Numerical and experimental characterization of a novel modular passive micromixer

This paper reports a new low-cost passive microfluidic mixer design, based on a replication of identical mixing units composed of microchannels with variable curvature (clothoid) geometry. The micromixer presents a compact and modular architecture that can be easily fabricated using a simple and reliable fabrication process. The particular clothoid-based geometry enhances the mixing by inducing transversal secondary flows and recirculation effects. The role of the relevant fluid mechanics mechanisms promoting the mixing in this geometry were analysed using computational fluid dynamics (CFD) for Reynolds numbers ranging from 1 to 110. A measure of mixing potency was quantitatively evaluated by calculating mixing efficiency, while a measure of particle dispersion was assessed through the lacunarity index. The results show that the secondary flow arrangement and recirculation effects are able to provide a mixing efficiency equal to 80 % at Reynolds number above 70. In addition, the analysis of particles distribution promotes the lacunarity as powerful tool to quantify the dispersion of fluid particles and, in turn, the overall mixing. On fabricated micromixer prototypes the microscopic-Laser-Induced-Fluorescence (μLIF) technique was applied to characterize mixing. The experimental results confirmed the mixing potency of the microdevice

Analysis of mixing of a clothoid based passive micromixer: A numerical study

A computational study of a novel passive micromixer is presented. In this work, we analysed a Clo-plus micromixer designed to achieve efficient mixing and characterized by a process of construction that can use a single planar soft lithography step. Mixing studies were carried out at different Reynolds numbers ranging from 1 to 100. The preliminary results suggest that at Re> 50, the Clo-plus micromixer is characterized by a good mixing because of stronger Dean secondary flow and recirculation effect

iIteratrial shunting through an asymptomatic patent foramen ovale in thoracic surgery

Background: Patent foramen ovale (PFO) is present in as many as 25% of the general population and is considered an irrelevant condition in healthy subjects. Here, we sought to determine an association between an asymptomatic PFO at baseline and postoperative short-term adverse events in patients undergoing major pulmonary resection for lung cancer. In addition, we evaluated for the rate of PFO after pulmonary resections. Methods: This prospective, observational study assessed patients by transcranial Doppler with contrast at baseline and discharge. To confirm interatrial shunting, patients with positive transcranial Doppler at baseline also underwent contrast transthoracic echocardiography. Multivariate logistic regression models were adopted to investigate for independent factors that could have been associated with complications. Backward stepwise procedure was used for model selection. Results: Median age was 67.7 ± 9.2 years (range, 36 to 86), and 67% were men. Overall, 18 patients underwent pneumonectomy, 11 bilobectomy, and 118 lobectomy; 54% underwent right-sided procedure and 46%, left-sided. One perioperative death was recorded, and 34 patients had one or more cardiopulmonary complications. At baseline, PFO was positive in 25% (37 of 147) and negative in 75% (110 of 147); of the latter, 11% were positive at discharge. Detection of PFO at baseline, on multivariate analysis, was significantly associated with a risk of postoperative complications (odds ratio 2.5; 95% confidence interval: 1.1 to 5.8). Specifically, we observed a significant association between atrial fibrillation and positive PFO at baseline (odds ratio 3.5; 95% confidence interval: 1.4 to 9.0). Conclusions: Preoperative asymptomatic PFO was independently associated with postoperative adverse events. Moreover, 11% of patients who had negative transcranial Doppler studies at baseline had asymptomatic PFOs at discharge. Larger prospective studies are needed to further investigate for a prognostic impact of PFO in thoracic surgery