Ball point pen creates hand drawn LEDs

Ball point pen creates hand drawn LEDs
Researchers at the Washington University in St. Louis have developed an ink pen that can write custom LEDs on paper, used to draw multicoloured designs on aluminium foil and to create light up sketches.

Developed in the laboratory of researcher Chuan Wang, the ink pens allow writers to handwrite flexible, stretchable optoelectronic devices on materials such as paper, textiles, rubber, plastics and 3D objects. Optoelectronics, used for emitting and detecting light, can bend, fold and flex while maintaining full functionality.

Writing in Nature Photonics, the researchers reported that the fabrication approach can create a custom LED or photodetector without the need for specialised training or bulky equipment.

The ballpoint pen is filled with custom inks made of conductive polymers, metal nanowires and crystalline materials, perovskites, to generate a spectrum of emission colours. By writing multiple layers with the functional inks, a variety of functional devices such as disposable electronics, smart packaging and personalised wearables such as biomedical sensors can be created cheaply and rapidly.

Each layer of the device is designed to b elastic, surviving deformation on flexible surfaces. The layers can be bent, stretched and twisted without impacting device performance, such as LED-infused gloves that can survive repeated grasping and releasing or LEDs on a rubber balloon that can maintain functionality throughout multiple inflation and deflation cycles.

The team previously developed printable inks to create stretchable LEDs with an inkjet printer and modified the technology to work within a ballpoint pen design.

Chuan Wang, associate professor, Washington university in St. Louis, commented: “Handwriting custom devices was a clear next step after the printer. We had the inks already, so it was a natural transition to take the technology we had already developed and modify it to work in regular ballpoint pens where it could be cheap and accessible to all.

“Cheap, customisable LEDs open up opportunities for hands-on education, more vivid textiles like light-up clothing or greeting cards, and smart packaging. 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.”

Photo credit: Junyi Zhao demonstrates using a simple ballpoint pen to write custom LEDs on paper (left). The same pens can be used to draw multicolored designs on aluminum foil (top right) and to create light up sketches (bottom right). (Images courtesy of Wang lab)

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