This work was supported by an AOARD grant (No. FA2386-18-1-4059), the Netherlands Organization for Scientific Research (NWO/OCW) as part of the Frontiers of Nanoscience program, and the Advanced Materials NWO-NSFC program (No. 729.001.016). The authors acknowledge laboratory assistance of Ramon van der Valk and Roland Kieffer.

1. Conversion of a commercial 3D printer into a 3D bioprinter
<ol>
	<li>Remove the extruder and the heater of a commercial 3D printer (Table of Materials) from the printer frame, and unplug the wiring controlling these elements from the main circuit board (Figure 1A). Since the sensor that controls the operational temperature of the printer needs to be functional to communicate with the printer software, remove from the printing software the algorithm that delays printing until operational temperature is reached.</li>
	<li>Connect a pipette tip (200 &#181;L tip) via silicon tubing (inner diameter of 1 mm) to a 5 mL syringe loaded into a syringe pump. Mount the pipette tip onto the 3D printer extruder head as a replacement for the original extruder (Figure 1B).</li>
	<li>If more than one type of bio-ink will be used, mount additional tubing system(s) and pipette tip(s) to the printer.</li>
</ol>
2. Substrate preparation for 3D printing
<ol>
	<li>Add 4 mL of 5 M CaCl2 solution to 400 mL of 1% w/v agar dissolved in Luria-Bertani broth (LB) medium, supplemented with appropriate antibiotics and inducers (here 34 &#181;g/mL chloramphenicol and 0.5% rhamnose).</li>
	<li>Dispense 20 mL of the LB-agar solution into each 150 mm x 15 mm Petri dish. Dry 30 min at room temperature with the lid half-open. 
	NOTE: The protocol can be paused here by storing these printing substrates at 4 &#176;C for up to several days.</li>
</ol>
3. Bio-ink preparation
<ol>
	<li>Prepare a sodium alginate solution (3% w/v), and heat to the boiling point three times to sterilize the solution. Store at 4 &#176;C until used.</li>
	<li>Grow E. coli MG1655 PRO &#916;csgA ompR234 (E. coli &#916;csgA) bacteria carrying plasmids pSB1C3-green fluorescent protein (GFP) (constitutive GFP expression)2 or pSB1C3-GFP-CsgA (constitutive GFP expression, rhamnose-inducible CsgA expression) overnight at 37 &#176;C with shaking at 250 rpm in 50 mL of LB medium containing 34 &#181;g/mL chloramphenicol and 0.5% rhamnose.</li>
	<li>Centrifuge the cell culture for 5 min at 3,220 x g to pellet the bacteria. Remove the supernatant.</li>
	<li>Re-suspend the bacteria pellet in 10 mL of LB medium and add 10 mL of sodium alginate (3% w/v).</li>
</ol>
4. 3D printing process
<ol>
	<li>Install and open the 3D printing software (Table of Materials) on a computer. Connect the 3D printer to the computer. Move the printhead to its home position&#160;by clicking the home button for the X, Y, and Z axes.</li>
	<li>For each print, place a prepared printing substrate onto a particular location on the printing bed.</li>
	<li>Calibrate the height of the printhead in the Z axis.
	<ol>
		<li>Raise the printhead to a height of 22&#160;mm under manual control, so that it will not collide with the edge of the petri dish when moving to the desired position. Position the printhead overtop of the plate, and move it down until the pipette tip contacts the printing surface. Assign this Z-axis position as Z1 (the height of the printing surface).</li>
		<li>Raise the printhead, and move it outside of the plate area by manual control in the X, Y, and Z axes. If the working distance between the printhead and the plate surface is defined as Z2, enter Z1 + Z2 into the printing program as the Z-value during printing.</li>
	</ol>
	</li>
	<li>Program the printing shape by a self-developed point-by-point coordinate-determined method according to the desired trajectory.
	<ol>
		<li>If the desired trajectory is a straight line, define only the start and end points. Including additional points on curved lines will result in smoother curves. Move the printhead manually to every point sequentially, and record the coordinates of these points in order. Enter all of these coordinates as well as the printhead moving speed for each printed segment into the G-code editor.</li>
	</ol>
	</li>
	<li>Both before and after printing, lift the printhead to a distance higher than the plate edge (20 mm), and move directly out of the plate region. Save this program as a G-code file and load directly for use in subsequent prints, while re-measuring the Z axis height for each new printing substrate. 
	NOTE: See Table 1 for an example G-code for printing a square.</li>
	<li>Load the pre-programmed G-code file. Open the G-code editor in the software, and program in the commands for printing the desired shape. At each command line, the position of the printhead may be changed in the X, Y, and/or Z axis. Input the Z value during all printing steps as Z1 + Z2 (height of printing surface + working distance). 
	NOTE: The moving speed is also adjustable; 9,000 mm/min is a suitable value for typical printing rates.</li>
	<li>Load the liquid bio-ink into syringe(s), and mount them in the syringe pump(s) of the 3D bioprinter.</li>
	<li>Print the bio-ink onto the printing substrate by clicking the Print button.</li>
	<li>During printing, control the printhead movement entirely by the software. Manually start the syringe pump before the printhead comes into contact with the printing surface. 
	NOTE: The coordination of the syringe pump and the printer is empirically determined depending on the extrusion speed, the speed at which the printhead moves to the first print point, and the initial position of the printhead. If the initial printhead position is 20 mm, with a printhead speed of 9,000 mm/min and an extrusion speed of 0.1 mL/h, start the syringe pump immediately after the printing is started. If the extrusion speed is changed from 0.1 mL/h to 0.3 mL/h, then wait 2&#8722;3 s to start the syringe pump after the printing is started.</li>
	<li>Stop the syringe pump as soon as the printhead arrives at the last point of printing. Halt the syringe pump before the printhead lifts up at the end of the printing process, otherwise excess bio-ink will drop onto the printing substrate and reduce the printing resolution.</li>
	<li>For the construction of 3D structures, control all movements of the printhead in the G-code editor. Type in the printing height of the first layer. Increase the Z-value in the G-code by 0.2 millimeters for the second layer to increase the printing height. Thereafter, increase the Z-value by 0.1 millimeters when moving to a higher layer. Do not move the plate during the printing process.</li>
	<li>To measure the width and height of the printed hydrogel, use a steel ruler placed underneath or alongside the sample.</li>
</ol>
5. Growing and testing the effectiveness of biofilm production by E. coli
<ol>
	<li>Incubate the printed samples at room temperature for 3&#8722;6 days to allow the production of biofilm components (curli fibers). Image the plates using a camera or fluorescent scanner.</li>
	<li>To dissolve the alginate matrix, add 20 mL of 0.5 M sodium citrate solution (pH = 7 adjusted with NaOH) to the printing substrates, and incubate for 2 h with 30 rpm shaking at room temperature. Discard the liquid and image the plates again to compare with the images of the plates before citrate treatment.</li>
</ol>

<ol>
	<li>Tibbitt, M. W., Rodell, C. B., Burdick, J. A., Anseth, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Progress+in+material+design+for+biomedical+applications.">Progress in material design for biomedical applications.</a> Proceedings of the National Academy of Sciences of the United States of America. 112 (47), 14444-14451 (2015).</li><li>Schmieden, D. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Printing+of+Patterned,+Engineered+E.+coli+Biofilms+with+a+Low-Cost+3D+Printer.">Printing of Patterned, Engineered E. coli Biofilms with a Low-Cost 3D Printer.</a> ACS Synthetic Biology. 7 (5), 1328-1337 (2018).</li><li>Mao, L. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthetic+nacre+by+predesigned+matrix-directed+mineralization.">Synthetic nacre by predesigned matrix-directed mineralization.</a> Science. 354 (6308), 107-110 (2016).</li><li>Gao, H. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mass+production+of+bulk+artificial+nacre+with+excellent+mechanical+properties.">Mass production of bulk artificial nacre with excellent mechanical properties.</a> Nature Communications. 8 (1), 287 (2017).</li><li>Poirier, Y., Nawrath, C., Somerville, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Production+of+Polyhydroxyalkanoates,+a+Family+of+Biodegradable+Plastics+and+Elastomers,+in+Bacteria+and+Plants.">Production of Polyhydroxyalkanoates, a Family of Biodegradable Plastics and Elastomers, in Bacteria and Plants.</a> Nature Biotechnology. 13, 142-150 (1995).</li><li>Choi, S. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=One-step+fermentative+production+of+poly(lactate-co-glycolate)+from+carbohydrates+in+Escherichia+coli.">One-step fermentative production of poly(lactate-co-glycolate) from carbohydrates in Escherichia coli.</a> Nature Biotechnology. 34 (4), 435-440 (2016).</li><li>Mohammadi, P., Toivonen, M. S., Ikkala, O., Wagermaier, W., Linder, M. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aligning+cellulose+nanofibril+dispersions+for+tougher+fibers.">Aligning cellulose nanofibril dispersions for tougher fibers.</a> Scientific Reports. 7 (1), 11860 (2017).</li><li>Jonkers, H. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bacteria-based+self-healing+concrete.">Bacteria-based self-healing concrete.</a> Heron. 56 (1/2), (2011).</li><li>Schmieden, D. T., Meyer, A. S., Aubin-Tam, M. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Using+bacteria+to+make+improved,+nacre-inspired+materials.">Using bacteria to make improved, nacre-inspired materials.</a> MRS Advances. 1 (8), 559-564 (2016).</li><li>Zhong, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strong+underwater+adhesives+made+by+self-assembling+multi-protein+nanofibres.">Strong underwater adhesives made by self-assembling multi-protein nanofibres.</a> Nature Nanotechnology. 9 (10), 858-866 (2014).</li><li>Chen, A. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+patterning+of+tunable+multiscale+materials+with+engineered+cells.">Synthesis and patterning of tunable multiscale materials with engineered cells.</a> Nature Materials. 13 (5), 515-523 (2014).</li><li>Gatenholm, P., Klemm, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bacterial+Nanocellulose+as+a+Renewable+Material+for+Biomedical+Applications.">Bacterial Nanocellulose as a Renewable Material for Biomedical Applications.</a> MRS Bulletin. 35, 208-213 (2010).</li><li>Rodriguez-Carmona, E., Villaverde, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanostructured+bacterial+materials+for+innovative+medicines.">Nanostructured bacterial materials for innovative medicines.</a> Trends in Microbiology. 18 (9), 423-430 (2010).</li><li>Hung, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Escherichia+coli+biofilms+have+an+organized+and+complex+extracellular+matrix+structure.">Escherichia coli biofilms have an organized and complex extracellular matrix structure.</a> MBio. 4 (5), (2013).</li><li>Donlan, R. M., Costerton, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biofilms:+Survival+Mechanisms+of+Clinically+Relevant+Microorganisms.">Biofilms: Survival Mechanisms of Clinically Relevant Microorganisms.</a> Clinical Microbiology Reviews. 15 (2), 167-193 (2002).</li><li>Wu, H., Moser, C., Wang, H. Z., Hoiby, N., Song, Z. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strategies+for+combating+bacterial+biofilm+infections.">Strategies for combating bacterial biofilm infections.</a> International Journal of Oral Science. 7 (1), 1-7 (2015).</li><li>Stewart, P. S., Franklin, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Physiological+heterogeneity+in+biofilms.">Physiological heterogeneity in biofilms.</a> Nature Reviews Microbiology. 6 (3), 199-210 (2008).</li><li>Kikuchi, T., Mizunoe, Y., Takade, A., Naito, S., Yoshida, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Curli+Fibers+Are+Required+for+Development+of+Biofilm+Architecture+in+Escherichia+coli+K-12+and+Enhance+Bacterial+Adherence+to+Human+Uroepithelial+Cells.">Curli Fibers Are Required for Development of Biofilm Architecture in Escherichia coli K-12 and Enhance Bacterial Adherence to Human Uroepithelial Cells.</a> Microbiology and Immunology. 49 (9), 875-884 (2005).</li><li>Cranford, S., Buehler, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Materiomics:+biological+protein+materials,+from+nano+to+macro.">Materiomics: biological protein materials, from nano to macro.</a> Nanotechnology, Science and Applications. 3, 127-148 (2010).</li><li>Lehner, B. A. E., Schmieden, D. T., Meyer, A. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Straightforward+Approach+for+3D+Bacterial+Printing.">A Straightforward Approach for 3D Bacterial Printing.</a> ACS Synthetic Biology. 6 (7), 1124-1130 (2017).</li><li>Wang, X., Smith, D. R., Jones, J. W., Chapman, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+polymerization+of+a+functional+Escherichia+coli+amyloid+protein.">In vitro polymerization of a functional Escherichia coli amyloid protein.</a> Journal of Biological Chemistry. 282 (6), 3713-3719 (2007).</li><li>Hammar, M., Bian, Z., Normark, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nucleator-dependent+intercellular+assembly+of+adhesive+curli+organelles+in+Escherichia+coli.">Nucleator-dependent intercellular assembly of adhesive curli organelles in Escherichia coli.</a> Proceedings of the National Academy of Sciences of the United States of America. 93 (13), 6562-6566 (1996).</li><li>Huang, Y. J., Xia, A. G., Yang, G., Jin, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bioprinting+Living+Biofilms+through+Optogenetic+Manipulation.">Bioprinting Living Biofilms through Optogenetic Manipulation.</a> ACS Synthetic Biology. 7 (5), 1195-1200 (2018).</li><li>Jin, X. F., Riedel-Kruse, I. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biofilm+Lithography+enables+high-resolution+cell+patterning+via+optogenetic+adhesin+expression.">Biofilm Lithography enables high-resolution cell patterning via optogenetic adhesin expression.</a> Proceedings of the National Academy of Sciences of the United States of America. 115 (14), 3698-3703 (2018).</li><li>Stewart, P. S., Franklin, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Physiological+heterogeneity+in+biofilms.">Physiological heterogeneity in biofilms.</a> Nature Reviews Microbiology. 6 (3), 199-210 (2008).</li><li>Percival, S. L., Suleman, L., Vuotto, C., Donelli, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Healthcare-associated+infections,+medical+devices+and+biofilms:+risk,+tolerance+and+control.">Healthcare-associated infections, medical devices and biofilms: risk, tolerance and control.</a> Journal of Medical Microbiology. 64, 323-334 (2015).</li></ol>

The authors have nothing to disclose.

The protocol presented here for 3D printing of engineered biofilms has two critical steps. First is the preparation of the agar printing surface, which is the most critical factor to producing a specific printing resolution. It is important to ensure that the printing surface is flat and that the pipette tip on the printhead is positioned at the correct height from the surface. If the surface is not flat, the working distance will change during the printing process. If the working distance is less than 0.1 mm, the CaCl<s...

There is currently an increasing need to develop environmentally-friendly, sustainable solutions for the production of spatially-patterned materials, due to the expanding number of markets for such materials1. This article presents a simple, economical method for the production of such materials and therefore offers a large spectrum of future applications. The method presented here allows three-dimensional (3D) printing of spatially-patterned structures using a bio-ink containing living bacteria. Bacteria remain viable within the printed structures for over one week, enabling the bacteria to perform natural or engineered metabolic activities. Printed bacteria can thereby produce and deposit desired components within the printed structure, for example creating a functional cross-linked biofilm2.
Traditional methods for the production of advanced materials involve high energy expenditures (e.g., high temperatures and/or pressures) and can produce large quantities of chemical waste, often toxic substances that require cost-extensive utilization3,4. In contrast, multiple bacterial species are able to produce materials that can be readily applicable in various industries. These materials include polymers such as polyhydroxyalkanoates (PHA)5 or poly(glycolide-co-lactide) (PGLA)6, bacterial cellulose7, bacterial concrete materials8, biomimetic composites9, amyloid-based adhesives10, or bio-based electrical switches11, among others. Moreover, bacterial production of valuable materials typically takes place at near-ambient temperatures and pressures and in aqueous environments, without requiring or producing toxic compounds. While producing materials with bacteria has been demonstrated in the literature and some industrial applications have already emerged12,13, a reliable method for spatial patterning of such materials remains a challenge.
This article demonstrates a straight-forward method of converting a low-cost commercial 3D printer into a 3D bacterial printer. The protocol shows how to prepare a bio-ink containing and sustaining the living bacteria, as well as how to prepare substrates onto which the 3D printing can be performed. This method is appropriate to use with a variety of natural and engineered bacterial strains able to produce materials. These bacteria can be spatially distributed within a 3D printed structure and still continue their metabolic activity, which will result in a spatial distribution of the desired materials produced by the bacteria.
This printing method enables additive manufacturing of biofilms, aggregates of bacteria surrounded by a self-produced extracellular matrix. Biofilms are heterogeneous 3D networks in which proteins, polymers, bacterial cells, oxygen, and nutrients are all spatially structured14. While in the form of a biofilm, bacteria exhibit an increased antibiotic resistance and structural robustness, making them difficult to eradicate from surfaces including medical catheters and implants. The key to biofilm properties, and also the largest challenge to biofilm research, seems to be the heterogeneity of biofilms15,16,17. Production of spatially-controlled model biofilms is of special interest as it would allow for either reproducing or tuning the spatial patterns of biofilm components, aiding the understanding of the stable deposition of biofilms on virtually any surface in nature.
This article presents a method for the production of biofilms using 3D-printed hydrogels containing engineered E. coli bacteria that produce biofilm proteins in the presence of an inducer, as well as methods of verification of biofilm formation2. The major extracellular matrix components of these biofilms are curli amyloid fibers18 that contain self-assembled CsgA proteins. When engineered E. coli bacteria are induced to express CsgA proteins, they form a stable model biofilm that protects the cells against being washed off of the printing surface. Such a 3D printed biofilm can be spatially controlled and can serve as a useful research tool for the investigation of multiscale biofilm structure-function mechanics or materiomics19. These bespoke biofilms will aid the understanding of the principles of biofilm formation and their mechanical properties, enabling further research into the mechanisms of antibiotic resistance among other applications.

<table>
	<tbody>
		<tr>
			<td>3D printer</td>
			<td>CoLiDo</td>
			<td>3D-P Kit</td>
			<td></td>
		</tr>
		<tr>
			<td>3D printing software</td>
			<td>CoLiDo</td>
			<td>Print-Rite ColiDo Repetier-Host v2.0.1</td>
			<td></td>
		</tr>
		<tr>
			<td>Agar</td>
			<td>Sigma-Aldrich</td>
			<td>05040</td>
			<td></td>
		</tr>
		<tr>
			<td>CaCl2 dihydrate</td>
			<td>Sigma-Aldrich</td>
			<td>C7902</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge</td>
			<td>Eppendorf</td>
			<td>5810 R</td>
			<td></td>
		</tr>
		<tr>
			<td>Chloramphenicol</td>
			<td>Sigma-Aldrich</td>
			<td>3886.1</td>
			<td></td>
		</tr>
		<tr>
			<td>LB broth powder</td>
			<td>Sigma-Aldrich</td>
			<td>L3022</td>
			<td></td>
		</tr>
		<tr>
			<td>Orbital shaker</td>
			<td>VWR</td>
			<td>89032-092</td>
			<td>Model 3500</td>
		</tr>
		<tr>
			<td>Petri dish</td>
			<td>VWR</td>
			<td>25384-326</td>
			<td>150 x 15 mm</td>
		</tr>
		<tr>
			<td>Rhamnose</td>
			<td>Sigma-Aldrich</td>
			<td>83650</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicon tubing</td>
			<td>VWR&#160;</td>
			<td>DENE 3100103/25</td>
			<td></td>
		</tr>
		<tr>
			<td>Syringe pump</td>
			<td>ProSense B.V.&#160;</td>
			<td>NE-300</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium alginate</td>
			<td>Sigma-Aldrich</td>
			<td>W201502</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium citrate monobasic</td>
			<td>Sigma-Aldrich</td>
			<td>71498</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium hydrooxide</td>
			<td>VWR</td>
			<td>28244.295</td>
			<td></td>
		</tr>
	</tbody>
</table>

three-dimensional patterning of engineered biofilms with a do-it-yourself bioprinter

Biofilms are aggregates of bacteria embedded in a self-produced spatially-patterned extracellular matrix. Bacteria within a biofilm develop enhanced antibiotic resistance, which poses potential health dangers, but can also be beneficial for environmental applications such as purification of drinking water. The further development of anti-bacterial therapeutics and biofilm-inspired applications will require the development of reproducible, engineerable methods for biofilm creation. Recently, a novel method of biofilm preparation using a modified three-dimensional (3D) printer with a bacterial ink has been developed. This article describes the steps necessary to build this efficient, low-cost 3D bioprinter that offers multiple applications in bacterially-induced materials processing. The protocol begins with an adapted commercial 3D printer in which the extruder has been replaced with a bio-ink dispenser connected to a syringe pump system enabling a controllable, continuous flow of bio-ink. To develop a bio-ink suitable for biofilm printing, engineered Escherichia coli bacteria were suspended in a solution of alginate, so that they solidify in contact with a surface containing calcium. The inclusion of an inducer chemical within the printing substrate drives expression of biofilm proteins within the printed bio-ink. This method enables 3D printing of various spatial patterns composed of discrete layers of printed biofilms. Such spatially-controlled biofilms can serve as model systems and can find applications in multiple fields that have a wide-ranging impact on society, including antibiotic resistance prevention or drinking water purification, among others.

The first step for successful 3D printing of biofilms is converting a commercial 3D printer into a bioprinter. This conversion is achieved by removing the extruder and heater of the printer, designed for printing with a polymeric ink, and replacing these with components appropriate for printing bio-ink containing living bacteria (Figure 1A). The extruder is replaced by a pipette tip (or tips, if multiple bio-inks will be used in the printing process) attached...

Watch this Scientific Journal Video about Three-dimensional Patterning of Engineered Biofilms with a Do-it-yourself Bioprinter at JoVE.com

Three-dimensional Patterning of Engineered Biofilms with a Do-it-yourself Bioprinter

This article describes a method of transforming a low-cost commercial 3D printer into a bacterial 3D printer that can facilitate printing of patterned biofilms. All necessary aspects of preparing the bioprinter and bio-ink are described, as well as verification methods to assess the formation of biofilms.

Biofilms are aggregates of bacteria embedded in a self-produced spatially-patterned extracellular matrix. Bacteria within a biofilm develop enhanced ...

three-dimensional-patterning-engineered-biofilms-with-do-it-yourself

Universidad de Cartagena UDEC

Research

JoVE Journal

Bioengineering

9.5K Views.  Delft University of Technology. This article describes a method of transforming a low-cost commercial 3D printer into a bacterial 3D printer that can facilitate printing of patterned biofilms. All necessary aspects of preparing the bioprinter and bio-ink are described, as well as verification methods to assess the formation of biofilms.

Video: Three-dimensional Patterning of Engineered Biofilms with a Do-it-yourself Bioprinter

Three-dimensional Optical-resolution Photoacoustic Microscopy

Optical microscopy, providing valuable insights at the cellular and organelle levels, has been widely recognized as an enabling biomedical technology. As the mainstays of in vivo three-dimensional (3-D) optical microscopy, single-/multi-photon fluorescence microscopy and optical coherence tomography (OCT) have demonstrated their extraordinary sensitivities to fluorescence and optical scattering contrasts, respectively. However, the optical absorption contrast of biological tissues, which encodes essential physiological/pathological information, has not yet been assessable. 
The emergence of biomedical photoacoustics has led to a new branch of optical microscopy optical-resolution photoacoustic microscopy (OR-PAM)1, where the optical irradiation is focused to the diffraction limit to achieve cellular1 or even subcellular2 level lateral resolution. As a valuable complement to existing optical microscopy technologies, OR-PAM brings in at least two novelties. First and most importantly, OR-PAM detects optical absorption contrasts with extraordinary sensitivity (i.e., 100%). Combining OR-PAM with fluorescence microscopy3 or with optical-scattering-based OCT4 (or with both) provides comprehensive optical properties of biological tissues. Second, OR-PAM encodes optical absorption into acoustic waves, in contrast to the pure optical processes in fluorescence microscopy and OCT, and provides background-free detection. The acoustic detection in OR-PAM mitigates the impacts of optical scattering on signal degradation and naturally eliminates possible interferences (i.e., crosstalks) between excitation and detection, which is a common problem in fluorescence microscopy due to the overlap between the excitation and fluorescence spectra. 
Unique for optical absorption imaging, OR-PAM has demonstrated broad biomedical applications since its invention, including, but not limited to, neurology5, 6, ophthalmology7, 8, vascular biology9, and dermatology10. In this video, we teach the system configuration and alignment of OR-PAM as well as the experimental procedures for in vivo functional microvascular imaging.

Optical-resolution photoacoustic microscopy (OR-PAM) is an emerging technology capable of imaging optical absorption contrasts in vivo with cellular resolution and sensitivity. Here, we provide a visualized instruction on the experimental protocols of OR-PAM, including system configuration, system alignment, typical in vivo experimental procedures, and functional imaging schemes.

Optical microscopy, providing valuable insights at the cellular and organelle levels, has been widely recognized as an enabling biomedical technology. As ...

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 ...

Analysis of Cell Migration within a Three-dimensional Collagen Matrix

The ability to migrate is a hallmark of various cell types and plays a crucial role in several physiological processes, including&#160;embryonic development, wound healing, and immune responses. However, cell migration is also a key mechanism in cancer enabling these cancer cells to detach from the primary tumor to start metastatic spreading. Within the past years various cell migration assays have been developed to analyze the migratory behavior of different cell types. Because the locomotory behavior of cells markedly differs between a two-dimensional (2D) and three-dimensional (3D) environment it can be assumed that the analysis of the migration of cells that are embedded within a 3D environment would yield in more significant cell migration data. The advantage of the described 3D collagen matrix migration assay is that cells are embedded within a physiological 3D network of collagen fibers representing the major component of the extracellular matrix. Due to time-lapse video microscopy real cell migration is measured allowing the determination of several migration parameters as well as their alterations in response to pro-migratory factors or inhibitors. Various cell types could be analyzed using this technique, including lymphocytes/leukocytes, stem cells, and tumor cells. Likewise, also cell clusters or spheroids could be embedded within the collagen matrix concomitant with analysis of the emigration of single cells from the cell cluster/ spheroid into the collagen lattice. We conclude that the 3D collagen matrix migration assay is a versatile method to analyze the migration of cells within a physiological-like 3D environment.

Cell migration is a biological phenomenon that is involved in a plethora of physiological, such as wound healing and immune responses, and pathophysiological processes, like cancer. The 3D-collagen matrix migration assay is a versatile tool to analyze the migratory properties of different cell types within in a 3D physiological-like environment.

The ability to migrate is a hallmark of various cell types and plays a crucial role in several physiological processes, including&#160;embryonic ...

Generation of a Three-dimensional Full Thickness Skin Equivalent and Automated Wounding

In vitro models are a cost effective and ethical alternative to study cutaneous wound healing processes. Moreover, by using human cells, these models reflect the human wound situation better than animal models. Although two-dimensional models are widely used to investigate processes such as cellular migration and proliferation, models that are more complex are required to gain a deeper knowledge about wound healing. Besides a suitable model system, the generation of precise and reproducible wounds is crucial to ensure comparable results between different test runs. In this study, the generation of a three-dimensional full thickness skin equivalent to study wound healing is shown. The dermal part of the models is comprised of human dermal fibroblast embedded in a rat-tail collagen type I hydrogel. Following the inoculation with human epidermal keratinocytes and consequent culture at the air-liquid interface, a multilayered epidermis is formed on top of the models. To study the wound healing process, we additionally developed an automated wounding device, which generates standardized wounds in a sterile atmosphere.

The goal of this protocol is to build up a three-dimensional full thickness skin equivalent, which resembles natural skin. With a specifically constructed automated wounding device, precise and reproducible wounds can be generated under maintenance of sterility.

In vitro models are a cost effective and ethical alternative to study cutaneous wound healing processes. Moreover, by using human cells, these models ...

Rapid Subtractive Patterning of Live Cell Layers with a Microfluidic Probe

The microfluidic probe (MFP) facilitates performing local chemistry on biological substrates by confining nanoliter volumes of liquids. Using one particular implementation of the MFP, the hierarchical hydrodynamic flow confinement (hHFC), multiple liquids are simultaneously brought in contact with a substrate. Local chemical action and liquid shaping using the hHFC, is exploited to create cell patterns by locally lysing and removing cells. By utilizing the scanning ability of the MFP, user-defined patterns of cell monolayers are created. This protocol enables rapid, real-time and spatially controlled cell patterning, which can allow selective cell-cell and cell-matrix interaction studies.

We present a protocol to perform subtractive patterning of live cell monolayers on a surface. This is achieved by local and selective lysis of adherent cells using a microfluidic probe (MFP). The cell lysate retrieved from local regions can be used for downstream analysis, enabling molecular profiling studies.

The microfluidic probe (MFP) facilitates performing local chemistry on biological substrates by confining nanoliter volumes of liquids. Using one ...

Three-dimensional Tissue Engineered Aligned Astrocyte Networks to Recapitulate Developmental Mechanisms and Facilitate Nervous System Regeneration

Neurotrauma and neurodegenerative disease often result in lasting neurological deficits due to the limited capacity of the central nervous system (CNS) to replace lost neurons and regenerate axonal pathways. However, during nervous system development, neuronal migration and axonal extension often occur along pathways formed by other cells, referred to as &#34;living scaffolds&#34;. Seeking to emulate these mechanisms and to design a strategy that circumvents the inhibitory environment of the CNS, this manuscript presents a protocol to fabricate tissue engineered astrocyte-based &#34;living scaffolds&#34;. To create these constructs, we employed a novel biomaterial encasement scheme to induce astrocytes to self-assemble into dense three-dimensional bundles of bipolar longitudinally-aligned somata and processes. First, hollow hydrogel micro-columns were assembled, and the inner lumen was coated with collagen extracellular-matrix. Dissociated cerebral cortical astrocytes were then delivered into the lumen of the cylindrical micro-column and, at a critical inner diameter of &#60;350 &#181;m, spontaneously self-aligned and contracted to produce long fiber-like cables consisting of dense bundles of astrocyte processes and collagen fibrils measuring &#60;150 &#181;m in diameter yet extending several cm in length. These engineered living scaffolds exhibited &#62;97% cell viability and were virtually exclusively comprised of astrocytes expressing a combination of the intermediate filament proteins glial-fibrillary acidic protein (GFAP), vimentin, and nestin. These aligned astrocyte networks were found to provide a permissive substrate for neuronal attachment and aligned neurite extension. Moreover, these constructs maintain integrity and alignment when extracted from the hydrogel encasement, making them suitable for CNS implantation. These preformed constructs structurally emulate key cytoarchitectural elements of naturally occurring glial-based &#34;living scaffolds&#34; in vivo. As such, these engineered living scaffolds may serve as test-beds to study neurodevelopmental mechanisms in vitro or facilitate neuroregeneration by directing neuronal migration and/or axonal pathfinding following CNS degeneration in vivo.

We showcase the development of self-assembled, three-dimensional bundles of longitudinally aligned astrocytic somata and processes within a novel biomaterial encasement. These engineered &#34;living scaffolds&#34;, exhibiting micron-scale diameter yet extending centimeters in length, may serve as test-beds to study neurodevelopmental mechanisms or facilitate neuroregeneration by directing neuronal migration and/or axonal pathfinding.

Neurotrauma and neurodegenerative disease often result in lasting neurological deficits due to the limited capacity of the central nervous system (CNS) to ...

Melt Electrospinning Writing of Three-dimensional Poly(&#949;-caprolactone) Scaffolds with Controllable Morphologies for Tissue Engineering Applications

This tutorial reflects on the fundamental principles and guidelines for electrospinning writing with polymer melts, an additive manufacturing technology with great potential for biomedical applications. The technique facilitates the direct deposition of biocompatible polymer fibers to fabricate well-ordered scaffolds in the sub-micron to micro scale range. The establishment of a stable, viscoelastic, polymer jet between a spinneret and a collector is achieved using an applied voltage and can be direct-written. A significant benefit of a typical porous scaffold is a high surface-to-volume ratio which provides increased effective adhesion sites for cell attachment and growth. Controlling the printing process by fine-tuning the system parameters enables high reproducibility in the quality of the printed scaffolds. It also provides a flexible manufacturing platform for users to tailor the morphological structures of the scaffolds to their specific requirements. For this purpose, we present a protocol to obtain different fiber diameters using melt electrospinning writing (MEW) with a guided amendment of the parameters, including flow rate, voltage and collection speed. Furthermore, we demonstrate how to optimize the jet, discuss often experienced technical challenges, explain troubleshooting techniques and showcase a wide range of printable scaffold architectures.

This protocol serves as a comprehensive guideline to fabricate scaffolds via electrospinning with polymer melts in a direct writing mode. We systematically outline the process and define the appropriate parameter settings for achieving targeted scaffold architectures.

This tutorial reflects on the fundamental principles and guidelines for electrospinning writing with polymer melts, an additive manufacturing technology ...

Three-dimensional Printing of Thermoplastic Materials to Create Automated Syringe Pumps with Feedback Control for Microfluidic Applications

Microfluidics has become a critical tool in research across the biological, chemical, and physical sciences. One important component of microfluidic experimentation is a stable fluid handling system capable of accurately providing an inlet flow rate or inlet pressure. Here, we have developed a syringe pump system capable of controlling and regulating the inlet fluid pressure delivered to a microfluidic device. This system was designed using low-cost materials and additive manufacturing principles, leveraging three-dimensional (3D) printing of thermoplastic materials and off-the-shelf components whenever possible. This system is composed of three main components: a syringe pump, a pressure transducer, and a programmable microcontroller. Within this paper, we detail a set of protocols for fabricating, assembling, and programming this syringe pump system. Furthermore, we have included representative results that demonstrate high-fidelity, feedback control of inlet pressure using this system. We expect this protocol will allow researchers to fabricate low-cost syringe pump systems, lowering the entry barrier for the use of microfluidics in biomedical, chemical, and materials research.

Here we present a protocol to construct a pressure-controlled syringe pump to be used in microfluidic applications. This syringe pump is made from an&#160;additively manufactured body, off-the-shelf hardware, and open-source electronics. The resulting system is low-cost, straightforward to build, and delivers well-regulated fluid flow to enable rapid microfluidic research.

Microfluidics has become a critical tool in research across the biological, chemical, and physical sciences. One important component of microfluidic ...

Lab-on-a-CD Platform for Generating Multicellular Three-dimensional Spheroids

A three-dimensional spheroid cell culture can obtain more useful results in cell experiments because it can better simulate cell microenvironments of the living body than two-dimensional cell culture. In this study, we fabricated an electrical motor-driven lab-on-a-CD (compact disc) platform, called a centrifugal microfluidic-based spheroid (CMS) culture system, to create three-dimensional (3D) cell spheroids implementing high centrifugal force. This device can vary rotation speeds to generate gravity conditions from 1 x g to 521 x g. The CMS system is 6 cm in diameter, has one hundred 400 &#956;m microwells, and is made by molding with polydimethylsiloxane in a polycarbonate mold premade by a computer numerical control machine. A barrier wall at the channel entrance of the CMS system uses centrifugal force to spread cells evenly inside the chip. At the end of the channel, there is a slide region that allows the cells to enter the microwells. As a demonstration, spheroids were generated by monoculture and coculture of human adipose-derived stem cells and human lung fibroblasts under high gravity conditions using the system. The CMS system used a simple operation scheme to produce coculture spheroids of various structures of concentric, Janus, and sandwich. The CMS system will be useful in cell biology and tissue engineering studies that require spheroids and organoid culture of single or multiple cell types.

We present a motor-powered centrifugal microfluidic device that can cultivate cell spheroids. Using this device, spheroids of single or multiple cell types could be easily cocultured under high gravity conditions.

A three-dimensional spheroid cell culture can obtain more useful results in cell experiments because it can better simulate cell microenvironments of the ...

Cultivating a Three-dimensional Reconstructed Human Epidermis at a Large Scale

A three-dimensional human epidermis model reconstructed from neonatal primary keratinocytes is presented. Herein, a protocol for the cultivation process and the characterization of the model is described. Neonatal primary keratinocytes are grown submerged on permeable polycarbonate inserts and lifted to the air-liquid interface three days after seeding. After fourteen days of stimulation with defined growth factors and ascorbic acid in high calcium culture medium, the model is fully differentiated. Histological analysis revealed a completely stratified epidermis, mimicking the morphology of native human skin. To characterize the model and its barrier functions, protein levels and localization specific for early-stage keratinocyte differentiation (i.e., keratin 10), late-stage differentiation (i.e., involucrin, loricrin, and filaggrin) and tissue adhesion (i.e., desmoglein 1), were assessed by immunofluorescence. The tissue barrier integrity was further evaluated by measuring transepithelial electrical resistance. Reconstructed human epidermis was responsive to proinflammatory stimuli (i.e., lipopolysaccharide and tumor necrosis factor alpha), leading to increased cytokine release (i.e., interleukin 1 alpha and interleukin 8). This protocol represents a straightforward and reproducible in vitro method to cultivate reconstructed human epidermis as a tool to assess environmental effects and a broad range of skin-related studies.

This protocol describes a straightforward method to cultivate three-dimensional reconstituted human epidermis in a reproducible and robust manner. Additionally, it characterizes the structure-function relationship of the epidermal barrier model. The biological responses of the reconstituted human epidermis upon proinflammatory stimuli are also presented.

A three-dimensional human epidermis model reconstructed from neonatal primary keratinocytes is presented. Herein, a protocol for the cultivation process ...