Research Highlights

In a study that broadens the potential of three-dimensional (3D) printing, scientists have modified a commercial 3D printer to print a liquid within another liquid for the first time¹. This offers the opportunity to create new kinds of materials that could find a wide range of applications.

Until now, all printing has used either a solid or a liquid that solidifies on cooling. For example, printing a photo requires a solid paper-based substrate, while 3D printers often use liquid polymers that become solid on cooling.

Now, by three-dimensionally printing water within oil, a team led by Thomas Russell of the AIMR at Tohoku University has printed stable structures consisting of a liquid in another liquid. They added gold nanoparticles to the water and a surfactant to the oil. The nanoparticles and surfactant are attracted to each other, but, because of energy considerations, neither wants to leave the medium it is in. Consequently, they link up across the interface between the water and oil, forming a nanoparticle−surfactant layer that straddles this interface. Despite being only 20 nanometers thick, this layer is stable like a solid, but can readily deform.

“Conventional 3D printers produce solid materials like plastics, metals, hydrogels and even biological matter such as cells and organs,” says first author Joe Forth at the Lawrence Berkeley National Laboratory, USA. “All these things are interesting and useful, but they’re based on old paradigms. What’s exciting about our technique is that it allows us to make a completely new type of material.”

The researchers automated the process by modifying a commercial 3D printer. “We did everything on the cheap,” recalls Forth. “We bought an entry-level 3D printer for printing plastics. We ripped out the printheads and replaced them with a syringe pump and some microfluidics tubing. If I could start over, I’d do it all differently, but what we did worked extremely well, given how little we knew about printing when we started.”

The new method opens a lot of possibilities. Since liquids can flow through these structures, they could be used in all-liquid microfluidic devices. Also, the printed aqueous shapes are promising as containers for living matter that can exchange chemicals across the oil−water interface.

“What’s really interesting will be to see what the global scientific community can think of to do with a material like this, which combines soft-matter physics and nanotech to produce a material that’s unlike anything else out there,” says Forth.

The team is using their printed liquids to explore the mechanical properties of two-dimensional materials. They will also investigate how the materials behave when a magnetic field is applied to them.