The Problem of Flexible Electronics in Wearable Device Tattoos

Researchers have created a printable electronic system that allows for a nano-material to flex with skin to create printable electrical tattoos.

We've been hearing about the promise of electronic tattoos for years now. They have the potential to make wearable tech truly wearable, adhering nearly weightlessly to skin and allowing for extraordinary data capturing for medical purposes. But no electronic tattoos, medical or otherwise, have hit the market. What's the holdup?

Medical Wearables: On-the-Go Diagnostics

What's the big deal about medical wearables? Well, imagine a typical visit to a doctor's office.
We've all been there, waiting in a for an appointment. When you finally get to see the doctor, the first five minutes are usually about medical history and background. If they need blood work (such as insulin levels) or some measurement, you may need to come back separately to have those taken (usually due to control measures).

Imagine, however, if you could present the doctor with all your medical data recorded over the past month instantaneously. Most symptomatic evidence would already be in the readings (such as heart rate, sweat chemical content, insulin levels, etc.). Not only would you be able to better inform your doctor about your daily health and reactions to medications, but medical professionals would have a much higher chance of diagnosing illnesses promptly and accurately.

This is what implanted medical equipment may do in the future, where medical data may be constantly gathered from the user, stored in a database, and then analyzed to find potential illnesses that may crop up.

Such devices may also have more immediate advantages that could prevent wearers from harming themselves or others. One classic example is drunk driving where people may mistakenly think they're sober enough to get behind the wheel. Imagine an implanted device that could warn the user when they're over the limit.

Can computers help us with drunk driving as well? Image courtesy of Maxpixel

Printable Circuit Tattoos

Medical monitoring devices have two options when it comes to integrating with the human body: implantation and mounting devices to the outside of the body.

Implantation involves inserting a device into the body. This option allows the use of everyday electronic components (albeit small ones) which makes designing and construction the circuitry relatively easy. However, implanting usually requires the device to be made of a material that is biologically inert. Otherwise, the body may reject the “foreign object”, causing serious medical issues (such as inflammation, immune responses, etc.).

The second option, mounting a medical device to the body on the outside, is a large portion of the wearable industry. However, this option is more limited in what measurements it can take, including heart rate, the chemical composition of sweat, and temperature. While this option is much safer, it also requires wearing a device on one's person.

Researchers from Waseda University in Japan, however, have created a thin, flexible polymer that allows for stretching and is 50 times more flexible than other polymer nanosheets. This material can be directly attached to skin with no negative effects on the circuits that are printed onto the material. The printed circuits can be made using standard inkjet printers at room temperature, eliminating the need for high-temperature curing cycles.

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The printed tattoo on an arm. Image courtesy of Waseda University, Japan

The Problem of Flexibility

So why are wearable circuit tattoos so hard to design? Up to this point, creating wearable electronics has required that most (if not all) of the components on the device be flexible, themselves. This is no easy feat. Yes, researchers have finally succeeded in creating flexible semiconductors, but there are many more challenges for other flexible components.

However, the researchers from Japan have a solution that may make such tattoos more practical. Instead of creating printed flexible components, they have successfully integrated chip components (i.e., very small surface-mount parts including resistors, LEDs, and capacitors) into their flexible membranes.

Instead of making the components flexible, they've made the electrical contacts that keep the components and printed silver on the membrane flexible. These keep the component connected, even when under flexing conditions. This allows for a tattoo to use parts already available to the electronics market.

Circuit Tattoos as Device Controllers

However, Waseda University is not the only contender in the printed tattoo field. Researchers at MIT are creating tattoos that can be used to control devices. MIT is using a simpler approach than Waseda University. They're using gold foil as a conductor, cut to create traces on flexible vinyl material. Their tattoo circuit types fall into three categories:

• Input – Take inputs from the user including touch, temperature, and stress
• Output – The tattoo changes color depending on the surface temperature of the skin
• Communication – This tattoo is used for near field communication

MIT researchers made these tattoos that can perform different functions. Image courtesy of DuoSkin

Summary

Research announcements typically promise a lot but deliver very little in return (until made commercially viable). This membrane, along with the flexible contacts, shows that the future of wearable electronics may not be in revolutionary materials but in finding ways to integrate such technology with already existing technology. Such an attitude in research may help get cooperation’s to fund more projects as the likely hood of a return is significantly increased when the finished product can easily be manufactured and sold.


As we progress into this century, health will become an increasing concern and any company that can produce a medical device that can take vital measurements without causing discomfort or being a nuisance could potentially become one of the richest companies to date.