Engineers at the University of California, San Diego have developed an innovative 3D printing method that utilizes a polymer ink and a salt water solution to create solid structures, offering a more sustainable and environmentally friendly approach to materials manufacturing. Published in Nature Communications, this breakthrough process simplifies 3D printing and reduces its environmental impact.

The method employs a liquid polymer solution known as poly(N-isopropylacrylamide), or PNIPAM. When extruded through a needle into a calcium chloride salt solution, the PNIPAM ink instantly solidifies upon contact. This rapid solidification is driven by the salting-out effect, where salt ions attract water molecules from the polymer solution. This attraction causes the hydrophobic polymer chains in the PNIPAM ink to aggregate densely, forming a solid structure.

“This process is conducted under ambient conditions without the need for additional steps, specialized equipment, toxic chemicals, heat, or pressure,” explained Jinhye Bae, a professor in the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering at the UC San Diego Jacobs School of Engineering and senior author of the study.

Traditional methods for solidifying polymers often require energy-intensive steps and harsh substances. In contrast, this new process uses the simple interaction between PNIPAM and salt water at room temperature to achieve the same result without the environmental cost. Moreover, the process is reversible. The solid structures can be easily dissolved in fresh water, reverting to their liquid form, allowing the PNIPAM ink to be reused for further printing. “This offers a simple and environmentally friendly approach to recycling polymer materials,” said Bae.

To demonstrate the versatility of their method, the researchers printed structures from PNIPAM inks containing other materials. For example, they successfully printed an electrical circuit using an ink made of PNIPAM mixed with carbon nanotubes, which powered a light bulb. This printed circuit could also be dissolved in fresh water, showcasing the potential for creating water-soluble and recyclable electronic components.

Bae and her team envision that this simple and reversible 3D printing technique could significantly contribute to the development of environmentally friendly polymer manufacturing technologies.

By Impact Lab