Printed Microfluidics

Microfluidics has become an important tool that is useful for a wide range of applications. A drawback for microfluidics is that many of the techniques that are commonly used to fabricate devices are not widely accessible, not scalable to high‐volume manufacturing processes, or both. Recently, a number of printing strategies that were originally developed for other applications have been applied to microfluidic device fabrication. These techniques, which include inkjet printing (IJP), screen printing (SP), and solid wax printing (SWP), are proposed to have a transformative effect on the field. Here microfluidics and printing, are introduced and a list of favorite examples is provided that highlights the accessibility and scalability that the combination is bringing to the field.     

Microfluidics meets MEMS

The use of planar fluidic devices for performing small-volume chemistry was first proposed by analytical chemists, who coined the term "miniaturized total chemical analysis systems" (/spl mu/TAS) for this concept. More recently, the /spl mu/TAS field has begun to encompass other areas of chemistry and biology. To reflect this expanded scope, the broader terms "microfluidics" and "lab-on-a-chip" are now often used in addition to /spl mu/TAS. Most microfluidics researchers rely on micromachining technologies at least to some extent to produce microflow systems based on interconnected micrometer-dimensioned channels. As members of the microelectromechanical systems (MEMS) community know, however, one can do more with these techniques. It is possible to impart higher levels of functionality by making features in different materials and at different levels within a microfluidic device. Increasingly, researchers have considered how to integrate electrical or electrochemical function into chips for purposes as diverse as heating, temperature sensing, electrochemical detection, and pumping. MEMS processes applied to new materials have also resulted in new approaches for fabrication of microchannels. This review paper explores these and other developments that have emerged from the increasing interaction between the MEMS and microfluidics worlds.     

Shape‐Memory Microfluidics

Materials with embedded vascular networks afford rapid and enhanced control over bulk material properties including thermoregulation and distribution of active compounds such as healing agents or stimuli. Vascularized materials have a wide range of potential applications in self‐healing systems and tissue engineering constructs. Here, the application of vascularized materials for accelerated phase transitions in stimuli‐responsive microfluidic networks is reported. Poly(ester amide) elastomers are hygroscopic and exhibit thermo‐mechanical properties (T_g ≈ 37 °C) that enable heating or hydration to be used as stimuli to induce glassy‐rubbery transitions. Hydration‐dependent elasticity serves as the basis for stimuli‐responsive shape‐memory microfluidic networks. Recovery kinetics in shape‐memory microfluidics are measured under several operating modes. Perfusion‐assisted delivery of stimulus to the bulk volume of shape‐memory microfluidics dramatically accelerates shape recovery kinetics compared to devices that are not perfused. The recovery times are 4.2 ± 0.1 h and 8.0 ± 0.3 h in the perfused and non‐perfused cases, respectively. The recovery kinetics of the shape‐memory microfluidic devices operating in various modes of stimuli delivery can be accurately predicted through finite element simulations. This work demonstrates the utility of vascularized materials as a strategy to reduce the characteristic length scale for diffusion, thereby accelerating the actuation of stimuli‐responsive bulk materials.     

Surface Textured Polymer Fibers for Microfluidics

This article introduces surface textured polymer fibers as a new platform for the fabrication of affordable microfluidic devices. Fibers are produced tens of meters‐long at a time and comprise 20 continuous and ordered channels (equilateral triangle grooves with side lengths as small as 30 micrometers) on their surfaces. Extreme anisotropic spreading behavior due to capillary action along the grooves of fibers is observed after surface modification with polydopamine (PDA). These flexible fibers can be fixed on any surface—independent of its material and shape—to form three‐dimensional arrays, which spontaneously spread liquid on predefined paths without the need for external pumps or actuators. Surface textured fibers offer high‐throughput fabrication of complex open microfluidic channel geometries, which is challenging to achieve using current photolithography‐based techniques. Several microfluidic systems are designed and prepared on either planar or 3D surfaces to demonstrate outstanding capability of the fiber arrays in control of fluid flow in both vertical and lateral directions. Surface textured fibers are well suited to the fabrication of flexible, robust, lightweight, and affordable microfluidic devices, which expand the role of microfluidics in a scope of fields including drug discovery, medical diagnostics, and monitoring food and water quality.     

Microfluidics for Rapid Detection of Live Pathogens

Rapid, sensitive, and selective detection of live pathogens remains a key priority for quality control and risk assessment. While conventional methods often require complicated workflows, costly reagents, lab equipment, and are time-consuming, rendering them inadequate for field testing and low-resource settings. Increased attention has been drawn to developing alternative low-cost and rapid methods to detect on-site live pathogens in different environmental matrices. Among them, microfluidic devices that integrate various laboratory functions in a miniaturized manner have proven to be a promising tool for the rapid and sensitive detection of pathogens. Herein, the development of microfluidic devices specifically designed for the detection of live pathogens is discussed along a concise summary of novel microfluidics systems recently developed, contrasted to conventional methods regarding assay time, the limit of detection, and target organisms. These include a variety of micro total analysis systems (µTAS) and microfluidic paper-based analytical devices (µPADs) in combination with molecular methods and traditional live cell detection techniques, such as cell culture, DNA intercalating dyes, resazurin, and immobilized bioreceptors (e.g., aptamers and capture antibodies). Furthermore, insights on the future perspectives of microfluidics for live pathogen detection with a highlight on the rapid and low-cost method development for field testing are provided.     

基于微流体的ZnO纳米线的合成

微流控芯片在纳米材料的合成方面具有突出的优势,在芯片中通过微流体的操控制备ZnO纳米线,并利用扫描电子显微镜(SEM)、X射线衍射仪(XRD)和能谱仪(EDS)对制备得到的ZnO纳米线的表面形貌、晶体结构及成分进行表征。实验结果表明,在具有微腔室结构的微通道中可以构建浓度梯度,从而在单一通道中制备得到形貌及尺寸不同的致密ZnO纳米线,成为高效探索纳米材料合成条件的便捷手段。分别以玻璃片、ZnO种子层和ZnO纳米线为载体,对异硫氰酸荧光素标记的羊抗牛IgG抗体进行荧光检测,发现ZnO纳米线可显著增强荧光信号。     

Liquid Shuttle Mediated by Microwick for Open-Air Microfluidics

Microfluidics has experienced rapid progress in additive manufacturing and microfluidic soft robots. The design of microfluidics is already moving into a more intelligent, integrated, and detachable direction. However, the pipeline resistance needs more external energy input to achieve high flow speed. Guided transport of liquid in the open-air-space microfluidics will be an effective solution. Inspired by the water shuttle on the pitcher plant tendril, herein, an open-air microfluidic transport device is designed that consists of a superhydrophilic microwick with multi-microgrooves by stereolithography. The liquid film confined in microgrooves can promote rapid fluid shuttle on the wet surface to enhance transport rate and inhibit the Rayleigh-Plateau instability from forming larger dripping drops. The dripping volume and threshold Capillary number are optimized for effective liquid transport and drainage. State-of-the-art microwick liquid shuttle technologies can guide liquid continuously in a prescribed direction or into multiple directions with 98% transport efficiency (the ratio of liquid collection volume and liquid injection volume) for water and 97% for ethanol in the closed-open-closed space. The proposed mechanism has the potential to streamline microfluidic applications—and, therefore, accelerate relevant liquid delivery development and ultimately their applications in microfluidic chip and additive manufacturing.     

基于微流控的人卵母细胞特性检测

人的卵母细胞特性的研究对于临床医学具有重要意义,可以通过卵母细胞的大小对其活性进行研究。采用微流控平台与MATLAB算法相结合的方法,利用微流控器件的沟道对卵母细胞进行挤压,由于卵母细胞的活性不同对于挤压的反应也不同,活性越好的卵母细胞通过沟道时变形性越好,经检测卵母细胞有很好的活性;拍摄卵母细胞发生形变与卵母细胞通过沟道的视频,利用MATLAB程序进行图像处理得到卵母细胞的大小,测得卵母细胞的直径约为170μm。这种方法有别于传统方法,在一定程度上使用了算法识别,提高了卵母细胞分析统计的准确度,提升了工作效率。由于人的卵母细胞比较珍贵,只进行了初期实验研究,证明此方法确实可行。     

一种双极板结构数字微流控芯片研制

基于介电润湿研制了一种将零电极布局为介电层表面的双极板结构数字微流控芯片.为了降低驱动电压并提高介电层的抗击穿能力,将介电层设计为Si3N4-SiO2层状复合结构.30 V直流电压作用下,成功实现了对0.5 μL去离子水微液滴的连续输运操控;且在100 V以内电压作用时,均未出现介电层击穿.实验结果表明所研制数字微流控芯片可行.     

LTCC腔体及微流道制作技术

简要介绍了LTCC腔体和微流道的用途、结构形式以及腔体的制作方法。详细分析了LTCC空腔在层压和共烧时产生变形的原因。重点阐述了腔体填充材料控制工艺形变的方法,碳基牺牲材料的特性、作用以及控制腔体变形的理论基础。通过工艺试验验证了碳基牺牲材料的有效性。说明采用合理的填充材料、恰当的工艺技术可以制作出满足要求的空腔结构。     

Adaptive Cooling of Integrated Circuits Using Digital Microfluidics

Thermal management is critical for integrated circuit (IC) design. With each new IC technology generation, feature sizes decrease, while operating speeds and package densities increase. These factors contribute to elevated die temperatures detrimental to circuit performance and reliability. Furthermore, hot spots due to spatially nonuniform heat flux in ICs can cause physical stress that further reduces reliability. While a number of chip cooling techniques have been proposed in the literature, most are still unable to address the varying thermal profiles of an IC and their capability to remove a large amount of heat is undermined by their lack of reconfigurability of flows. We present an alternative cooling technique based on a recently invented ";digital microfluidic"; platform. This novel digital fluid handling platform uses a phenomenon known as electrowetting, and allows for a vast array of discrete droplets of liquid, ranging from microliters to nanoliters, and potentially picoliters, to be independently moved along a substrate. While this technology was originally developed for a biological and chemical lab-on-a-chip, we show how it can be adapted to be used as a fully reconfigurable, adaptive cooling platform.     

Biomimetic Meta‐Structured Electro‐Microfluidics

Flexible membranes (i.e., paper, cloth, and polydimethylsiloxane (PDMS)) have received extensive attention. The rapid development of flexible microfluidics and electronics and their integration calls for complex substrate structures to allow for multiple functions. Inspired by nature, meta‐structured membranes (MSMs) as substrates for fabricating integrated microfluidics and electronics are presented. These flexible and freestanding MSMs are generated by the self‐assembly of elastic plastic copolymer nanoparticle photonic crystals on micropatterned PDMS templates. The final MSMs constitute with integrated ordered micro‐ and nanostructures and exhibit spontaneous liquid transfer, fluorescence enhancement, and intimate skin contact. MSMs with designed patterns can be fabricated by assembling polymer nanoparticles on patterned molds; complicated and highly integrated electro‐microfluidics are generated on one slice of MSMs by utilizing these patterns as microfluidic channels and electrocircuits. They can be used as chip‐on‐skin sensors for biochemical–physiological hybrid monitoring sensing of the human body and as organ chips for cell culture and metabolite analysis under drug treatment. Their excellent properties show their potential value in cross‐scale sensing and have broad potential applications.     

Droplet Microfluidics XRD Identifies Effective Nucleating Agents for Calcium Carbonate

The ability to control crystallization reactions is required in a vast range of processes including the production of functional inorganic materials and pharmaceuticals and the prevention of scale. However, it is currently limited by a lack of understanding of the mechanisms underlying crystal nucleation and growth. To address this challenge, it is necessary to carry out crystallization reactions in well‐defined environments, and ideally to perform in situ measurements. Here, a versatile microfluidic synchrotron‐based technique is presented to meet these demands. Droplet microfluidic‐coupled X‐ray diffraction (DMC‐XRD) enables the collection of time‐resolved, serial diffraction patterns from a stream of flowing droplets containing growing crystals. The droplets offer reproducible reaction environments, and radiation damage is effectively eliminated by the short residence time of each droplet in the beam. DMC‐XRD is then used to identify effective particulate nucleating agents for calcium carbonate and to study their influence on the crystallization pathway. Bioactive glasses and a model material for mineral dust are shown to significantly lower the induction time, highlighting the importance of both surface chemistry and topography on the nucleating efficiency of a surface. This technology is also extremely versatile, and could be used to study dynamic reactions with a wide range of synchrotron‐based techniques.     

And Yet it Moves! Microfluidics Without Channels and Troughs

A simple, versatile, rapid, and inexpensive procedure based on the immersion method is developed to fabricate chemical gradients on chemically activated Si/SiO₂ surfaces by a trichloro (1H,1H,2H,2H‐perfluorooctyl) silane self‐assembly monolayer (SAM). Contact angle measurements, atomic force microscopy, and X‐ray photoelectron spectroscopy data based on the intensity of the signals of C1s and F1s, which progressively increase, indicate that the surface is characterized by the presence of increasing amounts of the SAM along the gradient direction. Experimental conditions are optimized by maximizing the variation of the contact angle of water drops at the starting and the ending points of the gradient. The application of the chemical gradient to droplet motion is demonstrated. The results are rationalized by dissipative particle dynamics simulations that well match the observed contact angles and the velocities of the drops. The simulations also show that the intrinsic nature of the gradient affects the velocity of the motion.     

基于微流体技术的FBAR微质量传感器

基于微机电系统(MEMS)技术的薄膜体声波谐振器(FBAR)在无线通讯领域取得了巨大的成功后,由于其具备厚度薄,体积小,与IC兼容及谐振频率和灵敏度都远高于传统的微质量传感器(如石英晶体微天平)等优势,逐渐在微生物分子检测方面崭露头角.由于微生物分子大都生存于液体环境,而纵波模式下FBAR微质量传感器在液体环境中声波损耗大,其品质因数Q值只有3.53.因此,该文在分析了纵波模式下FBAR微质量传感器在气相和液相环境中的特性后,针对液相环境中传感器Q值较低问题,设计了一种具有微通道的FBAR微质量传感器,使其Q值达到30.85,增加了近9倍,从而提升了纵波模式下FBAR微质量传感器对液体中微生物分子检测的性能.     

Microfluidics structures for probing the dynamic behaviour of filamentous fungi

Although filamentous fungi live in physically and chemically complex natural environments that require optimal survival strategies, both at colony and individual cell level, their growth dynamics are usually studied on homogenous media. This study proposes a new research methodology based on the purposeful design, fabrication and operation of microfluidics structures to examine the temporal and spatial responses of filamentous fungi. Two model fungal strains, the wild type of Neurospora crassa – a commonly used model organisms – and the ro-1 mutant strain of this species impaired in hyphal growth and morphology, have been chosen to demonstrate the potential of this new methodology. Time-lapse observations of both species show that filamentous fungi respond rapidly to the physically microstructured environment without any detectable temporal or spatial adjustment period. Despite their genetic differences, and consequently different growth behaviour, both strains present efficient space-search strategies enabling them to solve the microsized networks successfully and in similar periods, thus demonstrating that the space-searching algorithms are robust and mutation-independent. Additionally, the use of the proposed methodology could put in evidence new biological mechanisms responsible for the apical extension of filamentous fungi, beyond the classical theory based on the central role of Spitzenkörper.