Microfluidic Control Research Articles

Portable and integrated microfluidic flow control system using off-the-shelf components towards organs-on-chip applications

Organ-on-a-chip (OoC) devices require the precise control of various media. This is mostly done using several fluid control components, which are much larger than the typical OoC device and connected through fluidic tubing, i.e., the fluidic system is not integrated, which inhibits the system’s portability. Here, we explore the limits of fluidic system integration using off-the-shelf fluidic control components. A flow control configuration is proposed that uses a vacuum to generate a fluctuation-free flow and minimizes the number of components used in the system. 3D printing is used to fabricate a custom-designed platform box for mounting the chosen smallest footprint components. It provides flexibility in arranging the various components to create experiment-specific systems. A demonstrator system is realized for lung-on-a-chip experiments. The 3D-printed platform box is 290 mm long, 240 mm wide and 37 mm tall. After integrating all the components, it weighs 4.8 kg. The system comprises of a switch valve, flow and pressure controllers, and a vacuum pump to control the diverse media flows. The system generates liquid flow rates ranging from 1.5 upmuLmin^{-1} to 68 upmuLmin^{-1} in the cell chambers, and a cyclic vacuum of 280 mbar below atmospheric pressure with 0.5 Hz frequency in the side channels to induce mechanical strain on the cells-substrate. The components are modular for easy exchange. The battery operated platform box can be mounted on either upright or inverted microscopes and fits in a standard incubator. Overall, it is shown that a compact integrated and portable fluidic system for OoC experiments can be constructed using off-the-shelf components. For further down-scaling, the fluidic control components, like the pump, switch valves, and flow controllers, require significant miniaturization while having a wide flow rate range with high resolution.

Magnetically Actuated Superhydrophilic Robot Sphere Fabricated by a Femtosecond Laser for Droplet Steering.

Droplet steering has important applications in biomedical detection, local chemical reactions, liquid collection, and microfluidic control. Presently, droplet steering methods typically require specific paths and can be challenging to operate, involving complex fabrications for the operating systems. Here, we show a magnetically actuated superhydrophilic robot sphere (MSR) based on femtosecond laser direct writing technology for droplet steering. Through femtosecond laser treatment, uniform micro-/nanostructures are constructed on the surface of a MSR. Additionally, the contactless magnetic actuator makes it possible to remotely steer the MSR to transport droplets. After preliminary exploration of the mechanism by which MSR drives the droplet movement, the ability of MSR to control the droplet movement was systematically tested and analyzed. Moreover, the applications of the MSR in complex path liquid collection and transport, three-dimensional space transport, self-cleaning, etc., are further verified. This strategy provides a novel and reliable path for droplet manipulation and broadens its application.

Dynamic control of high-voltage actuator arrays by light-pattern projection on photoconductive switches

The ability to control high-voltage actuator arrays relies, to date, on expensive microelectronic processes or on individual wiring of each actuator to a single off-chip high-voltage switch. Here we present an alternative approach that uses on-chip photoconductive switches together with a light projection system to individually address high-voltage actuators. Each actuator is connected to one or more switches that are nominally OFF unless turned ON using direct light illumination. We selected hydrogenated amorphous silicon (a-Si:H) as our photoconductive material, and we provide a complete characterization of its light to dark conductance, breakdown field, and spectral response. The resulting switches are very robust, and we provide full details of their fabrication processes. We demonstrate that the switches can be integrated into different architectures to support both AC and DC-driven actuators and provide engineering guidelines for their functional design. To demonstrate the versatility of our approach, we demonstrate the use of the photoconductive switches in two distinctly different applications—control of µm-sized gate electrodes for patterning flow fields in a microfluidic chamber and control of cm-sized electrostatic actuators for creating mechanical deformations for haptic displays.

Inclination‐Enabled Generalized Microfluid Rectifiers via Anisotropic Slippery Hollow Tracks

The power of spontaneous maneuvering of microfluids that allow gas or liquid to penetrate along a single direction, is usually endowed with the wettability gradient and the Laplace pressure difference through tailoring special solid‒gas interfacial geographies. Herein, inspired by the structures on rice leaves and the slippery surfaces of the pitcher plant, anisotropic slippery hollow tracks (ASHTs) are fabricated and thus propose a class of unique inclination‐enabled bubble “diode”, on which one‐way bubble penetration can be reversibly switched on/off. The minimum transition tilt angle is subject to the tract spacing and the infused oil amount. The underlying mechanism of bubble penetration is attributed to the competition between the variable buoyancy component and the interfacial energy gradient perpendicular to the samples. A wide spectrum of generalized microfluid maneuvering capabilities is further demonstrated, including heavy oil selective penetration, underwater CO2 gas collection, and even dry/wet environment management in smart buildings, which are challenging for conventional counterparts. This framework should facilitate the development of microfluid control with favorable retainability and wide applicability in multiple fluids.

Real-Time Monitoring Platform for Ocular Drug Delivery.

Real-time measurement is important in modern dissolution testing to aid in parallel drug characterisation and quality control (QC). The development of a real-time monitoring platform (microfluidic system, a novel eye movement platform with temperature sensors and accelerometers and a concentration probe setup) in conjunction with an in vitro model of the human eye (PK-Eye™) is reported. The importance of surface membrane permeability when modelling the PK-Eye™ was determined with a "pursing model" (a simplified setup of the hyaloid membrane). Parallel microfluidic control of PK-Eye™ models from a single source of pressure was performed with a ratio of 1:6 (pressure source:models) demonstrating scalability and reproducibility of pressure-flow data. Pore size and exposed surface area helped obtain a physiological range of intraocular pressure (IOP) within the models, demonstrating the need to reproduce in vitro dimensions as closely as possible to the real eye. Variation of aqueous humour flow rate throughout the day was demonstrated with a developed circadian rhythm program. Capabilities of different eye movements were programmed and achieved with an in-house eye movement platform. A concentration probe recorded the real-time concentration monitoring of injected albumin-conjugated Alexa Fluor 488 (Alexa albumin), which displayed constant release profiles. These results demonstrate the possibility of real-time monitoring of a pharmaceutical model for preclinical testing of ocular formulations.

Homogeneous, heterogeneous, and enzyme catalysis in microfluidics droplets

AbstractMicrofluidics has received extensive attention due to its ability to rapidly prepare a large number of microdroplets with controlled sizes and defined morphologies. In addition to having large surface areas and controllable confinement environments, these prepared microdroplets can be used as analytical detection devices to screen and optimize various kinetic parameters. This review summarizes recent advances in the microfluidic control of droplet‐based catalytic reactions and discusses the role of these droplets in both homogeneous and heterogeneous catalyzes and in the catalysis of macromolecular biological enzymes in water‐in‐oil and oil‐in‐oil environments. Additionally, the existing problems and future development directions of droplets in catalysis are highlighted to promote the development of catalytic reactions in droplet media and provide guidance for the high‐throughput screening of catalysts and the directed evolution of biological enzymes.

Development of a 3D printed micro simulated moving bed chromatography system

In the 1960s, chromatography processes were revolutionized by the invention of simulated moving bed chromatography. This method not only enhances the separation performance and resin utilization in comparison to batch-chromatography, it has also a much lower buffer consumption. While simulated moving bed chromatography nowadays is applied for a wide range of industrial applications, it was never transferred to the micro-scale (in regards to column and system volume). In our opinion a micro simulated moving bed chromatography system (µSMB) would be a useful tool for many applications, ranging from early process development and long term studies to downstream processing of speciality products. We implemented such a µSMB with a 3D printed central rotary valve and a microfluidic flow controller as flow source. We tested the system with a four zone open loop setup for the separation of bovine serum albumin and ammonium sulfate with size exclusion chromatography. We used four process points and could achieve desalting levels of BSA ranging from 94% to 99%, with yields ranging form 65% to 88%. Thus, we were able to achieve comparable results to common lab scale processes. With a total dead volume of 358 µL, including all sensors, connections and the valve, this is, to the best of our knowledge, the smallest SMB system that was ever built and we were able to perform experiments with feed flow rates reaching as low as 15 µL/min.

Development of a Marine Particles Analysis System by Electromagnetophoresis and Microfluidic Control

マイクロ流体デバイスを用いて，電磁泳動法に基づき液中に存在するプランクトンの特徴に応じて分離可能なシステムを開発した．プランクトンの異常増殖は赤潮等の公衆衛生上の問題や水産業への被害を引き起こすため，プランクトンの状態をその場で即時検査可能な小型システムは本課題の解決に大変有効である．本研究では，磁場と電流を互いに直交方向に印加した際に生じる電磁泳動とマイクロ流体デバイスを組み合わせることで，微粒子状の植物性プランクトンなど微生物を粒子径に応じて電磁泳動力が強まる現象を利用して分離可能なシステムを開発した．本システムは泳動距離及び泳動速度を画像解析によって計測することで，微生物のキャラクタリゼーションを行うことが可能である．作成したシステムを用いて，微粒子状円石藻類プランクトンであるプレウロクリシスを粒子径10 μmから50 μmの範囲で粒子のサイズ分離を行い，サイズごとの泳動距離及び泳動速度から微生物の高効率な分離を実現できる可能性が示された．

A three-dimensional numerical scheme for modeling discontinuous pinning at sharp edges using the Volume-of-Fluid method

We present a novel three-dimensional (3D) numerical scheme for modeling the discontinuous contact line pinning along sharp straight edges. The proposed scheme is devised for multi-phase flow solvers that rely on the Volume-of-Fluid (VOF) method, although its fundamental concepts can be extended and applied to other methods. Following the Piecewise-Linear-Interface-Construction (PLIC) approach in VOF, the discontinuous pinning is modeled by adjusting the orientation of PLIC polygons located near a sharp edge according to the pinning stage. That is achieved by solving a root-finding problem and using a 3D geometrical toolbox, where the advancing contact angle determines critical volume fractions in numerical cells neighboring the sharp edge. Implementing the proposed scheme in our multi-phase flow solver, we assessed its performance using several test cases where contact line pinning effects dominate. To demonstrate the scheme's efficacy, we present quantitative comparisons of our results at various grid resolutions and with a theoretical study. Furthermore, we show quantitatively that without a numerical treatment of contact line pinning, the simulation results will be drastically different. Contact line pinning plays a critical role in several technologies including separation, lithography, lens fabrication, micro-fluidic flow control among numerous others. The proposed scheme will help to accurately capture the pinning effects in computational simulations of such applications.

Transmission Enhancement through Sub-Wavelength Aperture Based on Regulable Water-Based Metamaterial

A realization form of the Mie resonance with adjustable characteristics based on a water-based metamaterial is proposed. A novel local electromagnetic field coupling mechanism based on a water-based metamaterial is established, which is used for transmission enhancement through the sub-wavelength aperture for the first time. The water-based metamaterial particle for transmission enhancement at a specific frequency is designed. By designing the microfluidic control system to control the water filling (i.e., height) of the metamaterial particle, the adjustable transmission enhancement characteristics are realized. The influence of bilateral symmetry and flexible deformation of the metamaterial particle on the transmission characteristics is analyzed. The influence of the design parameters on the enhanced transmission characteristics is discussed.

Integrating microneedle DNA extraction to hand-held microfluidic colorimetric LAMP chip system for meat adulteration detection

Most microfluidic-based “sample-in-result-out” systems suffer sophisticated microfluidic production processes, high-cost chips, and expensive instruments. They cannot be used in the meat market as well as farmer's markets in rural areas. Here, we developed a hand-held microfluidic chip system for on-site meat species qualitative authentication detection which integrated a simple microneedle DNA extraction and a visual loop-mediated isothermal amplification (LAMP). The chip can be used by easily pricking meat samples, simply hand-shaking the chip, and readily available isothermal heating instead of a complicated DNA extraction process and microfluidic control device. The system demonstrates high specificity and sensitivity for selected six species of meat samples and low to 1% simulated adulteration could be detected within 60 min. Besides, the whole cost was less than 1 dollar. The integrated hand-held microfluidic detection system offers a simple, fast, low-cost “sample-in-result-out” point-of-care device which could be extended to medical diagnosis and animal/plant disease identification.

Microfluidic Actuated and Controlled Systems and Application for Lab-on-Chip in Space Life Science

The use of space environment to carry out life science research is of great significance. However, there are limitations in complex manipulation, research models based on mammalian and 2-dimensional cell culture experiments, etc. Microfluidic chips possess the characteristics of integrating the relevant functions of traditional laboratories into micron-scale chips, with low energy consumption, high throughput, and automation. The application of microfluidic chips can overcome the challenges of space environments, the scarce experimental resources, and the unmanned operation problems to some extent. Moreover, microfluidic chips can realize long-term experimental operation and remote data recording and transmission. To carry out related research with microfluidic chips, the actuation and control of microfluidics are very important. In this paper, the microfluidic actuated and controlled technologies in microfluidic chips are reviewed, and then the application of microfluidic chips and microfluidic actuated and controlled systems in space life science is also briefly described.

Femtosecond-laser-patterned origami Janus membrane toward enhanced water fog harvesting.

Fog harvesting is an effective way to relieve water shortages in arid regions; thus, improving the efficiency of fog harvesting is urgently needed for both academic research and practical applications. Here, we report an origami patterned Janus (O-P-Janus) membrane using laser-ablated copper foams inspired by origami handcraft and traditional Chinese architecture. Compared to the planar fully ablated Janus membrane, our O-P-Janus membrane, with selectively ablated rectangular areas, exhibits an exceptional water collection rate (WCR) of approximately 267%. The underlying physical mechanism of WCR enhancement is revealed and attributed to the enhanced fog adsorbing capacity on the upper superhydrophobic origami structures and the accelerated removal of accumulated droplets beneath the lower superhydrophilic V-shaped tips. This O-P-Janus membrane with excellent fog collection performance should open up a new avenue for both device designs and potential applications toward structuring-enhanced fog collection and microfluidic control platforms.

Microfluid control method by vibrating multiple bubbles

Microfluid control method by vibrating multiple bubbles

Research progress of physics of electrowetting display devices

Electrowetting refers to the phenomenon of modifying the surface tension between a liquid and a solid by adjusting the externally applied electric potential between the liquid and solid electrodes, thereby changing the contact angle between the two and causing a deformation and displacement of the droplets. Electrowetting electronic paper display is a new reflective “paper-like” display technology based on a rapid response microfluidic control technology. It has the advantages of low energy consumption, visual health, and flexibility of commercial electrophoretic electronic paper display products, while breaking through the bottlenecks of “full-color” and “video-speed response” that currently restrict the application of electronic paper display technology. In this paper, several physical directions involved in electrowetting display devices, especially wetting and electrowetting, binary phase fluid mechanics, microscopic and interfacial physics, photophysics, dielectric physics, thermophysics, and transient physics, are systematically reviewed; the basic principles of device operation, microscopic and mesoscopic physical pictures, internal mechanisms of device operation, and device reliability are also discussed in detail.

Millifluidic valves and pumps made of tape and plastic.

There is growing interest in producing micro- and milli-fluidic technologies made of thermoplastic with integrated fluidic control elements that are easy to assemble and suitable for mass production. Here, we developed millifluidic valves and pumps made of acrylic layers bonded with double-sided tape that are simple and fast to assemble. We demonstrate that a layer of pressure-sensitive adhesive (PSA) is flexible enough to be deformed at relatively low pressures. A chemical treatment deposited on specific regions of the PSA prevents it from sticking to the thermoplastic, which enabled us to create three different types of valves in normally open or closed configurations. We characterized different aspects of their performance, their operating pressures, the cut-off pressure values to open or close the valves (for different configurations and sizes), and the flow rate and volume pumped by seven different micropumps. As an application, we implemented a glucose assay with integrated pumps and valves, automatically generating glucose dilutions and reagent mixing. The ability to create polymeric microfluidic control units made with tape paves the way for their mass manufacturing.

Broadband silicon-based tunable metamaterial microfluidic sensor

Tunable metamaterial absorbers play an important role in terahertz imaging and detection. We propose a multifunctional metamaterial absorber based on doped silicon. By introducing resonance and impedance matching into the absorber, a broadband absorption greater than 90% in the range of 0.8–10 THz is achieved. At the same time, the light regulation characteristics of the doped semiconductor are introduced into the absorber, and the precise amplitude control can be achieved in the range of 0.1–1.2 THz by changing the pump luminous flux. In addition, based on the principle of light-regulating the concentration of doped silicon carriers, the medium-doped silicon material is replaced by a highly doped silicon material, and a sensor with a sensitivity of up to 500 GHz/RIU is realized by combining the wave absorber with the microfluidic control. Finally, the broadband absorption characteristics and sensing performance of alcohol and water on the prepared device are verified by experiments, indicating that the absorber may have great potential in the field of sensor detection.

Fouling‐Proof Cooling (FP‐Cool) Fabric Hybrid with Enhanced Sweat‐Elimination and Heat‐Dissipation for Personal Thermal Regulation

AbstractPassive cooling fabric that facilitates sweat‐wicking and evaporation is highly desirable for promoting human body's thermal comfort and reducing energy consumption. However, highly hydrophilic sweat‐wicking fabric fails to repel external fouling due to the contradiction between hydrophilicity and lyophobicity. Moreover, conventional passive cooling fabrics show limited evaporation capacity when they reach the adsorption limit in intense perspiration scenarios. Herein, a fouling‐proof cooling (FP‐Cool) fabric with an interactive functional structure design for highly‐efficient personal thermal regulation is proposed by constructing spatially distributed superoleophobic Janus channels on an optimized heat conductive superomniphobic fabric. The dominant superomniphobicity and superoleophobic Janus feature endow the outer FP‐Cool fabric with durable performance (up to 3000 cycles’ abrasion) to repel oil/water‐based contaminations. The Janus channels rapidly pull sweat out of the inner fabric for efficient evaporation, ensuring a dry sense of skin. The FP‐Cool fabric preserves 40% higher thermal conductivity, and over 50% higher evaporation rate than conventional fabrics. In the sweat evaporation test, the FP‐Cool fabric shows up to 100% reduction in sweat gain ratio to cotton fabric. The concept would have implications for intelligent textiles design, and the synthesis strategy can be applied in various applications such as oil‐water separation and microfluidics control.

Test Article for automation purposes.

Digital recombinase polymerase amplification (dRPA) aims to quantify the initial amount of nucleic acid by dividing nucleic acid and all reagents required for the RPA reaction evenly into numerous individual reaction units, such as chambers or droplets. dRPA turns out to be a prominent technique for quantifying the absolute quantity of target nucleic acid because of its advantages including low equipment requirements, short time consumption, as well as high sensitivity and specificity. dRPA combined with microfluidics are recognized as simple, various, and high-throughput nucleic acid quantization systems. This paper classifies the microfluidic dRPA systems over the last decade. We analyze and summarize the vital technologies of various microfluidic dRPA systems (e.g., chip preparation process, segmentation principle, microfluidic control, and statistical analysis methods), and major efforts to address limitations (e.g., prevention of evaporation and contamination, accurate initiation, and reduction of manual operation). In addition, this paper summarizes key factors and potential constraints to the success of the microfluidic dRPA to help more researchers, and possible strategies to overcome the mentioned challenges. Lastly, actual suggestions and strategies are proposed for the subsequent development of microfluidic dRPA.

Multimodal collective swimming of magnetically articulated modular nanocomposite robots

Magnetically responsive composites can impart maneuverability to miniaturized robots. However, collective actuation of these composite robots has rarely been achieved, although conducting cooperative tasks is a promising strategy for accomplishing difficult missions with a single robot. Here, we report multimodal collective swimming of ternary-nanocomposite-based magnetic robots capable of on-demand switching between rectilinear translational swimming and rotational swimming. The nanocomposite robots comprise a stiff yet lightweight carbon nanotube yarn (CNTY) framework surrounded by a magnetic polymer composite, which mimics the hierarchical architecture of musculoskeletal systems, yielding magnetically articulated multiple robots with an agile above-water swimmability (~180 body lengths per second) and modularity. The multiple robots with multimodal swimming facilitate the generation and regulation of vortices, enabling novel vortex-induced transportation of thousands of floating microparticles and heavy semi-submerged cargos. The controllable collective actuation of these biomimetic nanocomposite robots can lead to versatile robotic functions, including microplastic removal, microfluidic vortex control, and transportation of pharmaceuticals.