Programming spatially-selective droplet motion using metamaterials

Motion control of droplets has generated much attention for its application to microfluidics, where precisely controlling small fluid volumes facilitates a variety of chemical and biological micro-processes. Mechanical vibrations have been used to induce controllable depinning, and the activation of a variety of drop-motion regimes. However, existing vibration-based strategies generate a homogeneous landscape of vibrations -- drops behave the same regardless of their location on a substrate – and therefore lack any tunability or spatial-selectivity. On the other hand, elastic metamaterials provide a framework for spatially and spectrally selective drop motion due to their ability to generate bandgaps – frequency intervals where vibrations are greatly attenuated. In this work, we experimentally demonstrate a variety of droplet motion capabilities on the surface of a vibrating metaplate endowed with resonant stubs. Furthermore, the LEGO® component-based framework used allows us to demonstrate on-demand tuning of the spectral and spatial selectivity of the metaplate. This work begins to explore the broader application of elastic metamaterials in a context where their signature wave- control capabilities are not the end goal, but rather a tool used to enable complex multi-physical effects.