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High-frequency acoustic waves (above MHz) are widely applied in ultrasonic imaging and many microfluidic applications. For many cases, the response of interfaces to high-frequency acoustic waves can be simplified as a reflection and refraction process, where only the effect of the interfaces on acoustic wave propagation is considered. But for some physical processes, such as bubble and droplet manipulation, the response of the interfaces plays a key role. However, the interaction processes between high-frequency acoustic waves and interfaces, especially fluid interfaces, are mostly highly nonlinear. Most of the related work focused on acoustic waves with frequencies ranging from DC to kHz. There are continuously new phenomena found and reported showing the effect of high-frequency acoustic waves on fluid interfaces contrary to previously discovered theorems and laws. Yet many of the phenomena are poorly understood and explained. We briefly introduced the background of high-frequency ultrasonic devices, including the selection of material, design principles, physical models, and some of the important applications. Observations and measurements on the interface dynamics with small amplitudes and high frequencies have always been a challenge to researchers. Gas vesicles (GV) are bubbles wrapped by a protein layer with submicron sizes, which put forward an even higher requirement for the equipment and experiment design. We reported a precise non-contact technique to monitor GV's vibrational behavior using laser Doppler vibrometry. The resonance frequencies of the single GV and agglomerated GV were found and verified by the simulation results. We then focused on the behavior of the GV affected by lower frequencies (1-10 MHz) associated with medical and industrial applications. The change of GV's vibrational response to the acoustic wave with varying power input was observed. The mechanism of GV's function on ultrasonic signal amplification can be well explained with the

Gas vesicles are gas-filled nanocompartments that allow a diverse group of bacteria and archaea to control their buoyancy. The molecular basis of their properties and assembly remains unclear. Here, we report the 3.2 Å cryo-EM structure of the gas vesicle shell made from the structural protein GvpA that self-assembles into hollow helical cylinders closed off by cone-shaped tips. Two helical half shells connect through a characteristic arrangement of GvpA monomers, suggesting a mechanism of gas vesicle biogenesis. The fold of GvpA features a corrugated wall structure typical for force-bearing thin-walled cylinders. Small pores enable gas molecules to diffuse across the shell, while the exceptionally hydrophobic interior surface effectively repels water. Comparative structural analysis confirms the evolutionary conservation of gas vesicle assemblies and demonstrates molecular features of shell reinforcement by GvpC. Our findings will further research into gas vesicle biology and facilitate molecular engineering of gas vesicles for ultrasound imaging., BN/Arjen Jakobi Lab, BN/Bionanoscience, ImPhys/Maresca group, BN/Afdelingsbureau, ImPhys/Medical Imaging