Pneumatic flow switching on centrifugal microfluidic platforms in motion

This paper describes a flow switching technique applicable to centrifugal microfluidic platforms, using a regulated stream of compressed gas. This pneumatic flow switching technique allows for flow control at a T-shaped junction between one inlet channel and two outlet channels. This technique provides a noncontact, robust, and efficient method for switching the direction of fluid flow while a disk is rotating at relatively low frequencies. The switching operation can be implemented reproducibly with applied gas flow rates between 17 and 58 L min(-1) and rotational frequencies between 400 rpm (6.6 Hz) and 1200 rpm (20 Hz).     

Automated liquid-liquid extraction by pneumatic recirculation on a centrifugal microfluidic platform

In this technical note, a liquid-liquid extraction technique was performed using pneumatic liquid recirculation on a centrifugal microfluidic device. Non-contact pneumatic pumping enabled a multi-cycle liquid-liquid extraction process using aqueous iodine in a potassium iodide solution and hexadecane while requiring a minimal amount of space on the device. The extraction process was completely automated on the device following sample introduction and required only 50 s for each extraction cycle. The pumping rate achieved during liquid recirculation was 120 ± 10 μL/min. A recycling process such as the one demonstrated would be difficult to implement in a conventional centrifugal microfluidic system.     

Microfluidic chips for the study of cell migration under the effect of chemicals

Numerical simulation of the formation of a chemoattractant gradient in reaction chambers of a chip having different geometries enabled the determination of a structure suitable for the study of cell migration, in accordance with which hybrid polymer–glass microfluidic devices were manufactured. Verification of the procedures of alignment of cells in the reaction chamber of the chip by centrifugal force and subsequent culturing of the cells showed that microfluidic chips can be used to study cell migration under the effect of the chemoattractant gradient in vitro.     

Optical detection strategies for centrifugal microfluidic platforms

Centrifugal microfluidic systems have become one of the principal platforms for implementing bioanalytical assays, most notably for biomedical point-of-care diagnostics. These so-called ‘lab-on-a-disc’ systems primarily utilise the rotationally controlled centrifugal field in combination with capillary forces to automate a range of laboratory unit operations (LUOs) for sample preparation, such as metering, aliquoting, mixing and extraction for biofluids as well as sorting, isolation and counting of bioparticles. These centrifugal microfluidic LUOs have been regularly surveyed in the literature. However, even though absolutely essential to provide true sample-to-answer functionality of lab-on-a-disc platforms, systematic examination of associated, often optical, read-out technologies has been so far neglected. This review focusses on the history and state-of-the-art of optical read-out strategies for centrifugal microfluidic platforms, arising (commercial) application potential and future opportunities.     

离心-温度复合试验箱温度场模拟分析

对离心-温度复合试验箱中离心环境对温度场均匀性影响进行了模拟研究,并分析了结构条件对温度均匀性的改善效果。研究了离心-温度复合条件下的控制方程,以此为基础采用有限元分析的方法,对不同结构条件的温度场分析了温度均匀性差异,并提出了进一步改善温度均匀性的方法。结果表明,离心环境下的科氏力对空气流场轴向运动的影响会导致试验箱内温度均匀性差异,试验箱中加入风扇和导流装置能够有效改善内部温度均匀性。     

Probing Cell Deformability via Acoustically Actuated Bubbles

An acoustically actuated, bubble‐based technique is developed to investigate the deformability of cells suspended in microfluidic devices. A microsized bubble is generated by an optothermal effect near the targeted cells, which are suspended in a microfluidic chamber. Subsequently, acoustic actuation is employed to create localized acoustic streaming. In turn, the streaming flow results in hydrodynamic forces that deform the cells in situ. The deformability of the cells is indicative of their mechanical properties. The method in this study measures mechanical biomarkers from multiple cells in a single experiment, and it can be conveniently integrated with other bioanalysis and drug‐screening platforms. Using this technique, the mean deformability of tens of HeLa, HEK, and HUVEC cells is measured to distinguish their mechanical properties. HeLa cells are deformed upon treatment with Cytochalasin. The technique also reveals the deformability of each subpopulation in a mixed, heterogeneous cell sample by the use of both fluorescent markers and mechanical biomarkers. The technique in this study, apart from being relevant to cell biology, will also enable biophysical cellular diagnosis.     

Microfabricated renewable beads-trapping/releasing flow cell for rapid antigen-antibody reaction in chemiluminescent immunoassay

A renewable flow cell integrating a microstructured pillar-array filter and a pneumatic microvalve was microfabricated to trap and release beads. A bead-based immunoassay using this device was also developed. This microfabricated device consists of a microfluidic channel connecting to a beads chamber in which the pillar-array filter is built. Underneath the filter, there is a pneumatic microvalve built across the chamber. Such a device can trap and release beads in the chamber by "closing" or "opening" the microvalve. On the basis of the pneumatic microvalve, the device can trap beads in the chamber before performing an assay and release the used beads after the assay. Therefore, this microfabricated device is suitable for "renewable surface analysis". A model analyte, 3,5,6-trichloropyridinol (TCP), was chosen to demonstrate the analytical performance of the device. The entire fluidic assay process, including beads trapping, immuno binding, beads washing, beads releasing, and chemiluminesence signal collection, could be completed in 10 min. The immunoassay of TCP using this microfabricated device showed a linear range of 0.20-70 ng/mL with a limit of detection of 0.080 ng/mL. The device was successfully used to detect TCP spiked in human plasma at the concentration range of 1.0-50 ng/mL, with an analytical recovery of 81-110%. The results demonstrated that this device can provide a rapid, sensitive, reusable, low-cost, and automatic tool for detecting various biomarkers in biological fluids.     

Investigation into the applicability of the centrifugal microfluidics platform for the development of protein-ligand binding assays incorporating enhanced green fluorescent protein as a fluorescent reporter

The incorporation of a protein-ligand binding assay into a centrifugal microfluidics platform is described. The platform itself is a disc-shaped polymer substrate, upon which a series of microfluidic channels and reservoirs have been machined. Centrifugal microfluidics platforms require no internal moving parts, and fluid propulsion is achieved solely through rotation of the disc. Fluid flow is controlled by passive valves, the opening of which is dependent on the angular frequency of the rotating platform, the channel dimensions, and the physical properties of the fluid. To evaluate the effectiveness of incorporating a protein-based assay onto the centrifugal microfluidics analytical platform, a class-selective, homogeneous assay for the detection of phenothiazine antidepressants was employed. This class of drugs is known to bind to calmodulin, a calcium binding protein. Specifically, a fusion protein between calmodulin and enhanced green fluorescent protein was utilized. Calmodulin undergoes a conformational change upon binding to phenothiazines that alters the fluorescence properties of the attached fluorescent protein, which can be correlated to the concentration of the drug present. Another important aspect of this work was to study the efficacy of the platform to perform reconstitution assays. To do this, the biological reagent was dried on the platform and rehydrated to carry out the assay. The ability to prealiquot reagents on the platform should enhance its versatility and portability. The integration of protein-based assays in this platform should be useful in the design of analytical systems for high-throughput screening of pharmaceuticals and clinical diagnostics.     

Development of a fully integrated analysis system for ions based on ion-selective optodes and centrifugal microfluidics

A fully integrated, miniaturized analysis system for ions based on a centrifugal microfluidics platform and ion-selective optode membranes is described. The microfluidic architecture is composed of channels, five solution reservoirs, a measuring chamber, and a waste reservoir manufactured onto a disk-shaped substrate of poly(methyl methacrylate). Ion-selective optode membranes, composed of plasticized poly(vinyl chloride) impregnated with an ionophore, a proton chromoionophore, and a lipophilic anionic additive, were cast, with a spin-on device, onto a support layer and then immobilized on the disk. Fluid propulsion is achieved by the centrifugal force that results from spinning the disk, while a system of valves is built onto the disk to control flow. These valves operate based on fluid properties and fluid/substrate interactions and are controlled by the angular frequency of rotation. With this system, we have been able to deliver calibrant solutions, washing buffers, or "test" solutions to the measuring chamber where the optode membrane is located. An analysis system based on a potassium-selective optode has been characterized. Results indicate that optodes immobilized on the platform demonstrate theoretical responses in an absorbance mode of measurement. Samples of unknown concentration can be quantified to within 3% error by fitting the response function for a given optode membrane using an acid (for measuring the signal for a fully protonated chromoionophore), a base (for fully deprotonated chromoionophore), and two standard solutions. Further, the ability to measure ion concentrations by employing one standard solution in conjunction with acid and base and with two standards alone were studied to delineate whether the current architecture could be simplified. Finally, the efficacy of incorporating washing steps into the calibration protocol was investigated.     

离心渗铸工艺中铝熔体在SiC多孔介质内的渗流传热过程特征及最弱环损伤模型

针对离心力场中铝熔体在SiC多孔介质内的渗流传热现象,考虑离心力对渗流传热过程的影响,根据局部非热平衡假设建立了多孔介质渗流传热模型。采用全隐格式TDMA算法和第一类迎风差分方法对渗流过程的温度场进行了数值计算。研究分析了不同复合层厚度下离心渗透过程中的流场和温度场瞬态变化规律。计算结果表明,在渗透区域,熔体与SiC颗粒存在着一定温差,而在渗透前沿,这种温差相对较大。渗流速度变化存在两个十分明显的阶段,渗流速度较高且急剧下降的初始渗透阶段以及渗流速度相当平稳的后续阶段。渗流速度的这种瞬态变化规律主要是多孔介质内流体流动与离心压力相互作用的结果。渗透初期形成的紊流状态,是导致熔体卷吸空气、使复合材料内部形成气孔的主要原因之一。选择合适的工艺参数对于确保铸件质量是十分关键的。     

Microfluidic Molding of Photonic Microparticles with Engraved Elastomeric Membranes

A microfluidic approach to prepare photonic microparticles by repeated molding of photocurable colloidal suspension is reported. An elastomeric membrane with negative relieves which vertically separates two microfluidic channels is integrated; bottom channel is used for suspension flow, whereas water‐filled top channel is used for pneumatic actuation of the membrane. Upon pressurization of the top channel, membrane is deformed to confine the suspension into its negative relieves, which is then polymerized by UV irradiation, making microparticles with mold shape. The microparticles are released from the mold by relieving the pneumatic pressure and flows through the bottom channel. This one cycle of molding, polymerization, and release can be repeatedly performed in microfluidic device of which pneumatic valves are actuated in a programmed manner. The microparticles exhibit structural colors when the suspension contains high concentration of silica nanoparticles; the nanoparticles form regular arrays and the microparticles reflect specific wavelength of light as a photonic crystals. The silica nanoparticles can be selectively removed to make pronounced structural colors. In addition, the microparticles can be further functionalized by embedding magnetic particles in the matrix of the microparticles, enabling the remote control of rotational motion of microparticles.     

气体腰轮流量计测量结果的不确定度分析

气体腰轮流量计属于气体容积式流量计的一种,根据其示值误差计算方法可分为A类气体腰轮流量计和B类气体腰轮流量计,使用仪表K系数计算示值误差的为A类,使用累积流量计算示值误差的为B类。针对这两类气体腰轮流量计的测量结果分别有不同的不确定度分析方法。     

Experimental Study of the Effect of the Helical Ribs in a Spirally Coiled Tube on the Friction Reactor and the Nusselt Number of a Nanofluid Flow in it

Journal of Engineering Physics and Thermophysics - The effect of the centrifugal force arising in a spirally coiled tube with helical ribs on the heat transfer in the fluid flow in it was...     

Microfluidic gradient formation for nanoflow chip LC

We report a method for forming a nanoflow liquid chromatography (nano-LC) gradient using a single fluid pump at flow rates below 1 muL/min by passively forming a gradient on a microfluidic device. This device works together with an Agilent HPLC-Chip to perform high-throughput nanoflow liquid chromatography/mass spectrometry (nano-LC/MS). The nanoflow gradient delay time is reduced from several minutes for a commercial LC nanoflow pump to only a few seconds with this microfluidic device, thus shortening the total analysis time and increasing the analysis throughput. With this microfluidic device, a nano-LC solvent delivery system can be greatly simplified and have increased robustness, reliability, reduced waste, and ease of use.     

离心泵转子动力学模型中流体力的简化

采用叶轮流体力的简化方式可以提高离心泵流体激励诱发振动的计算的准确程度。根据达朗伯原理对试验台架建立了包含离心泵基座的四圆盘三轴段转子动力学模型;将流体力分别简化为叶轮内20 %流体质量、40 %流体质量、CFD集中力与力矩,采用Newmark-隐式算法对转子动力学模型进行瞬态响应分析。结果表明,将叶轮上流体力简化为CFD;所得集中力与力矩时;可有效得出离心泵运转过程中流体激励所诱发的基座振动。而所获得的基座振动位移与加速度幅值均远大于将流体力简化为叶轮内20 %或40 %流体质量所获得的基座振动数值。另一方面,将流体力简化为叶轮内40 %流体质量所获得的基座振动大于简化为叶轮内20 %流体质量所获得的基座振动。     

Miniaturized Lab-on-a-Disc (miniLOAD)

A miniaturized centrifugal microfluidic platform for lab-on-a-chip applications is presented. Unlike its macroscopic Lab-on-a-CD counterpart, the miniature Lab-on-a-Disc (miniLOAD) device does not require moving parts to drive rotation of the disc, is inexpensive, disposable, and significantly smaller, comprising a 10-mm-diameter SU-8 disc fabricated through two-step photolithography. The disc is driven to rotate using surface acoustic wave irradiation incident upon a fluid coupling layer from a pair of offset, opposing single-phase unidirectional transducers patterned on a lithium niobate substrate. The irradiation causes azimuthally oriented acoustic streaming with sufficient intensity to rotate the disc at several thousand revolutions per minute. In this first proof-of-concept, the capability of the miniLOAD platform to drive capillary-based valving and mixing in microfluidic structures on a disc similar to much larger Lab-on-a-CD devices is shown. In addition, the ability to concentrate aqueous particle suspensions at radial positions in a channel in the disc dependent on the particles' size is demonstrated. To the best of our knowledge, the miniLOAD concept is the first centrifugal microfluidic platform small enough to be self-contained in a handheld device.     

Parameters influencing pulsed flow mixing in microchannels

The rapid mixing of reagents is a crucial step for on-chip chemical and biological analysis. It has been recently suggested that microfluidic mixing can be greatly enhanced by simply using time pulsing of the incoming flow rates of the two fluids to be mixed (Glasgow, I.; Aubry, N. Lab Chip 2003, 3, 114-120). This paper elaborates on the latter technique, showing through computational fluid dynamics how the mixing efficiency strongly depends on certain dimensionless parameters of the system, while remaining nearly insensitive to others. In particular, it is demonstrated that higher Strouhal numbers (ratio of flow characteristic time scale to the pulsing time period) and pulse volume ratios (ratio of the volume of fluid pulsed to the volume of inlet/outlet intersection) lead to better mixing. This paper also presents a physical device capable of mixing two reagents using pulsing, which shows improved mixing with greater values of the Strouhal number.     

Temperature measurement in microfluidic systems using a temperature-dependent fluorescent dye

A technique is described for the measurement of fluid temperatures in microfluidic systems based on temperature-dependent fluorescence. The technique is easy to implement with a standard fluorescence microscope and CCD camera. In addition, the method can be used to measure fluid temperatures with micrometer spatial resolution and millisecond time resolution. The efficacy of the method is demonstrated by measuring temperature distributions resulting from Joule heating in a variety of microfluidic circuits that are electrokinetically pumped. With the equipment used for these measurements, fluid temperatures ranging from room temperature to 90 degrees C were measured with a precision ranging from 0.03 to 3.5 degrees C-dependent on the amount of signal averaging done. The spatial and temporal resolutions achieved were 1 microm and 33 ms, respectively.     

Research on the particle movement in a flexible air chamber jig

Flexible air chamber jig is a new type jig, which has a wide application prospect. The stratification process of flexible air chamber jig was analyzed with discrete element method and computational fluid dynamic (DEM-CFD) model. Compared with other models, it can track the free surface and is closer to the actual situation. The analysis results were compared with the experimental results. The comparative results showed that the numerical analysis results were close to the experimental results, and the numerical analysis method was reasonable. For different stages of jigging, the stratification process and force of jigging particles were studied. According to the analysis results, the fluid plays different roles in different stages of particle movement. In the rising process, light particles were greatly affected by the fluid force, the time of this stage is important to stratification. The particle movement trajectory and stratification speed under different intake times was discussed, and it is concluded that intake time more than 18% of jigging cycle is reasonable.     

横向流体激振力作用下的不平衡离心叶轮转子分岔特性研究

将叶轮转子系统简化为Jeffcott转子，建立了不平衡离心叶轮转子在非线性横向流体激振力和非线线轴承油膜力作用下的振动模型，并推导了系统的无量纲运动方程。运用数值积分法研究了系统的分岔特性。最后分析了横向流体激振力以及叶轮不平质量对离心叶轮系统动力学性能的影响。