Monolithic Microchannels Research Articles

Sub-second synthesis of silver nanoparticles in 3D printed monolithic multilayered microfluidic chip: Enhanced chemiluminescence sensing predictions via machine learning algorithms

Futuristic microfluidics will require alternative ways to extend its potential in vast areas by integrating various facets such as automation of different subsystems, multiplexing, incorporation of cyber-physical capabilities, and rapid prototyping. On the rapid prototyping aspect, for the last decade, additive manufacturing (AM) or 3D printing (3DP) has advanced to become an alternative fabrication process for microfluidic devices, enabling industry-level abilities towards mass production. In this context, for the first time, this work demonstrates the fabrication of monolithic multilayer microfluidic devices (MMMD) from planar orientation (1 layer) to nonplanar (4 layers) monolithic microchannels. The developed MMM device was impeccable for synthesizing highly potentialized silver nanoparticles (AgNPs) in <1 s. Moreover, the transport of chemical species with laminar flow simulations was performed on the process along with the thorough characterizations of produced AgNPs, finding the mean AgNPs particle size of around 35 nm without any post-processing requirements. The well-known catalytic activity of AgNPs was leveraged to enhance weak chemiluminescence (CL) sensing signals by >1300 %, increasing CL sensitivity. Further, machine learning (ML) predictive models encouraged to obtain the experimental parameters without human intervention iterations for target-specific applications. The proposed methodology finds the potential to save resources, time, and enables automation with rapid prototyping, providing possibilities for mass fabrications.

Self-shrinking soft demoulding for complex high-aspect-ratio microchannels

Microchannels are the essential elements in animals, plants, and various artificial devices such as soft robotics, wearable sensors, and organs-on-a-chip. However, three-dimensional (3D) microchannels with complex geometry and a high aspect ratio remain challenging to generate by conventional methods such as soft lithography, template dissolution, and matrix swollen processes, although they are widespread in nature. Here, we propose a simple and solvent-free fabrication method capable of producing monolithic microchannels with complex 3D structures, long length, and small diameter. A soft template and a peeling-dominant template removal process are introduced to the demoulding process, which is referred to as soft demoulding here. In combination with thermal drawing technology, microchannels with a small diameter (10 µm), a high aspect ratio (6000, length-to-diameter), and intricate 3D geometries are generated. We demonstrate the vast applicability and significant impact of this technology in multiple scenarios, including soft robotics, wearable sensors, soft antennas, and artificial vessels.

Highly stable honeycomb structured 2D/2D vanadium aluminum carbide MAX coupled g-C3N4 composite for stimulating photocatalytic CO2 reduction to CO and CH4 in a monolith photoreactor

Developing efficient materials for photocatalytic conversion of CO2 to value added chemicals and fuels has gained significant attractions in the recent years. However, this is still a difficult task. In this work, a well-designed vanadium aluminum carbide (V2AlC) MAX coupled with porous graphitic carbon nitride (g-CN) to construct a nanocomposite for photocatalytic CO2 reduction has been investigated. 2D/2D V2AlC/g-CN performance was conducted in a fixed-bed and monolith photoreactor under UV and visible light. The V2AlC/g-CN exhibited photoactivity of 1747 and 67 µmol g−1 h−1 for CO and CH4 evolution, which were 4.13 and 1.94 folds more than their production compared to using pristine g-CN, respectively. More importantly, among the sacrificial reagents such as H2O, CH3OH, and H2, the highest productivity was obtained using CO2-CH3OH due to more attachment of methanol over g-C3N4 with more proton generation. Similarly, performance of V2AlC/g-CN under UV-light was promising due to the ability of long pathways to penetrate light inside the fixed bed reactor. In addition to photocatalysts, the performance comparison of reactors confirms that the monolith photoreactor has higher productivity for CO2 reduction to CO and CH4. This was evidently due to the large illuminated active surface area, and more light utilization, and proficient mass transfer inside the monolithic microchannels. The stability examination further confirms the unceasing evolution of CO and CH4 in the consecutive four cycles. Thus, V2AlC MAX is a promising layered material and can be coupled with semiconductors as a support or cocatalyst to achieve both photoactivity and stability for continuous fuel production.

Fabrication routes via projection stereolithography for 3D-printing of microfluidic geometries for nucleic acid amplification.

Digital Light Processing (DLP) stereolithography (SLA) as a high-resolution 3D printing process offers a low-cost alternative for prototyping of microfluidic geometries, compared to traditional clean-room and workshop-based methods. Here, we investigate DLP-SLA printing performance for the production of micro-chamber chip geometries suitable for Polymerase Chain Reaction (PCR), a key process in molecular diagnostics to amplify nucleic acid sequences. A DLP-SLA fabrication protocol for printed micro-chamber devices with monolithic micro-channels is developed and evaluated. Printed devices were post-processed with ultraviolet (UV) light and solvent baths to reduce PCR inhibiting residuals and further treated with silane coupling agents to passivate the surface, thereby limiting biomolecular adsorption occurences during the reaction. The printed devices were evaluated on a purpose-built infrared (IR) mediated PCR thermocycler. Amplification of 75 base pair long target sequences from genomic DNA templates on fluorosilane and glass modified chips produced amplicons consistent with the control reactions, unlike the non-silanized chips that produced faint or no amplicon. The results indicated good functionality of the IR thermocycler and good PCR compatibility of the printed and silanized SLA polymer. Based on the proposed methods, various microfluidic designs and ideas can be validated in-house at negligible costs without the requirement of tool manufacturing and workshop or clean-room access. Additionally, the versatile chemistry of 3D printing resins enables customised surface properties adding significant value to the printed prototypes. Considering the low setup and unit cost, design flexibility and flexible resin chemistries, DLP-SLA is anticipated to play a key role in future prototyping of microfluidics, particularly in the fields of research biology and molecular diagnostics. From a system point-of-view, the proposed method of thermocycling shows promise for portability and modular integration of funcitonalitites for diagnostic or research applications that utilize nucleic acid amplification technology.

3D Helical Micromixer Fabricated by Micro Lost‐Wax Casting

AbstractMicromixers produced by micro fabrication techniques have attracted attention for micro total analysis systems and lab‐on‐a‐chip applications in point‐of‐care testing. However, the fabrication and setup of micromixers have become more complex and more difficult. Considering the practical use of micromixers in medical and industrial applications, their designs can be simplified while maintaining high mixing efficiency. Rapid prototyping, represented by 3D printing having micro‐scale resolutions, is one promising technology to replace conventional fabrication methods such as soft lithography. Here, a 3D helical micromixer fabricated by micro‐scale lost‐wax casting is reported. The molds for lost‐wax casting are fabricated by fine 3D printing of a hard wax resin which can be removed from a polydimethylsiloxane block just by heating and washing with water, and a fine and smooth structure is realized. The optimized helical micromixer fabricated by lost‐wax casting promotes mixing efficiency compared with other micromixers. In addition, a monolithic microchannel having the helical 3D bridge structure is presented in this study. The demonstration is an important advancement toward the industrial applications of micromixers fabricated by micro‐scale 3D printing. The ability to fabricate complex structures can simply lead to the creation of more sophisticated mixers in the future.

Heat transfer enhancement by silver nanowire suspensions in microchannel heat sinks

Convection heat transfer and pressure drop characteristics of water based silver nanowire suspensions flowing through CMOS compatible monolithic microchannel heat sinks are investigated experimentally. Three different rectangular channels of 200 μm×50 μm, 100 μm×50 μm and 70 μm×50 μm cross sectional area are used during the experiments. The stability of the silver nanofluids is established by the added polyvinylpyrrolidone (PVP) as the surfactant. To investigate the potential heat transfer enhancement by the silver nanofluids, the experiments are performed with deionized (DI) water, PVP-DI water solution, and the silver nanofluid with added PVP. It is observed that the silver nanofluid had higher heat transfer coefficient than both the PVP-DI water solution, and DI water only. Moreover, all fluids have similar hydrodynamic performance. The prepared silver nanofluid sample is a successful example of a stable nanofluid that has very little surfactant such that the existence of the surfactant does not cause a decrease in the heat transfer coefficient, while maintaining the stability. Upto 56% enhancement in the heat transfer coefficient is reached with practically no increase in the pumping power. The study is the first in using silver nanowire suspensions for heat transfer enhancement.

Fabrication of biocompatible monolithic microchannels with high pressure‐resistance using direct polymerization of PEG‐modified PMMA

ABSTRACTWithstanding high pressures in polymeric microchannels is an important requirement for many biological applications. Here, a simple direct polymerization through a polyester photomask is applied to obtain monolithic polyethylene glycol (PEG)‐modified poly(methyl methacrylate) (PMMA) (PEGMA) microchannels, showing the ability to withstand pressure up to 12 MPa in burst pressure tests. The ability of withstanding high pressures is observed to increase with increasing ratio between the thickness of the cover polymer layer forming the microchannel lid and the width of the microchannel. A simplified finite element modeling model of the burst pressure test is set up to interpret the experimental findings. The outcomes of the modeling activity, along with direct scanning electron microscopy observation of the fracture surfaces, confirm the effectiveness of the polymerization method for the production of monolithic PEGMA microchannels. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41031.

Cost-Effective Three-Dimensional Printing of Visibly Transparent Microchips within Minutes

One-step fabrication of transparent three-dimensional (3D) microfluidic to millifluidic devices was demonstrated using a commercial 3D printer costing $2300 with 500 mL of clear resin for $138. It employs dynamic mask projection stereolithography, allowing fast concept-to-chip time. The fully automated system allows fabrication of models of up to 43 mm × 27 mm × 180 mm (x × y × z) at printing speeds of 20 mm/h in height regardless of the design complexity. The minimal cross sectional area of 250 μm was achieved for monolithic microchannels and 200 μm for positive structures (templates for soft lithography). The colorless resin's good light transmittance (>60% transmission at wavelengths of >430 nm) allows for on-chip optical detection, while the electrically insulating material allows electrophoretic separations. To demonstrate its applicability in microfluidics, the printer was used for the fabrication of a micromixer, a gradient generator, a droplet extractor, and a device for isotachophoresis. The mixing and gradient formation units were incorporated into a device for analysis of nitrate in tap water with standard addition as a single run and multiple depth detection cells to provide an extended linear range.

DNA sequencing in a monolithic microchannel device

DNA sequencing in a monolithic microchannel device

DNA sequencing in a monolithic microchannel device.

We present 50 cm long microchannels in a monolithic device for high resolution, long read-length DNA sequencing. These devices were fabricated and bonded in borofloat glass using unconventional photolithography techniques with 48-188 independent, straight microchannels. The microchannel DNA separation was tested with POP-6 polymer and a DNA sequencing ladder separated at room temperature and 200 V/cm. Single-base resolution greater than 600 bases was achieved and the sequence base called to 640 bases with 98% accuracy. Under the same experimental conditions, the performance of the microchip was identical to a fused-silica capillary with similar cross-sectional area.