Micropore Arrays Research Articles

Fabrication of oil–water separation copper filter by spatial light modulated femtosecond laser

Surface with oil–water separation performance has attracted more and more attention in the application of oil-containing wastewater purification. Much related work has been done by many researchers. However, there are still many difficulties in rapid manufacturing of filter membranes with special wettability. In this paper, an efficient, flexible method to fabricate microporous arrays by using a femtosecond (fs) laser combined with a spatial light modulator is proposed. The laser treated copper sheet surface shows hydrophobic and superoleophilic properties due to the microstructure. Meanwhile, the array of micro-through-holes on the surface can allow oil to penetrate through holes and prevent water from penetrating. The manufacturing process is not only extremely efficient, with a 10 × 10 focus array used in the ablation, but also it is without chemical method and the filter presents a long-term stable hydrophobic and superoleophilic performance.

Polariton Excitations in a Nonideal Two-Sublattice Array of Micropores

Dispersion characteristics of polariton excitations in a nonideal 1D lattice of micropores are studied versus concentrations of structural defects related to variations in the positions of the micropores that contain quantum dots in one sublattice. Such structural defects in the 1D sublattice array of micropores can be used to obtain desired changes of the energy structure of polariton excitations and, hence, optical properties of the system under study due to modification of electromagnetic spectrum.

Flow Homogenization Enables a Massively Parallel Fluidic Design for High-throughput and Multiplexed Cell Isolation.

Microfluidic devices are widely used for applications such as cell isolation. Currently, the most common method to improve throughput for microfluidic devices involves fabrication of multiple, identical channels in parallel. However, this 'numbering up' only occurs in one dimension, thereby limiting gains in volumetric throughput. In contrast, macro-fluidic devices permit high volumetric flow-rates but lack the finer control of microfluidics. Here, we demonstrate how a micro-pore array design enables flow homogenization across a magnetic cell capture device, thus creating a massively parallel series of micro-scale flow channels with consistent fluidic and magnetic properties, regardless of spatial location. This design enables scaling in 2-dimensions, allowing flow-rates exceeding 100 mL/hr while maintaining >90% capture efficiencies of spiked lung cancer cells from blood in a simulated circulating tumor cell system. Additionally, this design facilitates modularity in operation, which we demonstrate by combining two different devices in tandem for multiplexed cell separation in a single pass with no additional cell losses from processing.

On-chip multiplexed single-cell patterning and controllable intracellular delivery

Conventional electroporation approaches show limitations in the delivery of macromolecules in vitro and in vivo. These limitations include low efficiency, noticeable cell damage and nonuniform delivery of cells. Here, we present a simple 3D electroporation platform that enables massively parallel single-cell manipulation and the intracellular delivery of macromolecules and small molecules. A pyramid pit micropore array chip was fabricated based on a silicon wet-etching method. A controllable vacuum system was adopted to trap a single cell on each micropore. Using this chip, safe single-cell electroporation was performed at low voltage. Cargoes of various sizes ranging from oligonucleotides (molecular beacons, 22 bp) to plasmid DNA (CRISPR-Cas9 expression vectors, >9 kb) were delivered into targeted cells with a significantly higher transfection efficiency than that of multiple benchmark methods (e.g., commercial electroporation devices and Lipofectamine). The delivered dose of the chemotherapeutic drug could be controlled by adjusting the applied voltage. By using CRISPR-Cas9 transfection with this system, the p62 gene and CXCR7 gene were knocked out in tumor cells, which effectively inhibited their cellular activity. Overall, this vacuum-assisted micropore array platform provides a simple, efficient, high-throughput intracellular delivery method that may facilitate on-chip cell manipulation, intracellular investigation and cancer therapy.

Laser-Induced Wettability Gradient Surface of the Aluminum Matrix Used for Directional Transportation and Collection of Underwater Bubbles.

The control of underwater bubble behavior on a solid surface has great research significance. However, the control of the spontaneous directional transport and collection of numerous underwater bubbles remains a challenge. A new technique of a metal mesh with superhydrophobic/hydrophobic properties is demonstrated here, which creates a wettability gradient coupled with a microporous array by means of pulsed fiber laser ablation and chemical modification of the aluminum sheet. The resultant wettability surface effectively achieved the spontaneous movement of bubbles along the directional wettability gradient (superaerophobicity to aerophilicity) and through the metal mesh (aerophilicity to superaerophilicity) in the direction of decreasing free energy. Theoretical analysis accounted first for the spontaneous sliding of bubbles on the wettability gradient surface as a result of the action of an unbalanced surface tension force and second for the spontaneous transition of bubbles from the aerophilic to superaerophilic side as a result of the combined action of Laplace pressure and buoyancy. A device with the capability of directional transportation and collection of underwater bubbles was designed based on the samples with a wettability gradient and a superhydrophobic/hydrophobic microporous array as the core components. The potential application is laser ablation of wettability gradient surfaces and metal mesh with superhydrophobic/hydrophobic properties for directional transportation and collection of underwater bubbles.

Empirical modeling and Monte Carlo simulation of secondary electron yield reduction of laser drilled microporous gold surfaces

This work investigates secondary electron yield (SEY) mitigation from a metal surface with a microporous array fabricated using the laser drilling technique. We propose a general empirical model to fit the experimentally measured SEY of a flat gold surface for normal and oblique incidences of primary electrons. Using this empirical model, we develop a two-dimensional Monte Carlo (MC) simulation scheme to determine the effective SEY of a microporous array. It is found that the SEY from a porous surface is significantly reduced compared to that of the flat surface. By taking into account all the generations of secondary electrons inside a well, our MC results are found to be in very good agreement with the experimental data. The dependence of the SEY on the aspect ratio of the micropores and porosity of the surface is examined. A simple empirical formula has been proposed to evaluate the effective SEY of the gold microporous array for pores of arbitrary aspect ratios.

Bioinspired Janus Textile with Conical Micropores for Human Body Moisture and Thermal Management.

Excessive sweat secreted from the skin often causes undesired adhesion from wetted textiles and cold sensations. Traditional hydrophilic textiles such as cotton can absorb sweat but retain it. A hydrophobic/superhydrophilic Janus polyester/nitrocellulose textile embedded with a conical micropore array with a hydrophilic inner surface that can achieve directional liquid transport (with an ultrahigh directional water transport capability of 1246%) and maintain human body temperature (2-3 °C higher than with cotton textiles) is demonstrated. When the hydrophobic polyester layer with large opening of hydrophilic conical micropores contacts the liquid, the Janus polyester/nitrocellulose textile can pump it to the superhydrophilic nitrocellulose layer through the hydrophilic conical micropores driven by capillary force. The Janus polyester/nitrocellulose textile can weaken undesired wet adhesion and heat loss due to the removal of liquid. The water wicking and air permeability of the Janus polyester/nitrocellulose textile is comparable to those of traditional cloths. This study is valuable for designing of functional textiles with directional water transport properties for personal drying and warming applications.

A Capillary-Evaporation Micropump for Real-Time Sweat Rate Monitoring with an Electrochemical Sensor.

Sweat collection and real time monitoring of sweat rate play essential roles in physiology monitoring and assessment of an athlete’s performance during exercise. In this paper, we report a micropump for sweat simulant collection based on the capillary–evaporation effect. An electrochemical sensor is integrated into the micropump, which monitors the flow rate in real-time by detecting the current using three electrodes. The evaporation rate from micropore array, equivalent to the sweat rate, was theoretically and numerically investigated. The designed micropump yields the maximum collection rate as high as 0.235 L/min. In addition, the collection capability of the micropump was validated experimentally; the flow rate through the microchannel was further detected in real-time with the electrochemical sensor. The experimental maximum collection rate showed good consistency with the theoretical data. Our proposed device shows the potential for sweat collection and real-time monitoring of sweat rate, which is a promising candidate for being a wearable platform for real-time physiology and performance monitoring during exercise.

Development of superhydrophilic Al foil with micropore arrays via mask electrochemical machining and chemical immersion for efficient oil/water separation

Extreme wettability materials, which can enable high-efficiency oil/water separation, has become a widely discussed topic due to increasingly severe oil pollutions including frequent offshore oil-spills accidents and industrial oily wastewater emission. However, most of existing methods to prepare these materials involved complicated machining processes or dangerous operations, especially the use of corrosive or toxic chemicals. Herein, a novel and environment friendly method including mark electrochemical machining (MECM) and subsequent chemical immersion, was proposed to acquire micropore arrays on Al foil for efficient oil collection from oil/water mixtures. Micro-dimple arrays were generally fabricated by MECM process followed by CuCl2 immersion to make it through. Both simulation and experimental verification were conducted to elucidate how dimple structures varied with machining parameters. The micro-scale rectangular-shaped step-like structures on micropore arrays endowed as-prepared samples with excellent superhydrophibic and underwater superoleophobic properties. Moreover, oils with kinematic viscosities ranging from 0.41 to 74.4 cSt could be separated from water with separation efficiencies above 95%. The superhydrophilic Al foil still showed good durability through repeated oil/water separation tests, and retained its superhydrophilicity even after the storage in water for 120 hours. Therefore, this novel and green method gives researchers new insights into functional materials preparation for practical oil/water separation.

Influence of silicon wall thickness on the performance of structured CsI(Tl) scintillation screen based on oxidized silicon micropore array template in X-ray imaging.

The influence of silicon wall thickness on the performance of structured CsI(Tl) scintillation screen based on oxidized silicon micropore array template in X-ray imaging was simulated using Geant4 Monte Carlo simulation code in terms of light output (LO), modulation transfer function (MTF) and detective quantum efficiency (DQE). The results show that when the thickness of the silicon wall is less than 0.5 μm, the increase in the bottom light output (BLO) of the screen and the decrease in the spatial resolution of the X-ray imaging system using the screen become more significant as the thickness decreases. At low spatial frequency, the thicker the silicon wall, the lower the DQE. However, the DQE with a thick silicon wall can exceed the DQE with a thin silicon wall at high spatial frequency. All the results provide the quantitative relation between the silicon wall thickness of the structured CsI(Tl) scintillation screen and the quality of the X-ray imaging.

Edge-effect-mediated microfluidics for fabrication of microporous membrane with well-defined size and shape

Microporous membranes of well-defined porous size, shape, and distribution are significantly important for environmental engineering and biomedical treatment applications, where high-throughput precise filtration is required. However, efficient manufacturing of desired microporous membranes remains a great challenge. In this study, an cost-effective method, based on edge-effect-mediated microfluidics, is proposed for the fabrication of polymeric microsieves with well-defined micropore arrays. This method refers to a lateral spreading of a liquid prepolymer between the protruding parts of a template and the flat surface of a substrate. The edge effect enables the liquid prepolymer to bypass, instead of filling the microholes of the template. Based on the proposed method, two types of monodisperse SiO2 microspheres were separated by solution filtration.

Deformation Behavior of Pure Copper Castings with As-Cast Surfaces for Electrical Parts

Herein, the tensile deformation behavior of pure copper castings with as-cast surfaces was investigated. It was found that small and sufficiently large uniform elongation types corresponded, respectively, to the presence or absence of a Cu-Cu2O eutectic phase in the microstructure. Fissure defects were observed near the as-cast surfaces when the eutectic phase was present, probably leading to stress concentration. On the other hand, surface pinholes were observed when the eutectic phase was absent, and these were not prevented by directional solidification. Although the as-cast specimens (non-directionally solidified) exhibited a slightly reduced uniform elongation compared to the machined specimens in the absence of the eutectic phase, the directionally solidified as-cast samples exhibited a uniform elongation that was similar to that of the machined specimens. In addition, micropore arrays were formed along the grain boundaries inside the castings when the eutectic phase was absent, whereas almost no micropores were observed inside the directionally solidified as-cast specimens because the solidification process involved a faster cooling rate and/or higher temperature gradient. These results do not only suggest the existence of surface pinholes but also indicate that microporosity can reduce the cross-sectional area of the specimens, thus, affecting their uniform elongation.

Unidirectional self-transport of air bubble via a Janus membrane in aqueous environment

Inspired by natural creatures, bubble manipulation by surface microstructures in aqueous media has attracted great attention due to its promising applications in industrial production. Herein, a superhydrophobic/hydrophilic Janus aluminum membrane with tapered micropore arrays was fabricated by femtosecond laser drilling, surface fluorination, and subsequent fluorination removal. Compared with the single interception or penetration of double-faced hydrophilic or superhydrophobic membranes, the Janus membrane showed a distinctive unidirectional air bubble transport ability. In experiment, the air bubbles introduced on the lower hydrophilic surface could spontaneously move to the upper superhydrophobic surface, but they were prevented in the inverse direction. The dynamic process of unidirectional transport was in-situ monitored, and the physical mechanism was systemically investigated. In addition, the concepts of air-participating chemical/physical processes were demonstrated such as discoloration of purple litmus solution by CO2 injection, which proved the Janus membrane practicability.

Effect of CsI(Tl) micro-conical-frustums on the performance of the pixelated CsI(Tl) scintillation screen in X-ray imaging

The pixelated CsI(Tl) scintillation screen based on oxidized silicon micro-pore array template with CsI(Tl) micro-conical-frustums (CMCF) was proposed. The effect of the CMCF on the performance of the pixelated CsI(Tl) scintillation screen in X-ray imaging was studied by using Geant4 Monte Carlo simulation code. The variations of the light output (LO), modulation transfer function (MTF) and detective quantum efficiency (DQE) for the screen with the cone angle β of the CMCF in X-ray imaging were revealed. The results show that the LO of the pixelated scintillation screen with CMCF is superior to that of the screens with CsI(Tl) micro-cylinders (CMC) or with reversed CsI(Tl) micro-conical-frustums (RCMCF), but the spatial resolution of the X-ray imaging system by using the pixelated scintillation screen with RCMCF is better than that by using the screens with CMCF or with CMC. At low frequency, the cone angle β corresponding to DQEs from good to bad are 2.40°, 0.00°and -2.40°. But at high frequency, the cone angle β corresponding to DQEs from good to bad change to 2.40°, -2.40°and 0.00°. The reason is that, for a pixelated scintillation screen, the DQE for the screen not only depends on the efficiency of X-ray absorption, but also depends on the number of scintillation photons exiting the bottom the screen per interacting X-ray photon and its Poisson excess, and MTF. The simulated results of DQEs show that the comprehensive performance of the pixelated CsI(Tl) screen with CMCF in X-ray imaging is better than that of the screens with CMC or with CRMCF.

Microfabrication of Micropore Array for Cell Separation and Cell Assay.

Micropore arrays have attracted a substantial amount of attention due to their strong capability to separate specific cell types, such as rare tumor cells, from a heterogeneous sample and to perform cell assays on a single cell level. Micropore array filtration has been widely used in rare cell type separation because of its potential for a high sample throughput, which is a key parameter for practical clinical applications. However, most of the present micropore arrays suffer from a low throughput, resulting from a low porosity. Therefore, a robust microfabrication process for high-porosity micropore arrays is urgently demanded. This study investigated four microfabrication processes for micropore array preparation in parallel. The results revealed that the Parylene-C molding technique with a silicon micropillar array as the template is the optimized strategy for the robust preparation of a large-area and high-porosity micropore array, along with a high size controllability. The Parylene-C molding technique is compatible with the traditional micromechanical system (MEMS) process and ready for scale-up manufacture. The prepared Parylene-C micropore array is promising for various applications, such as rare tumor cell separation and cell assays in liquid biopsy for cancer precision medicine.

Morphology evolution of self-organized porous structures in silicon surface

Abstract We have investigated the morphology evolution of silicon surface by laser irradiation. A pulsed ns-laser interaction with silicon in aqueous medium can produce self-organized microporous concave cell array structure without any chemicals and auxiliary equipment. Low radiant power was applied to the photo-induced non-thermal silicon surface modification. At the early stage, hemispherical patterns of 2 ∼ 3 µm were formed, maintaining a constant distance from each other without merging. Due to the thermal properties of water, subsurface heating proceeds under the silicon surface. The molten surface leads to the surface modulation to form subsided areas or expansions by nucleation and coalescence, resulting in the formation of a concave cone-shaped porous surface with a diameter of 10 ∼ 20 µm. The AFM reveals that the hierarchical hemispherical structures of two different scales are progressing simultaneously from the early stage.

Simulated performances of pixelated CsI(Tl) scintillation screens with different micro-column shapes and array structures in X-ray imaging

The performances of the pixelated CsI(Tl) scintillation screens based on oxidized silicon micro-pore array templates with different CsI(Tl) micro-column shapes and array structures in X-ray imaging were simulated using the Geant4 Monte Carlo simulation code. The shapes of the micro-columns include square, hexagonal and circular, and the array structures include square and hexagonal arrangements. The pitch size of the pixelated CsI(Tl) scintillation screens was set to 4 µm, and the incident X-ray energy was set to 20 keV. The ratios of the number of scintillation photons that propagate along the CsI(Tl) micro-columns to the total number of scintillation photons of the micro-columns gradually decrease with the increase in total reflection time on the lateral surfaces of the micro-columns. However, these ratios are closely related to the shapes of the micro-columns and the incident positions of X-ray on the cross-sections of the micro-columns, especially for the circular micro-column. The sequence of bottom light outputs stimulated by a uniform flood field of X-ray from high to low corresponds to the circular, square and hexagonal CsI(Tl) micro-columns with the same cross-section areas. In addition, all spatial resolutions in terms of modulation transfer functions (MTFs) for the pixelated CsI(Tl) scintillation screens with square and hexagonal array structures are over 100 lp/mm. However, the resolution for the pixelated screen with the hexagonal array structure is approximately 8.5% higher than that for the screen with the square array structure. Moreover, the former screen has a higher detective quantum efficiency (DQE) than the latter screen at the same thickness. The pixelated CsI(Tl) scintillation screen with circular micro-column and hexagonal array structure in X-ray imaging has superior performance compared to other pixelated screens in this work.

In-Situ imaging detection of cell membrane and intracellular cholesterol via cascade reactions

Herein, an effective membrane-to-intracellular cholesterol detection strategy was designed based on cascade reactions. A biochip array was firstly fabricated by consecutively immobilizing luminol modified gold nanoparticles (Au@luminol), soybean peroxidase (SBP) and cholesterol oxidase (ChoX) on the cellulose acetate (CA) membrane functionalized home-made micropore array. When cholesterol existed, it was oxidized by ChoX generating H2O2, which further triggered the CL reaction under the SBP catalysis, the CL signals were collected by a charge-coupled device (CCD). The proposed strategy exhibited a wide linear range from 0.12 μM to 1000 μM and relatively low detection limit (LOD) of 0.08 μM. Furthermore，it could be used to in-situ detect membrane cholesterol and intracelluar esterified cholesterol in HepG2 cells. After activated HepG2 cells were added to the modified biochip, membrane cholesterol was detected directly. Intracelluar esterified cholesterol was detected through the introduction of triton X-100 and cholesteryl esterase (ChoE). Additionally, the cholesterol content in cells was changed after stimulated by drugs, such as apolipoprotein A-I (ApoA-I), pitavastatin or probucol. The correlation of the CL signal with the amount of cholesterol confirmed that our strategy was feasible to simultaneously detect membrane and intracellular cholesterol at different cellular states. The proposed strategy exhibited excellent sensitivity, selectivity, stability, and reproducibility in a simple, cheap way, which opened a new door for studying clinic treatment of the cholesterol-related diseases.

Hydroisomerization of n-dodecane over bi-porous Pt-containing bifunctional catalysts: Effects of alkene intermediates’ journey distances within the zeolite micropores

In this study, three micro/mesoporous composites with MCM-41 materials overgrowing on external surfaces of Y zeolite crystals were prepared. For the three composites, average crystal particle sizes of their zeolite components differed from each other, resulting from the different levels of alkali-treatments to the original Y zeolite before the composite synthesis. Hydroisomerization of n-dodecane (n-C12) was used to evaluate the catalytic performances of bi-porous Pt-loaded composite catalysts with similar metal-acid balances but different average zeolite crystal particle sizes, which leaded to the distinction of alkene intermediates’ journey distances inside the acid-rich micropores between two accessible Pt metal sites on three catalysts. The number of protonic sites encountered by alkene intermediates along their diffusion paths, determining the skeletal transformation frequencies, was considered to be proportional to the above-mentioned intermediates’ journey distances. Results showed that bifunctional catalysts with smaller average zeolite crystal particle sizes outperformed the catalyst containing the original Y zeolite in the regard of isomerization selectivity. This implied the significant effect of intermediates’ journey distances within the microporous arrays between two Pt sites on bifunctional behaviors of catalysts. It can be confirmed that shortening this distance within certain limits indeed contributed to inhibiting secondary reactions, including the skeletal multiple branching and cracking.

Micromachining of biocompatible polymer substrate for cancer cell separation applications

Isolation of circulating tumor cells from human blood plays a significant role in diagnosis and treatment of cancer. The most effective way of isolating cells is the use of lab on-chip microfluidic devices. This paper presents the development of cyclic olefin polymer membrane with an array of micropores for separating circulating tumour cells using ultrashort laser ablation process. Initially, the substrate is tested for its cell viability. The laser Fluence is varied from 1–12 J/cm2 and its observed that at a fluence of 2.5 J/cm2 the desired diameter of 12 μm with ablation depth of 1 μm is obtained which is necessary for CTC separation. The treated and untreated structure is characterized using Fourier transform infrared spectrometer and it shows that the treated region shows no significant shift in the spectrum after femtosecond laser ablation.