Rayleigh-Plateau 3D printing of mechanical metamaterials for elastic bandgap tuning

In the last few years, the interest on mechanical metamaterials has increased significantly. This interest has pushed the usual manufacturing boundaries to simple, fast and accurate new techniques wich harness simple fluid mechanical properties towards robust mechanical ones. In our work we present mechanical metamaterial 3D printer ruled by the Rayleigh-Plateau Instability of a thread of a viscous fluid encased within an immiscible curing elastomer solution. This method allows spherical inclusions of a fluid to be placed periodically within an elastic matrix thereby creating a periodic elastic material creating tailored elastic bandgaps by changing a handful of control parameters. The procedure allows a very simple and fast development of mechanical metamaterial samples, with a large application range. To wit, we present a 4D mechanic metamaterials by using a ferrofluid as the inclusion's material, which can be actuated by a constant or time-dependent external magnetic field, allowing the tuning of both the dispersion relation of elastic waves as well as their amplification and damping.