3D printing that is sustainable and reversible

This innovative approach, detailed in a study published in Nature Communications, utilises a polymer ink combined with a saltwater solution to create solid structures, offering a more sustainable alternative for materials manufacturing.

The core of this method is a liquid polymer solution called 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 process allows researchers to print solid structures with remarkable ease.

The rapid solidification is driven by a process known as the salting-out effect. In this phenomenon, salt ions attract water molecules away from the polymer solution, leading the hydrophobic polymer chains in the PNIPAM ink to densely aggregate and form a solid.

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

Traditional methods of solidifying polymers often involve energy-intensive procedures and the use of harsh chemicals. In contrast, this new technique leverages the simple interaction between PNIPAM and saltwater at room temperature to achieve the same outcome with a lower environmental impact.

Moreover, the process is reversible. The solid structures created can easily be dissolved in fresh water, returning the PNIPAM ink to its liquid state, allowing for reuse in future printing. “This provides a straightforward and eco-friendly method for recycling polymer materials,” Bae added.

To showcase the versatility of their method, the researchers printed various structures using PNIPAM inks mixed with other materials. For instance, they successfully printed an electrical circuit using an ink composed of PNIPAM and carbon nanotubes, which was able to power a light bulb. This circuit could also be dissolved in fresh water, demonstrating the potential for creating water-soluble and recyclable electronic components.

Bae and her team believe that this simple and reversible 3D printing technique could play a significant role in the future of environmentally sustainable polymer manufacturing.

Image credit: Donghwan Ji