Glass Channel Research Articles

Thermocavitation in gold-coated microchannels for needle-free jet injection

Continuous-wave lasers generated bubbles in microfluidic channels are proposed for applications such as needle-free jet injection due to their small size and affordable price of these lasers. However, water is transparent in the visible and near-IR regime, where the affordable diode lasers operate. Therefore, a dye is required for absorption, which is often unwanted in thermocavitation applications, such as vaccines or cosmetics. In this work, we explore a different mechanism of the absorption of optical energy. The microfluidic channel wall is partially covered with a thin gold layer, which absorbs light from a blue laser diode. This surface absorption is compared with the conventional volumetric absorption by a red dye. The results show that this surface absorption can be used to generate bubbles without the requirement of a dye. However, the generated bubbles are smaller and grow slower when compared to the dye-generated bubbles. Furthermore, heat dissipation in the glass channel walls affects the overall efficiency. Finally, degradation of the gold layer over time reduces the reproducibility and limits its lifetime. Further experiments and simulations are proposed to potentially solve these problems and optimize the bubble formation. Our findings can inform the design and operation of microfluidic devices used in phase transition experiments and other cavitation phenomena, such as jet injectors or liquid dispensing for bio-engineering.

In-situ glass transition of ZIF-62 based mixed matrix membranes for enhancing H2 fast separation

Mixed matrix membranes (MMMs), combining the advantages of polymer membranes and porous materials, processing the potential to realize large-scale gas separation applications. However, the interfacial defects in MMMs greatly hindered gas separation performance improvement. Therefore, designing an MMM with high loading and good interfacial compatibility remains a critical issue in promoting the application of MMMs. Herein, during in-situ heating process, the melting of liquid ZIF-62 in PBI polymer can largely fill the interfacial defects in MMMs. The microporous transport channels of ZIF-62 glass in MMMs promoted the H2 diffusion and inhibited the CO2 and CH4 diffusion, thus enhancing the H2/CO2 and H2/CH4 separation of MMMs. For mixed gas testing, the 45 wt% ZIF-62 glass/PBI membrane had the maximum H2 permeability of 459 barrer, and its H2/CO2 and H2/CH4 selectivities were 23 and 57, higher than the gas separation upper bonds. In addition, ZIF-62 glass/PBI membrane exhibited stable separation performance under 1–5 bar pressure. Therefore, the rational combination of MOF glass and polymer matrix could provide promising potential for reducing the interfacial defects of high-loading MMMs, thus enhancing the gas separation performance.

Contrastive Analysis of Interferometric Techniques for Small Channel Temperature Measurements

This research employs a state-of-the-art digital interferometric technique to investigate the temperature distribution within a confined rectangular channel, with a hydraulic diameter of 3 mm. The experimental setup incorporates an optical glass channel, with nanofluids (Aluminium oxide) as the test fluid at 0.001% volume concentration. To induce controlled heating, a heater filament is strategically placed along the bottom wall of the channel. Simultaneously, a T-type thermocouple is carefully placed to measure the temperature along the upper wall. Two distinct interferometric methods, namely the Michelson interferometer and the Mach-Zehnder interferometer, are employed to capture the complex details of fringes resulting from the evolving temperature field within the test section. A high-resolution CCD camera is employed to capture these fringes, and sophisticated digital image processing techniques are subsequently applied for in-depth fringe analysis. The culmination of these efforts results in the origin of a comprehensive localized temperature distribution map within the small-sized channel. The obtained temperature profiles are meticulously compared, providing valuable insights into the effectiveness and reliability of the Michelson and Mach-Zehnder interferometric techniques in this specific experimental context. This detailed comparative analysis contributes to the broader understanding of interferometric methods for temperature measurements in confined fluidic systems.

Spectral and Temporal Manipulation of Ultralong Phosphorescence Based on Melt‐Quenched Glassy Metal–Organic Complexes for Multi‐Mode Photonic Functions

AbstractTransparent glasses are ideal and robust hosts for a range of emission centers, while the simultaneous manipulation of the temporal and spectral characteristics of emission remains a tremendous challenge for inorganic glasses. Here, the development and functionalization of melt‐quenched transparent coordinate polymer glasses with a tailorable ultralong room‐temperature phosphorescence are demonstrated. Dynamic modulation of the phosphorescence is achieved by utilization of the high molecular rigidity and manipulation of the spin‐orbital coupling effects within the glass systems. By introducing dye molecules into the glasses, Phosphorescence resonance energy transfer from the glass matrix to the dye molecules is exploited and controllable multicolor long‐lived luminescence is demonstrated. Further design of the component and concentration of the encapsulated dyes allows for wavelength‐tunable long‐lived delayed fluorescence via an efficient delayed sensitization process, featuring a tunable emission spectrum covering a wide range from 520 to 630 nm. Leveraging the multiple spectral tuning channels of the hybrid glass, multi‐mode optical information storage, and dynamic anti‐counterfeiting applications are further demonstrated. This work provides a new hybrid material platform and design methodology for realizing lifetime‐adjustable and wavelength‐tunable long‐lived luminescence, which can find wide applications in time‐rsesolved information display, high‐density information storage, and dynamic anti‐counterfeiting.

Effect of in-plane and out-of-plane bifurcated microfluidic channels on the flow of aggregating red blood cells.

The blood flow through our microvascular system is a renowned difficult process to understand because the complex flow behavior of blood is intertwined with the complex geometry it has to flow through. Conventional 2D microfluidics has provided important insights, but progress is hampered by the limitation of 2-D confinement. Here we use selective laser-induced etching to excavate non-planar 3-D microfluidic channels in glass that consist of two generations of bifurcations, heading towards more physiological geometries. We identify a cross-talk between the first and second bifurcation only when both bifurcations are in the same plane, as observed in 2D microfluidics. Contrarily, the flow in the branch where the second bifurcation is perpendicular to the first is hardly affected by the initial distortion. This difference in flow behavior is only observed when red blood cells are aggregated, due to the presence of dextran, and disappears by increasing the distance between both generations of bifurcations. Thus, 3-D structures scramble in-plane flow distortions, exemplifying the importance of experimenting with truly 3D microfluidic designs in order to understand complex physiological flow behavior.

Thermal Performance Investigation of Greenhouse Glazing Units Containing PCM with Different Thermophysical and Optical Properties

Improved thermal storage capacity and reduced building energy consumption can be attained by utilizing phase-change materials (PCM) in glass enclosure structures, which can effectively utilize solar energy to improve the building’s thermal performance. This article investigates the thermal performance of double-layer glass filled with PCM as a function of relevant thermal physical parameters. Numerical analyses were conducted on the PCM glass units to assess the glass greenhouse thermal performance. Results indicate that the temperature distribution of the glass channel is mainly influenced by the absorption coefficient of the paraffin material. Compared to the absorption coefficient, the refractive index has a smaller impact on the temperature of the glass channel. On the other hand, the transmittance of the interior surface of the glass channel is greatly affected by solar radiation. According to the outdoor meteorological conditions of different seasons, increasing the latent heat of paraffin materials within a certain range with a reasonable density and melting temperature can greatly improve the thermal performances. Meanwhile, the thermal conductivity of paraffin materials and the change in the specific heat of paraffin materials have little impact on the improvement of thermal performance.

Characterization of liquid flow and electricity generation in a glass channel based evaporation-driven electrokinetic energy conversion device

Evaporation-driven spontaneous capillary flow presents a promising approach for driving electrolytes through electrically charged channels and pores in electrokinetic energy conversion devices. However, there are no literature reports of detailed flow visualization in these systems and/or experimental observations relating the liquid velocity and evaporation rate to the generated voltage and current. In this manuscript, we describe such a visualization study for a glass channel based electrokinetic energy conversion device with one of its channel terminals left open to ambient air for facilitating the evaporation process. Fluorescence microscopy was used to measure the liquid velocity in the electrokinetic energy conversion channel by observing the advancement of an electrolyte solution dyed with a neutral tracer. The accumulation of the same dye tracer was also imaged at the open terminal of this glass conduit to estimate the rate of solvent evaporation, which was found to be consistent with the flow velocity measurements. Additionally, an electrochemical analyzer was employed to record the electrical voltage and current produced by the device under different operating conditions. The highest electrical power output was derived in our experiments upon flowing de-ionized water through a 1 μm deep channel, which also produced the fastest liquid velocity in it. Moreover, the energy conversion efficiency of our device was observed to increase for shallower channels and lower ionic strength electrolytes, consistent with previous literature reports on electrokinetic energy conversion platforms.

How does surfactant aid the displacement of oil by water in nanoscale cracks?

The displacement of oil by water is the central concern in enhanced oil recovery. In this paper, we present an experimental study of the displacement of oil by water in a nano-scale, glass channel. The channel was 100 nm thick, composed of hydrophilic glass, and was closed at one end. Displacement was examined under zero applied pressure. Three surfactants were examined for their ability to aid displacement of oil: sodium dodecylsulfate (SDS), an anionic surfactant; Aerosol OT (AOT), an anionic surfactant; and dodecyltrimethylammonium bromide (DTAB), a cationic surfactant. AOT was the only surfactant that caused displacement of oil within 12 h. AOT is also the only one of the three surfactants that can form reverse micelles in the oil phase, and we attribute the oil displacement to the delivery of water to the hydrophilic glass by reverse micelles. We support this conclusion with experiments showing (a) lesser displacement with fewer reverse micelles and (b) that the water phase is discontinuous. The latter implies transport of water through the oil phase. Therefore, the conclusion of this work is that the surfactant aids oil recovery from a hydrophilic channel by enhancing transport of water through oil. The delivered water can adsorb at the solid and continued transport can spontaneously grow a bulk water phase, thereby displacing the oil.

Fused silica microchannel fabrication with smooth surface and high etching selectivity

Channel fabrication technology has become increasingly important for microfluidic and nanofluidic devices. In particular, glass channels have high chemical and physical stability, high optical transparency, and ease of surface modification, so that there is increasing interest in glass microfluidic devices for chemical experiments in microfluidics and nanofluidics. For the fabrication of glass channels, especially those with a high aspect ratio (depth/width), lithography using a metal resist and dry etching have mainly been used. However, there are still issues involving the surface roughness of the etched channel and the low etching selectivity. In this study, a microchannel fabrication method with high etching selectivity that produces a smooth etched surface was developed. First, interference during dry etching by remaining Cr particles after the photolithography and Cr etching processes was assumed as the cause of the rough etched surface. Three different dry etching processes were introduced to verify this. In process 1 without removal of the Cr particles, the etched surface was not flat and had a 1 μm scale roughness. In process 2 where a cleaning process was included and high power etching was conducted, a smooth surface with a 1 nm scale roughness and a faster etching rate of 0.3 μm min−1 were obtained. For this high-power etching condition, the etching selectivity (fused silica/Cr) was relatively low at approximately 39–43. In process 3 with a cleaning process and low-power etching, although the etching rate was relatively low at 0.1 μm min−1, a smooth surface with 1 nm scale roughness (10 nm scale roughness deeper than 40 μm in the depth region) and a much higher etching selectivity of approximately 79–84 were obtained. The dry etching method presented in this study represents a significant contribution to microfluidics/nanofluidics for microchannel/nanochannel fabrication.

Bending Loss Analysis of Chalcogenide Glass Channel Waveguides for Mid-Infrared Astrophotonic Devices

In this study, the bending losses of chalcogenide glass channel optical waveguides consisting of an As2Se3 core and an As2S3 lower cladding layer were numerically evaluated across the astronomical N-band, which is the mid-infrared spectral range between the 8 µm and 12 µm wavelengths. The results reveal the design rules for bent waveguides in mid-infrared astrophotonic devices.

Effect of a novel cooling window on a recuperated solar-dish Brayton cycle

A recuperated solar-dish Brayton cycle using an off-the-shelf turbocharger as a micro-turbine and a rectangular cavity receiver with integrated thermal storage is considered in this study. Due to the high temperatures that these solar receivers operate at, a considerable amount of heat is lost to the environment through the aperture, decreasing the solar-to-mechanical efficiency of the cycle. In this work, the heat losses from the solar receiver were reduced by utilising a novel glass channel on the inside of the cavity receiver, running parallel to the receiver walls and cooled by the working fluid (air) flowing from the compressor. The objective of this conceptual study was to investigate the impact of the novel air-cooled window on the performance of the cycle at steady state. An entropy generation minimisation technique combined with a SolTrace analysis was used. Results showed that the maximum solar-to-mechanical efficiencies were on average between 41% and 45% lower than for the cycle without the window. However, it was found that the exhaust temperature of the cycle with the window was higher. Therefore, a higher energy utilisation factor of between 9% and 11% was found when cogeneration was included.

Micro-particle image velocimetry for blood flow in thick round glass micro-channels: Channel fabrication and velocity profile characterization

This method describes the use of thick round borosilicate glass micro-channels for blood flow visualization using micro-particle image velocimetry (µPIV) techniques. In contrast with popular methods using squared polydimethylsiloxane channels, this method allows for visualization of blood flow in channel geometries that resemble more the natural physiology of human blood vessels. With a custom designed enclosure, the microchannels were submerged in glycerol to reduce light refraction occurring during µPIV due to the thick walls of the glass channels. A method is proposed to correct the extracted velocity profiles from the µPIV to account for out-of-focus error. The customized elements of this method include:• The use of thick circular glass micro-channels,• a custom designed mounting solution for the channels on a glass slide for flow visualization,• a MATLAB code to correct velocity profile accounting for out-of-focus error.

Pneumatic controlled nanosieve for efficient capture and release of nanoparticles

A pneumatic controlled nanosieve device is demonstrated for the efficient capture and release of 15 nm quantum dots. This device consists of a 200 nm deep glass channel and a polydimethylsiloxane-based pneumatic pressure layer to enhance target capture. The fluid motion inside the nanosieve is studied by computational fluidic dynamics (CFD) and microfluidic experiments, enabling efficient target capture with a flow rate as high as 100 μl/min. In addition, microgrooves are fabricated inside the nanosieve to create low flow rate regions, which further improves the target capture efficiency. A velocity contour plot is constructed with CFD, revealing that the flow rate is the lowest at the top and bottom of the microgrooves. This phenomenon is supported by the observed nanoparticle clusters surrounding the microgrooves. By changing the morphology and pneumatic pressure, this device will also facilitate rapid capture and release of various biomolecules.

Optimization of the Formations Parameters of Hollow Channels in Glass by Direct Laser Writing and Selective Etching

Optimization of the Formations Parameters of Hollow Channels in Glass by Direct Laser Writing and Selective Etching

Application of an electrokinetic backflow for enhancing pressure-driven charge based separations in sub-micrometer deep channels

In this article, we report significant improvements in the resolving power of pressure-driven charge based separations performed in sub-micrometer deep glass channels upon introducing an electrokinetic backflow in the system. Such improvements are realized as axial electrophoresis aids the pressure-driven separation process in negatively charged glass conduits under these conditions. In addition, the electroosmotic backflow slows down the bulk transport of the background electrolyte subjecting the sample to the separation field for prolonged periods and yields a higher fluid shear across the channel depth further assisting the separation process. Although this increased shear also contributes to additional hydrodynamic dispersion, such contributions are usually small due to fast diffusion across the flow streamlines in sub-micrometer deep channels. In the present work, the pressure-driven flow was generated on-chip by fabricating a polyacrylamide based gel membrane within a chosen access hole upstream of the separation channel. Upon application of an electric field across this structure, the electroosmotic flow generated in the open channel interfacing the membrane was partially blocked producing the needed pressure-gradient. Optimization of the electrical voltage applied to the downstream end of the separation channel then yielded a suitable electrokinetic backflow that significantly improved the resolving power of our separations. For a sample comprising of three 5-TAMRA, SE-labeled amino acids, the noted strategy improved the separation resolution by over an order of magnitude compared to the case when no electrokinetic backflow was present. The band broadening in these separations was also assessed to understand its dependence on the operating conditions.

Using motile cells to characterize surface acoustic wave-based acoustofluidic devices

Acoustic microfluidics is a robust and powerful method to manipulate cells and cell-like particles on chip, having good biocompatibility and ease of incorporation into multioperation microfluidic devices compared to optical manipulation. However, the use of acoustic microfluidics is largely confined to research settings. The primary barrier to translation of this technology toward clinical and industrial uses is the inability to experimentally determine the pressure field (shape and amplitude) and associated acoustophoretic forces in real time as device conditions vary. Despite the multitude of previous characterization methods, none provide the flexibility of motile cells (e.g., the unicellular alga Chlamydomonas reinhardtii) as probes to map evolving pressure fields on chip. We have previously developed this approach for use with bulk acoustic wave (BAW)-based devices. Here, we extend the method to qualitatively assess device resonances and relative field strengths for surface acoustic wave (SAW)-based devices with straight channels and circular chambers driven at 6 MHz and 20 MHz. The fabrication and electrical characterization of hybrid BAW/SAW devices with glass channels are also discussed. Upon testing, the optimal device operating parameters are identified using impedance measurements, as well as visual identification of resonant frequencies using the swimming algae cells.

Fabrication of Microfluidic Tesla Valve Employing Femtosecond Bursts.

Expansion of the microfluidics field dictates the necessity to constantly improve technologies used to produce such systems. One of the approaches which are used more and more is femtosecond (fs) direct laser writing (DLW). The subtractive model of DLW allows for directly producing microfluidic channels via ablation in an extremely simple and cost-effective manner. However, channel surface roughens are always a concern when direct fs ablation is used, as it normally yields an RMS value in the range of a few µm. One solution to improve it is the usage of fs bursts. Thus, in this work, we show how fs burst mode ablation can be optimized to achieve sub-µm surface roughness in glass channel fabrication. It is done without compromising on manufacturing throughput. Furthermore, we show that a simple and cost-effective channel sealing methodology of thermal bonding can be employed. Together, it allows for production functional Tesla valves, which are tested. Demonstrated capabilities are discussed.

CELL CO-CULTURE MICROFLUIDICS PLATFORM WITH AN INTEGRATED HYDRAULIC VALVE FOR INVESTIGATION OF SIGNAL-MEDIATED INTERACTIONS IN THE BLOOD-BRAIN BARRIER

Lab-on-a-chip systems for real-time analysis of neural cell communication is an emerging topic of neuroscience research that can provide a better understanding of brain functionality. Astrocyte and HBEC5i co-culture provide in vitro model of the blood-brain barrier. The successful employment of lab-on-achip cell co-culture devices in research settings requires fabricating materials that are not cytotoxic to the cells. Controlled and reversible separation of cell culture chambers is crucial for real-time studies of extracellular-mediated cell-to-cell communications. This study demonstrated a 3D printed cell co-culture microfluidic platform that enables controlled separation of the chambers and provides the long-term viability of HEBC-5i cells. The platform consists of two 27.5 mm × 35 mm × 10 mm cell culture chambers separated by an Elastic Resin 3D stereolithography printed valve (10 mm × 35 mm × 9.5 mm). The actuation of the valve is controlled using hydraulic pressure exerted by the chamber positioned directly above the valve. The deflection of the valve barrier provides separation of the cell chambers and the individual microenvironments. Upon the release of the pressure, the valve returns to its original position and allows the exchange of signaling molecules between the cells. The lower glass channel wall of the microfluidic device was coated with gelatin, polydopamine (PDA), and poly-L-lysine (PLL) to provide cellular attachment for HBEC-5i cells and astrocytes. The polyelectrolyte immobilization efficacy was assessed via atomic force microscopy while the viability of the HBEC-5i cell was assessed using fluorescent-based methods.

OPTIMIZATION OF THE HOLLOW CHANNELS FORMATION PARAMETERS INSIDE GLASS BY DIRECT LASER WRITING AND SELECTIVE ETCHING

Two-stage method of hollow channels formation inside glass by direct laser writing and selective etching is perspective way for microfluidics devices manufacturing. In this work the influence of the etching solution concentration and laser writing conditions (the laser beam scanning speed, pulse energy) on the etching rate, selectivity and roughness of hollow channels in quartz glass is studied. The use of 1M NaOH makes it possible to increase the etching rate of hollow channels up to 300 µm/h while maintaining high selectivity up to 680.

Energy and exergy analyses of a low-concentration photovoltaic/thermal module with glass channel

As a form of solar energy utilization, photovoltaic/thermal (PV/T) modules generate heat and electricity at the same time. Compared with individual photovoltaic or photothermal, it has a higher efficiency. In this paper, a simulation process coupling optical, electrical and thermal models for a water based low-concentration photovoltaic/thermal module is established. The optical characteristics of the module are simulated by Monte Carlo method. The electrical and thermal characteristics are numerically simulated using the finite volume method. The simulated values of outlet water temperature, output current and output power are fit well with experimental values, which verifies the reliability of the simulation process. The effects of water inlet velocity, solar irradiation, water inlet temperature, ambient temperature and wind speed on the energy and exergy performances of the module are analyzed. Results show that the direct contact of the HTF with the backside of the solar panel and the use of bifacial solar cells endowed the module with good electrical efficiency, and the overall efficiency exceeds 65% in all simulations. By connecting modules in series, the outlet water temperature can be increased and the application scenario can be extended.