The graphite pencil is one of our oldest extant technologies. Dating back to the discovery of a large deposit of solid-form graphite in 1565, in Borrowdale Parish in Cumbria, England, the first graphite writing utensils were sticks cut from blocks of this material and wrapped in string or leather. Since then this universal writing tool has been recording, communicating, sketching, and calculating for any who prefer pencils to pens.
Now an engineering team at the University of Missouri-Columbia has announced their research into a surprising new use for this ancient tool. In a paper first published on July 13, 2020, in the Proceedings of the National Academy of Sciences titled Pencil-paper on-skin electronics, the engineers describe their method for drawing electronic circuits on paper that can be attached to the skin for health monitoring and other purposes (see top photo). Due to unique properties inherent in graphite and the surface of human skin, the team has found that it’s possible to replace the expensive process of printing conventional circuits on flexible polymer substrates with those drawn in pencil on ordinary office copy paper.
The standard #2 graphite pencil is only 7.5 inches, but it can draw a line 35 miles long or write approximately 45,000 words before your sharpener reaches the eraser. Perhaps even more surprising is the fact that the scribed lines can conduct electricity. The skin is the largest organ of the body. It’s an ideal surface for noninvasive monitoring using tactile, biochemical, temperature, and electrophysiological sensors because it’s constantly emitting streams of important information about the processes going on beneath.
The University of Missouri-Columbia researchers discovered that pencils with 93% graphite content could draw circuits on ordinary paper. These could replace the much more expensive biomedical sensors already in use. Zheng Yan, an assistant professor in the University of Missouri-Columbia college of engineering, is one of the paper’s authors. He writes that the “discovery could have broad future applications in home-based, personalized healthcare, education, and remote scientific research such as during the COVID-19 pandemic.”
Along with cost and convenience, there is an environmental advantage. Yan points out that paper decomposes in about a week whereas conventional biosensors have electronic components that don’t easily break down. “The next step,” he explains, “would be to further develop and test the use of the biomedical components, including electrophysiological, temperature, and bio-chemical sensors.”
Beyond the tracings you would make on paper for the circuits you might need, there are also the issues of a power source, how you read its data, and how you wear the thing. A biocompatible spray-on adhesive is used to attach the paper circuit to your arm, side, or wherever. The power can come from a small physical battery glued to one end of the circuit, but there’s a better way. A medical engineering team at CalTech is working on small circuits that can collect and distribute power from perspiration on the skin. These could be incorporated into your drawing. The interface, monitor, and library for the data are on your smartphone. An app would use the device’s Bluetooth to receive, display, and archive the information you’re collecting.
A VARIETY OF DEVICES
Among the numerous technologies that have been swept up and rapidly pushed along by the pandemic, the development of wearable biosensors has taken on an urgency that will propel the makers of elastic-skin sensors, smart watches, and other wearables.
To monitor its players, the NBA issued Oura rings to all to prepare for the eventual return to the courts. The rings constantly monitor pulse and movement, and NTC temperature sensors detect one of the most important symptoms of COVID-19, fever.
Smart watches can measure heart rate, using light to measure pulsing differences in blood flow, body temperature with thermistors, movement with accelerometers, ECGs, blood oxygen levels, and blood pressure. The devices seem only limited by what can be detected at skin level.
If pencil-paper on-skin electronics can be proven to be consistently reliable and accurate, it seems there will now be one more benefit we can derive from the 500-year-old technology that we generally take for granted.