Microfluidic Design of Magnetoresponsive Photonic Microcylinders with Multicompartments

Colloidal photonic structures have been designed to have granular format to use them for paint pigments, encoded carriers, and display pixels. However, conventional approaches only provide spherical or discoid shapes, restricting their applications. Cylindrical granules with fan‐shaped compartments in the cross section are appealing for microcarriers with abundant optical codes and active display pigments for color switching. In this work, a stratified laminar flow of concentrated silica particles is employed, formed in a cylindrical microchannel, to produce cylindrical photonic microparticles with multiple compartments. To accomplish this, a microfluidic device is designed to have one cylindrical main channel connected with four branch channels. Four different photocurable suspensions are independently injected through the branches to form quarter‐cylindrically compartmentalized streams in the main channel. Local ultraviolet irradiation on the main channel polymerizes the suspension, thereby forming cylindrical microparticles with four compartments. In each compartment, silica particles form ordered array which develops particle size–dependent structural color. Therefore, different colors can be incorporated into single microcylinder by employing different sizes of silica particles. Moreover, one of the compartments can be rendered to be magnetoresponsive by embedding aligned magnetic particles, which enables the remote control of microcylinder orientation and therefore the switching of structural colors.     

微流控芯片基片与盖片一体化注塑成型研究

针对微流控芯片基片与盖片的结构特点,提出了定模先行抽芯机构,设计制造了微流控芯片基片与盖片一体化注塑成型模具,并进行注塑成型试验研究.结果表明:定模先行抽芯机构可以有效解决盖片上圆孔状储液池成型与脱模的技术难题,如何使微通道复制完全是微流控芯片基片注塑成型的主要技术难点;模具温度对提高微通道复制度起决定性作用,注射速度和熔体温度是次要因素,而注射压力相对其他因素影响力较差,但必须保持在一个较高的水平,依此形成塑料微流控芯片的注塑成型工艺规范.     

Metallosupramolecular Photonic Elastomers with Self‐Healing Capability and Angle‐Independent Color

Photonic elastomers that can change colors like a chameleon have shown great promise in various applications. However, it still remains a challenge to produce artificial photonic elastomers with desired optical and mechanical properties. Here, the generation of metallosupramolecular polymer‐based photonic elastomers with tunable mechanical strength, angle‐independent structural color, and self‐healing capability is reported. The photonic elastomers are prepared by incorporating isotropically arranged monodispersed SiO₂ nanoparticles within a supramolecular elastomeric matrix based on metal coordination interaction between amino‐terminated poly(dimethylsiloxane) and cerium trichloride. The photonic elastomers exhibit angle‐independent structural colors, while Young's modulus and elongation at break of the as‐formed photonic elastomers reach 0.24 MPa and 150%, respectively. The superior elasticity of photonic elastomers enables their chameleon‐skin‐like mechanochromic capability. Moreover, the photonic elastomers are capable of healing scratches or cuts to ensure sustainable optical and mechanical properties, which is crucial to their applications in wearable devices, optical coating, and visualized force sensing.     

Fabrication of topologically complex three-dimensional microfluidic systems in PDMS by rapid prototyping

This paper describes a procedure for making topologically complex three-dimensional microfluidic channel systems in poly(dimethylsiloxane) (PDMS). This procedure is called the "membrane sandwich" method to suggest the structure of the final system: a thin membrane having channel structures molded on each face (and with connections between the faces) sandwiched between two thicker, flat slabs that provide structural support. Two "masters" are fabricated by rapid prototyping using two-level photolithography and replica molding. They are aligned face to face, under pressure, with PDMS prepolymer between them. The PDMS is cured thermally. The masters have complementary alignment tracks, so registration is straightforward. The resulting, thin PDMS membrane can be transferred and sealed to another membrane or slab of PDMS by a sequence of steps in which the two masters are removed one at a time; these steps take place without distortion of the features. This method can fabricate a membrane containing a channel that crosses over and under itself, but does not intersect itself and, therefore, can be fabricated in the form of any knot. It follows that this method can generate topologically complex microfluidic systems; this capability is demonstrated by the fabrication of a "basketweave" structure. By filling the channels and removing the membrane, complex microstructures can be made. Stacking and sealing more than one membrane allows even more complicated geometries than are possible in one membrane. A square coiled channel that surrounds, but does not connect to, a straight channel illustrates this type of complexity.     

A Polymer Microfluidic Chip With Interdigitated Electrodes Arrays for Simultaneous Dielectrophoretic Manipulation and Impedimetric Detection of Microparticles

This paper presents the design, fabrication, and characterization of a polymer microfluidic biochip with integrated interdigitated electrodes arrays (IDAs) used to simultaneously separate, manipulate, and detect microparticles using dielectrophoresis (DEP) and electrochemical impedance spectroscopy (EIS) methods. The DEP response of silica microspheres has been characterized, and microspheres of different sizes (1.8 and 3.5 in diameter) have been DEP flow separated and individually trapped in different microchambers by IDAs in a single run. Simultaneously, the impedance change caused by microspheres captured on IDAs has been analyzed for quantification. High-throughput polymer microfabrication techniques such as micro injection molding were used in this work, so that the polymer microfluidic chip can be produced in a low-cost, disposable platform. This low-cost microfluidic chip provides a generic platform for developing multifunctional lab-on-a-chip devices that require the ability to handle and sense microparticles.     

塑料微流控芯片的注塑成型

有别于传统的微流控芯片压塑成型方法,本文提出注塑成型加工塑料微流控芯片的新工艺.采用UV-LIGA技术制作成型微通道的型芯,设计制造了微流控芯片注塑模具.充模试验表明,如何使微通道复制完全是微流控芯片注塑成型的主要技术难点.模拟与理论分析表明,熔体在微通道处出现滞流现象是复制不完全的主要原因;搭建了可视化装置对此加以试验验证.利用正交试验方法进行充模试验,研究各工艺参数对微通道复制度的影响.试验表明模具温度对提高微通道复制度起决定性作用;注射速度和熔体温度是次要因素,而注射压力相对其他因素影响力较差,但必须保持在一个较高的水平.依此形成塑料微流控芯片的注塑成型工艺,对于宽80μm、深50μm截面的微通道而言,可使微通道复制度由70%提高到90%,满足使用要求.     

Label-Free Photonic Crystal Biosensor Integrated Microfluidic Chip for Determination of Kinetic Reaction Rate Constants

We demonstrate a photonic crystal integrated microfluidic chip that is compatible with a 384-well microplate format for measuring kinetic reaction rate constants in high-throughput biomolecular interaction screening applications. The device enables low volume kinetic analysis of protein-protein interactions with low flow latency, and control of five analyte flow channels with a single control point. The structure is fabricated with a replica molding process that produces the submicron photonic crystal structure simultaneously with the micrometer-scale fluid channel structure. The device significantly reduces the kinetic assay time required compared with a conventional biosensor microplate in which reagents reach the active detection surface by diffusion. Using the photonic crystal sensor fluid network system, we demonstrate determination of the kinetic association/dissociation rate constants between immobilized ligands and analytes in the flow stream, using the heparin/lactoferrin system as an example.     

A New Approach to In‐Situ “Micromanufacturing”: Microfluidic Fabrication of Magnetic and Fluorescent Chains Using Chitosan Microparticles as Building Blocks

An in situ microfluidic assembly approach is described that can both produce microsized building blocks and assemble them into complex multiparticle configurations in the same microfluidic device. The building blocks are microparticles of the biopolymer chitosan, which is intentionally selected because its chemistry allows for simultaneous intraparticle and interparticle linking. Monodisperse chitosan‐bearing droplets are created by shearing off a chitosan solution at a microfluidic T‐junction with a stream of hexadecane containing a nonionic detergent. These droplets are then interfacially crosslinked into stable microparticles by a downstream flow of glutaraldehyde (GA). The functional properties of these robust microparticles can be easily varied by introducing various payloads, such as magnetic nanoparticles and/or fluorescent dyes, into the chitosan solution. The on‐chip connection of such individual particles into well‐defined microchains is demonstrated using GA again as the chemical “glue” and microchannel confinement as the spatial template. Chain flexibility can be tuned by adjusting the crosslinking conditions: both rigid chains and semiflexible chains are created. Additionally, the arrangement of particles within a chain can also be controlled, for example, to generate chains with alternating fluorescent and nonfluorescent microparticles. Such microassembled chains could find applications as microfluidic mixers, delivery vehicles, microscale sensors, or miniature biomimetic robots.     

Hydrogel-based microreactors as a functional component of microfluidic systems

A simple two-step method for fabricating poly(ethylene glycol) (PEG) hydrogel-based microreactors and microsensors within microfluidic channels is described. The intrachannel micropatches contain either a dye, which can report the pH of a solution within a fluidic channel, or enzymes that are able to selectively catalyze specific reactions. Analytes present within the microfluidic channel are able to diffuse into the micropatches, encounter the enzymes, and undergo conversion to products, and then the products interact with the coencapsulated dye to signal the presence of the original substrate. The micropatches are prepared by photopolymerizing the PEG precursor within the channel of a microfluidic system consisting of a poly(dimethylsiloxane) mold and a glass plate. Exposure takes place through a slit mask oriented perpendicular to the channel, so the size of the resulting micropatch is defined by the channel dimensions and the width of the slit mask. Following polymerization, the mold is removed, leaving behind the micropatch(es) atop the glass substrate. The final microfluidic device is assembled by irreversibly binding the hydrogel-patterned glass slide to a second PDMS mold that contains a larger channel. Multiple micropatches containing the same or different enzymes can be fabricated within a single channel. The viability of this approach is demonstrated by sensing glucose using micropatches copolymerized with glucose oxidase, horseradish peroxidase, and a pH-sensitive dye.     

Printed circuit technology for fabrication of plastic-based microfluidic devices

One of the primary advantages of using plastic-based substrates for microfluidic systems is the ease with which devices can be fabricated with minimal dependence on specialized laboratory equipment. These devices are often produced using soft lithography techniques to cast replicas of a rigid mold or master incorporating a negative image of the desired surface structures. Conventional photolithographic micromachining processes are typically used to construct these masters in either thick photoresist, etched silicon, or etched glass substrates. The speed at which new masters can be produced using these techniques, however, can be relatively slow and often limits the rate at which new device designs can be built and tested. In this paper, we show that inexpensive photosensitized copper clad circuit board substrates can be employed to produce master molds using conventional printed circuit technology. This process offers the benefits of parallel fabrication associated with photolithography without the need for cleanroom facilities, thereby providing a degree of speed and simplicity that allows microfluidic master molds with well-defined and reproducible structural features to be constructed in approximately 30 min in any laboratory. Precise control of channel heights ranging from 15 to 120 microm can be easily achieved through selection of the appropriate copper layer thickness, and channel widths as small as 50 microm can be reproducibly obtained. We use these masters to produce a variety of plastic-based microfluidic channel networks and demonstrate their suitability for DNA electrophoresis and microfluidic mixing studies.     

导流介质对真空导入模塑工艺树脂流动行为的影响

采用可视化流动实验方法研究了高渗透率导流介质对真空导入模塑工艺中树脂流动行为的影响。结果表明: 导流介质能较大幅度地减少树脂的充模流动时间, 且充模时间随着导流介质使用比例的增加而呈线性减少的关系; 导流介质的提速作用随着预成型体厚度的增加而逐渐减弱; 预成型体上下表面树脂流动前沿位置差距与预成型体厚度呈良好的线性增加关系, 说明导流介质的影响作用具有明显的厚度效应。厚度效应原理为真空导入模塑工艺过程的参数优化和保证制品质量提供了理论依据。      

一种无浇口废料电雷管脚线塞的新型注射模具设计

目前,在进行电雷管(含数码电子雷管)脚线塞生产制造过程中,由于模具注塑料供料通道设计不合理等原因,导致部分通道余料残存于注塑制品上,且去除浇口废料费时费力。新型注射模结构在传统注塑模具中增加了堵孔部件,一次注塑完成后,堵孔杆下移,使注射料通道和模型腔内物料分离。生产实践证明,该新型注射模结构能够实现电雷管注塑产品表面无浇口废料,表面光洁并不需进行人工剔除,同时节约了注塑原辅材料。     

Study of microscale hydraulic jump phenomenon for hydrodynamic trap-and-release of microparticles

Easy trap-and-release of microparticles is necessary to study biological cellular behavior. The hydraulic jump phenomenon inspired us to conceive a microfluidic device for the hydrodynamic trap-and-release of microparticles. A sudden height increase in a microfluidic channel leads to a dramatic decrease in flow velocity, allowing effective trapping of the microparticles by energy conversion. The trapped particles can be released by stronger inertial force based on simply increasing the flow velocity. We present a systematic, numerical study of trap-and-release of the microparticles using multiphase Navier-Stokes equations. Effect of geometry flow velocity, particle diameter, and adhesion force on trap-and-release was studied.     

Continuous sorting of microparticles using dielectrophoresis

Sorting of particles such as cells is a critical process for many biomedical applications, and it is challenging to integrate it into an analytical microdevice. We report an effective and flexible dielectrophoresis (DEP)-based microfluidic device for continuous sorting of multiple particles in a microchannel. The particle sorter is composed of two components-a DEP focusing unit and a Movable DEP Trap (MDT). The trap is formed by an array of microelectrodes at the bottom of the channel and a transparent electrode plate placed at the top. The location of the trap is dependent on the configuration of voltages on the array and therefore is addressable. Flowing particles are first directed and focused into a single particle stream by the focusing unit. The streamed particles are then sorted into different fractions using the movable trap by rapidly switching the applied voltage. The performance of the sorter is demonstrated by successfully sorting microparticles in a continuous flow. The proposed DEP-based microfluidic sorter can be implemented in applications such as sample preparation and cell sorting for subsequent analytical processing, where sorting of particles is needed.     

Preparation of P(St-NMA) microsphere inks and their application in photonic crystal patterns with brilliant structural colors

Patterned photonic crystals with structural colors on textile substrates have attracted a special attention due to the great advantages in application, which currently become a research hot-spot. This study utilized an ink-jet printing technology to prepare high-quality photonic crystal patterns with structural colors on polyester substrates. The self-assembly temperature of poly(styrene-N-methylol acrylamide) (P(St-NMA)) microspheres set to construct photonic crystals were deeply optimized. Moreover, the structural colors of prepared photonic crystal patterns were characterized and evaluated. When the mass fraction of P(St-NMA) microspheres was 1.0 wt.%, the pH value ranged from 5 to 7, and the surface tension was in the range of 63.79 to 71.20 mN/m, inks could present the best print performance. At 60 °C, prepared P(St-NMA) microsphere inks were good for printing to obtain patterned photonic crystals with regular arrangement and beautiful structural colors. Specifically, photonic crystals with different colors could be constructed by regulating the diameter of microspheres in inks, and prepared structural colors exhibited distinct iridescent phenomenon. The present results could provide a theoretical basis for the industrial realization of patterned photonic crystals by ink-jet printing technology.     

Thermoplastic microfluidic device for on-chip purification of nucleic acids for disposable diagnostics

A polymeric microfluidic device for solid-phase extraction (SPE)-based isolation of nucleic acids is demonstrated. The plastic chip can function as a disposable sample preparation system for different biological and diagnostic applications. The chip was fabricated in a cyclic polyolefin by hot-embossing with a master mold. The solid phase consisted of a porous monolithic polymer column impregnated with silica particles. The extraction was achieved due to the binding of nucleic acids to the silica particles in the monolith. The solid phase was formed within the channels of the device by in situ photoinitiated polymerization of a mixture of methacrylate and dimethacrylate monomers, UV-sensitive free-radical initiator, and porogenic solvents. The channel surfaces were pretreated via photografting to covalently attach the monolith to the channel walls. The solid phase prepared by this method allowed for successful extraction and elution of nucleic acids in the polymeric microchip.     

Bio‐Inspired Bright Structurally Colored Colloidal Amorphous Array Enhanced by Controlling Thickness and Black Background

Inspired by Steller's jay, which displays angle‐independent structural colors, angle‐independent structurally colored materials are created, which are composed of amorphous arrays of submicrometer‐sized fine spherical silica colloidal particles. When the colloidal amorphous arrays are thick, they do not appear colorful but almost white. However, the saturation of the structural color can be increased by (i) appropriately controlling the thickness of the array and (ii) placing the black background substrate. This is similar in the case of the blue feather of Steller's jay. Based on the knowledge gained through the biomimicry of structural colored materials, colloidal amorphous arrays on the surface of a black particle as the core particle are also prepared as colorful photonic pigments. Moreover, a structural color on–off system is successfully built by controlling the background brightness of the colloidal amorphous arrays.     

Antibacterial Action of Nanoparticles by Lethal Stretching of Bacterial Cell Membranes

It is commonly accepted that nanoparticles (NPs) can kill bacteria; however, the mechanism of antimicrobial action remains obscure for large NPs that cannot translocate the bacterial cell wall. It is demonstrated that the increase in membrane tension caused by the adsorption of NPs is responsible for mechanical deformation, leading to cell rupture and death. A biophysical model of the NP–membrane interactions is presented which suggests that adsorbed NPs cause membrane stretching and squeezing. This general phenomenon is demonstrated experimentally using both model membranes and Pseudomonas aeruginosa and Staphylococcus aureus, representing Gram-positive and Gram-negative bacteria. Hydrophilic and hydrophobic quasi-spherical and star-shaped gold (Au)NPs are synthesized to explore the antibacterial mechanism of non-translocating AuNPs. Direct observation of nanoparticle-induced membrane tension and squeezing is demonstrated using a custom-designed microfluidic device, which relieves contraction of the model membrane surface area and eventual lipid bilayer collapse. Quasi-spherical nanoparticles exhibit a greater bactericidal action due to a higher interactive affinity, resulting in greater membrane stretching and rupturing, corroborating the theoretical model. Electron microscopy techniques are used to characterize the NP–bacterial-membrane interactions. This combination of experimental and theoretical results confirm the proposed mechanism of membrane-tension-induced (mechanical) killing of bacterial cells by non-translocating NPs.     

Addressable Microfluidic Polymer Chip for DNA‐Directed Immobilization of Oligonucleotide‐Tagged Compounds

A microfluidic polymer chip for the self‐assembly of DNA conjugates through DNA‐directed immobilization is developed. The chip is fabricated from two parts, one of which contains a microfluidic channel produced from poly(dimethylsiloxane) (PDMS) by replica‐casting technique using a mold prepared by photolithographic techniques. The microfluidic part is sealed by covalent bonding with a chemically activated glass slide containing a DNA oligonucleotide microarray. The dimension of the PDMS–glass microfluidic chip is equivalent to standard microscope slides (76 × 26 mm²). The DNA microarray surface inside the microfluidic channels is configured through conventional spotting, and the resulting DNA patches can be conveniently addressed with compounds containing complementary DNA tags. To demonstrate the utility of the addressable surface within the microfluidic channel, DNA‐directed immobilization (DDI) of DNA‐modified gold nanoparticles (AuNPs) and DNA‐conjugates of the enzymes glucose oxidase (GOx) and horseradish peroxidase (HRP) are carried out. DDI of AuNPs is used to demonstrate site selectivity and reversibility of the surface‐modification process. In the case of the DNA–enzyme conjugates, the patterned assembly of the two enzymes allows the establishment and investigation of the coupled reaction of GOx and HRP, with particular emphasis on surface coverage and lateral flow rates. The results demonstrate that this addressable chip is well suited for the generation of fluidically coupled multi‐enzyme microreactors.     

Direct writing of metal nanoparticle films inside sealed microfluidic channels

Herein we demonstrate the ability to pattern Ag nanoparticle films of arbitrary geometry inside sealed PDMS/TiO2/glass microfluidic devices. The technique can be employed with aqueous solutions at room temperature under mild conditions. A 6 nm TiO2 film is first deposited onto a planar Pyrex or silica substrate, which is subsequently bonded to a PDMS mold. UV light is then exposed through the device to reduce Ag+ from an aqueous solution to create a monolayer-thick film of Ag nanoparticles. We demonstrate that this on-chip deposition method can be exploited in a parallel fashion to synthesize nanoparticles of varying size by independently controlling the solution conditions in each microchannel in which the film is formed. The film morphology was checked by atomic force microscopy, and the results showed that the size of the nanoparticles was sensitive to solution pH. Additionally, we illustrate the ability to biofunctionalize these films with ligands for protein capture. The results indicated that this could be done with good discrimination between addressed locations and background. The technique appears to be quite general, and films of Pd, Cu, and Au could also be patterned.