Acoustic actuation of fluids at small scales may finally enable a comprehensive lab-on-a-chip revolution in microfluidics, overcoming long-standing difficulties in fluid and particle manipulation on-chip. In this comprehensive review, we examine the fundamentals of piezoelectricity, piezoelectric materials, and transducers; revisit the basics of acoustofluidics; and give the reader a detailed look at recent technological advances and current scientific discussions in the discipline. Recent achievements are placed in the context of classic reports for the actuation of fluid and particles via acoustic waves, both within sessile drops and closed channels. Other aspects of micro/nano acoustofluidics are examined: atomization, translation, mixing, jetting, and particle manipulation in the context of sessile drops and fluid mixing and pumping, particle manipulation, and formation of droplets in the context of closed channels, plus the most recent results at the nanoscale. These achievements will enable applications across the disciplines of chemistry, biology, medicine, energy, manufacturing, and we suspect a number of others yet unimagined. Basic design concepts and illustrative applications are highlighted in each section, with an emphasis on lab-on-a-chip applications.

The COVID‐19 pandemic has produced critical shortages of ventilators worldwide. There is an unmet need for rapidly deployable, emergency‐use ventilators with sufficient functionality to manage COVID‐19 patients with severe acute respiratory distress syndrome. Here, we show the development and validation of a simple, portable and low‐cost ventilator that may be rapidly manufactured with minimal susceptibility to supply chain disruptions. This single‐mode continuous, mandatory, closed‐loop, pressure‐controlled, time‐terminated emergency ventilator offers robust safety and functionality absent in existing solutions to the ventilator shortage. Validated using certified test lungs over a wide range of compliances, pressures, volumes and resistances to meet U.S. Food and Drug Administration standards of safety and efficacy, an Emergency Use Authorization is in review for this system. This emergency ventilator could eliminate controversial ventilator rationing or splitting to serve multiple patients. All design and validation information is provided to facilitate ventilator production even in resource‐limited settings.

Acoustofluidics has promised to enable lab-on-a-chip and point-of-care devices in ways difficult to achieve using other methods. Piezoelectric ultrasonic transducers---as small as the chips they actuate---provide rapid fluid and suspended...

Tumor cells express a unique cell surface glycocalyx with upregulation of sulfated glycosaminoglycans and charged glycoproteins. Little is known about how electromagnetic fields interact with this layer, particularly with regard to harnessing unique properties for therapeutic benefit. We applied a pulsed 20-millitesla (mT) magnetic field with rate of rise (dB/dt) in the msec range to cultured tumor cells to assess whether this affects membrane integrity as measured using cytolytic assays. A 10-min exposure of A549 human lung cancer cells to sequential 50- and 385-Hz oscillating magnetic fields was sufficient to induce intracellular protease release, suggesting altered membrane integrity after the field exposure. Heparinase treatment, which digests anionic sulfated glycan polymers, before exposure rendered cells insensitive to this effect. We further examined a non-neoplastic human primary cell line (lung lymphatic endothelial cells) as a typical normal host cell from the lung cancer microenvironment and found no effect of field exposure on membrane integrity. The field exposure was also sufficient to alter proliferation of tumor cells in culture, but not that of normal lymphatic cells. Pulsed magnetic field exposure of human breast cancer cells that express a sialic-acid rich glycocalyx also induced protease release, and this was partially abrogated by sialidase pretreatment, which removes cell surface anionic sialic acid. Scanning electron microscopy showed that field exposure may induce unique membrane “rippling” along with nanoscale pores on A549 cells. These effects were caused by a short exposure to pulsed 20-mT magnetic fields, and future work may examine greater magnitude effects. The proof of concept herein points to a mechanistic basis for possible applications of pulsed magnetic fields in novel anticancer strategies.

We study the nozzle-free ejection of liquid droplets at controlled angles from a sessile drop actuated from two, mutually opposed directions by focused surface acoustic waves with dissimilar parameters. Previous researchers assumed that jets formed in this way are limited by the Rayleigh angle. However, when we carefully account for surface tension in addition to the driving force, acoustic streaming, we find a quantitative model that reduces to the Rayleigh angle only when inertia is dominant, and suggests larger ejection angles are possible in many practical situations. We confirm this in demonstrating ejection at more than double the Rayleigh angle. Our model explains the effects of both fluid and input parameters on experiments with a range of liquids. We extract, from this model, a dimensionless number that serves as an analog for the typical Weber number for predicting single droplet events.

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We study capillary wave turbulence (WT) inherently spanning multiple dynamical regimes and geometries-from weakly to strongly nonlinear WT (SWT) and from shallow to deep domains-all within a 40 µL volume. These conditions violate idealizations used in modern WT theories. This study is now viable with recent advances in ultra-high-speed digital holographic microscopy, providing 10-µs time and 10-nm spatial resolutions for images across the entire field of view, encompassing a complete wave system. We derive tractable parameters permitting direct identification of four fundamental WT regimes, all present in this system. A proposed nonlinearity measure permits comparative analysis over varied inputs. Results indicate SWT precedes ultrasonic atomization. Our findings promote further SWT study toward improving associated applications. This work augments current understanding of WT regimes and behaviors, and directly applies to many fields beyond fluid mechanics. Curated data (300 GB) are freely provided for download [1].

When an otherwise quiescent minuscule (O(≤10−6) μl) basin of water is driven by ultrasonic vibrations at high frequencies (O(≥106)Hz) and with nanoscale (O(≤10−9)m) amplitudes, turbulent capillary waves that are visible by eye (O(10−2)m amplitudes and O(10−1)s periods) form at the air-water interface. Classical mechanisms typically attributed to such instabilities—such as Faraday wave theory—are absent. Contemporary wave turbulence studies have been mainly limited to weakly nonlinear regimes. In this talk, we present detailed measurements of strongly nonlinear, microscopic capillary wave turbulence. We show that this regime is reliably statistically characterized as an alpha-stable Lévy flight with a varying tail parameter. Our results demonstrate that as input power is increased, the heaviness of distribution tails also increases so that rogue events play an increasingly prevalent role in the overall wave system. Implications for future study and potential applications within the area of controlled atomization are discussed.