A micropump using amplified deformation of resilient membranes through oil hydraulics

Toward the development of micropumps that operate under low external air pressures, a new polydimethylsiloxane (PDMS), pneumatic micropump using amplified deformation of resilient PDMS membranes through oil hydraulics was presented in this study. The new micropump employed oil-hydraulic chambers with pre-filled mineral oil to amplify the deformation of flexible PDMS membranes; it therefore delivered a higher pumping rate and withstood a greater back pressure while requiring a significantly lower external air pressure for actuation. The optimized pumping rate and back pressure of the oil-hydraulic micropump compared favorably to previous pneumatic micropumps. Characterization of the micropump revealed that the oil hydraulics amplified the deformation of PDMS membranes by approximately threefold and improved the pumping rate and the back pressure by 77 and 21 %, respectively. With high pumping performances and the capability to be driven with only a low air pressure, this new micropump may therefore become a key component in future microfluidic devices and lab-on-a-chip systems.     

单泵控制聚焦流形态的微流控芯片的研制

研究一种单动力源、聚焦流形态可控的用于细胞排队的微流控芯片。建立了样品沟道与鞘流沟道不同长度比例、不同夹角的模型并进行了不同负压条件下聚焦流形态仿真,运用SPSS软件进行了回归分析并进行了模型优化。在芯片的微加工过程中,利用印刷电路板(PCB)制作了母板,以聚二甲基硅氧烷(PDMS)为芯片主要材料,制作了PDMS—PDMS,PDMS—玻璃及PCB—PDMS三种芯片。制作的芯片能够在单个动力源条件下控制聚焦流宽度,使不同大小的微粒及细胞呈单个排列流动。研究结果为分析不同尺寸的细胞而选择合适的样品流沟道与鞘流沟道长度、夹角等条件提供了依据,所制作的芯片也达到了廉价且实用的目的。     

高聚物微流控芯片上集成化气动微阀的研制

报道了一种新型的聚甲基丙烯酸甲酯(PMMA)/聚二甲基硅氧烷(PDMS)复合芯片。该芯片采用PMMA-PDMS…PDMS-PMMA的四层构型,以在芯片上集成气动微阀。具有液路和控制通道网路的PMMA基片与PDMS弹性膜间采用不可逆封接,分别形成液路半芯片和控制半芯片,而2个半芯片则依靠PDMS膜间的粘性实现可逆封接,组成带有微阀的全芯片。这种制备方法解决了制备PMMA-PDMS-PMMA三层结构芯片的封接难题,封接过程简单可靠。其控制部分和液路部分可以单独更换,可进一步降低使用成本,尤其适合一次性应用场合。初步实验表明:该微阀具有良好的开关性能和耐用性。     

Novel surface acoustic wave (SAW)-driven closed PDMS flow chamber

In this article, we demonstrate a novel microfluidic flow chamber driven by surface acoustic waves. Our device is a closed loop channel with an integrated acoustic micropump without external fluidic connections that allows for the investigation of small fluid samples in a continuous flow. The fabrication of the channels is particularly simple and uses standard milling and PDMS molding. The micropump consists of gold electrodes deposited on a piezoelectric substrate employing photolithography. We show that the pump generates a pressure-driven Poiseuille flow, investigate the acoustic actuation mechanism, characterize the flow profile for different channel geometries, and evaluate the driving pressure, efficiency and response time of the acoustic micropump. The fast response time of our pump permits the generation of non-stationary flows. To demonstrate the versatility of the device, we have pumped a red blood cell suspension at a physiological rate of 60?beats/min.     

Mathematical analysis of oxygen transfer through polydimethylsiloxane membrane between double layers of cell culture channel and gas chamber in microfluidic oxygenator

For successful cell culture in microfluidic devices, precise control of the microenvironment, including gas transfer between the cells and the surrounding medium, is exceptionally important. The work is motivated by a polydimethylsiloxane (PDMS) microfluidic oxygenator chip for mammalian cell culture suggesting that the speed of the oxygen transfer may vary depending on the thickness of a PDMS membrane or the height of a fluid channel. In this paper, a model is presented to describe the oxygen transfer dynamics in the PDMS microfluidic oxygenator chip for mammalian cell culture. Theoretical studies were carried out to evaluate the oxygen profile within the multilayer device, consisting of a gas reservoir, a PDMS membrane, a fluid channel containing growth media, and a cell culture layer. The corresponding semi-analytical solution was derived to evaluate dissolved oxygen concentration within the heterogeneous materials, and was found to be in good agreement with the numerical solution. In addition, a separate analytical solution was obtained to investigate the oxygen pressure drop (OPD) along the cell layer due to oxygen uptake of cells, with experimental validation of the OPD model carried out using human umbilical vein endothelial cells cultured in a PDMS microfluidic oxygenator. Within the theoretical framework, the effects of several microfluidic oxygenator design parameters were studied, including cell type and critical device dimensions.     

A low molecular weight cut-off polymer–silicate membrane for microfluidic applications

In this article, we report a novel approach to fabricating a low molecular weight cut-off membrane that could readily be employed for several microfluidic applications. The reported structure was created by selectively retaining a precursor solution [5% (w/v) maleic anhydride, 21% (v/v) (37:1) acrylamide/bisacrylamide, and 0.2% (w/v) VA-086 photoinitiator] in a chosen location of a microfluidic network via capillary forces and then photo-polymerizing the mixture. The pores in the resulting membrane were subsequently filled with 3-aminopropyltriethoxysilane, heated, and then treated with sodium silicate solution and heated again, giving a structure having reduced porosity. The composite membrane thus created has been shown to have a molecular weight cut-off that is at least an order of magnitude smaller than other photo-polymerized microfluidic membranes reported in the literature. Moreover, this polymer–silicate structure was observed to be capable of blocking electroosmotic flow, thereby generating a pressure gradient around its interface with an open microchannel upon application of an electric field across the microchannel-membrane junction. In this study, a fraction of the resulting hydrodynamic flow was successfully guided to an electric field free analysis channel to implement a pressure-driven assay. With our current design pressure-driven velocities, up to 1.8 mm/s was generated in the electric field free analysis channel for an applied voltage of 2 kV in the pumping section. Finally, the functionality of this integrated microfluidic device was demonstrated by implementing a reverse phase chromatographic separation using the pressure-driven flow generated on-chip.     

Inhibition of on-chip PCR using PDMS–glass hybrid microfluidic chips

In the course of developing a microfluidic analytical platform incorporating the polymerase chain reaction (PCR) and subsequent capillary electrophoresis (CE) analysis for a variety of bio-assays, we examined PCR inhibition through surface interactions with the chip materials. Our devices perform PCR in a three-layer chip, a glass–poly(dimethylsiloxane)–glass sandwich in which the poly(dimethylsiloxane) (PDMS, a silicone rubber) layer is used for pneumatic membrane pumping and valving of the PCR reagents. Initial on-chip PCR–CE tests of BK virus replicated in multiple uncoated chips showed variable results, usually yielding no detectable product at the target sample concentrations used. Subsequent “chip-flush” experiments, where water or reagents were flushed through a chip and subsequently incorporated in off-chip PCR, highlighted bovine serum albumin (BSA) amongst other pre-treatments, chip materials and PCR recipes as being effective in mitigating inhibition. When the BSA channel pre-coating was applied to on-chip PCR–CE experiments, a substantial improvement (10× to 40×) in signal-to-noise (S/N) of the CE product peak was conferred, and was shown with high confidence despite high S/N variability. This is the first study to quantitatively examine BSA’s ability to reduce inhibition of PCR performed on PDMS chips, and one of very few microfluidic PCR inhibition studies of any kind to use a large number of microfluidic chips (~400). The simplicity and effectiveness of our BSA coating suggest that passivating materials applied to microfluidic device channel networks may provide a viable pathway for development of bio-compatible devices with reduced complexity and cost.     

Precise control of the pressure-driven flows considering the pressure fluctuations induced by the process of droplet formation

The pressure-driven device is designed to control the flow rates of the droplet microfluidic systems, which can significantly reduce the flow-rate fluctuations coming from the pump source. As monodisperse droplets are formed in the microchannel, periodic pressure fluctuations can be induced by the dynamic process of droplet formation, which can influence the stability and control precision of the pressure-driven flows. The effects of the pressure fluctuations induced by the droplet formation process on the dynamic characteristics of the open-loop and closed-loop control pressure-driven devices are comparatively studied. Particularly, a proportional–integral controller (PI controller) is integrated with the closed-loop control pressure-driven device and the effects of the PI controller parameters on the stability and control accuracy of the pressure-driven flows are tested experimentally. Particularly, by properly choosing the parameters of the PI controller, the magnitude of the periodic pressure fluctuations can be reduced drastically, which obviously increases the control precision of the pressure-driven flows.     

Normally-closed peristaltic micropump with re-usable actuator and disposable fluidic chip

We present a new peristaltic micropump offering three key features: (i) a disposable pump body and a re-useable actuator unit, (ii) an intrinsic normally-closed mechanism blocking unintended liquid flows up to a pressure of 100 kPa and (iii) a backpressure independent pump performance up to 40 kPa. The modular concept basing on a re-usable actuator unit and a low-cost disposable microfluidic chip enables an easy and cost-efficient exchange of all contaminated parts after use, which addresses especially the needs in the health care sector. The intrinsic normally-closed feature blocks liquid flow in both directions up to a pressure difference of 100 kPa when the electric power is off. The micropump is actuated in a peristaltic manner by three piezostack actuators. Up to a frequency of 15 Hz the pump rate increases linearly with operation frequency leading to a pump rate of 120 μL/min. This was proved for an operation voltage of 140 V by pumping water. In addition the pump rate is independent on backpressure up to 40 kPa and shows a linear decrease for higher pressure differences. The maximum achievable backpressure at zero flow rate was extrapolated to be 180 kPa. As for all peristaltic micropumps, the pump is bidirectional, e.g. the pump direction can be changed forward to reverse mode.     

A self-converging atomized mist spray device using surface acoustic wave

This paper presents an innovative versatile method aiming at rapid fabrication of a master for polydimethylsiloxane (PDMS) molding. This technology is relying on liquid dielectrophoresis electromechanical microfluidic transduction for programmable ultraviolet (UV) glue manipulation. It enables formation of the master in a tailor-made approach, avoiding the need of micromachined structures unlike in conventional methods. The principle is simple: UV glue, while in liquid phase, is actuated onto an array of electrodes patterned on a Si substrate and cured afterward by UV exposure. The silicon chip and the glue microstructures defined atop of it then play the role of a master for PDMS molding. The glue microstructures’ shape is hemispherical which is of high interest for many microfluidic applications. This concept is assessed and validated with two different PDMS chip replica designs, both of them illustrating representative applications in continuous microfluidic: a T-junction design for inflow droplet generation and a “Quake” type valve. Lastly, this protocol has shown to be recyclable since the UV glue microstructures once formed can be easily removed by immersion in an acetone bath, such as the chip is reset and can be reprogrammed afterward to build another glue channels geometry.     

新型双并联电渗微泵的制备与测试

设计了一个双并联电渗驱动泵,它由三条并联的主通道和叉指型电极两部分组成,其中每条主通道由若干个与电渗流形成方向成45°角的沟槽并联构成。通过选用ITO载玻片作为芯片基底并获得其最佳工艺参数,制作了带电极的PDMS-玻璃微流控芯片。最后对制作的电渗微泵进行测试,通过记录一段时间内单个主通道泵输送液体的体积,得出单个主通道的流速与微泵总流速。实验发现在5V内,微泵泵送液体的能力随着电压的增加而增大,微泵流速可以达到正常人体眼球房水生成速度,该结构在未来房水引流器件制作方面具有潜在的应用价值。     

Printing 3D microfluidic chips with a 3D sugar printer

This study demonstrated how to quickly and effectively print two-dimensional (2D) and three-dimensional (3D) microfluidic chips with a low-cost 3D sugar printer. The sugar printer was modified from a desktop 3D printer by redesigning the extruder, so the melting sugar could be extruded with pneumatic driving. Sacrificial sugar lines were first printed on a base layer followed by casting polydimethylsiloxane (PDMS) onto the layer and repeating. Microchannels were then printed in the PDMS solvent, microfluidic chips dropped into hot water to dissolve the sugar lines after the PDMS was solidified, and the microfluidic chips did not need further sealing. Different types of sugar utilized for printing material were studied with results indicating that maltitol exhibited a stable flow property compared with other sugars such as caramel or sucrose. Low cost is a significant advantage of this type of sugar printer as the machine may be purchased for only approximately $800. Additionally, as demonstrated in this study, the printed 3D microfluidic chip is a useful tool utilized for cell culture, thus proving the 3D printer is a powerful tool for medical/biological research.     

Thermo-pneumatic pumping in centrifugal microfluidic platforms

The pumping of fluids in microfluidic discs by centrifugal forces has several advantages, however, centrifugal pumping only permits unidirectional fluid flow, restricting the number of processing steps that can be integrated before fluids reach the edge of the disc. As a solution to this critical limitation, we present a novel pumping technique for the centrifugal microfluidic disc platform, termed the thermo-pneumatic pump (TPP), that enables fluids to be transferred the center of a rotating disc by the thermal expansion of air. The TPP is easy to fabricate as it is a structural feature with no moving components and thermal energy is delivered to the pump via peripheral infrared (IR) equipment, enabling pumping while the disc is in rotation. In this report, an analytical model for the operation of the TPP is presented and experimentally validated. We demonstrate that the experimental behavior of the pump agrees well with theory and that flow rates can be controlled by changing how well the pump absorbs IR energy. Overall, the TPP enables for fluids to be stored near the edge of the disc and transferred to the center on demand, offering significant advantages to the microfluidic disc platform in terms of the handling and storage of liquids.     

Detection of Cellular Parameters Using a Microfluidic Chip-Based System

Lab-on-a-chip technology achieves a reduction of sample and reagent volume and automates complex laboratory processes. Here, we present the implementation of cell assays on a microfluidic platform using disposable microfluidic chips. The applications are based on the controlled movement of cells by pressure-driven flow inside networks of microfluidic channels. Cells are hydrodynamically focused and pass the fluorescence detector in single file. Initial applications are the determination of protein expression and apoptosis parameters. The microfluidic system allows unattended measurement of six samples per chip. Results obtained with the microfluidic chips showed good correlation with data obtained using a standard flow cytometer.     

Stamp-and-stick room-temperature bonding technique for microdevices

Multilayer MEMS and microfluidic designs using diverse materials demand separate fabrication of device components followed by assembly to make the final device. Structural and moving components, labile bio-molecules, fluids and temperature-sensitive materials place special restrictions on the bonding processes that can be used for assembly of MEMS devices. We describe a room temperature "stamp and stick (SAS)" transfer bonding technique for silicon, glass and nitride surfaces using a UV curable adhesive. Alternatively, poly(dimethylsiloxane) (PDMS) can also be used as the adhesive; this is particularly useful for bonding PDMS devices. A thin layer of adhesive is first spun on a flat wafer. This adhesive layer is then selectively transferred to the device chip from the wafer using a stamping process. The device chip can then be aligned and bonded to other chips/wafers. This bonding process is conformal and works even on surfaces with uneven topography. This aspect is especially relevant to microfluidics, where good sealing can be difficult to obtain with channels on uneven surfaces. Burst pressure tests suggest that wafer bonds using the UV curable adhesive could withstand pressures of 700 kPa (7 atmospheres); those with PDMS could withstand 200 to 700 kPa (2-7 atmospheres) depending on the geometry and configuration of the device.     

SOI technology for future high-performance smart cards

Chips based on silicon-on-insulator (SOI) technology meet the tough performance and security requirements presented by smart cards. A test chip manufactured in a fully depleted SOI process incorporates a charge pump and random-number generator, critical smart-card circuit blocks.     

3D-printed peristaltic microfluidic systems fabricated from thermoplastic elastomer

Recent advancements in 3D printing technology have provided a potential low-cost and time-saving alternative to conventional PDMS (polydimethylsiloxane)-based microfabrication for microfluidic systems. In addition to reducing the complexity of the fabrication procedure by eliminating such intermediate steps as molding and bonding, 3D printing also offers more flexibility in terms of structural design than the PDMS micromolding process. At present, 3D-printed microfluidic systems typically utilize a relatively ‘stiff’ printing material such as ABS (acrylonitrile butadiene styrene copolymers), which limits the implementation of large mechanical actuation for active pumping and mixing as routinely carried out in a PDMS system. In this paper, we report the development of an active 3D-printed microfluidic system with moving parts fabricated from a flexible thermoplastic elastomer (TPE). The 3D-printed microfluidic system consists of two pneumatically actuated micropumps and one micromixer. The completed system was successfully applied to the detection of low-level insulin concentration using a chemiluminescence immunoassay, and the test result compares favorably with a similarly designed PDMS microfluidic system. Prior to system fabrication and testing, the material properties of TPE were extensively evaluated. The result indicated that TPE is compatible with biological materials and its 3D-printed surface is hydrophilic as opposed to hydrophobic for a molded PDMS surface. The Young’s modulus of TPE is measured to be 16 MPa, which is approximately eight times higher than that of PDMS, but over one hundred times lower than that of ABS.     

Syringe-assisted point-of-care micropumping utilizing the gas permeability of polydimethylsiloxane

By utilizing the high gas permeability of polydimethylsiloxane (PDMS), a simple syringe-assisted pumping method was introduced. A dead-end microfluidic channel was partially surrounded by an embedded microchamber, with a thin PDMS wall isolating the dead-end channel and the embedded microchamber. A syringe was connected with the microchamber port by a short tube, and the syringe plunger was manually pulled out to generate low pressure inside the microchamber. When sample liquid was loaded in the inlet port, air trapped in the dead-end channel would diffuse into the surrounding microchamber through the PDMS wall, creating an instantaneous pumping of the liquid inside the dead-end channel. By only pulling the syringe manually, a constant low flow with a rate ranging from 0.089 to 4 nl/s was realized as functions of two key parameters: the PDMS wall thickness and the overlap area between the dead-end channel and the surrounded microchamber. This method enabled point-of-care pumping without pre-evacuating the PDMS devices in a bulky vacuum chamber.     

Valveless micropump with acoustically featured pumping chamber

This article presents a new design of a valveless micropump. The pump consists of a nozzle-shaped actuation chamber with acoustic resonator profile, which functions as both pumping chamber and flow rectification structure. The pump is fabricated by lamination of layers made of polymethyl-methacrylate (PMMA) and dry adhesives, and is driven by a piezoelectric disk. The performance of the pump has been studied by both experimental characterization and numerical simulations. Both the experimental and numerical results show that the pump works well at low frequencies of 20–100 Hz to produce relatively high backpressures and flowrates. Moreover, the numerical simulations show that in the pumping frequency range, the flow patterns inside the chamber are found to be asymmetric in one pumping cycle so as to create a net flowrate, while outside the pumping frequency range, the flow patterns become symmetric in the pumping cycle. The pumping frequency can be shifted by modifying the pump configuration and dimensions. The pump is suitable for microfluidic integrations.     

Characterization of a high-resolution solid-state micropump that can be integrated into microfluidic systems

Ni–Mn–Ga is a magnetic shape memory (MSM) alloy that can strain up to 6 % when a magnetic field is applied to it. By applying a localized magnetic field to the MSM element, the strain can be precisely controlled and manipulated. By using Ni–Mn–Ga and a local magnetic field, an MSM micropump that is capable of controlling the flow within a microfluidic system has been developed. A computational fluid dynamics analysis illustrates the flow of the liquid at the outlet of the micropump and will be used to optimize future models of the pump. The performance of the MSM micropump, such as its flow rate and pumping pressure, is measured and presented in this study. Beyond its performance, there are also several advantages intrinsic to the MSM micropump. It is controlled by a magnetic field and is therefore contact-free. Depending upon the magnetic field, the MSM micropump can act as either a valve or a reversible pump. It is self-priming and capable of pumping gases as well as viscous liquids, and it has a simple design which consists primarily of the MSM alloy itself. Coupled with its scalability, it is clear that the MSM micropump is a strong candidate for an integratable flow control solution.