Plastic Microfluidic Devices Research Articles

Thermal scribing to prototype plastic microfluidic devices, applied to study the formation of neutrophil extracellular traps.

Innovation in microfluidics-based biological research has been aided by the growing accessibility of versatile microscale fabrication techniques, particularly in rapid prototyping of elastomeric polydimethylsiloxane (PDMS) based devices. However, the use of PDMS presents considerable and often unexpected limitations, particularly in interpreting and validating biological data. To rapidly prototype microfluidic culture systems in conventional plastics commonly used in cell culture, we developed 'thermal scribing', a one-step micromachining technique in which thermoplastics are locally patterned by a heated tip, moving in user-controlled patterns. To demonstrate and study the thermal scribing process, we modified an inexpensive desktop hobby craft cutter with a soldering iron to scribe micropatterns on polystyrene substrates. The thermal scribing technique is useful for creating a variety of channel profiles and geometries, which cannot be readily achieved using other microfabrication approaches. The entire fabrication process, including post-processing operations needed to fabricate devices, can be completed within a few hours without the need for skilled engineering expertise or expensive equipment. We apply this technique to demonstrate that induction of functional neutrophil extracellular traps (NETs) can be significantly enhanced over previous studies, when experiments are conducted in microfluidic channels prototyped in an appropriate material. These results ultimately inform the design of neutrophil culture systems and suggest that the inherent ability of neutrophils to form NETs may have been significantly under-reported.

Automated leukocyte processing by microfluidic deterministic lateral displacement.

We previously developed a Deterministic Lateral Displacement (DLD) microfluidic method in silicon to separate cells of various sizes from blood (Davis et al., Proc Natl Acad Sci 2006;103:14779-14784; Huang et al., Science 2004;304:987-990). Here, we present the reduction-to-practice of this technology with a commercially produced, high precision plastic microfluidic chip-based device designed for automated preparation of human leukocytes (white blood cells; WBCs) for flow cytometry, without centrifugation or manual handling of samples. After a human blood sample was incubated with fluorochrome-conjugated monoclonal antibodies (mAbs), the mixture was input to a DLD microfluidic chip (microchip) where it was driven through a micropost array designed to deflect WBCs via DLD on the basis of cell size from the Input flow stream into a buffer stream, thus separating WBCs and any larger cells from smaller cells and particles and washing them simultaneously. We developed a microfluidic cell processing protocol that recovered 88% (average) of input WBCs and removed 99.985% (average) of Input erythrocytes (red blood cells) and >99% of unbound mAb in 18 min (average). Flow cytometric evaluation of the microchip Product, with no further processing, lysis or centrifugation, revealed excellent forward and side light scattering and fluorescence characteristics of immunolabeled WBCs. These results indicate that cost-effective plastic DLD microchips can speed and automate leukocyte processing for high quality flow cytometry analysis, and suggest their utility for multiple other research and clinical applications involving enrichment or depletion of common or rare cell types from blood or tissue samples. © 2016 International Society for Advancement of Cytometry.

Combined hot embossing and milling for medium volume production of thermoplastic microfluidic devices

Current methods for fabricating thermoplastic microfluidic devices are either appropriate for prototyping in research labs, or for mass production for commercialization purposes. However, methods for fabricating plastic microfluidic devices in medium volume production have not been demonstrated, and thus, creates a gap in manufacturing methods. A medium volume manufacturing method would be practical and necessary during the technology development phase when many fabricated devices may be required for testing and validation, but design modifications may still be required, thereby making mass production unnecessary and not economical. This study demonstrates the feasibility of combining hot embossing and milling methods to achieve medium volume production of thermoplastic microfluidic devices with high replication fidelity. Hot embossing parameters were tested and optimized on two different embossing systems and for two different plastics (COP and PMMA). Using these optimal hot embossing parameters together with improvements in epoxy mold fabrication and a streamlined milling procedure, a production rate of ∼50 devices per week was achieved during a proof-of-concept medium volume production run. Importantly, this approach also provides a flexible strategy that can accommodate prototype design changes without resulting in long development delays. Overall, results provide evidence that medium production levels can be performed in research labs and in industry, thereby providing an accelerated path to commercialization.

Non-contact reflectometric readout of disposable microfluidic devices by near infra-red low-coherence interferometry

We are here demonstrating the functionality of infra-red low-coherence reflectometry for the spot optical readout of solution concentrations in commercially available microfluidic devices. Disposable polymeric microfluidic devices composed by 100-µm-deep channels were connected to an external fluidic path that allowed flow-through of water-glucose solutions at different concentrations. Measurements were performed with near-infrared low-power sources, namely a tungsten lamp and a Superluminescent Light Emitting Diode (SLED), allowing the read-out in a wavelength region of minimum invasiveness for biological fluids. The selected optical scheme based on an all-fiber Michelson configuration is well suited for non-contact, remote investigations of the fluids flowing in plastic microfluidic devices, with arbitrary layout and thickness. For the first time, using the SLED, we exploited the double round trip of light in the fluid channel for doubling the sensitivity with respect to the standard single pass set-up, previously demonstrated.

プラスチック製マイクロデバイスのシール技術

プラスチック製マイクロデバイスのシール技術

TiO2 coated microfluidic devices for recoverable hydrophilic and hydrophobic patterns

We report a simple method for modifying the surfaces of plastic microfluidic devices through dynamic coating process with a nano-colloidal TiO2 sol. The surface of the thermoplastic, cyclic olefin copolymer (COC) was coated with the TiO2 film, that displayed an effective photocatalytic property. The hydrophilic surface is obtained in the TiO2-coated zone of a microfluidic channel, and TiO2 coated surface degradation can be reversed easily by UV irradiation. The present work shows a photocatalytic activity concerning the effect of TiO2 coating density, which is controlled by the number of coating cycles. The hydrophilized surface was characterized by the contact angle of water and the TiO2 coated COC surface reduced the water contact angle from 85° to less than 10° upon UV irradiation. The photocatalytic effect of the layer that was coated five times with TiO2 was excellent, and the super-hydrophilicity of the TiO2 surface could be promptly recovered after 10 months of storage at atmospheric conditions. The COC microfluidic devices, in which TiO2 has been freshly deposited and aged for 10 months, were capable of generating water-in oil-in water (W/O/W) double emulsions easily and uniformly by simple control of the flow rates for demonstration of excellent hydrophilic patterning and recovery of the TiO2 coated in the microchannels.

Automatic droplet transportation on a plastic microfluidic device having wettability gradient surface

This paper presents a microfluidic device that can automatically transport a droplet on a plastic plate. This device consists of a Cyclo Olefin Polymer (COP) plate and a SiO2 membrane and has wettability gradient surface. Lithographic patterns of hydrophilic SiO2 permitted wettability modification of a hydrophobic COP surface. A series of alternate hydrophobic and hydrophilic wedge-shaped patterns generated a required gradient in wettability. When we dropped a droplet on the wettability gradient surface, it moved along the wettability gradient due to an imbalance between surface tension forces acting on the opposite sides of the droplet edge. The droplet transportation test was carried out using water of 5 μl. As a result, we succeeded in automatically transporting the droplet on the SiO2/COP wettability gradient pattern. We also carried out droplet transportation in an enclosed microchannel for preventing droplet evaporation using DI (Deionized) water of 5 μl. In this case, the droplet was automatically transported by forming the wettability gradient pattern at the top and bottom in an enclosed microchannel without evaporation.

Liquid phase solvent bonding of plastic microfluidic devices assisted by retention grooves.

We report a novel method for achieving consistent liquid phase solvent bonding of plastic microfluidic devices via the use of retention grooves at the bonding interface. The grooves are patterned during the regular microfabrication process, and can be placed at the periphery of a device, or surrounding microfluidic features with open ports, where they effectively mitigate solvent evaporation, and thus substantially reduce poor bond coverage. This method is broadly applicable to a variety of plastics and solvents, and produces devices with high bond quality (i.e., coverage, strength, and microfeature fidelity) that are suitable for studies in physics, chemistry, and cell biology at the microscale.

Micromilling: a method for ultra-rapid prototyping of plastic microfluidic devices.

This tutorial review offers protocols, tips, insight, and considerations for practitioners interested in using micromilling to create microfluidic devices. The objective is to provide a potential user with information to guide them on whether micromilling would fill a specific need within their overall fabrication strategy. Comparisons are made between micromilling and other common fabrication methods for plastics in terms of technical capabilities and cost. The main discussion focuses on "how-to" aspects of micromilling, to enable a user to select proper equipment and tools, and obtain usable microfluidic parts with minimal start-up time and effort. The supplementary information provides more extensive discussion on CNC mill setup, alignment, and programming. We aim to reach an audience with minimal prior experience in milling, but with strong interests in fabrication of microfluidic devices.

Graphene Protein Field Effect Biomedical Sensor for Glucose Measurements

ABSTRACTThe need for improved medical sensors based on lab-on-a-chip technologies has increased significantly because of the dramatic growth in the number of people with chronic diseases and the associated costs for their healthcare. Development and initial results of a hybrid plastic microfluidic device with an integrated graphene-protein biosensor chip for use in point-of-care (POC) is described. The initial prototype is a glucometer that uses optimized glucose oxidase bound to a graphene field effect sensor. Technologies required for development of the prototype include modification of the glucose oxidase for improved performance by protein engineering, methods to bind the enzyme to the graphene attached to the silicon oxide surface of sensor chip, and integration into a thermoplastic microfluidic device. Initial results indicate the prototype glucometer can measure glucose concentrations from low physiological levels to molar concentrations.

Confined chemiluminescence detection of nanomolar levels of H2O2 in a paper–plastic disposable microfluidic device using a smartphone

We report the design and characterization of a disposable light shielded paper-plastic microfluidic device that can detect nanomolar levels of H2O2 using a smartphone camera and a light sealed accessory. Chemiluminescence reaction of H2O2 with bis(2,4,6-trichlorophenyl)oxalate in the presence of rubrene and imidazole is confined to a paper reaction site where the individual reagents are delivered via plastic microfluidic channels. The net photon emission from the chemiluminescence reactions, detected by using a smartphone, is correlated with H2O2 concentrations. With a total reagent volume of 25 μL, the sensor system was able to detect H2O2 concentrations as low as 250 nM. The smartphone based chemiluminescence sensing system has great potential as a point of care diagnostic tool for monitoring nanomolar levels of H2O2 in biological samples.

Integration of Heteromaterial Microelements into Plastic Microfluidic Devices by Capillary-force-assisted Micromolding

Integration of Heteromaterial Microelements into Plastic Microfluidic Devices by Capillary-force-assisted Micromolding

Shrink-induced sorting using integrated nanoscale magnetic traps.

We present a plastic microfluidic device with integrated nanoscale magnetic traps (NSMTs) that separates magnetic from non-magnetic beads with high purity and throughput, and unprecedented enrichments. Numerical simulations indicate significantly higher localized magnetic field gradients than previously reported. We demonstrated >20 000-fold enrichment for 0.001% magnetic bead mixtures. Since we achieve high purity at all flow-rates tested, this is a robust, rapid, portable, and simple solution to sort target species from small volumes amenable for point-of-care applications. We used the NSMT in a 96 well format to extract DNA from small sample volumes for quantitative polymerase chain reaction (qPCR).

A facile method for detecting calcium/calmodulin-dependent protein kinase using radio phosphorylation of a GBP-fused enzyme substrate in a lab-on-a-chip

A protein-fused substrate for calcium/calmodulin-dependent protein kinase (CaMKII) was constructed by genetically fusing a gold binding polypeptide (GBP) to the putative spermidine synthase (PSPD) of Selenomonas ruminantium. DNA encoding the CaMKII substrate Autocamtide-2, the amino acid sequence of which is KKALRRQETVDAL, was cloned and fused to the C-terminal 32kDa of PSPD. In the present study, the GBP-PSPD-fusion Autocamtide-2 substrate (GBP-SP-AC2) was used to detect signal intensities reflecting CaMKII action, on gold-coated glass slides. Construction of a lab-on-a-chip (LOC) employing radioisotopes (RIs) requires the appropriate design, fabrication, and testing of plastic microfluidic devices allowing on-chip substrate preparation and employment of protein microarrays. We investigated the feasibility of RI detection techniques used to measure phosphorylation of a GBP-fused substrate, in turn facilitating highly sensitive detection of CaMKII, employing an LOC. Our LOC device designed for use in applications employing radioisotopes is architecturally simple, affords rapid testing, is cost-effective, and generates minimal amounts of radioactive waste. This strategy can be used in the general development of LOCs for high-throughput screening in biological and medical research.

Rapid fabrication of nickel molds for prototyping embossed plastic microfluidic devices

The production of hot embossed plastic microfluidic devices is demonstrated in 1-2 h by exploiting vinyl adhesive stickers as masks for electroplating nickel molds. The sticker masks are cut directly from a CAD design using a cutting plotter and transferred to steel wafers for nickel electroplating. The resulting nickel molds are used to hot emboss a variety of plastic substrates, including cyclo-olefin copolymer and THV fluorinated thermoplastic elastomer. Completed devices are formed by bonding a blank sheet to the embossed layer using a solvent-assisted lamination method. For example, a microfluidic valve array or automaton and a droplet generator were fabricated with less than 100 μm x-y plane feature resolution, to within 9% of the target height, and with 90 ± 11% height uniformity over 5 cm. This approach for mold fabrication, embossing, and bonding reduces fabrication time and cost for research applications by avoiding photoresists, lithography masks, and the cleanroom.

Assessment of Enhanced Autofluorescence and Impact on Cell Microscopy for Microfabricated Thermoplastic Devices

Thermoplastics such as polystyrene (PS) and cyclo-olefin polymer (COP) have become common materials for fabrication of microfluidic cell-based systems because of a number of attractive properties. However, thermoplastics are also known to exhibit autofluorescence levels that may hinder their utility for cell-based and imaging applications. Here, we identify and characterize a phenomenon causing an increase in the autofluorescence of polystyrene after thermal treatment. This effect is of particular importance for plastic microfluidic device fabrication because the ranges of pressures and temperatures causing this effect match the same range as those used for polystyrene bonding. Further, we find that the enhanced autofluorescence has significant impact on the image quality, accuracy, and ability to identify and quantify fluorescently labeled cells. We tested two alternative strategies, solvent bonding of PS or thermal bonding of COP, to alleviate the adverse effects of heterogeneous and enhanced autofluorescence on cell image analysis, and demonstrate that both strategies are viable options to thermal bonding of PS for specific applications where cellular imaging is of primary interest.

Direct loading of polymer matrices in plastic microchips for rapid DNA analysis: A comparative study

We report the design and performance validation of microfluidic separation technologies for human identification using a disposable plastic device suitable for integration into an automated rapid DNA analysis system. A fabrication process for a 15-cm long hot-embossed plastic microfluidic devices with a smooth semielliptical cross section out of cyclic olefin copolymer is presented. We propose a mixed polymer solution of 95% w/v hydroxyethylcellulose and 5% w/v polyvinylpyrrolidone for a final polymer concentration of 2.5 or 3.0% to be used as coating and sieving matrix for DNA separation. This formulation allows preparing the microchip without pretreatment in a single-loading step and provides high-resolution separation (≈1.2 bp for fragments <200 bp), which is superior to existing commercial matrices under the same conditions. The hot-embossed device performance is characterized and compared to injection-molded devices made out of cyclic olefin copolymer based on their respective injector geometry, channel shape, and surface charges. Each device design is assessed by fluorescence videomicroscopy to evaluate the formation of injection plugs, then by comparing electropherograms for the separation of a DNA size standard relevant to human identification.

Optimization of multiplexed PCR on an integrated microfluidic forensic platform for rapid DNA analysis

This study reports the design, prototyping, and assay development of multiplexed polymerase chain reaction (PCR) on a plastic microfluidic device. Amplification of 17 DNA loci is carried out directly on-chip as part of a system for continuous workflow processing from sample preparation (SP) to capillary electrophoresis (CE). For enhanced performance of on-chip PCR amplification, improved control systems have been developed making use of customized Peltier assemblies, valve actuators, software, and amplification chemistry protocols. Multiple enhancements to the microfluidic chip design have been enacted to improve the reliability of sample delivery through the various on-chip modules. This work has been enabled by the encapsulation of PCR reagents into a solid phase material through an optimized Solid Phase Encapsulating Assay Mix (SPEAM) bead-based hydrogel fabrication process. SPEAM bead technology is reliably coupled with precise microfluidic metering and dispensing for efficient amplification and subsequent DNA short tandem repeat (STR) fragment analysis. This provides a means of on-chip reagent storage suitable for microfluidic automation, with the long shelf-life necessary for point-of-care (POC) or field deployable applications. This paper reports the first high quality 17-plex forensic STR amplification from a reference sample in a microfluidic chip with preloaded solid phase reagents, that is designed for integration with up and downstream processing.

Hot embossing of plastic microfluidic devices using poly(dimethylsiloxane) molds

We present a poly(dimethylsiloxane) (PDMS)-based hot embossing process for low-cost rapid prototyping of plastic microfluidic devices. Unlike the conventional hot embossing process, the process presented here uses a 2 mm thick PDMS mold, two 3/4” wide binder clips, two standard 1 mm thick 1” × 3” microscope glass slides and a standard laboratory oven. Micro-scale features were successfully replicated in 1.5 mm thick polystyrene slides from various PDMS molds. Also, the PDMS molds can be reused for many replications without any damage.

Micro-Laser Welding of Plastics for the Applications in Micro-Fluidic Devices

This study aims to investigate laser welding process for the bonding of micro-fluidic devices. PMMA was selected for the investigation. The devices consist of an opaque substrate with micro-channels and a transparent cover. The welding process was optimized according to laser power, welding speed and clamping pressure. The cross-sectional analysis, flow and pressure tests, as well as the lap-shear test were conducted on the samples welded with the optimized process parameters. The results show that the laser welding can meet the requirements for bonding the plastic micro-fluidic devices.