Researchers led by Assistant Professor Michael McAlpine at Princeton University have fabricated the world's first fully 3D printed light-emitting diodes. The process involves interweaving printable electrodes, polymers, and semiconductors, all of which are suspended in solvents to prevent the materials from bleeding into each other, during the printing process. The technology could be used to make smart contact lenses, electronics-embedded implants, and much more.

A paper published in Nano Letters describes the project:

"To date, 3D printing has been limited to specific plastics, passive conductors, and a few biological materials. Here, we show that diverse classes of materials can be 3D printed and fully integrated into device components with active properties. Specifically, we demonstrate the seamless interweaving of five different materials, including (1) emissive semiconducting inorganic nanoparticles, (2) an elastomeric matrix, (3) organic polymers as charge transport layers, (4) solid and liquid metal leads, and (5) a UV-adhesive transparent substrate layer. As a proof of concept for demonstrating the integrated functionality of these materials, we 3D printed quantum dot–based light-emitting diodes (QD-LEDs) that exhibit pure and tunable color emission properties. By further incorporating the 3D scanning of surface topologies, we demonstrate the ability to conformally print devices onto curvilinear surfaces, such as contact lenses."

This is not McAlpine's first foray into the outer limits of 3D printing. Last year, he printed a bionic ear using living cells, a supportive matrix of hydrogel, and conductive ink that formed an electrical coil capable of receiving radio signals, reports MIT Technology Review.

Having conquered conductive ink, McAlpine chose as his next frontier 3D printing semiconducting materials. He and his team had to build their own 3D printer to accommodate multiple materials and to print at micrometer-scale resolutions. The resulting LED is just part of the puzzle of 3D printing active electronics, McAlpine told Technology Review. Notably, he envisions "things that people haven't imagined yet, like 3D structures that could be used in the body," he told Popular Science. Bionic implants that use light to stimulate nerves are one avenue of exploration.

McAlpine is, apparently, well on his way to further expanding the possibilities of 3D printing. He reportedly has printed custom biomedical devices using the technology, which he is now testing on animals, and has started to make complex electronic devices using living cells.