At Graphene Week 2019 in Helsinki last September, I spoke with three Graphene Flagship scientists and experts in flexible electronics: Maria Smolander and Henrik Sandberg from Graphene Flagship partner VTT, Finland, and Daniel Neumaier from Graphene Flagship partner AMO, Germany. We spoke about how wearable electronics have the potential to shape the future of personal devices.
Graphene could play an integral role in getting this fringe technology into the hands of consumers, as its astounding physical properties continue to find their way into new kinds of applications. This is the focus of WearGraph: one of the Graphene Flagship Spearhead projects designed to bring graphene-based wearables to the market. Smolander, Sandberg and Neumaier stressed the benefits of incorporating graphene into these designs – as well as the challenges waiting in store for scientists willing to try.
Ten years ago, not long after the release of the original iPhone, you'd struggle to find someone walking down the street with a smartphone in their pocket. But now, they are everywhere, and they are tightly woven into the fabric of almost every aspect of modern life. In a similar way, smartwatches have broken into the market, and every day, new types of wearable technologies pop up – Google Glass and Fitbit being two prominent recent examples. "These days, everyone is expected to wear some kind of device," Sandberg says. "However, a lot of people still find them a bit too bulky, and not very durable. Using graphene, we could make something that's really wearable and unobtrusive." He believes that a new generation of smaller, more subtle wearable electronics could have a big impact on the consumer market.
But current technology can only go so far. Most of the materials used in electronics today are tough and brittle, meaning they would be uncomfortable to wear and easy to break, and they aren't machine washable. Furthermore, circuits often contain metal components that may be harmful to the human body, like lead and cobalt – which with increasing demand are becoming more and more scarce, and may need to be extracted from deposits in dangerous regions and conflict zones. Silicon and other currently available materials aren't a good fit for electronics woven into textiles or directly worn on the skin. These novel e-textiles could therefore find many uses in health and fitness monitoring, location tracking, virtual reality, and beyond.
Tailoring graphene's potential
Scientists need a new material that can cope with these demands, and graphene fits the bill. "It's the thinnest material, making it an excellent choice for new sensing devices. It's also a more sustainable solution, as graphene-based circuits can be printed without requiring rare or precious metals," comments Smolander. Furthermore, despite its thinness, it is more flexible and durable than any other material on the market today.
"One of the best things about graphene is that you can use it to make stretchable structures that are also really strong, with great electronic properties. This gives it fantastic potential for wearables," Smolander continues. Because of these outstanding properties, she dreams that one of the first wearable graphene technologies to hit the market will be biosensors worn directly on our skin. "There are a lot of opportunities for graphene wearables to be used in diagnostic products for well-being and health, like blood pressure and heart rate monitoring," she says. Neumaier elaborates: "The sensors could even have wireless connections and be paired to our mobile devices, so the measured parameters could be read out with an app. This could warn patients or doctors when something isn't right, or provide immediate feedback on training sessions."
Sandberg agrees, and talks about their endeavours at VTT to incorporate graphene into new device prototypes. "Our effort is two-fold: we do solution processing with graphene platelets, and we do chemical vapour deposition (CVD) to make high-quality graphene for higher-end devices. Both are important for wearables – the first for sensors, and the second for high-performance electronics," he explains.
In fact, Sandberg says that there are already prototypes in the pipeline that should be market-ready in five to ten years. He showcased two of their recent developments at VTT – a biocompatible, screen-printed radio frequency identification (RFID) tag for location tracking using radio waves, and a conductive graphene-based ink printed on stretchable fabric for flexible electronic circuits.
When asked about the potential impact of technology like this on real-world applications, Neumaier talks excitedly: "Flexible sensing devices are important because they connect electronics with the outside world. For the Internet of Things, and to enhance mobile communication technology, this is going to be invaluable." We are entering an age with an unprecedented level of connectivity between people and devices – and the more subtle and less intrusive these devices are, the better.
Neumaier continues, saying that RFID electronics are his favourite area of research. "This is the next big thing for communications, and graphene has most potential in wearable electronics," he comments. A flexible graphene-based RFID tag could be easily integrated into clothing or worn on the skin, and used alongside a GPS app to keep track of young children. When paired with biosensors, it could help locate mountaineers and hikers in dangerous regions and monitor their vital signs. It could even revolutionise motion capture and virtual reality gaming, as RFID tags worn on the skin could precisely track limb movements while sensors gather data on heart rate and perspiration.
But can the Graphene Flagship thread the needle?
There are still a few kinks to iron out before designs like this can be fully commercialised. Smolander, Sandberg and Neumaier all agree that the biggest challenge will be to develop a reliable and consistent process to make high-quality graphene on a large scale. "This is the most important thing to bear in mind," Neumaier says. "It's not enough to have perfect performance in the lab for a single device – you need to be able to reproduce it again and again, for a low cost." Researchers will also need to develop a new method to integrate graphene into existing screen printing and textile manufacturing processes.
"Another big question, when it comes to wearable electronics in textiles, is that they need to be washable," remarks Sandberg. He explains that normal circuitry would be easily damaged by regular washing, and would need special protection to be water resistant. "This is something we're going to address in the next phase of the Graphene Flagship, where we'll venture much further into the intricacies of encapsulating and shielding the active structures, so they can be protected during washing cycles."
On top of that, any wearable device will need to be powered somehow. "The devices could use a tiny, unintrusive battery, or have some sort of energy-harvesting functionality to avoid requiring a separate power source," Neumaier explains. It's very possible that the devices could be powered using body heat, whereby differences in temperature can be used to generate a current – or using the movement of the wearer's arm, like in kinetic watches – the first demonstrations of which date back as early as the 18th century.
The devices will also need to be completely safe, with no harmful effects on the human body after prolonged skin contact. Tests into the biosafety of graphene and related materials are ongoing, but the results so far look promising. "It really makes a difference if the raw materials are biofriendly – especially if you're printing large areas of graphene inks onto clothing," comments Sandberg. The screen-printed RFID antennae made by Sandberg and Smolander at VTT are great examples of this. "The RFID antennae we print are completely biocompatible, and the whole thing is disposable," he continues.
When asked about the most promising developments on the horizon, Smolander answered with certainty that biofriendly 'skin patch'-type wearables for health and fitness monitoring will be the first to emerge. Sandberg and Neumaier both agree that, for now, this will be the main scope of wearable technologies enabled by graphene. But the future is bright and broad, with huge potential in other areas too. One thing is certain: we are barreling towards a new generation of personal electronic devices, and they will be more entwined with our health, our hobbies and our daily routines than ever before.