Microfluidic operations using deformable polymer membranes fabricated by single layer soft lithography

We show that it is possible to use single layer soft lithography to create deformable polymer membranes within microfluidic chips for performing a variety of microfluidic operations. Single layer microfluidic chips were designed, fabricated, and characterized to demonstrate pumping, sorting, and mixing. Flow rates as high as 0.39 microl min(-1) were obtained by peristaltic pumping using pneumatically-actuated membrane devices. Sorting was attained via pneumatic actuation of membrane units placed alongside the branch channels. An active mixer was also demonstrated using single-layer deformable membrane units.     

Fabrication of silver-coated silica microspheres through mussel-inspired surface functionalization

This paper reports a droplet-based microfluidic device composed of patterned co-planar electrodes in an all-in-a-single-plate arrangement and coated with dielectric layers for electrowetting-on-dielectric (EWOD) actuation of discrete droplets. The co-planar arrangement is preferred over conventional two-plate electrowetting devices because it provides simpler manufacturing process, reduced viscous drag, and easier liquid-handling procedures. These advantages lead to more versatile and efficient microfluidic devices capable of generating higher droplet speed and can incorporate various other droplet manipulation functions into the system for biological, sensing, and other microfluidic applications. We have designed, fabricated, and tested the devices using an insulating layer with materials having relatively high dielectric constant (SiO(2)) and compared the results with polymer coatings (Cytop) with low dielectric constant. Results show that the device with high dielectric layer generates more reproducible droplet transfer over a longer distance with a 25% reduction in the actuation voltage with respect to the polymer coatings, leading to more energy efficient microfluidic applications. We can generate droplet speeds as high as 26 cm/s using materials with high dielectric constant such as SiO(2).     

响应性交联液晶高分子仿生致动器的研究进展

交联液晶高分子兼具液晶取向有序性和交联聚合物熵弹性等特点,能够以动态可调节和可逆的方式来模仿生物体的行为,在仿生器件、柔性机器人、智能表面、生物医药等领域具有良好的应用前景.本综述总结了近几年智能响应性交联液晶高分子在仿生致动器方面的研究进展,从响应性交联液晶高分子的结构和驱动机理出发,讨论了响应性交联液晶高分子的合成工艺、制备技术和成型方法,以及响应性交联液晶高分子对光、热、磁、湿度的响应.此外,介绍了响应性交联液晶高分子致动器在柔性机器人、人工肌肉、微流体运输等领域的应用.最后,对响应性交联液晶高分子的发展前景进行了展望.这项工作主要讨论了响应性交联液晶高分子,旨在为具有新颖功能和更有挑战性的智能微型致动器提供新的设计思路.     

Conducting polymers in redox devices and intelligent materials systems

Applications opportunities are described for conducting polymer devices, including (1) batteries and redox capacitors, (2) electromechanical actuators, (3) electrochromic windows and displays, (4) chemical separation and chemical delivery systems, and (5) indicators and sensors. Each of these potential application areas depends upon the dramatic property changes which occur during chemical or electrochemical doping. Since the properties profiles of conducting polymers can be reversibly changed either chemically or electrochemically, these polymers also provide exciting candidates for intelligent materials systems - where sensor, logic element, and actuator functions can be either partially or fully integrated. Results of device and properties investigations are used to evaluate future possibilities for conducting polymers in intelligent material systems.     

Wireless Electrochemical Actuation of Conducting Polymers

Electrochemical actuation of conducting polymers usually requires a direct connection to an electric power supply. In this contribution, we suggest to overcome this issue by using the concept of bipolar electrochemistry. This allows changing the oxidation state of the polymer in a gradual and wireless way. Free‐standing polypyrrole films were synthesized with an intrinsic morphological asymmetry of their two faces in order to form a bilayer structure. Immersing such objects in an electrolyte solution and exposing them to a potential gradient leads to the asymmetric oxidation/reduction of the polymer, resulting in differential shrinking and swelling along the main axis. This additional asymmetry is responsible for a structural deformation. Optimization allowed highly efficient bending, which is expected to open up completely new directions in the field of actuation due to the wireless mode of action.     

Cholera toxin subunit B detection in microfluidic devices

Fluorescence and electrochemical microfluidic biosensors were developed for the detection of cholera toxin subunit B (CTB) as a model analyte. The microfluidic devices were made from polydimethylsiloxane (PDMS) using soft lithography from silicon templates. The polymer channels were sealed with a glass plate and packaged in a polymethylmethacrylate housing that provided leakproof sealing and a connection to a syringe pump. In the electrochemical format, an interdigitated ultramicroelectrode array (IDUA) was patterned onto the glass slide using photolithography, gold evaporation and lift-off processes. For CTB recognition, CTB-specific antibodies were immobilized onto superparamagnetic beads and ganglioside GM₁ was incorporated into liposomes. The fluorescence dye sulforhodamine B (SRB) and the electroactive compounds potassium hexacyanoferrate (II)/hexacyanoferrate (III) were used as detection markers that were encapsulated inside the liposomes for the fluorescence and electrochemical detection formats, respectively. Initial optimization experiments were carried out by applying the superparamagnetic beads in microtiter plate assays and SRB liposomes before they were transferred to the microfluidic systems. The limits of detection (LoD) of both assay formats for CTB were found to be 6.6 and 1.0 ng mL⁻¹ for the fluorescence and electrochemical formats, respectively. Changing the detection system was very easy, requiring only the synthesis of different marker-encapsulating liposomes, as well as the exchange of the detection unit. It was found that, in addition to a lower LoD, the electrochemical format assay showed advantages over the fluorescence format in terms of flexibility and reliability of signal recording.     

Thermoplastic Dielectric Elastomer of Triblock Copolymer with High Electromechanical Performance

Dielectric elastomer (DE) actuators have been shown to have promising applications as soft electromechanical transducers in many emerging technologies. The DE actuators, which are capable of large actuation strain over a wide range of excitation frequencies, are highly desirable. Here, the first single‐component DE of a triblock copolymer with attractive electromechanical performance is reported. Symmetric poly(styrene‐b‐butyl acrylate‐b‐styrene) (SBAS) is designed and synthesized. The SBAS actuator exhibits about 100% static actuation area strain and excellent dynamic performance, as evidenced by a wide half bandwidth of 300 Hz and a very high specific power of 1.2 W g^–1 within the excitation frequency range of 300–800 Hz.     

In situ growth of interdigitated electrodes made of polypyrrole for active fiber composites

Active fiber composites are electromechanical actuators based on piezo-ceramic fibers, which are embedded in a polymer matrix. The fibers are electrically contacted through so-called interdigitated electrodes (IDEs). State-of-the-art metallic IDEs only contact the fibers at two small sections of their circumference at the top and bottom of the composite ply, respectively. This paper presents an original technique to manufacture IDEs made of a conducting polymer (polypyrrole/p-toluene sulfonic acid), where the polymer electrodes contact the fibers around their whole circumference. The necessary process steps are discussed, namely design of the master electrodes and electrochemical polymer growth with and without fibers. Processing issues are discussed and solutions are suggested. Copyright © 2007 John Wiley & Sons, Ltd.     

Electrolysis-reducing electrodes for electrokinetic devices

Direct current electrokinetic systems generally require Faradaic reactions to occur at a pair of electrodes to maintain an electric field in an electrolyte connecting them. The vast majority of such systems, e.g. electrophoretic separations (capillary electrophoresis) or electroosmotic pumps (EOPs), employ electrolysis of the solvent in these reactions. In many cases, the electrolytic products, such as H+ and OH? in the case of water, can negatively influence the chemical or biological species being transported or separated, and gaseous products such as O? and H? can break the electrochemical circuit in microfluidic devices. This article presents an EOP that employs the oxidation/reduction of the conjugated polymer poly(3,4-ethylenedioxythiophene), rather than electrolysis of a solvent, to drive flow in a capillary. Devices made with poly(3,4-ethylenedioxythiophene) electrodes are compared with devices made with Pt electrodes in terms of flow and local pH change at the electrodes. Furthermore, we demonstrate that flow is driven for applied potentials under 2?V, and the electrodes are stable for potentials of at least 100?V. Electrochemically active electrodes like those presented here minimize the disadvantage of integrated EOP in, e.g. lab-on-a-chip applications, and may open new possibilities, especially for battery-powered disposable point-of-care devices.     

Multilayer soft lithography of perfluoropolyether based elastomer for microfluidic device fabrication

The compatibility of microfluidic devices with solvents and other chemicals is extremely important for many applications such as organic synthesis in microreactors and drug screening. We report the successful fabrication of microfluidic devices from a novel perfluoropolyether based polymer utilizing the Multilayer Soft Lithography? (MSL) technique with simple, straightforward processing. The perfluorinated polymer SIFEL X-71 8115 is a highly chemically resistant elastomeric material. We demonstrate fabrication of a microfluidic device using an off-ratio bonding technique to bond multiple SIFEL layers, each patterned lithographically. The mechanical properties of the SIFEL MSL valves (including actuation pressures) are similar to PDMS MSL valves of the same geometry. Chemical compatibility tests highlight SIFEL's remarkable resistance to organic solvents, acids and alkalis.     

本征导电聚合物的智能性

在化学掺杂或电化学掺杂过程中，性质发生可逆性变化的本征导电聚合物是一种潜在的智能材料，可望实现或部分实现传感、处理和执竽功能，适于制成电机执行器、智能窗、化学分离与释放体系、传感器和非线性光学器件等。     

Wireless Coupling of Conducting Polymer Actuators with Light Emission

Combining the actuation of conducting polymers with additional functionalities is an interesting fundamental scientific challenge and increases their application potential. Herein we demonstrate the possibility of direct integration of a miniaturized light emitting diode (LED) in a polypyrrole (PPy) matrix in order to achieve simultaneous wireless actuation and light emission. A light emitting diode is used as a part of an electroactive surface on which electrochemical polymerization allows direct incorporation of the electronic device into the polymer. The resulting free-standing polymer/LED hybrid can be addressed by bipolar electrochemistry to trigger simultaneously oxidation and reduction reactions at its opposite extremities, leading to a controlled deformation and an electron flow through the integrated LED. Such a dual response in the form of actuation and light emission opens up interesting perspectives in the field of microrobotics.     

Microfluidic Device： A Miniaturized Platform for Chemical Reactions

Microfluidic devices, as a new miniaturized platform stemming from the field of micro-electromechanical sys-tems, have been used in many disciplines. In the field of chemical reactions, microfluidic device-based microreac-tors have shown great promise in building new chemical technologies and processes with increased speed and reli- ability and reduced sample consumption and cost. This technology has also become a new and effective tool for precise, high-throughput, and automatic analysis of chemical synthesis processes. Compared with conventional chemical laboratory batch methodologies, microfluidic reactors have a number of features, such as high mixing ef- ficiency, short reaction time, high heat-transfer coefficient, small reactant volume, controllable residence time, and high surface-to-volume ratio, among others. Combined with recent advances in microfluidic devices for chemical reactions, this review aims to give an overview of the features and applications of microfluidic devices in the field of chemical synthesis. It also aims to stimulate the development of microfluidic device applications in the field of chemical reactions.     

Influence of Plasticizers on the Electromechanical Behavior of a P(VDF‐TrFE‐CTFE) Terpolymer: Toward a High Performance of Electrostrictive Blends

This work aims at providing a complete analysis of the effect of plasticizers on the electrostrictive terpolymer performance. To achieve this, several plasticizing agents such as 2‐ethylhexyl phtalate (DEHP), diisononyl phtalate (DINP), and palamoll 652 have been incorporated in the polymer matrix. Experimental results demonstrate that the proposed novel materials exhibited excellent electromechanical enhancement in terms of transverse strain and mechanical energy density under a moderate electric field, which is definitively critical in recent microscale actuation. Another objective of this article was to explore material characteristics as a function of the DINP content, and it was found that the plasticizer weigh fraction was the key parameter determining performance of the modified fluorinate terpolymer blends. Accordingly, it was revealed that high performance flexible actuators can be achieved merely by employing a simple and cheap plasticizer, thus making it possible to overcome the current technological barrier of conventional electroactive polymers that suffer from the high applied electric field usually required to reach sufficient strain. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 355–369     

Characterisation of torsional actuation in highly twisted yarns and fibres

Highly twisted oriented polymer fibres and carbon nanotube yarns show large scale torsional actuation from volume expansion that can be induced, for example, thermally or by electrochemical charging. When formed into spring-like coils, the torsional actuation within the fibre or yarn generates powerful tensile actuation per muscle weight. For further development of these coil actuators and for the practical application of torsional actuators, it is important to standardise methods for characterising both the torsional stroke (rotation) and torque generated. By analogy with tensile actuators, we here introduce a method to measure both the free stroke and blocked torque in a one-end-tethered fibre. In addition, the torsional actuation can be measured when operating against an externally applied torque (isotonic) and actuation against a return spring fibre (variable torque). A theoretical treatment of torsional actuation was formulated using torsion mechanics and evaluated using a commercially available highly-oriented polyamide fibre. Good agreement between experimental measurements and calculated values was obtained. The analysis allows the prediction of torsional stroke under any external loading condition based on the fundamental characteristics of the actuator: free stroke and stiffness.     

Integrated electrofluidic circuits: pressure sensing with analog and digital operation functionalities for microfluidics

Microfluidic technology plays an essential role in various lab on a chip devices due to its desired advantages. An automated microfluidic system integrated with actuators and sensors can further achieve better controllability. A number of microfluidic actuation schemes have been well developed. In contrast, most of the existing sensing methods still heavily rely on optical observations and external transducers, which have drawbacks including: costly instrumentation, professional operation, tedious interfacing, and difficulties of scaling up and further signal processing. This paper reports the concept of electrofluidic circuits - electrical circuits which are constructed using ionic liquid (IL)-filled fluidic channels. The developed electrofluidic circuits can be fabricated using a well-developed multi-layer soft lithography (MSL) process with polydimethylsiloxane (PDMS) microfluidic channels. Electrofluidic circuits allow seamless integration of pressure sensors with analog and digital operation functions into microfluidic systems and provide electrical readouts for further signal processing. In the experiments, the analog operation device is constructed based on electrofluidic Wheatstone bridge circuits with electrical outputs of the addition and subtraction results of the applied pressures. The digital operation (AND, OR, and XOR) devices are constructed using the electrofluidic pressure controlled switches, and output electrical signals of digital operations of the applied pressures. The experimental results demonstrate the designed functions for analog and digital operations of applied pressures are successfully achieved using the developed electrofluidic circuits, making them promising to develop integrated microfluidic systems with capabilities of precise pressure monitoring and further feedback control for advanced lab on a chip applications.     

Electrochemical fabrication of conducting polymer nanowires in an integrated microfluidic system

In this paper, we introduce a new approach for the in situ electrochemical fabrication of an individually addressable array of conducting polymer nanowires (CPNWs) positioned within an integrated microfluidic device and also demonstrate that such an integrated device can be used as a chemical sensor immediately after its construction.     

A micro-spherical heart pump powered by cultured cardiomyocytes

Miniaturization of chemical or biochemical systems creates extremely efficient devices exploiting the advantages of microspaces. Although they are often targeted for implanted tissue engineered organs or drug-delivery devices because of their highly integrated systems, microfluidic devices are usually powered by external energy sources and therefore difficult to be used in vivo. A microfluidic device powered without the need for external energy sources or stimuli is needed. Previously, we demonstrated the concept of a cardiomyocyte pump using only chemical energy input to cells as a driver (Yo Tanaka, Keisuke Morishima, Tatsuya Shimizu, Akihiko Kikuchi, Masayuki Yamato, Teruo Okano and Takehiko Kitamori, Lab Chip, 6(3), pp. 362-368). However, the structure of this prototype pump described there included complicated mechanical components and fabricated compartments. Here, we have created a micro-spherical heart-like pump powered by spontaneously contracting cardiomyocyte sheets driven without a need for external energy sources or coupled stimuli. This device was fabricated by wrapping a beating cardiomyocyte sheet exhibiting large contractile forces around a fabricated hollow elastomeric sphere (5 mm diameter, 250 microm polymer thickness) fixed with inlet and outlet ports. Fluid oscillations in a capillary connected to the hollow sphere induced by the synchronously pulsating cardiomyocyte sheet were confirmed, and the device continually worked for at least 5 days in this system. This bio/artificial hybrid fluidic pump device is innovative not only because it is driven by cells using only chemical energy input, but also because the design is an optimum structure (sphere). We anticipate that this device might be applied for various purposes including a bio-actuator for medical implant devices that relies on biochemical energy, not electrical interfacing.     

Graphene actuators: quantum-mechanical and electrostatic double-layer effects

The electrochemical actuation of covalent carbon materials, such as graphene, immersed in liquid electrolytes has shown immense promise for a myriad of applications. To realize this potential, an intimate understanding of the physics behind the actuation is essential. With the use of ab initio density functional calculations, it is shown that the strain induced in monolayer graphene by the formation of an electrostatic double-layer (DL) is the dominant actuation mechanism. The DL-induced strain (~1%) is found to exceed the quantum-mechanical strain (~0.2%) due to charge injection only, for charges and electric potentials of greater than -0.08 e/C-atom and 1 V, respectively. Various methods of calculating the graphene atomic charges based on first principle charge densities are compared and contrasted. The electrochemical charge-strain and potential-strain relationships for monolayer graphene are shown to be parabolic in nature. This study proves that the origin of the high electrochemical strains in covalent carbon materials is the electrostatic DL potential, and demonstrates the true viability of using monolayer graphene for nanoelectromechanical systems (NEMS) actuators.