Fabrication Of Microfluidic Channels Research Articles

On the Machinability and Formation of Gas Film Thickness in ECDM of Silica based Pyrex Glass

Electrochemical discharge machining (ECDM) stands out as a preferred method for microfluidic channel fabrication due to its ability to produce required shapes with the least thermal damage along with close tolerances and dimensional accuracy. Recently, there has been significant progress made in the domain of ECDM for parametric analysis, focusing on discharge regime characteristics, but precise control of the hydrodynamic regime remains a challenge. With this view, the present study has been targeted on analyzing the effect of various auxiliary electrodes on the formation of gas film thickness and discharge energy during the fabrication of microchannels using ECDM on silica-based Pyrex glass under varying conditions. Experiments were conducted on an ECDM setup to achieve near damage-free edges of microchannels on the surface silica-based Pyrex glass. Results show the effect of various auxiliary electrodes, applied voltage, and electrolyte concentration on gas film thickness, spark energy, rate of material removal (MRR), and width of overcut (WOC). The optimum parametric level of applied voltage, electrolyte concentration, and auxiliary electrode were 68 V, 35 wt%, and A2 auxiliary electrode, respectively and the best response values were 0.4134 mg min−1, and 40 μm, respectively, for MRR and WOC. In addition, tool wear rate, heat affected zone, and surface morphology of fabricated microchannels was examined using scanning electron microscopy, optical microscope, and energy-dispersive X-ray spectroscopy.

Rapid and versatile, micro-patterning and functionalization of complex structures on ultra-thin and flexible polymeric substrates

Microscale patterning on flexible substrates is important in many applications such as in wearable sensors and microfluidics-based diagnostics, therefore low-cost fabrication methods which are scalable and amenable to mass production have attracted the interest of many companies and research groups. Dry film resists (DFRs) are commercially available materials with properties compatible with their implementation on flexible substrates to cover a wide range of applications, which also offer environmental and sustainability benefits due to the low waste generation compared to the liquid resists. However, there are limited detailed reports in the literature regarding the use of DFRs for the fabrication of microfluidic channels or other micropatterns (i.e., posts) on thin and flexible substrates. Herein we present in detail the fabrication of: a) microfluidic channels of width ranging from 50 μm up to 800 μm, and depth ranging from 30 μm up to 270 μm and b) square posts 80 μm × 80 μm in size and 30 μm in height. Particularly, our method enables the fabrication of ultra-deep microchannels (depth > 250 μm), highly ordered post arrays over large area (appr. 60 cm2), as well as complex designs with hierarchical scale features (80 μm posts inside 800 μm microchannels or micro-nanotexturing inside microchannels) on ultra-thin flexible substrates. To demonstrate the versatility of the method, three different DFRs were used on ultra-thin (30 μm), flexible, single-sided copper-clad polyimide substrates. It is also demonstrated that DFRs can be effectively modified using plasma etching to tune the surface wetting properties towards applications such as pumpless capillary action, where such functionality is required.

Evolution of materials, geometries, and fabrication of sweat patches and their use in high-throughput point-of-care/onsite sensing

Sweat is a non-invasive fluid used to monitor various medically relevant analytes for disease diagnosis and healthcare monitoring. Sweat patches are used to collect contaminant-free sweat from individuals in any setting. In the past 50 years, sweat patches have evolved on various fronts, like fabrication methods, materials, and microfluidic channel designs. The primary goal of this study is to explore the evolution of sweat patches over the last 50 years in terms of materials such as polydimethylsiloxane (PDMS), adhesives, and other polymers, as well as microfluidic channel geometries and fabrication approaches. In addition, modern sweat patches are integrated with electrodes and electronic systems that enable sweat collection and in-situ analysis. The sweat patches are classified into two classes: early and modern sweat patches. Further, applications of these sweat patches in monitoring hydration, performance, metabolites, and disease diagnosis have been elaborately discussed. In the end, the conclusion and future outlook are discussed to give insight into further research.

Multimaterial extrusion of programmable periodic filament structures via modularly designed extruder heads

There is a growing interest in patterning multimaterial structures into one-dimensional, two-dimensional, and three-dimensional motifs with spatially programmable inner structures. Harnessing material extrusion technology with customizable extruder heads greatly expands the possibilities of 3D printing to generate diverse multimaterial structures. However, the current choices of extruder heads are still limited largely due to the complexity in the design and fabrication of high-resolution microfluidic channels for multimaterial ink extrusion. Here, we report a modular strategy in multimaterial extrusion to program periodic structures and material compositions in printed objects. Our modular design greatly simplifies the design and manufacturing of multimaterial extruder heads to rapidly print complex multilayered architectures. Moreover, different extruder head modules can be combined in series or in parallel and different filament morphologies can be controlled by adjusting printing parameters such as flow rate and pressure. As exemplars, two immiscible materials with similar rheological properties but different mechanical properties are used for co-extrusion. The lamellar composite filaments and printed woodpile structures exhibit high toughness and superior energy-absorption capability, respectively. Our strategy provides new insights for the design of innovative filament structures for 3D printing and shows broad application prospects in tissue engineering, structural systems, optoelectronics, and beyond.

Manipulation of Microparticles in Optofluidic Devices Fabricated by Femtosecond Laser Micromachining

This study reports the fabrication of three-dimensional microfluidic channels in fused silica, using femtosecond laser micromachining, to achieve two-dimensional hydrodynamic flow focusing in either the horizontal or the vertical directions. Spatial focusing of 3 μm polystyrene particles was successfully demonstrated, showing the ability of the fabricated devices to confine microparticles within a 6 μm layer over a channel width of 420 μm and within a 5 μm layer over a channel height of 260 μm. Integration of laser-direct written optical waveguides inside a microfluidic chip and orthogonal to the channel also enabled the implementation of a dual-beam optical trap, with trapping of polystyrene microparticles using a 1550 nm beam being demonstrated.

Direct fabrication of glass microfluidic channel using CO2 laser

The design and development of small and compact devices with numerous new functions and vast benefits to the society is steadily receiving global attention. These sophisticated small devices require the production of accurate and intricate micro and nano-scale patterns with different three-dimensional (3D) shapes, sizes, and aspect ratios. Microfluidic device or so-called lab-on-a-chip (LOC) is one example of a highly sensitive and compact integrated device capable of detecting multiple analytes, usually used as a diagnostic device. In this study, we demonstrate the feasibility study for direct fabrication of microfluidic channel on transparent optical glass substrate via CO2 direct laser structuring. A custom-built direct laser structuring setup mainly consist of a commercial continuous type of CO2 laser source and glass preheating apparatus is utilized. First, the relationship between the process parameters, mainly the laser scanning speed, number of lasers passes and initial glass preheating temperature to the formation of microchannel of different width, height and shape were established. Then, the form accuracy and the morphology of the microchannels were characterized using laser scanning confocal microscope (LSCM) and surface profiler. Overall, the result reveals that the combination of higher laser power, lower scanning speed and higher number of laser passes promotes the increase of both the width and height of the microchannel. Preheating was found to be necessary for the glass used in this study in avoiding either micro-cracks or bulk glass cracking. Based on the relationship between laser scanning speed and the number of laser passes, a prototype of a microfluidic channel with average width and height of about 235 ± 10 µm and 6 ± 0.3 µm, respectively was successfully fabricated. This study opens an opportunity for further improvement and research for fabrication of crack-free and smooth microfluidic channels using low-cost CO2 laser structuring setup.

Unlocking the potential of 3D printed microfluidics for mass spectrometry analysis using liquid infused surfaces

Combining microfluidics with mass spectrometry (MS) analysis has great potential for enabling new analytical applications and simplifying existing MS workflows. The rapid development of 3D printing technology has enabled direct fabrication of microfluidic channels using consumer grade 3D printers, which holds great promise to facilitate the adoption of microfluidic devices by the MS community. However, photo polymerization-based 3D printed devices have an issue with chemical leeching, which can introduce contaminant molecules that may present as isobaric ions and/or severely suppress the ionization of target analytes when combined with MS analysis. Although extra cure and washing steps have alleviated the leeching issue, many such contaminant peaks can still show up in mass spectra. In this work, we report a simple surface modification strategy to isolate the chemical leachates from the channel solution thereby eliminating the contaminant peaks for MS analysis. The channel was prepared by fabricating a layer of polydimethylsiloxane graft followed by wetting the graft using silicone oil. The resulting liquid infused surface (LIS) showed significant reduction in contaminant peaks and improvement in the signal intensity of target analytes. The coating showed good stability after long-term usage (7 days) and long-term storage (∼6 months). Finally, the utility of the coating strategy was demonstrated by printing herringbone microfluidic mixers for studying fast reaction kinetics, which obtained comparable reaction rates to literature values. The effectiveness, simplicity, and stability of the present method will promote the adoption of 3D printed microdevices by the MS community.

Gold polycarbonate microchannels for electrochemical applications

AbstractIn this paper, we present gold‐plating polycarbonate (PC) microchannels. The fabrication of the gold microfluidic channels is achieved by tuning the sequence of reagent insertion into milled and closed submillimeter PC system channels. The resulting gold surface can be utilized in many applications where the benefits of microfluidics, (bio)chemistry of surfaces, and electrochemistry can be combined.Here, we combine the advantages of electrochemistry with microfluidics by mixing the gold sensor with microfluidics. This approach differs from the classic one – the sensor will undergo modifications (e. g., shape and size) depending on the specific scientific problem and will be designed individually; hence its characteristics will be changed. Our goal in this work is to indicate new possibilities for combining two methodologies – electrochemistry and microfluidics. In our work, we emphasize that it confirms the validity of our chosen concept (proof‐of‐concept).In this work, we present one such application, the use of a gold microfluidic channel as a working electrode (WE). We describe the microchip‘s construction and electrochemical characterization, including the gold flow‐through WE, the Ag/AgCl wire pseudo‐reference, and the Pt auxiliary electrode. The measured current is the result of the flow through a rectangular duct of the gold microchannel electrode embedded in the four walls of the chip.

INFLUENCE OF INTER- AND INTRA-CELLULOSE FIBERS IN PAPER SUBSTRATE FOR FLEXIBLE MICROFLUIDIC CHANNEL INTEGRATION

In recent times, among all the substrates used in microfluidic systems, cellulose paper is used as a handy, low-cost substrate that has gained attention for carrying fluid on its surface over capillary pressure. Cellulose paper substrate has exhibited great potential on microfluidic devices owing to prevalent obtainability, easy fluid (sample) flow system, flexibility, and low cost. Cellulose paper is fibrous, biocompatible, and hydrophilic in nature due to the hydroxyl group of the cellulose molecule. Based on the dominance of functional hydroxyl groups, cellulose is very reactive and every single cellulose fiber acts like a microchannel on the paper substrates. Aggregation of inter- and intra-cellulose fiber chains has a strong binding affinity to it and toward materials containing hydroxyls groups. In this paper, impact of inter- and intra-cellulose fiber on the paper substrate has been discussed through an experimental study. For the addition of work a “hydrophobic penetration-on-paper substrate (Hyp-POP)” method has been shown by using TiO2 ink as a hydrophobic material to design the microfluidic channel on the Whatman cellulose filter paper (grade 1) as a paper substrate. In this experimental study, the intra-cellulose fibers of paper substrate interact through hydrogen bonds with water molecules and form a hydrophilic surface on paper substrate while TiO2 binds with intra-cellulose fibers by electrostatic forces which change the crystallinity of intra-cellulose fiber and make the surface of paper substrate; hydrophobic. Field Emission Scanning Electron Microscope (FESEM) analysis is conceded for microfluidic channel analysis on the paper surface and EDS is carried out for TiO2 ink contents analysis. It has been experimentally observed that the printing material of TiO2 ink with 17.2% Ti content is suitable to integrate hydrophobic barrier on paper substrate for microfluidic channel fabrication. The wetting ability of Whatman cellulose filter paper (grade 1) was further evaluated by contact angle measurements (Data physics OCA 15EC). Using “Hyp-POP” method a hydrophobic pattern (width 3140 [Formula: see text]m) on paper substrate has been made for the flow of liquid (blue fountain ink) into a paper fluidic channel (width 1860 [Formula: see text]m) without any leakage.

Fabrication of microfluidic paper-based channels by inkjet printing process for analytical applications

Microfluidic paper-based channels play an important role in microfluidic paper-based analytical devices (μPADs). There are some fabrication methods which could be utilised to fabricate microfluidic channels on paper substrate. Among these methods, inkjet printing process is considered as a promising fabrication method with many advantages such as low-cost, material saving, high precision, etc. The aim of this work is to apply inkjet printing technology to fabricate paper channels of μPADs. A new design of μPAD was proposed in this paper to demonstrate how to fabricate inkjet-printed hydrophobic lines to make paper-based biosensor. Biological target of our μPADs is human chOrionic gonadotropin (hCG). Colorimetric signals from μPADs were captured by digital camera and measured by ImageJ software, which showed that these μPADs can determine hCG in the range from 1,000 to 10,000 ng ml−1. These results showed that piezoelectric inkjet printing technology can fabricate 250 μm-width hydrophobic lines on paper substrate, helping in fabricating μPADs in next applications.

Polymeric Microfluidic Fuel Cells with Controlled Printed Patterns.

Since its first appearance almost a couple of decades ago, microfluidic fuel cells (MFFCs) have gained considerable research momentum due to their potential applications in portable devices. The main focus has been on the effective fabrication of microfluidic channels with different materials, where the manufacturing limitations proved to be the main stumbling blocks. Paper-based MFFCs have been reported with some success, where the porosity of the flow channel medium drives the reactants, greatly reducing the need for elaborate external devices and complex manufacturing obstacles, although the longevity of these cells remains questionable. The current article addresses this issue by replacing the paper-based flow channels with 3D-printed substrates of different structural forms to serve as pathways for controlled flow and mixing responses of the reactant liquids without the use of other devices, such as micro pumps and valves. The line-by-line material consolidation mechanics of fused filament fabrication and the porous mesostructural responses of a commercial polymer filament are combined to build the microfluidic fuel channels of varying configurations. Numerical and experimental characterizations proved the cells to perform better than the current paper-based counterparts, apart from better longevity and possible new opportunities for future improvements based on more complex micro-, meso-, and macrostructural advances.

Design and fabrication of aspiration microfluidic channel for oocyte characterization

The development potential for oocytes can be predicted by their mechanical properties. One important parameter that is measured to calculate oocyte hardness is Cortical Tension (CT). In this work, for the first time, we present the design, simulation, and fabrication of a new aspiration microfluidic chip to measure the CT of oocytes and then predict their maturation capability in the Germinal Vesicle (GV) stage. This high-performance technique facilitates oocyte characterization and is a promising alternative to traditional methods such as MicroPipette Aspiration (MPA). The proposed technique involves considerably simpler operation, less specialized equipment, and less technical skill than MPA. The proposed microfluidic channel also promises faster measurements. It is shown that in order to completely continue the growth process of oocytes in GV stage, the CT should be in a certain range: very low or very high CTs lead to unsuccessful growth. The obtained results show that 79% of oocytes with the CT between 1.5 and 3 nN/μm reach the Metaphase II (MII) stage, whereas the growth for 78% of oocytes with the CT less than 1.5 nN/μm or higher than 3 nN/μm stops at the GV or Germinal Vesicle Break Down (GVBD) stages. Another property, kvis, that points to the viscous behavior of oocytes is also measured. It is seen that 80% of GV oocytes with the kvis values between 15 and 30 k Pa s/m reach the MII stage.

Fabrication of elastomeric microfluidic channels based on light-curing electrostatic printing

Fabrication of elastomeric microfluidic channels based on light-curing electrostatic printing

Chromium oxide – A novel sacrificial layer material for MEMS/NEMS and micro/nanofluidic device fabrication

Free standing membranes for fluidic devices typically require long etching times due to the slow, diffusion limited exchange of etchant and etch products when large etch distances are involved. In these cases, high etch selectivity is required between the sacrificial and channel-wall materials. Here, we introduce chromium oxide, Cr2O3, as a versatile sacrificial layer material for the fabrication of microfluidic and nanofluidic channels. Chromium oxide has many desirable attributes as a sacrificial layer: it can be deposited by sputtering to form stress-controlled films, it adheres well to both metal and dielectric surfaces, it is resistant to most acids and bases, but etches rapidly in standard chromium etchants, and has minimal tendencies to react with other commonly used materials. In addition, typical chromium etchants are highly selective to materials commonly used in microfabricated systems. To fully explore the process characteristics of this material we performed a comprehensive set of experiments to quantify its behavior in ways relevant to its use in device fabrication. The results presented in this paper will provide a starting point to optimize Cr2O3 for fabrication of fluidic devices.

Polymeric micro gas preconcentrators based on graphene oxide and carbon nanopowder adsorbents for gas detection application

In this study, an application of novel polymer-based microfluidic channels for preconcentration and detection of methane gas is investigated. Poly (methyl methacrylate) (PMMA) microfluidic channel is filled by graphene oxide (GO) as a new adsorbent for thermal preconcentration and carbon nanopowder is loaded into a polydimethylsiloxane (PDMS) microfluidic channel. The effective microfluidic channels area is 14 mm × 10 mm. The laser cutting and etching followed by thermally-solvent bonding process are used for PMMA microfluidic channel fabrication. Also, PDMS microfluidic channel is fabricated by SU-8 molding technique, lithography process, and oxygen plasma bonding on glass. SEM, Raman spectroscopy, and FTIR characterizations are carried out for investigation of the synthesized GO. The amount of electrical power consumption of devices is also investigated by simulation and experiment. The performance of both micro preconcentrators (μPCs) are compared through the similar experimental tests which exhibit the suitable performance of fabricated μPCs with proper repeatability for preconcentration purposes. The effect of gas flow rate, heating rate, gas exposure time, and gas concentration are investigated for both microfluidic channels and their optimized values were obtained. According to the lower desorption temperature of GO, despite its slightly lower response (10.41) compared to carbon nanopowder μPCs (12.34), due to its almost half power consumption (0.375 W in comparison with 0.8 W), it can be an appropriate candidate for preconcentration applications. PMMA and PDMS-based microfluidic channels show promising choices in the preconcentration application for the adsorbents with low desorption temperatures. As a result, PMMA as a low-cost material with a simple fabrication process in microchannels and GO as the novel adsorbent material can be suitable candidates in low working temperature and rapid preconcentration devices. • Microfluidic channels are fabricated based on poly (methyl methacrylate) (PMMA), and polydimethylsiloxane (PDMS) • Graphene oxide (GO) and carbon nanopowder are used as the adsorbent materials for PMMA and PDMS microfluidic channels, respectively. • The effect of gas flow rate, heating rate, gas exposure time, and gas concentration are investigated to achieve the optimized values. • The power consumption and temperature distribution of heater are studied through the simulation.

Super-hydrophobic microfluidic channels fabricated via xurography-based polydimethylsiloxane (PDMS) micromolding

The facile and rapid fabrication of super-hydrophobic microfluidic channels has numerous bio- and physico-chemical applications. In this study, we present a simple, fast, and inexpensive method to fabricate a super-hydrophobic polydimethylsiloxane (PDMS) microchannel. The method involves using xurography-based PDMS micromolding with a silicon carbide paper. The microchannel exhibited a micro-textured surface with a water contact angle of 152° and minimum feature size of 300 μm. To demonstrate the utility of our method, we generated water-in-oil droplets over a wide range of input flow rates. Compared to conventional PDMS microchannels of the same size, our super-hydrophobic channels produced the droplets at four times faster rate with higher size uniformity. This method was further used for the gelation of alginate droplets, which can be broadly utilized in drug delivery and biosensing applications. Furthermore, spatially selective formation of super-hydrophobic surfaces was used to passively control the two merging flows via capillary action.

JMEMS Letters Fabrication of Self-Sealed Circular Microfluidic Channels in Glass by Thermal Blowing Method

We report fabrication of circular glass microchannels with radius less than 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> using the glass blowing technique. Silicon trenches filled with nitrogen are used for microchannel fabrication. We report an interesting reflow regime where the flowing glass fills the silicon trenches to form a completely circular microchannel. Circular microchannels have symmetric velocity profile and do not suffer from flow stagnation problems observed in rectangular channels. Besides circular shape, fabrication conditions of the semi-circular and elliptically shaped channels are also discussed. A mathematical model explaining the observation is also presented and is compared with the experimental results. [2021-0183]

In-situ transfer vat photopolymerization for transparent microfluidic device fabrication

While vat photopolymerization has many advantages over soft lithography in fabricating microfluidic devices, including efficiency and shape complexity, it has difficulty achieving well-controlled micrometer-sized (smaller than 100 μm) channels in the layer building direction. The considerable light penetration depth of transparent resin leads to over-curing that inevitably cures the residual resin inside flow channels, causing clogs. In this paper, a 3D printing process — in-situ transfer vat photopolymerization is reported to solve this critical over-curing issue in fabricating microfluidic devices. We demonstrate microchannels with high Z-resolution (within 10 μm level) and high accuracy (within 2 μm level) using a general method with no requirements on liquid resins such as reduced transparency nor leads to a reduced fabrication speed. Compared with all other vat photopolymerization-based techniques specialized for microfluidic channel fabrication, our universal approach is compatible with commonly used 405 nm light sources and commercial photocurable resins. The process has been verified by multifunctional devices, including 3D serpentine microfluidic channels, microfluidic valves, and particle sorting devices. This work solves a critical barrier in 3D printing microfluidic channels using the high-speed vat photopolymerization process and broadens the material options. It also significantly advances vat photopolymerization’s use in applications requiring small gaps with high accuracy in the Z-direction.

Isolation of exosome from the culture medium of Nasopharyngeal cancer (NPC) C666-1 cells using inertial based Microfluidic channel.

Isolation of exosome from culture medium in an effective way is desired for a less time consuming, cost saving technology in running the diagnostic test on cancer. In this study, we aim to develop an inertial microfluidic channel to separate the nano-size exosome from C666-1 cell culture medium as a selective sample. Simulation was carried out to obtain the optimum flow rate for determining the dimension of the channels for the exosome separation from the medium. The optimal dimension was then brought forward for the actual microfluidic channel fabrication, which consisted of the stages of mask printing, SU8 mould fabrication and ended with PDMS microchannel curing process. The prototype was then used to verify the optimum flow rate with polystyrene particles for its capabilities in actual task on particle separation as a control outcome. Next, the microchip was employed to separate the selected samples, exosome from the culture medium and compared the outcome from the conventional exosome extraction kit to study the level of effectiveness of the prototype. The exosome outcome from both the prototype and extraction kits were characterized through zetasizer, western blot and Transmission electron microscopy (TEM). The microfluidic chip designed in this study obtained a successful separation of exosome from the culture medium. Besides, the extra benefit from this microfluidic channels in particle separation brought an evenly distributed exosome upon collection while the exosomes separated through extraction kit was found clustered together. Therefore, this work has shown the microfluidic channel is suitable for continuous separation of exosome from the culture medium for a clinical study in the future.

Multi-jet ice 3D printing

PurposeMulti-jet deposition of the materials is a matured technology used for graphic printing and 3 D printing for a wide range of materials. The multi-jet technology is fine-tuned for liquids with a specific range of viscosity and surface tension. However, the use of multi-jet for low viscosity fluids like water is not very popular. This paper aims to demonstrate the technique, particularly for the water-ice 3 D printing. 3 D printed ice parts can be used as patterns for investment casting, templates for microfluidic channel fabrication, support material for polymer 3 D printing, etc.Design/methodology/approachMulti-jet ice 3 D printing is a novel technique for producing ice parts by selective deposition and freezing water layers. The paper confers the design, embodiment and integration of various subsystems of multi-jet ice 3 D printer. The outcomes of the machine trials are reported as case studies with elaborate details.FindingsThe prismatic geometries are realized by ice 3 D printing. The accuracy of 0.1 mm is found in the build direction. The part height tends to increase due to volumetric expansion during the phase change.Originality/valueThe present paper gives a novel architecture of the ice 3 D printer that produces the ice parts with good accuracy. The potential applications of the process are deliberated in this paper.