Thanks to Sebastian Malke and Nadine Dreiack for laboratory support.

1. Protocol requirements
<ol>
	<li>Purchase a 3D printing pen capable of generating temperatures &#62; 200 &#176;C (Figure 1) to be able to print filaments with a higher print temperature (e.g., ABS or filaments with additives) to compare different filaments. Different 3D pens are available online.</li>
	<li>Purchase filaments with a diameter of 1.75 mm, suitable for the 3D pen. A variety of standard PLA and ABS filaments as well as filaments with additives are available online on different websites.</li>
	<li>For an easy setup, use a desiccator (18.5 L) as the emission chamber.
	<ol>
		<li>Make sure the chamber is clean. Choose a desiccator with an inlet on one side to be able to insert the 3D printing pen and an outlet on the top to insert the sampling tube.</li>
		<li>Make sure that an air inlet at the connection to the 3D pen is established. Ambient air will used as background. The outlet tubing should be 10 cm away from the tip of the 3D printing pen to mimic the distance between the user&#8217;s head and the emission source.</li>
		<li>Use conductive tubing to minimize particle loss. The tubing length should be as short as possible and free of bends.</li>
	</ol>
	</li>
	<li>Use Condensation Particle Counter (CPC) and Scanning Mobility Particle Sizer (SMPS) or other particle tracking devices for the online measurement of particle concentration and particle size distribution (Figure 2).</li>
	<li>Use a microwave and respective chemicals for digesting filament samples.</li>
	<li>Use an ICP-MS or another multi-element analysis instrument to quantify the metal content in the samples.</li>
	<li>Use an electron microscope to characterize the particle morphology.</li>
</ol>
2. Aerosol measurements of 3D Pen emissions
<ol>
	<li>Preparation before the experiment
	<ol>
		<li>Switch on the respective online measurement instruments (SMPS, CPC). There is a button in the back of the machine. Warm up the instruments for around 10 min.</li>
		<li>Preload the 3D pen with a chosen filament (start with PLA as the most used material) and let the pen cool down.</li>
		<li>Attach a HEPA filter to the SMPS inlet and run a clean check measurement with the SMPS to ensure that the SMPS is not contaminated from previous measurements. Do not measure any particles if the SMPS is not clean.</li>
		<li>Connect the chamber outlet to the CPC inlet. Check the concentration inside the chamber with the CPC to ensure the chamber is clean (&#60; 103 particles/m3) and experiments are running under the same conditions. Start a measurement.</li>
	</ol>
	</li>
	<li>Experimental procedure
	<ol>
		<li>Insert the preloaded and cooled down 3D pen into the chamber.</li>
		<li>Make sure the outlet tubing of the chamber is connected to the CPC.</li>
		<li>Start the computer connected to the CPC. Open a new file with a name suitable to the measurements. Make sure the CPC flow setting is set to 0.3 L/min and sampling time is set to at least 90 minutes. Start the CPC measurement to measure the background concentration for 10 minutes. 
		NOTE: Flow settings of 0.3 L/min and the chamber volume of 18.5 L will result in an air exchange rate (ACH) of 1.0 h-1.</li>
		<li>After 10 min, switch on the 3D pen. Select the needed temperature for the chosen filament.</li>
		<li>After the needed temperature is reached, start the printing process. Let the 3D pen print for 15 minutes. 
		NOTE: No object, but a continuous string will be printed and collected on the bottom.</li>
		<li>After 15 minutes, stop the 3D pen, connect the outlet tubing to the SMPS and start the size distribution measurements every 3 minutes for the next 1 hour.</li>
		<li>After the experiment is finished remove the printed filament and clean the chamber.</li>
		<li>Repeat every measurement three times.</li>
	</ol>
	</li>
</ol>
3. Particle morphology using TEM
<ol>
	<li>To ensure that the measured signals originate from emitted particles and not from vapor molecules use transmission electron microscopy (TEM) to analyze the aerosol.</li>
	<li>TEM grid preparation
	<ol>
		<li>Use 400 mesh 3.5 mm copper grids.</li>
		<li>Coat the grids with Collodion. Let the grids dry overnight and store them in a desiccation chamber until further use. Alternatively, use precoated grids (e.g., SF162-4 Formvar-Film on 400 mesh Cu-net).</li>
		<li>On the day of the experiment, the grids should be hydrophilized with 2% Alcian Blue in 0.3% acetic acid solution.</li>
		<li>Pipette 30 &#181;L of the prepared Alcian blue solution on to a surface, for example a piece of parafilm. Let the grids float on the Alcian blue droplets for 5 to 10 minutes and dry them using a filter paper.</li>
	</ol>
	</li>
	<li>Place the prepared TEM grids inside the chamber during the printing process and leave in place afterwards for 5 hours to allow particle sedimentation. 
	NOTE: For easier handling of the grids, place the grids on a platform coated with parafilm.</li>
	<li>Examine at least four different areas of each grid with TEM and use diffraction patterns from published resources to identify material composition.</li>
</ol>
4. Quantitation of metal content before and after printing using ICP-MS
<ol>
	<li>Sample Preparation
	<ol>
		<li>Print filament on a plastic surface to avoid contamination with metal.</li>
		<li>Weigh approximately 150 mg of bulk filament and printed filament. To avoid contamination with metal, use a ceramic knife to cut smaller pieces.</li>
	</ol>
	</li>
	<li>Microwave digestion
	<ol>
		<li>Transfer weighted filaments into microwave vessels.</li>
		<li>Add 1.5 mL of water (e.g., MilliQ), 3.5 mL of nitric acid and 1 mL of hydrogen peroxide to each sample. 
		CAUTION: Add water first and then acid!</li>
		<li>Place the vessels into the microwave and start the digestion. Heat up to 200 &#176;C and hold for 20 minutes.</li>
	</ol>
	</li>
	<li>Determinate metal concentration with ICP-MS
	<ol>
		<li>Dilute all samples of filaments where a high metal concentration is known or suspected to avoid contamination of the ICP-MS.</li>
		<li>Use a survey scan to determinate which metals are in the samples.</li>
		<li>Quantify the metal content of the specific metals using the appropriate calibrations standards.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

The protocol shows a fast, inexpensive and user-friendly method to analyze emissions of a 3D printing pen. Besides the comparison of PLA and ABS, filaments containing significant amounts of metals and CNTs can be investigated.
Critical steps are cleaning the chamber to avoid cross contamination and to ensure that the background concentration is low. We used a desiccator as an available chamber option, but other chambers might be used.
Particle concentrations and particle size distributions are measured online during and after the printing process. In this study, particle concentrations reaching values above 106 particles/cm3 were recorded, which might be of concern. In particular, when particles smaller than 100 nm were found. The aerosol measurements allowed particle concentration measurements with the CPC in the size range 4 nm to 3 &#181;m. The SMPS measurements only allowed particle size distribution measurements between 14.4 nm and 673.2 nm. Smaller or larger particles might be missed in those measurements.
The method confirms particle presence in 3D pen emissions by offline TEM analysis. In the study nanoparticles of the different thermoplastic materials as well as of metal particles and CNTs were detected.
For the TEM analysis, we relied on the sedimentation of the particles over time as other sampling methods did not work, but improvement or modification of the sampling might be useful. The concentration of the ambient air was very low and insignificant to the emissions concentrations, but the use of an inlet filters might be valuable. In the future, other chamber volumes will be used to compare the result to 3D printer emissions. The protocol focused on the release of particles, but open questions remain, as for example, with regard to the emission of volatile organic compounds (VOCs). For 3D printers it was already shown that in addition to particles, VOCs are being released9,10,11,12,13,14,15,16,17,18,33. It can be assumed that 3D pens may cause similar emissions.
3D printers can be started and then print without the user&#8217;s presence. 3D printing pens are, however, handheld devices and are mostly operated manually. Therefore, the user remains closer to the device during the entire printing process resulting in a potentially higher exposure. This should especially be noted as 3D pens are often advertised for being usable by children. In general, particle emissions from FFF 3D processes are comparable to laser printers, in terms of particle number concentrations34. Accordingly, precautions should be taken to reduce the level of exposure. It seems reasonable to advice that 3D pens should be used at low printing temperatures and only in well ventilated environments. Filaments with metal or other additives should be used with care, as the release of potentially harmful metal nanoparticles or fibers is likely.
In the future, this protocol can be used to compare more filaments and different 3D printing pens to gain a better understanding of the emissions of these devices and the possible risk for consumers. Furthermore, this protocol can be used to analyze other aerosol generating cases (e.g., spray products).

3D printing is a promising additive manufacturing method, which besides its industrial applications is also used in homes, schools and so-called maker spaces. 3D printers can now be purchased starting already from 200 &#8364;, thus making them attractive to consumers. These printers can be used to produce replacement parts, household items, gifts or other objects. Children can even make their own toys using 3D printers. Due to their easy handling and low price, printers based on fused filament fabrication (FFF) are the most widespread type in the hobby sector1. In this printing method a thermoplastic material, called filament, is melted, pushed through a nozzle and applied layer by layer using a movable print head until the three-dimensional object is finished. Digital computer-aided design (CAD) models needed for FFF printing are freely available online or can be designed in many different CAD drawing programs.
Initial studies have shown that during the printing process of the filament, ultrafine particles2,3,4,5,6,7,8 and volatile substances9,10,11,12,13,14,15,16,17,18 are released. Ultrafine particles can penetrate deeper into the respiratory system and might be harder to clear from the body19. In a study with employees regularly using 3D printers 59% have reported respiratory symptoms20. Most of the hobbyist&#39;s printers are not hermetically sealed and do not have exhaust fume extraction devices. Emissions are therefore released directly into the ambient air and could pose a risk to the user upon inhalation.
Previous studies have focused on emissions of the most commonly used filaments polylactide (PLA) and acrylonitrile butadiene styrene (ABS). Some studies have analyzed different filaments, such as nylon and high-impact polystyrene (HIPS)4,10,13. Furthermore, new filaments, which are provided with additives such as metal or wood, are constantly being launched to the market. Those filaments enable the consumer to print objects that look and feel like natural wood or metal. Other filaments allow to print conductive materials containing graphene or carbon nanotubes (CNTs)21. Metal nanoparticles22 and CNTs show cytotoxic effects and caused DNA damage23. So far, only little research was conducted regarding filaments containing additives. Floyed et al.13 analyzed PLA supplemented with bronze; Stabile et al.3 investigated PLA blended with copper, wood, bamboo and a filament with carbon fiber. Both studies measured particle concentration and size distribution however the morphology and composition of the released particles was not further investigated. Especially high aspect ratio nanoparticles (HARN) such as CNTs or asbestos fibers are known to cause hazardous health effects24. A recent study by Stefaniak et al.25 analyzed filaments with CNTs and observed emission of respirable polymer particles containing visible CNTs.
3D pens use the same FFF method as 3D printers, but so far only one study examining 3D pens has been published26. The authors used PLA and ABS filaments, but none with additives were analyzed. Due to their handheld use, 3D pens are even easier to use than 3D printers. They are more intuitive, have a small size and do not require the use of CAD models. 3D pens can be used to draw or create objects, and moreover to repair 3D printed parts and other plastic items. Prices start from as low as 30 &#8364;, different shapes and colors are available to target lower age groups. But particularly, children are more vulnerable to particle emissions. Their lung defense mechanisms against particulate and gaseous pollution are not fully evolved and they are breathing a higher volume of air per body weight27.
For a better understanding of the release and the health risks of 3D pen emissions, we investigated different filaments consisting of the standard materials PLA and ABS in different colors. Furthermore, filaments with copper, aluminum, steel and CNT additives and a filament with glow-in-the-dark effect were investigated. To gain comprehensive insights into the 3D pen printing process and the particulate emissions analysis was conducted by online aerosol measurement of particle number concentrations and size distributions, by transmission electron microscopy (TEM) examination for the morphology and materials identification and by inductively coupled plasma mass spectrometry (ICP-MS) for quantitative metal assessment of the filaments.

<table><tbody><tr><td>3D printing pen</td><td>lovebay</td><td></td><td>bought on: www.amazon.de</td></tr><tr><td>ABS black</td><td>Filamentworld</td><td>ABS175XBLK</td><td>bought on: www.filamentworld.de</td></tr><tr><td>ABS blue</td><td>Filamentworld</td><td>ABS175XSB</td><td>bought on: www.filamentworld.de</td></tr><tr><td>ABS glow in the dark</td><td>Formfutura</td><td>ABS175XGID</td><td>bought on: www.filamentworld.de</td></tr><tr><td>Alcian Blue</td><td>Sigma Aldrich, Germany</td><td></td><td></td></tr><tr><td>Collodion</td><td>Electron Microscopy Services GmbH, Germany</td><td></td><td></td></tr><tr><td>CPC</td><td>TSI Inc.</td><td>Model 3775</td><td>other particle tracking measurement devices can be used</td></tr><tr><td>Hydrogen peroxide</td><td>Merck KGaA</td><td></td><td>30%, suprapur</td></tr><tr><td>Imaging camera</td><td>Olympus, Germany</td><td>Veleta G2 camera</td><td></td></tr><tr><td>iTEM software</td><td>Olympus, Germany</td><td></td><td></td></tr><tr><td>MilliQ water</td><td>Merck KGaA</td><td></td><td>Milli-Q&amp;reg; System</td></tr><tr><td>Nitric acid</td><td></td><td></td><td>69%, In-house cleaned by distillation</td></tr><tr><td>PLA black</td><td>Filamentworld</td><td>PLA175XBLK</td><td>bought on: www.filamentworld.de</td></tr><tr><td>PLA blue</td><td>Filamentworld</td><td>PLA175XSBL</td><td>bought on: www.filamentworld.de</td></tr><tr><td>PLA clear</td><td>Filamentworld</td><td>PLA175XCLR</td><td>bought on: www.filamentworld.de</td></tr><tr><td>PLA red</td><td>Filamentworld</td><td>PLA175XRED</td><td>bought on: www.filamentworld.de</td></tr><tr><td>PLA white</td><td>Filamentworld</td><td>PLA175XWHT</td><td>bought on: www.filamentworld.de</td></tr><tr><td>PLA wiht Aluminium</td><td>Formfutura</td><td>GPLA175XTSI</td><td>bought on: www.filamentworld.de</td></tr><tr><td>PLA wiht CNTs</td><td>3DXTech</td><td>3DX175XPLAESD</td><td>bought on: www.filamentworld.de</td></tr><tr><td>PLA with Copper</td><td>Formfutura</td><td>MFL175XCOP</td><td>bought on: www.filamentworld.de</td></tr><tr><td>PLA with Steel</td><td>Proto-Pasta</td><td>PP175X500SST</td><td>bought on: www.filamentworld.de</td></tr><tr><td>SMPS</td><td>TSI Inc.</td><td>Model 3938</td><td>other particle tracking measurement devices can be used</td></tr><tr><td>TEM</td><td>Jeol GmbH, Germany</td><td>Jeol 1400 Plus</td><td></td></tr><tr><td>TEM grids alternative (plastic coated): Formvar-Film auf 400 mesh Cu-Netzchen</td><td>Plano GmbH, Germany</td><td>SF162-4</td><td></td></tr><tr><td>TEM grids: 400 mesh 3.5 mm copper grids</td><td>Plano GmbH, Germany</td><td></td><td></td></tr></tbody></table>

3d printing - evaluating particle emissions of a 3d printing pen

Three-dimensional (3D) printing as a type of additive manufacturing shows continuing increase in application and consumer popularity. The fused filament fabrication (FFF) is an inexpensive method used most frequently by consumers. Studies with 3D printers have shown that during the printing process particulate and volatile substances are released. Handheld 3D printing pens also use the FFF method but the consumer&#8217;s proximity to the 3D pens gives reason to higher exposure compared to a 3D printer. At the same time, 3D printing pens are often marketed for children who could be more sensitive to the printing emission. The aim of this study was to implement a low cost method to analyze the emissions of 3D printing pens. Polylactide (PLA) and acrylonitrile butadiene styrene (ABS) filaments of different colors were tested. In addition, filaments containing metal and carbon nanotubes (CNTs) were analyzed. An 18.5 L chamber and sampling close to the emission source was used to characterize emissions and concentrations near the breathing zone of the user.
Particle emissions and particle size distributions were measured and the potential release of metal particles and CNTs investigated. Particle number concentrations were found in a range of 105 - 106 particles/cm3, which is comparable to previous reports from 3D printers. Transmission electron microscopy (TEM) analysis showed nanoparticles of the different thermoplastic materials as well as of metal particles and CNTs. High contents of metal were observed by inductively coupled plasma mass spectrometry (ICP-MS).
These results call for a cautious use of 3D pens due to potential risk to the consumers.

Particle number concentration 
The highest peak particle number concentration was measured for PLA-copper with 4.8 x 106 #/cm3 and the lowest for PLA-black with 4.3 x 105 #/cm3. In general, a higher emission for ABS &#62; 106 #/cm3 compared to PLA was observed. Nevertheless, some PLA filaments resulted in particle concentrations above 106 #/cm3 (PLA-white and PLA-blue). The different particle concentrations might be related to the use of additives. Zhang et al.28 have stated that particles might be formed by some additives as for example pigments, however not by the bulk material. Thus, the use of different pigments for different colors might influence the number of particles released.
In Figure 3 examples of particle emission increase during the printing process are shown for PLA-black and ABS-black. The results are in agreement with previous 3D printer studies, showing particle concentrations of 105-106 #/cm3 and higher values for ABS compared to PLA12,13. Floyd et al.13 measured peak concentration of 3.5 x 106 #/cm3 for ABS and 1.1 x 106 #/cm3 for PLA. It is important to mention, that ABS is generally printed at higher temperatures compared to PLA. To analyze the influence of the printing temperature on particle release, experiments using PLA-black were carried out at 210 &#176;C (standard setting for ABS). Results were compared to the standard setting of 200 &#176;C for PLA. With the higher temperature setting, particle concentration increased almost one order of magnitude. The average concentration during printing with PLA-black increased from 2.6 x 105 #/cm3 at 200&#176;C to 1.3 x 106 #/cm3 at 210 &#176;C. Higher emissions caused by a higher printing temperature were already observed in earlier studies with 3D printers3.
Particle size distribution in emissions of different filaments 
Figure 4 shows particle size distributions for PLA at 200 and 210 &#176;C and for ABS at 210 &#176;C. Printing ABS resulted in a higher particle concentration and larger particles compared to PLA. The temperature increase during printing of PLA resulted in higher particle number concentrations but had no significant effect on the geometric mean diameter (GMD). This is in agreement with a previous study28.
Figure 5 shows the GMD based on the number count for all measured filaments. There was a clear trend in difference observed between particles emitted during printing with ABS or PLA filaments. The ABS samples had the largest GMD ranging from 203.9 nm for ABS-green and up to 262.1 nm for ABS-blue. ABS-green is made by a different manufacturer than the other ABS filaments; this could be the reason of a slightly different particle size. PLA filaments emitted smaller particles with GMDs &#60; 100 nm (63.8 nm for PLA-clear up to 88.3 nm PLA-blue). For the other filaments with additives, the GMD ranged from 73.1 nm for PLA-steel to 183.9 nm for PLA-copper. Reproducibility of measurements is evident from the low relative standard deviations (RSD) of particle size measurements. The range was mostly between 0.96 and 5.58%. Only in the case of PLA with steel (10.55%) and PLA with CNTs (18.52%) a higher range was observed. This could, however, be due to inhomogeneity in the filaments. Products with additives are a mixture of a thermoplastic (e.g., in this case PLA) and metal or other small particles. The particles might not be evenly distributed and could thereby cause a higher standard deviation. The geometric standard deviations ranged between 1.6 and 1.9, indicating a single modal distribution in the fine and ultrafine particle range, as observed in previous studies of 3D printers13.
The results show a significant difference in particle emissions between PLA and ABS filaments; this was not yet clear from previous publications as often only one or two filaments had been analyzed29. Some authors described larger particles for ABS5,12, some larger ones for PLA2,9. In further studies, no difference in size at all was observed4,13. Byrley et al.29 reviewed 13 publications and described mean particle diameters ranging from 14.0 nm to 108.1 nm for PLA and from 10.5 nm to 88.5 nm for ABS. The difference in particle sizes could be due to measurements at different time points. Some measured at the highest concentration12,13 and some reported the sizes for the whole printing process5,9. The only study of 3D pens available so far reports particles up to 60.4 nm for PLA and up to 173.8 nm for ABS26, which is similar to the findings here.
The size distribution measurement represents a one moment snapshot only. In order to observe time variability regarding the size of the emitted aerosol the particle size distribution for Filament PLA-black was measured 10 times every 3 minutes after the printing was stopped (Figure 6A). The measurements show an increase in GMD (Figure 6B) and a decrease in particle concentration (Figure 6C) with each consecutive measurement run. The increase in particle size could be due to agglomeration, which would also explain the decrease in particle concentration. Interestingly, this occurrence of particle size increase and concentration decrease was not only observed after the printing has stopped, but also during printing processes. This shows that the measurement time is an important factor.
Quantitation of metal content before and after printing using ICP-MS 
A comparison of the filaments containing metal additives before and after the printing process revealed no difference in regard to their metal content. This unchanged metal-polymer ratio indicates that the released particles are not solely polymer, as this would lead to a higher metal concentration in the printed material due to the polymer loss. Released metal nanoparticles could imply higher health risk for the user22. In general, the high amount of metal in advanced filaments should be noted. Metals may cause adverse health effects and especially the release of nanoscale particles requires safety precautions in daily life scenarios30.
For the PLA-copper filament we measured a weight percentage of 70 for copper. For the steel filament we measured weight percentages of 30% Fe, 8% Cr and 6% Ni in the filament. Often the exact composition of the filaments is not declared, and possible risks are therefore not known to the user. Exposure to nickel may have adverse effects on human health and can cause skin allergies, lung fibrosis, cardiovascular and kidney diseases. The element is suspected human carcinogen31.
Besides the metal filaments, PLA clear was analyzed before and after printing. Here, an increase of Cu, Zn, Fe, Cr and Ni was measured after the printing process. This could be due to other materials having been extracted through the 3D pen before and resulting in a memory effect. Measurements were repeated with a newly purchased 3D pen and here no significant increase could be observed (Figure 7).
Particle morphology using TEM 
The TEM images confirmed the presence of particles and verified the difference in particle size between ABS and PLA, measured with the SMPS. TEM images showed particle sizes mostly around 50 nm for PLA (Figure 8A). ABS black showed almost consistently larger particles up to 100 nm (Figure 8B). The difference of particle sizes between PLA and ABS, as seen with the SMPS, could be confirmed. However, smaller sizes were measured by TEM. The smaller sizes could be due to the SMPS measuring particle agglomerates, as described previously, and TEM images showing non agglomerated particles.
PLA-copper filament contained copper as well as PLA particles (Figure 8C). Copper was mostly in crystalline form with sizes around 150 nm. This fits the SMPS measurement of the copper filament, which resulted in mean GMD of 178 nm (Figure 5). Figure 8D possibly depicts a released CNT from the PLA-CNT filament. Furthermore, the release of small steel particles during the printing with PLA-steel filament was observed (Figure 8E). The aluminum filament was described as &#8220;PLA compound - with an incredibly high amount of silver aluminum-flakes added&#8221;32. Figure 8F shows possible an agglomeration of those flakes as the size is much bigger compared to the measured GMD of 124 nm using SMPS.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61829/61829fig01.jpg" /> 
Figure 1: Picture of 3D printing pens and schematic construction of a 3D printing pen.&#160;The 3D printing pen heats the filament to the chosen temperature and extrudes the melted thermoplastic. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61829/61829fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61829/61829fig02.jpg" /> 
Figure 2: Experimental setup for online aerosol measurement.&#160;The particle concentration is measured with a CPC and the particle size distribution with a SMPS. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61829/61829fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61829/61829fig03.jpg" /> 
Figure 3: CPC measurement of particle concentrations.&#160;The measurements show an increase after print start and higher concentrations for ABS compared to PLA. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61829/61829fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61829/61829fig04.jpg" /> 
Figure 4: Particle Size Distribution measured with SMPS with standard deviation (n=3).&#160;PLA printing results in smaller particle compare to ABS. Temperature increase results in higher concentration but shows no significant effect on the particle size. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61829/61829fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/61829/61829fig05.jpg" /> 
Figure 5: Average geometric mean diameter with standard deviation (n=3) for all filaments analyzed.&#160;Printing with PLA resulted in smaller particles compare to ABS. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61829/61829fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/61829/61829fig06.jpg" /> 
Figure 6: Particle size distribution measured just after print stop.&#160;(A) Particle size distribution measured every 3 minutes over a period of 30 minutes after a printing process with PLA-black. (B) Increase of GMD. (C) Decrease in concentration. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61829/61829fig06large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/61829/61829fig07.jpg" /> 
Figure 7: Metal content in digested filaments measured with ICP-MS.&#160;Increase of metal content in PLA-clear filament after printing process. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61829/61829fig07large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/61829/61829fig08.jpg" /> 
Figure 8: TEM-Images of samples from printing process:&#160;(A) PLA-black filament resulting in PLA particles around 50 nm. (B) ABS-black filament resulting in ABS particles up to 100 nm. (C) PLA-copper filament resulting in Copper crystals (120-150 nm) in addition to PLA. (D) PLA-CNT filament resulting in CNT release. (E) PLA-steel filament resulting in released steel fragments. (F) PLA-Aluminum filament resulting in big aluminum particles. (C) &#8211; (D): Arrows indicating PLA and circles metal or CNT respectively. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61829/61829fig08large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about 3D Printing - Evaluating Particle Emissions of a 3D Printing Pen at JoVE.com

3D Printing - Evaluating Particle Emissions of a 3D Printing Pen

This protocol presents a method to analyze the emission of 3D printing pens. Particle concentration and particle size distribution of the released particle is measured. Released particles are further analyzed with transmission electron microscopy (TEM). Metal content in filaments is quantified by inductively coupled plasma mass spectrometry (ICP-MS).

Three-dimensional (3D) printing as a type of additive manufacturing shows continuing increase in application and consumer popularity. The fused filament ...

3d-printing-evaluating-particle-emissions-of-a-3d-printing-pen

Nanyang Technological University

Research

JoVE Journal

Engineering

8.4K Views.  German Federal Institute for Risk Assessment (BfR). 3D-printers en -pennen kunnen deeltjes en vluchtige stoffen afgeven. We hebben een methode ontwikkeld om de uitstoot van 3D-pennen te analyseren. Onze methode is eenvoudig, eenvoudig te implementeren en kosteneffectief op te zetten.Het kan worden gebruikt om de deeltjesemissies in de buurt van de ademhalingszone van de gebruiker te karakteriseren. Deze techniek kan ook worden gebruikt om aerosolemissies van andere bronnen en apparaten zoals spuitproducten of ablatieprocessen te analyse...

Video: 3D Printing - Evaluating Particle Emissions of a 3D Printing Pen

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.

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 ...

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 ...

Planar and Three-Dimensional Printing of Conductive Inks

Printed electronics rely on low-cost, large-area fabrication routes to create flexible or multidimensional electronic, optoelectronic, and biomedical devices1-3. In this paper, we focus on one- (1D), two- (2D), and three-dimensional (3D) printing of conductive metallic inks in the form of flexible, stretchable, and spanning microelectrodes.
Direct-write assembly4,5 is a 1-to-3D printing technique that enables the fabrication of features ranging from simple lines to complex structures by the deposition of concentrated inks through fine nozzles (~0.1 - 250 &mu;m). This printing method consists of a computer-controlled 3-axis translation stage, an ink reservoir and nozzle, and 10x telescopic lens for visualization. Unlike inkjet printing, a droplet-based process, direct-write assembly involves the extrusion of ink filaments either in- or out-of-plane. The printed filaments typically conform to the nozzle size. Hence, microscale features (&lt; 1 &mu;m) can be patterned and assembled into larger arrays and multidimensional architectures.
In this paper, we first synthesize a highly concentrated silver nanoparticle ink for planar and 3D printing via direct-write assembly. Next, a standard protocol for printing microelectrodes in multidimensional motifs is demonstrated. Finally, applications of printed microelectrodes for electrically small antennas, solar cells, and light-emitting diodes are highlighted.

Planar and three-dimensional printing of conductive metallic inks is described. Our approach provides new avenues for fabricating printed electronic, optoelectronic, and biomedical devices in unusual layouts at the microscale.

Printed electronics rely on low-cost, large-area fabrication routes to create flexible or multidimensional electronic, optoelectronic, and biomedical ...

Bioengineering

Experimental Protocol to Investigate Particle Aerosolization of a Product Under Abrasion and Under Environmental Weathering

The present article presents an experimental protocol to investigate particle aerosolization of a product under abrasion and under environmental weathering, which is a fundamental element to the approach of nanosafety-by-design of nanostructured products for their durable development. This approach is basically a preemptive one in which the focus is put on minimizing the emission of engineered nanomaterials' aerosols during the usage phase of the product's life cycle. This can be attained by altering its material properties during its design phase without compromising with any of its added benefits. In this article, an experimental protocol is presented to investigate the nanosafety-by-design of three commercial nanostructured products with respect to their mechanical solicitation and environmental weathering. The means chosen for applying the mechanical solicitation is an abrasion process and for the environmental weathering, it is an accelerated UV exposure in the presence of humidity and heat. The eventual emission of engineered nanomaterials is studied in terms of their number concentration, size distribution, morphology and chemical composition. The purpose of the protocol is to study the emission for test samples and experimental conditions which are corresponding to real life situations. It was found that the application of the mechanical stresses alone emits the engineered nanomaterials' aerosols in which the engineered nanomaterial is always embedded inside the product matrix, thus, a representative product element. In such a case, the emitted aerosols comprise of both nanoparticles as well as microparticles. But if the mechanical stresses are coupled with the environmental weathering, the experimental protocol reveals then the eventual deterioration of the product, after a certain weathering duration, may lead to the emission of the free engineered nanomaterial aerosols too.

In this article, an experimental protocol to investigate particle aerosolization of a product under abrasion and under environmental weathering is presented. Results on the emission of engineered nanomaterials, in the form of aerosols are presented. The specific experimental set-up is described in detail.

The present article presents an experimental protocol to investigate particle aerosolization of a product under abrasion and under environmental ...

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 ...

Measuring Sub-23 Nanometer Real Driving Particle Number Emissions Using the Portable DownToTen Sampling System

The current particle size threshold of the European Particle Number (PN) emission standards is 23 nm. This threshold could change because future combustion engine vehicle technology may emit large amounts of sub-23 nm particles. The Horizon 2020 funded project DownToTen (DTT) developed a sampling and measurement method to characterize particle emissions in this currently unregulated size range. A PN measurement system was developed based on an extensive review of the literature and laboratory experiments testing a variety of PN measurement and sampling approaches. The measurement system developed is characterized by high particle penetration and versatility, which enables the assessment of primary particles, delayed primary particles, and secondary aerosols, starting from a few nanometers in diameter. This paper provides instruction on how to install and operate this Portable Emission Measurement System (PEMS) for Real Drive Emissions (RDE) measurements and assess particle number emissions below the current legislative limit of 23 nm.

Presented here is the DownToTen (DTT) portable emission measurement system to assess real driving automotive emissions of sub-23 nm particles.

The current particle size threshold of the European Particle Number (PN) emission standards is 23 nm. This threshold could change because future ...

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.

The development of novel imaging techniques of molecular and colloidal transport, including nanoparticles, is an area of active investigation in ...

Additive Manufacturing-Enabled Low-Cost Particle Detector

As particles with a size of 1 &#181;m or smaller pose a severe health risk to the human body, the detection and regulation of particle emissions are of great importance. A large share of particulate emissions are emitted by the transport sector. Most of the commercially available particle detectors are bulky, very expensive, and need additional equipment. This paper presents a protocol to build and test a standalone particle detector that is small and cost-efficient. 
The focus of this paper lies in the description of the detailed construction manual with video and the sensor evaluation procedure. The computer-aided design model of the sensor is included in the supplemental material. The manual explains all the construction steps, from 3D printing to the fully operational sensor. The sensor can detect charged particles and is therefore suitable for a wide range of applications. A possible field of application would be soot detection from power plants, wildfires, industries, and automobiles.

Here, we present a protocol on how to build and test a simple but efficient low-cost particle detector.

As particles with a size of 1 &#181;m or smaller pose a severe health risk to the human body, the detection and regulation of particle emissions are of ...

Visualizing Polymer Dynamics for Optimizing 3D Printing Quality

Real-Time Imaging of Bonding in 3D-Printed Layers

In recent times, 3D printing technology has revolutionized our ability to design and produce products, but optimizing the print quality can be challenging. The process of extrusion 3D printing involves pressuring molten material through a thin nozzle and depositing it onto previously extruded material. This method relies on bonding between the consecutive layers to create a strong and visually appealing final product. This is no easy task, as many parameters, such as the nozzle temperature, layer thickness, and printing speed, must be fine-tuned to achieve optimal results. In this study, a method for visualizing the polymer dynamics during extrusion is presented, giving insight into the layer bonding process. Using laser speckle imaging, the plastic flow and fusion can be resolved non-invasively, internally, and with high spatiotemporal resolution. This measurement, which is easy to perform, provides an in-depth understanding of the underlying mechanics influencing the final print quality. This methodology was tested with a range of cooling fan speeds, and the results showed increased polymer motion with lower fan speeds and, thus, explained the poor printing quality when the cooling fan was turned off. These findings show that this methodology allows for optimizing the printing settings and understanding the material behavior. This information can be used for the development and testing of novel printing materials or advanced slicing procedures. With this approach, a deeper understanding of extrusion can be built to take 3D printing to the next level.

Author Spotlight: Real-Time Imaging of Bonding in 3D-Printed Layers  

With a non-invasive and real-time technique, nanoscopic polymer motion inside a polymer filament is imaged during 3D printing. Fine-tuning this motion is crucial for producing constructs with optimal performance and appearance. This method reaches the core of plastic layer fusion, thus offering insights into optimal printing conditions and material design criteria.

In recent times, 3D printing technology has revolutionized our ability to design and produce products, but optimizing the print quality can be ...

Evaluating Regional Pulmonary Deposition using Patient-Specific 3D Printed Lung Models

Development of targeted therapies for pulmonary diseases is limited by the availability of preclinical testing methods with the ability to predict regional aerosol delivery. Leveraging 3D printing to generate patient-specific lung models, we outline the design of a high-throughput, in vitro experimental setup for quantifying lobular pulmonary deposition. This system is made with a combination of commercially available and 3D printed components and allows the flow rate through each lobe of the lung to be independently controlled. Delivery of fluorescent aerosols to each lobe is measured using fluorescence microscopy. This protocol has the potential to promote the growth of personalized medicine for respiratory diseases through its ability to model a wide range of patient demographics and disease states. Both the geometry of the 3D printed lung model and the air flow profile setting can be easily modulated to reflect clinical data for patients with varying age, race, and gender. Clinically relevant drug delivery devices, such as the endotracheal tube shown here, can be incorporated into the testing setup to more accurately predict a device&#8217;s capacity to target therapeutic delivery to a diseased region of the lung. The versatility of this experimental setup allows it to be customized to reflect a multitude of inhalation conditions, enhancing the rigor of preclinical therapeutic testing.

We present a high-throughput, in vitro method for quantifying regional pulmonary deposition at the lobe level using CT scan-derived, 3D printed lung models with tunable air flow profiles.

3D Printing - Evaluating Particle Emissions of a 3D Printing Pen

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