Editorial for the Special Issue on Analysis, Design and Fabrication of Micromixers II.

Micromixers are important components of lab-on-a-chip systems, and also have many biological and chemical applications [...].

Kinematic Properties of a Twisted Double Planetary Chaotic Mixer: A Three-Dimensional Numerical Investigation.

In this study, a numerical investigation based on the CFD method is carried out to study the unsteady laminar flow of Newtonian fluid with a high viscosity in a three-dimensional simulation of a twisted double planetary mixer, which is composed of two agitating rods inside a moving tank. The considered stirring protocol is a "Continuous sine squared motion" by using the dynamic mesh model and user-defined functions (UDFs)to define the velocity profiles. The chaotic advection is obtained in our active mixers by the temporal modulation of rotational velocities of the moving walls in order to enhance the mixing of the fluid for a low Reynolds number and a high Peclet number. For this goal, we applied the Poincaré section and Lyapunov exponent as reliable mathematic tools for checking mixing quality by tracking a number of massless particles inside the fluid domain. Additionally, we investigated the development of fluid kinematics proprieties, such as vorticity, helicity, strain rate and elongation rate, at various time periods in order to view the impact of temporal modulation on the flow properties. The results of the mentioned simulation showed that it is possible to obtain a chaotic advection after a relatively short time, which can deeply enhance mixing fluid efficiency.

Evaluation of Hydrodynamic and Thermal Behaviour of Non-Newtonian-Nanofluid Mixing in a Chaotic Micromixer.

Three-dimensional numerical investigations of a novel passive micromixer were carried out to analyze the hydrodynamic and thermal behaviors of Nano-Non-Newtonian fluids. Mass and heat transfer characteristics of two heated fluids have been investigated to understand the quantitative and qualitative fluid faction distributions with temperature homogenization. The effect of fluid behavior and different Al2O3 nanoparticles concentrations on the pressure drop and thermal mixing performances were studied for different Reynolds number (from 0.1 to 25). The performance improvement simulation was conducted in intervals of various Nanoparticles concentrations (φ = 0 to 5%) with Power-law index (n) using CFD. The proposed micromixer displayed a mixing energy cost of 50-60 comparable to that achieved for a recent micromixer (2021y) in terms of fluid homogenization. The analysis exhibited that for high nanofluid concentrations, having a strong chaotic flow enhances significantly the hydrodynamic and thermal performances for all Reynolds numbers. The visualization of vortex core region of mass fraction and path lines presents that the proposed design exhibits a rapid thermal mixing rate that tends to 0.99%, and a mass fraction mixing rate of more than 0.93% with very low pressure losses, thus the proposed micromixer can be utilized to enhance homogenization in different Nano-Non-Newtonian mechanism with minimum energy.

Does the morphology of the umbilicus influence the incidence of surgical site infections in transumbilical single-incision laparoscopic appendectomy?

Background: Transumbilical laparoscopic appendectomy (TULA) may be a feasible alternative to conventional laparoscopic appendectomy. However, a transumbilical incision may increase incisional surgical site infections (SSIs) compared to conventional laparoscopic appendectomy. This study aimed to investigate the relationship between the morphology of the umbilicus and the incidence of SSIs in patients who underwent TULA. Patients and Methods: This retrospective study analysed the medical records of consecutive patients who underwent surgery for acute appendicitis at our institution from June 2016 to October 2020. The patients were assigned to the SSI group (those with an SSI) or the non-SSI group. The morphology of the umbilicus was calculated by measuring its width and depth on preoperative computed tomography images and was compared between the SSI and non-SSI groups. Results: The SSI group included 23 patients, while the non-SSI group included 252 patients. The width of the umbilicus was significantly shorter in the SSI group than in the non-SSI group (29 ± 10 mm vs. 34 ± 9 mm, P = 0.027). The umbilicus was slightly deeper in the SSI group than in the non-SSI group; however, the difference was not significant (16 mm vs. 15 mm, P = 0.384). Conclusions: This was the first study investigating the correlation between the morphology of the umbilicus and SSI development in TULA. SSIs tended to occur more commonly in a narrow and deep umbilicus. An extension of the umbilical incision may help prevent SSI in patients with this umbilical morphology.

Mixing Enhancement of Non-Newtonian Shear-Thinning Fluid for a Kenics Micromixer.

In this work, a numerical investigation was analyzed to exhibit the mixing behaviors of non-Newtonian shear-thinning fluids in Kenics micromixers. The numerical analysis was performed using the computational fluid dynamic (CFD) tool to solve 3D Navier-Stokes equations with the species transport equations. The efficiency of mixing is estimated by the calculation of the mixing index for different cases of Reynolds number. The geometry of micro Kenics collected with a series of six helical elements twisted 180° and arranged alternately to achieve the higher level of chaotic mixing, inside a pipe with a Y-inlet. Under a wide range of Reynolds numbers between 0.1 to 500 and the carboxymethyl cellulose (CMC) solutions with power-law indices among 1 to 0.49, the micro-Kenics proves high mixing Performances at low and high Reynolds number. Moreover the pressure losses of the shear-thinning fluids for different Reynolds numbers was validated and represented.

Editorial for the Special Issue on Analysis, Design and Fabrication of Micromixers.

During the last couple of decades, there have been rapid developments in analysis, design, and fabrication of micromixers [...].

Kinematic Measurements of Novel Chaotic Micromixers to Enhance Mixing Performances at Low Reynolds Numbers: Comparative Study.

In this work, a comparative investigation of chaotic flow behavior inside multi-layer crossing channels was numerically carried out to select suitable micromixers. New micromixers were proposed and compared with an efficient passive mixer called a Two-Layer Crossing Channel Micromixer (TLCCM), which was investigated recently. The computational evaluation was a concern to the mixing enhancement and kinematic measurements, such as vorticity, deformation, stretching, and folding rates for various low Reynolds number regimes. The 3D continuity, momentum, and species transport equations were solved by a Fluent ANSYS CFD code. For various cases of fluid regimes (0.1 to 25 values of Reynolds number), the new configuration displayed a mixing enhancement of 40%-60% relative to that obtained in the older TLCCM in terms of kinematic measurement, which was studied recently. The results revealed that all proposed micromixers have a strong secondary flow, which significantly enhances the fluid kinematic performances at low Reynolds numbers. The visualization of mass fraction and path-lines presents that the TLCCM configuration is inefficient at low Reynolds numbers, while the new designs exhibit rapid mixing with lower pressure losses. Thus, it can be used to enhance the homogenization in several microfluidic systems.

Enhancement of Mixing Performance of Two-Layer Crossing Micromixer through Surrogate-Based Optimization.

Optimum configuration of a micromixer with two-layer crossing microstructure was performed using mixing analysis, surrogate modeling, along with an optimization algorithm. Mixing performance was used to determine the optimum designs at Reynolds number 40. A surrogate modeling method based on a radial basis neural network (RBNN) was used to approximate the value of the objective function. The optimization study was carried out with three design variables; viz., the ratio of the main channel thickness to the pitch length (H/PI), the ratio of the thickness of the diagonal channel to the pitch length (W/PI), and the ratio of the depth of the channel to the pitch length (d/PI). Through a primary parametric study, the design space was constrained. The design points surrounded by the design constraints were chosen using a well-known technique called Latin hypercube sampling (LHS). The optimal design confirmed a 32.0% enhancement of the mixing index as compared to the reference design.

A Review of Passive Micromixers with a Comparative Analysis.

A wide range of existing passive micromixers are reviewed, and quantitative analyses of ten typical passive micromixers were performed to compare their mixing indices, pressure drops, and mixing costs under the same axial length and flow conditions across a wide Reynolds number range of 0.01-120. The tested micromixers were selected from five types of micromixer designs. The analyses of flow and mixing were performed using continuity, Navier-Stokes and convection-diffusion equations. The results of the comparative analysis were presented for three different Reynolds number ranges: low-Re (Re ≤ 1), intermediate-Re (1 < Re ≤ 40), and high-Re (Re > 40) ranges, where the mixing mechanisms are different. The results show a two-dimensional micromixer of Tesla structure is recommended in the intermediate- and high-Re ranges, while two three-dimensional micromixers with two layers are recommended in the low-Re range due to their excellent mixing performance.

Effects of Bridge-Shaped Microchannel Geometry on the Performance of a Micro Laminar Flow Fuel Cell.

A laminar flow micro fuel cell comprising of bridge-shaped microchannel is investigated to find out the effects of the cross-section shape of the microchannel on the performance. A parametric study is performed by varying the heights and widths of the channel and bridge shape. Nine different microchannel cross-section shapes are evaluated to find effective microchannel cross-sections by combining three bridge shapes with three channel shapes. A three-dimensional fully coupled numerical model is used to calculate the fuel cell's performance. Navier-Stokes, convection and diffusion, and Butler-Volmer equations are implemented using the numerical model. A narrow channel with a wide bridge shape shows the best performance among the tested nine cross-sectional shapes, which is increased by about 78% compared to the square channel with the square bridge shape.

Asymmetrical Split-and-Recombine Micromixer with Baffles.

The present work proposes a planar micromixer design comprising hybrid mixing modules of split-and-recombine units and curved channels with radial baffles. The mixing performance was evaluated numerically by solving the continuity and momentum equations along with the advection-diffusion equation in a Reynolds number range of 0.1-80. The variance of the concentration of the mixed species was considered to quantify the mixing index. The micromixer showed far better mixing performance over whole Reynolds number range than an earlier split-and-recombine micromixer. The mixer achieved mixing indices greater than 90% at Re ≥ 20 and a mixing index of 99.8% at Re = 80. The response of the mixing quality to the change of three geometrical parameters was also studied. A mixing index over 80% was achieved within 63% of the full length at Re = 20.

Single and Multi-Objective Optimization of a Three-Dimensional Unbalanced Split-and-Recombine Micromixer.

The three-dimensional geometry of a micromixer with an asymmetrical split-and-recombine mechanism was optimized to enhance the fluid-mixing capability at a Reynolds number of 20. Single and multi-objective optimizations were carried out by using particle swarm optimization and a genetic algorithm on a modeled surrogate surface. Surrogate modeling was performed using the computational results for the mixing. Mixing and flow analyses were carried out by solving the convection-diffusion equation in combination with the three-dimensional continuity and momentum equations. The optimization was carried out with two design variables related to dimensionless geometric parameters. The mixing effectiveness was chosen as the objective function for the single-objective optimization, and the pressure drop and mixing index at the outlet were chosen for the multi-objective optimization. The sampling points in the design space were determined using a design of experiment technique called Latin hypercube sampling. The surrogates for the objective functions were developed using a Kriging model. The single-objective optimization resulted in 58.9% enhancement of the mixing effectiveness compared to the reference design. The multi-objective optimization provided Pareto-optimal solutions that showed a maximum increase of 48.5% in the mixing index and a maximum decrease of 55.0% in the pressure drop in comparison to the reference design.

Effectiveness of Antithymocyte Globulin Induction Dosing Regimens in Kidney Transplantation Patients: A Network Meta-analysis.

BACKGROUND: Antithymocyte globulin (ATG) is an induction therapy in kidney transplantation, but our knowledge about the relation between outcomes and ATG regimens is limited. We compared ATG effectiveness in kidney transplantation according to dosage and administration schedule. METHODS: Reports from 1970 until May 2018 in CENTRAL, MEDLINE, EMBASE, and Science Citation Index Expanded were searched. We performed direct and indirect network meta-analysis using Bayesian models and generated rankings for ATG dosage and injection number variations by generation mixed treatment comparison.We compared ATG dose and schedule in kidney transplantation in relation to all-cause death, graft failure, antibody-mediated rejection, T-cell mediated rejection, biopsy-proven acute rejection, and bacterial and viral infection. RESULTS: Ten studies (N = 1065) were analyzed by forming 6 groups: ATG alternate doses, 9 mg/kg, 6 mg/kg, and 4.5 mg/kg; single dose, 6 mg/kg, and 4.5 mg/kg; and control. Compared to placebo, ATG regimen variations were not associated with significant differences in survival, viral infection, renal function, or graft survival. ATG regimens 9 and 4.5 mg alternate dosing tended to reduce biopsy-proven acute rejection but without statistical significance. According to the highest rank probability, the 9 mg alternate dosing group had the highest tendency for cytomegalovirus and bacterial infections but without statistical significance. CONCLUSIONS: The rejection frequency tended to be lower for the 9 and 4.5 mg alternate dosing groups. Infections occurred at a higher rate in the 9 mg alternate dosing group, but the differences in the risk of infection among the groups with different ATG regimens were not statistically significant.

Transumbilical Single-Incision Laparoscopic-Assisted Appendectomy (TULAA) Is Useful in Adults and Young Adolescents: Comparison with Multi-Port Laparoscopic Appendectomy.

Background and objectives: Single-port laparoscopic appendectomy (SLA) in most previous studies has used intracorporeal excision of the appendix and needed a longer operative time than multi-port laparoscopic appendectomy (MLA), although SLA does have the potential benefit of an almost invisible scar within the umbilicus. Some studies have reported that extracorporeal transumbilical single-incision laparoscopic-assisted appendectomy (TULAA) in children took a considerably reduced operative time compared to MLA. We adopted TULAA in adults, adding routine dissection of the peritoneal attachment of the appendix. The aim was to compare the operative outcomes between TULAA and MLA. Materials and Methods: Between March 2013 and January 2016, 770 patients with acute uncomplicated and complicated appendicitis from 15 to 75 years of age were enrolled retrospectively. The operation was performed as early (EA) and interval appendectomy (IA). Results: Operative time was shorter in the TULAA group than in the MLA group, except for IA. No open conversion occurred in the TULAA group, except one case of ileocecal resection for IA. No intra-abdominal fluid collection was found in the TULAA group. Extended resection (especially partial cecectomy) was performed less frequently in the TULAA group than in the MLA group for IA. Mean postoperative hospital stay was shorter in the TULAA group for uncomplicated appendicitis. When the data of the EA group and the IA group were compared, operative time was significantly shorter in the IA group for both MLA and TULAA. The open conversion rate and the complication rate tended to be lower in the IA group. Confined to IA, the TULAA group tended to have shorter mean initial, postoperative, and total hospital stays. Conclusions: TULAA can be a useful surgical alternative to MLA in adults and young adolescents, because it lacks open conversion and provides both a shorter operative time and a shorter postoperative hospital stay. TULAA is feasible for IA in that it showed a lower rate of extended resection and complications.

Multi-Objective Optimizations of a Serpentine Micromixer with Crossing Channels at Low and High Reynolds Numbers.

In order to maximize the mixing performance of a micromixer with an integrated three-dimensional serpentine and split-and-recombination configuration, multi-objective optimizations were performed at two different Reynolds numbers, 1 and 120, based on numerical simulation. Numerical analyses of fluid flow and mixing in the micromixer were performed using three-dimensional Navier-Stokes equations and convection-diffusion equation. Three dimensionless design variables that were related to the geometry of the micromixer were selected as design variables for optimization. Mixing index at the exit and pressure drop through the micromixer were employed as two objective functions. A parametric study was carried out to explore the effects of the design variables on the objective functions. Latin hypercube sampling method as a design-of-experiment technique has been used to select design points in the design space. Surrogate modeling of the objective functions was performed by using radial basis neural network. Concave Pareto-optimal curves comprising of Pareto-optimal solutions that represents the trade-off between the objective functions were obtained using a multi-objective genetic algorithm at Re = 1 and 120. Through the optimizations, maximum enhancements of 18.8% and 6.0% in mixing index were achieved at Re = 1 and 120, respectively.

Numerical and Experimental Study on Mixing Performances of Simple and Vortex Micro T-Mixers.

Vortex flow increases the interface area of fluid streams by stretching along with providing continuous stirring action to the fluids in micromixers. In this study, experimental and numerical analyses on a design of micromixer that creates vortex flow were carried out, and the mixing performance was compared with a simple micro T-mixer. In the vortex micro T-mixer, the height of the inlet channels is half of the height of the main mixing channel. The inlet channel connects to the main mixing channel (micromixer) at the one end at an offset position in a fashion that creates vortex flow. In the simple micro T-mixer, the height of the inlet channels is equal to the height of the channel after connection (main mixing channel). Mixing of fluids and flow field have been analyzed for Reynolds numbers in a range from 1⁻80. The study has been further extended to planar serpentine microchannels, which were combined with a simple and a vortex T-junction, to evaluate and verify their mixing performances. The mixing performance of the vortex T-mixer is higher than the simple T-mixer and significantly increases with the Reynolds number. The design is promising for efficiently increasing mixing simply at the T-junction and can be applied to all micromixers.

Editorial for the Special Issue on Passive Micromixers.

Micromixers are important components of microfluidic systems [...].

Flavans and diphenylpropanes with PTP1B inhibition from Broussonetia kazinoki.

Three new (1a/1b and 2b) and five known flavans (2a, 6a/6b, 7, and 8), one new flavan glycoside (3), and two new (4 and 5) and six known 1,3-diphenylpropanes (9-14) were isolated from the twigs of Broussonetia kazinoki. Compounds 1, 2, and 6 are scalemic mixtures, and were resolved by chiral HPLC to provide 1a/1b, 2a/2b, and 6a/6b. The structures of these compounds were elucidated by extensive spectroscopic methods, including NMR, MS, and ECD analyses. Compounds 1, 2, 5, 8, 9, 11, and 12 showed in vitro inhibition of protein tyrosine phosphatase 1B (PTP1B).

Early experience of transilluminated cryosurgery for varicose vein with saphenofemoral reflux: review of 84 patients (131 limbs).

PURPOSE: Varicose veins with great saphenous vein (GSV) insufficiency is prevalent. Among various surgical treatments for varicose veins, cryosurgery of GSV is an alternative minimally invasive technique that could leave fewer scars and replace conventional stripping with ambulatory phlebectomy. This study sought to assess outcomes including efficacy and safety of cryosurgery for varicose veins. METHODS: One hundred thirty-one limbs in 84 patients (37 male, 47 female; mean age, 53.3 years) with varicose veins were treated with cryosurgery over a 2-year period. The patients were followed for postoperative complication with surveillance of recurrence. The analyzed variables included age, sex, symptom, operative time (from skin incision to the application of elastic bandages on the legs for compression purposes), and postoperative complications including bruising, hematoma, superficial thrombophlebitis, cellulitis, seroma, cutaneous nerve damage, and wound complication. RESULTS: The mean operative time was 64.7 minutes for both limbs and 44 minutes for single limbs. The median number of incisions was 2. For stripping of GSV, one incision at the groin was necessary. Postoperative complications included an episode of hematoma in 3 limbs (2.3%), cutaneous nerve damage in 3 limbs (2.3%), cellulitis in 2 patients (1.5%), and seroma in 1 limb (0.8%). No wound infection, thrombophlebitis or deep venous thrombosis was observed. During follow-up (mean follow-up period, 13.5 months; range, 3-28 months), there was no recurrence. CONCLUSION: Cryosurgery to treat varicose veins is an effective and safe treatment modality in terms of postoperative complication, cosmetic result, and recurrence.

Parametric Study of an Electroosmotic Micromixer with Heterogeneous Charged Surface Patches.

A T-shaped micromixer featuring electroosmotic flow with heterogeneous charged surface patches on the channel walls was analyzed, and an improved design was proposed to enhance mixing performance. Numerical analysis was performed using steady Navier-Stokes equations with an additional electrokinetic body force. The numerical results for species concentration were validated with available experimental data. A parametric analysis of the micromixer was performed by varying channel height, channel width, patch width, and externally applied voltage. The effects of these parameters on the flow structure and mixing performance were analyzed in detail. A quantitative measurement based upon the mass variance was employed to quantify the mixing performance. Numerical results of the parametric study were used to propose an improved micromixer design with spacing between adjacent charged patches. The proposed design provided a more favorable flow structure to allow for enhanced mixing performance.