3D Printing Water-In-Water

One of the hallmarks of biology is the ability to compartmentalize and coordinate system functions, which has been difficult to reproduce even in the most sophisticated synthetic mimics. We show how to fabricate flexible, 3D structured water-in-water systems embodying both principles by using the interface of immiscible polymer solutions to generate tubular membranes held in shape by an elastic polyanion-polycation complex. Using a 3D printer, the length, shape, and diameter of printed tubules water-in-water systems can be controlled. We demonstrate directional diffusion and separation of ionic species confined to each liquid phase according to their preferential affinity for the polyelectrolyte in the opposite phase. By coupling compartmentalization with flow-driven directed material transport, continuous molecular separation can be achieved in such water-in-water systems. A layer-by-layer strategy is also used to further strengthen and functionalize the flexible tubules, significantly extending the potential applications of these all-aqueous 3D printed tubular systems.