PMMA Microfluidic Devices Research Articles

Quantification of Lanthanides on a PMMA Microfluidic Device with Three Optical Pathlengths Using PCR of UV-Visible, NIR, and Raman Spectroscopy.

Microfluidic devices (MFDs) offer customizable, low-cost, and low-waste platforms for performing chemical analyses. Optical spectroscopy techniques provide nondestructive monitoring of small sample volumes within microfluidic channels. Optical spectroscopy can probe speciation, oxidation state, and concentration of analytes as well as detect counterions and provide information about matrix composition. Here, ultraviolet-visible (UV-vis) absorbance, near-infrared (NIR) absorbance, and Raman spectroscopy are utilized on a custom poly(methyl methacrylate) (PMMA) MFD for the detection of three lanthanide nitrates in solution. Absorbance spectroscopies are conducted across three pathlengths using three portions of a contiguous channel within the MFD. Univariate and chemometric multivariate modeling, specifically Beer's law regression and principal component regression (PCR), respectively, are utilized to quantify the three lanthanides and the nitrate counterion. Models are composed of spectra from one or multiple pathlengths. Models are also constructed from multiblock spectra composed of UV-vis, NIR, and Raman spectra at one or multiple pathlengths. Root-mean-square errors (RMSE), limit of detection (LOD), and residual predictive deviation (RPD) values are compared for univariate, multivariate, multi-pathlength, and multiblock models. Univariate modeling produces acceptable results for analytes with a simple signal, such as samarium cations, producing an LOD of 5.49 mM. Multivariate and multiblock models produce enhanced quantification for analytes that experience spectral overlap and interfering nonanalyte signals, such as holmium, which had an LOD reduction from 7.21 mM for the univariate model down to 3.96 mM for the multiblock model. Multi-pathlength models are developed that maintain model errors in line with single-pathlength models. Multi-pathlength models have RPDs from 9.18 to 46.4, while incorporating absorbance spectra collected at optical paths of up to 10-fold difference in length.

Rapid Tooling for Microinjection Moulding of Proof-of-Concept Microfluidic Device: Resin Insert Capability and Preliminary Validation

Producing sustainable microfluidic devices on a large scale has become a trend in the biomedical field. However, the transition from laboratory prototyping to large-scale industrial production poses several challenges due to the gap between academia and industry. In this context, prototyping with a mass production approach could be the novel strategy necessary to bridge academic research to the market. Here, the performance of polymer inserts to produce PMMA microfluidic devices using the microinjection moulding process is presented. Inserts were fabricated with an additive manufacturing process: material jetting technology. The importance of the inserts’ orientation on the printing plate in order to produce samples with more uniform thickness and lower roughness has been demonstrated using a flat cavity insert. In addition, preliminary tests were carried out on microstructured inserts with inverted channels of various cross-section shapes (semi-circular or trapezoidal) and widths (200 or 300 µm) in order to investigate the microstructures’ resistance during the moulding cycles. The best geometry was found in the channel with the trapezoidal cross-section with a width equal to 300 µm. Finally, a preliminary microfluidic test was performed to demonstrate the devices’ workability.

A simple solvent-assisted method for thermal bonding of large-surface, multilayer PMMA microfluidic devices

A simple solvent-assisted method for thermal bonding of large-surface, multilayer PMMA microfluidic devices

Rapid assembly of PMMA microfluidic devices with PETE membranes for studying the endothelium

Biomicrofluidic devices and organ-on-a-chip (OOC) systems with integrated membranes are often fabricated from two different thermoplastic materials but bonding of such dissimilar thermoplastics remains challenging to manufacture at scale. Here, we present a method to bond poly(methylmethacrylate) layers to a polyethylene terephthalate porous membrane to create membrane-based microfluidic devices for biological barrier modeling. By combining milling, laser cutting and chlorocarbon-based solvent bonding supported by retention grooves, we achieved a fabrication rate of 36 devices in 5 h. Chlorocarbon-based solvent bonding resulted in bond strength of ~10 J/m2 and did not adversely affect the membrane pore structure or the channel cross-sectional shape. The bonded devices were found to support long term culture of human endothelial cells that developed expected morphology and cell-cell adhesion contacts as evidenced by immunofluorescent labeling of VE-cadherin. Barrier permeability was measured to be 3.38 × 106 cm/s for 10 kDa dextran using a sampling-based method compatible with mass spectrometry and scintillation techniques and was in agreement with literature. To validate the devices for cell migration experiments, THP-1 monocytes were introduced into devices with confluent endothelial monolayers. Monocytes adhered to and migrated through the endothelium. Activation of the endothelium with TNF-α prior to introducing monocytes significantly increased monocyte adhesion. Overall, the rapid device fabrication method achieved medium-volume production rates and was found to support both cell culture and experiments associated with measuring barrier and endothelial function. This fabrication method has potential to both accelerate biomicrofluidics and OOC research in the lab and accelerate development of commercialized microfluidic membrane devices.

Cost-effective and rapid prototyping of PMMA microfluidic device via polymer-assisted bonding

Cost-effective and rapid prototyping of PMMA microfluidic device via polymer-assisted bonding

Mixing characterization of binary-coalesced droplets in microchannels using deep neural network.

Real-time object identification and classification are essential in many microfluidic applications especially in the droplet microfluidics. This paper discusses the application of convolutional neural networks to detect the merged microdroplet in the flow field and classify them in an on-the-go manner based on the extent of mixing. The droplets are generated in PMMA microfluidic devices employing flow-focusing and cross-flow configurations. The visualization of binary coalescence of droplets is performed by a CCD camera attached to a microscope, and the sequence of images is recorded. Different real-time object localization and classification networks such as You Only Look Once and Singleshot Multibox Detector are deployed for droplet detection and characterization. A custom dataset to train these deep neural networks to detect and classify is created from the captured images and labeled manually. The merged droplets are segregated based on the degree of mixing into three categories: low mixing, intermediate mixing, and high mixing. The trained model is tested against images taken at different ambient conditions, droplet shapes, droplet sizes, and binary-fluid combinations, which indeed exhibited high accuracy and precision in predictions. In addition, it is demonstrated that these schemes are efficient in localization of coalesced binary droplets from the recorded video or image and classify them based on grade of mixing irrespective of experimental conditions in real time.

Robust chemical bonding of PMMA microfluidic devices to porous PETE membranes for reliable cytotoxicity testing of drugs.

Here, we report a simple yet reliable method for bonding poly(methyl methacrylate) (PMMA) to polyethylene terephthalate (PETE) track-etched membranes using (3-glycidyloxypropyl)trimethoxysilane (GLYMO), which enables reliable cytotoxicity tests in a microfluidic device impermeable to small molecules, such as anti-cancer drugs. The porous PETE membranes treated with 5% GLYMO were assembled with microfluidic channel-engraved PMMA substrates after air plasma treatment for 1 minute, followed by heating at 100 °C for 2 minutes, which permits irreversible and complete bonding to be achieved within 1 h. The bonding strength between the two substrates (1.97 × 107 kg m-2) was robust enough to flow culture medium through the device without leakage even at a gauge pressure of above 135 kPa. For validation of its utility in drugs testing, we successfully demonstrated that human lung adenocarcinoma cells cultured in the PMMA devices show more reliable cytotoxicity results for vincristine in comparison to conventional polydimethylsiloxane (PDMS) devices due to the inherent property of PMMA of it being impervious to small molecules. Given that the current organ-on-a-chip fabrication methods mostly rely on PDMS, this bonding strategy will expand simple fabrication capability using various thermoplastics and porous track-etched membranes, and allow us to create 3D-micro-constructs that more precisely mimic organ-level physiological conditions.

Flexible micro manufacturing platform for the fabrication of PMMA microfluidic devices

In this work we present a micro manufacturing platform for the production of polymeric microfluidic devices on a mass scale, based on the integration of microinjection moulding and femtosecond laser (fs-laser) micromachining technologies. A mould prototype was designed for the fabrication of polymeric thin plates characterized by simplified microfeatures representative of typical Lab-on-a-Chip (LoC) devices. The injection moulding master tool includes replaceable metallic inserts, which were fabricated by exploiting the extreme flexibility and accuracy of fs-laser milling. Here, the laser process parameters have been studied and properly adjusted to meet the target geometry and surface quality of the mould inserts, which were subsequently characterized by confocal and SEM microscopy. The micro injection moulding (μIM) process parameters for the device production have been defined by complete three-dimensional filling and packing process simulations. Finally, the micro-injection mould with reconfigurable inserts was employed for the production of thin plates with simplified microfeatures using PMMA. The ability to reproduce these microfeatures via μIM is an essential step to approach to the mass-production of a polymeric LoC and the use of replaceable micro-inserts fabricated by direct fs-laser ablation promises high flexibility in the design and manufacturing of such devices.

Controlled Shear Flow Directs Osteogenesis on UHMWPE-Based Hybrid Nanobiocomposites in a Custom-Designed PMMA Microfluidic Device.

The combinatorial influence of a biophysical cue (substrate stiffness) and biomechanical cue (shear flow) on the osteogenesis modulation of human mesenchymal stem cells (hMSCs) is studied for bone regenerative applications. In this work, we report stem cell differentiation on an ultra high molecular weight polyethylene (UHMWPE)-based hybrid nanobiocomposite [reinforced with a multiwalled carbon nanotube (MWCNT) and/or nanohydroxyapatite (nHA)] under a physiologically relevant shear flow (1 Pa) in a custom-built microfluidic device. Using a genotypic assessment with qRT-PCR and phenotypic assessment through analysis of cytoskeletal remodelling and marker proteins, the role of shear on the progression of osteogenesis modulation has been quantitatively established with statistically significant differences between nHA-reinforced and MWCNT-reinforced UHMWPE. Early-stage (alkaline phosphatase activity at day 8), middle-stage (matrix collagenation at day 14), and late-stage (matrix calcification at day 20) events were analyzed using mRNA expression changes of a limited cell volume after microfluidic culture experiments. The conventional Petri dish culture (static) exhibited an increased osteogenesis for nanoparticle-reinforced UHMWPE, irrespective of the type of nanoparticle. The shear-mediated culture experiments resulted in noticeable differences in the degree of osteogenesis with MWCNT being more effective than nHA reinforcement. The shear-mediated osteogenesis has been attributed to the skewed cellular morphology with a higher cell adhesion (vinculin expression) on UHMWPE and nHA than that of UHMWPE and MWCNT. The signatures of the cytoskeletal changes are reflected in terms of left-to-right (L-R) chirality as well as alignment and pattern of actin fibers. Moreover, stemness (vimentin expression) was found to be decreased because of differentiation. The electrophysiological analysis using patch clamp experiments also revealed a higher inward calcium current and intracellular calcium activity for the cells grown on the UHMWPE and nHA nanobiocomposite under shear. Overall, the present study conclusively establishes the synergistic role of substrate stiffness and shear on osteogenesis of hMSCs, in vitro.

One-step selective-wettability modification of PMMA microfluidic devices by using controllable gradient UV irradiation (CGUI)

Poly (methyl methacrylate) (PMMA) has become increasingly popular to fabricate microfluidic devices. In a microfluidic device, different functional areas usually require different wettability to achieve a better performance. However, most of the existing wettability modification methods have been applied to the whole PMMA surface making the device have minimum wettability difference. In this paper, a controllable gradient UV irradiation (CGUI) method was presented. In this method, a series of quartz plates sputtered with different thickness of Cu were arranged on top of the PMMA surface. By controlling the thickness of Cu film, the UV irradiation, which transmitted though the quartz plates onto the PMMA surface, can be adjusted making the modification performance able to be varied accordingly. The validation of the proposed CGUI was conducted through contact angle measurements. Our results showed that through 5 min CGUI process, the contact angle for different parts of the PMMA surface can be varied from 45.48° to 77.41° continuously with a long-term stability of 60 days. To demonstrate this method, a fully integrated Point-of-Care Test (POCT) device was designed and fabricated for the detection of cardiac Troponin I achieving the lower detection limit of 85 pg/ml within 10 min.

Simplified immobilisation method for histidine-tagged enzymes in poly(methyl methacrylate) microfluidic devices

Poly(methyl methacrylate) (PMMA) microfluidic devices have become promising platforms for a wide range of applications. Here we report a simple method for immobilising histidine-tagged enzymes suitable for PMMA microfluidic devices. The 1-step-immobilisation described is based on the affinity of the His-tag/Ni-NTA interaction and does not require prior amination of the PMMA surface, unlike many existing protocols. We compared it with a 3-step immobilisation protocol involving amination of PMMA and linking NTA via a glutaraldehyde cross-linker. These methods were applied to immobilise transketolase (TK) in PMMA microfluidic devices. Binding efficiency studies showed that about 15% of the supplied TK was bound using the 1-step method and about 26% of the enzyme was bound by the 3-step method. However, the TK-catalysed reaction producing l-erythrulose performed in microfluidic devices showed that specific activity of TK in the device utilising the 1-step immobilisation method was approximately 30% higher than that of its counterpart. Reusability of the microfluidic device produced via the 1-step method was tested for three cycles of enzymatic reaction and at least 85% of the initial productivity was maintained. The device could be operated for up to 40 h in a continuous flow and on average 70% of the initial productivity was maintained. The simplified immobilisation method required fewer chemicals and less time for preparation of the immobilised microfluidic device compared to the 3-step method while achieving higher specific enzyme activity. The method represents a promising approach for the development of immobilised enzymatic microfluidic devices and could potentially be applied to combine protein purification with immobilisation.

Experimental Investigations on the Effects of Surface Modifications to Control the Surface-Driven Capillary Flow of Aqueous Working Liquids in the PMMA Microfluidic Devices

Experimental Investigations on the Effects of Surface Modifications to Control the Surface-Driven Capillary Flow of Aqueous Working Liquids in the PMMA Microfluidic Devices

Solvent Bonding for Fabrication of PMMA and COP Microfluidic Devices

Solvent Bonding for Fabrication of PMMA and COP Microfluidic Devices

Solvent Bonding for Fabrication of PMMA and COP Microfluidic Devices.

Thermoplastic microfluidic devices offer many advantages over those made from silicone elastomers, but bonding procedures must be developed for each thermoplastic of interest. Solvent bonding is a simple and versatile method that can be used to fabricate devices from a variety of plastics. An appropriate solvent is added between two device layers to be bonded, and heat and pressure are applied to the device to facilitate the bonding. By using an appropriate combination of solvent, plastic, heat, and pressure, the device can be sealed with a high quality bond, characterized as having high bond coverage, bond strength, optical clarity, durability over time, and low deformation or damage to microfeature geometry. We describe the procedure for bonding devices made from two popular thermoplastics, poly(methyl-methacrylate) (PMMA), and cyclo-olefin polymer (COP), as well as a variety of methods to characterize the quality of the resulting bonds, and strategies to troubleshoot low quality bonds. These methods can be used to develop new solvent bonding protocols for other plastic-solvent systems.

Safe and cost-effective rapid-prototyping of multilayer PMMA microfluidic devices

The rapid translation of research from bench to bedside, as well as the generation of commercial impact, has never been more important for both academic and industrial researchers. It is therefore unsurprising that more and more microfluidic groups are investigating research using a wide range of thermoplastics which can be readily translated to large-scale manufacturing, if the technology is taken to commercialisation. While structuring, via additive or subtractive manufacturing, is becoming relatively easy through the use of commercial-grade devices, reliable and fast assembly remains a challenge. In this article, we propose an innocuous and cost-effective, under 2-min technique which enables the bonding of multiple poly(methyl methacrylate) layers. This bonding technique relies on the application of small amounts (10 µl/cm2) of ethanol, low temperatures (70 °C) and relatively low pressures (~1.6 MPa). Our characterisation analysis shows that using a bonding time of 2 min is enough to produce a strong bond able to withstand pressures always above 6.2 MPa (with mean of 8 MPa, highest reported in the literature), with minimal channel deformation (<5%). This technique, which we demonstrate on assembly comprising up to 19 layers, presents an exciting improvement in the field of rapid prototyping of microfluidic devices, enabling extremely fast design cycles in microfluidic research with a material compatible with mass manufacturing, thus allowing a smoother transition from the laboratory to the market. Beyond the research community, this robust prototyping technique has the potential to impact on the deliverability of other scientific endeavours including educational projects and will directly fuel the fluidic maker movement.

Microwave Induced Ethanol Bath Bonding for PMMA Microfluidic Device

High bonding strength, low deformation and convenient procedure are all very important aspects in the microfluidic device fabrication process. In this paper, an improved microwave induced bonding technology is proposed to fabricate microfluidic device based on methyl methacrylate (PMMA). This method employs pure ethanol as the bonding assisted solvent. The ethanol not only acts as the microwave absorbing material, but also works as the organic solvent in bath. The presented research work has shown that the bonding process can be completed in less than 45 s. Furthermore, the convenient bonding only applies microwave oven, beakers and binder clips. Then, we discuss effects of microwave power, bonding time on bonding strength and deformation of microstructures on PMMA microfluidic device. Finally, a 4 layers micro-mixer has been fabricated using the proposed bonding technique which includes 15 trapezoid micro-channels, 9 T-type mix units and an X-type mix unit. Experimental results show that the proposed bonding method have some advantages compared with several traditional bonding technologies, such as hot pressing bonding, ultrasonic bonding and solvent assisted bonding methods in respect of bonding strength, deformation and bonding process. The presented work would be helpful for low coat mass production of multilayer polymer microfluidic devices in lab.

High throughput blood plasma separation using a passive PMMA microfluidic device

Since plasma is rich in many biomarkers used in clinical diagnostic experiments, microscale blood plasma separation is a primitive step in most of microfluidic analytical chips. In this paper, a passive microfluidic device for on-chip blood plasma separation based on Zweifach---Fung effect and plasma skimming was designed and fabricated by hot embossing of microchannels on a PMMA substrate and thermal bonding process. Human blood was diluted in various times and injected into the device. The main novelty of the proposed microfluidic device is the design of diffuser-shaped daughter channels. Our results demonstrated that this design exerted a considerable positive influence on the separation efficiency of the passive separator device, and the separation efficiency of 66.6 % was achieved. The optimum purity efficiency of 70 % was achieved for 1:100 dilution times.

Improvement of Surface Properties of Micro-Mold via SAM Coating for Fabrication of Microfluidic Device

N-octadecyltrichlorosilane [OTS, CH3(CH2)17SiCl3] self-assembled monolayer (SAM) coatings were deposited on Si micromolds by dip-coating. Chemical composition, surface roughness, friction coefficient, thermal stability and surface energy of coatings were investigated. OTS coated silicon (Si) micromolds were used to fabricate PMMA microfluidic devices by hot-embossed process. All OTS coatings were thermally stable up to 180 °C, which is higher than hot-embossing temperature of PMMA. OTS coated micromolds had low friction coefficient, adhesion and superior molding efficiency, which improved lifetime of a uncoated Si micromold from 3 to 27 times.

Microchip immunoaffinity electrophoresis of antibody-thymidine kinase 1 complex.

Thymidine kinase 1 (TK1) is an important cancer biomarker whose serum levels are elevated in early cancer development. We developed a microchip electrophoresis immunoaffinity assay to measure recombinant purified TK1 (pTK1) using an antibody (Ab) that binds to human TK1. We fabricated PMMA microfluidic devices to test the feasibility of detecting Ab-pTK1 immune complexes as a step toward TK1 analysis in clinical serum samples. We were able to separate immune complexes from unbound Abs using 0.5× PBS (pH 7.4) containing 0.01% Tween-20, with 1% w/v methylcellulose that acts as a dynamic surface coating and sieving matrix. Separation of the Ab and Ab-pTK1 complex was observed within a 5 mm effective separation length. This method of detecting pTK1 is easy to perform, requires only a 10 μL sample volume, and takes just 1 min for separation.

Low temperature and deformation-free bonding of PMMA microfluidic devices with stable hydrophilicity via oxygen plasma treatment and PVA coating

A deformation-free bonding method with stable hydrophilicity in PMMA devices has been proposed through oxygen plasma treatment and PVA coating.