Conformable Wearable Electrodes: From Fabrication to Electrophysiological Assessment

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.