Fabrication Of Channels Research Articles

The fabrication of paper separation channel based SERS substrate and its recyclable separation and detection of pesticides.

In this article, a modified paper separation channel SERS substrate was fabricated by a pen writing method for the simultaneous separation and detection of thiuram and dimethoate. The hydrophilic channel was fabricated with both sides of hydrophobic barrier by the Alkylketene dimer (AKD) modified paper substrate, of which the flow dynamic was well conformed to the Lucas-Washburn model and could be used to separate pesticides effectively. As modified by Ag nanoparticles (AgNPs) and ZnO nanoparticles (ZnONPs), the hydrophilic channel exhibited high recyclable SERS detection activity and stability. The separation and detection performance with different target proportion, channel width and sample volume were studied in detail, which have significant influence on the diffusion process. Additionally, the Raman detects intensity on the substrate also showed linear relationship from 100 to 1000μg/L. The calculated limit of detects (LODs) under optimal experimental conditions were 54.57 and 19.16μg/L for dimethoate and thiuram, respectively. Due to the loading of ZnONPs, the substrate could be used repeatably with good stability. The convenient preparation, effective separation and repeatability make this paper based separation channel SERS substrate have great potential application on the fast separation and simultaneous detection of various pesticides in complex field.

Sulfonated Sub-1-nm Metal-Organic Framework Channels with Ultrahigh Proton Selectivity.

Biological proton channels are sub-1-nm protein pores with ultrahigh proton (H+) selectivity over other ions. Inspired by biological proton channels, developing artificial proton channels with biological-level selectivity is of fundamental significance for separation science. Herein we report synthetic proton channels fabrication based on sulfonated metal-organic frameworks (MOFs), UiO-66-X, X = SAG, NH-SAG, (NH-SAG)2 (SAG: sulfonic acid groups), which have sub-1-nm windows and a high density of sulfonic acid groups mimicking natural proton channels. The ion conductance of UiO-66-X channels follows the sequence: H+ ≫ K+ > Na+> Li+, and the sulfonated UiO-66 derivative channels show proton selectivity much higher than that of the pristine UiO-66 channels. Particularly, the UiO-66-(NH-SAG)2 channels exhibit ultrahigh proton selectivities, H+/Li+ up to ∼100, H+/Na+ of ∼80, and H+/K+ of ∼70, which are ∼3 times ofthat of UiO-66-NH-SAG channels, and ∼15 times ofthat of UiO-66@SAG channels. The ultrahigh proton selectivity in the sulfonated sub-1-nm MOF channels is mainly attributed to the narrow window-cavity pore structure functionalized with nanoconfined high-density sulfonic acid groups that facilitate fast proton transport and simultaneously exclude other cations. Our work opens an avenue to develop functional MOF channels for selective ion conduction and efficient ion separation.

Fabrication of Perfusable Vascular Channels and Capillaries in 3D Liver-like Tissue

Although various production methods for 3D vascularised tissues have been developed, constructing capillary-like structures branching from perfusable large channels remains difficult. This study describes a method to fabricate tube-shaped 3D liver-like tissue (tubular liver tissue) with large channels and capillary-like structures using a perfusion device. The perfusion device functions as an interface between the tissue and an external pump, as it has connectors equipped with anchors that hold the tissue in response to its shrinkage, which is accompanied by the self-organisation of capillary-like structures. Histological analysis revealed that perfusion via the large channel induced capillary formation around the channel and maintained proper tissue functions. Accompanied by structural examinations, global gene expression analysis supported this finding; specifically, genes involved in angiogenesis were enriched in the perfused condition. Furthermore, we confirmed the penetrability of the capillary-like structures by infusing India ink, as well as substance exchange by measuring the amounts of secreted albumin. These lines of evidence indicate that our method can be used to construct 3D tissues, which is useful for fields of in vitro tissue regeneration for drug development and regenerative medicine.

Fluid shear stress coupled with narrow constrictions induce cell type-dependent morphological and molecular changes in SK-BR-3 and MDA-MB-231 cells

Cancer mortality mainly arises from metastases, due to cells that escape from a primary tumor, circulate in the blood as circulating tumor cells (CTCs), permeate across blood vessels and nest in distant organs. It is still unclear how CTCs overcome the harsh conditions of fluid shear stress and mechanical constraints within the microcirculation. Here, a minimal model of the blood microcirculation was established through the fabrication of microfluidic channels comprising constrictions. Metastatic breast cancer cells of epithelial-like and mesenchymal-like phenotypes were flowed into the microfluidic device. These cells were visualized during circulation and analyzed for their dynamical behavior, revealing long-lived plastic deformations and significant differences in biomechanics between cell types. γ-H2AX staining of cells retrieved post-circulation showed significant increase of DNA damage response in epithelial-like SK-BR-3 cells, while gene expression analysis of key regulators of epithelial-to-mesenchymal transition revealed significant changes upon circulation. This work thus documents first results of the changes at the cellular, subcellular and molecular scales induced by the two main mechanical stimuli arising from circulatory conditions, and suggest a significant role of this still elusive step of the metastatic cascade in cancer cells heterogeneity and aggressiveness.

Experimental study on direct fabrication of micro channel on fused silica by picosecond laser

Ultrafast laser ablation, known for its high precision and the depressed thermal influence during processing, is fevered in micro channel fabrication on the glass bulk. In present work, a micro channel structure fabricated on fused silica bulk by a picosecond pulsed laser is parametrically investigated with different processing environments, scanning velocities, pulse energies, hatch distances and repetitive scans. The best processing parameters are determined through the material remove rate and the bottom surface roughness of the channel. Moreover, the fabrication defect attributed to the heat accumulation effect is analyzed by Raman spectrum. A scanning strategy is put forward to compensate the asymmetry in the cross section of the micro channels.

Layer-by-Layer Self-Assembly of Metal/Metal Oxide Superstructures: Self-Etching Enables Boosted Photoredox Catalysis.

The capability of noble metal nanoparticles (NPs) as efficient charge transfer mediators to stimulate Schottky-junction-triggered charge flow in multifarious photocatalysis has garnered enormous attention in the past decade. Nevertheless, fine-tuning and controllable fabrication of a directional charge transport channel in metal/semiconductor heterostructures via suitable interface engineering is poorly investigated. Here, we report the progressive fabrication of a tailor-made directional charge transfer channel in Pt nanoparticles (NPs)-inlaid WO3 (Pt-WO3) nanocomposites via an efficient electrostatic layer-by-layer (LbL) self-assembly integrated with a thermal reduction treatment, by which oppositely charged metal precursor ions and polyelectrolyte building blocks were intimately and alternately assembled on the WO3 nanorods (NRs) by substantial electrostatic interaction. LbL self-assembly buildup and in situ self-etching-induced structural variation of WO3 NRs to a microsized superstructure occur simultaneously. We found that such exquisitely crafted Pt-WO3 nanocomposites exhibit conspicuously enhanced and versatile photoactivities for nonselective mineralizing of organic dye pollution and reduction of heavy metal ions at ambient conditions under both visible and simulated sunlight irradiation, demonstrating a synergistic effect. This is attributed to the imperative contribution of Pt NPs as electron traps to accelerate the directional high-efficiency electron transport from WO3 to Pt NPs, surpassing the confinement of electron transfer kinetics of WO3 owing to low conduction level. More intriguingly, photoredox catalysis can also be triggered simultaneously in the same reaction system. The primary in situ produced active species in the photocatalytic reactions were specifically analyzed, and underlying photocatalytic mechanisms were determined. Our work would provide a universal synthesis strategy for constructing various metal-decorated semiconductor nanocomposites for widespread photocatalytic utilizations.

Investigation of formability of metallic bipolar plates via stamping for light-weight PEM fuel cells

Bipolar plates (BPs) are one of the main members which constitute a significant percentage of a fuel cell system in terms of cost, weight and structural strength. Although frequently used graphite BPs have low density, high conductivity and corrosion resistance, machining the desired flow channels on the graphite plates is an important issue. On the other hand, metallic BPs can be considered a reasonable alternative material to graphite in the view of the material cost, fabrication of flow channels and some post-processes in which the large-scale manufacturing of graphite BPs is more complex compared to cutting and stamping processes for metal ones. This study offers a comparison of the formability of four different metals with four flow channel depths as bipolar plates formed by stamping. 304 Stainless Steel (SS 304), pure Titanium - Grade2 (CP–Ti) and Aliminium (Al 6016 and Al 3104) are chosen as the BP materials. A serpentine type flow channel with two different channel widths are formed on to 0.1 mm thick sheets. The channel width is chosen as 1.2 mm and 1.8 mm for the channel depths of 0.36 mm–0.55 mm, and 0.54 mm–0.82 mm, respectively. The stamping processes of the BPs materials are simulated via commercially available eta/Dynaform v5.9.4. software and formability characteristics are obtained for sixteen various cases. As a result, it is determined that SS 304 is the more appropriate material in the view of the formability for such a complex form.

Fabrication of Nanoheight Channels Incorporating Surface Acoustic Wave Actuation via Lithium Niobate for Acoustic Nanofluidics.

Controlled nanoscale manipulation of fluids is known to be exceptionally difficult due to the dominance of surface and viscous forces. Megahertz-order surface acoustic wave (SAW) devices generate tremendous acceleration on their surface, up to 108 m/s2, in turn responsible for many of the observed effects that have come to define acoustofluidics: acoustic streaming and acoustic radiation forces. These effects have been used for particle, cell, and fluid manipulation at the microscale, although more recently SAW has been used to produce similar phenomena at the nanoscale through an entirely different set of mechanisms. Controllable nanoscale fluid manipulation offers a broad range of opportunities in ultrafast fluid pumping and biomacromolecule dynamics useful for physical and biological applications. Here, we demonstrate nanoscale-height channel fabrication via room-temperature lithium niobate (LN) bonding integrated with a SAW device. We describe the entire experimental process including nano-height channel fabrication via dry etching, plasma-activated bonding on lithium niobate, the appropriate optical setup for subsequent imaging, and SAW actuation. We show representative results for fluid capillary filling and fluid draining in a nanoscale channel induced by SAW. This procedure offers a practical protocol for nanoscale channel fabrication and integration with SAW devices useful to build upon for future nanofluidics applications.

Bioinspired Unidirectional Liquid Spreading Channel–Principle, Design, and Manufacture

AbstractLiquid unidirectional spreading without energy input has attracted worldwide attentions owing to its potential applications in various fields. The liquid transfer between the adjacent microcavities on the peristome of Nepenthes alata provides great inspiration in that the concave curvature edge structure has the possibility to induce liquid directional spreading. Herein, the effect of concave curvature edge on liquid spreading is found to be different from that of the solid edge described by the Gibbs inequality condition. In this condition, there exist two liquid transfer states, namely conduction and resistance. Taking the advantages of the concave curvature edge, a new unidirectional liquid spreading channel is designed and fabricated by the traditional machining method, and its liquid directional spreading function is validated. This article provides a theoretical and technical support for the design and fabrication of liquid unidirectional spreading channel without an external energy input.

Fabrication of paper-based microfluidic channels by electrohydrodynamic inkjet printing technology for analytical biochemistry applications

Paper-based microchannels are important components in paper-based microfluidic devices. Paper-based microchannels are usually manufactured by creating lines with hydrophobic patterns enclosing an area of hydrophilic paper inside. Among the many techniques for making hydrophobic lines, the printing method in general and inkjet printing in particular have become more common because of their advantages in terms of material saving, high precision, low-cost, etc. In this paper, the electrohydrodynamic (EHD) inkjet printing method, which has been studied and developed in recent years, has been used to drop glycol ether solvent-based ink onto a nitrocellulose paper. The results of the field emission scanning electron microscope (FE-SEM) show that the solvent based ink could dissolve through membrane and form a transparent hydrophobic layer on the created space. The width of the barrier lines can be controlled from about 200 μm to 260 μm, which is quite small when compared to other manufacturing methods. Based on this fabrication process, paper-based microfluidic analytical devices have been designed and fabricated for use in analytical biochemistry assays. Human chorionic gonadotropin (hCG) was selected as the biological target for this assay. Initial results have shown that the target for hCG can be quantitatively determined by these devices with a coefficient of determination (R2) of approximately 0.99. Therefore, EHD inkjet printing technology can be used for the manufacture of paper-based microfluidic analytical devices (μPADs) that may be applied in the future for analytical biochemistry assays.

Fabrication of unconventional inertial microfluidic channels using wax 3D printing.

Inertial microfluidics has emerged over the past decade as a powerful tool to accurately control cells and microparticles for diverse biological and medical applications. Many approaches have been proposed to date in order to increase the efficiency and accuracy of inertial microfluidic systems. However, the effects of channel cross-section and solution properties (Newtonian or non-Newtonian) have not been fully explored, primarily due to limitations in current microfabrication methods. In this study, we overcome many of these limitations using wax 3D printing technology and soft lithography through a novel workflow, which eliminates the need for the use of silicon lithography and polydimethylsiloxane (PDMS) bonding. We have shown that by adding dummy structures to reinforce the main channels, optimizing the gap between the dummy and main structures, and dissolving the support wax on a PDMS slab to minimize the additional handling steps, one can make various non-conventional microchannels. These substantially improve upon previous wax printed microfluidic devices where the working area falls into the realm of macrofluidics rather than microfluidics. Results revealed a surface roughness of 1.75 μm for the printed channels, which does not affect the performance of inertial microfluidic devices used in this study. Channels with complex cross-sections were fabricated and then analyzed to investigate the effects of viscoelasticity and superposition on the lateral migration of the particles. Finally, as a proof of concept, microcarriers were separated from human mesenchymal stem cells using an optimized channel with maximum cell-holding capacity, demonstrating the suitability of these microchannels in the bioprocessing industry.

Experimental characterization to fabricate CO2 laser ablated PMMA microchannel with homogeneous surface

Polymethyl methacrylate (PMMA) is widely used for fabrication of microfluidic devices. PMMA, in the recent times, has emerged as an alternative to glass base microfluidic devices owing its convenience in handling, low cost, less weight and excellent optical properties. Due to the high transparency of PMMA and absorption properties in near infrared and UV regions, laser machining can be employed. This work reports characterization of a CO2 laser system, with a wavelength of 10.6 µm, for microfluidic channel fabrication on PMMA. Variety of channels were fabricated by varying CO2 laser system parameters – power, scan speed, pulse frequency and resolution. Power was varied up to its limiting value of 30 W. Surface profile for each of the fabricated channel was recorded and obtained data was analysed. Optimization was done to identify and establish parameters to obtain channels corresponding to specified width and depth. The profile of the channels was observed to have Guassian profile which can be attributed to the Guassian nature of incident laser beam. Effects of post processing using acetone and dichloromethane (DCM) vapour exposure were also studied.

Open Complementary Split-Ring Resonator Sensor for Dropping-Based Liquid Dielectric Characterization

A microwave sensor with a coplanar waveguide semilumped meander open complementary split-ring resonator (MOCSRR) is proposed to analyze the dielectric properties of liquid. The proposed method operates at subgigahertz frequencies and uses a small volume of liquid (>0.08 mL) on a substrate-integrated slot container. A resonance reflection coefficient notch frequency and its magnitude in decibels are observed for complex permittivity ( $\varepsilon'+j \varepsilon $ ”) characterization. A strong electric field distributed on the edge of the designed MOCSRR slot provides a sensitive compact area to detect small variations in the liquid sample or concentration. Operations need not be constrained to micropipette operations or microfluidic channel fabrication. A specific volume of the sample liquid must be dropped in the detection zone to analyze complex permittivity. To test the proposed methods, binary mixtures of ethanol and water were loaded, and a 58.7 MHz shift in resonant frequency and a variation of 6.77 dB were attributed to a complex permittivity perturbation phenomenon when ethanol concentration was varied from 0% to 100%. Different concentrations of ethanol and liquid were evaluated and analyzed. The proposed sensor exhibited repeatability and easy operation in detecting liquids with high relative permittivity, such as water and lossy liquids.

Force modeling to develop a novel method for fabrication of hollow channels inside a gel structure.

Fabrication of hollow channels with user-defined dimensions and patterns inside viscoelastic, gel-type materials is required for several applications, especially in biomedical engineering domain. These include objectives of obtaining vascularized tissues and enclosed or subsurface microfluidic devices. However, presently there is no suitable manufacturing technology that can create such channels and networks in a gel structure. The advent of three-dimensional bioprinting has opened new possibilities for fabricating structures with complex geometries. However, application of this technique to fabricate internal hollow channels in viscoelastic material has not been yet explored to a great extent. In this article, we present the theoretical modeling/background of a proposed manufacturing paradigm through which hollow channels can be conveniently fabricated inside a gel structure. We propose that a tip connected to a robotic arm can be moved in X-, Y-, and Z-axis as per the desired design. The tip can be moved by a magnet or mechanical force. If the tip is further trailed with porous tube and moved inside the viscoelastic material, corresponding internal channels can be fabricated. To achieve this, however, force modeling to understand the forces that will be required to move the tip inside viscoelastic material should be known and understood. Therefore, in our first attempt, we developed the computational force modeling of the tip movement inside gels with different viscoelastic properties to create the channels.

Increased Flexibility in Lab-on-Chip Design with a Polymer Patchwork Approach.

Nanofluidic structures are often the key element of many lab-on-chips for biomedical and environmental applications. The demand for these devices to be able to perform increasingly complex tasks triggers a request for increasing the performance of the fabrication methods. Soft lithography and poly(dimethylsiloxane) (PDMS) have since long been the basic ingredients for producing low-cost, biocompatible and flexible devices, replicating nanostructured masters. However, when the desired functionalities require the fabrication of shallow channels, the “roof collapse” phenomenon, that can occur when sealing the replica, can impair the device functionalities. In this study, we demonstrate that a “focused drop-casting” of h-PDMS (hard PDMS) on nanostructured regions, provides the necessary stiffness to avoid roof collapse, without increasing the probability of deep cracks formation, a drawback that shows up in the peel-off step, when h-PDMS is used all over the device area. With this new approach, we efficiently fabricate working devices with reproducible sub-100 nm structures. We verify the absence of roof collapse and deep cracks by optical microscopy and, in order to assess the advantages that are introduced by the proposed technique, the acquired images are compared with those of cracked devices, whose top layer, of h-PDMS, and with those of collapsed devices, made of standard PDMS. The geometry of the critical regions is studied by atomic force microscopy of their resin casts. The electrical resistance of the nanochannels is measured and shown to be compatible with the estimates that can be obtained from the geometry. The simplicity of the method and its reliability make it suitable for increasing the fabrication yield and reducing the costs of nanofluidic polymeric lab-on-chips.

High aspect ratio channel fabrication with near-infrared laser-induced backside wet etching

Abstract Laser-induced backside wet etching (LIBWE) is one of the most promising manufacturing processes for fabricating high aspect ratio microfeatures of glass. However, cracks inside the glass during the LIBWE process due to high thermal stress limits the manufacturable shape. In this study, we propose a new technique to prevent the crack generation in the near-infrared (NIR) LIBWE process by adding phosphoric acid to the absorbent. It was possible to increase the maximum fabricable depth by approximately five times compared to the absorbent without phosphoric acid. The nature of the crack suppression mechanism in the absorbent with added phosphoric acid was investigated by in situ observation of the process and chemical analysis. To investigate the effects of phosphoric acid on LIBWE with added phosphoric acid, the influences of phosphoric acid concentration on maximum fabricable depth, fabrication speed and sidewall roughness were studied. Based on the investigated principle and process characteristics, we found that high aspect ratio microchannels of different shapes could be produced.

Sidewall channel fabrication using membrane projection lithography and metal assisted chemical etching

Channels that run parallel and beneath the surface of an Si substrate are fabricated by first forming submicrometer sized disks of Au onto etched sidewall features in Si. The disks are formed by fabricating a patterned membrane mask of electron beam resist and evaporating Au at a 45° angle with respect to the substrate surface. Metal assisted chemical etching is then applied to remove the Si beneath the Au disks to form channels that lie perpendicular to these disk surfaces. Channels on the order of 300 nm in diameter have been fabricated by the combination of these techniques.

Rapid prototyping of microfluidic chip with burr-free PMMA microchannel fabricated by revolving tip-based micro-cutting

Abstract Cost-effective and rapid prototyping of microfluidic chips has become increasingly possible. However, micromilling, as a popular method for the fabrication of a microfluidic channel, shows no advantage when dealing with a microchannel with a width of less than 50 μm. In this paper, a mimic of the micromilling method, revolving tip-based micro-cutting, was employed to achieve direct writing of a microchannel on polymethylmethacrylate (PMMA) with a width ranging from several micrometres to hundreds of micrometres. A piezoelectric actuator was used to revolve a three-sided nanoindenter instead of a spindle to rotate a mill. Based on the characteristics of revolving cutting, optimization analysis, which focuses on burr formation and surface quality, was performed, and the obtained microchannels exhibited burr-free sides with a bottom surface roughness of Sa = 19 nm. To verify the effectiveness of the proposed micromachining method, two low-cost preparation processes for a microfluidic chip with a fabricated PMMA microchannel were demonstrated. One was directly bonding the fabricated PMMA sheet to another sheet with UV-assisted solvent bonding, where it was concluded that the burr-free sides of the channel played a critical effect on bonding the shallow microchannel. The other was using the fabricated PMMA as a mould to transfer the microchannel to a casted polydimethylsiloxane (PDMS) chip. Finally, a fabricated micro-cross channel was tested to generate a microdroplet, and it was observed that the size and generation rate of microdroplets were controllable.

Microfluidic Channels Fabrication Based on Underwater Superpolymphobic Microgrooves Produced by Femtosecond Laser Direct Writing.

A strategy is proposed here to fabricate microfluidic channels based on underwater superpolymphobic microgrooves with nanoscale rough surface structure on glass surface produced by femtosecond (fs) laser processing. The fs laser-induced micro/nanostructure on glass surface can repel liquid polydimethylsiloxane (PDMS) underwater, with the contact angle (CA) of 155.5 ± 2.5° and CA hysteresis of 2.7 ± 1.5° to a liquid PDMS droplet. Such a phenomenon is defined as the underwater “superpolymphobicity”. Microchannels as well as microfluidic systems are easily prepared and formed between the underwater superpolymphobic microgroove-textured glass substrate and the cured PDMS layer. Because the tracks of the laser scanning lines are programmable, arbitrary-shaped microchannels and complex microfluidic systems can be potentially designed and prepared through fs laser direct writing technology. The concept of “underwater superpolymphobicity” presented here offers us a new strategy for selectively avoiding the adhesion at the polymer/substrate interface and controlling the shape of cured polymers; none of these applications can find analogues in previously reported superwetting materials.

Shear-induced platelet aggregation: 3D-grayscale microfluidics for repeatable and localized occlusive thrombosis.

Atherothrombosis leads to complications of myocardial infarction and stroke as a result of shear-induced platelet aggregation (SIPA). Clinicians and researchers may benefit from diagnostic and benchtop microfluidic assays that assess the thrombotic activity of an individual. Currently, there are several different proposed point-of-care diagnostics and microfluidic thrombosis assays with different design parameters and end points. The microfluidic geometry, surface coatings, and anticoagulation may strongly influence the precision of these assays. Variability in selected end points also persists, leading to ambiguous results. This study aims to assess the effects of three physiologically relevant extrinsic design factors on the variability of a single end point to provide a quantified rationale for design parameter and end-point standardization. Using a design of experiments approach, we show that the methods of channel fabrication and collagen surface coating significantly impact the variability of occlusion time from porcine whole blood, while anticoagulant selection between heparin and citrate did not significantly impact the variability. No factor was determined to significantly impact the mean occlusion time within the assay. Occlusive thrombus was found to consistently form in the first third (333 μm) of the high shear zone and not in the shear gradient regions. The selection of these factors in the design of point-of-care diagnostics and experimental SIPA assays may lead to increased precision and specificity in high shear thrombosis studies.