PRINTABLE CONDUCTIVE POLYMERS
Modified tattoo electrodes can be used to measure brain activity
by James Ives / May 14 2020
“In 2015 Francesco Greco, head of the Laboratory of Applied Materials for Printed and Soft electronics (LAMPSe) at the Institute of Solid State Physics at Graz University of Technology, developed so-called “tattoo electrodes” together with Italian scientists. These are conductive polymers that are printed using an inkjet printer on standard tattoo paper and then stuck to the skin like transfers to measure heart or muscle activity.
This type of electrode, optimized in 2018, opened up completely new paths in electrophysiological examinations, such as electrocardiography (ECG) or electromyography (EMG). Thanks to a thickness of 700 to 800 nanometres – that is about 100 times thinner than a human hair – the tattoos adapt to uneven skin and are hardly noticeable on the body. Moreover, the “tattoos” are dry electrodes; in contrast to gel electrodes, they work without a liquid interface and cannot dry out. They are excellently suited for long-term measurements. Even hairs growing through the tattoo do not interfere with the signal recording.
Building on this pioneering achievement, Greco, together with Esma Ismailova (Department of Bioelectronics, École Nationale Supérieure des Mines de Saint-Étienne, France) and Laura Ferrari (The BioRobotics Institute, Scuola Superiore Sant’Anna, Italy), has now achieved a further milestone in the measurement of bioelectrical signals: the group has modified the tattoo electrodes in such a way that they can also be used in electroencephalography (EEG) – i.e. to measure brain activity.
To do this, the researchers used the same approach as in 2018, i.e. inkjet printing of conductive polymer on tattoo paper. The composition and thickness of the transfer paper and conductive polymer have been optimized to achieve an even better connection between the tattoo electrode and the skin and to record the EEG signals with maximum quality, because: “Brain waves are in the low frequency range and EEG signals have a very low amplitude. They are much more difficult to capture in high quality than EMG or ECG signals,” explains Laura Ferrari, who worked on this project during her PhD and is now a postdoc researcher in France. Tests under real clinical conditions have shown that the EEG measurement with the optimized tattoos is as successful as with conventional EEG electrodes. “Due to inkjet printing and the commercially available substrates, however, our tattoos are significantly less expensive than current EEG electrodes and also offer more advantages in terms of wearing comfort and long-term measurements in direct comparison,” explained Dr. Greco.
The new tattoo electrodes are the very first dry electrode type that is suitable for long-term EEG measurements and at the same time compatible with magneto-encephalography (MEG). MEG is a well-established method for monitoring brain activity, for which so far only so-called “wet electrodes” can be used. Such electrodes work on the basis of electrolyte, gel or an electrode paste, and thus dry out quickly and are unsuitable for long-term measurements. The new generation of tattoo electrodes consists exclusively of conductive polymers, i.e. it does not contain any metals which can be problematic for MEG examinations, and is printed exclusively with inkjet. “With our method, we produce the perfect MEG-compatible electrode while reducing costs and production time,” says Greco happily. The TU Graz researcher is currently spinning ideas on how this technology can be used in clinics and in neuroengineering as well as in the field of brain computer interfaces.”
Flexible Electrode for Medical Applications Made on an Inkjet Printed Tattoo
by Siobhan Treacy / 27 March 2018
“In diagnostic methods like an electrocardiogram (ECG) or electromyography (EMG), typically gel electrodes are what doctors use to transmit electric impulses from a patient’s heart or muscle. The electrodes can be difficult to work with. Electrodes are stiff, uncomfortable and can restrict the patient’s movements. In addition, the gel that is used on the electrodes dries quickly so the doctors have to work quickly to get a measurement.
Researchers from Instituto Italiano di Tecnologia (IIT) Pontedera, Università delgi Studi in Milan, Scuola Superiore Sant Anna in Pisa and the Institute of Solid State Physics at TU Graz have developed a new method that can raise transmission of electrical impulses with tattooed electrodes. The new method uses polymers that are printed on a commercial, temporary tattoo paper that produces single or multiple electrode arrangements. External connections that are needed to transmit signals are already put into the tattoo at the printing process. The tattoo electrodes are placed on the skin much like the temporary tattoos.
The electrodes are incredibly thin, measuring at less than one micrometer. This means that the electrodes can be adapted perfectly to human skin, even though it is not a flat surface. The electrode tattoo can be applied where traditional electrodes cannot. “With this method, we have managed to take a big step forward in further developing epidermal electronics. We are on a direct road to making an extremely economical and simple as well as versatile applicable system which has enormous market potential,” said Francesco Greco, a materials scientist at the Institute of Solid State Physics of TU Graz.
There is nothing that can affect the reading of the electrode tattoo. If there is a hair in the way of the electrode, the conductivity of the electrode will not be affected. If the electrode needs to be applied for the long term, then doctors don’t have to worry about hair growth affecting the readings. The researchers tested the tattoo electrode for three days and found no issues. The team could also produce electrodes of different sizes that are shaped specifically for different parts of the body. “We are working on the development of wireless tattoo electrodes with an integrated transistor which would make it possible to both send and receive signals. Not only could we measure impulses using this method, but we could also stimulate body regions in a targeted way,” said Greco.”
Temporary Tattoos Could Make Electronic Telepathy, Telekinesis Possible
by Charles Q. Choi / 2013
“Commanding machines using the brain is no longer the stuff of science fiction. In recent years, brain implants have enabled people to control robotics using only their minds, raising the prospect that one day patients could overcome disabilities using bionic limbs or mechanical exoskeletons. But brain implants are invasive technologies, probably of use only to people in medical need of them. Instead, electrical engineer Todd Coleman at the University of California at San Diego is devising noninvasive means of controlling machines via the mind, techniques virtually everyone might be able to use.
His team is developing wireless flexible electronics one can apply on the forehead just like temporary tattoos to read brain activity. “We want something we can use in the coffee shop to have fun,” Coleman says. The devices are less than 100 microns thick, the average diameter of a human hair. They consist of circuitry embedded in a layer or rubbery polyester that allow them to stretch, bend and wrinkle. They are barely visible when placed on skin, making them easy to conceal from others.
The devices can detect electrical signals linked with brain waves, and incorporate solar cells for power and antennas that allow them to communicate wirelessly or receive energy. Other elements can be added as well, like thermal sensors to monitor skin temperature and light detectors to analyze blood oxygen levels.
Using the electronic tattoos, Coleman and his colleagues have found they can detect brain signals reflective of mental states, such as recognition of familiar images. One application they are now pursuing is monitoring premature babies to detect the onset of seizures that can lead to epilepsy or brain development problems. The devices are now being commercialized for use as consumer, digital health, medical device, and industrial and defense products by startup MC10 in Cambridge, Mass.
In past studies, Coleman’s team found that volunteers could use caps studded with electrodes to remotely control airplanes and flew an unmanned aerial vehicle over cornfields in Illinois. Although the electronic tattoos currently cannot be used to pilot planes, “we’re actively working on that,” Coleman says. These devices can also be put on other parts of the body, such as the throat. When people think about talking, their throat muscles move even if they do not speak, a phenomenon known as subvocalization.
Electronic tattoos placed on the throat could therefore behave as subvocal microphones through which people could communicate silently and wirelessly. “We’ve demonstrated our sensors can pick up the electrical signals of muscle movements in the throat so that people can communicate just with thought,” Coleman says. Electronic tattoos placed over the throat could also pick up signals that would help smartphones with speech recognition, he added.”
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