Acoustofluidics, offering contact-free and precise manipulation of micro-objects, has emerged as a transformative tool for various biological and medical applications. In recent years, significant advancements have been made in droplet manipulation using acoustic waves. This review provides an in-depth exploration of acoustofluidic techniques for droplet manipulation, presenting a balanced perspective on the role of this versatile platform across diverse applications. The paper begins by introducing the underlying mechanism of acoustic forces acting on the droplets, followed by a comprehensive discussion of acoustofluidic techniques tailored for essential unit operations, such as droplet generation, separation, merging, splitting, steering, trapping, in-droplet sample manipulation, sample control within sessile droplets, and digital acoustofluidics. Finally, the prospects and limitations of acoustofluidics for droplet manipulations are also discussed, suggesting the future direction of droplet acoustofluidics research.

This review comprehensively summarizes working mechanisms of various microfluidic shape-based separation for cells and particles and provides future perspectives based on current challenges for biomedical and clinical applications.

In this study, a new machining approach (aqueous machining) is applied for mill machining and its performance is compared with traditional wet machining. AISI 1020 steel is employed as the test material and Taguchi statistical methodology is implemented to analyze and compare the performance of the two machining approaches. The cutting speed, feed rate, and depth of cut were the machining parameters used for both types of machining, while the selected response variables were surface roughness and hardness. Temperature variations were also recorded in aqueous machining. Compared with wet machining, aqueous machining resulted in lower surface roughness (up to 13%) for the same operating conditions and about 14% to 16% enhancement in hardness due to the formation of finer pearlite, as revealed by the microstructure analysis. Compared to the parent unmachined surface, the hardness of machined surfaces was 24% to 31% higher in wet machining and 44% to 51% higher in aqueous machining. Another benefit of aqueous machining was the energy gain, which ranged from 718 to 8615.96 J. This amount of heat energy can be used as waste heat for preheating domestic hot water, running the organic Rankine cycle with waste heat and preheating the inlet saline water for desalination, vacuum desalination, etc. If successfully implemented in the future, this idea will provide a step towards achieving sustainable machining by saving lubricants and toxic wastes in addition to saving energy for secondary applications.