New Metallic Gel Adds a Fourth Dimension to 3D Printing

Researchers at North Carolina State University have developed a new, electrically conductive metallic gel that can be used with commercial-grade 3D printers. As well as conducting electricity, the novel printing material also reacts to heat as it dries, meaning it can print in a fourth dimension – time. A paper detailing the use of this conductive gel in 3D and 4D printing has been published in the journal Matter.

Learning to print metal

3D printing has opened up a whole new world of possibilities. It is easier than ever for designers to generate and test prototypes of their products, for artists to create custom molds and for educators to build models and dioramas for their audiences.

But 3D printing, at least with the simple machines available for home use, has largely been limited to plastic. Metals can be 3D printed, but the process is far more involved. Now, researchers have developed a new metallic gel that is compatible with conventional printing nozzles at room temperature.

“3D printing has revolutionized manufacturing, but we’re not aware of previous technologies that allowed you to print 3D metal objects at room temperature in a single step,” says Michael Dickey, co-corresponding author of the paper and the Camille and Henry Dreyfus Professor of Chemical and Biomolecular Engineering at North Carolina State University. “This opens the door to manufacturing a wide range of electronic components and devices.”

Creating the gel begins with a solution of micron-scale copper particles suspended in water. After adding in a small amount of liquid metal indium–gallium alloy and some thorough mixing, the liquid metal and copper particles begin to stick together in such a way that they form a metallic gel “network” within the aqueous solution.

“This gel-like consistency is important, because it means you have a fairly uniform distribution of copper particles throughout the material,” Dickey says. “This does two things. First, it means the network of particles connect to form electrical pathways. And second, it means that the copper particles aren’t settling out of solution and clogging the printer.”

Metal spider demonstrates the power of 4D printing

Because of its metal-particles-in-suspension design, the new gel also has some interesting properties that can be exploited to print more novel structures.

As the researchers report in their new paper, applying heat to a gel-printed object while it dries creates a significant amount of stress inside the material. The stress caused by this accelerated water evaporation is large enough that it can cause additional changes in shape over time – effectively introducing time as a fourth dimension in the printing process.

“Ultimately, this sort of four-dimensional printing – the traditional three dimensions, plus time – is one more tool that can be used to create structures with the desired dimensions,” Dickey says. “But what we find most exciting about this material is its conductivity.”

“Because the printed objects end up being as much as 97.5% metal, they are highly conductive. It’s obviously not as conductive as conventional copper wire, but it’s impossible to 3D print copper wire at room temperature. And what we’ve developed is far more conductive than anything else that can be printed. We’re pretty excited about the applications here.”

To demonstrate this, the researchers used their metallic gel to print a “conductive spider”. Printed on a flat surface, the researchers saw the spider slowly begin to lift and assemble itself as it dried under heating. The resulting structure retained its conductivity, being able to light up two LED “eyes” when connected to a 6-volt battery.

“We’re open to working with industry partners to explore potential applications, and are always happy to talk with potential collaborators about future directions for research,” Dickey adds.

Reference: Xing R, Yang J, et al. Metallic gels for conductive 3D and 4D printing. Matter. 2023. doi: 10.1016/j.matt.2023.06.015

This article is a rework of a press release issued by North Carolina State University. Material has been edited for length and content.