Generation Characteristics of Highly Uniform Nonspherical Droplets of Soybean Oil Using Microchannel Array Devices

This paper investigated the generation characteristics of nonspherical oil-in-water (O/W) droplets consisting of food-grade components using microchannel (MC) array devices that have many rectangular MCs with shallow wells. The well height was designed to be twice the MC height. Two hydrophilic MC array devices made of surface-oxidized single-crystal silicon with equivalent MC diameters of 3.2 and 8.4 μm were used. Refined soybean oil was used as the to-be-dispersed phase, and a Milli-Q water solution of 1.0 wt% polyoxyethylene (20) sorbitan monolaurate (Tween20) was used as the continuous phase. Highly uniform discoid droplets with diameters of 9.0 and 21.5 μm, heights of 4.6 and 9.8 μm, and coefficients of variation of less than 4% were generated by simply forcing a to-be-dispersed phase via rectangular MCs into a well filled with a continuous phase. The to-be-dispersed phase pressures necessary for droplet generation were less than 8 kPa. The detailed generation process of the discoid droplets was analyzed using movie clips taken by a high-speed camera. Key phenomena during the detachment process were considered to be rapid flow of the to-be-dispersed phase into the well and instantaneous pinch-off of the neck. The effect of the to-be-dispersed phase velocity inside a rectangular MC (U _d,MC) on the resultant droplet diameter and the droplet-generation rate was also analyzed. Size-controlled discoid droplets were stably generated via the rectangular MC below the critical U _d,MC, and the droplet-generation rate became maximum at the critical U _d,MC.     

微通道经皮肾镜取石术和标准通道经皮肾镜取石术的临床对比研究

目的：比较微通道经皮肾镜取石术和标准通道经皮肾镜取石术的临床效果。方法：选取2010 年1 月至2014 年5 月我院收 治的118 例肾结石患者,根据治疗方案分为微通道经皮肾镜取石术（MPCNL）（M 组,62 例）和标准通道经皮肾镜取石术（SPCNL） （S组,56 例）,比较两组术中术后相关指标和并发症情况。结果：与S 组相比,M组的手术时间更长,冲水量更多,但手术中出血量 更少,差异有统计学意义（P<0.05）;M 组术后血肌酐(Scr)、住院时间、卧床时间以及术后费用均小于或短于S 组,差异有统计学意 义（P<0.05）;两组结石清除率没有显著差异（P>0.05）;两组术后发热、出血、介入栓塞、结合穿孔、脓毒血症等并发症比较差异无统 计学意义（P>0.05）。结论：行MPCNL患者相比行SPCNL患者术后效果更好,临床上可根据结石的大小选择手术类型。     

Preparation of astaxanthin by lipase-catalyzed hydrolysis from its esters in a slug-flow microchannel reactor

Natural astaxanthin is widely used as a food and cosmetics additive because of its multiple biological activities. However, astaxanthin produced by Haematococcus pluvialis is generally esterified, and its activity is far less than that of free astaxanthin. Hydrolysis of astaxanthin esters to free astaxanthin by enzymes can overcome the drawbacks of chemical saponification methods. In this paper, a slug-flow microchannel reactor was constructed and tested in enzymatic hydrolysis of astaxanthin esters. The reactor consists of a “T” slug-flow generator, a stainless-steel microchannel, two constant-flow pumps, and a temperature controller. The reactor has the advantages of simple configuration and easy scale-up, and is suitable for two-phase biochemical reactions. Using the microchannel reactor, astaxanthin esters in H. pluvialis oil were efficiently hydrolyzed to free astaxanthin by lipase from Aspergillus niger. After hydrolysis, the content of free astaxanthin in H. pluvialis oil was 18.8 mg/L, 7.83-times higher than that before hydrolysis (2.13 mg/L). The hydrolysis rate reached 75.4 %. These results indicate that the microchannel reactor can be useful for the production of free astaxanthin from its esters.     

Enhanced dibenzothiophene biodesulfurization in a microchannel reactor

A microchannel reactor system was used in a biodesulfurization process in which the rate of biodesulfurization in the oil/water phase of the microchannel reaction was more than nine-fold that in a batch (control) reaction. In addition, the microchannel reaction system using a bacterial cell suspension degraded alkylated dibenzothiophene that was not degraded by the batch reaction system. This work provides a foundation for the application of a microchannel reactor system consisting of biological catalysts using an oil/water phase reaction.     

Three-dimensional focusing of red blood cells in microchannel flows for bio-sensing applications

Three-dimensional (3D) focusing of particles in microchannels has been a long-standing issue in the design of biochemical/biomedical microdevices. Current microdevices for 3D cell or bioparticle focusing involve complex channel geometries in view of their fabrication because they require multiple layers and/or sheath flows. This paper proposes a simple method for 3D focusing of red blood cells (RBCs) in a single circular microcapillary, without any sheath flows, which is inspired from the fluid dynamics phenomenon in that a spherical particle lagging behind a Poiseuille flow migrates toward and along the channel axis. More explicitly, electrophoresis of RBCs superimposed on the pressure-driven flow is utilized to generate an RBC migration mode analogous to this phenomenon. A particle-tracking scheme with a sub-pixel resolution is implemented to spatially position red blood cells flowing through the channel, so that a probability density function (PDF) is constructed to evaluate the tightness of the cell focusing. Above a specific strength of the electric field, approximately 90% of the sheep RBCs laden in the flow are tightly focused within a beam diameter that is three times the cell dimension. Particle shape effect on the focusing is discussed by making comparisons between the RBCs and the spherical particles. The lateral migration velocity, predicted by an existing theoretical model, is in good agreement with the present experimental data. It is noteworthy that 3D focusing of non-spherical particles, such as RBCs, has been achieved in a circular microchannel, which is a significant improvement over previous focusing methodologies.     

Visualization study of motion and deformation of red blood cells in a microchannel with straight,divergent and convergent sections

The size of red blood cells (RBC) is on the same order as the diameter of microvascular vessels. Therefore, blood should be regarded as a two-phase flow system of RBCs suspended in plasma rather than a continuous medium of microcirculation. It is of great physiological and pathological significance to investigate the effects of deformation and aggregation of RBCs on microcirculation. In this study, a visualization experiment was conducted to study the microcirculatory behavior of RBCs in suspension. Motion and deformation of RBCs in a microfluidic chip with straight, divergent, and convergent microchannel sections have been captured by microscope and high-speed camera. Meanwhile, deformation and movement of RBCs were investigated under different viscosity, hematocrit, and flow rate in this system. For low velocity and viscosity, RBCs behaved in their normal biconcave disc shape and their motion was found as a flipping motion: they not only deformed their shapes along the flow direction, but also rolled and rotated themselves. RBCs were also found to aggregate, forming rouleaux at very low flow rate and viscosity. However, for high velocity and viscosity, RBCs deformed obviously under the shear stress. They elongated along the flow direction and performed a tank-treading motion.     

Epithelial cell patterns on a PDMS polymer surface using a micro plasma structure

We developed a simple and reproducible epithelial cell-patterning tool on a PDMS (polydimethylsiloxane) polymer surface using a micro plasma structure that did not require chemical or biological treatment. The concept behind this novel approach was based on the fact that cells should easily adhere to the plasma-treated PDMS surface and not the inherent PDMS surface. The micro plasma structure consisted of copper and SU-8 photoresist on a glass substrate. A predetermined space (micro plasma chamber) was formed between the copper electrode layer on the upper part and the PDMS plate surrounded by the SU-8 photoresist structure. The single cell pattern was achieved by introducing a micro-plasma structure of 30 μm in width. Using this approach, a closed cell pattern was successfully developed using a micro chamber structure that was 200 μm in diameter with a microchannel that was 10 μm in width.     

微通道与标准通道经皮肾镜碎石术对上尿路结石患者肾功能及机体氧化应激反应的影响

目的:探讨微通道与标准通道经皮肾镜碎石术(PCNL)对上尿路结石患者肾功能及机体氧化应激反应的影响。方法:选取2017年3月到2018年9月在成都医学院第一附属医院接受治疗的上尿路结石患者106例,根据随机数字表法将患者分为微通道组与标准通道组各53例,其中微通道组采用微通道PCNL进行治疗,标准通道组采用标准通道PCNL进行治疗。比较两组患者的手术时间、术中出血量、一次性结石清除率、住院时间、手术感染率。比较两组患者术前、术后1d、术后3d的血尿素氮(BUN)、血肌酐(SCr)、C反应蛋白(CRP)、肿瘤坏死因子-α(TNF-α)、白介素-6(IL-6)、皮质醇(Cor)、肾上腺素(AD)和去甲肾上腺素(NE)。结果:微通道组的手术时间长于标准通道组,术中出血量少于标准通道组(P0.05)。两组患者各个时间点的BUN、SCr水平比较无统计学差异(P0.05),两组患者术后1d的BUN、SCr水平高于术前(P0.05)。两组患者术后1d、术后3d的CRP、TNF-α、IL-6水平较术前明显升高(P0.05);微通道组术后3d的CRP、TNF-α、IL-6水平低于标准通道组(P0.05)。两组患者术后1d、术后3d的Cor、AD、NE水平较术前明显升高(P0.05);微通道组术后1d、术后3d的Cor、AD、NE水平低于标准通道组(P0.05)。结论:微通道PCNL与标准通道PCNL治疗上尿路结石患者具有较好的疗效,但微通道PCNL术中出血量更少,且患者的炎症反应和氧化应激程度更轻。     

24-gauge ultrafine cryoprobe with diameter of 550 μm and its cooling performance

This paper describes the development of a novel cryoprobe with the same size as a 24-gauge injection needle and the evaluation of its cooling performance. This ultrafine cryoprobe was designed to reduce the invasiveness and extend application areas of cryosurgery. The ultrafine cryoprobe has a double-tube structure and consists of two stainless steel microtubes. The outer diameter of the cryoprobe is 550 μm, and the inner tube has a 70-μm inner diameter to depressurize the high-pressure refrigerant. By solving the bioheat transfer equation and considering freezing phenomena, the relationship between the size of the frozen region and the heat transfer coefficient of the refrigerant flow in an ultrafine cryoprobe was derived analytically. The results showed that the size of the frozen region is strongly affected by the heat transfer coefficient. A high heat transfer coefficient such as that of phase change heat transfer is required to generate a frozen region of sufficient size. In the experiment, trifluoromethane (HFC-23) was used as the refrigerant, and the cooling effects of the gas and liquid phase states at the inlet were evaluated. When the ultrafine cryoprobe was cooled using a liquid refrigerant, the surface temperature was approximately −50 °C, and the temperature distribution on the surface was uniform for a thermally insulated condition. However, for the case with vaporized refrigerant, the temperature distribution was not uniform. Therefore, it was concluded that the cooling mechanism using liquid refrigerant was suitable for ultrafine cryoprobes. Furthermore, to simulate cryosurgery, a cooling experiment using hydrogel was conducted. The results showed that the surface temperature of the ultrafine cryoprobe reached −35 °C and formed a frozen region with a radius of 4 mm in 4 min. These results indicate that the ultrafine cryoprobe can be applied in actual cryosurgeries for small affected areas.     

Enhanced thermal stability and mismatch discrimination of mutation-carrying DNA duplexes and their kinetic and thermodynamic properties in microchannel laminar flow

This article reports the enhancement of thermal stability involving normal duplex and mutation-carrying DNA duplexes in microchannel laminar flow. The application of an in-house temperature-controllable microchannel-type flow cell is demonstrated for improved discrimination of mismatch base pairs such as A-G and T-G that are difficult to distinguish due to the rather small thermal destabilizations. Enhancement in thermal stability is reflected by an increased thermal melting temperature achieved in microchannel laminar flow as compared with batch reactions. To examine the kinetics and thermodynamics of duplex-coil equilibrium of DNA oligomers, denaturation-renaturation hysteresis curves were measured. The influence of microchannel laminar flow on DNA base mismatch analysis was described from the kinetic and thermodynamic perspectives. An increasing trend was observed for association rate constant as flow rate increased. In contrast, an apparent decrease in dissociation rate constant was observed with increasing flow rate. The magnitudes of the activation energies of dissociation were nearly constant for both the batch and microchannel laminar flow systems at all flow rates. In contrast, the magnitudes of activation energies of association decreased as flow rate increased. These results clearly show how microchannel laminar flow induces change in reaction rate by effecting change in activation energy. We anticipate, therefore, that this approach based on microchannel laminar flow system holds great promise for improved mismatch discrimination in DNA analyses, particularly on single-base-pair mismatch, by pronouncedly enhancing thermal stability.