Analyzing the effects of helical flow in blood vessels using acoustofluidic-based dynamic flow generator.

The effects of helical flow in a blood vessel are investigated in a dynamic flow generator using surface acoustic wave (SAW) in the microfluidic device. The SAW, generated by an interdigital transducer (IDT), induces acoustic streaming, resulting in a stable and consistent helical flow pattern in microscale channels. This approach allows rapid development of helical flow within the channel without directly contacting the medium. The precise design of the window enables the creation of distinct unidirectional vortices, which can be controlled by adjusting the amplitude of the SAW. Within this device, optimal operational parameters of the dynamic flow generator to preserve the integrity of endothelial cells are found, and in such settings, the actin filaments within the cells are aligned to the desired state. Our findings reveal that intracellular Ca2+ concentrations vary in response to flow conditions. Specifically, comparable maximum intensity and graphical patterns were observed between low-flow rate helical flow and high-flow rate Hagen-Poiseuille flow. These suggest that the cells respond to the helical flow through mechanosensitive ion channels. Finally, adherence of monocytes is effectively reduced under helical flow conditions in an inflammatory environment, highlighting the atheroprotective role of helical flow. STATEMENT OF SIGNIFICANCE: Helical flow in blood vessels is well known to prevent atherosclerosis. However, despite efforts to replicate helical flow in microscale channels, there is still a lack of in vitro models which can generate helical flow for analyzing its effects on the vascular system. In this study, we developed a method for generating steady and constant helical flow in microfluidic channel using acoustofluidic techniques. By utilizing this dynamic flow generator, we were able to observe the atheroprotective aspects of helical flow in vitro, including the enhancement of calcium ion flux and reduction of monocyte adhesion. This study paves the way for an in vitro model of dynamic cell culture and offers advanced investigation into helical flow in our circulatory system.

Antibiotic susceptibility test under a linear concentration gradient using travelling surface acoustic waves.

An efficient and accurate antibiotic susceptibility test (AST) is indispensable for measuring the antimicrobial resistance of pathogenic bacteria. A minimal inhibitory concentration (MIC) can be obtained without performing repeated dilutions of the antibiotic by forming a linear antibiotic concentration gradient in a microfluidic channel. We demonstrated a device designed to use travelling surface acoustic waves (TSAWs) to enable a rapid formation of an antibiotic gradient in a few seconds. The TSAWs produced by a focused interdigital transducer deposited on the surface of a piezoelectric (LiNbO3) substrate generated an acoustic streaming flow inside a microfluidic channel, which mixed confluent streams of antibiotics in a controlled fashion. The growth of bacteria exposed to the antibiotic gradient was determined by measuring the MIC, which was used as an indicator of the effectiveness of the AST. The concentration gradient produced using our device was linear, a feature that enhanced the reliability of measurements throughout the microchannel. Two ASTs, namely Pseudomonas aeruginosa against gentamicin and levofloxacin were chosen for the case of slowly proliferating bacteria, and one AST, namely Escherichia coli against gentamicin, were chosen for the rapidly proliferating case. Appropriate antibiotic doses for Pseudomonas aeruginosa and Escherichia coli were each obtained in an efficient manner.

Adaptive characterization of recrystallization kinetics in IF steel by electron backscatter diffraction.

In this study, a rigorous methodology for quantifying recrystallization kinetics by electron backscatter diffraction is proposed in order to reduce errors associated with the operator's skill. An adaptive criterion to determine adjustable grain orientation spread depending on the recrystallization stage is proposed to better identify the recrystallized grains in the partially recrystallized microstructure. The proposed method was applied in characterizing the microstructure evolution during annealing of interstitial-free steel cold rolled to low and high true strain levels of 0.7 and 1.6, respectively. The recrystallization kinetics determined by the proposed method was found to be consistent with the standard method of Vickers microhardness. The application of the proposed method to the overall recrystallization stages showed that it can be used for the rigorous characterization of progressive microstructure evolution, especially for the severely deformed material.