Poly Methyl Methacrylate Microfluidic Chips Research Articles

Precision electroforming of nickel nanocomposite mould for defects-free demoulding in polymer micro replication: Surface properties, performance validation and mould release mechanism

Microinjection moulding and micro/nano hot embossing are two promising manufacturing processes for the mass production of polymer workpieces with micro/nano structures. However, adhesion and friction between polymer workpieces and mould tools can cause structural distortion and surface damage. Besides, the nickel mould's lifetime is limited by its low hardness and wear resistance. To address these issues, we proposed a new methodology to codeposit micro/nanomaterials into nickel mould for microhardness enhancement and effective mould release. In this study, polytetrafluoroethylene (PTFE) microparticles, tungsten disulfide (WS2) and molybdenum disulfide (MoS2) nanosheets were incorporated into nickel mould by electroforming. Cobalt was added as a secondary phase to improve the microhardness and wear resistance of the composite mould. The result indicated that WS2 nanosheets achieved the most significant performance enhancement among three micro/nanomaterials, represented as the microhardness improved from 191 HV for pure nickel to 564 HV for nickel/WS2 nanocomposites, along with the coefficient of friction (COF) against the polymethyl methacrylate (PMMA) pin reducing from 0.72 to 0.10 in the initial stage of the sliding. With the incorporation of micro/nanomaterials, the wettability altered from hydrophilic for pure nickel to hydrophobic for the composite moulds. The study shows that the addition of cobalt improved the microhardness of the composite moulds but meanwhile induced more adhesive wear during the pin-on-disc test. Finally, a nickel/WS2 nanocomposite mould is successfully fabricated via electroforming with feature sizes from 70 to 180 μm and its lubricating properties are validated by micro hot embossing PMMA microfluidic chips with good surface quality and structural integrity.

Rapid fabrication of microfluidic mixer chip by non-isothermal molding method based on resistance heating principle and its application in pesticide residue detection

This paper proposed a rapid fabrication process for polymethylmethacrylate (PMMA) microfluidic mixer chip by non-isothermal method based on resistance heating principle, and the prepared microfluidic mixer chip was successfully applied to the portable pesticide residue detection device. Firstly, the creep test of PMMA was carried out and the six units Maxwell constitutive model was fitted by Prony series. Secondly, the resistance heating device was designed, the influence of current on heating temperature and heating time was investigated, the effect of current on energy consumption was analyzed. Thirdly, the non-isothermal molding simulation and experiment of PMMA were carried out, the quality of PMMA microfluidic mixer chip fabricated by non-isothermal molding was investigated. Finally, the microfluidic mixer chip was adopted to the designed pesticide residue detection device, and the detection sensitivity of the device is 0.0375 mol−1. The research results provide a reference for the efficient preparation of microchannels and the development of portable detection equipment.

Synthesis of two-dimensional WS2/nickel nanocomposites via electroforming for high-performance micro/nano mould tools

To reduce the adhesion and friction between polymer and mould surfaces during polymeric micro/nano structures replication, we have used tungsten disulfide (WS2) nanosheets to fabricate high-performance nickel/WS2 nanocomposite mould using electroforming. However, the aggregation of WS2 nanosheets in the electroforming solution is a critical issue that influences the mechanical and tribological properties of the mould. In this study, we first propose a new strategy of combining anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant cetyltrimethylammonium bromide (CTAB) to achieve uniform dispersion and incorporation of WS2 nanosheets in the electroformed nickel mould. Our results indicate that appropriately designing the structure of CTAB-SDS complex can achieve a stable WS2 dispersion, contributing to the uniform co-deposition of WS2 nanosheets into nickel mould. The combination of high concentration of CTAB and SDS (1.0 g/L CTAB and 1.0 g/L SDS) significantly improved the dispersibility and incorporation of WS2 into the nickel matrix, compared to individual SDS or CTAB. Consequently, the maximum hardness enhanced by 350% from 284 HV for pure nickel to 1280 HV for nickel/WS2 nanocomposite mould, along with the coefficient of friction (COF) against the polymethyl methacrylate (PMMA) pin reducing from 0.75 to 0.31. It is also found that CTAB promotes particle encapsulation while SDS improves the particle dispersion but cannot control the particle incorporation. The surface wettability of nickel/WS2 mould altered to hydrophobicity from hydrophilicity of nickel mould, where the adhesion-induced wear caused by polymer pin significantly reduced. Moreover, the surface roughness did not change much with the incorporation of WS2 into the mould, which is acceptable for mould applications. Finally, the nickel/WS2 nanocomposite mould was successfully fabricated via electroforming and its self-lubricating properties was validated by micro hot embossing PMMA microfluidic chips with good surface quality.

Sterilization of PMMA microfluidic chips by various techniques and investigation of material characteristics

The sterilization of microfluidic chips is a vital step of the fabrication process prior to the customer use in biomedical applications. The aim of this study was to analyze the influence of different sterilization techniques and to compare the characteristics of the material before and after sterilization of polymethylmethacrylate (PMMA) microchips. For this, supercritical carbon dioxide (SC-CO2) along with standard sterilization methods such as ultraviolet (UV), heat (autoclaving), ethylene oxide (EtO) and hydrogen peroxide (H2O2) were applied. The treated microchips were analyzed by Scanning Electron Microscopy, Differential Scanning Calorimetry, Fourier Transform Infrared Spectroscopy and Laser Scanning Microscopy in order to ascertain any changes in the chemical structure and surface morphology. The optimum sterilization parameters for SC-CO2 were elicited as 120bar, 40°C and 60min which provided complete sterility and did not alter the main properties of the polymer along with EtO and H2O2 sterilizations unlike heat and UV treatments. However, surface roughness and microchannel profiles were negatively affected. Although complete sterility was achieved, each protocol has its own strengths and weaknesses.

Integrated microfluidic array chip and LED photometer system for sulfur dioxide and methanol concentration detection

An integrated platform comprising a PMMA (Polymethyl-Methacrylate) microfluidic array chip and a LED photometer system is proposed for the concentration detection of sulfur dioxide (SO2) and methanol (CH4O). In the proposed device, the sample and reagent are injected into six open chambers on the microfluidic chip and are mixed via a vortex stirring effect. Following the mixing process, a colorimetric reaction is induced between the sample and the reagent by means of a microhotplate positioned beneath the microfluidic chip array. The microfluidic chip is then transferred to a LED photometer system for detection purposes. The experimental results show that correlation coefficients of R2=0.9915 and R2=0.9941 are obtained when plotting the photometer output voltage against the SO2 and CH4O concentrations of control samples with known concentrations ranging from 50 to 500ppm. The real-world applicability of the proposed experimental platform is demonstrated by measuring the SO2 concentration in two commercial Chinese herbs and the CH4O concentration in two commercial wines. It is shown that the concentration measurements obtained using the proposed system deviate by no more than 9% from those obtained using standard macroscale methods. Overall, the results presented in this study show that the proposed integrated microfluidic platform provides a compact and reliable tool for SO2 and CH4O concentration measurement purposes.

Convenient quantification of methanol concentration detection utilizing an integrated microfluidic chip.

A rapid and simple technique is proposed for methanol concentration detection using a PMMA (Polymethyl-Methacrylate) microfluidic chip patterned using a commercially available CO2 laser scriber. In the proposed device, methanol and methanol oxidase (MOX) are injected into a three-dimensional circular chamber and are mixed via a vortex stirring effect. The mixture is heated to prompt the formation of formaldehyde and is flowed into a rectangular chamber, to which fuchsin-sulphurous acid is then added. Finally, the microchip is transferred to a UV spectrophotometer for methanol detection purposes. The experimental results show that a correlation coefficient of R(2) = 0.9940 is obtained when plotting the optical density against the methanol concentration for samples and an accuracy as high as 93.1% are compared with the determined by the high quality gas chromatography with concentrations in the range of 2 ∼ 100 ppm. The methanol concentrations of four commercial red wines are successfully detected using the developed device. Overall, the results show that the proposed device provides a rapid and accurate means of detecting the methanol concentration for a variety of applications in the alcoholic beverage inspection and control field.

Rapid Detection of Methanol in an Integration Microfluidic Chip

A rapid and simple technique was developed for detecting methanol with very small amount of sample by using PMMA (Polymethyl-Methacrylate) microfluidic chip, which fabricated by a commercially available CO2 laser scriber. The experimental results indicate that linearity expression R2 can approximate 0.936 using the proposed integrating microfluidic chip when the 2 unit methanol oxidase (MOX) and basic fuchsin to detect methanol. Hence, the current device provides a valuable tool for rapid methanol detection, while its micro mixer system delivers a simple yet effective solution for mixing problems in the micro-total-analysis -systems field.

A low temperature ultrasonic bonding method for PMMA microfluidic chips

Bonding is a bottleneck for mass-production of polymer microfluidic devices. A novel ultrasonic bonding method for rapid and deformation-free bonding of polymethyl methacrylate (PMMA) microfluidic chips is presented in this paper. Convex structures, usually named energy director in ultrasonic welding, were designed and fabricated around micro-channels and reservoirs on the substrates. Under low amplitude ultrasonic vibration, localized heating was generated only on the interface between energy director and cover plate, with peak temperature lower than T g (glass transition temperature) of PMMA. With the increasing of temperature, solution of PMMA in isopropanol (IPA) increases and bonding was realized between the contacting surfaces of energy director and cover plate while no solution occurs on the surfaces of other part as their lower temperature. PMMA microfluidic chips with micro-channels of 80 μm × 80 μm were successfully bonded with high strength and low dimension loss using this method.

Chitosan microfiber fabrication using a microfluidic chip and its application to cell cultures

In this study, a poly-methyl-methacrylate (PMMA) microfluidic chip with a 45° cross-junction microchannel is fabricated using a CO2 laser machine to generate chitosan microfibers. Chitosan solution and sodium tripolyphosphate (STPP) solution were injected into the cross-junction microchannel of the microfluidic chip. The laminar flow of the chitosan solution was generated by hydrodynamic focusing. The diameter of laminar flow, which ranged from 30 to 50 μm, was controlled by changing the ratio between chitosan solution and STPP solution flow rates in the PMMA microfluidic chip. The laminar flow of the chitosan solution was converted into chitosan microfibers with STPP solution via the cross-linking reaction; the diameter of chitosan microfibers was in the range of 50–200 μm. The chitosan microfibers were then coated with collagen for cell cultivation. The results show that the chitosan microfibers provide good growth conditions for cells. They could be used as a scaffold for cell cultures in tissue engineering applications. This novel method has advantages of ease of fabrication, simple and low-cost process.

Multi-layer PMMA microfluidic chips with channel networks for liquid sample operation

The emphasis of this paper lies in the fabrications of an eight-layer chip for liquid mixing and a seven-layer chip for liquid sample dilution. In this paper, the microchannels, fabricated by CO 2 laser, constructed three-dimensional serpentine channel networks for liquid sample operation. The eight-layer mixing chip used the “F”-shape mixing units to achieve splitting and recombination mixing. Furthermore, mixing was enhanced by chaotic flow induced by three-dimensional serpentine channel path. The seven-layer dilution chip created eight diluted fluid streams mixed in same volumetric proportions. Prior to thermal bonding, the polymethylmethacrylate (PMMA) substrates were treated by oxygen plasma to improve their surface properties. The increased surface properties served to reduce thermal bonding temperature and pressure, which minimized the deformation of microchannel. The mixing and diluting experiments showed high levels of mixing and diluting performances were obtained with the chips.

Microfluidic chip made of COP (cyclo-olefin polymer) and comparion to PMMA (polymethylmethacrylate) microfluidic chip

Hot embossing method was studied for the fabrication of microfluidic microchannels on COP (cyclo-olefin polymer) chip. The ending temperature of heating stage, i.e. embossing reference temperature ( T r), was determined by the viscoelastic property of the COP, according to variable temperature quasi-creep experiments. Taguchi method was used to decide the processing parameters in cooling and demolding stage. The optimized parameters of hot embossing are: embossing reference temperature 143 °C, temperature and pressure holding time 2 min, pressure at cooling and demolding stage 1.6 MPa, the demolding temperature in the lower heating plate 80 °C and temperature difference between the upper and lower heating plate 10 °C. Experiment shows that microchannel fabricated with the above parameters has high repeatability and low substrate deformation, average repeatability is 97.6% in width and 94.3% in depth. Experiments on background fluorescence, electrophoresis, and DNA separation and detection were carried out on COP and PMMA (polymethylmethacrylate) chips, respectively. Compared to the PMMA chip, the COP chip has higher signal to noise ratio, higher electrophoresis efficiency, and lower peak area relative standard deviation (R.S.D.). In separation 6 μg/ml ϕ X174 RF DNA Hinc II, 11 DNA fragments have been identified in less than 2 min on the COP chip, thus it has large application potential in biochemical analysis.

Electrophysiological recordings of single ion channels in planar lipid bilayers using a polymethyl methacrylate microfluidic chip

Planar lipid bilayers are used for functional studies of ion channel proteins using electrophysiological techniques. We have been developing a plastic micro-fluidic device for the reconstitution of planar lipid bilayers and electrophysiological recordings toward a "membrane protein chip" for high-throughput screening. In the previous report [Suzuki, H., Tabata, K.V., Noji, H., Takeuchi, S., 2006. Highly reproducible method of planar lipid bilayer reconstitution in polymethyl methacrylate microfluidic chip. Langmuir 22 (4), 1937-1942], we presented the method and device in which the reproducibility of planar lipid bilayers reached 90%, and multiple bilayers were formed simultaneously. In this communication, we show that our device has excellent electric properties suitable for ion channel analysis down to single molecular level. Additional aspects on the optical accessibility and controllability on lipid bilayer formation are also presented.

Determination of EOF of PMMA microfluidic chip by indirect laser-induced fluorescence detection

A simplified method for mobility determination of electroosmotic flow (EOF) of polymethyl methacrylate (PMMA) microfluidic chips is developed with indirect laser-induced fluorescence detection (IDLIFD). Based on the interval between the beginning of separation and the apex of converse peak, the present technique highlights in circumventing the great demand for sensitivity and baseline stability of routine methods. IDLIFD is performed by a home-made laser-induced fluorescence detector of confocal optical configuration, mainly composed of a 473 nm laser diode double-pumped solid state laser (LD-DPSSL) and a 520 nm band-pass interference filter. Amino acetate (NH 4Ac) solution containing Vitamin B 2 is used as the background fluorescent reagent (BFR) solution. The pre-treatment procedures of chip inter-surface and the voltage program of injection and separation are studied. Reasons for the low background fluorescent response during injection are also discussed. Even this phenomenon has a good effect on the accurate recording of the interval between the baseline starting of separation and the lowest point of the converse peak. The results demonstrate that the reciprocals of EOF mobility ( υ eo) of PMMA microfluidic chip are in line with the ion strength of background electrolyte (BGE) solution. Furthermore, the υ eo of PMMA material is related to the pH of BGE solution. Compared with those results obtained from the Current-Monitoring method, no apparent difference has been found.

Microfabricated plastic chips by hot embossing methods and their applications for DNA separation and detection

Design and fabrication of microfluidic devices on polymethylmethacrylate (PMMA) substrates for analytical chemistry and biomedical-related applications using novel microfabrication methods are described. The image of microstructures is transferred from quartz master templates possessing the inverse image of the devices to plastic plates by using hot embossing methods. The microchannels on quartz master templates are formed by the combination of metal etch mask and wet chemical etching of a photomask blank. The micromachined quartz templates can be used repeatedly to replicate cheap and disposable plastic devices. The reproducibility of the hot embossing method is evaluated using 10 channels on different PMMA plastics. The relative standard deviation of the channel profile on the plastic chips is less than 1%. In this study, the PMMA microfluidic chips have been demonstrated as a microcapillary electrophoresis (μ-CE) device for DNA separation and detection. The capability of the fabricated chip for electrophoretic injection and separation is characterized via the analysis of DNA fragments ∅X-174-RF Hae III digest. Experimental results indicate that all of the 11 DNA fragments of the size marker could be identified in less than 2 min with relative standard deviations less than 0.4 and 8% for migration time and peak area, respectively. Moreover, with the use of a near-infrared (IR) dye, fluorescence signals of the higher molecular weight fragments (>603 bp in length) could be detected at total DNA concentrations as low as 0.1 μg/ml. In addition to DNA fragments ∅X-174-RF Hae III digest, DNA sizing of hepatitis C viral (HCV) amplicon is also achieved using microchip electrophoresis on PMMA substrates.