The authors would like to acknowledge Innovate UK for funding this research under the DIRECT (33417-239227) and PCAP (27508-196153) projects. The authors would also like to thank PVOH Polymers Ltd., for providing materials and professional guidance during this work, and Unilever, AkzoNobel, and Carclo Technical Plastics, for their support.

1. Ink Formulation
<ol>
	<li>Prepare the solution for IJP by dissolving polyvinyl alcohol (8 wt.% PVOH in water) in purified water heated to 60 &#176;C.</li>
	<li>Add 10 g of mono-propylene glycol (MPG) (10 wt.% mono-propylene glycol in water), as a humectant, to the solution. 
	NOTE: The role of the humectant is to prevent blockages in the printhead.</li>
	<li>Stir the solution for several hours to ensure homogeneity and then filter it through a 5 &#181;m filter to remove any particulates that might block the nozzles.</li>
	<li>Visually assess the ink for homogeneity, especially for any incidence of sedimentation. If sedimentation is observed, then either stir/ultra-sonicate the solution for a long time (days) or formulate a new water-based solution with a PVOH with low molecular weight. 
	NOTE: Store all fluids in sealed beakers at room temperature.</li>
</ol>
2. Ink Characterization
<ol>
	<li>Perform all the ink characterization tests at room temperature in a clean room environment.</li>
	<li>Measure the viscosity of the solution using a viscometer. 
	NOTE: This test is required in order to ensure that the formulated ink is compatible with the IJP hardware. The inkjet printing process requires a low-viscosity solution of 4-20 cP. Measure the viscosity of the ink as a function of the shear rate using a rotational viscometer.</li>
	<li>Test the surface tension of the ink at room temperature using the pendant drop method. Use an appropriate measurement tool such as a tensiometer. Use the manufacturer&#39;s protocol. 
	NOTE: A typical solution for inkjet printing has a surface tension of 30-40 mN/m.</li>
	<li>Test the pH using a pH meter. Use the manufacturer&#39;s protocol. 
	NOTE: The pH is an essential parameter in water-based inks, as it provides essential information about both the properties and the stability of the formulated solutions. A neutral solution pH of 7 guarantees a stable process and a good lifetime for the printhead.</li>
	<li>Assess the wettability of the ink on different substrates by measuring the contact angle via a sessile drop experiment. Use a tensiometer to measure the surface energy of the possible substrates (e.g., glass, plastic, and paper). Measure the surface energy using the protocol supplied by the tensiometer manufacturer. 
	NOTE: The interaction between the drop and the substrate has a strong impact on the printing quality. To ensure the good adhesion of the ink to the substrate, the surface energy of the substrate should exceed the surface tension of the ink by 10-15 mN/m.</li>
</ol>
3. Inkjet Printing
NOTE: All the inkjet printing depositions were carried out at room temperature. The PVOH multilayers were deposited using a piezoelectric hybrid ink jet printing machine. A printhead with 512 nozzles (256 x 2 rows), a 30 &#181;m nozzle diameter, and a 42-pL drop size was used in this work.
<ol>
	<li>Prior to printing, thoroughly clean the glass substrates with acetone/methanol/isopropanol and Di water. Dry the substrates with an N2 gun.</li>
	<li>Load the substrate onto the print-bed and secure it firmly.</li>
	<li>Prepare the cartridge by flushing the ink through the print head. Remove any air or cleaning solution from the reservoir and nozzles.</li>
	<li>Imbed the cartridge into the printer. Connect the printhead to the global inkjet systems (GIS) print manager via the head personality board.</li>
	<li>Load the solution into the 150 mL syringe situated above the cartridge and seal the syringe with an airtight cap.</li>
	<li>Purge the ink through the nozzle by pressing the purge button. 
	NOTE: The nozzle-substrate distance has a strong influence on the jet trajectory and hence on the quality of the printed pattern. Therefore, adjust the nozzle-substrate distance using the software of the printer to reduce jet spreading.</li>
	<li>Set up the waveform and printing parameters using the GIS print software and Table 2. 
	NOTE: The GIS software interface allows control over both the draw and release amplitude and the width.</li>
	<li>Load the desired image file for printing using the GIS print manager software.</li>
	<li>Start the digital process and print the image pattern onto the substrate.</li>
</ol>
4. Analysis of the Printed Pattern
<ol>
	<li>Investigate the quality of the printed patterns using an optical microscope. Check for the presence of defects within printed features and assess the improvement in the quality when more layers were printed.</li>
	<li>Evaluate the surface topology and thickness profile of the inkjet-printed multilayers using a non-contact 3D surface profilometer (based on white light interferometry) via a 3D optical microscope. 
	NOTE: More details about measurements and the instruments that were used to formulate/print and characterize the printed patterns are presented in reference21.</li>
</ol>

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<li>Supaphol, P., Chuangchote, S. <a target="_blank" href="http://onlinelibrary.wiley.com/doi/10.1002/app.27664/full">On the electrospinning of poly(vinyl alcohol) nanofiber mats: A revisit.</a> J. Appl. Polym. Sci. 108 (2), 969-978 (2008).</li>
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<li>Hoath, S. D., et al. Links between Ink rheology, drop-on-demand jet formation, and printability. J Imaging Sci Technol. 53 (4), 1-8 (2009).</li>
<li>Pan, Z., et al. <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S0272884215012407">Recent development on preparation of ceramic inks in ink-jet printing.</a> Ceram Int. 41, 12515-12528 (2015).</li>
<li>Kamyshny, A., Magdassi, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Conductive+nanomaterials+for+printed+electronics%5BTitle%5D)+AND+%22Small%22%5BJournal%5D)">Conductive nanomaterials for printed electronics.</a> Small. 10 (17), 3515-3535 (2014).</li>
<li>Li, J., Lemme, M. C., Östling, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Inkjet+Printing+of+2D+Layered+Materials%5BTitle%5D)+AND+%22ChemPhysChem%22%5BJournal%5D)">Inkjet Printing of 2D Layered Materials.</a> ChemPhysChem. 15, 3427-3434 (2014).</li>
<li>Choi, H. W., Zhou, T., Singh, M., Jabbour, G. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Recent+developments+and+directions+in+printed+nanomaterials%5BTitle%5D)+AND+%22Nanoscale%22%5BJournal%5D)">Recent developments and directions in printed nanomaterials.</a> Nanoscale. 7, 3338-3355 (2015).</li>
<li>Basirico, L., Cosseddu, P., Fraboni, B., Bonfiglio, A. <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S0040609011010297">Inkjet printing of transparent, flexible, organic transistors.</a> Thin Solid Films. 520 (4), 1291-1294 (2011).</li>
<li>Komuro, N., Takaki, S., Suzuki, K., Citterio, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Inkjet+printed+%28bio%29chemical+sensing+devices%5BTitle%5D)+AND+%22Anal.Bioanal.Chem%22%5BJournal%5D)">Inkjet printed (bio)chemical sensing devices.</a> Anal.Bioanal.Chem. 405 (17), 5785-5805 (2013).</li>
<li>Cherrington, R., Wood, B. M., Salaoru, I., Goodship, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Digital+printing+of+titanium+dioxide+for+dye+sensitized+solar+cells%5BTitle%5D)+AND+%22J.+Vis.+Exp%22%5BJournal%5D)">Digital printing of titanium dioxide for dye sensitized solar cells.</a> J. Vis. Exp. , (2016).</li>
<li>Nelo, M., et al. <a target="_blank" href="http://iopscience.iop.org/article/10.7567/JJAP.52.05DB21/meta">Inkjet-printed memristor: Printing process development.</a> Jpn. J. Appl. Phys. 52, 1-6 (2013).</li>
<li>Jacot-Descombes, L., Gullo, R. M., Mastrangeli, M., Cadarso, V. J., Brugger, J. <a target="_blank" href="http://ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel7%2F11102%2F6651440%2F06651462.pdf&authDecision=-203">Inkjet-printed SU-8 Hemispherical Microcapsules and Silicon chip Embedding.</a> IET Micro & Nano Letters. 8 (10), 633-636 (2013).</li>
<li>Martin, G. D., Hoath, S. D., Hutchings, I. M. <a target="_blank" href="http://iopscience.iop.org/article/10.1088/1742-6596/105/1/012001/meta">Inkjet printing - the physics of manipulating liquid jets and drops.</a> J Phys Conf Series. 105, 012001(2008).</li>
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</ol>

The authors have nothing to disclose.

In this work, we successfully demonstrated the ability of inkjet printing technology to deposit polymer multilayers. The rheological behavior was investigated, and the experimental results demonstrate that the formulated ink displays pseudoplastic shear thinning behavior. Also, the PVOH ink is a neutral solution (pH 7) and shows good stability over time. Notably, it was successfully demonstrated that IJP technology is capable of producing polyvinyl alcohol multilayer structures, but further improvements in printing cover...

Polyvinyl alcohol is semicrystalline, artificial, non-toxic, water-soluble, insoluble in most organic solvents, biodegradable, and biocompatible in human tissues and has excellent gas-barrier properties1. Furthermore, due to its many useful properties, PVOH is widely used in a large number of applications. Nowadays, PVOH is used in: the manufacture of cleaning and detergent products, the food packaging industry, water treatment, textile, agriculture, and construction (as additives)1. However, PVOH has recently attracted an increased amount of attention for pharmaceutical uses2 (i.e., drug delivery) and in medical applications3,4 (e.g., wound dressing, soft contact lenses, eye drops, and soft implants for cartilage replacement). PVOH films are produced either through a melt or solution form. Melt processing is compatible only with PVOH with low hydrolysis levels or heavily plasticized PVOH. Thus, when using this pathway, some properties can be sacrificed1. On the other hand, a PVOH layer can be deposited via the solution form by drop casting5, spin coating6, or electrospinning7. However, these methods have a number of limitations in terms of the waste of unwanted material. For example, in the case of spin coating, it has been reported8 that 95% of the material is wasted. Additionally, these methods are quite rigid in term of design/features (no patterning capability) and have high overall processing costs. In order to overcome the limitation of the conventional solution processing, we here explore the potential of inkjet printing technology to provide a novel platform to produce polyvinyl alcohol (PVOH) multi-layer structures that have a strong impact on both the material and application perspectives.
Recent developments in the manufacturing sector have focused on cheap, simple, eco-friendly, and energy-saving processes. Inkjet printing (IJP) is a modern fabrication process that fits perfectly within this framework. The major advantages of IJP technology are the efficiency of material use, the digital (mask-free) and additive patterning, the large area capability, the compatibility with rigid/flexible substrates, and the low cost.
IJP is a deposition method that uses polymeric materials dispersed in a solvent. To date, functional polymer-9, ceramic-10, conductive nanomaterial-11, 2D-12, biologically-, and pharmaceutically-based13 materials have been successfully deposited. Recently, it has been reported that IJP was involved in the deposition of components as part of electronic devices, such as transistors14, sensors15, solar cells16, and memory devices17, as well in electronic packaging18.
The ink, cartridge, and substrate are equally important components that are employed in the printing process. First, the physical properties of the ink, such as the surface tension and the rheological properties (i.e., shear viscosity), have a significant impact on the printability behavior. Also, the pH plays an important role on both the solution (e.g., drying, foaming, and viscosity) and on the lifetime of the IJP print cartridge. Second, for the cartridge (piezoelectric), the driving voltage waveform actually defines the drop formation and both the directionality and the uniformity of the liquid jet. Finally, it is imperative that the ink/substrate interaction is very well understood, as the resolution and accuracy of the printed object are strongly dependent upon this interface. Solvent evaporation, phase changes from liquid to solid, and chemical reactions are the main processes that occur between the fluid drop and the substrate. All aspects involved in the IJP, from ink properties to drop/substrate mechanisms, are highlighted in review papers by Hutchings19 and by Derby20.
In this study, we explore the capabilities of IJP to manufacture polyvinyl alcohol multilayers. First, a PVOH water-based ink was formulated, and the main physical properties, such as rheological behavior, surface tension, and pH, were investigated. In this work, a piezoelectric inkjet printer was employed, and the appropriate waveform parameters were then identified. PVOH multilayers were printed, and the quality and surface/thickness profiles were assessed by optical microscopy.

<table><tbody><tr><td>Polyvinyl alcohol&amp;nbsp;</td><td>PVOH Polymers Ltd, UK</td><td>Poval 4-88</td><td></td></tr><tr><td>Mono-propylene glycol&amp;nbsp;</td><td>Sigma Aldrich, UK</td><td>W29004</td><td></td></tr><tr><td>DV2T viscometer&amp;nbsp;</td><td>Brookfield, UK</td><td></td><td></td></tr><tr><td>Attension Theta Optical Tensiometer&amp;nbsp;</td><td>Biolin Scientific, Sweden</td><td></td><td></td></tr><tr><td>HANNA pH meter&amp;nbsp;</td><td>HANNA Instruments, UK</td><td></td><td></td></tr><tr><td>industrial Inkjet XYPrint100Z</td><td>Industrial Inkjet Ltd, UK</td><td></td><td></td></tr><tr><td>ContourGT-K 3D optical microscope&amp;nbsp;</td><td>Bruker Corp, USA</td><td></td><td></td></tr></tbody></table>

inkjet-printed polyvinyl alcohol multilayers

Inkjet printing is a modern method for polymer processing, and in this work, we demonstrate that this technology is capable of producing polyvinyl alcohol (PVOH) multilayer structures. A polyvinyl alcohol aqueous solution was formulated. The intrinsic properties of the ink, such as surface tension, viscosity, pH, and time stability, were investigated. The PVOH-based ink was a neutral solution (pH 6.7) with a surface tension of 39.3 mN/m and a viscosity of 7.5 cP. The ink displayed pseudoplastic (non-Newtonian shear thinning) behavior at low shear rates, and overall, it demonstrated good time stability. The wettability of the ink on different substrates was investigated, and glass was identified as the most suitable substrate in this particular case. A proprietary 3D inkjet printer was employed to manufacture polymer multilayer structures. The morphology, surface profile, and thickness uniformity of inkjet-printed multilayers were evaluated via optical microscopy.

The physical properties of PVOH water-based ink, such as surface tension, viscosity/rheological behavior, pH, wetting, and time stability, were investigated. The viscosity of the ink used in this work was 7.5 cP, and the surface tension was 39.3 mN/m. Additionally, the formulated ink was neutral (pH 7), with the results summarized in Table 1.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Ink</...

Watch this Scientific Journal Video about Inkjet-printed Polyvinyl Alcohol Multilayers at JoVE.com

Inkjet-printed Polyvinyl Alcohol Multilayers

An inkjet printer was used to manufacture polyvinyl alcohol multilayers. Polyvinyl alcohol water-based ink was formulated, and the main physical properties were investigated.

Inkjet printing is a modern method for polymer processing, and in this work, we demonstrate that this technology is capable of producing polyvinyl alcohol ...

inkjet-printed-polyvinyl-alcohol-multilayers

Research

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Engineering

12.6K Views.  De Montfort University. An inkjet printer was used to manufacture polyvinyl alcohol multilayers. Polyvinyl alcohol water-based ink was formulated, and the main physical properties were investigated. 

Video: Inkjet-printed Polyvinyl Alcohol Multilayers

Polymer Microarrays for High Throughput Discovery of Biomaterials

The discovery of novel biomaterials that are optimized for a specific biological application is readily achieved using polymer microarrays, which allows a combinatorial library of materials to be screened in a parallel, high throughput format1. Herein is described the formation and characterization of a polymer microarray using an on-chip photopolymerization technique 2. This involves mixing monomers at varied ratios to produce a library of monomer solutions, transferring the solution to a glass slide format using a robotic printing device and curing with UV irradiation. This format is readily amenable to many biological assays, including stem cell attachment and proliferation, cell sorting and low bacterial adhesion, allowing the ready identification of 'hit' materials that fulfill a specific biological criterion3-5. Furthermore, the use of high throughput surface characterization (HTSC) allows the biological performance to be correlated with physio-chemical properties, hence elucidating the biological-material interaction6. HTSC makes use of water contact angle (WCA) measurements, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). In particular, ToF-SIMS provides a chemically rich analysis of the sample that can be used to correlate the cell response with a molecular moiety. In some cases, the biological performance can be predicted from the ToF-SIMS spectra, demonstrating the chemical dependence of a biological-material interaction, and informing the development of hit materials5,3.

A description of the formation of a polymer microarray using an on-chip photopolymerization technique. The high throughput surface characterization using atomic force microscopy, water contact angle measurements, X-ray photoelectron spectroscopy and time of flight secondary ion mass spectrometry and a cell attachment assay is also described.

The discovery of novel biomaterials that are optimized for a specific biological application is readily achieved using polymer microarrays, which allows a ...

Bioengineering

Layer-by-layer Synthesis and Transfer of Freestanding Conjugated Microporous Polymer Nanomembranes

CMP as large surface area materials have attracted growing interest recently, due to their high variability in the incorporation of functional groups in combination with their outstanding thermal and chemical stability, and low densities. However, their insoluble nature causes problems in their processing since usually applied techniques such as spin coating are not available. Especially for membrane applications, where the processing of CMP as thin films is desirable, the processing problems have hindered their commercial application.
Here we describe the interfacial synthesis of CMP thin films on functionalized substrates via molecular layer-by-layer (l-b-l) synthesis. This process allows the preparation of films with desired thickness and composition and even desired composition gradients.
The use of sacrificial supports allows the preparation of freestanding membranes by dissolution of the support after the synthesis. To handle such ultra-thin freestanding membranes the protection with sacrificial coatings showed great promise, to avoid rupture of the nanomembranes. To transfer the nanomembranes to the desired substrate, the coated membranes are upfloated at the air-liquid interface and then transferred via dip coating.

In this paper we describe the interfacial synthesis of conjugated microporous polymers (CMP) on sacrificial substrates, and the dissolution of the substrate for the preparation of freestanding CMP nanomembranes. In addition, we will describe how the fragile nanomembranes can be transferred to other substrates.

CMP as large surface area materials have attracted growing interest recently, due to their high variability in the incorporation of functional groups in ...

Chemistry

Reactive Vapor Deposition of Conjugated Polymer Films on Arbitrary Substrates

We demonstrate a method of conformally coating conjugated polymers on arbitrary substrates using a custom-designed, low-pressure reaction chamber. Conductive polymers, poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-propylenedioxythiophene) (PProDOT), and a semiconducting polymer, poly(thieno[3,2-b]thiophene) (PTT), were deposited on unconventional highly-disordered and textured substrates with high surface areas, such as paper, towels and fabrics. This reported deposition chamber is an improvement of previous vapor reactors because our system can accommodate both volatile and nonvolatile monomers, such as 3,4-propylenedioxythiophene and thieno[3,2-b]thiophene. Utilization of both solid and liquid oxidants are also demonstrated. One limitation of this method is that it lacks sophisticated in situ thickness monitors. Polymer coatings made by the commonly used solution-based coating methods, such as spin-coating and surface grafting, are often not uniform or susceptible to mechanical degradation. This reported vapor phase deposition method overcomes those drawbacks and is a strong alternative to common solution-based coating methods. Notably, polymer films coated by the reported method are uniform and conformal on rough surfaces, even at a micrometer scale. This feature allows for future application of vapor deposited polymers in electronics devices on flexible and highly textured substrates.

This paper presents a protocol for reactive vapor deposition of poly(3,4-ethylenedioxythiophene), poly(3,4-propylenedioxythiophene), and poly(thieno[3,2-b]thiophene) films on glass slides and rough substrates, such as textiles and paper.

We demonstrate a method of conformally coating conjugated polymers on arbitrary substrates using a custom-designed, low-pressure reaction chamber. ...

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 ...

Polymeric Microneedle Array Fabrication by Photolithography

This manuscript describes the fabrication of polymeric microneedle (MN) arrays by photolithography. It involves a simple mold-free process by using a photomask consisting of embedded micro-lenses. Embedded micro-lenses were found to influence MN geometry (sharpness). Robust MN arrays with tip diameters ranging between 41.5 &#181;m &#177; 8.4 &#181;m and 71.6 &#181;m &#177; 13.7 &#181;m, with two different lengths (1,336 &#181;m &#177; 193 &#181;m and 957 &#181;m &#177; 171 &#181;m) were fabricated. These MN arrays may provide potential applications in delivery of low molecular and macromolecular therapeutic agents through skin.

Here, we present a protocol describing a mold-free fabrication process of the polymeric microneedles by photolithography.

This manuscript describes the fabrication of polymeric microneedle (MN) arrays by photolithography. It involves a simple mold-free process by using a ...

Inkjet Printing All Inorganic Halide Perovskite Inks for Photovoltaic Applications

A method for synthesizing photoactive inorganic&#160;perovskite quantum dot inks and an inkjet printer deposition method, using the synthesized inks, are demonstrated. The ink synthesis is based on a simple wet chemical reaction and the inkjet printing protocol is a facile step by step method. The inkjet printed thin films have been characterized by X-ray diffraction, optical absorption spectroscopy, photoluminescent spectroscopy, and electronic transport measurements. X-ray diffraction of the printed quantum dot films indicates a crystal structure consistent with an orthorhombic room temperature phase with (001) orientation. In conjunction with other characterization methods, the X-ray diffraction&#160;measurements show high quality films can be obtained through the inkjet printing method.

A protocol for synthesizing inorganic-lead-halide hybrid perovskite quantum dot inks for inkjet printing and the protocol for preparing and printing the quantum dot inks in an inkjet printer with post characterization techniques are presented.

A method for synthesizing photoactive inorganic&#160;perovskite quantum dot inks and an inkjet printer deposition method, using the synthesized inks, are ...

Hybrid Printing for the Fabrication of Smart Sensors

A method to combine additively manufactured substrates or foils and multilayer inkjet printing for the fabrication of sensor devices is presented. First, three substrates (acrylate, ceramics, and copper) are prepared. To determine the resulting material properties of these substrates, profilometer, contact angle, scanning electron microscope (SEM), and focused ion beam (FIB) measurements are done. The achievable printing resolution and suitable drop volume for each substrate are, then, found through the drop size tests. Then, layers of insulating and conductive ink are inkjet printed alternately to fabricate the target sensor structures. After each printing step, the respective layers are individually treated by photonic curing. The parameters used for the curing of each layer are adapted depending on the printed ink, as well as on the surface properties of the respective substrate. To confirm the resulting conductivity and to determine the quality of the printed surface, four-point probe and profilometer measurements are done. Finally, a measurement set-up and results achieved by such an all-printed sensor system are shown to demonstrate the achievable quality.

Here we present a protocol for the fabrication of inkjet-printed multilayer sensor structures on additively manufactured substrates and foil.

A method to combine additively manufactured substrates or foils and multilayer inkjet printing for the fabrication of sensor devices is presented. First, ...

Multimodal 3D Printing of Phantoms to Simulate Biological Tissue

Biomedical optical imaging is playing an important role in diagnosis and treatment of various diseases. However, the accuracy and the reproducibility of an optical imaging device are greatly affected by the performance characteristics of its components, the test environment, and the operations. Therefore, it is necessary to calibrate these devices by traceable phantom standards. However, most of the currently available phantoms are homogeneous phantoms that cannot simulate multimodal and dynamic characteristics of biological tissue. Here, we show the fabrication of heterogeneous tissue-simulating phantoms using a production line integrating a spin coating module, a polyjet module, a fused deposition modeling (FDM) module, and an automatic control framework. The structural information and the optical parameters of a &#34;digital optical phantom&#34; are defined in a prototype file, imported to the production line, and fabricated layer-by-layer with sequential switch between different printing modalities. Technical capability of such a production line is exemplified by the automatic printing of skin-simulating phantoms that comprise the epidermis, dermis, subcutaneous tissue, and an embedded tumor.

Spin coating, polyjet printing, and fused deposition modeling are integrated to produce multilayered heterogeneous phantoms that simulate structural and functional properties of biological tissue.

Biomedical optical imaging is playing an important role in diagnosis and treatment of various diseases. However, the accuracy and the reproducibility of ...

Multi-step Variable Height Photolithography for Valved Multilayer Microfluidic Devices

Microfluidic systems have enabled powerful new approaches to high-throughput biochemical and biological analysis. However, there remains a barrier to entry for non-specialists who would benefit greatly from the ability to develop their own microfluidic devices to address research questions. Particularly lacking has been the open dissemination of protocols related to photolithography, a key step in the development of a replica mold for the manufacture of polydimethylsiloxane (PDMS) devices. While the fabrication of single height silicon masters has been explored extensively in literature, fabrication steps for more complicated photolithography features necessary for many interesting device functionalities (such as feature rounding to make valve structures, multi-height single-mold patterning, or high aspect ratio definition) are often not explicitly outlined. 
Here, we provide a complete protocol for making multilayer microfluidic devices with valves and complex multi-height geometries, tunable for any application. These fabrication procedures are presented in the context of a microfluidic hydrogel bead synthesizer and demonstrate the production of droplets containing polyethylene glycol (PEG diacrylate) and a photoinitiator that can be polymerized into solid beads. This protocol and accompanying discussion provide a foundation of design principles and fabrication methods that enables development of a wide variety of microfluidic devices. The details included here should allow non-specialists to design and fabricate novel devices, thereby bringing a host of recently developed technologies to their most exciting applications in biological laboratories.

Multilayer microfluidic devices often involve the fabrication of master molds with complex geometries for functionality. This article presents a complete protocol for multi-step photolithography with valves and variable height features tunable to any application. As a demonstration, we fabricate a microfluidic droplet generator capable of producing hydrogel beads.

Microfluidic systems have enabled powerful new approaches to high-throughput biochemical and biological analysis. However, there remains a barrier to ...

Frugal Imaging Technique of Capillary Flow Through Three-Dimensional Polymeric Printing Powders

The development of novel imaging techniques of molecular and colloidal transport, including nanoparticles, is an area of active investigation in microfluidic and millifluidic studies. With the advent of three-dimensional (3D) printing, a new domain of materials has emerged, thereby increasing the demand for novel polymers. Specifically, polymeric powders, with average particle sizes on the order of a micron, are experiencing a growing interest from academic and industrial communities. Controlling material tunability at the mesoscopic to microscopic length scales creates opportunities to develop innovative materials, such as gradient materials. Recently, a need for micron-sized polymeric powders has been growing, as clear applications for the material are developing. Three-dimensional printing provides a high-throughput process with a direct link to new applications, driving investigations into the physio-chemical and transport interactions on a mesoscale. The protocol that is discussed in this article provides a non-invasive technique to image fluid flow in packed powder beds, providing high temporal and spatial resolution while leveraging mobile technology that is readily available from mobile devices, such as smartphones. By utilizing a common mobile device, the imaging costs that would normally be associated with an optical microscope are eliminated, resulting in a frugal-science approach. The proposed protocol has successfully characterized a variety of combinations of fluids and powders, creating a diagnostic platform for quickly imaging and identifying an optimal combination of fluid and powder.

The proposed technique will provide a novel, efficient, frugal, and non-invasive approach for imaging fluidic flow through a packed powder bed, yielding high spatial and temporal resolution.