiological recordings. 
The sensors are developed through a cost-effective and scalable process of cutaneous electrode patterning using poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), the most popular conductive polymer in bioelectronics, on off-the-shelf, wearable substrates. This paper presents key steps in electrode characterization through impedance spectroscopy to investigate their performance in signal transduction when coupled with the skin. Comparative studies are required to position the performance of novel sensors with respect to the clinical gold standard. To validate the fabricated sensors' performance, this protocol shows how to perform various biosignal recordings from different configurations through a user-friendly and portable electronic setup in a laboratory environment. This methods paper will allow multiple experimental initiatives to advance the current state of the art in wearable sensors for human body health monitoring.

This paper shows the fabrication of comfortable skin-contact electrodes by inkjet printing and a method to characterize them and perform electrophysiology recordings. We reported the fabrication steps of PEDOT:PSS inkjet printing directly on different substrates, such as fabric (Figure 1A), PEN (Figure 1B), and tattoo paper (Figure 1C,D) for reference. The proposed designs in protocol step 1.2.1. and step 1.3.1.5. d...

Watch this Scientific Journal Video about Conformable Wearable Electrodes: From Fabrication to Electrophysiological Assessment at JoVE.com

Conformable Wearable Electrodes: From Fabrication to Electrophysiological Assessment

Two recent technologies-tattoo and textiles-have demonstrated promising results in cutaneous sensing. Here, we present the fabrication and evaluation methods of tattoo and textile electrodes for cutaneous electrophysiological sensing. These electronic interfaces made of conductive polymers outperform the existing standards in terms of comfort and sensitivity.

Wearable electronic devices are becoming key players in monitoring the body signals predominantly altered during physical activity tracking. Considering ...

Wearable electronic devices are today's key players in the human body signal monitoring. Conformable skin interfaces are needed to be developed to provide high signal resolution and long-term operation of cutaneous sensors. Here we'll present how to easily fabricate, characterize, and use tactile and soft textile electrodes as a wearable organic electronic sensors.To validate the performance of our fabricated sensors, we apply a portable electronic system to record various electrophysiological signals from the human body. We propose multiple configuration to record various physiological signals simply in the lab. The following protocol has been used to fabricate electrodes on commercially flexible substrates, such as tattoo paper and textile.The commercial tattoo paper kit is also provided with the glue sheet. Tattoo paper has a layered structure including a supporting paper sheet, a water soluble polyvinyl alcohol layer, a releasable polyurethane film, and a topmost PVA layer. To fabricate wearable sensor, start with cutting the subset of interest.Place the subset on the printer plate, taping its border to keep it flat. Then, fill the printer cartridge with the PWSs commercial ink after filtering it. This is an accurate dispersion of the conductive polymer.Then print your design on the substrate. For tattoo paper and textile, which have more the high surface energy, set in the print parameters address spacing around 15 or 20 micrometer. After, dry electrode in the oven at 110 Celsius degrees for 15 minutes to complete solvent evaporation.The final printed sensor should look like this on tattoo paper, fabric, PET, and stretchable textile. To fabricate external connector to the position system, cut a rectangular piece of ultra thin substrate, such as PEN. Print on top of it a rectangular design with three PWSs layers.Laminate the ultra thin interconnection onto the two electrode. Cut a hole in tattoo paper glue sheet. Align this all with the signal sensing part of the tattoo PWSs electrode.Add a piece of polymer tape onto the free end of the PEN interconnection. To transfer the tattoo electrode, remove the glue liner. Place the tattoo onto the desired portion of the skin.Damp right the back support paper, keeping the tattoo in position. Once the back support paper is soaked, slide it to remove it, leaving only the electrode end of the transferable ultra film on the skin. Then, plug the flat PEN contact to the external acquisition unit.To characterize the fabricated electrode using electrochemical impedance spectroscopy, perform on body measurement. Firstly, ensure that the volunteer is comfortably seated with an arm placed on the table at rest. Then place one electrode on the skin and connect it to the working sensing couple of the potential start.Then place another electrode three centimeter apart from the first one and connect it to the counter electrode. Finally, place the third electrode on the elbow and connect it to the reference electrode cable. Then start the measurement with the potential start.Apply a current between the counter and the working electrodes, and measure the potential variation across the reference and the sensing couple. Note that the output impedance computed at each frequency consist of two contributions. The skin impedance, and the skin-electrode contact impedance.The following section describes the laddered placement for each bio signal of interest. An example of electro visual article monitoring using commercially available C-left and C-right electrodes. For ECG, adapt a configuration with three electrodes, one used as a ground.For the brain electrical activity, EEG, place the electrodes on the forehead and around the outer ears. For the electrodermal activity measurement, EDA, place two electrodes on the top of the left hand. Then perform the recording while the subject is at rest or doing physical exercise.To characterize the electrode's performances, we reported the representative impedance of textile electrodes. Textile electrodes exhibit slightly higher but comparable impedance than CI sintered right standard electrodes. The shape of the impedance models indicates a slightly higher resistive behavior in the case of textile electrodes.Whereas, the standard CI sintered right show typical resistive capacity behavior. By placing electrodes on the skin in different body areas, we have access to multiple bio signals. The EEG tracing displaced the electrical activity recording of population of active neurons.One of the basic group of brain waves is the Alpha between 8 and 13 hertz. The Alpha waves reflect the state of the brain under relaxation and can be induced by asking the subject to close their eyes. The gray vertical dash line marks the moment in the recording when the volunteer was asked to open his eyes.The ECG tracing shows the polarization and the polarization of the atrium and ventricles of the heart, represented by the characteristic pattern consisting of the P wave, IQRS complex, and a T wave. The R peaks show the highest amplitude and are used to calculate the heart rate by considering the time between two consecutive ones. We recorded the EMG tracing while the volunteer progressively increased the force of the R muscles.The intensified muscle activity is quantified by the increase amplitude of the voltage peaks. In an EMG tracing, spikes with amplitude from few microvolt to few mini volt in the frequency range of 10 to thousand hertz reflect the muscle of the hyper activity, driven by the motor unit action potentials. The EDA tracing is typically composed of a tonic and a fuzzy components.The tonic component reflects the skin conductance level and corresponds to the background signal. The fuzzy component reflects the response of the subject to a specific stimulus, and it's detectable by change in the skin conductance value. This tracing is used to evaluate human stress level and body hydration.With our protocol, we obtain soft and comfortable skin sensor to the patterning of a conductive ink on often soft cell straight. And the printing is a local and scalable technique that stand out from traditional micro electronic fabrication processes. The proposed method describe how to acquire electro signal that vary from weak neuro activity to high power muscle contraction.The signal allow getting inside into the user body physiological status. Of a role, we present the initial step on the feasibility of seamless verbal devices for a variety of my medical application, which has spun from fitness to healthcare monitoring.

Research

JoVE Journal

Bioengineering

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