The team from the University of Texas at Austin has invented a liquid electronic tattoo ink for the first time, which doctors can print on patients' scalp as a sensor to measure brain activity. This study can provide a promising alternative solution for monitoring brain waves and diagnosing neurological diseases, which is expected to improve the design of non-invasive brain computer interface devices and expand their application scope. The related paper was published on the 2nd in the journal Cell Biomaterials. The team has been developing an electronic tattoo sensor that can track body signals on the surface of human skin. Applying it to the chest can measure cardiac activity, to the muscles can measure fatigue, and to the armpits can measure sweat composition. In the past, electronic tattoo sensors were typically printed on a thin layer of adhesive material and then transferred to the skin, but this method was only applicable to hairless areas. Designing materials that are compatible with hair and skin has always been a long-term challenge in the development of electronic tattoo sensor technology. Now, the team has designed a liquid ink made of conductive polymer. This ink can flow through hair to reach the scalp, and after drying, it can act as a thin film sensor to collect brain activity through the scalp. Using computer algorithms, the team can identify the location of the EEG electrode on the patient's scalp. Then, use a CNC inkjet printer to spray a thin layer of electronic tattoo ink onto these dots. The process is fast, contactless, and does not cause discomfort to the patient. The team printed ink on the scalp of 5 participants with shorter hair. At the same time, they also attached traditional EEG electrodes next to the electronic tattoo. As a result, it was found that this ink performed equally well in detecting brainwaves, with minimal noise. The gel on the traditional electrode began to dry after 6 hours, and more than one third of the electrodes failed to receive any signal. And the electronic tattoo ink maintained a stable connection for at least 24 hours. The team plans to embed wireless data transmitters in ink in the future to achieve fully wireless EEG processes. People are not unfamiliar with electronic ink technology, and electronic ink screens, mobile phones, wallets, and remote controls are common applications. One major advantage of this technology is its softness, which can be used on various surfaces such as paper, cloth, and even skin. In addition, electronic ink does not require a constant power supply, and its energy consumption is minimal. In fact, electronic ink tattoos were originally just tattoos, and young people used them to "instantly switch patterns" and showcase their "personality". Nowadays, people with a heart are combining it with medical technology, opening up vast application space and becoming a truly "black technology". Magical technology lurks around us and requires creativity to summon it out. (New Society)