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The locations where we place these thin, flexible, stretchable displays won’t be limited to the skin; the displays will be equally easy to apply to the curved surfaces of clothes and other objects. Their color, brightness, or patterns could change in response to your activity or in reaction to the world around you.
Stretchy, thin, bright, water-resistant displays that stick to skin without adhesives are going to start appearing in coming years. They’ll be on the hands and arms of not just the elderly but also on those of athletes, travelers, hipsters, and early adopters. They’re going to unobtrusively update runners and cyclists on heart rate and hydration needs, ultraviolet exposure, and even show maps of the route ahead.
For the elderly or infirm, these displays could show electrocardiogram waveforms, collecting the data from wireless electrodes placed elsewhere on the body. They could also alert someone who is hard of hearing to an incoming phone call or a knock on the door.
A skin display isn’t much use unless it has interesting data to communicate to its wearer. To gather this data, we turn to skin-conforming sensors, capable of detecting signals from the heart, brain, skin, muscles, and other organs.
Displays based on organic LEDs (OLEDs) have no such limitation. These OLED displays are indeed printable onto thin, flexible substrates. Today’s rollable displays take advantage of that capability. To date, however, no one has yet commercialized an OLED display that can stretch and bend in multiple directions, although Samsung has reportedly been working on one. In our laboratory, we did produce a prototype low-resolution OLED display. Still, it will take researchers a considerable amount of time to develop a stretchy, long-lasting material that can also be used to protect devices against oxygen and water vapor.
They’ll be used to send secret messages between friends and lovers. The fashion-forward will undoubtedly flash messages and vital stats at each other at parties and festivals. Such a display might even share emotional cues with observers, suggesting that you are interested, anxious, available, or excited. Depending on the setting, it might foster friendship, deeper communication, or splendid isolation.
As she reaches for her teacup, the square lights up with a message: “TAKE YOUR BLOOD PRESSURE MEDICINE.” She smiles, remembering how she used to struggle and often fail to remember, even though her smartphone had been programmed to send her such alerts. But now, thanks to that business-card-size patch on her hand, she hasn’t missed a single dose. Indeed, her blood pressure value, which she can now see on the display, is well within a healthy range.
To make this stretchable display, we start with a very thin plastic substrate. We then use screen printing to define the wiring that connects the pixels into a circuit. For this wiring, we use silver paste—a resin containing silver flakes. When dry, this silver paste is elastic, conducting electricity even as it expands and contracts.