This work was sponsored by the National Natural Science Foundation of China (51375176); the Guangdong Provincial Natural Science Foundation of China (2014A030313264); and the Science and Technology Planning Project of Guangdong Province, China (2014B010126003).

Caution: Please consult all relevant material safety data sheets (MSDS) before use. Acetone is highly flammable and can cause irritation to the eyes and respiratory tract. The voltage involved is as high as several thousand volts; hence, electrical sparks are expected when conducting the experiment. Carry out the experiments in a room with good ventilation to avoid explosions and fire from the sparks.
1. Fabrication of the Plates and Holder
NOTE: In this work, the electrode plates and holder are fabricated by a production line in a factory. Only the material and the parameters of all parts in this paper will be introduced due to the complicated processes.
<ol>
	<li>Material and size of the electrode plate
	<ol>
		<li>Fabricate the electrode plates using 1.4 mm FR-4 CCL with a thin copper layer of 35 &#181;m. See Figure 1 for detailed parameters of the electrode plate.</li>
	</ol>
	</li>
	<li>Parameters of the electrodes
	<ol>
		<li>Order the electrode plates from the factory. See Figure 2 for more details.</li>
	</ol>
	</li>
	<li>Inspection of the electrode plate
	<ol>
		<li>After the preparation of the electrode plate, use an electron microscope to inspect the electrodes for any noticeable flaws under 100X and 300X magnification. Note that any tiny defects on the surface of the electrodes can cause short-circuiting, as shown in Figure 3.</li>
		<li>Inspect and measure the electrode width and spacing to determine whether the dimension accuracy meets the requirement.</li>
		<li>Test the plate with an amperemeter to see if an electrical short-circuit occurs.</li>
	</ol>
	</li>
	<li>Preparation of the chamber plate
	<ol>
		<li>Cut some silicone membrane to the same size as the electrode plate, as shown in Figure 4. Choose silicone membranes with different thicknesses to make chamber plates with different heights.</li>
		<li>Use a special punching tool to punch the chamber hole, as shown in Figure 5.</li>
	</ol>
	</li>
	<li>Processing of the holder
	<ol>
		<li>Order the holder from a factory. The detailed parameters are shown in Figure 6.</li>
	</ol>
	</li>
	<li>Fabrication of the cover plate
	<ol>
		<li>Drill two holes on the top of the cover plate using a drilling machine to install the inlet and outlet tubes. See Figure 7 for their positions and sizes.</li>
	</ol>
	</li>
</ol>
2. Assembly of the Micropump
<ol>
	<li>Use acetone to wash all the plates, the holder, the inlet and outlet tubes, and other tools used in the experiments. Put these tools and plates inside a beaker and then pour enough 99.5% acetone to immerse them. Put the beaker inside the ultrasonic washer. Turn on the ultrasonic washer and set the timer to 5 min.</li>
	<li>Insert the inlet and outlet stainless-steel tubes into the two holes on the cover plate.</li>
	<li>Place a chamber plate made of silicone membrane on the electrode plate and then cover it with the cover plate.</li>
	<li>Stack and align the cover plate, the chamber plate, and the electrode plate from top to bottom and insert the aligned plates into the holder.
	<ol>
		<li>Use an M5 bolt to fix the plates inside the holder. See the explosion view and normal view of the assembled micropump, as shown in Figure 8 and Figure 9, respectively.</li>
		<li>Press the plates together by tightening the bolts. 
		NOTE: The tubes and the cavity on the chamber plate will form a passage for the working liquid. The elastic chamber plate can also seal off the gap between plates to prevent liquid from flowing out. See the explosion view and the normal view of the assembled micropump in Figure 8 and Figure 9, respectively.</li>
	</ol>
	</li>
	<li>Use two polyurethane hoses with external diameters of 4 mm and internal diameters of 2 mm to connect the inlet and outlet stainless-steel tubes.</li>
	<li>Connect an amperemeter, a 500 V DC power source, and the micropump in series. Insert a 1 mA fuse between the amperemeter and the power source to protect the amperemeter in case the micropump is shorted.</li>
	<li>Insert the inlet hose into a 50 mL beaker with 20-30 mL of acetone inside. 
	NOTE: Figure 10 shows the completed platform.</li>
</ol>
3. Experimental Procedure
<ol>
	<li>Preparatory work before the experiment
	<ol>
		<li>Use a cylinder to inject acetone to fill up the micropump. After the liquid level reaches the outlet hose, continue to inject 10 mL of acetone inside until all bubbles are pushed away from the chamber. 
		NOTE: It is impossible to see if there are any bubbles left inside the chamber because the cover plate and the electrode plate are not transparent. Continuously injecting acetone helps to remove bubbles, but it cannot guarantee that no bubbles are left inside the micropump. Bubbles may block the passage of liquid, or they may short the circuits and cause a micro-explosion inside the micropump, which will burn the electrodes. The effect of bubbles on the pump operation is not totally clear yet, but the breakdowns they cause have been observed several times.</li>
		<li>Pour 20-30 mL of acetone into the beaker and put the inlet hose inside the beaker. Ensure that the liquid level is at least 5 mm higher than the inlet so that acetone can flow into the pump and no air can be sucked into the micropump chamber.</li>
	</ol>
	</li>
	<li>Static pressure test
	<ol>
		<li>Attach the outlet hose to a small frame so that the hose can remain straight and vertical. Put a ruler alongside the outlet hose to measure the liquid level.</li>
		<li>Connect the micropump to the power source.</li>
		<li>Start the test by pressing the switch and then mark down the initial liquid level.</li>
		<li>After the liquid level becomes stable, record the time, the final liquid level, and the electric current.</li>
		<li>Continue to record the liquid level and the current every 10 s until the micropump breaks down.</li>
	</ol>
	</li>
	<li>Flow rate test
	<ol>
		<li>Use a large measuring cylinder to collect the liquid coming out of the outlet hose. Be sure to fix the outlet hose so that the end remains at the same altitude as the liquid level in the beaker.</li>
		<li>Connect the micropump to the power source.</li>
		<li>Start the test by pressing the switch and then mark down the initial liquid level.</li>
		<li>As the liquid starts to flow out of the outlet hose, record the volume of acetone inside the measuring cylinder every 10 s. As the experiment goes on, add acetone to the beaker to maintain the liquid level.</li>
	</ol>
	</li>
	<li>Reliability test
	<ol>
		<li>Use the average working time to evaluate the reliability of the pump. During the flow rate test and the static pressure test, record the operation time before the pump breaks down. Record the detailed phenomena of each breakdown during the experiment and inspect the electrode plate surface afterwards for further analysis.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Kazemi, P. Z., Selvaganapathy, P. R., Ching, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+micropillar+electrode+spacing+on+the+performance+of+electrohydrodynamic+micropumps.">Effect of micropillar electrode spacing on the performance of electrohydrodynamic micropumps.</a> J Electrostat. 68 (4), 376-383 (2010).</li><li>Kano, I., Nishina, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+electrode+arrangements+on+EHD+conduction+pumping.">Effect of electrode arrangements on EHD conduction pumping.</a> IEEE Trans Ind Appl. 49 (2), 679-684 (2013).</li><li>Laser, D. J., Santiago, J. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+review+of+micropumps.">A review of micropumps.</a> J Micromech Microeng. 14 (6), R35 (2004).</li><li>Fylladitakis, E. D., Theodoridis, M. P., Moronis, A. X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Review+on+the+history,+research,+and+applications+of+electrohydrodynamics.">Review on the history, research, and applications of electrohydrodynamics.</a> IEEE Trans Plasma Sci. 42 (2), 358-375 (2014).</li><li>Yazdani, M., Seyed-Yagoobi, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Electrostatics Joint Conf. , (2009).</li><li>Gharraei, R., Esmaeilzadeh, E., Hemayatkhah, M., Danaeefar, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+investigation+of+electrohydrodynamic+conduction+pumping+of+various+liquids+film+using+flush+electrodes.">Experimental investigation of electrohydrodynamic conduction pumping of various liquids film using flush electrodes.</a> J Electrostat. 69 (1), 43-53 (2011).</li><li>Gharraei, R., Esmaeilzadeh, E., Nobari, M. R. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Numerical+investigation+of+conduction+pumping+of+dielectric+liquid+film+using+flush-mounted+electrodes.">Numerical investigation of conduction pumping of dielectric liquid film using flush-mounted electrodes.</a> Theor Comp Fluid Dyn. 28 (1), 89 (2014).</li><li>Jeong, S. -. I., Seyed-Yagoobi, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+study+of+electrohydrodynamic+pumping+through+conduction+phenomenon.">Experimental study of electrohydrodynamic pumping through conduction phenomenon.</a> J Electrostat. 56 (2), 123-133 (2002).</li><li>Seyed-Yagoobi, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrohydrodynamic+pumping+of+dielectric+liquids.">Electrohydrodynamic pumping of dielectric liquids.</a> J Electrostat. 63 (6), 861-869 (2005).</li><li>Hojjati, M., Esmaeilzadeh, E., Sadri, B., Gharraei, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrohydrodynamic+conduction+pumps+with+cylindrical+electrodes+for+pumping+of+dielectric+liquid+film+in+an+open+channel.">Electrohydrodynamic conduction pumps with cylindrical electrodes for pumping of dielectric liquid film in an open channel.</a> Colloid Surface A. 392 (1), 294-299 (2011).</li><li>Yazdani, M., Seyed-Yagoobi, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Numerical+investigation+of+electrohydrodynamic-conduction+pumping+of+liquid+film+in+the+presence+of+evaporation.">Numerical investigation of electrohydrodynamic-conduction pumping of liquid film in the presence of evaporation.</a> J Heat Trans-T ASME. 131 (1), 011602 (2009).</li><li>Vafaie, R. H., Ghavifekr, H. B., Lintel, H., Brugger, J., Renaud, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bi-directional+AC+electrothermal+micropump+for+on-chip+biological+applications.">Bi-directional AC electrothermal micropump for on-chip biological applications.</a> Electrophoresis. 37 (5-6), 719-726 (2016).</li><li>Pearson, M. R., Seyed-Yagoobi, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+Study+of+Linear+and+Radial+Two-Phase+Heat+Transport+Devices+Driven+by+Electrohydrodynamic+Conduction+Pumping.">Experimental Study of Linear and Radial Two-Phase Heat Transport Devices Driven by Electrohydrodynamic Conduction Pumping.</a> J Heat Trans-T ASME. 137 (2), 022901 (2015).</li></ol>

The authors have nothing to disclose.

One of the critical steps within the protocol is to inspect the electrode plate carefully. Small burrs on the edge of an electrode can result in a short-circuit, and surface integrity can greatly affect pump performance. The cleaning of the electrode plate and holder is also very important. The electrode chamber height is less than 1 mm, so small dust particles may block the working liquid flow and cause a short-circuit. Before the test, injecting acetone into the chamber can remove the bubbles outside of the chamber.</p...

Micropumps can drive liquid flow on a much smaller scale than most pumps. In recent years, various driving schemes have been applied successfully to microfluidic systems1,2,3,4,5. The electrohydrodynamic (EHD) pump can exert forces directly on the liquid, without any moving parts, which makes it simpler and easier to fabricate6. According to the charge types, EHD pumps can be classified as injection pumps, induction pumps, or conduction pumps. Induction pumps do not work on isothermal liquids, while injection pumps change the liquid conductivity. Because they lack such problems, conduction pumps are more stable and have a wider application.
The conduction pump is based on the mismatch of the dissociation and recombination rates of liquid molecules. Normally, the dissociation and recombination process can be expressed as follows7,8: 
<img alt="Equation" src="/files/ftp_upload/55867/55867eq1.jpg" /> 
where the recombination rate kr is constant while the dissociation rate kd is a function of the electric field strength. When the electric field strength reaches a certain value, the dissociation rate will exceed the recombination rate. Then, more and more free charges travel to the two electrodes of opposite polarity, and heterocharge layers form. These heterocharge layers are the key to the pump, as the movement of the charges pushes the liquid molecules forward. Therefore, net body force can be generated in the liquid within the chamber using asymmetric electrodes or the mismatch of the mobility of positive and negative ions9,10,11,12.
This work introduces a new way of fabricating a symmetric planar electrode plate for a conduction pump. The electrode plate is prepared on FR-4 CCL, and the pump chamber is prepared by micromachining. The fabrication processes are relatively simpler and more convenient than those of other manufacturing methods, such as nanolithography. A testing platform is set up to investigate the performance of the conduction micropump under different conditions. Furthermore, the reliability of the conduction micropump is also investigated under different circumstances.

<table><tbody><tr><td>Amperemeter</td><td>-</td><td>85C1-MA</td><td></td></tr><tr><td>DC high voltage power supply</td><td>NanTong Jianuo electric device company</td><td>GY-WY500-1</td><td></td></tr><tr><td>Fuse</td><td>-</td><td>-</td><td></td></tr><tr><td>Ultrasonic cleaner</td><td>Derui ultrasonic device company</td><td>-</td><td></td></tr><tr><td>Soldering iron</td><td>-</td><td>-</td><td></td></tr></tbody></table>

a performance-testing platform for a conduction micropump with an fr-4 copper-clad electrode plate

Here, a conduction micropump with symmetric planar electrode pairs prepared on flame-retardant glass-reinforced epoxy (FR-4) copper-clad laminate (CCL) is fabricated. It is used to investigate the influence of chamber dimensions on the performance of a conduction micropump and to determine the reliability of the conduction pump when acetone is used as the working fluid. A testing platform is set up to evaluate conduction micropump performance under different conditions. When the chamber height is 0.2 mm, the pump pressure reaches its peak value.

As shown in Figure 11, the pump pressure and its increasing rate rise when the voltage increases. When the voltage reaches 500 V, the pump pressure reaches 1,100 Pa.
The pump static pressure rises with the pump chamber height increasing when the chamber height is under 0.2 mm. The pump performance reaches its highest point when the chamber height is 0.2 mm. Then, the static pressure drops when the c...

Watch this Scientific Journal Video about A Performance-testing Platform for a Conduction Micropump with an FR-4 Copper-clad Electrode Plate at JoVE.com

A Performance-testing Platform for a Conduction Micropump with an FR-4 Copper-clad Electrode Plate

This paper presents a protocol for the fabrication of a conduction micropump using symmetric planar electrodes on flame-retardant glass-reinforced epoxy (FR-4) copper-clad laminate (CCL) to test the influence of chamber dimensions on the performance of a conduction micropump.

Here, a conduction micropump with symmetric planar electrode pairs prepared on flame-retardant glass-reinforced epoxy (FR-4) copper-clad laminate (CCL) is ...

a-performance-testing-platform-for-conduction-micropump-with-an-fr-4

Universidad de Cartagena UDEC

Research

JoVE Journal

Bioengineering

5.9K Views.  South China University of Technology. This paper presents a protocol for the fabrication of a conduction micropump using symmetric planar electrodes on flame-retardant glass-reinforced epoxy (FR-4) copper-clad laminate (CCL) to test the influence of chamber dimensions on the performance of a conduction micropump.

Video: A Performance-testing Platform for a Conduction Micropump with an FR-4 Copper-clad Electrode Plate

Hollow Microneedle-based Sensor for Multiplexed Transdermal Electrochemical Sensing

The development of a minimally invasive multiplexed monitoring system for rapid analysis of biologically-relevant molecules could offer individuals suffering from chronic medical conditions facile assessment of their immediate physiological state. Furthermore, it could serve as a research tool for analysis of complex, multifactorial medical conditions. In order for such a multianalyte sensor to be realized, it must be minimally invasive, sampling of interstitial fluid must occur without pain or harm to the user, and analysis must be rapid as well as selective.
Initially developed for pain-free drug delivery, microneedles have been used to deliver vaccines and pharmacologic agents (e.g., insulin) through the skin.1-2 Since these devices access the interstitial space, microneedles that are integrated with microelectrodes can be used as transdermal electrochemical sensors. Selective detection of glucose, glutamate, lactate, hydrogen peroxide, and ascorbic acid has been demonstrated using integrated microneedle-electrode devices with carbon fibers, modified carbon pastes, and platinum-coated polymer microneedles serving as transducing elements.3-7,8
This microneedle sensor technology has enabled a novel and sophisticated analytical approach for in situ and simultaneous detection of multiple analytes. Multiplexing offers the possibility of monitoring complex microenvironments, which are otherwise difficult to characterize in a rapid and minimally invasive manner. For example, this technology could be utilized for simultaneous monitoring of extracellular levels of, glucose, lactate and pH,9 which are important metabolic indicators of disease states7,10-14 (e.g., cancer proliferation) and exercise-induced acidosis.15

This article details the construction of a multiplexed microneedle-based sensor. The device is being developed for in situ sampling and electrochemical analysis of multiple analytes in a rapid and selective manner. We envision clinical medicine and biomedical research uses for these microneedle-based sensors.

The development of a minimally invasive multiplexed monitoring system for rapid analysis of biologically-relevant molecules could offer individuals ...

High Throughput Microfluidic Rapid and Low Cost Prototyping Packaging Methods

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In this article we describe different techniques for microfluidic rapid prototyping platforms. The proposed techniques are based on ultraviolet (UV) sensitive and temperature curing epoxies, polydimethylsiloxane (PDMS) based tubing, wire-bonding, and anisotropic adhesive films. The assembling procedures presented are developed for both one-time use devices as well as reusable microfluidic systems.

In this work, 3 different packaging and assembly techniques are presented. They can be classified into two categories: one-time use and reusable packaging ...

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and forging. Adoption of this technique is proceeding despite disagreement concerning the underlying mechanism responsible for EAD. The experimental procedure described herein enables a more explicit study compared to previous EAD research by removing thermal effects, which are responsible for disagreement in interpreting previous EAD results. Furthermore, as the procedure described here enables EAD observation in situ and in real time in a transmission electron microscope (TEM), it is superior to existing post-mortem methods that observe EAD effects post-test. Test samples consist of a single crystal copper (SCC) foil having a free-standing tensile test section of nanoscale thickness, fabricated using a combination of laser and ion beam milling. The SCC is mounted to an etched silicon base that provides mechanical support and electrical isolation while serving as a heat sink. Using this geometry, even at high current density (~3,500 A/mm2), the test section experiences a negligible temperature increase (&#60;0.02 &#176;C), thus eliminating Joule heating effects. Monitoring material deformation and identifying the corresponding changes to microstructures, e.g. dislocations, are accomplished by acquiring and analyzing a series of TEM images. Our sample preparation and in situ experiment procedures are robust and versatile as they can be readily utilized to test materials with different microstructures, e.g., single and polycrystalline copper.

A Novel Method for In Situ Electromechanical Characterization of Nanoscale Specimens

Isolating electrical and thermal effects on electrically assisted deformation (EAD) is very difficult using macroscopic samples. Metallic sample micro- and nanostructures together with a custom test procedure have been developed to evaluate the impact of applied current on the formation without joule heating and evolution of dislocations on these samples.

Electrically assisted deformation (EAD) is increasingly being used to improve the formability of metals during processes such as sheet metal rolling and ...

Engineering

Microscale Vortex-assisted Electroporator for Sequential Molecular Delivery

Electroporation has received increasing attention in the past years, because it is a very powerful technique for physically introducing non-permeant exogenous molecular probes into cells. This work reports a microfluidic electroporation platform capable of performing multiple molecule delivery to mammalian cells with precise and molecular-dependent parameter control. The system&#8217;s ability to isolate cells with uniform size distribution allows for less variation in electroporation efficiency per given electric field strength; hence enhanced sample viability. Moreover, its process visualization feature allows for observation of the fluorescent molecular uptake process in real-time, which permits prompt molecular delivery parameter adjustments in situ for efficiency enhancement. To show the vast capabilities of the reported platform, macromolecules with different sizes and electrical charges (e.g., Dextran with MW of 3,000 and 70,000 Da) were delivered to metastatic breast cancer cells with high delivery efficiencies (&#62;70%) for all tested molecules. The developed platform has proven its potential for use in the expansion of research fields where on-chip electroporation techniques can be beneficial.

A microfluidic vortex assisted electroporation platform was developed for sequential delivery of multiple molecules into identical cell populations with precise and independent dosage control. The system&#8217;s size based target cell purification step preceding electroporation aided to enhance molecular delivery efficiency and processed cell viability.

Electroporation has received increasing attention in the past years, because it is a very powerful technique for physically introducing non-permeant ...

Fabrication and Characterization of Thickness Mode Piezoelectric Devices for Atomization and Acoustofluidics

We present a technique to fabricate simple thickness mode piezoelectric devices using lithium niobate (LN). Such devices have been shown to atomize liquid more efficiently, in terms of &#64258;ow rate per power input, than those that rely on Rayleigh waves and other modes of vibration in LN or lead zirconate titanate (PZT). The complete device is composed of a transducer, a transducer holder, and a &#64258;uid supply system. The fundamentals of acoustic liquid atomization are not well known, so techniques to characterize the devices and to study the phenomena are also described. Laser Doppler vibrometry (LDV) provides vibration information essential in comparing acoustic transducers and, in this case, indicates whether a device will perform well in thickness vibration. It can also be used to &#64257;nd the resonance frequency of the device, though this information is obtained more quickly via impedance analysis. Continuous &#64258;uid atomization, as an example application, requires careful &#64258;uid flow control, and we present such a method with high-speed imaging and droplet size distribution measurements via laser scattering.

Fabrication of piezoelectric thickness mode transducers via direct current sputtering of plate electrodes on lithium niobate is described. Additionally, reliable operation is achieved with a transducer holder and &#64258;uid supply system and characterization is demonstrated via impedance analysis, laser doppler vibrometry, high-speed imaging, and droplet size distribution using laser scattering.

We present a technique to fabricate simple thickness mode piezoelectric devices using lithium niobate (LN). Such devices have been shown to atomize liquid ...

Microfluidic Channel-Based Soft Electrodes for Capacitive Pressure Sensing

Microfluidic Channel-Based Soft Electrodes and Their Application in Capacitive Pressure Sensing

Flexible and stretchable electrodes are essential components in soft artificial sensory systems. Despite recent advances in flexible electronics, most electrodes are either restricted by the patterning resolution or the capability of inkjet printing with high-viscosity super-elastic materials. In this paper, we present a simple strategy to fabricate microchannel-based stretchable composite electrodes, which can be achieved by scraping elastic conductive polymer composites (ECPCs) into lithographically embossed microfluidic channels. The ECPCs were prepared by a volatile solvent evaporation method, which achieves a uniform dispersion of carbon nanotubes (CNTs) in a polydimethylsiloxane (PDMS) matrix. Compared to conventional fabrication methods, the proposed technique can facilitate the rapid fabrication of well-defined stretchable electrodes with high-viscosity slurry. Since the electrodes in this work were made up of all-elastomeric materials, strong interlinks can be formed between the ECPCs-based electrodes and the PDMS-based substrate at the interfaces of the microchannel walls, which allows the electrodes to exhibit mechanical robustness under high tensile strains. In addition, the mechanical-electric response of the electrodes was also systematically studied. Finally, a soft pressure sensor was developed by combining a dielectric silicone foam and an interdigitated electrodes (IDE) layer, and this demonstrated great potential for pressure sensors in soft robotic tactile sensing applications.

Author Spotlight: Microfluidic Channel-Based Soft Electrodes and Their Application in Capacitive Pressure Sensing  

Flexible electrodes have a wide range of applications in soft robotics and wearable electronics. The present protocol demonstrates a new strategy to fabricate highly stretchable electrodes with high resolution via lithographically defined microfluidic channels, which paves the way for future high-performance soft pressure sensors.

Flexible and stretchable electrodes are essential components in soft artificial sensory systems. Despite recent advances in flexible electronics, most ...

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The on-chip bioassay immobilization is performed by the adsorption of the biomolecules to the channel surface. The glucose oxidase enzyme is used as a transducer for electrochemical signal generation. In the presence of the substrate, glucose, hydrogen peroxide is produced, which is detected at the platinum working electrode. The stop-flow technique is applied to obtain signal amplification along with rapid detection. Different biomolecules can quantitatively be measured by means of the introduced microfluidic system, giving an indication of different types of diseases, or, in regard to therapeutic drug monitoring, facilitating a personalized therapy.

A microfluidic biosensor platform was designed and fabricated using low-cost dry film photoresist technology for the rapid and sensitive quantification of various analytes. This single-use system allows for the electrochemical readout of on-chip-immobilized enzyme-linked assays by means of the stop-flow technique.

In recent years, biomarker diagnostics became an indispensable tool for the diagnosis of human disease, especially for the point-of-care diagnostics. An ...

Fabrication and Validation of an Organ-on-chip System with Integrated Electrodes to Directly Quantify Transendothelial Electrical Resistance

Organs-on-chips, in vitro models involving the culture of (human) tissues inside microfluidic devices, are rapidly emerging and promise to provide useful research tools for studying human health and disease. To characterize the barrier function of cell layers cultured inside organ-on-chip devices, often transendothelial or transepithelial electrical resistance (TEER) is measured. To this end, electrodes are usually integrated into the chip by micromachining methods to provide more stable measurements than is achieved with manual insertion of electrodes into the inlets of the chip. However, these electrodes frequently hamper visual inspection of the studied cell layer or require expensive cleanroom processes for fabrication. To overcome these limitations, the device described here contains four easily integrated electrodes that are placed and fixed outside of the culture area, making visual inspection possible. Using these four electrodes the resistance of six measurement paths can be quantified, from which the TEER can be directly isolated, independent of the resistance of culture medium-filled microchannels. The blood-brain barrier was replicated in this device and its TEER was monitored to show the device applicability. This chip, the integrated electrodes and the TEER determination method are generally applicable in organs-on-chips, both to mimic other organs or to be incorporated into existing organ-on-chip systems.

This publication describes the fabrication of an organ-on-chip device with integrated electrodes for direct quantification of transendothelial electrical resistance (TEER). For validation, the blood-brain barrier was mimicked inside this microfluidic device and its barrier function was monitored. The presented methods for electrode integration and direct TEER quantification are generally applicable.

Organs-on-chips, in vitro models involving the culture of (human) tissues inside microfluidic devices, are rapidly emerging and promise to provide useful ...

Mechano-Node-Pore Sensing: A Rapid, Label-Free Platform for Multi-Parameter Single-Cell Viscoelastic Measurements

Cellular mechanical properties are involved in a wide variety of biological processes and diseases, ranging from stem cell differentiation to cancer metastasis. Conventional methods for measuring these properties, such as atomic force microscopy (AFM) and micropipette aspiration (MA), capture rich information, reflecting a cell's full viscoelastic response; however, these methods are limited by very low throughput. High-throughput approaches, such as real-time deformability cytometry (RT-DC), can only measure limited mechanical information, as they are often restricted to single-parameter readouts that only reflect a cell's elastic properties. In contrast to these methods, mechano-node-pore sensing (mechano-NPS) is a flexible, label-free microfluidic platform that bridges the gap in achieving multi-parameter viscoelastic measurements of a cell with moderate throughput. A direct current (DC) measurement is used to monitor cells as they transit a microfluidic channel, tracking their size and velocity before, during, and after they are forced through a narrow constriction. This information (i.e., size and velocity) is used to quantify each cell's transverse deformation, resistance to deformation, and recovery from deformation. In general, this electronics-based microfluidic platform provides multiple viscoelastic cell properties, and thus a more complete picture of a cell's mechanical state. Because it requires minimal sample preparation, utilizes a straightforward electronic measurement (in contrast to a high-speed camera), and takes advantage of standard soft lithography fabrication, the implementation of this platform is simple, accessible, and adaptable to downstream analysis. This platform's flexibility, utility, and sensitivity have provided unique mechanical information on a diverse range of cells, with the potential for many more applications in basic science and clinical diagnostics.

Presented here is a method to mechanically phenotype single cells using an electronics-based microfluidic platform called mechano-node-pore sensing (mechano-NPS). This platform maintains moderate throughput of 1-10 cells/s while measuring both the elastic and viscous biophysical properties of cells.

Cellular mechanical properties are involved in a wide variety of biological processes and diseases, ranging from stem cell differentiation to cancer ...

Mechanical Fatigue Testing of RBCs by Amplitude-Modulated Electrodeformation

Amplitude-Modulated Electrodeformation to Evaluate Mechanical Fatigue of Biological Cells

Red blood cells (RBCs) are known for their remarkable deformability. They repeatedly undergo considerable deformation when passing through the microcirculation. Reduced deformability is seen in physiologically aged RBCs. Existing techniques to measure cell deformability cannot easily be used for measuring fatigue, the gradual degradation in cell membranes caused by cyclic loads. We present a protocol to evaluate mechanical degradation in RBCs from cyclic shear stresses using amplitude shift keying (ASK) modulation-based electrodeformation in a microfluidic channel. Briefly, the interdigitated electrodes in the microfluidic channel are excited with a low voltage alternating current at radio frequencies using a signal generator. RBCs in suspension respond to the electric field and exhibit positive dielectrophoresis (DEP), which moves cells to the electrode edges. Cells are then stretched due to the electrical forces exerted on the two cell halves, resulting in uniaxial stretching, known as electrodeformation. The level of shear stress and the resultant deformation can be easily adjusted by changing the amplitude of the excitation wave. This enables quantifications of nonlinear deformability of RBCs in response to small and large deformations at high throughput. Modifying the excitation wave with the ASK strategy induces cyclic electrodeformation with programmable loading rates and frequencies. This provides a convenient way for the characterization of RBC fatigue. Our ASK-modulated electrodeformation approach enables, for the first time, a direct measurement of RBC fatigue from cyclic loads. It can be used as a tool for general biomechanical testing, for analyses of cell deformability and fatigue in other cell types and diseased conditions, and can also be combined with strategies to control the microenvironment of cells, such as oxygen tension and biological and chemical cues.

Author Spotlight: Studying Biomechanics of Circulating Cells by Modulating Their Electrodeformation Behavior 

Presented here is a protocol for mechanical fatigue testing in the case of human red blood cells using an amplitude-modulated electrodeformation approach. This general approach can be used to measure the systematic changes in morphological and biomechanical characteristics of biological cells in a suspension from cyclic deformation.

A Performance-testing Platform for a Conduction Micropump with an FR-4 Copper-clad Electrode Plate

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Fabrication and Validation of an Organ-on-chip System with Integrated Electrodes to Directly Quantify Transendothelial Electrical Resistance

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Amplitude-Modulated Electrodeformation to Evaluate Mechanical Fatigue of Biological Cells