Flexi-Tubes: Liquid-in-Liquid 3D Printing with Emulsion Shells

Liquid-in-liquid 3D printing has gained significant attention with promising applications in many sciences and technological areas. In spite of considerable progress, current approaches face some shortcomings, such as the lack of internal structures and incompatible cargo encapsulation that hinder their utilization in real-world applications. This work presents the spontaneous generation of a new interfacial material with unique layered microemulsion shells that form 3D tube-like structures in a liquid medium, which we demonstrate enables new opportunities in 3D printing. Silica nanoparticles stabilize liquid filaments at Weber numbers two orders of magnitude smaller than previously reported in liquid-liquid systems, expand the oil-water interfacial area rapidly, and arrest the extended emulsion zone in an interconnected configuration with the oil phase. The interfacial skin, separating water and oil, forms in a fraction of a second and is regenerated when damaged. The printed tube is highly stable, for over two months, and is flexible, expanding or shrinking depending on the liquid flow rate inside the tube. The 3D structure is porous, which enables interactions between the printed frame and surrounding media, resembling miniaturized versions of “tube sponges” in the oceans. The technique, depositing an aqueous phase into an oil medium and consequently turning the printed phase into a structured network of emulsion droplets in-situ, opens new possibilities for all-in-liquid printing materials.