This work was supported by the Institute of Information &#38; Communications Technology Planning and Evaluation (IITP) grant funded by the Korean government (MSIT) (No. 2018-0-01290, the Development of an open dataset and cognitive processing technology for the recognition of features derived from unstructured humans (police officers, traffic safety officers, pedestrians, etc.) motions used in self-driving cars) and the GIST Research Institute (GRI) grant funded by the GIST in 2019.

1. Blood vessel mock-up design for the demonstration
<ol>
	<li>Set the diameter of the proximal main vessel to 25 mm, the diameters of the distal main vessel and the side branch equal to 22 mm. Set the total length of the vessels equal to 140 mm. Set the length of the proximal main vessel, the distal main vessel and the side branch to 65 mm, 75 mm and 65 mm, respectively. The complete blood vessel is shown in Figure 2 and Figure 3.</li>
	<li>Print the computer model of the branched vessel by using an FDM 3D printer. Use a polycarbonate filament.</li>
</ol>
2. Blood vessel mock-up fabrication by molding
<ol>
	<li>Create a box-shaped container that will house the 3D printed part. Set the container dimensions to 110 x 105 x 70 mm and use an acrylic plate.</li>
	<li>With the 3D printed branched vessel placed at the center of the box, gently pour the silicone inside the container to minimize bubble formation. Dry the liquid silicone and harden it for 36~48 h.</li>
	<li>Remove solidified silicone from the container and cut it in half to remove the 3D printed part. Rejoin the divided silicone at the cut plane. The resulting joined body is the blood vessel mockup. The final result is shown Figure 4.</li>
</ol>
3. Design of the branched stent based on kirigami
NOTE: The size of the branched stent is made to snuggly fit inside the Y-shaped pathway of the blood vessel mockup. The interior is made hollow, and the surface tubular meshes are designed to functionally fold and return to the full unfolded configuration.
<ol>
	<li>Design the trunk of the bifurcated stent following wavy patterns similar to conventional stents. Set the diameter of the trunk to 22 mm and the length of the trunk to 38 mm.</li>
	<li>Design the bifurcated branches to be a cylinder, as shown in Figure 5B. Set the diameter of the branch to 18 mm and the length of the branch to 34 mm.</li>
	<li>Set the total length of the stent to 72 mm. The final shape is shown in Figure 6.</li>
</ol>
4. 3D printing with SMP filaments
<ol>
	<li>Print the bifurcated stent in an FDM 3D printer using an SMP filament. The major composition of this filament is polyurethane. The commercial vendor also provides these filaments in the form of pellets so that the end user can also add additional substances to tailor the characteristics of the material (Figure 7).</li>
	<li>Use slicing software for model slicing and to control the settings of the 3D printer. Set the extruder temperature to 230 &#176;C and the temperature of the printer bed to room temperature. Set the layer height to 0.1 mm to minimize the staircase effect.</li>
	<li>Set the printing speed to 3,600 mm/min. Set the amount of interior fill percentage to 80%. Include the supporter formation during printing, which is needed because the structure is hollow in the interior. Figure 8 illustrates the printing process.</li>
</ol>
5. Smoothing out the surface
NOTE: The following steps are required because rough surfaces can damage the vessels by abrasion.
<ol>
	<li>Remove the supporters using cutters (Figure 9A). The supporters are attached at the interior of the stent. When removing the stents, exercise extreme caution to avoid tearing the stents.</li>
	<li>Rub the surface against sandpaper (Figure 9B) to remove the layer lines, striations, or blemishes on the printed surface. Repeated polishing may be needed where the supporters are removed by the cutters.</li>
	<li>Paint the surface using a spray in a well-ventilated location, and wear a personal mask. Clean, sand, and dry the surface. Protect from overspraying by applying thin layers of repeated paints. Use black paints to enhance the contrast between the silicone vessel mockup and the stent (Figure 9C).</li>
</ol>
6. Deforming the bifurcated stent
<ol>
	<li>Place the bifurcated stents in warm water such that the temperature is above the glass transition temperature. When the stent becomes softened, push one half of the branch against the other half. Nest one half within the other half, as shown in Figure 10A.</li>
	<li>Fold the two branches into a single cylinder so that it can travel through the main vessel. Perform the same nesting process to the other branch. Subsequently, the two halves of the cylinders are closed into one, as shown in Figure 10B.</li>
</ol>
7. Insertion of the bifurcated stent into the vessels
<ol>
	<li>Fill a tank with warm water. Set the water temperature to 55-60 &#176;C. Immerse the silicone vessel mockup inside the tank. Orient the mockup such that the main vessel is above and the branches are below.</li>
	<li>Insert the folded bifurcated stent into the opening of the silicone vessel mockup from above. Orient the folded bifurcated stent such that its branches are towards the opening. The folded bifurcated stent will start to expand, and the lower branches will divide such that each branch will slide towards its mating pathway from the bifurcation core of the Y-shaped vessels (Figure 12).</li>
</ol>

<ol>
	<li>Migliavacca, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stainless+and+shape+memory+alloy+coronary+stents:+a+computational+study+on+the+interaction+with+the+vascular+wall.">Stainless and shape memory alloy coronary stents: a computational study on the interaction with the vascular wall.</a> Biomechanics and Modeling in Mechanobiology. 2 (4), 205-217 (2004).</li><li>Kuribayashi, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-deployable+origami+stent+grafts+as+a+biomedical+application+of+Ni-rich+TiNi+shape+memory+alloy+foil.">Self-deployable origami stent grafts as a biomedical application of Ni-rich TiNi shape memory alloy foil.</a> Material Science and Engineering A. 419, 131-137 (2006).</li><li>Suwaidi, A. I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immediate+and+long-term+outcome+of+intracoronary+stent+implantation+for+true+bifurcation+lesions.">Immediate and long-term outcome of intracoronary stent implantation for true bifurcation lesions.</a> Journal of the American College of Cardiology. 35 (4), 929-936 (2000).</li><li>Mao, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sequential+self-folding+structures+by+3D+printed+digital+shape+memory+polymers.">Sequential self-folding structures by 3D printed digital shape memory polymers.</a> Scientific Reports. 5, 13616 (2015).</li><li>Ge, Q., Qi, H. J., Dunn, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Active+materials+by+four-dimension+printing.">Active materials by four-dimension printing.</a> Applied Physics Letters. 103, 131901 (2013).</li><li>Wu, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multi-shape+active+composites+by+3D+printing+of+digital+shape+memory+polymers.">Multi-shape active composites by 3D printing of digital shape memory polymers.</a> Scientific Reports. 6, 24224 (2016).</li><li>Chen, S., Zhang, Q., Feng, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=3D+printing+of+tunable+shape+memory+polymer+blends.">3D printing of tunable shape memory polymer blends.</a> Journal of Materials Chemistry C. 5, 8361-8365 (2017).</li><li>Qi, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multimaterial+4D+printing+with+tailorable+shape+memory+polymers.">Multimaterial 4D printing with tailorable shape memory polymers.</a> Scientific Reports. 6, 31110 (2016).</li><li>Lendlein, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biodegradable,+elastic+shape-memory+polymers+for+potential+biomedical+applications.">Biodegradable, elastic shape-memory polymers for potential biomedical applications.</a> Science. 296, 1673-1676 (2002).</li><li>Lendlein, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Shape+memory+polymers.">Shape memory polymers.</a> Angewandte chemie. 41, 2034-2057 (2002).</li><li>Baer, G. 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C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+kirigami+approach+to+engineering+elasticity+in+nanocomposites+through+patterned+defects.">A kirigami approach to engineering elasticity in nanocomposites through patterned defects.</a> Nature Materials. 14, 785-789 (2015).</li><li>Rossiter, J., Sareh, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kirigami+design+and+fabrication+for+biomimetic+robotics.">Kirigami design and fabrication for biomimetic robotics.</a> Proc. SPIE. 9055, (2014).</li><li>Kim, T., Lee, Y. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Shape+transformable+bifurcated+stents.">Shape transformable bifurcated stents.</a> Scientific Reports. 8, 13911 (2018).</li></ol>

The authors have nothing to disclose.

Stents are often used to clear the clogged internal pathways such as the blood vessels and airways of patients. Surgical operation of inserting stents requires the careful consideration of the patient&#8217;s illness and human anatomical characteristics. The shape of the vessel is complex, and diverse branching conditions exist. However, the standard stent operational procedures are based on mass-produced stents with standard sizes. In this protocol, we showed how to personally tailor the fabrication of the stent based o...

Stents are used to widen narrowed or stenosed passages in humans, such as blood vessels and airways. Stents are tubular structures that resemble the passages and mechanically support the passages from further collapsing. Typically, self-expanding metal stents (SEMS) are widely adopted. These stents are made from alloys composed of cobalt-chromium (stainless-steel) and nickel-titanium (nitinol)1,2. The downside of metal stents is that pressure necrosis can exist where the metal wires of the stent come into contact with the live tissues and the stents are impacted. Furthermore, the vessels of the body can be irregularly shaped and are much more complex than simple tubular structures. In particular, there are many specialized clinical procedures to install stents in branched lumens. In a Y-shaped lumen, two cylindrical stents are simultaneously inserted and joined at a branch3. For each additional branch, an additional surgical procedure needs to be conducted. The procedure requires specially trained doctors, and the insertion is extremely challenging due to the protruding features of the branched stents.
The complexity of the shape of bifurcated stents makes it a very suitable target for 3D printing. Conventional stents are mass produced in standardized sizes and shapes. Using the 3D printing fabrication methodology, it is possible to customize the shape of the stent for each patient. Because shapes are made by repeatedly adding layer-by-layer of the sectional shapes of the target object, in theory, this method can be used to fabricate parts of any shape and size. Conventional stents are mostly cylindrical in shape. However, human vessels have branches, and the diameters change along the tubes. Using the proposed approach, all these variations in shapes and sizes can be accommodated. Additionally, although not demonstrated, the used materials can also change within a single stent. For example, we can use stiffer materials where support is needed and softer materials where more flexibility is required.
The shape changing requirement of bifurcated stents calls for 4D printing, namely, 3D printing with the additional consideration of time. 3D printed structures formed using specialized materials can be programmed to change their shape by an external stimulation, such as heat. The transformation is self-sustained and requires no external power sources. One special material that is suitable for 4D printing is an SMP4,5,6,7,8,9, which exhibits shape memory effects when exposed to a material-specific triggering glass transition temperature. At this temperature, the segments become soft so that the structure returns to its original shape. After the structure is 3D printed, it is heated to a temperature slightly above the glass transition temperature. At this point, the structure becomes soft, and we are able to deform the shape by applying forces. While maintaining the applied forces, the structure is cooled down, becomes hardened and retains its deformed shape, even after the applied forces are removed. Subsequently, at the final stage, when the structure needs to return to its original shape, such as the moment when the structure reaches the target site, heat is supplied so that the structure reaches its glass transition temperature. Finally, the structure returns to its memorized original shape. Figure 1 illustrates the various stages previously explained. The SMPs can be easily stretched, and there are some SMPs that are biocompatible and biodegradable9,10. There are many uses for SMPs in the field of medicine9,10, and stents11,12 are one of them.
The patterns of the stents and the folding design follow the Japanese paper cutting design called &#34;kirigami.&#34;&#160;This process resembles the well-known paper folding technique called &#34;origami,&#34;&#160;but the difference is that in addition to folding, cutting of the paper is also allowed in the design. This technique has been used in arts and has also been applied in engineering applications2,3,13,14. In short, kirigami can be used to transform a planar structure to a three-dimensional structure by applying forces at specifically designed spots. In our design requirements, the stent needs to be a simple cylindrical shape when inserted into the pathways, and the cylinder should divide along its length where each half should unfold to a fully cylindrical shape at the targeted branched vessel. The solution lies in the fact that the main vessel and the side branches are folded into a single cylinder such that the side branches will not interfere with the walls of the vessels during the insertion. The unfolding command signal comes from the increase in the ambient temperature above the glass transition temperature of the SMP. Additionally, the folding will be conducted outside the patient body by softening the 3D printed bifurcated stent and folding the side branch into the main vessel.
Conventional methods required the insertion of multiple cylindrical stents whose number equals the number of branches. This method was inevitable because the protrusions of the side branches hampered the walls of the pathways and made it impossible to insert a complete bifurcated stent in its entirety. Using the kirigami structure and 4D printing, the above problems can be resolved. This protocol also shows the visualization of the effectiveness of the proposed method using a silicone vessel model fabricated after the shape of blood vessels. Through this mock-up, the effectiveness of the proposed invention during the insertion process and further possibilities of new applications can be seen.
The purpose of this protocol is to clearly outline the steps involved in printing an SMP using a fused deposition modeling (FDM) printer. Additionally, techniques involved in deforming the printed bifurcated stents to the folded state, the insertion of the folded bifurcated stents to the target site, and the signaling and unfolding of the structure to its original shape are given in detail. The demonstration of the insertion utilizes a silicone mock-up of blood vessels. The protocol also provides the procedures involved in fabricating this mock-up using a 3D printer and molding.

<table border="0" cellpadding="0" cellspacing="0" style="width:965px;" width="965">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">Fortus380mc</td>
			<td style="width:169px;">Stratasys</td>
			<td style="width:199px;">Fortus 380mc</td>
			<td style="width:343px;">FDM 3D printer for printing blood vessel mock-up</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">Moment1 3D printer</td>
			<td style="width:169px;">Moment</td>
			<td style="width:199px;">Moment 1</td>
			<td>FDM 3D printer for printing bifurcated stent</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">PC(white) Filament Canister</td>
			<td>Stratasys</td>
			<td>PC(white) Filament Canister</td>
			<td>PC filament for printing blood vessel mock-up</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;width:255px;">PLM software NX 10.0</td>
			<td style="width:169px;">Siemens</td>
			<td style="width:199px;">NX 10.0</td>
			<td>3D CAD modeling software</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">Sandpaper</td>
			<td>DAESUNG</td>
			<td>CC-600CW</td>
			<td>Smooting out the surface of the bifurcated stent&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Shape Memory Polymer filament</td>
			<td>SMP Technologies Inc</td>
			<td style="width:199px;">MM-5520</td>
			<td>Shape memory polymer filament</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:255px;">silicon</td>
			<td style="width:169px;">Shinetus</td>
			<td style="width:199px;">KE-1606</td>
			<td>silicon for blood vessel mock-up</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Simplify3D</td>
			<td>Simplify3D</td>
			<td>Simplify3D 4.0.1</td>
			<td>Slicing software for model slicing&#160;</td>
		</tr>
	</tbody>
</table>

4d printed bifurcated stents with kirigami-inspired structures

Branched vessels, typically in the form of the letter &#34;Y,&#34;&#160;can be narrowed or blocked, resulting in serious health problems. Bifurcated stents, which are hollow in the interior and exteriorly shaped to the branched vessels, surgically inserted inside the branched vessels, act as a supporting structure so that bodily fluids can freely travel through the interior of the stents without being obstructed by the narrowed or blocked vessels. For a bifurcated stent to be deployed at the target site, it needs to be injected inside the vessel and travel within the vessel to reach the target site. The diameter of the vessel is much smaller than the bounding sphere of the bifurcated stent; thus, a technique is required so that the bifurcated stent remains small enough to travel through the vessel and expands at the targeted branched vessel. These two conflicting conditions, that is, small enough to pass through and large enough to structurally support narrowed passages, are extremely difficult to satisfy simultaneously. We use two techniques to fulfill the above requirements. First, on the material side, a shape memory polymer (SMP) is used to self-initiate shape changes from small to large, that is, being small when inserted and becoming large at the target site. Second, on the design side, a kirigami pattern is used to fold the branching tubes into a single tube with a smaller diameter. The presented techniques can be used to engineer structures that can be compacted during transportation and return to their functionally adept shape when activated. Although our work is targeted on medical stents, biocompatibility issues need to be solved before actual clinical use.

In this protocol, we showed the procedures required to fabricate a bifurcated stent. The stent uses a kirigami structure to allow the bifurcated stent to fold into a compact cylindrical tube, which is very suitable for sliding through the narrow pathways of blood vessels. The SMP allows the folded structure to return to its original shape when the temperature reaches the glass transition temperature. The original shape, 3D printed using the SMP material, closely matches the branched vessels. In other words, the interior ...

Watch this Scientific Journal Video about 4D Printed Bifurcated Stents with Kirigami-Inspired Structures at JoVE.com

4D Printed Bifurcated Stents with Kirigami-Inspired Structures

Using a 3D printer, a shape memory polymer filament is extruded to form a branched tubular structure. The structure is patterned and shaped such that it can contract into a compact form once folded and then return to its formed shape when heated.

Branched vessels, typically in the form of the letter &#34;Y,&#34;&#160;can be narrowed or blocked, resulting in serious health problems. Bifurcated ...

4d-printed-bifurcated-stents-with-kirigami-inspired-structures

Research

JoVE Journal

Engineering

7.8K Views.  Gwangju Institution of Science and Technology. Using a 3D printer, a shape memory polymer filament is extruded to form a branched tubular structure. The structure is patterned and shaped such that it can contract into a compact form once folded and then return to its formed shape when heated.

Video: 4D Printed Bifurcated Stents with Kirigami-Inspired Structures

Prescribed 3-D Direct Writing of Suspended Micron/Sub-micron Scale Fiber Structures via a Robotic Dispensing System

A 3-axis dispensing system is utilized to control the initiating and terminating fiber positions and trajectory via the dispensing software. The polymer fiber length and orientation is defined by the spatial positioning of the dispensing system 3-axis stages. The fiber diameter is defined by the prescribed dispense time of the dispensing system valve, the feed rate (the speed at which the stage traverses from an initiating to a terminating position), the gauge diameter of the dispensing tip, the viscosity and surface tension of the polymer solution, and the programmed drawing length. The stage feed rate affects the polymer solution&#8217;s evaporation rate and capillary breakup of the filaments. The dispensing system consists of a pneumatic valve controller, a droplet-dispensing valve and a dispensing tip. Characterization of the direct write process to determine the optimum combination of factors leads to repeatedly acquiring the desired range of fiber diameters. The advantage of this robotic dispensing system is the ease of obtaining a precise range of micron/sub-micron fibers onto a desired, programmed location via automated process control. Here, the discussed self-assembled micron/sub-micron scale 3D structures have been employed to fabricate suspended structures to create micron/sub-micron fluidic devices and bioengineered scaffolds.

Here, we present a protocol to fabricate freely-suspended, micron/sub-micron scale polymer fibers and &#8220;web-like&#8221; structures generated via automated direct writing procedure by means of a 3-axis dispensing system.

A 3-axis dispensing system is utilized to control the initiating and terminating fiber positions and trajectory via the dispensing software. The polymer ...

Methods for Measuring the Orientation and Rotation Rate of 3D-printed Particles in Turbulence

Experimental methods are presented for measuring the rotational and translational motion of anisotropic particles in turbulent fluid flows. 3D printing technology is used to fabricate particles with slender arms connected at a common center. Shapes explored are crosses (two perpendicular rods), jacks (three perpendicular rods), triads (three rods in triangular planar symmetry), and tetrads (four arms in tetrahedral symmetry). Methods for producing on the order of 10,000 fluorescently dyed particles are described. Time-resolved measurements of their orientation and solid-body rotation rate are obtained from four synchronized videos of their motion in a turbulent flow between oscillating grids with R&#955; = 91. In this relatively low-Reynolds number flow, the advected particles are small enough that they approximate ellipsoidal tracer particles. We present results of time-resolved 3D trajectories of position and orientation of the particles as well as measurements of their rotation rates.

We use 3D printing to fabricate anisotropic particles in the shapes of jacks, crosses, tetrads, and triads, whose alignments and rotations in turbulent fluid flow can be measured from multiple simultaneous video images.

Experimental methods are presented for measuring the rotational and translational motion of anisotropic particles in turbulent fluid flows. 3D printing ...

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.

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 ...

Experimental Protocol to Determine the Chloride Threshold Value for Corrosion in Samples Taken from Reinforced Concrete Structures

The aging of reinforced concrete infrastructure in developed countries imposes an urgent need for methods to reliably assess the condition of these structures. Corrosion of the embedded reinforcing steel is the most frequent cause for degradation. While it is well known that the ability of a structure to withstand corrosion depends strongly on factors such as the materials used or the age, it is common practice to rely on threshold values stipulated in standards or textbooks. These threshold values for corrosion initiation (Ccrit) are independent of the actual properties of a certain structure, which clearly limits the accuracy of condition assessments and service life predictions. The practice of using tabulated values can be traced to the lack of reliable methods to determine Ccrit on-site and in the laboratory.
Here, an experimental protocol to determine Ccrit for individual engineering structures or structural members is presented. A number of reinforced concrete samples are taken from structures and laboratory corrosion testing is performed. The main advantage of this method is that it ensures real conditions concerning parameters that are well known to greatly influence Ccrit, such as the steel-concrete interface, which cannot be representatively mimicked in laboratory-produced samples. At the same time, the accelerated corrosion test in the laboratory permits the reliable determination of Ccrit prior to corrosion initiation on the tested structure; this is a major advantage over all common condition assessment methods that only permit estimating the conditions for corrosion after initiation, i.e., when the structure is already damaged.
The protocol yields the statistical distribution of Ccrit for the tested structure. This serves as a basis for probabilistic prediction models for the remaining time to corrosion, which is needed for maintenance planning. This method can potentially be used in material testing of civil infrastructures, similar to established methods used for mechanical testing.

We propose a method to measure a parameter that is highly relevant for corrosion assessments or predictions of reinforced concrete structures, with the main advantage of permitting testing of samples from engineering structures. This ensures real conditions at the steel-concrete interface, which are crucial to avoid artifacts of laboratory-made samples.

The aging of reinforced concrete infrastructure in developed countries imposes an urgent need for methods to reliably assess the condition of these ...

Preparation of Large-area Vertical 2D Crystal Hetero-structures Through the Sulfurization of Transition Metal Films for Device Fabrication

We have demonstrated that through the sulfurization of transition metal films such as molybdenum (Mo) and tungsten (W), large-area and uniform transition metal dichalcogenides (TMDs) MoS2 and WS2 can be prepared on sapphire substrates. By controlling the metal film thicknesses, good layer number controllability, down to a single layer of TMDs, can be obtained using this growth technique. Based on the results obtained from the Mo film sulfurized under the sulfur deficient condition, there are two mechanisms of (a) planar MoS2 growth and (b) Mo oxide segregation observed during the sulfurization procedure. When the background sulfur is sufficient, planar TMD growth is the dominant growth mechanism, which will result in a uniform MoS2 film after the sulfurization procedure. If the background sulfur is deficient, Mo oxide segregation will be the dominant growth mechanism at the initial stage of the sulfurization procedure. In this case, the sample with Mo oxide clusters covered with few-layer MoS2 will be obtained. After sequential Mo deposition/sulfurization and W deposition/sulfurization procedures, vertical WS2/MoS2 hetero-structures are established using this growth technique. Raman peaks corresponding to WS2 and MoS2, respectively, and the identical layer number of the hetero-structure with the summation of individual 2D materials have confirmed the successful establishment of the vertical 2D crystal hetero-structure. After transferring the WS2/MoS2 film onto a SiO2/Si substrate with pre-patterned source/drain electrodes, a bottom-gate transistor is fabricated. Compared with the transistor with only MoS2 channels, the higher drain currents of the device with the WS2/MoS2 hetero-structure have exhibited that with the introduction of 2D crystal hetero-structures, superior device performance can be obtained. The results have revealed the potential of this growth technique for the practical application of 2D crystals.

Through the sulfurization of pre-deposited transition metals, large-area and vertical 2D crystal hetero-structures can be fabricated. The film transferring and device fabrication procedures are also demonstrated in this report.

We have demonstrated that through the sulfurization of transition metal films such as molybdenum (Mo) and tungsten (W), large-area and uniform transition ...

A 3D-printed Chamber for Organic Optoelectronic Device Degradation Testing

In this manuscript, we outline the manufacture of a small, portable, easy-to-use atmospheric chamber for organic and perovskite optoelectronic devices, using 3D-printing. As these types of devices are sensitive to moisture and oxygen, such a chamber can aid researchers in characterizing the electronic and stability properties. The chamber is intended to be used as a temporary, reusable, and stable environment with controlled properties (including humidity, gas introduction, and temperature). It can be used to protect air-sensitive materials or to expose them to contaminants in a controlled way for degradation studies. To characterize the properties of the chamber, we outline a simple procedure to determine the water vapor transmission rate (WVTR) using relative humidity as measured by a standard humidity sensor. This standard operating procedure, using a 50% infill density of polylactic acid (PLA), results in a chamber that can be used for weeks without any significant loss of device properties. The versatility and ease of use of the chamber allows it to be adapted to any characterization condition that requires a compact-controlled atmosphere.

Here, we present a protocol for the design, manufacture, and use of a simple, versatile 3D-printed and controlled atmospheric chamber for the optical and electrical characterization of air-sensitive organic optoelectronic devices.

In this manuscript, we outline the manufacture of a small, portable, easy-to-use atmospheric chamber for organic and perovskite optoelectronic devices, ...

Enhanced Electron Injection and Exciton Confinement for Pure Blue Quantum-Dot Light-Emitting Diodes by Introducing Partially Oxidized Aluminum Cathode

Stable and efficient red (R), green (G), and blue (B) light sources based on solution-processed quantum dots (QDs) play important roles in next-generation displays and solid-state lighting technologies. The brightness and efficiency of blue QDs-based light-emitting diodes (LEDs) remain inferior to their red and green counterparts, due to the inherently unfavorable energy levels of different colors of light. To solve these problems, a device structure should be designed to balance the injection holes and electrons into the emissive QD layer. Herein, through a simple autoxidation strategy, pure blue QD-LEDs which are highly bright and efficient are demonstrated, with a structure of ITO/PEDOT:PSS/Poly-TPD/QDs/Al:Al2O3. The autoxidized Al:Al2O3 cathode can effectively balance the injected charges and enhance radiative recombination without introducing an additional electron transport layer (ETL). As a result, high color-saturated blue QD-LEDs are achieved with a maximum luminance over 13,000 cd m-2, and a maximum current efficiency of 1.15 cd A-1. The easily controlled autoxidation procedure paves the way for achieving high-performance blue QD-LEDs.

A protocol is presented for fabricating high-performance, pure blue ZnCdS/ZnS-based quantum dots light-emitting diodes by employing an autoxidized aluminum cathode.

Stable and efficient red (R), green (G), and blue (B) light sources based on solution-processed quantum dots (QDs) play important roles in next-generation ...

Multiscale Structures Aggregated by Imprinted Nanofibers for Functional Surfaces

Multiscale surface structures have attracted increasing interest owing to several potential applications in surface devices. However, an existing challenge in the field is the fabrication of hybrid micro-nano structures using a facile, cost-effective, and high-throughput method. To overcome these challenges, this paper proposes a protocol to fabricate multiscale structures using only an imprint process with an anodic aluminum oxide (AAO) filter and an evaporative self-aggregation process of nanofibers. Unlike previous attempts that have aimed to straighten nanofibers, we demonstrate a unique fabrication method for multiscale aggregated nanofibers with high aspect ratios. Furthermore, the surface morphology and wettability of these structures on various liquids were investigated to facilitate their use in multifunctional surfaces.

Presented is an easy method to fabricate nano-micro multiscale structures, for functional surfaces, by aggregating nanofibers fabricated using an anodic aluminum oxide filter.

Multiscale surface structures have attracted increasing interest owing to several potential applications in surface devices. However, an existing ...

Optimized Sealing Process and Real-Time Monitoring of Glass-to-Metal Seal Structures

Residual stress is an essential factor to keeping the hermeticity and robustness of a glass-to-metal seal structure. The purpose of this report is to demonstrate a novel protocol to characterize and measure residual stress in a glass-to-metal seal structure without destroying the insulation and hermeticity of sealing materials. In this research, a femto-laser inscribed fiber Bragg grating sensor is used. The glass-to-metal seal structure that is measured consists of a metal shell, sealing glass, and Kovar conductor. To make the measurements worthwhile, the specific heat treatment of metal-to-glass seal (MTGS) structure is explored to obtain the model with best hermeticity. Then, the FBG sensor is embedded into the path of sealing glass and becomes well-fused with the glass as the temperature cools to RT. The Bragg wavelength of FBG shifts with the residual stress generated in sealing the glass. To calculate the residual stress, the relationship between Bragg wavelength shift and strain is applied, and the finite element method is also used to make the results reliable. The online monitoring experiments of residual stress in sealing glass are carried out at different loads, such as high temperature and high pressure, to broaden functions of this protocol in harsh environments.

Key procedures to optimize the sealing process and achieve real-time monitoring of the metal-to-glass seal (MTGS) structure are described in detail. The embedded fiber Bragg grating (FBG) sensor is designed to achieve online monitoring of temperature and high-level residual stress in the MTGS with simultaneous environmental pressure monitoring.

Residual stress is an essential factor to keeping the hermeticity and robustness of a glass-to-metal seal structure. The purpose of this report is to ...

Design and Development of a Three-Dimensionally Printed Microscope Mask Alignment Adapter for the Fabrication of Multilayer Microfluidic Devices

This project aims to develop an easy-to-use and cost-effective platform for the fabrication of precise, multilayer microfluidic devices, which typically can only be achieved using costly equipment in a clean room setting. The key part of the platform is a three dimensionally (3D) printed microscope mask alignment adapter (MMAA) compatible with regular optical microscopes and ultraviolet (UV) light exposure systems. The overall process of creating the device has been vastly simplified because of the work done to optimize the device design. The process entails finding the proper dimensions for the equipment available in the laboratory and 3D-printing the MMAA with the optimized specifications. Experimental results show that the optimized MMAA designed and manufactured by 3D printing performs well with a common microscope and light exposure system. Using a master mold prepared by the 3D-printed MMAA, the resulting microfluidic devices with multilayered structures contain alignment errors of &lt;10 &#181;m, which is sufficient for common microchips. Although human error through transportation of the device to the UV light exposure system can cause larger fabrication errors, the minimal errors achieved in this study are attainable with practice and care. Furthermore, the MMAA can be customized to fit any microscope and UV exposure system by making changes to the modeling file in the 3D printing system. This project provides smaller laboratories with a useful research tool as it only requires the use of equipment that is typically already available to laboratories that produce and use microfluidic devices. The following detailed protocol outlines the design and 3D printing process for the MMAA. In addition, the steps for procuring a multilayer master mold using the MMAA and producing poly(dimethylsiloxane) (PDMS) microfluidic chips is also described herein.

This project allows small laboratories to develop an easy-to-use platform for the fabrication of precise multilayer microfluidic devices. The platform consists of a three-dimensionally printed microscope mask alignment adapter using which multilayer microfluidic devices with alignment errors of &lt;10 &#181;m were achieved.

This project aims to develop an easy-to-use and cost-effective platform for the fabrication of precise, multilayer microfluidic devices, which typically ...