Read an article the other day, titled Light-emitting tattoo engineered in ScienceDaily. Which was reporting on research done by University College London and Istituto Italiano di Tecnologia (Italian Institute of Technology) (Ultrathin, ultra-comfortable and free-standing, tattooable LEDs – behind paywall).
The new technology out of their research can construct OLEDs, found in TVs, phones, and other displays, and apply them as temporary tattoos. The tattoos will eventually degrade, wash off but while present on the skin they can light up and display information.
According to the Nanowerk news article reporting on the research, (see Light emitting tattoos engineered for the 1st time), the OLEDs are printed onto paper which can then be transferred to skin by the application of water. The picture above shows a number of the OLED tattoos ready for application.
The vision is that OLED tattoos along with other flexible electronics could provide wearable sensors of bio-chemical activity of a person. Such sensors could be used in hospitals and in the home to display dehydration, glucose status, oxygenation, etc. as well as be able to display heart and breath rates. But in order to get to that vision there’s a few steps that are needed.
Flexible, stretchable electronics
There have been a number of articles about creating flexible electronics, (e.g., see A design to improve the resilience and electrical performance thin metal film based electrodes). This article was reporting on research done at the University of Illinois, Champaign-Urbana reported in Nature (behind paywall) but one of the researchers blogged about in NaturePortfolio Devices & Materials (see: An atom-thick interlayer enables the electrical ductility of thin-film metal electrodes).
Flexible electronics can be constructed by creating a thin metal film with the electronics embedded in it placed on top of a flexible substrate. However, when that flexible substrate starts to deform or stretch it induces cracks in the thin metal films which lead to loss of conductivity, or loss of electronics function.
The research cited in the article above showed videos of cracking that takes place during deformation and stretching which would lead to loss of conductivity.
But the researchers at UofI found out that if you place a thin layer of graphene or other 2D sheet of material between the electronic thin film and the flexible substrate, the cracks that eventually happen are much less harmful to electronic conduction or functioning or provide electronic ductability. To add ductablity to an electronic circuit using LEDs the team applied an atomically thin (<1nm), 2D layer of graphene between it and the flexible substrate.
Somehow the graphene provided a mechanical buffer between the flexible substrate and the thin film electronics that allowed the circuits to have much more ductility. It appears that this mechanical buffer changed the type of cracking that occurs on the thin metal film such that they are shorter and more varied in direction rather than straight across and this helped them retain functioning longer than without the
The researchers at U of I actually created a led display that could be bent without failure. See a video of them comparing the thin film vs thin film with 2D substrate.
Moreover, there have been a number of articles discussing new wearable technologies that could be used to sense a persons bio-chemical state. For example, research reported on recently (see Do Sweat It! Wearable Microfluidic Sensor to Measure Lactate Concentration in Real Time) done at the Tokyo University of Science, published in Electochimica Acta (behind paywall) talks about a sweat sensor that can be applied to skin to determine when athletes or others are getting dehydrated.
This sensor uses a micro-fluidics device which printed with electronic ink. Such a device could be manufactured in volume and be readily printed onto surfaces, that could be applied to the skin, anywhere sweat was being produced.
Wearable sensors already surround us. We have watches that can tell our heart rates, walk/running speed/rates, step counts, etc. It doesn’t take much to imagine that most if not all of these could be fabricated on a thin film and with the proper 2D substrate layer be applied as a tattoo to a person while in the hospital but all these sensors have lacked a read out or display up until now. With OLED readouts wearable sensors now have a reasonable display capability.
The sweat sensor above uses microfluidics to do a lactate assay of sweat. The motion sensors in my watch uses MEMs and onboard IMU/GPS to determine speed and direction of movement. Electronic temperature sensors use thermoelectric effects. Blood oxygen sensors use LEDs and light sensors. None of these appears unable to be fabricated, miniaturized and printed on thin films. Adding OLEDs and why do we need a watch anymore?
What seems to be the most glaring omission is gas sensors (although the lactate micro-fluidic sensor is close). If we could somehow miniaturize gas sensors with enough sensitivity to glucose levels, immunological load, specific diseases (COVID19), then maybe there’d be a mass market for such devices, outside of a hospital or smart watch users.
Then with OLED and electronics that can be temporarily tattooed onto a person skin., why couldn’t this be a fashion accessory. I can imagine lot’s of people would have interest in lighting up messages, iconography or other data on their arms, hands, or other areas of a person’s body. I wonder if it could be used to display hair on the top of my head :)?
And of course these OLED-electronics based tattoos are temporary. But if they are all made from electronic ink, it seems to me that such tattoos could be permanently printed (implanted?) onto a persons skin.
Maybe at some future point a permanent OLED-electronics based tattoo could provide an electronic display and input device that could be used in conjunction with a phone or a smart-watch. All it would take would be blue-tooth.
- From the Nanowerk News article Light-emitting tattoo engineered for the first time
- From the NaturePortfolio Devices & Materials engineering blog article An atom-thick interlayer enables the electrical ductility of thin-film metal electrodes