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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. 

Topological states of matter, first discovered in quantum systems, have opened new avenues for wave manipulation beyond the quantum realm. In elastic media, realizing these topological effects requires identifying lattices that support the corresponding topological bands. However, among the vast number of theoretically predicted topological states, only a small fraction has been physically realized. To close this gap, we present a strategy capable of systematically and efficiently discovering metamaterials with desired topological state. Our approach builds on topological quantum chemistry, which systematically classifies topological states by analyzing symmetry properties at selected wavevectors. Because this method condenses the topological character into mathematical information at a small set of wavevectors, it encodes a clear and computationally efficient objective for topology optimization algorithms. We demonstrate that, for certain lattice symmetries, this classification can be further reduced to intuitive morphological features of the phonon band structure. By incorporating these band morphology constraints into topology optimization algorithms and further fabricating obtained designs, we enable the automated discovery and physical realization of metamaterials with targeted topological properties. This methodology establishes a paradigm for engineering topological elastic lattices on demand, addressing the bottleneck in material realization and paving the way for a comprehensive database of topological metamaterial configurations. 

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. 

The concepts of origami and kirigami have often been presented separately. Here, we put forth a synergistic approach—the folded kirigami—in which kirigami assemblies are complemented by means of folding, typical of origami patterns. Besides the emerging patterns themselves, the synergistic approach also leads to topological mechanical metamaterials. While kirigami metamaterials have been fabricated by various methods, such as 3D printing, cutting, casting, and assemblage of building blocks, the “folded kirigami” claim their distinctive properties from the universal folding protocols. For a target kirigami pattern, we design an extended high-genus pattern with appropriate sets of creases and cuts, and proceed to fold it sequentially to yield the cellular structure of a 2D lattice endowed with finite out-of-plane thickness. The strategy combines two features that are generally mutually exclusive in canonical methods: fabrication involving a single piece of material and realization of nearly ideal intercell hinges. We test the approach against a diverse portfolio of triangular and quadrilateral kirigami configurations. We demonstrate a plethora of emerging metamaterial functionalities, including topological phase-switching reconfigurability between polarized and nonpolarized states in kagome kirigami, and availability of nonreciprocal mechanical response in square-rhombus kirigami.