Although we're hearing more and more about stretchable electronics, the fabrication of such devices' components is far beyond most people's abilities. Now, however, scientists have created inks that let anyone draw stretchable LEDS onto various surfaces using regular ballpoint pens.
The inks were produced at Missouri's Washington University in St. Louis, by a team led by Assoc. Prof. Chuan Wang and graduate student Junyi Zhao. Previously, the scientists had developed inks that could be used to produce stretchable LEDs via an inkjet printer.
Adapting those inks for use in ballpoint pens involved adjusting their wettability (a liquid's ability to maintain contact with a solid surface) and improving their writability. The researchers also had to boost their ability to be applied to porous or fibrous surfaces – like paper or fabric – without running or mixing with one another.
So, just how do the inks work?
Well, ordinarily, LEDs are put together sort of like sandwiches. They're made up of at least three layers – an anode layer, an emissive layer, and a cathode layer. The three pen inks, which are separately applied one over the other without mixing, perform these roles. One ink incorporates conductive polymers, one contains metal nanowires, and one incorporates crystalline materials known as perovskites.
When connected to an electrical current, this flexible, stretchable combination of inks is capable of emitting a wide range of colors.
"Cheap, customizable LEDs open up opportunities for hands-on education, more vivid textiles like light-up clothing or greeting cards, and smart packaging," said Wang. "One area we’re really excited about is medical applications. Handwritten light emitters and detectors allow more patient-specific flexibility in creating wearable biomedical sensors and bandages that could have photodetectors and infrared LEDs drawn onto them for measuring pulse oximetry or to speed wound healing."
A paper on the research was recently published in the journal Nature Photonics.
