The authors would like to thank Joseph Muskin and Matthew Ragusa at the University of Illinois at Urbana-Champaign for providing cross-sectional images for 3D structures shown in Figure 1D.

1. Preparation of Prepolymer Solution
<ol>
	<li>Mix poly(ethylene glycol) diacrylate (PEG-DA) (average molecular weight ~575, Sigma-Aldrich) and poly(ethylene glycol) (PEG) (average molecular weight ~200, Sigma-Aldrich) at 1:2 weight ratio.</li>
	<li>Add 0.67 %wt. photo-initiator (Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, Sigma-Aldrich). The solution should be kept in dark environment from this point on.</li>
	<li>Add 0.05 %wt. photo-absorber (Sudan I, Sigma-Aldrich).</li>
	<li>Mix the solution for 24 hr at room temperature using a magnetic stirrer.</li>
</ol>
2. Setting Up a Desktop 3D Printer Using a Digital Data Projector
<ol>
	<li>Place a digital data projector on a flat and stable position, and connect it to a computer with Microsoft PowerPoint installed.</li>
	<li>Place a convex lens right in front of the beam output lens of the digital projector. Choose a convex lens to make the focal plane about 10 cm away from the projector. (Optical resolution becomes smaller for a lens with shorter focal length, but one needs to reserve some space for optical components.)</li>
	<li>Place a mirror after the convex lens on the beam path at 45&deg; angle to direct the beam straight down.</li>
	<li>Place a sample holder at the focal plane of the projected beam. The sample holder should be attached to a linear stage by which the vertical position of the sample holder is controlled.</li>
	<li>Place a resin bath underneath the sample holder.</li>
</ol>
3. Design and Fabrication of Gel Tubes
<ol>
	<li>Determine diameter, wall thickness, and height of the gel tube to be fabricated.</li>
	<li>Draw cross-sectional images for the gel tube. The images should be in white with black background. Insert these image in Microsoft PowerPoint slides.</li>
	<li>Start slideshow in Microsoft PowerPoint and project any image. Place the sample holder at the focal plane by adjusting the vertical position using attached stage.</li>
	<li>Switch to a "dummy" black image so that there will be no unwanted polymerization while putting prepolymer solution.</li>
	<li>Pour prepolymer solution to resin bath. Fill the bath until the solution slightly covers the sample holder. Now it is ready for print 3D object.</li>
	<li>Switch to the slide containing the first cross-sectional image of the gel tube to polymerize the first layer. Keep projecting the image for 8 sec and switch back to "blackout" slide.</li>
	<li>Rotate the knob on the linear stage by &frac14; turn (~160 &mu;m) to lower the sample holder. Now fresh resin flows in to cover the polymerized first layer.</li>
	<li>Project the cross-sectional image again to polymerize the second layer on top of the proceeding one. Repeat steps 3.6-3.8 until the gel tube of the desired height is fabricated.</li>
	<li>Once all layers are complete, lift the sample holder out of the prepolymer solution, and retrieve the fabricated sample carefully using a razor blade.</li>
	<li>Rinse the sample in acetone for ~3 hr, and then allow it to dry for ~1 hr.</li>
</ol>
4. Swelling Experiment for Prescribed Pattern Formation by Elastic Instability
<ol>
	<li>Prepare water-oil dual layer liquid in a transparent glass dish.</li>
	<li>Attach the dry sample on a sample holder using super glue.</li>
	<li>Flip the sample holder so that the sample is upside down. Immerse the sample in the water-oil liquid bath. Approach the sample to water-oil interface from the oil layer. The sample begins to swell when the sample touches the water surface while the base substrate part on which the gel tube was fixed stayed in the top oil layer. In this way, water can diffuse into the tube wall allowing the sample swell before the constraining base relaxes by wetting. Monitor the pattern change as the gel tube swells using a digital camera.</li>
</ol>

<ol>
	<li>Timoshenko, S. P., Gere, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Theory of Elastic Stability. , (1961).</li><li>Sharon, E., Marder, M., Swinney, H. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Leaves+Flowers+and+Garbage+Bags:+Making+Waves.">Leaves Flowers and Garbage Bags: Making Waves.</a> American Scientist. 92, 254-261 (2004).</li><li>K&#252;cken, M., Newell, A. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fingerprint+formation.">Fingerprint formation.</a> Journal of Theoretical Biology. 235, 71-83 (2005).</li><li>Liang, H., Mahadevan, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+shape+of+a+long+leaf.">The shape of a long leaf.</a> Proceedings of the National Academy of Sciences. 106, 22049-22054 (2009).</li><li>Bayer, S. A., Altman, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The human brain during the second trimester. , (2005).</li><li>Trujillo, V., Kim, J., Hayward, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Creasing+instability+of+surface-attached+hydrogels.">Creasing instability of surface-attached hydrogels.</a> Soft Matter. 4, 564 (2008).</li><li>Breid, D., Crosby, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+stress+state+on+wrinkle+morphology.">Effect of stress state on wrinkle morphology.</a> Soft Matter. 7, 4490 (2011).</li><li>Mora, T., Boudaoud, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Buckling+of+swelling+gels.">Buckling of swelling gels.</a> The European Physical Journal E. 20, 119-124 (2006).</li><li>DuPont, S. J., Cates, R. S., Stroot, P. G., Toomey, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Swelling-induced+instabilities+in+microscale,+surface-confined+poly(N-isopropylacryamide)+hydrogels.">Swelling-induced instabilities in microscale, surface-confined poly(N-isopropylacryamide) hydrogels.</a> Soft Matter. 6, 3876-3882 (2010).</li><li>Dervaux, J., Couder, Y., Guedeau-Boudeville, M. -. A., Ben Amar, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Shape+Transition+in+Artificial+Tumors:+From+Smooth+Buckles+to+Singular+Creases.">Shape Transition in Artificial Tumors: From Smooth Buckles to Singular Creases.</a> Physical Review Letters. 107, 018103 (2011).</li><li>Jang, J. -. H., Koh, C. Y., Bertoldi, K., Boyce, M. C., Thomas, E. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Combining+Pattern+Instability+and+Shape-Memory+Hysteresis+for+Phononic+Switching.">Combining Pattern Instability and Shape-Memory Hysteresis for Phononic Switching.</a> Nano Letters. 9, 2113-2119 (2009).</li><li>Lee, H., Zhang, J., Jiang, H., Fang, N. X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prescribed+Pattern+Transformation+in+Swelling+Gel+Tubes+by+Elastic+Instability.">Prescribed Pattern Transformation in Swelling Gel Tubes by Elastic Instability.</a> Physical Review Letters. 108, 214304 (2012).</li><li>Sun, C., Fang, N., Wu, D. M., Zhang, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Projection+micro-stereolithography+using+digital+micro-mirror+dynamic+mask.">Projection micro-stereolithography using digital micro-mirror dynamic mask.</a> Sensors and Actuators A: Physical. 121, 113-120 (2005).</li><li>Muskin, J., Ragusa, M., Gelsthorpe, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-Dimensional+Printing+Using+a+Photoinitiated+Polymer.">Three-Dimensional Printing Using a Photoinitiated Polymer.</a> Journal of Chemical Education. 87, 512-514 (2010).</li></ol>

No conflicts of interest declared.

In swelling of tubular hydrogel constrained on the substrate, stability depends only on t/h and buckling mode depends only on h/D12. Four groups of samples (I-IV) with different levels of normalized thickness t/h were fabricated, with group I being thicker and group IV being more slender. Each group consists of four samples (i-iv) with different levels of normalized height h/D, with the sample i being shorter and the sample iv being taller. Dimensions of the fabricated samples are presented in Table 1. Group I and II are designed to stay stable during swelling, whereas group III and IV are designed to buckle and transform upon swelling. For buckling samples, buckling mode should decrease with sample height. Figure 3A shows experimental result. As theory predicts, samples in group I and II were stable and remained circular on swelling, while samples in group III and IV all went through elastic instability and buckled. Also, samples with the same h/D displayed similar buckling mode. Figure 3B compares experimentally observed buckling modes of samples in group III and IV with theoretical prediction. We can see that samples with the same h/D pose the same post-buckling pattern regardless of the thickness and that experimental results agree well with the theory.
We present how to build up a simple desktop 3D printing system using a commercially available digital data projector. The proposed approach relies on photocuring of polymer to construct 3D structures, and therefore, any photocurable polymers can be also used in general, as far as the photoinitiator has appropriate absorbance in visible wavelength range. Note that many commercially available photoinitiators are designed for ultra-violet (UV) wavelengths, but the photoinitiator used here has relatively higher absorbance at wavelengths longer than 400 nm. Offering an easy and rapid way to fabricate 3D objects, this method will find many applications in various fields including soft materials mechanics as demonstrated here.

<table border="1">
 <tbody>
 <tr>
 <td>Name of the reagent</td>
 <td>Company</td>
 <td>Catalogue number</td>
 <td>Comments (optional)</td>
 </tr>
 <tr>
 <td>Poly(ethylene glycol) diacrylate</td>
 <td>Sigma-Aldrich</td>
 <td>437441</td>
 <td>Mw~575</td>
 </tr>
 <tr>
 <td>Poly(ethylene glycol)</td>
 <td>Sigma-Aldrich</td>
 <td>P3015</td>
 <td>Mw~200</td>
 </tr>
 <tr>
 <td>phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide</td>
 <td>Sigma-Aldrich</td>
 <td>511447</td>
 <td>Photo-initiator</td>
 </tr>
 <tr>
 <td>Sudan I</td>
 <td>Sigma-Aldrich</td>
 <td>103624</td>
 <td>Photo-absorber</td>
 </tr>
 <tr>
 <td>Digital data projector</td>
 <td>Viewsonic</td>
 <td>PJD6221</td>
 <td></td>
 </tr>
 <tr>
 <td>Convex lens</td>
 <td>Thorlabs</td>
 <td>LA1145</td>
 <td>f = 75.0 mm</td>
 </tr>
 <tr>
 <td>Mirror</td>
 <td></td>
 <td></td>
 <td>4" silicon wafer</td>
 </tr>
 <tr>
 <td>Manual stage</td>
 <td>Velmex</td>
 <td>A2506DE-S2.5</td>
 <td></td>
 </tr>
 </tbody>
</table>

micro 3d printing using a digital projector and its application in the study of soft materials mechanics

Buckling is a classical topic in mechanics. While buckling has long been studied as one of the major structural failure modes1, it has recently drawn new attention as a unique mechanism for pattern transformation. Nature is full of such examples where a wealth of exotic patterns are formed through mechanical instability2-5. Inspired by this elegant mechanism, many studies have demonstrated creation and transformation of patterns using soft materials such as elastomers and hydrogels6-11. Swelling gels are of particular interest because they can spontaneously trigger mechanical instability to create various patterns without the need of external force6-10. Recently, we have reported demonstration of full control over buckling pattern of micro-scaled tubular gels using projection micro-stereolithography (P&mu;SL), a three-dimensional (3D) manufacturing technology capable of rapidly converting computer generated 3D models into physical objects at high resolution12,13. Here we present a simple method to build up a simplified P&mu;SL system using a commercially available digital data projector to study swelling-induced buckling instability for controlled pattern transformation.
A simple desktop 3D printer is built using an off-the-shelf digital data projector and simple optical components such as a convex lens and a mirror14. Cross-sectional images extracted from a 3D solid model is projected on the photosensitive resin surface in sequence, polymerizing liquid resin into a desired 3D solid structure in a layer-by-layer fashion. Even with this simple configuration and easy process, arbitrary 3D objects can be readily fabricated with sub-100 &mu;m resolution.
This desktop 3D printer holds potential in the study of soft material mechanics by offering a great opportunity to explore various 3D geometries. We use this system to fabricate tubular shaped hydrogel structure with different dimensions. Fixed on the bottom to the substrate, the tubular gel develops inhomogeneous stress during swelling, which gives rise to buckling instability. Various wavy patterns appear along the circumference of the tube when the gel structures undergo buckling. Experiment shows that circumferential buckling of desired mode can be created in a controlled manner. Pattern transformation of three-dimensionally structured tubular gels has significant implication not only in mechanics and material science, but also in many other emerging fields such as tunable matamaterials.

A simple P&mu;SL system using an off-the-shelf digital data projector is shown in Figure 1. A convex lens with a focal length of 75 mm concentrates the beam into small illumination area of 2 cm by 2 cm. Resulting in-plane optical resolution is about 45 &mu;m. Vertical resolution is determined by the precision level of the linear stage. Layer thickness of the structures made for this study is 160 &mu;m. Each layer was polymerized for 8 sec light illumination. A representative 3D structure fabricated by the system is shown in Figure 1D. This objects consists of 58 layers of PEGDA.
We prepared photo-curable PEGDA hydrogel. Low crosslinking, therefore large swelling, of PEGDA hydrogel was achieved by adding non-crosslinking PEG into prepolymer solution. Length-wise swelling ratio of the resulting PEGDA hydrogel is 1.5, which corresponds to higher than 300% volumetric expansion.
A set of PEGDA hydrogel tubes were designed and fabricated based on our theory12. We placed a sample upside down and put in the bath with water covered with oil layer on top as illustrated in Figure 2A. Depending on the dimensional parameters, circular tubes either remained stable or transformed into a wavy pattern as shown in Figure 2B. The wide variety of swelling pattern of different samples was captured by a digital camera and presented in Figure 3A.
<img alt="Figure 1" src="/files/ftp_upload/4457/4457fig1.jpg" /> 
 Figure 1. A desktop projection micro-stereolithography system (a) schematic representation (b) actual system (c) close-up view of components (d) representative 3D structures. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/4457/4457fig1large.jpg" target="_blank"> Click here to view larger figure</a>.
<img alt="Figure 2" src="/files/ftp_upload/4457/4457fig2.jpg" /> 
 Figure 2. (a) Experimental setup for hydrogel tube swelling (b) constrained hydrogel tube transforms into different patterns. Scale bar indicates 5 mm.
<img alt="Figure 3" src="/files/ftp_upload/4457/4457fig3.jpg" /> 
 Figure 3. (a) Patterns formed in swelling experiment. Vertical axis indicates t/h (thus stability), and horizontal axis indicates h/D (thus buckling mode). Scale bar indicates 5 mm. (b) Buckling mode depends only on h/D. Experimental result agrees well with theoretical prediction. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/4457/4457fig3large.jpg" target="_blank"> Click here to view larger figure</a>.
<table border="1">
	<tbody>
		<tr>
			<td colspan="2">Sample</td>
			<td>D (&mu;m) </td>
			<td>t (&mu;m) </td>
			<td>h (&mu;m) </td>
		</tr>
		<tr>
			<td rowspan="4">I</td>
			<td>i</td>
			<td>9300 &plusmn; 420</td>
			<td>760 &plusmn; 40</td>
			<td>840 &plusmn; 40</td>
		</tr>
		<tr>
			<td>ii</td>
			<td>9700 &plusmn; 420</td>
			<td>1040 &plusmn; 40</td>
			<td>1060 &plusmn; 40</td>
		</tr>
		<tr>
			<td>iii</td>
			<td>9700 &plusmn; 420</td>
			<td>1210 &plusmn; 40</td>
			<td>1340 &plusmn; 40</td>
		</tr>
		<tr>
			<td>iv</td>
			<td>9700 &plusmn; 420</td>
			<td>1660 &plusmn; 40</td>
			<td>1680 &plusmn; 40</td>
		</tr>
		<tr>
			<td rowspan="4">II</td>
			<td>i</td>
			<td>9000 &plusmn; 420</td>
			<td>480 &plusmn; 40</td>
			<td>880 &plusmn; 40</td>
		</tr>
		<tr>
			<td>ii</td>
			<td>9000 &plusmn; 420</td>
			<td>660 &plusmn; 40</td>
			<td>1060 &plusmn; 40</td>
		</tr>
		<tr>
			<td>iii</td>
			<td>9500 &plusmn; 420</td>
			<td>740 &plusmn; 40</td>
			<td>1350 &plusmn; 40</td>
		</tr>
		<tr>
			<td>iv</td>
			<td>9200 &plusmn; 420</td>
			<td>970 &plusmn; 40</td>
			<td>1650 &plusmn; 40</td>
		</tr>
		<tr>
			<td rowspan="4">III</td>
			<td>i</td>
			<td>8900 &plusmn; 420</td>
			<td>160 &plusmn; 40</td>
			<td>790 &plusmn; 40</td>
		</tr>
		<tr>
			<td>ii</td>
			<td>8900 &plusmn; 420</td>
			<td>300 &plusmn; 40</td>
			<td>1020 &plusmn; 40</td>
		</tr>
		<tr>
			<td>iii</td>
			<td>9100 &plusmn; 420</td>
			<td>380 &plusmn; 40</td>
			<td>1330 &plusmn; 40</td>
		</tr>
		<tr>
			<td>iv</td>
			<td>9000 &plusmn; 420</td>
			<td>490 &plusmn; 40</td>
			<td>1630 &plusmn; 40</td>
		</tr>
		<tr>
			<td rowspan="4">IV</td>
			<td>i</td>
			<td>8900 &plusmn; 420</td>
			<td>140 &plusmn; 40</td>
			<td>780 &plusmn; 40</td>
		</tr>
		<tr>
			<td>ii</td>
			<td>8800 &plusmn; 420</td>
			<td>190 &plusmn; 40</td>
			<td>1010 &plusmn; 40</td>
		</tr>
		<tr>
			<td>iii</td>
			<td>9300 &plusmn; 420</td>
			<td>230 &plusmn; 40</td>
			<td>1340 &plusmn; 40</td>
		</tr>
		<tr>
			<td>iv</td>
			<td>8900 &plusmn; 420</td>
			<td>290 &plusmn; 40</td>
			<td>1650 &plusmn; 40</td>
		</tr>
	</tbody>
</table>
Table 1. Sample dimensions measured through optical microscope. Errors indicate measurement uncertainty.

Watch this Scientific Journal Video about Micro 3D Printing Using a Digital Projector and its Application in the Study of Soft Materials Mechanics at JoVE.com

Micro 3D Printing Using a Digital Projector and its Application in the Study of Soft Materials Mechanics

We demonstrate controlled pattern transformation of swelling gel tubes by elastic instability. A simple projection micro stereo-lithography setup is built using an off-the-shelf digital data projector to fabricate three-dimensional polymeric structures in a layer-by-layer fashion. Swelling hydrogel tubes under mechanical constraint display various circumferential buckling modes depending on dimension.

Buckling is a classical topic in mechanics. While buckling has long been studied as one of the major structural failure modes1, it has recently drawn new ...

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25.2K Views.  Massachusetts Institute of Technology. We demonstrate controlled pattern transformation of swelling gel tubes by elastic instability. A simple projection micro stereo-lithography setup is built using an off-the-shelf digital data projector to fabricate three-dimensional polymeric structures in a layer-by-layer fashion. Swelling hydrogel tubes under mechanical constraint display various circumferential buckling modes depending on dimension.

Video: Micro 3D Printing Using a Digital Projector and its Application in the Study of Soft Materials Mechanics

Controlling the Size, Shape and Stability of Supramolecular Polymers in Water

For aqueous based supramolecular polymers, the simultaneous control over shape, size and stability is very difficult1. At the same time, the ability to do so is highly important in view of a number of applications in functional soft matter including electronics, biomedical engineering, and sensors. In the past, successful strategies to control the size and shape of supramolecular polymers typically focused on the use of templates2,3, end cappers4 or selective solvent techniques5. 
Here we disclose a strategy based on self-assembling discotic amphiphiles that leads to the control over stack length and shape of ordered, chiral columnar aggregates. By balancing electrostatic repulsive interactions on the hydrophilic rim and attractive non-covalent forces within the hydrophobic core of the polymerizing building block, we manage to create small and discrete spherical objects6,7. Increasing the salt concentration to screen the charges induces a sphere-to-rod transition. Intriguingly, this transition is expressed in an increase of cooperativity in the temperature-dependent self-assembly mechanism, and more stable aggregates are obtained. 
For our study we select a benzene-1,3,5-tricarboxamide (BTA) core connected to a hydrophilic metal chelate via a hydrophobic, fluorinated L-phenylalanine based spacer (Scheme 1). The metal chelate selected is a Gd(III)-DTPA complex that contains two overall remaining charges per complex and necessarily two counter ions. The one-dimensional growth of the aggregate is directed by &pi;-&pi; stacking and intermolecular hydrogen bonding. However, the electrostatic, repulsive forces that arise from the charges on the Gd(III)-DTPA complex start limiting the one-dimensional growth of the BTA-based discotic once a certain size is reached. At millimolar concentrations the formed aggregate has a spherical shape and a diameter of around 5 nm as inferred from 1H-NMR spectroscopy, small angle X-ray scattering, and cryogenic transmission electron microscopy (cryo-TEM). The strength of the electrostatic repulsive interactions between molecules can be reduced by increasing the salt concentration of the buffered solutions. This screening of the charges induces a transition from spherical aggregates into elongated rods with a length &gt; 25 nm. Cryo-TEM allows to visualise the changes in shape and size. In addition, CD spectroscopy permits to derive the mechanistic details of the self-assembly processes before and after the addition of salt. Importantly, the cooperativity -a key feature that dictates the physical properties of the produced supramolecular polymers- increases dramatically upon screening the electrostatic interactions. This increase in cooperativity results in a significant increase in the molecular weight of the formed supramolecular polymers in water.

The goal of this experiment is to determine and control the size, shape and stability of self-assembled discotic amphiphiles in water. For aqueous based supramolecular polymers such level of control is very difficult. We apply a strategy using both repulsive and attractive interactions. The experimental techniques applied to characterize this system are broadly applicable.

For aqueous based supramolecular polymers, the simultaneous control over shape, size and stability is very difficult1. At the same time, the ability to do ...

High-resolution, High-speed, Three-dimensional Video Imaging with Digital Fringe Projection Techniques

Digital fringe projection (DFP) techniques provide dense 3D measurements of dynamically changing surfaces.&#160;Like the human eyes and brain, DFP uses triangulation between matching points in two views of the same scene at different angles to compute depth.&#160;However, unlike a stereo-based method, DFP uses a digital video projector to replace one of the cameras1. The projector rapidly projects a known sinusoidal pattern onto the subject, and the surface of the subject distorts these patterns in the camera&#8217;s field of view. Three distorted patterns (fringe images) from the camera can be used to compute the depth using triangulation.
Unlike other 3D measurement methods, DFP techniques lead to systems that tend to be faster, lower in equipment cost, more flexible, and easier to develop.&#160;DFP systems can also achieve the same measurement resolution as the camera.&#160;For this reason, DFP and other digital structured light techniques have recently been the focus of intense research (as summarized in1-5). Taking advantage of DFP, the graphics processing unit, and optimized algorithms, we have developed a system capable of 30&#160;Hz 3D video data acquisition, reconstruction, and display for over 300,000 measurement points per frame6,7.&#160;Binary defocusing DFP methods can achieve even greater speeds8.
Diverse applications can benefit from DFP techniques. Our collaborators have used our systems for facial function analysis9, facial animation10, cardiac mechanics studies11, and fluid surface measurements, but many other potential applications exist.&#160;This video will teach the fundamentals of DFP techniques and illustrate the design and operation of a binary defocusing DFP system.

This video describes the fundamentals of digital fringe projection techniques, which provide dense 3D measurements of dynamically changing surfaces.&#160;It also demonstrates the design and operation of a high-speed binary defocusing system based on these techniques.

Digital fringe projection (DFP) techniques provide dense 3D measurements of dynamically changing surfaces.&#160;Like the human eyes and brain, DFP uses ...

Synthesis and Functionalization of 3D Nano-graphene Materials: Graphene Aerogels and Graphene Macro Assemblies

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. Additionally, most reported graphene assemblies are held together through physical interactions (e.g., van der Waals forces) rather than chemical bonds, which limit their mechanical strength and conductivity. This video method details recently developed strategies to fabricate mass-producible, graphene-based bulk materials derived from either polymer foams or single layer graphene oxide. These materials consist primarily of individual graphene sheets connected through covalently bound carbon linkers. They maintain the favorable properties of graphene such as high surface area and high electrical and thermal conductivity, combined with tunable pore morphology and exceptional mechanical strength and elasticity. This flexible synthetic method can be extended to the fabrication of polymer/carbon nanotube (CNT) and polymer/graphene oxide (GO) composite materials. Furthermore, additional post-synthetic functionalization with anthraquinone is described, which enables a dramatic increase in charge storage performance in supercapacitor applications.

This video method describes the synthesis of high surface area, monolithic 3D graphene-based materials derived from polymer precursors as well as single layer graphene oxide.

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. ...

Quantification of Hydrogen Concentrations in Surface and Interface Layers and Bulk Materials through Depth Profiling with Nuclear Reaction Analysis

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and non-destructively reveals the hydrogen density distribution at surfaces, at interfaces, and in the volume of solid materials with high depth resolution. The technique applies a 15N ion beam of 6.385 MeV provided by an electrostatic accelerator and specifically detects the 1H isotope in depths up to about 2 &#956;m from the target surface. Surface H coverages are measured with a sensitivity in the order of ~1013 cm-2 (~1% of a typical atomic monolayer density) and H volume concentrations with a detection limit of ~1018 cm-3 (~100 at. ppm). The near-surface depth resolution is 2-5 nm for surface-normal 15N ion incidence onto the target and can be enhanced to values below 1 nm for very flat targets by adopting a surface-grazing incidence geometry. The method is versatile and readily applied to any high vacuum compatible homogeneous material with a smooth surface (no pores). Electrically conductive targets usually tolerate the ion beam irradiation with negligible degradation. Hydrogen quantitation and correct depth analysis require knowledge of the elementary composition (besides hydrogen) and mass density of the target material. Especially in combination with ultra-high vacuum methods for in-situ target preparation and characterization, 1H(15N,&#945;&#947;)12C NRA is ideally suited for hydrogen analysis at atomically controlled surfaces and nanostructured interfaces. We exemplarily demonstrate here the application of 15N NRA at the MALT Tandem accelerator facility of the University of Tokyo to (1) quantitatively measure the surface coverage and the bulk concentration of hydrogen in the near-surface region of a H2 exposed Pd(110) single crystal, and (2) to determine the depth location and layer density of hydrogen near the interfaces of thin SiO2 films on Si(100).

We illustrate the application of 1H(15N,&#945;&#947;)12C resonant nuclear reaction analysis (NRA) to quantitatively evaluate the density of hydrogen atoms on the surface, in the volume, and at an interfacial layer of solid materials. The near-surface hydrogen depth profiling of a Pd(110) single crystal and of SiO2/Si(100) stacks is described.

Nuclear reaction analysis (NRA) via the resonant 1H(15N,&#945;&#947;)12C reaction is a highly effective method of depth profiling that quantitatively and ...

Wicking Tests for Unidirectional Fabrics: Measurements of Capillary Parameters to Evaluate Capillary Pressure in Liquid Composite Molding Processes

During impregnation of a fibrous reinforcement in liquid composite molding (LCM) processes, capillary effects have to be understood in order to identify their influence on void formation in composite parts. Wicking in a fibrous medium described by the Washburn equation was considered equivalent to a flow under the effect of capillary pressure according to the Darcy law. Experimental tests for the characterization of wicking were conducted with both carbon and flax fiber reinforcement. Quasi-unidirectional fabrics were then tested by means of a tensiometer to determine the morphological and wetting parameters along the fiber direction. The procedure was shown to be promising when the morphology of the fabric is unchanged during capillary wicking. In the case of carbon fabrics, the capillary pressure can be calculated. Flax fibers are sensitive to moisture sorption and swell in water. This phenomenon has to be taken into account to assess the wetting parameters. In order to make fibers less sensitive to water sorption, a thermal treatment was carried out on flax reinforcements. This treatment enhances fiber morphological stability and prevents swelling in water. It was shown that treated fabrics have a linear wicking trend similar to those found in carbon fabrics, allowing for the determination of capillary pressure.

An experimental method to measure geometrical parameters and the apparent advancing contact angles describing capillary wicking in unidirectional synthetic and natural fabrics is proposed. These parameters are mandatory for the determination of the capillary pressures that must be taken into account for liquid composite molding (LCM) applications.

During impregnation of a fibrous reinforcement in liquid composite molding (LCM) processes, capillary effects have to be understood in order to identify ...

Challenges in Rheological Characterization of Highly Concentrated Suspensions &#8212; A Case Study for Screen-printing Silver Pastes

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the manifold requirements during processing and application of such complex fluids. In this investigation, measuring protocols for a conclusive assessment of different process relevant rheological parameters have been evaluated. This includes the determination of yield stress, viscosity, wall slip velocity, structural recovery after large deformation and elongation at break as well as tensile force during filament stretching.
The importance of concomitant video recordings during parallel-plate rotational rheometry for a significant determination of rheological quantities is demonstrated. The deformation profile and flow field at the sample edge can be determined using appropriate markers. Thus, measurement parameter settings and plate roughness values can be identified for which yield stress and viscosity measurements are possible. Slip velocity can be measured directly and measuring conditions at which plug flow, shear banding or sample spillover occur can be identified clearly. 
Video recordings further confirm that the change in shear moduli observed during three stage oscillatory shear tests with small deformation amplitude in stage I and III but large oscillation amplitude in stage II can be directly attributed to structural break down and recovery. For the pastes investigated here, the degree of irreversible, shear-induced structural change increases with increasing deformation amplitude in stage II until a saturation is reached at deformations corresponding to the crossover of G' and G'', but the irreversible damage is independent of the duration of large amplitude shear. 
A capillary breakup elongational rheometer and a tensile tester have been used to characterize deformation and breakup behavior of highly filled pastes in uniaxial elongation. Significant differences were observed in all experiments described above for two commercial screen-printing silver pastes used for front side metallization of Si-solar cells.

A protocol for a robust and application relevant rheological characterization of highly concentrated suspensions is presented. Silver pastes used for screen-printing application in solar cell production are employed as model systems.

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the ...

A Soft Tooling Process Chain for Injection Molding of a 3D Component with Micro Pillars

The purpose of this paper is to present the method of a soft tooling process chain employing Additive Manufacturing (AM) for fabrication of injection molding inserts with micro surface features. The Soft Tooling inserts are manufactured by Digital Light Processing (vat photo polymerization) using a photopolymer that can withstand relatively high temperaturea. The part manufactured here has four tines with an angle of 60&#176;. Micro pillars (&#216;200 &#181;m, aspect ratio of 1) are arranged on the surfaces by two rows. Polyethylene (PE) injection molding with the soft tooling inserts is used to fabricate the final parts. This method demonstrates that it is feasible to obtain injection-molded parts with microstructures on complex geometry by additive manufactured inserts. The machining time and cost is reduced significantly compared to conventional tooling processes based on computer numerical control (CNC) machining. The dimensions of the micro features are influenced by the applied additive manufacturing process. The lifetime of the inserts determines that this process is more suitable for pilot production. The precision of the inserts production is limited by the additive manufacturing process as well.

A protocol for fabricating injection molding inserts for complex geometry with micro features on surfaces employing Additive Manufacturing (AM) is presented.

The purpose of this paper is to present the method of a soft tooling process chain employing Additive Manufacturing (AM) for fabrication of injection ...

Studying Large Amplitude Oscillatory Shear Response of Soft Materials

We investigate the sequence of physical processes exhibited during large amplitude oscillatory shearing (LAOS) of polyethylene oxide (PEO) in dimethyl sulfoxide (DMSO) and xanthan gum in water &#8212; two concentrated polymer solutions used as viscosifiers in foods, enhanced oil recovery, and soil remediation. Understanding the nonlinear rheological behavior of soft materials is important in the design and controlled manufacturing of many consumer products. It is shown how the response to LAOS of these polymer solutions can be interpreted in terms of a clear transition from linear viscoelasticity to viscoplastic deformation and back again during a period. The LAOS results are analyzed via the fully quantitative Sequence of Physical Processes (SPP) technique, using free MATLAB-based software. A detailed protocol of performing a LAOS measurement with a commercial rheometer, analyzing nonlinear stress responses with the freeware, and interpreting physical processes under LAOS is presented. It is further shown that, within the SPP framework, a LAOS response contains information regarding the linear viscoelasticity, the transient flow curves, and the critical strain responsible for the onset of nonlinearity.

We present a detailed protocol outlining how to perform nonlinear oscillatory shear rheology on soft materials, and how to run the SPP-LAOS analysis to understand the responses as a sequence of physical processes.

We investigate the sequence of physical processes exhibited during large amplitude oscillatory shearing (LAOS) of polyethylene oxide (PEO) in dimethyl ...

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 ...

In Situ Transmission Electron Microscopy with Biasing and Fabrication of Asymmetric Crossbars Based on Mixed-Phased a-VOx

Resistive switching crossbar architecture is highly desired in the field of digital memories due to low cost and high-density benefits. Different materials show variability in resistive switching properties due to the intrinsic nature of the material used, leading to discrepancies in the field because of underlying operation mechanisms. This highlights a need for a reliable technique to understand mechanisms using nanostructural observations. This protocol explains a detailed process and methodology of in&#160;situ nanostructural analysis as a result of electrical biasing using transmission electron microscopy (TEM). It provides visual and reliable evidence of underlying nanostructural changes in real time memory operations. Also included is the methodology of fabrication and electrical characterizations for asymmetric crossbar structures incorporating amorphous vanadium oxide. The protocol explained here for vanadium oxide films can be easily extended to any other materials in a metal-dielectric-metal sandwiched structure. Resistive switching crossbars are predicted to serve the programmable logic and neuromorphic circuits for next-generation memory devices, given the understanding of the operation mechanisms. This protocol reveals the switching mechanism in a reliable, timely, and cost-effective way in any type of resistive switching materials, and thereby predicts the device&#39;s applicability.

In Situ Transmission Electron Microscopy with Biasing and Fabrication of Asymmetric Crossbars Based on Mixed-Phased a-VOx

Presented here is a protocol for analyzing nanostructural changes during in&#160;situ biasing with transmission electron microscopy (TEM) for a stacked metal-insulator-metal structure. It has significant applications in resistive switching crossbars for the next generation of programmable logic circuits and neuromimicking hardware, to reveal their underlying operation mechanisms and practical applicability.

Micro 3D Printing Using a Digital Projector and its Application in the Study of Soft Materials Mechanics

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