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Bioconductive Iongels for Cutaneous Electrophysiology

Periodic Reporting for period 1 - BIKE (Bioconductive Iongels for Cutaneous Electrophysiology)

Reporting period: 2018-01-01 to 2019-12-31

Electrodes placed on the skin, cutaneous electrodes, are used to monitor the electrical activity of specific organs such as the brain (electroencephalography, EEG), the heart (electrocardiography, ECG) or particular muscles (electromyography, EMG). The quality of the electrophysiological recording depends on the impedance of the interface between the skin of the patient and the cutaneous electrode. Standard medical procedures use cutaneous electrodes based on silver / silver chloride (Ag/AgCl) conductive layers that require the application of a water-based electrolyte (hydrogel) to reduce impedance across the electrode and the skin interface.

This has a number of limitations: the aqueous hydrogel dries out after several hours causing the loss of electrophysiological signal, the water evaporation causes short circuits and refilling the aqueous hydrogel is time-consuming and discomfortable.

This project addresses these problems associated with the use of water-based electrolytes through the development of a new generation of gels, bioconductive iongels.

The healthcare sector needs a new generation of materials with soft mechanical properties and superior ionic/electrical conductivity in order to interface between human tissue and electronics. For example, as discussed above, the performance of commercial, widely used cutaneous electrodes is limited due to the poor stability of the electronic-skin interface. Consequently, this project is potentially high social impact and it will lead to the development of new materials to improve the electronic-skin interface ensuring the adequate acquisition of electrical signals to monitor the activity of an organ. Higher- quality data will enable the early detection of different diseases related to the heart, brain or muscles, such as arrhythmias, epilepsy or muscular problems.

To overcome problems associated with the use of water-based electrolytes in electrophysiological diagnostic procedures, this project aims to develop innovative materials: iongels, ionic liquid integrated into a polymer network. Due to the negligible vapor pressure of ionic liquids, long-term recordings can be made without the problem of evaporation. Moreover, the iongel can decrease impedance at the interface with a patient’s skin, thus improving the stability of the electronic-skin interface. The iongels have been fabricated ensuring good adhesion, biocompatibility with skin, conductivity and biodegradability.

Overall, the focus of this project is to create a new generation of bioconductive iongels and determine the potential of these state-of-the-art materials for improving the performance and lifetime of electrical health monitoring systems.
In particular, a fully biodegrable iongel for cutaneous electrophysiology has been developed to avoid skin irritation. In this study, thermal, electrical and rheological properties of the iongels by varying the amount of ionic liquid in the polymeric matrix have been tested. Cutaneous electrodes have been fabricated with biodegradable iongels and electrode/skin impedance measurements were carried out to measure the performance of the electrodes. Moreover, these electrodes have been used in electrocardiography (ECG) recordings on a healthy volunteer.

A new conducting hydrogel with high Na+ content has been prepared to use in organic electronic devices. This novel hydrogel was synthesized by the photopolymerization of poly(ethylene glycol)-dimethacrylate and sodium acrylate. Specifically, an organic electrochemical transistor (OECT) has been fabricated to use the Na+- hydrogel. The vast majority of the OECTs reported in literature operate using a liquid aqueous electrolyte. We show that the performance of the Na+ hydrogel in OECTs is as good as the performance of the common liquid electrolytes used for OECTs, but with the Na+- hydrogel the stability of the device is higher.

In order to understand the electronic - skin cell interactions, a 3D platform able to host and monitor the cell growth has been prepared. To develop the 3D platform, an electrically conductive polymer, PEDOT and a natural polysaccharide, Xantham Gum, has been combined.

To enhance the electrophysiological recordings, materials that can reduce impedance across the interface between the electrode and the skin have been synthesised : PEDOT:PSS/Ionic Liquid films. PEDOT:PSS/Ionic Liquid films are PEDOT polymers that can retain ionic liquid, combining ionic and electronic conduction to fabricated all-in-one electrodes.

Finally new electroactive materials that can incorporate bio(functionality) or thermoresponsiveness have been designed.

The exploitation and dissemination of the scientific results was done through publications in peer reviewed international journals and presentations at international conferences. During this year, I deliver oral communications in two international conferences and I publish five articles .
The global bioelectronics market is sustainable significant and is growing rapidly: in 2018 it is valued at €11,000 million and is estimated to double to reach €22,000 million in 2024, an indication of the remarkable impact of bioelectronics tools including that of these cutaneous electrodes now used routinely to measure the integrity of an organ or a specific physiological function. As it is mentioned above, this project aims at synthetizing bioconductive materials with mixed conduction that would result in improvements in biomedical devices that record vital signals such as cardiac activity (ECG) or muscular activity (EMG). As a result of the work carried during this year, new materials have been developed with unique and improved properties. Some applications have been successfully tested and we expect that many more will also be successful due to the potential of these materials to be employed in biomedical devices

Moreover, the outreach activities of these findings are likely to generate great public interest, providing European citizens with greater awareness about the actions that the EU is undertaking to improve their health and social wealth (Horizon 2020 program).
Figure1 of the report