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
NOTE: The following protocol has been used to fabricate electrodes for electrophysiology on commercial, flexible substrates-tattoo paper6 and textile21. The same approach has been largely adopted to make electrodes on flexible substrates such as thin plastic foils22. In all cases, an inkjet printer was used for the patterning of PEDOT:PSS (see the Table of Materials).
<ol>
	<li>Electrode substrate preprocessing
	<ol>
		<li>Cut a piece of the substrate of interest.
		<ol>
			<li>When using a tattoo substrate, wash it with water before printing to remove the topmost, water-soluble layer from the paper23. 
			NOTE: The tattoo paper kit is also provided with a glue sheet used in this work, both to enhance the tattoo adhesion and as a passivation layer. Tattoo paper has a layered structure (Supplemental Figure S1), including a supporting paper sheet, a water-soluble polyvinylalcohol (PVA) layer, a releasable polyurethane film, and a topmost PVA layer. The glue sheet has a layered structure composed of silicone paper as the support, water-based acrylic glue, and a top release liner.</li>
		</ol>
		</li>
		<li>To fabricate wearable sensors, start cutting the substrate of interest. Place the substrate on the printer plate, taping its border to keep it flat.</li>
	</ol>
	</li>
	<li>Printing of PEDOT:PSS ink
	<ol>
		<li>Prepare the design to print, such as a circle (12 mm diameter) with a rectangular pad at the bottom (3 mm x 7 mm), the latter to be used for the interconnection.</li>
		<li>Fill the printer cartridges (10 pl) with the PEDOT:PSS commercial ink after filtering it. This is an aqueous dispersion of the conductive polymer.</li>
		<li>Print the design on the substrate.
		<ol>
			<li>When using tattoo paper and textile, which have moderate-high surface energy and absorbing properties, respectively, print with a drop spacing of ~20 &#181;m.</li>
			<li>Print multiple PEDOT:PSS layers, either consecutively or by applying a drying process (110 &#176;C for 15 min) between the layers to create a homogeneous and continuous conductive pattern. 
			NOTE: This is especially required in the case of textile electrodes, where the 3D-like structure of textiles requires more ink content to create a continuous conductive path within the fabric.</li>
		</ol>
		</li>
		<li>Dry the electrode at 110 &#176;C for 15 min in the oven to complete solvent evaporation. 
		NOTE: Electrodes obtained on textile, PET, and tattoo paper (Figure 1A-C) by printing multiple devices in one run (Figure 1D) can now be stored in a closed, clean, and dry environment before continuing with the next steps.</li>
	</ol>
	</li>
	<li>External connector fabrication
	<ol>
		<li>Tattoo electrodes
		<ol>
			<li>Cut a rectangular piece of polyethylene naphthalate (PEN) substrate (8 mm x 12 mm, 1.3 mm thickness).</li>
			<li>Print a rectangular design (3 mm x 12 mm) with three PEDOT:PSS layers on top of the substrate.</li>
			<li>Dry the printed sample in the oven at 110 &#176;C for 15 min.</li>
			<li>Laminate the PEN interconnection onto the tattoo electrode, with the PEDOT:PSS rectangular parts facing each other.</li>
			<li>Cut a hole (diameter 11.3 mm) in the tattoo paper glue sheet. Align this hole of the glue sheet with the circular sensing part of the tattoo PEDOT:PSS electrode. Add a piece of polyimide tape (see the Table of Materials) onto the free end of the PEN interconnection.</li>
		</ol>
		</li>
		<li>Textile and plastic foil electrodes
		<ol>
			<li>Attach a piece of conductive tape (e.g., copper tape) around the rectangular printed connection to obtain a robust and stable interconnection.</li>
			<li>Plug a pogo pin connector into the copper tape and connect the pogo pin to the recording system.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Tattoo electrode transfer
	<ol>
		<li>Remove the glue liner. Place the tattoo onto the desired portion of the skin.</li>
		<li>Wet 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 made of the transferable ultrathin film on the skin.</li>
		<li>Plug the flat PEN contact into the external acquisition unit. See section 1.3.</li>
	</ol>
	</li>
	<li>Textile electrode positioning
	<ol>
		<li>Place the electrode on the skin. With the help of a fabric sports bracelet or medical tape, keep the electrode in stable contact with the skin to ensure high-quality signal recordings during movement.</li>
	</ol>
	</li>
	<li>Perform the desired surface electrophysiological recording. Wash the tattoo electrodes away after the recordings by rubbing them with a wet sponge.</li>
</ol>
2. Electrode characterization using electrochemical impedance spectroscopy
<ol>
	<li>On-body measurement
	<ol>
		<li>Ensure that the volunteer is comfortably seated with an arm placed on a table at rest. 
		NOTE: No skin cleaning or scrubbing is needed.</li>
	</ol>
	</li>
	<li>Electrode placement
	<ol>
		<li>Place one electrode on the skin and connect it to the working electrode-sensing electrode (WE-S) of the EIS.</li>
		<li>Place another electrode 3 cm apart from the first one and connect it to the counter electrode (CE) of the EIS.</li>
		<li>Place the third electrode on the elbow and connect it to the reference electrode (RE) of the EIS. See Figure 2A for the setup of the three electrodes . 
		NOTE: The electrodes connected to the CE and RE of the EIS can be both Ag/AgCl electrodes or made of PEDOT:PSS, as is the case for the WE in this study.</li>
	</ol>
	</li>
	<li>Start the recording on the EIS potentiostat. Apply a current between the counter and the working electrodes. Measure the potential variation across the reference and sensing couple. 
	&#8203;NOTE: The tattoo and textile electrode connection with the acquisition system can be made with a clip to form a stable electrical connection with the potentiostat cables. The output impedance computed at each frequency consists of two contributions: skin impedance and skin-electrode contact impedance.</li>
</ol>
3. Surface electrophysiological recordings
NOTE: The following section describes the electrode placement for each biosignal of interest. Once the electrodes are correctly placed and well attached to the skin, they can be connected to the portable acquisition system to start the recordings. The video content of this article shows an example of electrophysiological monitoring using commercially available Ag/AgCl electrodes and a portable electronic unit.
<ol>
	<li>For ECG, adopt a wearable configuration with two or three (one used as ground) electrodes. Place the electrodes in multiple body areas (e.g., chest, wrists, ribs) with a minimum interelectrode distance of 6 cm to get an appreciable signal. 
	NOTE: A classical location entails the placement of two electrodes on the left and right clavicles; in this case, the ground electrode can be placed on the left iliac crest.</li>
	<li>For muscle electrical activity recording (EMG), place the electrodes along the muscle of interest (e.g., on the biceps or the calf). Place the ground electrode on a static location such as an adjacent bone.</li>
	<li>For brain electrical activity recording (EEG), place the electrodes in multiple locations on the head. 
	NOTE: Comfortable locations are the forehead and around the outer ears. A reference electrode may be required, typically behind the ear on the mastoid bone.</li>
	<li>For electrodermal activity measurements (EDA), place two electrodes on the palm of the left hand. Perform the recording when the subject is at rest or doing physical exercise. 
	NOTE: Skin impedance can be measured over the whole body surface (e.g., the ribs, on the back, on the foot sole); a sufficient interelectrode distance of 6 cm ensures good monitoring.</li>
</ol>

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The authors have no conflicts of interest to disclose.

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><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 &amp;amp; Co. KG</td><td>CLEVIOS Pjet 700</td><td></td></tr><tr><td>Polyethylene naphthalene (PEN) foil</td><td>&amp;nbsp;Goodfellow</td><td>thickness 1.3 &amp;mu;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 &amp;mu;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 ...

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Research

JoVE Journal

Bioengineering

4.3K Views.  Mines Saint-Etienne. 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. 

Video: Conformable Wearable Electrodes: From Fabrication to Electrophysiological Assessment

Bridging the Bio-Electronic Interface with Biofabrication

Advancements in lab-on-a-chip technology promise to revolutionize both research and medicine through lower costs, better sensitivity, portability, and higher throughput. The incorporation of biological components onto biological microelectromechanical systems (bioMEMS) has shown great potential for achieving these goals. Microfabricated electronic chips allow for micrometer-scale features as well as an electrical connection for sensing and actuation. Functional biological components give the system the capacity for specific detection of analytes, enzymatic functions, and whole-cell capabilities. Standard microfabrication processes and bio-analytical techniques have been successfully utilized for decades in the computer and biological industries, respectively. Their combination and interfacing in a lab-on-a-chip environment, however, brings forth new challenges. There is a call for techniques that can build an interface between the electrode and biological component that is mild and is easy to fabricate and pattern.
Biofabrication, described here, is one such approach that has shown great promise for its easy-to-assemble incorporation of biological components with versatility in the on-chip functions that are enabled. Biofabrication uses biological materials and biological mechanisms (self-assembly, enzymatic assembly) for bottom-up hierarchical assembly. While our labs have demonstrated these concepts in many formats 1,2,3, here we demonstrate the assembly process based on electrodeposition followed by multiple applications of signal-based interactions. The assembly process consists of the electrodeposition of biocompatible stimuli-responsive polymer films on electrodes and their subsequent functionalization with biological components such as DNA, enzymes, or live cells 4,5. Electrodeposition takes advantage of the pH gradient created at the surface of a biased electrode from the electrolysis of water 6,7,. Chitosan and alginate are stimuli-responsive biological polymers that can be triggered to self-assemble into hydrogel films in response to imposed electrical signals 8. The thickness of these hydrogels is determined by the extent to which the pH gradient extends from the electrode. This can be modified using varying current densities and deposition times 6,7. This protocol will describe how chitosan films are deposited and functionalized by covalently attaching biological components to the abundant primary amine groups present on the film through either enzymatic or electrochemical methods 9,10. Alginate films and their entrapment of live cells will also be addressed 11. Finally, the utility of biofabrication is demonstrated through examples of signal-based interaction, including chemical-to-electrical, cell-to-cell, and also enzyme-to-cell signal transmission. 
Both the electrodeposition and functionalization can be performed under near-physiological conditions without the need for reagents and thus spare labile biological components from harsh conditions. Additionally, both chitosan and alginate have long been used for biologically-relevant purposes 12,13. Overall, biofabrication, a rapid technique that can be simply performed on a benchtop, can be used for creating micron scale patterns of functional biological components on electrodes and can be used for a variety of lab-on-a-chip applications.

This article describes a biofabrication approach: deposition of stimuli-responsive polysaccharides in the presence of biased electrodes to create biocompatible films which can be functionalized with cells or proteins. We demonstrate a bench-top strategy for the generation of the films as well as their basic uses for creating interactive biofunctionalized surfaces for lab-on-a-chip applications.

Advancements in lab-on-a-chip technology promise to revolutionize both research and medicine through lower costs, better sensitivity, portability, and ...

Scalable Solution-processed Fabrication Strategy for High-performance, Flexible, Transparent Electrodes with Embedded Metal Mesh

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a polymer film. This paper also presents a low-cost, vacuum-free fabrication method for this novel TE; the approach combines lithography, electroplating, and imprint transfer (LEIT) processing. The embedded nature of the EMTEs offers many advantages, such as high surface smoothness, which is essential for organic electronic device production; superior mechanical stability during bending; favorable resistance to chemicals and moisture; and strong adhesion with plastic film. LEIT fabrication features an electroplating process for vacuum-free metal deposition and is favorable for industrial mass production. Furthermore, LEIT allows for the fabrication of metal mesh with a high aspect ratio (i.e., thickness to linewidth), significantly enhancing its electrical conductance without adversely losing optical transmittance. We demonstrate several prototypes of flexible EMTEs, with sheet resistances lower than 1 &#937;/sq and transmittances greater than 90%, resulting in very high figures of merit (FoM) &#8211; up to 1.5 x 104 &#8211; which are amongst the best values in the published literature.

This protocol describes a solution-based fabrication strategy for high-performance, flexible, transparent electrodes with fully-embedded, thick metal mesh. Flexible transparent electrodes fabricated by this process demonstrate among the highest reported performances, including ultra-low sheet resistance, high optical transmittance, mechanical stability under bending, strong substrate adhesion, surface smoothness, and environmental stability.

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a ...

Engineering

Fabrication and Characterization of a Conformal Skin-like Electronic System for Quantitative, Cutaneous Wound Management

Recent advances in the development of electronic technologies and biomedical devices offer opportunities for non-invasive, quantitative assessment of cutaneous wound healing on the skin. Existing methods, however, still rely on visual inspections through various microscopic tools and devices that normally include high-cost, sophisticated systems and require well trained personnel for operation and data analysis. Here, we describe methods and protocols to fabricate a conformal, skin-like electronics system that enables conformal lamination to the skin surface near the wound tissues, which provides recording of high fidelity electrical signals such as skin temperature and thermal conductivity. The methods of device fabrication provide details of step-by-step preparation of the microelectronic system that is completely enclosed with elastomeric silicone materials to offer electrical isolation. The experimental study presents multifunctional, biocompatible, waterproof, reusable, and flexible/stretchable characteristics of the device for clinical applications. Protocols of clinical testing provide an overview and sequential process of cleaning, testing setup, system operation, and data acquisition with the skin-like electronics, gently mounted on hypersensitive, cutaneous wound and contralateral tissues on patients.

This article presents methods to fabricate and characterize a conformal, skin-like electronic system and protocols for the use in clinical applications, particularly on cutaneous wound management.

Recent advances in the development of electronic technologies and biomedical devices offer opportunities for non-invasive, quantitative assessment of ...

A Simple and Scalable Fabrication Method for Organic Electronic Devices on Textiles

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.

In this paper, we present a protocol to selectively deposit organic materials on textiles, which allows for the direct integration of organic electronic devices with wearables. The fabricated devices can be fully integrated in textiles, respecting their mechanical appearance and enabling sensing capabilities.

Today, wearable electronics devices combine a large variety of functional, stretchable, and flexible technologies. However, in many cases, these devices ...

Microfluidic Channel-Based Soft Electrodes for Capacitive Pressure Sensing

Microfluidic Channel-Based Soft Electrodes and Their Application in Capacitive Pressure Sensing

Flexible and stretchable electrodes are essential components in soft artificial sensory systems. Despite recent advances in flexible electronics, most electrodes are either restricted by the patterning resolution or the capability of inkjet printing with high-viscosity super-elastic materials. In this paper, we present a simple strategy to fabricate microchannel-based stretchable composite electrodes, which can be achieved by scraping elastic conductive polymer composites (ECPCs) into lithographically embossed microfluidic channels. The ECPCs were prepared by a volatile solvent evaporation method, which achieves a uniform dispersion of carbon nanotubes (CNTs) in a polydimethylsiloxane (PDMS) matrix. Compared to conventional fabrication methods, the proposed technique can facilitate the rapid fabrication of well-defined stretchable electrodes with high-viscosity slurry. Since the electrodes in this work were made up of all-elastomeric materials, strong interlinks can be formed between the ECPCs-based electrodes and the PDMS-based substrate at the interfaces of the microchannel walls, which allows the electrodes to exhibit mechanical robustness under high tensile strains. In addition, the mechanical-electric response of the electrodes was also systematically studied. Finally, a soft pressure sensor was developed by combining a dielectric silicone foam and an interdigitated electrodes (IDE) layer, and this demonstrated great potential for pressure sensors in soft robotic tactile sensing applications.

Author Spotlight: Microfluidic Channel-Based Soft Electrodes and Their Application in Capacitive Pressure Sensing  

Flexible electrodes have a wide range of applications in soft robotics and wearable electronics. The present protocol demonstrates a new strategy to fabricate highly stretchable electrodes with high resolution via lithographically defined microfluidic channels, which paves the way for future high-performance soft pressure sensors.

Flexible and stretchable electrodes are essential components in soft artificial sensory systems. Despite recent advances in flexible electronics, most ...

Fabrication of High Contact-Density, Flat-Interface Nerve Electrodes for Recording and Stimulation Applications

Many attempts have been made to manufacture multi-contact nerve cuff electrodes that are safe, robust and reliable for long term neuroprosthetic applications. This protocol describes a fabrication technique of a modified cylindrical nerve cuff electrode to meet these criteria. Minimum computer-aided design and manufacturing (CAD and CAM) skills are necessary to consistently produce cuffs with high precision (contact placement 0.51 &#177; 0.04 mm) and various cuff sizes. The precision in spatially distributing the contacts and the ability to retain a predefined geometry accomplished with this design are two criteria essential to optimize the cuff&#39;s interface for selective recording and stimulation. The presented design also maximizes the flexibility in the longitudinal direction while maintaining sufficient rigidity in the transverse direction to reshape the nerve by using materials with different elasticities. The expansion of the cuff&#39;s cross sectional area as a result of increasing the pressure inside the cuff was observed to be 25% at 67 mm Hg. This test demonstrates the flexibility of the cuff and its response to nerve swelling post-implant. The stability of the contacts&#39; interface and recording quality were also examined with contacts&#39; impedance and signal-to-noise ratio metrics from a chronically implanted cuff (7.5 months), and observed to be 2.55 &#177; 0.25 k&#8486; and 5.10 &#177; 0.81 dB respectively.

This article provides a detailed description on the fabrication process of a high contact-density flat interface nerve electrode (FINE). This electrode is optimized for recording and stimulating neural activity selectively within peripheral nerves.

Many attempts have been made to manufacture multi-contact nerve cuff electrodes that are safe, robust and reliable for long term neuroprosthetic ...

Neuroscience

Fabrication of Ti3C2 MXene Microelectrode Arrays for In Vivo Neural Recording

Implantable microelectrode technologies have been widely used to elucidate neural dynamics at the microscale to gain a deeper understanding of the neural underpinnings of brain disease and injury. As electrodes are miniaturized to the scale of individual cells, a corresponding rise in the interface impedance limits the quality of recorded signals. Additionally, conventional electrode materials are stiff, resulting in a significant mechanical mismatch between the electrode and the surrounding brain tissue, which elicits an inflammatory response that eventually leads to a degradation of the device performance. To address these challenges, we have developed a process to fabricate flexible microelectrodes based on Ti3C2 MXene, a recently discovered nanomaterial that possesses remarkably high volumetric capacitance, electrical conductivity, surface functionality, and processability in aqueous dispersions. Flexible arrays of Ti3C2 MXene microelectrodes have remarkably low impedance due to the high conductivity and high specific surface area of the Ti3C2 MXene films, and they have proven to be exquisitely sensitive for recording neuronal activity. In this protocol, we describe a novel method for micropatterning Ti3C2 MXene into microelectrode arrays on flexible polymeric substrates and outline their use for in vivo micro-electrocorticography recording. This method can easily be extended to create MXene electrode arrays of arbitrary size or geometry for a range of other applications in bioelectronics and it can also be adapted for use with other conductive inks besides Ti3C2 MXene. This protocol enables simple and scalable fabrication of microelectrodes from solution-based conductive inks, and specifically allows harnessing the unique properties of hydrophilic Ti3C2 MXene to overcome many of the barriers that have long hindered the widespread adoption of carbon-based nanomaterials for high-fidelity neural microelectrodes.

Fabrication of Ti3C2 MXene Microelectrode Arrays for In Vivo Neural Recording

We describe here a method for fabricating Ti3C2 MXene microelectrode arrays and utilizing them for in vivo neural recording.

Implantable microelectrode technologies have been widely used to elucidate neural dynamics at the microscale to gain a deeper understanding of the neural ...

Stimulating Mouse Brain with a Low-Cost EEG and Millimeter-Sized Coil

Low-Cost Electroencephalographic Recording System Combined with a Millimeter-Sized Coil to Transcranially Stimulate the Mouse Brain In Vivo

A low-cost electroencephalographic (EEG) recording system is proposed here to drive transcranial magnetic stimulation (TMS) of the mouse brain in vivo, utilizing a millimeter-sized coil. Using conventional screw electrodes combined with a custom-made, flexible, multielectrode array substrate, multi-site recording can be carried out from the mouse brain. In addition, we explain how a millimeter-sized coil is produced using low-cost equipment usually found in laboratories. Practical procedures for fabricating the flexible multielectrode array substrate and the surgical implantation technique for screw electrodes are also presented, which are necessary to produce low-noise EEG signals. Although the methodology is useful for recording from the brain of any small animal, the present report focuses on electrode implementation in an anesthetized mouse skull. Furthermore, this method can be easily extended to an awake small animal that is connected with tethered cables via a common adapter and fixed with a TMS device to the head during recording.The present version of the EEG-TMS system, which can include a maximum of 32 EEG channels (a device with 16 channels is presented as an example with fewer channels) and one TMS channel device, is described. Additionally, typical results obtained by the application of the EEG-TMS system to anesthetized mice are briefly reported.

Author Spotlight: Low-Cost Electroencephalographic Recording System Combined with a Millimeter-Sized Coil to Transcranially Stimulate the Mouse Brain In Vivo  

A low-cost electroencephalographic recording system combined with a millimeter-sized coil is proposed to drive transcranial magnetic stimulation of the mouse brain in vivo. Using conventional screw electrodes with a custom-made, flexible, multielectrode array substrate, multi-site recording can be carried out from the mouse brain in response to transcranial magnetic stimulation.

A low-cost electroencephalographic (EEG) recording system is proposed here to drive transcranial magnetic stimulation (TMS) of the mouse brain in vivo, ...

 Fabricating Epimysial EMG Electrodes for Preclinical Rodent Models 

Development of a Low-cost Epimysial Electromyography Electrode: A Simplified Workflow for Fabrication and Testing

Electromyography (EMG) is a valuable diagnostic tool for detecting neuromuscular abnormalities. Implantable epimysial electrodes are commonly used to measure EMG signals in preclinical models. Although classical resources exist describing the principles of epimysial electrode fabrication, there is a sparsity of illustrative information translating electrode theory to practice. To remedy this, we provide an updated, easy-to-follow guide on fabricating and testing a low-cost epimysial electrode. 
Electrodes were made by folding and inserting two platinum-iridium foils into a precut silicone base to form the contact surfaces. Next, coated stainless steel wires were welded to each contact surface to form the electrode leads. Lastly, a silicone mixture was used to seal the electrode. Ex vivo testing was conducted to compare our custom-fabricated electrode to an industry standard electrode in a saline bath, where high levels of signal agreement (sine [intraclass correlation - ICC= 0.993], square [ICC = 0.995], triangle [ICC = 0.958]), and temporal-synchrony (sine [r = 0.987], square [r = 0.990], triangle [r= 0.931]) were found across all waveforms. Low levels of electrode impedance were also quantified via electrochemical impedance spectroscopy. 
An in vivo performance assessment was also conducted where the vastus lateralis muscle of a rat was surgically instrumented with the custom-fabricated electrode and signaling was acquired during uphill and downhill walking. As expected, peak EMG activity was significantly lower during downhill walking (0.008 &plusmn; 0.005 mV) than uphill (0.031 &plusmn; 0.180 mV, p = 0.005), supporting the validity of the device. The reliability and biocompatibility of the device were also supported by consistent signaling during level walking at 14 days and 56 days post implantation (0.01 &plusmn; 0.007 mV, 0.012 &plusmn; 0.007 mV respectively; p &gt; 0.05) and the absence of histological inflammation. Collectively, we provide an updated workflow for the fabrication and testing of low-cost epimysial electrodes.

Author Spotlight: Epimysial Electrode Fabrication and Testing in ACL Injury Studies

Our purpose was to provide an updated, easy-to-follow guide on the fabrication and testing of epimysial electromyography electrodes. To that end, we provide instructions for material sourcing and a detailed walkthrough of the fabrication and testing process.

Electromyography (EMG) is a valuable diagnostic tool for detecting neuromuscular abnormalities. Implantable epimysial electrodes are commonly used to ...

Flexible Multi-Region Neural Recording Device for Epilepsy Research

An Integrated Method for Crafting Flexible and Convenient Electrophysiological Optrodes for Multi-Region In Vivo Recording

Epilepsy is a neurological disorder characterized by synchronized abnormal discharges involving multiple brain regions. Focal lesions facilitate the propagation of epileptic signals through associated neural circuits. Therefore, in vivo recording of local field potential (LFP) from the critical brain regions is&#160;essential for deciphering the circuits involved in seizure propagation. However, current methods for electrode fabrication and implantation lack flexibility. Here, we present a handy device designed for electrophysiological recordings (LFPs and electroencephalography [EEG]) across multiple regions. Additionally, we seamlessly integrated optogenetic manipulation and calcium signaling recording with LFP recording. Robust after-discharges were observed in several separate regions during epileptic seizures, accompanied by increasing&#160;calcium signaling. The approach used in this study offers a convenient and flexible strategy for synchronous neural recordings across diverse regions of the brain. It holds the potential for advancing research on neurological disorders by providing insights into the neural profiles of multiple regions involved in these disorders.

Author Spotlight: Unraveling Neural Communication and Circuit Interactions in Health and Disease

We have developed a simplified and cost-effective approach for electrode fabrication and conducted recordings of signals across multiple regions in freely moving mice. Utilizing optogenetics, alongside multi-region electrophysiology and calcium signal recording, enabled the revelation of neuronal activities across regions in the seizure kindling model.

Epilepsy is a neurological disorder characterized by synchronized abnormal discharges involving multiple brain regions. Focal lesions facilitate the ...