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Drops on a vibrating substrate can experience a variety of motion regimes, including directional motion and climbing. The key ingredient to elicit these regimes is simultaneously activating the in-plane and out-of-plane degrees of freedom of the substrate with the proper phase difference. This is typically achieved by imposing a prescribed rigid-body motion of the entire substrate. However, this framework is unable to establish different motion conditions in different regions of the substrate, thus lacking the precious spatial selectivity necessary to elicit complex drop control patterns. Challenging this paradigm, we leverage the inherent elasticity of the substrate to provide the required in-plane and out-of-plane modal characteristics and spatial diversity. To this end, we design architected substrates exhibiting a rich landscape of deformation modes, and we exploit their multimodal response to switch between drop motion regimes and select desired spatial patterns, using the excitation frequency as our tuning parameter. 

Motion control of droplets has generated much attention for its application to microfluidics, where precisely controlling small fluid volumes is an imperative requirement. Mechanical vibrations can induce controllable depinning and activation of a variety of drop-motion regimes. However, existing vibration-based strategies establish homogeneous rigid-body dynamics on the entire substrate, thus lacking any form of spatial heterogeneity and tuning. Addressing this limitation, elastic metamaterials provide an ideal platform to achieve spectrally and spatially selective drop-motion control. This capability results from the intrinsic ability of metamaterials to attenuate vibrations in selected frequency bands and regions of an elastic domain. In this work, we experimentally demonstrate a variety of droplet motion capabilities on the surface of a vibrating metaplate endowed with locally resonant stubs. The experiments leverage the design reconfigurability of a LEGO^®component-enabled prototyping platform, which allows us to switch in an agile manner between different configurations of resonators. We use laser vibrometry measurements with high spatial resolution to capture the spatial variability of the metaplate response. Beyond the discipline-specific boundaries, this work begins to illustrate a broader employment of elastic metamaterials in applications where their signature wave control capability is not the end goal, but rather an enabling tool for other more complex multiphysical effects.