This work was supported by the Aircraft Equipment Reliability and Maintainability Improvement Program and the Patuxent Partnership. Townsend was supported by an ONR Faculty Research Fellowship. The authors also acknowledge the general support of the SMCM Chemistry and Biochemistry Department faculty and students, including support from the SMCM football team.

1. Preparing coating salts
CAUTION: Nickel salts and boric acid are toxic and should be handled with proper personal protective equipment including nitrile gloves, goggles and a lab coat. Strong acids and bases should be handled in the fume hood, and all waste chemicals should be disposed of as hazardous waste.
<ol>
	<li>Using a balance, weigh out the following powders in these ratios: 10.000 g of NiSO4&#183;6H2O, 2.120 g of NiCl2&#183;6H2O, 1.600 g of H3BO3 and combine in a vial together. See Table 1 for concentrations.</li>
	<li>Weigh out 1.800 g of SrAl2O4:Eu2+, Dy3+ phosphor or alternative phosphors including europium doped yttrium oxide, europium doped barium magnesium aluminate, or replace with alternative oxide, metal, or organic composite material depending on the desired effect. 
	NOTE: The amount added here may vary based on the properties of the composite material and the desired qualities of the metal-composite film.</li>
	<li>Using a porcelain mortar and pestle, grind the composite powder for approximately 10 minutes until it becomes a fine powder. 
	NOTE: This does not change the particle size, but does separate aggregated particles.</li>
	<li>Likewise, grind the salt mixture from step 1.1 in batches until it becomes a fine powder.</li>
	<li>Combine the ground phosphor with the ground salt mixture in a container for storage.</li>
	<li>Weigh out 0.188 grams of the mixture per cm2 of coating area, as prepared in step 1.5 and add to a container with an open top that is easy to access.</li>
	<li>To this, add 40 &#181;L of water per cm2 of coating area, and stir to partially dissolve the salts forming a thick paste. Set this aside. 
	NOTE: The protocol can be paused here.</li>
</ol>
2. Preparing the electrodes
<ol>
	<li>Using scissors, cut the anode to the size and shape that matches the object to be plated. In this example, we prepare a 4 cm2 nickel foil to be coated, and a 4 cm2 nickel anode is cut to match this. 
	NOTE: Other objects can be coated including large objects. In this case, select the area on the object to be coated, and cut out the anode to match the coating area.</li>
	<li>Using a cotton swab or a cloth, clean the surface of the anode foil and the cathode (coating object surface) with concentrated (10 M) potassium hydroxide or sodium hydroxide base to remove organic material. Next, rinse the surfaces with water to remove excess base.</li>
	<li>Using a cotton swab or a cloth, activate the object surface with concentrated acid. In the case of nickel, 37% vol/vol HCl is used, although for steel, 10% by volume aqueous HCl may be more appropriate. Please refer to the recommendations for activating metal surfaces provided elsewhere to determine the appropriate method for activating specific metals or alloys23,24. 
	NOTE: After this step, the metal surface is reactive and the surface will start to react with oxygen in the air to form an oxide layer. This will cause the surface to be inactive, so the following steps (2.4 &#8211; 3.5) should be performed in the next 5 minutes; otherwise, step 2.3 should be repeated before continuing. 
	CAUTION: This step should be performed in a fume hood to avoid exposure to HCl vapors.</li>
	<li>Quickly, deposit the coating paste onto the cathode object. In this case, the cathode is a 4 cm2 nickel foil on the benchtop. Cover the object area to be plated evenly and try to avoid gaps in the paste. 
	NOTE: In this example, we are painting on this paste with two scoopulas, however, other options may include spraying, dipping or doctor blading to increase the speed and efficiency of this step.</li>
	<li>Using a cotton swab or a cloth, activate the anode with concentrated acid by dipping the swab in the acid and gently rubbing the cathode surface. In the case of nickel, 70% vol/vol HNO3 can be used. 
	NOTE: However, other acids may be more appropriate for specific metals and alloys. Please refer to the recommendations provided elsewhere for the appropriate reagent to activate specific anode surfaces23,24. 
	CAUTION: This step should be performed in a fume hood to avoid exposure to NO2, a toxic brown gas that is formed during the reaction. Continue treating the surface until the surface becomes grey and textured. After this step, the metal surface is reactive and the surface will start to react with oxygen in the air to form an oxide layer, so the following steps should be performed quickly to avoid inactivation of the anode.</li>
	<li>If calculating the current efficiency is desired, use an analytical balance to record the mass of the anode and the cathode.</li>
</ol>
3. Assembly and coating
<ol>
	<li>Pre-set a power supply to the desired current in constant current mode or voltage, if constant voltage mode is desired. In this example, constant current mode is used with a current of 0.1 Amperes (0.1 A per 4 cm2 = 0.025 A/cm2). 
	NOTE: For larger or irregularly shaped objects, the coating area can be predetermined with a grid or using a photo with scale bar and an imaging software like ImageJ. The applied current can be scaled to deliver the same current density required for the coating area.</li>
	<li>Cut a piece of nylon sheet (or alternative hydrophilic membrane) to a size larger than the anode so that the anode does not make direct contact with the cathode object.
	<ol>
		<li>Place the nylon sheet on top of the coating paste, and then add a small amount of paste to this.</li>
	</ol>
	</li>
	<li>Next, add 1-2 drops of water from a pipette to allow the salt to partially dissolve. Steps 3.2.1 &#8211; 3.3 make the nylon sheet conductive and allow for the mass transport of ions through the electrolyte, which is necessary to balance charge in the coating reaction.</li>
	<li>Finally, add the activated anode on top and attach the negative lead to the cathode object and the positive lead to the anode. 
	NOTE: It might be helpful to tape down these leads so that the setup remains stationary, especially if the experiment involves small pieces of metal foil. This is less important for large objects.</li>
	<li>Cover the system with plastic or seal to help retain water, and apply moderate pressure (~100 g per cm2 area), turn on the power supply and continue coating for the desired duration.</li>
	<li>Turn off the power supply and expose the system.</li>
	<li>Disconnect the leads, separate the electrodes and rinse the cathode object with water into a waste container.
	<ol>
		<li>Soak the other items in water to remove salts and dispose of this aqueous solution in the properly labeled hazardous waste container</li>
		<li>Wearing gloves, gently rub the cathode object by hand to remove any uncoated composite particles. The coating is complete and ready for characterization.</li>
		<li>Using an analytical balance, record the mass of the anode and the cathode and find the difference between these values and their original mass.</li>
		<li>Use Faraday&#8217;s Laws of electrolysis to calculate the current efficiency. The theoretical moles of metal coating can be determined using Equation 1. 
		<img alt="Equation 1" src="/files/ftp_upload/61484/61484equ01.jpg" />&#160; &#160; Equation 1 
		where n is the amount of metal deposited (units: mol), I is the applied current, t is the coating time, F is Faraday&#8217;s constant (96485 coulombs per mole) and z is the charge of the metal ion. Calculate this value based on the experimental parameters.</li>
		<li>Divide the experimentally determined deposit mass obtained from the masses of the cathode or anode (Steps 2.6 and 3.7.3) by the theoretical mass lost (anode) or gained (cathode) to calculate the current efficiency using Equation 2. 
		<img alt="Equation 2" src="/files/ftp_upload/61484/61484equ02.jpg" />&#160; &#160; Equation 2 
		[NOTE: At a current efficiency of 100%, under constant voltage, a theoretical deposit mass is expected of approximately 1.095 g of nickel or 12.3 &#181;m of nickel per hour, given 0.04 A and 4 cm2 area. Likewise, under constant current, approximately 614.6 &#181;m nickel would theoretically deposit per unit of 1 A&#8729;cm-2 after 30 min.]</li>
	</ol>
	</li>
</ol>
4. Characterization with electrochemistry
<ol>
	<li>Use chronopotentiometry to monitor changes in voltage under constant current, and chronoamperometry to monitor changes in current under constant voltage.
	<ol>
		<li>Turn on the potentiostat and designate the duration and the applied current or voltage.</li>
		<li>Repeat steps 3.2 &#8211; 3.5 to prepare the coating.</li>
		<li>Use a calibrated 3-electrode system to normalize the voltage to a reference standard.
		<ol>
			<li>Place a platinum wire pseudo reference electrode between on top of the nylon sheet and below the anode. In order to ensure that the reference electrode does not make direct contact with the anode, use a separate nylon sheet (or alternative membrane) placed on top of the reference followed by a few drops of water, a small amount of coating paste (repeat steps 3.2 &#8211; 3.3) and then the anode.</li>
		</ol>
		</li>
		<li>Connect the leads to the electrodes, seal, press, begin coating and monitor changes in voltage or current.</li>
	</ol>
	</li>
</ol>
5. Characterization with quantum yield fluorescence spectroscopy
<ol>
	<li>If the coating contains fluorescent composite particles, use a fluorometer equipped with an integrating sphere to obtain absolute quantum yield measurements.
	<ol>
		<li>Place the coating into the fluorimeter stage with the fluorescent coating facing 45&#176; from the excitation source and 315&#176; from the detector.</li>
		<li>Record the fluorescence spectra starting at a wavelength below the excitation wavelength to record the areas of the excitation peak and the fluorescence peak.</li>
		<li>Remove the sample from the fluorometer, and repeat step 5.1.2 to record the blank excitation peak. Calculate the quantum yield (QY) from the ratios of the areas of the excitation and emission peaks (Equation 3 and Figure 3B). 
		<img alt="Equation 3" src="/files/ftp_upload/61484/61484equ03.jpg" />&#160; &#160; Equation 3 
		where Aem, Aex and Ao are the peak areas at the emission wavelength of the sample, the excitation wavelength of the sample and the excitation wavelength of the blank, respectively.</li>
	</ol>
	</li>
</ol>
6. Characterization with optical microscopy
<ol>
	<li>Place the sample on the stage of a calibrated optical microscope with the coating side facing the lenses and bring the surface into focus.</li>
	<li>Record surface images at the desired magnifications and surface sample sites.</li>
	<li>Using image analysis software (ex. ImageJ (IJ 1.46r)), calculate and plot the surface coverage and average composite particle size.</li>
	<li>To determine coating thickness and cross-section features, cut the cathode foil with scissors. Set the coating on the side and re-adjust the focus. Repeat steps 6.2 &#8211; 6.3.</li>
</ol>

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The authors have nothing to disclose.

Critical steps of electrostamping. Bathless electrostamping shares many of the same critical steps with traditional bath electroplating. These include proper cleaning of the electrodes, mixing metal ions into the electrolyte and applying and external or chemical (electroless plating) potential to cause reduction of metal onto the cathode. In addition, the oxidation of the anode and cathode should be avoided after acid activation by quickly rinsing with water and adding these electrodes to the setup.
...

Traditional electroplating is widely used to deposit thin films of a variety of metals, alloys, and metal-composites onto conductive surfaces to functionalize them for the intended application1,2,3,4,5,6,7,8,9,10,11,12. This method adds a metal finish to parts used in the manufacturing of aerospace, automotive, military, medical, and electronic equipment. &#173;&#173;&#173;&#173;The object to be plated, the cathode, is submerged in an aqueous bath containing metal salt precursors, which are reduced to metal at the surface of the object by the application of a chemical or electrical potential. Non-charged composite particles can be incorporated into the metal film by adding these to the bath during coating to enhance the film properties for increased hardness in the case of metal oxides and carbides, smoothness with polymers or lubrication with liquid oils12,13. However, because these particles lack an inherent attraction to the cathode, the ratio of composite that is incorporated into the metal remains low for bath plating13,14,15. This is especially problematic for large particles that do not adsorb to the cathode long enough to be embedded by the growing metal film. Additionally, hygroscopic particles solvate in aqueous solutions and their hydration shell acts as a physical barrier impeding contact with the cathode16.
Some promising methods have been shown to mitigate this effect by using dry non-polar solvents to remove the hydration barrier completely17, or by decorating the composite particles with charged surfactant molecules16 that disrupt the hydration shell to allow contact between the particle and the cathode. However, because these methods involve organic materials, carbon contamination is possible in the film and breakdown of these organic materials could occur at the electrodes. For example, the organic solvents used (DMSO2 and acetamide) are heated to 130 &#176;C in an inert atmosphere for air-free coating; however, we found them to be unstable during coating in air. Due to resistive heating at the electrodes, redox reactions with organic materials may result in impurities or sites for heterogeneous nucleation and growth of metal nanoparticles18. As a result, there is a need for an organic-free aqueous electroplating method that addresses the long-standing challenge of particle-cathode adsorption. So far, metal-composite bath coating has been shown to embed particles up to a few micrometers in diameter19 and as high as 15 % loading16,17.
In response to this, we describe an inorganic bathless electrostamping method that forces composite particles to become embedded into the film at high surface coverages despite their large size and hygroscopic nature20. By removing the bath, the process does not involve containers of hazardous coating liquids and the object to be plated does not need to be submerged. Therefore, large, cumbersome or otherwise corrosion- or water-sensitive objects, can be plated or &#8220;stamped&#8221; in select areas with the composite material. In addition, the removal of excess water requires less clean-up of liquid hazardous waste.
Here, we demonstrate this method to produce bright fluorescent metal films by co-depositing non-toxic and air-stable europium and dysprosium doped, strontium aluminate (87 &#177; 30 &#181;m) with nickel at high loadings (up to 80%). This comes in contrast to previous examples that were plated in a bath and therefore were limited to small (nanometers to a few micrometers) phosphors12. In addition, previously reported electrodeposited films fluoresce only under short-wave UV-light, with the exception of a recent report that grew 1 &#8211; 5 &#181;m luminescent strontium aluminate crystals in an alumina film with plasma electrolyte oxidation21. Fluorescent metal films could have far-reaching applications in many industries involving dim-light environments including road sign illumination21, aircraft maintenance equipment location and identification20, automobile and toy decorations, invisible messages, product authentication22, safety lighting, mechanochromic stress identification10 and tribological wear visual inspection12,16. Despite these potential uses for glowing metal surfaces, this method could also be expanded to include additional large and/or hygroscopic composite particles to produce a new variety of metal-composite functional coatings that were previously not possible via electroplating.

<table><tbody><tr><td>37% M Hydrochloric Acid (aq)</td><td>SigmaAldrich</td><td>320331-500ML</td><td>corrosive - handle in fume hood</td></tr><tr><td>70% Nitric Acid (aq)</td><td>SigmaAldrich</td><td>438073-500ML</td><td>corrosive - handle in fume hood</td></tr><tr><td>Barium magnesium aluminate, europium doped (s)</td><td>SigmaAldrich</td><td>756512-25G</td><td>fine powder</td></tr><tr><td>Boric Acid (s)</td><td>SigmaAldrich</td><td>B6768-500G</td><td>toxic</td></tr><tr><td>Cotton Swab</td><td>Q-tips</td><td>Q-tips Cotton Swabs</td><td></td></tr><tr><td>ImageJ</td><td>National Institutes of Health</td><td>IJ 1.46r</td><td>free software</td></tr><tr><td>Nickel (II) chloride hexahydrate (s)</td><td>SigmaAldrich</td><td>223387-500G</td><td>toxic</td></tr><tr><td>Nickel (II) sulfate hexahydrate (s)</td><td>SigmaAldrich</td><td>227676-500G</td><td>toxic</td></tr><tr><td>Nickel foil (s)</td><td>AliExpress</td><td>Ni99.999</td><td></td></tr><tr><td>Nitrile gloves</td><td>Fisher Scientific</td><td>19-149-863B</td><td></td></tr><tr><td>nylon membrane (s)</td><td>Tisch Scientific</td><td>RS10133</td><td></td></tr><tr><td>Optical Microscope equipped with FTIC filter (470 &amp;plusmn; 20 nm)</td><td>Nikon</td><td>Eclipse 80i</td><td></td></tr><tr><td>Plastic Wrap</td><td>Fisher Scientific</td><td>22-305654</td><td></td></tr><tr><td>Porcelain Mortar</td><td>Fisher Scientific</td><td>FB961A</td><td></td></tr><tr><td>Porcelain Pestle</td><td>Fisher Scientific</td><td>FB961K</td><td></td></tr><tr><td>Potassium Hydroxide (s)</td><td>SigmaAldrich</td><td>221473-25G</td><td>corrosive</td></tr><tr><td>Potentiostat with platinum wire</td><td>Gamry Instruments</td><td>1000E</td><td></td></tr><tr><td>Scoopula</td><td>Fisher Scientific</td><td>14-357Q</td><td></td></tr><tr><td>Spectrofluorometer</td><td>Photon Technology International</td><td>QM-40</td><td></td></tr><tr><td>Strontium aluminate, europium and dysprosium doped (s)</td><td>GloNation</td><td>756539-25G</td><td>powder</td></tr><tr><td>Variable linear DC power supply</td><td>Tekpower</td><td>TP3005T</td><td></td></tr><tr><td>Yttrium oxide, europium doped (s)</td><td>SigmaAldrich</td><td>756490-25G</td><td>fine powder</td></tr></tbody></table>

localized bathless metal-composite plating via electrostamping

Composite plating with particles embedded into the metal matrix can enhance the properties of the metal coating to make it more or less conductive, hard, durable, lubricated or fluorescent. However, it can be more challenging than metal plating, because the composite particles are either 1) not charged so they do not have a strong electrostatic attraction to the cathode, 2) are hygroscopic and are blocked by a hydration shell, or 3) too large to remain stagnate at the cathode while stirring. Here, we describe the details of a bathless plating method that involves anode and cathode nickel plates sandwiching an aqueous concentrated electrolyte paste containing large hygroscopic phosphorescent particles and a hydrophilic membrane. After applying a potential, the nickel metal is deposited around the stagnant phosphor particles, trapping them in the film. The composite coatings are characterized by optical microscopy for film roughness, thickness and composite surface loading. In addition, fluorescence spectroscopy can be used to quantify the illumination brightness of these films to assess the effects of various current densities, coating duration and phosphor loading.

After following this protocol, a thin coating of metal should become plated onto the cathode surface and contain the composite particles that were added to the coating paste. Fluorescent or colored particle incorporation can be observed by visual inspection as a result of a change in appearance compared to the uncoated surface (Figure 1A1-A3). To investigate the percent surface coverage of the composite particles and to observe the surface morphology of the coating, optical ...

Watch this Scientific Journal Video about Localized Bathless Metal-Composite Plating via Electrostamping at JoVE.com

Localized Bathless Metal-Composite Plating via Electrostamping

Presented here is a protocol of bathless electroplating, where a stagnant metal salt paste containing composite particles are reduced to form metal composites at high loading. This method addresses the challenges faced by other common forms of electroplating (jet, brush, bath) of embedding composites particles into the metal matrix.

Composite plating with particles embedded into the metal matrix can enhance the properties of the metal coating to make it more or less conductive, hard, ...

localized-bathless-metal-composite-plating-via-electrostamping

Universidad de Cartagena UDEC

Research

JoVE Journal

Chemistry

4.1K Views.  St. Mary's College of Maryland. Presented here is a protocol of bathless electroplating, where a stagnant metal salt paste containing composite particles are reduced to form metal composites at high loading. This method addresses the challenges faced by other common forms of electroplating (jet, brush, bath) of embedding composites particles into the metal matrix.

Video: Localized Bathless Metal-Composite Plating via Electrostamping

Creating Two-Dimensional Patterned Substrates for Protein and Cell Confinement

Microcontact printing provides a rapid, highly reproducible method for the creation of well-defined patterned substrates.1 While microcontact printing can be employed to directly print a large number of molecules, including proteins,2 DNA,3 and silanes,4 the formation of self-assembled monolayers (SAMs) from long chain alkane thiols on gold provides a simple way to confine proteins and cells to specific patterns containing adhesive and resistant regions. This confinement can be used to control cell morphology and is useful for examining a variety of questions in protein and cell biology. Here, we describe a general method for the creation of well-defined protein patterns for cellular studies.5 This process involves three steps: the production of a patterned master using photolithography, the creation of a PDMS stamp, and microcontact printing of a gold-coated substrate. Once patterned, these cell culture substrates are capable of confining proteins and/or cells (primary cells or cell lines) to the pattern.
The use of self-assembled monolayer chemistry allows for precise control over the patterned protein/cell adhesive regions and non-adhesive regions; this cannot be achieved using direct protein stamping. Hexadecanethiol, the long chain alkane thiol used in the microcontact printing step, produces a hydrophobic surface that readily adsorbs protein from solution. The glycol-terminated thiol, used for backfilling the non-printed regions of the substrate, creates a monolayer that is resistant to protein adsorption and therefore cell growth.6 These thiol monomers produce highly structured monolayers that precisely define regions of the substrate that can support protein adsorption and cell growth. As a result, these substrates are useful for a wide variety of applications from the study of intercellular behavior7 to the creation of microelectronics.8
While other types of monolayer chemistry have been used for cell culture studies, including work from our group using trichlorosilanes to create patterns directly on glass substrates,9 patterned monolayers formed from alkane thiols on gold are straight-forward to prepare. Moreover, the monomers used for monolayer preparation are commercially available, stable, and do not require storage or handling under inert atmosphere. Patterned substrates prepared from alkane thiols can also be recycled and reused several times, maintaining cell confinement.10

Self-assembled monolayers (SAMs) formed from long chain alkane thiols on gold provide well-defined substrates for the formation of protein patterns and cell confinement. Microcontact printing of hexadecanethiol using a polydimethylsiloxane (PDMS) stamp followed by backfilling with a glycol-terminated alkane thiol monomer produces a pattern where protein and cells adsorb only to the stamped hexadecanethiol region.

Microcontact printing provides a rapid, highly reproducible method for the creation of well-defined patterned substrates.1  While microcontact printing ...

Bioengineering

A Method to Manipulate Surface Tension of a Liquid Metal via Surface Oxidation and Reduction

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where interfacial tension is a dominant force. A variety of methods exist for controlling the interfacial tension of aqueous and organic liquids on this scale; however, these techniques have limited utility for liquid metals due to their large interfacial tension.
Liquid metals can form soft, stretchable, and shape-reconfigurable components in electronic and electromagnetic devices. Although it is possible to manipulate these fluids via mechanical methods (e.g., pumping), electrical methods are easier to miniaturize, control, and implement. However, most electrical techniques have their own constraints: electrowetting-on-dielectric requires large (kV) potentials for modest actuation, electrocapillarity can affect relatively small changes in the interfacial tension, and continuous electrowetting is limited to plugs of the liquid metal in capillaries.
Here, we present a method for actuating gallium and gallium-based liquid metal alloys via an electrochemical surface reaction. Controlling the electrochemical potential on the surface of the liquid metal in electrolyte rapidly and reversibly changes the interfacial tension by over two orders of magnitude ( &#820;500 mN/m to near zero). Furthermore, this method requires only a very modest potential (&#60; 1 V) applied relative to a counter electrode. The resulting change in tension is due primarily to the electrochemical deposition of a surface oxide layer, which acts as a surfactant; removal of the oxide increases the interfacial tension, and vice versa. This technique can be applied in a wide variety of electrolytes and is independent of the substrate on which it rests.

We present a method to control the interfacial energy of a liquid metal in an electrolyte via electrochemical deposition (or removal) of a surface oxide layer. This simple method can control the capillary behavior of gallium-based liquid metals by tuning the interfacial energy rapidly, significantly, and reversibly using modest voltages.

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where ...

AC Electrokinetic Phenomena Generated by Microelectrode Structures

The field of AC electrokinetics is rapidly growing due to its ability to perform dynamic fluid and particle manipulation on the micro- and nano-scale, which is essential for Lab-on-a-Chip applications. AC electrokinetic phenomena use electric fields to generate forces that act on fluids or suspended particles (including those made of dielectric or biological material) and cause them to move in astonishing ways1, 2. Within a single channel, AC electrokinetics can accomplish many essential on-chip operations such as active micro-mixing, particle separation, particle positioning and micro-pattering. A single device may accomplish several of those operations by simply adjusting operating parameters such as frequency or amplitude of the applied voltage. Suitable electric fields can be readily created by micro-electrodes integrated into microchannels. It is clear from the tremendous growth in this field that AC electrokinetics will likely have a profound effect on healthcare diagnostics3-5, environmental monitoring6 and homeland security7.

In general, there are three AC Electrokinetic phenomena (AC electroosmosis, dielectrophoresis and AC electrothermal effect) each with unique dependencies on the operating parameters. A change in these operating parameters can cause one phenomena to become dominant over another, thus changing the particle or fluid behavior. 

It is difficult to predict the behavior of particles and fluids due to the complicated physics that underlie AC electrokinetics. It is the goal of this publication to explain the physics and elucidate particle and fluid behavior. Our analysis also covers how to fabricate the electrode structures that generate them, and how to interpret a wide number of experimental observations using several popular device designs. This video article will help scientists and engineers understand these phenomena and may encourage them to start using AC Electrokinetics in their research.

Manipulating fluids and suspended particles in the micro- and nano-scale is becoming more of a reality as enabling technologies, like AC electrokinetics, continue to develop. Here, we discuss the physics behind AC electrokinetics, how to fabricate these devices and how to interpret the experimental observations.

The field of AC electrokinetics is rapidly growing due to its ability to perform dynamic fluid and particle manipulation on the micro- and nano-scale, ...

Biology

Experimental Implementation of a New Composite Fabrication Method: Exposing Bare Fibers on the Composite Surface by the Soft Layer Method

The bipolar plate is a key component in proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs). It is a multi-functional component that should have high electrical conductivity, high mechanical properties, and high productivity.
In this regard, a carbon fiber/epoxy resin composite can be an ideal material to replace the conventional graphite bipolar plate, which often leads to the catastrophic failure of the entire system because of its inherent brittleness. Though the carbon/epoxy composite has high mechanical properties and is easy to manufacture, the electrical conductivity in the through-thickness direction is poor because of the resin-rich layer that forms on its surface. Therefore, an expanded graphite coating was adopted to solve the electrical conductivity issue. However, the expanded graphite coating not only increases the manufacturing costs but also has poor mechanical properties.
In this study, a method to expose fibers on the composite surface is demonstrated. There are currently many methods that can expose fibers by surface treatment after the fabrication of the composite. This new method, however, does not require surface treatment because the fibers are exposed during the manufacture of the composite. By exposing bare carbon fibers on the surface, the electrical conductivity and mechanical strength of the composite are increased drastically.

A protocol to expose bare fibers on the composite surface by eliminating resin rich area is presented. The fibers are exposed during fabrication of the composites, not by the post surface treatment. The exposed carbon composites exhibit high electrical conductivity in the through-thickness direction and high mechanical property.

The bipolar plate is a key component in proton exchange membrane fuel cells (PEMFCs) and vanadium redox flow batteries (VRFBs). It is a multi-functional ...

Engineering

Scalable Solution-processed Fabrication Strategy for High-performance, Flexible, Transparent Electrodes with Embedded Metal Mesh

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a polymer film. This paper also presents a low-cost, vacuum-free fabrication method for this novel TE; the approach combines lithography, electroplating, and imprint transfer (LEIT) processing. The embedded nature of the EMTEs offers many advantages, such as high surface smoothness, which is essential for organic electronic device production; superior mechanical stability during bending; favorable resistance to chemicals and moisture; and strong adhesion with plastic film. LEIT fabrication features an electroplating process for vacuum-free metal deposition and is favorable for industrial mass production. Furthermore, LEIT allows for the fabrication of metal mesh with a high aspect ratio (i.e., thickness to linewidth), significantly enhancing its electrical conductance without adversely losing optical transmittance. We demonstrate several prototypes of flexible EMTEs, with sheet resistances lower than 1 &#937;/sq and transmittances greater than 90%, resulting in very high figures of merit (FoM) &#8211; up to 1.5 x 104 &#8211; which are amongst the best values in the published literature.

This protocol describes a solution-based fabrication strategy for high-performance, flexible, transparent electrodes with fully-embedded, thick metal mesh. Flexible transparent electrodes fabricated by this process demonstrate among the highest reported performances, including ultra-low sheet resistance, high optical transmittance, mechanical stability under bending, strong substrate adhesion, surface smoothness, and environmental stability.

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a ...

Fabricating Complex Culture Substrates Using Robotic Microcontact Printing (R-&#181;CP) and Sequential Nucleophilic Substitution

In tissue engineering, it is desirable to exhibit spatial control of tissue morphology and cell fate in culture on the micron scale. Culture substrates presenting grafted poly(ethylene glycol) (PEG) brushes can be used to achieve this task by creating microscale, non-fouling and cell adhesion resistant regions as well as regions where cells participate in biospecific interactions with covalently tethered ligands. To engineer complex tissues using such substrates, it will be necessary to sequentially pattern multiple PEG brushes functionalized to confer differential bioactivities and aligned in microscale orientations that mimic in vivo niches. Microcontact printing (&#956;CP) is a versatile technique to pattern such grafted PEG brushes, but manual &#956;CP cannot be performed with microscale precision. Thus, we combined advanced robotics with soft-lithography techniques and emerging surface chemistry reactions to develop a robotic microcontact printing (R-&#956;CP)-assisted method for fabricating culture substrates with complex, microscale, and highly ordered patterns of PEG brushes presenting orthogonal &#8216;click&#8217; chemistries. Here, we describe in detail the workflow to manufacture such substrates.

Fabricating Complex Culture Substrates Using Robotic Microcontact Printing R- &#181;CP and Sequential Nucleophilic Substitution

Cell culture substrates functionalized with microscale patterns of biological ligands have immense utility in the field of tissue engineering. Here, we demonstrate the versatile and automated manufacture of tissue culture substrates with multiple, micropatterned poly(ethylene glycol) brushes presenting orthogonal chemistries that enable spatially precise and site-specific immobilization of biological ligands.

In tissue engineering, it is desirable to exhibit spatial control of tissue morphology and cell fate in culture on the micron scale. Culture substrates ...

Fabricating Reactive Surfaces with Brush-like and Crosslinked Films of Azlactone-Functionalized Block Co-Polymers

In this paper, fabrication methods that generate novel surfaces using the azlactone-based block co-polymer, poly (glycidyl methacrylate)-block-poly (vinyl dimethyl azlactone) (PGMA-b-PVDMA), are presented. Due to the high reactivity of azlactone groups towards amine, thiol, and hydroxyl groups, PGMA-b-PVDMA surfaces can be modified with secondary molecules to create chemically or biologically functionalized interfaces for a variety of applications. Previous reports of patterned PGMA-b-PVDMA interfaces have used traditional top-down patterning techniques that generate non-uniform films and poorly controlled background chemistries. Here, we describe customized patterning techniques that enable precise deposition of highly uniform PGMA-b-PVDMA films in backgrounds that are chemically inert or that have biomolecule-repellent properties. Importantly, these methods are designed to deposit PGMA-b-PVDMA films in a manner that completely preserves azlactone functionality through each processing step. Patterned films show well-controlled thicknesses that correspond to polymer brushes (~90 nm) or to highly crosslinked structures (~1-10 &#956;m). Brush patterns are generated using either the parylene lift-off or interface directed assembly methods described and are useful for precise modulation of overall chemical surface reactivity by adjusting either the PGMA-b-PVDMA pattern density or the length of the VDMA block. In contrast, the thick, crosslinked PGMA-b-PVDMA patterns are obtained using a customized micro-contact printing technique and offer the benefit of higher loading or capture of secondary material due to higher surface area to volume ratios. Detailed experimental steps, critical film characterizations, and trouble-shooting guides for each fabrication method are discussed.

Surface fabrication methods for patterned deposition of nanometer thick brushes or micron thick, crosslinked films of an azlactone block co-polymer are reported. Critical experimental steps, representative results, and limitations of each method are discussed. These methods are useful for creating functional interfaces with tailored physical features and tunable surface reactivity.

In this paper, fabrication methods that generate novel surfaces using the azlactone-based block co-polymer, poly (glycidyl methacrylate)-block-poly (vinyl ...

Scalable Stamp Printing and Fabrication of Hemiwicking Surfaces

Hemiwicking is a process where a fluid wets a patterned surface beyond its normal wetting length due to a combination of capillary action and imbibition. This wetting phenomenon is important in many technical fields ranging from physiology to aerospace engineering. Currently, several different techniques exist for fabricating hemiwicking structures. These conventional methods, however, are often time consuming and are difficult to scale-up for large areas or are difficult to customize for specific, nonhomogeneous patterning geometries. The presented protocol provides researchers with a simple, scalable, and cost-effective method for fabricating micro-patterned hemiwicking surfaces. The method fabricates wicking structures through the use of stamp printing, polydimethylsiloxane (PDMS) molding, and thin-film surface coatings. The protocol is demonstrated for hemiwicking with ethanol on PDMS micropillar arrays coated with a 70 nm thick aluminum thin-film.

A simple protocol is provided for the fabrication of hemiwicking structures of varying sizes, shapes, and materials. The protocol uses a combination of physical stamping, PDMS molding, and thin-film surface modifications via common materials deposition techniques.

Hemiwicking is a process where a fluid wets a patterned surface beyond its normal wetting length due to a combination of capillary action and imbibition. ...

Metal-Assisted Electrochemical Nanoimprinting of Porous and Solid Silicon Wafers

Metal-assisted electrochemical imprinting (Mac-Imprint) is a combination of metal-assisted chemical etching (MACE) and nanoimprint lithography that is capable of direct patterning 3D micro- and nanoscale features in monocrystalline group IV (e.g., Si) and III-V (e.g., GaAs) semiconductors without the need of sacrificial templates and lithographical steps. During this process, a reusable stamp coated with a noble metal catalyst is brought in contact with a Si wafer in the presence of a hydrofluoric acid (HF) and hydrogen peroxide (H2O2) mixture, which leads to the selective etching of Si at the metal-semiconductor contact interface. In this protocol, we discuss the stamp and substrate preparation methods applied in two Mac-Imprint configurations: (1) Porous Si Mac-Imprint with a solid catalyst; and (2) Solid Si Mac-Imprint with a porous catalyst. This process is high throughput and is capable of centimeter-scale parallel patterning with sub-20 nm resolution. It also provides low defect density and large area patterning in a single operation and bypasses the need for dry etching such as deep reactive ion etching (DRIE).

A protocol for metal-assisted chemical imprinting of 3D microscale features with sub-20 nm shape accuracy into solid and porous silicon wafers is presented.

Metal-assisted electrochemical imprinting (Mac-Imprint) is a combination of metal-assisted chemical etching (MACE) and nanoimprint lithography that is ...

Direct-Contact Co-culture of Astrocytes and Glioblastoma Cells Patterned using Polyelectrolyte Multilayer Templates

Glioblastoma Multiforme (GBM) is the most abundant and fatal malignant brain cancer. There are more than 13,000 cases projected in the United States in 2020 and 2021. GBM tumors most often arise from astrocytes and are characterized by their invasive nature, often recruiting healthy tissues into tumor tissue. Understanding communication between astrocytes and glioblastoma cells is vital for the molecular understanding of tumor progression. This protocol demonstrates a novel patterned co-culture method to investigate contact-mediated effects of astrocytes on GBM employing layer-by-layer assembly and micro-capillary-force driven patterning. Advantages include a protein-free cell culture environment and precise control of cellular interaction dictated by the pattern dimensions. This technique provides a versatile, economical, reproducible protocol for mimicking cellular interaction between glioma and astrocytes in glioma tumors. This model can further be used to tease apart changes in GBM molecular biology due to physical contact with astrocytes or with non-contact mediated soluble cofactor communication.

This protocol describes a patterned direct contact glioma-astrocyte co-culture utilizing micro-contact printing on polyelectrolyte multilayers (PEMs) to pattern U87 or A172 GBM cells and primary astrocytes.

Glioblastoma Multiforme (GBM) is the most abundant and fatal malignant brain cancer. There are more than 13,000 cases projected in the United States in ...