Engineers at the University of California, San Diego, have developed a groundbreaking 3D printing method that could significantly advance sustainable and environmentally friendly manufacturing. The innovative technique, detailed in Nature Communications, utilizes a polymer ink and a saltwater solution to create solid structures with remarkable simplicity.

The process revolves around a liquid polymer solution known as poly(N-isopropylacrylamide), or PNIPAM. When this ink is extruded through a needle into a calcium chloride salt solution, it immediately solidifies upon contact. This rapid transformation is driven by a phenomenon known as the “salting-out effect,” where the salt ions attract water molecules away from the polymer solution. The removal of water causes the hydrophobic polymer chains in the PNIPAM ink to densely aggregate, forming a solid structure.

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

Traditional methods of polymer solidification often require energy-intensive processes and harsh chemicals. In contrast, this new technique leverages the simple interaction between PNIPAM and saltwater at room temperature, achieving similar results with minimal environmental impact. Moreover, the process is reversible: the solid structures can easily be dissolved in fresh water, allowing the PNIPAM ink to return to its liquid state for reuse. “This offers a straightforward and eco-friendly approach to recycling polymer materials,” Bae added.

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

Bae and her team believe that this simple, reversible 3D printing technique could pave the way for more sustainable polymer manufacturing technologies, contributing to a future where material production is both efficient and environmentally responsible.

By Impact Lab