Unstable liquid flow in syringe pump-driven systems due to the low-speed vibration of the step motor is commonly observed as an unfavorable phenomenon, especially when the flow rate is relatively small. Upon the design of a convenient and cost-efficient microfluidic standing air bubble system, this paper studies the physical principles behind the flow stabilization phenomenon of the bubble-based hydraulic capacitors. A bubble-based hydraulic capacitor consists of three parts: tunable microfluidic standing air bubbles in specially designed crevices on the fluidic channel wall, a proximal pneumatic channel, and porous barriers between them. Micro-bubbles formed in the crevices during liquid flow and the volume of the bubble can be actively controlled by the pneumatic pressure changing in the proximal channel. When there is a flowrate fluctuation from the upstream, the flexible air-liquid interface would deform under the pressure variation, which is analogous to the capacitive charging/discharging process. The theoretical model based on Euler law and the microfluidic equivalent circuit was developed to understand the multiphysical phenomenon. Experimental data characterize the liquid flow stabilization performance of the flow stabilizer with multiple key parameters, such as the number and the size of microbubbles. The developed bubble-based hydraulic capacitor could minimize the flow pulses from syringe pumping by 75.3%. Furthermore, a portable system is demonstrated and compared with a commercial pressure-driven flow system. This study can enhance the understanding of the bubble-based hydraulic capacitors that would be beneficial in microfluidic systems where the precise and stable liquid flow is required.

engineering, [2] drug delivery, [3] and biomedical research. [4] Until now, micromanipulation methods based on direct physical contact have been used widely.To achieve capture and transportation, different end-effectors have been introduced into systems, such as a microgripper for direct grasping [5] or driven by negative pressure [6] and a cantilever. [7] Through visual feedback, micromanipulation can be realized efficiently and effectively. However, direct contact between solid manipulation tools and bioentities may cause potential damage to living cells that would be difficult to observe by the naked eye. [8] Despite the potential damage to living cells during the manipulation process, the release of micro-objects also poses a significant challenge because of the adhesion force at the microscale due to direct physical contact.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.202104579.

Microbubbles are often used in chemistry, biophysics, and medicine. Properly controlled microbubbles have been proved beneficial for various applications by previous scientific endeavors. However, there is still a plenty of room for further development of efficient microbubble handling methods. Here, this paper introduces a tunable, stable, and robust microbubble interface handling mechanism, named as microfluidic standing air bubbles (μSABs), by studying the multiphysical phenomena behind the gas-liquid interface formation and variation. A basic μSAB system consists specially structured fluidic channels, pneumatic channels, and selectively permeable porous barriers between them. The μSABs originate inside the crevice structures on the fluidic channel walls in a repeatable and robust manner. The volumetric variation of the μSAB is a multiphysical phenomenon that dominated by the air diffusion between the pneumatic channel and the bubble. Theoretical analysis and experimental data illustrate the coupling processes of the repeatable and linear μSAB volumetric variation when operated under common handling conditions (control pneumatic pressure: −90 kPa to 200 kPa). Furthermore, an adjustable acoustic microstreaming is demonstrated as an application using the alterable μSAB gas-liquid interface. Derived equations and microscopic observations elucidate the mechanism of the continuous and linear regulation of the acoustic microstreaming using varying μSAB gas-liquid interfaces. The μSAB system provides a new tool to handle the flexible and controllable gas-liquid interfaces in a repeatable and robust manner, which makes it a promising candidate for innovative biochemical, biophysical, and medical applications.

No abstract

Using the 2019 China Invested Firms and Employees Survey (CIFES), this study explores the convergence of Chinese enterprise and employee (E&E) evaluation in Southeast Asian countries. The results show that convergence varies greatly across the nine Southeast Asian countries. Union organisations and economic factors play a key role in convergence. Firms with labour unions report a more effective corporate social responsibility (CSR) performance than others, while employees in the construction sector report their firms’ CSR and those in the manufacturing and service sectors. Interestingly, the number of years worked by an employee correlates positively with their perception of firms’ CSR performance.