Rapid prototyping of thermoset polyester microfluidic devices

This paper presents a simple procedure for the fabrication of thermoset polyester (TPE) microfluidic systems and discusses the properties of the final devices. TPE chips are fabricated in less than 3 h by casting TPE resin directly on a lithographically patterned (SU-8) silicon master. Thorough curing of the devices is obtained through the combined use of ultraviolet light and heat, as both an ultraviolet and a thermal initiator are employed in the resin mixture. Features on the order of micrometers and greater are routinely reproduced using the presented procedure, including complex designs and multilayer features. The surface of TPE was characterized using contact angle measurements and X-ray photoelectron spectroscopy (XPS). Following oxygen plasma treatment, the hydrophilicity of the surface of TPE increases (determined by contact angle measurements) and the proportion of oxygen-containing functional groups also increases (determined by XPS), which indicates a correlated increase in the charge density on the surface. Native TPE microchannels support electroosmotic flow (EOF) toward the cathode, with an average electroosmotic mobility of 1.3 x 10(-4) cm(2) V(-1) s(-1) for a 50-microm square channel (20 mM borate at pH 9); following plasma treatment (5 min at 30 W and 0.3 mbar), EOF is enhanced by a factor of 2. This enhancement of the EOF from plasma treatment is stable for days, with no significant decrease noted during the 5-day period that we monitored. Using plasma-treated TPE microchannels, we demonstrate the separation of a mixture of fluorescein-tagged amino acids (glycine, glutamic acid, aspartic acid). TPE devices are up to 90% transparent (for approximately 2-mm-thick sample) to visible light (400-800 nm). The compatibility of TPE with a wide range of solvents was tested over a 24-h period, and the material performed well with acids, bases, alcohols, cyclohexane, n-heptane, and toluene but not with chlorinated solvents (dichloromethane, chloroform).     

Effect of deposition temperature and thermal annealing on the dry etch rate of a-C: H films for the dry etch hard process of semiconductor devices

The effect of deposition and thermal annealing temperatures on the dry etch rate of a-C:H films was investigated to increase our fundamental understanding of the relationship between thermal annealing and dry etch rate and to obtain a low dry etch rate hard mask. The hydrocarbon contents and hydrogen concentration were decreased with increasing deposition and annealing temperatures. The I(D)/I(G) intensity ratio and extinction coefficient of the a-C:H films were increased with increasing deposition and annealing temperatures because of the increase of sp² bonds in the a-C:H films. There was no relationship between the density of the unpaired electrons and the deposition temperature, or between the density of the unpaired electrons and the annealing temperature. However, the thermally annealed a-C:H films had fewer unpaired electrons compared with the as-deposited ones. Transmission electron microscopy analysis showed the absence of any crystallographic change after thermal annealing. The density of the as-deposited films was increased with increasing deposition temperature. The density of the 600 °C annealed a-C:H films deposited under 450 °C was decreased but at 550 °C was increased, and the density of all 800 °C annealed films was increased. The dry etch rate of the as-deposited a-C:H films was negatively correlated with the deposition temperature. The dry etch rate of the 600 °C annealed a-C:H films deposited at 350 °C and 450 °C was faster than that of the as-deposited film and that of the 800 °C annealed a-C:H films deposited at 350 °C and 450 °C was 17% faster than that of the as-deposited film. However, the dry etch rate of the 550 °C deposited a-C:H film was decreased after annealing at 600 °C and 800 °C. The dry etch rate of the as-deposited films was decreased with increasing density but that of the annealed a-C:H films was not. These results indicated that the dry etch rate of a-C:H films for dry etch hard masks can be further decreased by thermal annealing of the high density, as-deposited a-C:H films. Furthermore, not only the density itself but also the variation of density with thermal annealing need to be elucidated in order to understand the dry etch properties of annealed a-C:H films.     

Organic transistor based circuit as drive for planar microfluidic devices

Organic transistor based circuits are a promising candidate for acting as drivers for microfluidic devices handling discrete droplets. The ease of fabrication along with the ability to generate desired voltage levels for performing electrowetting based actuation of liquids make them an ideal match for discrete droplet based microfluidic systems. In this article, we report the implementation of an organic transistor based complementary metal-oxide semiconductor (CMOS) inverter used to actuate microliter quantities of droplets on a simple planar microfluidic device. We also present two approaches for fabricating an open-structured device for different applications. The inverter is fabricated using Pentacene and N, N′- bis (n-octyl) dicyanoperylene-3, 4:9, 10-bis (dicarboxyimide) (PDI-8CN₂) (Northwestern University). The inverter output is stable and repeatable and is used to actuate droplets over adjacent electrodes as well as in merging of discrete droplets.     

真空器件排气玻璃封接工艺研究

本文通过对真空器件排气玻璃封接工作中所见玻璃不透明现象的分析,结合反复工艺试验和相关资料,逐一提出了具体有效的解决方法、规避手段或减少(小)措施.通过高倍光学显微镜对比分析改进前后的封接效果,进一步证明解决方法有效,基本解决了文中所述的异常问题,给真空器件的科研生产工作提供了有力保障.     

A method for filling complex polymeric microfluidic devices and arrays

This paper describes an improved method for filling microfluidic structures with aqueous solutions. The method, channel outgas technique (COT), is based on a filling procedure carried out at reduced pressures. This procedure is compared with previously reported methods in which microfluidic channels are filled either by using capillary forces or by applying a pressure gradient at one or more empty reservoirs. The technique has proven to be > 90% effective in eliminating the formation of bubbles within microfluidic networks. It can be applied to many devices, including those containing PDMS-terminated channel features, a single channel inlet, and three-dimensional arrays.     

Electrophoretic analysis of N-glycans on microfluidic devices

We report rapid and efficient electrophoretic separations of N-glycans on microfluidic devices. Using a separation length of 22 cm and an electric field strength of 750 V/cm, analysis times were less than 3 min, and separation efficiencies were between 400,000 and 655,000 plates for the N-glycans and up to 960,000 plates for other sample components. These high efficiencies were necessary to separate N-glycan positional isomers derived from ribonuclease B and linkage isomers from asialofetuin. Structural isomers of N-glycans derived from a blood serum sample of a cancer patient were also analyzed to demonstrate that clinically relevant, complex samples could be separated on-chip with efficiencies similar to those derived from model glycoproteins. In addition, we compared microchip and capillary electrophoresis under similar separation conditions, and the microchips performed as well as the capillaries. These results confirmed that the noncircular cross section of the microchannel did not hamper separation performance. For all experiments, the glycan samples were derivatized with 8-aminopyrene-1,3,6-trisulfonic acid to impart needed charge for electrophoresis and a fluorescent label for detection.     

Surface-reactive acrylic copolymer for fabrication of microfluidic devices

A surface-reactive acrylic polymer, poly(glycidyl methacrylate-co-methyl methacrylate) (PGMAMMA), was synthesized and evaluated for suitability as a substrate for fabrication of microfluidic devices for chemical analysis. This polymer has good thermal and optical properties and is mechanically robust for cutting and hot embossing. A key advantage of this polymeric material is that the surface can be easily modified to control inertness and electroosmotic flow using a variety of chemical procedures. In this work, the procedures for aminolysis, photografting of linear polyacrylamide, and atom-transfer radical polymerization on microchannel surfaces in PGMAMMA substrates were developed, and the performance of resultant microfluidic electrophoresis devices was demonstrated for the separation of amino acids, peptides, and proteins. Separation efficiencies as high as 4.6 x 10(4) plates for a 3.5-cm-long separation channel were obtained. The results indicate that PGMAMMA is an excellent substrate for microfabricated fluidic devices, and a broad range of applications should be possible.     

去除光刻胶的新干法工艺

除去干刻或高剂量等离子注入后的光刻胶，一般是采用化学溶剂和酸类等湿刻法，以前有时采用干燥氧的等离子灰化法，然而成本高，具有危险性和污染性的化学湿刻法直接造成了环境污染，使得全球气候变暖，能源的大量消耗，地下水受到污染等等，一种新的干式去胶并且处理后可用去离子水DI清洗残留物的工艺方法（ENVIRO）已经在半导体芯片厂被成功地使用了12个多月。对于产量10000片／周的芯片厂，相对于化学湿刻法一年可以节省5百万美元溶剂消耗。     

Chemotaxis assays of mouse sperm on microfluidic devices

Sperm chemotaxis is an area of significant interest to scientists involved in reproductive science. Understanding how and when sperm cells are attracted to the egg could have profound effects on reproduction and contraception. In an effort to systematically study this problem, we have fabricated and evaluated a microfluidic device to measure sperm chemotaxis. The device was designed with a flow-through configuration using a spatially and temporally stable chemical gradient. Mouse sperm cells were introduced into the chemotaxis chamber between confluent flows of mouse ovary extract and buffer. The sperm experiencing chemotaxis swam toward the extract and were counted relative to those that swam toward the buffer. The ovary extracts were diluted from 10(2) to 10(7) times, and each extract dilution was screened for chemotaxis. Four out of six ovaries showed a strong chemotactic response at extract dilutions of 10(-3) to 10(-5). This device provided a convenient, disposable platform on which to conduct chemotaxis assays, and the flow-through design overcomes difficulties associated with distinguishing chemotaxis from trapping.     

Printed circuit technology for fabrication of plastic-based microfluidic devices

One of the primary advantages of using plastic-based substrates for microfluidic systems is the ease with which devices can be fabricated with minimal dependence on specialized laboratory equipment. These devices are often produced using soft lithography techniques to cast replicas of a rigid mold or master incorporating a negative image of the desired surface structures. Conventional photolithographic micromachining processes are typically used to construct these masters in either thick photoresist, etched silicon, or etched glass substrates. The speed at which new masters can be produced using these techniques, however, can be relatively slow and often limits the rate at which new device designs can be built and tested. In this paper, we show that inexpensive photosensitized copper clad circuit board substrates can be employed to produce master molds using conventional printed circuit technology. This process offers the benefits of parallel fabrication associated with photolithography without the need for cleanroom facilities, thereby providing a degree of speed and simplicity that allows microfluidic master molds with well-defined and reproducible structural features to be constructed in approximately 30 min in any laboratory. Precise control of channel heights ranging from 15 to 120 microm can be easily achieved through selection of the appropriate copper layer thickness, and channel widths as small as 50 microm can be reproducibly obtained. We use these masters to produce a variety of plastic-based microfluidic channel networks and demonstrate their suitability for DNA electrophoresis and microfluidic mixing studies.     

Calcium-assisted glass-to-glass bonding for fabrication of glass microfluidic devices

Glass is a desired material for many microfluidics applications. It is chemically resistant and has desirable characteristics for capillary electrophoresis. The process to make a glass chip, however, is lengthy and inconvenient, with the most difficult step often being the bonding of two planar glass substrates. Here we describe a new glass bonding technique, which requires only washing of the glass surfaces with a calcium solution and 1-2 h of bonding at 115 degrees C. We found calcium uniquely allows for this simple and efficient low-temperature bonding to occur, and none of the other cations we tried (e.g., Na (+), Mg (2+), Mn (3+)) resulted in satisfactory bonding. We determined this bond is able to withstand high applied field strengths of at least up to 4 kV x cm (-1). When intense pressure was applied to a fluid inlet, a circular portion of the coverslip beneath the well exploded outward but very little of the glass-glass interface debonded. In combination with the directed hydrofluoric acid etching of a glass substrate using a poly(dimethylsiloxane) (PDMS) etch guide, we were able to make glass chips with better than 90% yield within 6 h. This technique is compatible with inexpensive unpolished glass and is limited in resolution by the PDMS etch guide used and the intrinsic properties of isotropic etching.     

Versatile sensing devices for self-driven designated therapy based on robust breathable composite films

Flexible wearable electronics were developed for applications such as electronic skins,human-machine interactions,healthcare monitoring,and anti-infection therapy.But conventional materials showed impermeability,single sensing ability,and no designated therapy,which hindered their applications.Thus it was still a great challenge to develop electronic devices with multifunctional sensing properties and self-driven anti-infection therapy.Herein,flexible and breathable on-skin electronic devices for multifunctional fabric based sensing and self-driven designated anti-infection therapy were prepared successfully with cellulose nanocrystals/iron(Ⅲ)ion/polyvinyl alcohol(CNC/Fe³⁺/PVA)composite.The resultant composite films possessed robust mechanical performances,outstanding conductivity,and distinguished breathability(3.03 kg/(m²·d)),which benefited from the multiple interactions of weak hydrogen bonds and Fe³⁺ chelation and synergistic effects among CNC,polyaniline(PANI),and PVA.Surprisingly,the film could be assembled as a multifunctional sensor to actively monitor real-time physical and infection related signals such as temperature,moisture,pH,NH3,and human movements even at sweat states.More importantly,this multifunctional device could act as a self-driven therapist to eliminate bacterial by the release of Fe³⁺,which was driven by the damage of metal coordination Fe-O bonds due to the high temperature caused by infection at wound sites.Thus,the composite films had potential versatile applications in electronic skins,smart wound dressings,human-machine interactions,and self-driven anti-infection therapy.     

In situ lamination of starch‐based baked foam packaging with degradable films

A technique for making biodegradable food service packaging comprising a starch–fibre core and a biodegradable film laminate is described. The biodegradable films were made of polylactic acid (PLA), polybutylene succinate/terephthalate (PBST), rubber latex and polybutylene adipate/terephthalate (PBAT). The technique involved an in situ process for laminating a baked foam product in a single step. A critical element of the in situ technique involved using a heat insulating fibre sheet to stabilize heat‐sensitive laminate films during the baking/lamination process. The PLA‐, PBST‐ and PBAT‐laminated samples were baked for 6min at 120°C. The latex‐laminated sample, which was much more heat‐stable, did not need the insulating sheet and was baked for 3min at 160°C. Starch‐based foam laminated with PLA, PBST or PBAT generally had higher density and greater tensile and flexural strength than the non‐laminated control. Starch foam laminated with a rubber latex film had tensile and flexural properties similar to the non‐laminated control, due to the low modulus and elasticity of the latex film. The in situ lamination process improved the adhesion of the starch foam core with the fibre sheet, PLA and latex films compared to a post‐lamination process. All of the laminate materials provided a low water vapour permeance. The films degraded in a compost mixture but at a much slower rate compared to starch. Copyright © 2006 John Wiley & Sons, Ltd.     

Raman spectroscopy for quality control and process optimization of chalcopyrite thin films and devices

We will demonstrate in this paper that Raman scattering of visible light is a versatile tool both for research and industrial process monitoring of thin chalcopyrite films for solar cells. Thin films of Cu(In, Ga)(S,Se)₂ (CIGSSe) are produced by rapid thermal processing of stacked elemental Cu-In-Ga-Se layers. The Raman investigations are accompanied by grazing incidence X-ray diffraction (GI-XRD) and X-ray florescence (XRF) measurements. GI-XRD measurements confirm that the films show a two-fold elemental gradient: a sulfur gradient from the top and a Ga gradient from the CIGSSe/Mo interface. By Rietveld refinement of the GI-XRD spectra of the surface-near (∼ 100nm) ratio of sulfur to selenium can be obtained which corresponds well to the intensity ratio of the two Raman A1 modes of CuInS₂ and CuInSe₂. The asymmetric line shape of both XRD diffractograms and Raman spectra is attributed to the sulfur gradient. In addition we show that the intensity ratio of the satellite Raman B and E modes shows a correlation with the Cu to In + Ga ratio obtained by XRF.     

Flow cytometry of Escherichia coli on microfluidic devices.

Flow cytometry of the bacterium Escherichia coli was demonstrated on a microfabricated fluidic device (microchip). The channels were coated with poly(dimethylacrylamide) to prevent cell adhesion, and the cells were transported electrophoretically by applying potentials to the fluid reservoirs. The cells were electrophoretically focused at the channel cross and detected by coincident light scattering and fluorescence. The E. coli were labeled with a membrane-permeable nucleic acid stain (Syto15), a membrane-impermeable nucleic acid stain (propidium iodide), or a fluorescein-labeled antibody and counted at rates from 30 to 85 Hz. The observed labeling efficiencies for the dyes and antibody were greater than 94%.     

Patterned solvent delivery and etching for the fabrication of plastic microfluidic devices

A very simple method for micropatterning flat plastic substrates that can be used to build microfluidic devices is demonstrated. Patterned poly(dimethylsiloxane) elastomer is used as a template to control the flow path of an etching solvent through a channel design to be reproduced on the plastic substrate. The etching solvent was a acetone/ethanol mixture for poly(methyl methacrylate) substrates or a dimethylformamide/acetone mixture for polystyrene. The method is extremely fast in that duplicate plastic substrates can be patterned in just a few minutes each. We identified conditions that lead to smooth channel surfaces and characterized the rate of etching under these conditions. We determined that, for sufficiently short etching times (shallow channel depths), the etch rate is independent of the linear flow rate. This is very important since it means that the etch depth is approximately constant even in complex channel geometries where there will be a wide range of etchant flow rates at different positions in the pattern to be reproduced. We also demonstrate that the method can be used to produce channels with different depths on the same substrate as well as channels that intersect to form a continuous fluid junction. The method provides a nice alternative to existing methods to rapidly fabricate microfluidic devices in rigid plastics without the need for specialized equipment.     

A two-step optimization scheme for maximum stiffness design of laminated plates based on lamination parameters

The purpose of this paper is to propose an effective solution scheme of simultaneous optimization design of layup configuration and fiber distribution for maximum stiffness design of laminated plates. Firstly, a numerical analysis of the lamination parameters feasible region for a laminated plate consisting of various given number of ply groups (each ply group may have different thickness and all the fibers in one ply group are orientated in an identical direction) is carried out, and it is found that the feasible region based on only a few ply groups is very close to the overall one determined by infinite plies. Therefore, it is suggested that the feasible region of lamination parameters of a laminated plate could be approximately determined by the layup configuration of least ply groups. Secondly, a two-step simultaneous optimization scheme of layup configuration and fiber distribution for maximum stiffness design of laminated plates is proposed. Accordingly, by using ply thickness, fiber orientation angle and fiber volume fraction in a laminated plate of least ply groups as design variables, the optimal lamination parameters for maximum stiffness is obtained. Then, taking the optimal lamination parameters as the design objective, a detailed layup design optimization is implemented by considering some limitations on manufacturing, such as preset ply thickness, and specific fiber orientation angle and a limited maximum number of consecutive plies in the same fiber orientation. Numerical examples are also presented to validate the proposed two-step optimization scheme.     

Flame hydrolysis deposition of glass on silicon for the integration of optical and microfluidic devices

Flame hydrolysis deposition (FHD) of glasses has previously found applications in the telecommunications industry. This paper shows how the technology can be used to deposit silica with different refractive indices and thereby produce low-loss planar waveguides for use in analytical applications. We also show that the glasses can be patterned using a new reactive ion etch and sealed using a modification of anodic bonding, such that the resulting microstructures can be readily incorporated within a lithographically defined "chip", integrating both optical and fluidic circuitry on the same device. In the example described in this paper, waveguides, analytical microtiter chambers and fluidic capillary channels, with the necessary high aspect ratio features (and with depths up to 40 microm) were all produced in glass, using the appropriate deposition and etching technologies. The performance of the chip was assessed in the framework of a low-volume fluorescence assay, using waveguides to address miniaturized microtiter chambers with volumes of 230 and 570 pL. Devices featuring different optical detection configurations, including both in-line and orthogonal waveguide geometries, were fabricated. In the optimal configuration, the experimental detection limit was determined as ca. 20 pM (equivalent to 10 zmol) of a cyanine fluorophore, Cy5. The applicability of the device as a biochip platform was further illustrated by analytical measurements on fluorescently labeled oligodeoxynucleotides.     

A comparative study of EVA with and without thermal history for different lamination process parameters

In more than 80% of the worldwide photovoltaic (PV) modules, mostly very fragile and 200 μm thick, crystalline silicon solar cells are encapsulated into ethylene-vinyl acetate (EVA) foils, which bond the module components together, provide physical protection, electrical insulation and a barrier for moisture ingress. The understanding of what can happen with EVA during its transport, storage and lamination process is necessary to optimize the quality of the PV module for its long exposure to outdoor weather conditions. Achieving a proper cross-link density of over 70%, it is essential to overcome the cold flow of EVA and to make the module durable. In this work, the feasibility of the use of differential scanning calorimetry (DSC) compared with the solvent extraction (SE) method by toluene were evaluated in order to provide structural information on the EVA curing kinetics and the cross-link density. DSC tests were performed on a DTA DuPont1600 tester. The temperature range for the test was from −50 °C to 200 °C, with the heating rate of 10 °C/min, and the endothermic and exothermic peaks were evaluated. Toluene solvent extractions were performed on the same set of samples that were analyzed by DSC. The measured cross-link density shows a direct dependence on the pre-lamination conditions of EVA, which is in good agreement with the data obtained with the DSC method.     

High-efficiency, two-dimensional separations of protein digests on microfluidic devices

High-efficiency, two-dimensional separations of tryptic digests were achieved using glass microfluidic devices. Following micellar electrokinetic chromatography (MEKC) separations in a 19.6-cm-long serpentine channel, the peptides were rapidly sampled into a 1.3-cm-long second-dimension channel, where they were separated by capillary electrophoresis (CE). The turns in the serpentine channel were asymmetrically tapered to minimize geometrical contributions to band broadening and to provide ample channel length for high-efficiency chromatographic separations. Analysis of rhodamine B injections routinely produced plate numbers of 230000 and 40000 in the first (MEKC) and second (CE) dimensions, respectively, corresponding to plate heights of 0.9 and 0.3 microm. The electric field strengths were 200 V/cm for MEKC and 2400 V/cm for CE. In analysis times less than 15 min, two-dimensional separation of bovine serum albumin tryptic digest produced a peak capacity of 4200 (110 in the first dimension and 38 in the second dimension). The system was used to identify a peptide from a tryptic digest of ovalbumin using standard addition and to distinguish between tryptic digests of human and bovine hemoglobin.