What if markings on your skin could unlock your phone or get you access to entrance doors? And what if they could also measure your blood pressure or hydration level constantly in the background only alerting you in case of values out of the normal range? Digital tattoos could act as minilabs rendering our skin an interactive display and making healthcare more invisible at the same time. Here’s our summary of the latest trends and research efforts to make it happen.

Our bodies are the next frontier for technology

In the course of the development of medical devices, a general trend has emerged: tools are getting more miniaturized, digitised and connected than ever. While in the past, the ultimate goal of medical instruments was to somehow measure health parameters or to somehow record measurements, currently, the question is how to measure more accurately, more easily and simply by using aptly designed means.

However, the triumphant march of health sensors and wearables does not stop at creating ever tinier, more and more streamlined smartwatches or clothing clips – such as the Lumo Run -, the next frontier for technological advancement definitely takes us the closest to the human body that we have ever been. Seamless, thin and unrecognizable sensors made of flexible materials appear first interwoven with our clothes, then on our skin as digital tattoos, in our bellies as digestibles or in our blood vessels as nanobots.

In sports medicine, there are already digitised garments for improving performance. For example, HexoSkin developed a shirt with sensors woven into it that measures heart rate, breathing, counts steps taken, pace, and calories burned. Moreover, researchers working in nanotechnology are experimenting with exceptionally micro-sized – smaller than a millimeter – robots that literally swim through your bodily fluids; and the FDA approved the first digital pill with a digital ingestion tracking system in 2017. Now, let’s see how digital tattoos want to crawl onto our skins.

digital tattoos
Source: www.wtvox.com

What do we call a digital tattoo?

With the development in 3D printing as well as circuit printing technologies, flexible electronics and materials, applying the so-called digital tattoos or electronic tattoos on the skin for some days or even weeks became possible. Some researchers use gold nanorods, others graphene or various polymers with rubber backing to apply the tattoo on the skin without causing irritation. Certain experts believe that these skin patches or tattoos are only the beginning, and in the future, other skin techniques such as henna, tanning, and makeup will also be tested.

These flexible, waterproof materials impervious to stretching and twisting coupled with tiny electrodes are able to record and transmit information about the wearer to smartphones or other connected devices. That’s why fantasies about digital tattoos unlocking tablets, opening doors or supporting border crossing took off. In 2014, Motorola Corporation launched the digital tattoo for the identification of its Moto X handset. The digital tattoo sticker unlocks the smartphone without the need for any passwords or patterns.

As the tiny patches can measure electrophysiological parameters, they could allow healthcare experts to monitor and diagnose critical health conditions such as heart arrhythmia, heart activities of premature babies, sleep disorders and brain activities noninvasively. Moreover, by tracking vital signs 24 hours a day without the need for a charger, it is especially suited for following patients with high risks of stroke, for example. The digital tattoo could send alerts to medical systems, it might call the ambulance and transmit pertinent data, too.

In the future, tiny multifaceted patches might as well track muscle movements around speech when applied to the throat, potentially turning the tattoos into half of a wireless hands-free kit. Since you don’t actually have to speak out loud, it could pick up sub-vocal commands, too. Alternatively, the figurative or non-figurative, well-designed electronic tattoos can even track brain signals with enough accuracy to control a computer. However, that’s still the distant future. Anyhow, here are some projects and research efforts which already made digital tattoos happen.

digital tattoos
Source: www.emergeinteractive.com

The most advanced digital tattoos to date

1. Wearable glucose monitoring with enzymes

Nanoengineers at the University of California, San Diego have been working on these technologies for quite a while. It started when they developed a temporary tattoo that both extracts and measures the level of glucose in the fluid in between skin cells. The flexible device consists of carefully patterned electrodes printed on temporary tattoo paper. The two electrodes apply a tiny amount of electrical current that forces glucose molecules that reside below the skin to rise to the surface, allowing for the measurement of blood sugar. In the spring of 2018, the research center started a clinical trial with 50 adults, aged 18 to 75, with either type 1 or 2 diabetes or diabetes due to other causes. According to the latest reports, the trials are still running, but they might have come close to their finish.

But the University of California San Diego also has a more recent announcement, dubbed ‘Lab on the skin’, a wearable device capable of monitoring not only glucose but also alcohol and lactate levels. The device is about the size of a stack of six quarters. It is applied to the skin through a Velcro-like patch of microscopic needles, or microneedles, that are each about one-fifth the width of a human hair. Wearing the device is not painful—the microneedles barely penetrate the surface of the skin to sense biomolecules in interstitial fluid, which is the fluid surrounding the cells beneath the skin. The device can be worn on the upper arm and it sends data wirelessly to a custom smartphone app.

‘Lab on the skin’ patch from the UCSD team. Image source

The wearable consists of a disposable microneedle patch connected to a case of electronics. Different enzymes on the tips of the microneedles react with glucose, alcohol and lactate in interstitial fluid. The wearable was tested on five volunteers, who wore the device on their upper arms while exercising, eating and drinking, and the readings closely matched the control values, measured by standard lab equipment.

1.2 Non-enzyme glucose monitoring from sweat

Another route taken by the research team of Penn State University aims to measure glucose levels from sweat. The low-cost sensor consists of laser-induced graphene and a nickel-gold alloy that can detect very low levels of glucose in sweat without the use of enzymes. The sensor contains a microfluidic chamber into which sweat is drawn, and then an alkaline solution reacts with the glucose in the sweat, causing a reaction in the alloy and a substantial electrical signal.

The wearable by the Penn State University Research Team. Image source

The technology involves drawing sweat into a microfluidic chamber, where glucose reacts with an alkaline solution to form a compound that can react with a nickel-gold alloy present in the device. This reaction causes an electrical signal that can indicate the amount of glucose present in the sweat.

So far, the researchers have tested it with some volunteers and found that it could successfully track changes in blood glucose before and after a meal.

“We want to work with physicians and other health care providers to see how we can apply this technology for daily monitoring of a patient,” said Huanyu Cheng, a researcher involved in the study in the press release.

South Korean researchers have created something similar a while before, also with the help of graphene. Seoul National University assistant professor Dae-Hyeong Kim and a team of researchers manufactured specific sensors that can detect your temperature and the pH/chemical composition of the sweat of people with e.g. type II diabetes. It then beams the data it collects to an accompanying smartphone app. If the system infers that the wearers need medicine based on the state of their sweat, the app computes the amount of necessary medication. The patch’s microneedle array then injects the right amount into the body.

digital tattoos
Image source

 2. MC10

The Cambridge, Massachusetts-based company has been the best-known enterprise specialised in the advancement of digital tattoos in the last ten years. John Rogers and his research team gave the groundwork for the revolutionary technology in stretchable electronics, on which MC10’s operation is based. The company tirelessly develops silicon devices thinned to a fraction of the width of a human hair, uses stretchable metallic interconnects, and elastic rubberlike polymers to form complete powered systems that sense, measure, analyse, and communicate information.

In 2016, MC10 marketed its BioStampRC sensor, a waterproof, band-aid-like patch that sticks to the skin and monitors movement, muscle performance or heart activity. The tiny wearable even has a Bluetooth radio and a miniature battery.

digital tattoos
Image source

3. Graphene-based electronic tattoo

A group of researchers based at the University of Texas created graphene-based, almost transparent tattoos. While researchers usually use gold in electronic components, here, they applied graphene – a more conductive, hundreds of times thinner material allowing to naturally wrinkle with the skin.

Due to graphene’s unique electronic properties, these patches work like wearable electronic devices, enabling biometric uses, such as monitoring the electrical activity of the brain, heart, and muscles. The tattoos would even allow the wearer to directly interact with machines. These tattoos offer complete functionality for several days but can be removed simply with a piece of adhesive tape. It is hoped that as the cost of graphene falls, such tattoos will become affordable for medical use.

4. Dermal Abyss

Researchers at Harvard and the Massachusetts Institute of Technology developed colour-changing digital tattoos within the project entitled Dermal Abyss, a bunch of biosensitive inks changing colours parallel how changes in your body occur. The inks can measure the concentration of glucose, sodium, and pH in the skin’s interstitial fluid, which surrounds cells.

The researchers have so far created a green ink that intensifies as the wearer’s sodium levels rise, which is often a sign of dehydration. Another green ink turns brown as glucose levels rise, which could be used by people with diabetes for monitoring their condition in the future. In early tests, pink inks turned blue as pH levels increased, but researchers are still testing various new inks for future use.

Digital tattoos will help make healthcare seamless and invisible

Can you imagine a dolphin-shaped digital tattoo measuring your heart rate on your ankle? And what about a glucose monitor forming a sailing boat on your belly? The Medical Futurist recommends you get used to this thought as the latest trend in the health sensor and wearable market shows that digital tattoos are the future. These seamless, thin and unrecognizable sensors could replace smartwatches or wrist-worn wearables as they won’t need batteries – they will get the necessary energy through electrophysiological processes -, and they will be more accurate due to constant skin contact.

It is an astonishingly hopeful phenomenon for shifting from reactive “sick care” to preventive as well as predictive health. These tiny digital tattoos could immediately signal if a measurement is out of range or significantly differs from the average – and the user or the doctor could promptly respond to it.

In other industries that already works. Isn’t it ridiculous and terrifying at the same time that we bring our cars to the mechanic at the moment that it indicates a problem, however, we don’t do that with our own signals? We don’t deal with them, or we don’t even know there was a sign. The Medical Futurist hopes that the beautifully designed digital tattoos will change the situation soon.

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