The origin of the idea of moving objects by acoustic vibration can be traced back to 1787, when Ernst Chladni reported the first detailed studies on the aggregation of sand onto nodal lines of a vibrating plate. Since then and to this date, the prevailing view has been that the particle motion out of nodal lines is random, implying uncontrollability. But how random really is the out-of-nodal-lines motion on a Chladni plate? Here we show that the motion is sufficiently regular to be statistically modelled, predicted and controlled. By playing carefully selected musical notes, we can control the position of multiple objects simultaneously and independently using a single acoustic actuator. Our method allows independent trajectory following, pattern transformation and sorting of multiple miniature objects in a wide range of materials, including electronic components, water droplets loaded on solid carriers, plant seeds, candy balls and metal parts.

Droplets slip and bounce on superhydrophobic surfaces, enabling remarkable functions in biology and technology. These surfaces often contain microscopic irregularities in surface texture and chemical composition, which may affect or even govern macroscopic wetting phenomena. However, effective ways to quantify and map microscopic variations of wettability are still missing, because existing contact angle and force-based methods lack sensitivity and spatial resolution. Here, we introduce wetting maps that visualize local variations in wetting through droplet adhesion forces, which correlate with wettability. We develop scanning droplet adhesion microscopy, a technique to obtain wetting maps with spatial resolution down to 10 µm and three orders of magnitude better force sensitivity than current tensiometers. The microscope allows characterization of challenging non-flat surfaces, like the butterfly wing, previously difficult to characterize by contact angle method due to obscured view. Furthermore, the technique reveals wetting heterogeneity of micropillared model surfaces previously assumed to be uniform.

No abstract

No abstract

Surface tension-driven self-alignment is a passive and highly-accurate positioning mechanism that can significantly simplify and enhance the construction of advanced microsystems. After years of research, demonstrations and developments, the surface engineering and manufacturing technology enabling capillary self-alignment has achieved a degree of maturity conducive to a successful transfer to industrial practice. In view of this transition, a broad and accessible review of the physics, material science and applications of capillary self-alignment is presented. Statics and dynamics of the self-aligning action of deformed liquid bridges are explained through simple models and experiments, and all fundamental aspects of surface patterning and conditioning, of choice, deposition and confinement of liquids, and of component feeding and interconnection to substrates are illustrated through relevant applications in micro- and nanotechnology. A final outline addresses remaining challenges and additional extensions envisioned to further spread the use and fully exploit the potential of the technique.

In biomedical sciences, there is demand for electronic skins with highly sensitive tactile sensors, having applications in patient monitoring, human–machine interfaces, and on‐body sensors. In clinical applications, it would be especially beneficial if the sensors would be disposable. Here, an all plant‐material‐based biodegradable capacitive tactile pressure sensor for disposable electronic skins is reported. Silver‐nanowire‐coated leaf skeletons are used as breathable and flexible electrodes while freeze‐dried rose petals are used as the dielectric layer. The leaf skeleton electrodes have a rough fractal‐like architecture, which provides good adhesion to the silver nanowires and maintains interconnections between the silver nanowires when the electrodes are bent. The electrodes display low constant resistance up to curvature of 800 m−1. The rose petal dielectric layer has a multiscale 3D cell wall microstructure, which compresses elastically when subjected to pressure. The fabricated sensor can respond to pressures ranging from 0.007 to at least 60 kPa, with a maximum sensitivity of ≈0.08 kPa−1. The signal is stable for at least 5000 pressure cycles, after an initial break‐in period. Owing to the all biomaterial constituents, the sensor is biodegradable under aqueous conditions. The sensor is successfully applied as an e‐skin in touch sensing and gesture monitoring.

Controlled spreading of liquids deposited on a solid surface has seen an increasing research interest over the past decade. Since the groundbreaking work by Wenzel [ 1 ] and Cassie, [ 2 ] topographical and chemical surface structuring has been employed to create a multitude of new engineered surfaces for various applications. These surfaces are often inspired by nature (e.g., the lotus leaf [ 3 ] ) and can have wetting properties from superhydrophilic, [ 4 ] superhydrophobic, [ 5 , 6 ] to superoleophilic and superoleophobic, [7][8][9] and even omniphobic. [10][11][12] Surface structures can also induce anisotropic wetting [ 13 , 14 ] or directional wetting, [ 15 , 16 ] allowing a great degree of control over liquid spreading. On the other hand, inhibiting liquid spreading at one, well-defi ned boundary is the critical issue in a wide range of applications, from surface-directed liquid fl ow, [17][18][19] droplet-based microfl uidics, [ 20 ] capillary imbibition, [ 21 ] to passive fi lling of fl uidic channels by capillary action, [ 22 ] droplet shape control in biomedical applications, [ 23 ] microfl uidics for biological studies, [ 24 ] fl uidic optics, [ 25 ] and self-alignment of microchips. [26][27][28] In these applications, liquid overfl ow at the boundary would be catastrophic. Therefore, it is crucial to maximize the advancing contact angle at the boundary, regardless of whether the liquid is in the Cassie or the Wenzel state. In this paper, we report an easy-to-fabricate, purely topographical structure of undercut edge that can pin the triple contact line (TCL) of liquid on any single edge. By mere periodic repetition of such edges, we show that multiple droplets can be patterned in well-controlled shapes, and highly anisotropic wetting can also be achieved at large scale. The pinning property of the structure also does not depend on surface tension of the liquid. Our microfabrication method for the edges is simple, does not involve chemical surface modifi cation, and consequently can be applied to a wide range of materials, including silicon-based, glass and metals.The structure is designed based on a purely geometrical rule, known as the Gibbs inequality, that constrains the apparent contact angle of a spreading liquid meeting a sharp edge. The ability of sharp edges to impede liquid spreading has been long known, and studied both theoretically [ 29 ] and experimentally. [ 30 ] For the case where a liquid droplet meets a mathematically sharp edge, Gibbs [ 31 ] constructed a geometrical relation that describes the range of possible contact angles at the edge ( Figure 1 a):

Hierarchical assembly of self-healing adhesive proteins creates strong and robust structural and interfacial materials, but understanding of the molecular design and structure–property relationships of structural proteins remains unclear. Elucidating this relationship would allow rational design of next generation genetically engineered self-healing structural proteins. Here we report a general self-healing and -assembly strategy based on a multiphase recombinant protein based material. Segmented structure of the protein shows soft glycine- and tyrosine-rich segments with self-healing capability and hard beta-sheet segments. The soft segments are strongly plasticized by water, lowering the self-healing temperature close to body temperature. The hard segments self-assemble into nanoconfined domains to reinforce the material. The healing strength scales sublinearly with contact time, which associates with diffusion and wetting of autohesion. The finding suggests that recombinant structural proteins from heterologous expression have potential as strong and repairable engineering materials.