New 3D printer ink makes recyclable electric circuits without heat or light

Scientists from the U.S. and Korea have developed an innovative new ink for 3D printing that can build easy-to-recycle electric circuits and other structures without the need for heat, light, or toxic chemicals. Their research was recently published in Nature Communications, supported by the National Science Foundation in the U.S. and the National Research Foundation of Korea.

In most forms of 3D printing, the raw material requires a combination of heat, pressure, and light to become a rigid structure. In FDM printing, the filament must be melted and then cooled into its formed shape. With resin 3D printing, ultraviolet light is applied to the liquid material to harden and cure it.

In this new approach, the research team uses a polymer called poly(N-isopropylacrylamide), or PNIPAM. PNIPAM is non-toxic and used by the pharmaceutical industry for drug delivery systems. In 3D printing, all that’s needed to solidify the PNIPAM is salt water at room temperature. 

The researchers extruded the polymer using a commercial healthcare-grade 3D printer to pump the material into mixtures of calcium chloride and water. It solidified immediately into neat, intricate structures capable of conducting electricity.

The team used the method to make an electric circuit mixed with carbon nanotubes, which then powered a small light bulb. Recycling the material was accomplished by dissolving the structures in fresh water and then evaporating the water in an oven at 158º F (70º C).

Senior author Professor Jinhye Bae from the University of California, San Diego, pointed out that the method “is all done under ambient conditions, with no need for additional steps, specialized equipment, toxic chemicals, heat or pressure.” Since the polymer is easily reverted to its raw state, structures made with PNIPAM could be useful for disposable electronics, robotic components, and prototyping.

“This offers a simple and environmentally friendly approach to recycle polymer materials,” Bae added. Given the increasing need to deal with e-waste, the ability to recycle electrical circuits from devices so easily could be a real boon to being more environmentally friendly.