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Microfluidics, the science and technology of manipulating fluids in microscale channels, offers numerous advantages, such as low energy consumption, compact device size, precise control, fast reaction, and enhanced portability. These benefits have led to applications in biomedical assays, disease diagnostics, drug discovery, neuroscience, and so on. Fluid flow within microfluidic channels is typically in the laminar flow region, which is characterized by low Reynolds numbers but brings the challenge of efficient mixing of fluids. Periodic flows are time-dependent fluid flows, featuring repetitive patterns that can significantly improve fluid mixing and extend the effective length of microchannels for submicron and nanoparticle manipulation. Besides, periodic flow is crucial in organ-on-a-chip (OoC) for accurately modeling physiological processes, advancing disease understanding, drug development, and personalized medicine. Various techniques for generating periodic flows have been reported, including syringe pumps, peristalsis, and actuation based on electric, magnetic, acoustic, mechanical, pneumatic, and fluidic forces, yet comprehensive reviews on this topic remain limited. This paper aims to provide a comprehensive review of periodic flows in microfluidics, from fundamental mechanisms to generation techniques and applications. The challenges and future perspectives are also discussed to exploit the potential of periodic flows in microfluidics., (© 2024 The Author(s). Small published by Wiley‐VCH GmbH.)

The removal of oil from solid surfaces, such as textiles and plates, remains a challenge due to the strong binding affinity of the oil. Conventional methods for surface cleaning often require surfactants and mechanical abrasion to enhance the cleaning process. However, in excess, these can pose adverse effects on the environment and to the material. This study investigated how bulk nanobubble water can clean oil microdroplets deposited on surfaces like glass coverslips and dishes. Microscopy imaging and further image analysis clearly revealed that these microdroplets detached from both hydrophobic and hydrophilic surfaces when washed with bulk nanobubble water within a fluidic microchannel. Oil contaminant cleaning was also conducted in water as mobile phase to mimic the circumstances that occur in a dishwasher and washing machine. Cleaning on a larger scale also proved very successful in the removal of oil from a porcelain bowl. These results indicate that nanobubble water can easily remove oil contaminants from glass and porcelain surfaces without the assistance of surfactants. This is in stark contrast to negligible results obtained with a control solution without nanobubbles. This study indicates that nanobubble technology is an innovative, low-cost, eco-friendly approach for oil removal, demonstrating its potential for broad practical applications., (© 2024 Wiley-VCH GmbH.)