This study was supported by GreenPAC Polymer Application Centre as part of Project 140413: &#34;3D Printing in Production&#34;.&#160;We would like to acknowledge Albert Hartman, Corinne van Noordenne, Rens van Leeuwen, Anniek Bruins, Femke Tamminga, Jur van Dijken and Albert Woortman for facilitating the video shooting.

CAUTION: Please consult all relevant material safety data sheets (MSDS) before use.
1. Preparation of Photocurable Resin
NOTE: Please use personal protective equipment (safety glasses, gloves, lab coat) during the following procedure. See our previous work12 for more details on this section.
<ol>
	<li>Pour 50 g of 1,10-decanediol diacrylate (SA5201) in a 500 mL Erlenmeyer flask.</li>
	<li>Add 1.0 g of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) and 0.40 g of 2,5-bis(5-tert-butyl-benzoxazol-2-yl)thiophene (BBOT) to the flask.</li>
	<li>Equip the flask with a mechanical stirrer and stir the mixture at 200 rpm for 5 min at room temperature in order to dissolve TPO and BBOT in the acrylate monomer.</li>
	<li>Add 100 g of pentaerythritol tetraacrylate and 100 g of multifunctional epoxy acrylate (see Table of Materials) to the mixture.</li>
	<li>Stir the mixture at 200 rpm for 30 min at 50 &#176;C to ensure a homogeneous resin.</li>
	<li>Remove the mechanical stirrer and fit the flask with a stopper. The flask is wrapped in aluminium foil to protect the biobased acrylate photopolymer resin (BAPR) from light. 
	NOTE: The protocol can be paused here.</li>
	<li>Cover the bottom plate of a rheometer with parallel-plate geometry with the photoresin.</li>
	<li>Set the gap between the plates at 1 mm and cover the rheometer with a UV resistant hood.</li>
	<li>Measure the resin viscosity at room temperature at shear rates from 0.1 to 100 s-1; e.g.,0.100, 0.126, 0.158, 0.200, 0.251, 0.316, 0.398, 0.501, 0.631, 0.794, 1.00, 1.26, 1.58, 2.00, 2.51, 3.16, 3.98, 5.01, 6.31, 7.94, 10.0, 12.6, 15.8, 20.0, 25.1, 31.6, 39.8, 50.1, 63.1, 79.4, and 100 s-1.</li>
</ol>
2. Stereolithographic 3D Printing with Biobased Acrylates
NOTE: See our previous work12 for more details on this section.
<ol>
	<li>Turn on the SLA 3D printer and select open mode.</li>
	<li>Start the model preparation software on a computer. Choose the desired print settings: material (Clear), version (V4) and layer thickness (50 &#181;m).</li>
	<li>Open the digital model of the complex-shaped prototype, a standard tessellation language (.stl) file (see Supplemental Coding File) and choose the location and orientation on the build platform.&#160; Upload the print job from the model preparation software to the SLA 3D printer. 
	NOTE: Depending on the architecture of the product, a support structure can be integrated in the 3D model to stabilize the construct during fabrication. In case of the complex-shaped prototype demonstrated here, a support structure is not required if printed normal to the build direction.</li>
	<li>Pour 200 mL of the biobased photoresin into a resin tank. Open the 3D printer and mount the resin tank properly.</li>
	<li>Mount the build platform and close the 3D printer.</li>
	<li>Start the print job.</li>
	<li>Allow the 3D printer to fabricate complex shaped prototypes.&#160; Do not open the printer until the print job is finished. 
	NOTE: Before printing, make sure the 3D printer is leveled. For the demonstrated protocol, the wavelength of the UV laser is 405 nm. The print time of the object is 2.5 h.</li>
</ol>
3. Post-treatment of 3D Printed Objects
NOTE: Please use personal protective equipment (safety glasses, gloves) during the following procedure.
<ol>
	<li>When the print job is finished, open the printer. Remove the build platform, with the produced parts attached, and close the printer.</li>
	<li>Open the washing station, filled with isopropyl alcohol, and insert the build platform. Start the procedure and rinse for 20 min to remove any unreacted resin.</li>
	<li>When the rinsing procedure is finished, remove the build platform from the washing station and detach the prototypes from the build platform.</li>
	<li>Allow the prototypes to air dry for 30 min. In the meantime, preheat the UV oven at 60 &#176;C. 
	NOTE: Preheating will take at least 15 min. The UV wavelength of the oven is 405 nm, identical to the wavelength of the SLA laser.</li>
	<li>Open the UV oven and quickly place the prototypes on the rotating platform. Close the UV oven and cure for 60 min at 60 &#176;C to ensure complete conversion.</li>
	<li>When the post-curing procedure is finished, open the UV oven and take out the prototypes.</li>
</ol>
4. Characterization of Surface Morphology of Complex-shaped Prototypes
NOTE: See our previous work12 for more details on this section.
<ol>
	<li>Cut ca. 1 cm of internal helix from the complex shaped prototype using a razor blade.</li>
	<li>Attach the sample to the sample holder with double sided carbon conductive tape.</li>
	<li>Prior to imaging, coat the sample with 30 nm Pt/Pd (80:20) on a sputtering system.</li>
	<li>Insert the sample into a scanning electron microscope operating at an accelerating voltage of 5 kV. Acquire several images of the sample at 30X and 120X magnification.</li>
</ol>

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<li>Miao, S., Zhu, W., Castro, N. J., Nowicki, M., Zhou, X., Cui, H., Fisher, J. P., Zhang, L. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((4D+printing+smart+biomedical+scaffolds+with+novel+soybean+oil+epoxidized+acrylate%5BTitle%5D)+AND+%22Scientific+Reports%22%5BJournal%5D)">4D printing smart biomedical scaffolds with novel soybean oil epoxidized acrylate.</a> Scientific Reports. 6, 27226(2016).</li>
<li>Voet, V. S. D., Strating, T., Schnelting, G. H. M., Dijkstra, P., Tietema, M., Xu, J., Woortman, A. J. J., Loos, K., Jager, J., Folkersma, R. <a target="_blank" href="https://pubs.acs.org/doi/abs/10.1021/acsomega.7b01648">Biobased acrylate photocurable resin formulation for stereolithographic 3D printing.</a> ACS Omega. 3, 1403-1408 (2018).</li>
<li>Ligon-Auer, S. C., Liska, R., Stampfl, J., Gurr, M., Mülhaupt, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Polymers+for+3D+Printing+and+Customized+Additive+Manufacturing%5BTitle%5D)+AND+%22Chemical+Reviews%22%5BJournal%5D)">Polymers for 3D Printing and Customized Additive Manufacturing.</a> Chemical Reviews. 117, 10212-10290 (2017).</li>
<li>Weng, Z., Zhou, Y., Lin, W., Senthil, T., Wu, L. <a target="_blank" href="https://www-sciencedirect-com.remotexs.ntu.edu.sg/science/article/pii/S1359835X16301725">Structure-property relationship of nano enhanced stereolithography resin for desktop SLA 3D printer.</a> Composites: Part A. 88, 234-242 (2016).</li>
<li>Scalera, F., Esposito Corcione, C., Montagna, F., Sannino, A., Maffezzoli, A. <a target="_blank" href="https://www-sciencedirect-com.remotexs.ntu.edu.sg/science/article/pii/S0272884214010165">Development and characterization of UV curable epoxy/hydroxyapatite suspensions for stereolithography applied to bone tissue engineering.</a> Ceramics International. 40, 15455-15462 (2014).</li>
<li>Lee, H., Fang, N. X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Micro+3D+Printing+using+a+digital+projector+and+its+application+in+the+study+of+soft+materials+mechanics%5BTitle%5D)+AND+%22Journal+of+Visualized+Experiments%22%5BJournal%5D)">Micro 3D Printing using a digital projector and its application in the study of soft materials mechanics.</a> Journal of Visualized Experiments. (69), e4457(2012).</li>
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</ol>

The authors have nothing to disclose.

Additive manufacturing is applied in fabrication of tailor-made prototypes and small series, when the higher production costs per part can compete with conventional processes since there is no need for production of molds and tools. In the last decade, the revenues from services and products related to additive manufacturing have grown exponentially13. The largest fraction of material sales is from photopolymers. The growth attracted attention and initiated the investments of major industries, e.g., aerospace, automotive, medical. Therefore, the field of 3D printing is expected to further expand in the upcoming years.
We have demonstrated an efficient method for the accurate and on-demand fabrication of sustainable products with renewable photopolymer resins on a stereolithographic 3D printer. The use of low-cost biobased acrylates as the main component makes these resins potentially cost-competitive with respect to their commercial counterparts. Moreover, the bioresin formulations were successfully applied in a standardized SLA 3D printing process, thereby using the same procedure and settings as applied for commercial resins. The viscosity of the acrylate resin is an essential parameter in the 3D printing process and is controlled by the monomer to oligomer ratio. Typically, a shear rate of 100 s-1 is achieved during the recoat of liquid resin in the printing process14,15. In this region, all bioresins have a viscosity below 5 Pa&#183;s (Figure 1) and are appropriate for application in stereolithographic printing equipment.
Lithography-based additive manufacturing is recognized for its excellent surface quality and precision in comparison to FDM and selective laser sintering (SLS)16,17. This is clearly demonstrated by the photographic and microscopic images representing the complex shaped prototypes (Figure 4). To the contrary, the mechanical properties of produced parts are limited due to the limited choice of materials suited for the SLA process18,19. Acrylate systems in general show brittleness and poor impact resistance due to high crosslink density and inhomogeneous network architecture. Consequently, the materials 3D printed from the renewable acrylate resins have an ultimate strength of 2-8 MPa (Figure 2), which is lower in comparison to commercial products12. Nevertheless, optimization of the post-treatment, by varying the duration of washing, drying, curing and temperature of curing, leads to a significant improvement in mechanical performance (Figure 3).
Microscopic analysis reveals the high feature resolution and excellent surface finishing of the produced prototypes under high magnification (Figure 4). The serrated vertical edges of the helices arise from the layer-by-layer SLA printing process, in which the top of an exposed layer receives a larger UV dose compared to the back of a layer8. The cracks observed on the surface of the fabricated prototypes can result from shrinkage forces developed in the UV curing process. Shrinkage in acrylate systems is found to be inversely related to the resin viscosity20,21. Hence, the extent of cracking (Figure 4) is reduced when applying more viscous photoresins (Figure 1).

Rapid prototyping enables on-demand production and design freedom and allows the efficient manufacturing of 3D constructs in a layer-by-layer manner1. As a result, 3D printing as a fabrication technique has developed rapidly in recent years2. Various technologies are available, all relying on the translation of virtual models into physical objects, and applying processes such as extrusion, direct energy deposition, powder solidification, sheet lamination and photopolymerization. The latter involves stepwise UV curing of liquid photopolymer resins. In 1986, Hull and co-workers developed the stereolithography apparatus (SLA), a UV laser-based 3D printer. More recently, a similar process called digital light processing (DLP) has become available, in which photopolymerization is initiated by a light projector. Together, DLP and SLA are referred to as stereolithography 3D printing3.
SLA is applied in high-resolution prototyping and fabrication of biomedical devices4,5. This technology is superior to the widely used fused deposition modeling (FDM) in terms of accuracy, surface finishing and resolution6. Depending on the architecture of the product, a support structure is integrated in the 3D model to stabilize the construct during fabrication. Furthermore, a post-printing treatment of manufactured parts is required7,8. Typically, printed objects are washed in an alcohol bath to dissolve unreacted resin, and subsequent curing in an UV oven is performed to guarantee full conversion of the polymerization9.
In general, resins for lithography-based additive manufacturing rely on photocurable systems containing multifunctional acrylates or epoxides10. Current photopolymer resins on the commercial market are fossil-based and expensive, while the availability of low-cost renewable resins is needed to facilitate waste-free and local manufacturing of sustainable 3D products for a biobased economy1,6. Recently, photopolymer resins based on renewable acrylates were developed and successfully applied in stereolithography 3D printing11,12. In this detailed protocol, we demonstrate the rapid prototyping with biobased resins on a commercial stereolithography apparatus. Special attention is paid to critical steps in the procedure, i.e., resin formulation and post-printing treatments, to help new practitioners in the field of additive manufacturing.

<table><tbody><tr><td>Isobornyl acrylate&amp;nbsp;</td><td>Sartomer</td><td>SA5102</td><td>Acrylate monomer</td></tr><tr><td>1,10-decanediol diacrylate</td><td>Sartomer</td><td>SA5201</td><td>Acrylate monomer</td></tr><tr><td>Pentaerythritol tetraacrylate</td><td>Sartomer</td><td>SA5400</td><td>Acrylate monomer</td></tr><tr><td>Multifunctional epoxy acrylate</td><td>Sartomer</td><td>SA7101</td><td>Acrylate oligomer</td></tr><tr><td>Diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO), 97%</td><td>Sigma Aldrich</td><td>415952</td><td>Photoinitiator</td></tr><tr><td>2,5-bis(5-&lt;em&gt;tert&lt;/em&gt;-butyl-benzoxazol-2-yl)thiophene (BBOT), 99%</td><td>Sigma Aldrich</td><td>223999</td><td>Optical absorber</td></tr><tr><td>Isopropyl alcohol (IPA), 99%</td><td>Bleko</td><td>1010500</td><td>For alcohol bath (applied in Form Wash)</td></tr><tr><td>Paar Physica MCR300&amp;nbsp;</td><td>Anton Paar</td><td>-</td><td>Rheometer with parallel plate geometry</td></tr><tr><td>Form 2 Printer</td><td>Formlabs</td><td>-</td><td>Desktop SLA 3D printer</td></tr><tr><td>Form Wash&amp;nbsp;</td><td>Formlabs</td><td>-</td><td>Washing station</td></tr><tr><td>Form Cure</td><td>Formlabs</td><td>-</td><td>UV oven</td></tr><tr><td>Instron 4301 1KN Series IX</td><td>Instron</td><td>-</td><td>Universal testing machine</td></tr><tr><td>Philips XL30 ESEM-FEG&amp;nbsp;</td><td>Philips</td><td>-</td><td>Scanning electron microscope</td></tr></tbody></table>

stereolithographic 3d printing with renewable acrylates

The accessibility of cost-competitive renewable materials and their application in additive manufacturing is essential for an efficient biobased economy. We demonstrate the rapid prototyping of sustainable resins using a stereolithographic 3D printer. Resin formulation takes place by straightforward mixing of biobased acrylate monomers and oligomers with a photoinitiatior and optical absorber. Resin viscosity is controlled by the monomer to oligomer ratio and is determined as a function of shear rate by a rheometer with parallel plate geometry. A stereolithographic apparatus charged with the biobased resins is employed to produce complex shaped prototypes with high accuracy. The products require a post-treatment, including alcohol rinsing and UV irradiation, to ensure complete curing. The high feature resolution and excellent surface finishing of the prototypes is revealed by scanning electron microscopy.

Four representative resin compositions are displayed in Table 1, along with their average biobased carbon content (BC) derived from the individual BC of the components. The resin viscosity (Figure 1) is influenced by the ratio of acrylate monomers and oligomers and typically demonstrates Newtonian behavior. The mechanical properties of parts manufactured from various resins were determined by stress-strain analysis. Figure 2 displays the representative outcome on a universal testing machine in terms of E-modulus and tensile strength. The effect of the post-printing treatment on the product performance is depicted in Figure 3. The smooth surface and high feature resolution of complex shaped prototypes is revealed by the electron microscope (Figure 4). The extent of surface cracking is related to the initial resin viscosity.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td rowspan="2">Resin</td>
			<td>TPO</td>
			<td>BBOT</td>
			<td>SA5102</td>
			<td>SA5201</td>
			<td>SA5400</td>
			<td>SA7101</td>
			<td>BC</td>
		</tr>
		<tr>
			<td>% w/w</td>
			<td>% w/w</td>
			<td>% w/w</td>
			<td>% w/w</td>
			<td>% w/w</td>
			<td>% w/w</td>
			<td>%</td>
		</tr>
		<tr>
			<td>BAPR-&#945;</td>
			<td>0.40</td>
			<td>0.16</td>
			<td>20</td>
			<td>40</td>
			<td></td>
			<td>40</td>
			<td>67</td>
		</tr>
		<tr>
			<td>BAPR-&#946;</td>
			<td>0.40</td>
			<td>0.16</td>
			<td></td>
			<td>60</td>
			<td></td>
			<td>40</td>
			<td>64</td>
		</tr>
		<tr>
			<td>BAPR-&#947;</td>
			<td>0.40</td>
			<td>0.16</td>
			<td></td>
			<td>20</td>
			<td>40</td>
			<td>40</td>
			<td>44</td>
		</tr>
		<tr>
			<td>BAPR-&#948;</td>
			<td>0.40</td>
			<td>0.16</td>
			<td></td>
			<td></td>
			<td>60</td>
			<td>40</td>
			<td>34</td>
		</tr>
	</tbody>
</table>
Table 1: Renewable acrylate resin formulation. Characteristics of representative bioacrylate resins, depicting resin composition and biobased carbon content.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/58177/58177fig1.jpg" /> 
Figure 1: Rheological behavior of renewable acrylate resins prior to 3D printing. Viscosity as a function of shear rate for uncured BAPR samples. Figure is adapted with permission (copyright 2018 American Chemical Society).12 <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58177/58177fig1large.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/58177/58177fig2.jpg" /> 
Figure 2: Mechanical performance of 3D products fabricated from various bioresins by a stereolithography apparatus. Tensile strength (red) and Young&#39;s modulus (cyan) of produced parts from cured BAPRs. The tensile bars (ISO 527-2-1BA) were printed normal to the build direction. Error bars indicate the standard deviation. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58177/58177fig2large.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/58177/58177fig3.jpg" /> 
Figure 3: Influence of post-printing treatment on mechanical performance of 3D products. Tensile strength of produced parts post-treated under various conditions. The tensile bars (ISO 527-2-1BA) were printed normal to the build direction. Error bars indicate the standard deviation. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58177/58177fig3large.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/58177/58177fig4.jpg" /> 
Figure 4: Visual and microscopic representation of complex-shaped prototypes fabricated from various bioresins by a stereolithography apparatus. (A) Photo of rook tower prototype printed with BAPR-&#945; (top) and SEM images of corresponding internal helix (bottom). (B) Photo of rook tower prototype printed with BAPR-&#946; (top) and SEM images of corresponding internal helix (bottom). (C) Photo of rook tower prototype printed with BAPR-&#947; (top) and SEM images of corresponding internal helix (bottom). (D) Photo of rook tower prototype printed with BAPR-&#948; (top) and SEM images of corresponding internal helix (bottom). Figure is adapted with permission (copyright 2018 American Chemical Society)12. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/58177/58177fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Stereolithographic 3D Printing with Renewable Acrylates at JoVE.com

Stereolithographic 3D Printing with Renewable Acrylates

A protocol for additive manufacturing with renewable photopolymer resins on a stereolithography apparatus is presented.

The accessibility of cost-competitive renewable materials and their application in additive manufacturing is essential for an efficient biobased economy. ...

stereolithographic-3d-printing-with-renewable-acrylates

Nanyang Technological University

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JoVE Journal

Chemistry

9.4K Views.  NHL Stenden University of Applied Sciences. Een protocol voor additieve productie met hernieuwbare fotopolymeer harsen op een stereolithography-apparaat wordt gepresenteerd.

Video: Stereolithographic 3D Printing with Renewable Acrylates

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

3D Printing of Biomolecular Models for Research and Pedagogy

The construction of physical three-dimensional (3D) models of biomolecules can uniquely contribute to the study of the structure-function relationship. 3D structures are most often perceived using the two-dimensional and exclusively visual medium of the computer screen. Converting digital 3D molecular data into real objects enables information to be perceived through an expanded range of human senses, including direct stereoscopic vision, touch, and interaction. Such tangible models facilitate new insights, enable hypothesis testing, and serve as psychological or sensory anchors for conceptual information about the functions of biomolecules. Recent advances in consumer 3D printing technology enable, for the first time, the cost-effective fabrication of high-quality and scientifically accurate models of biomolecules in a variety of molecular representations. However, the optimization of the virtual model and its printing parameters is difficult and time consuming without detailed guidance. Here, we provide a guide on the digital design and physical fabrication of biomolecule models for research and pedagogy using open source or low-cost software and low-cost 3D printers that use fused filament fabrication technology.

Physical models of biomolecules can facilitate an understanding of their structure-function for the researcher, aid in communication between researchers, and serve as an educational tool in pedagogical endeavors. Here, we provide detailed guidance for the 3D printing of accurate models of biomolecules using fused filament fabrication desktop 3D printers.

The construction of physical three-dimensional (3D) models of biomolecules can uniquely contribute to the study of the structure-function relationship. 3D ...

Engineering

Printing Thermoresponsive Reverse Molds for the Creation of Patterned Two-component Hydrogels for 3D Cell Culture

Bioprinting is an emerging technology that has its origins in the rapid prototyping industry. The different printing processes can be divided into contact bioprinting1-4 (extrusion, dip pen and soft lithography), contactless bioprinting5-7 (laser forward transfer, ink-jet deposition) and laser based techniques such as two photon photopolymerization8. It can be used for many applications such as tissue engineering9-13, biosensor microfabrication14-16 and as a tool to answer basic biological questions such as influences of co-culturing of different cell types17. Unlike common photolithographic or soft-lithographic methods, extrusion bioprinting has the advantage that it does not require a separate mask or stamp. Using CAD software, the design of the structure can quickly be changed and adjusted according to the requirements of the operator. This makes bioprinting more flexible than lithography-based approaches.
Here we demonstrate the printing of a sacrificial mold to create a multi-material 3D structure using an array of pillars within a hydrogel as an example. These pillars could represent hollow structures for a vascular network or the tubes within a nerve guide conduit. The material chosen for the sacrificial mold was poloxamer 407, a thermoresponsive polymer with excellent printing properties which is liquid at 4 &deg;C and a solid above its gelation temperature ~20 &deg;C for 24.5% w/v solutions18. This property allows the poloxamer-based sacrificial mold to be eluted on demand and has advantages over the slow dissolution of a solid material especially for narrow geometries. Poloxamer was printed on microscope glass slides to create the sacrificial mold. Agarose was pipetted into the mold and cooled until gelation. After elution of the poloxamer in ice cold water, the voids in the agarose mold were filled with alginate methacrylate spiked with FITC labeled fibrinogen. The filled voids were then cross-linked with UV and the construct was imaged with an epi-fluorescence microscope.

A bioprinter was used to create patterned hydrogels based on a sacrificial mold. The poloxamer mold was backfilled with a second hydrogel and then eluted, leaving voids which were filled with a third hydrogel. This method uses fast elution and good printability of poloxamer to generate complex architectures from biopolymers.

Bioprinting is an emerging technology that has its origins in the rapid prototyping industry. The different printing processes can be divided into contact ...

Immunology and Infection

Procedure for the Transfer of Polymer Films Onto Porous Substrates with Minimized Defects

The fabrication of devices containing thin film composite membranes necessitates the transfer of these films onto the surfaces of arbitrary support substrates. Accomplishing this transfer in a highly controlled, mechanized, and reproducible manner can eliminate the creation of macroscale defect structures (e.g., tears, cracks, and wrinkles) within the thin film that compromise device performance and the usable area per sample. Here, we describe a general protocol for the highly controlled and mechanized transfer of a polymeric thin film onto an arbitrary porous support substrate for eventual use as a water filtration membrane device. Specifically, we fabricate a block copolymer (BCP) thin film on top of a sacrificial, water-soluble poly(acrylic acid) (PAA) layer and silicon wafer substrate. We then utilize a custom-designed, 3D-printed transfer tool and drain chamber system to deposit, lift-off, and transfer the BCP thin film onto the center of a porous anodized aluminum oxide (AAO) support disc. The transferred BCP thin film is shown to be consistently placed onto the center of the support surface due to the guidance of the meniscus formed between the water and the 3D-printed plastic drain chamber. We also compare our mechanized transfer-processed thin films to those that have been transferred by hand with the use of tweezers. Optical inspection and image analysis of the transferred thin films from the mechanized process confirm that little-to-no macroscale inhomogeneities or plastic deformations are produced, as compared to the multitude of tears and wrinkles produced from manual transfer by hand. Our results suggest that the proposed strategy for thin film transfer can reduce defects when compared to other methods across many systems and applications.

We present a procedure for highly controlled and wrinkle-free transfer of block copolymer thin films onto porous support substrates using a 3D-printed drain chamber. The drain chamber design is of general relevance to all procedures involving transfer of macromolecular films onto porous substrates, which is normally done by hand in an irreproducible fashion.

The fabrication of devices containing thin film composite membranes necessitates the transfer of these films onto the surfaces of arbitrary support ...

Three-dimensional Biomimetic Technology: Novel Biorubber Creates Defined Micro- and Macro-scale Architectures in Collagen Hydrogels

Tissue scaffolds play a crucial role in the tissue regeneration process. The ideal scaffold must fulfill several requirements such as having proper composition, targeted modulus, and well-defined architectural features. Biomaterials that recapitulate the intrinsic architecture of in vivo tissue are vital for studying diseases as well as to facilitate the regeneration of lost and malformed soft tissue. A novel biofabrication technique was developed which combines state of the art imaging, three-dimensional (3D) printing, and selective enzymatic activity to create a new generation of biomaterials for research and clinical application. The developed material, Bovine Serum Albumin rubber, is reaction injected into a mold that upholds specific geometrical features. This sacrificial material allows the adequate transfer of architectural features to a natural scaffold material. The prototype consists of a 3D collagen scaffold with 4 and 3 mm channels that represent a branched architecture. This paper emphasizes the use of this biofabrication technique for the generation of natural constructs. This protocol utilizes a computer-aided software (CAD) to manufacture a solid mold which will be reaction injected with BSA rubber followed by the enzymatic digestion of the rubber, leaving its architectural features within the scaffold material.

An innovative biofabrication technique was developed to engineer three-dimensional constructs that resemble the architectural features, components, and mechanical properties of in vivo tissue. This technique features a newly developed sacrificial material, BSA rubber, which transfers detailed spatial features, reproducing the in vivo architectures of a wide variety of tissues.

Tissue scaffolds play a crucial role in the tissue regeneration process. The ideal scaffold must fulfill several requirements such as having proper ...

Multimodal 3D Printing of Phantoms to Simulate Biological Tissue

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

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

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

Interactive Molecular Model Assembly with 3D Printing

With the growth in accessibility of 3D printing, there has been a growing application of and interest in additive manufacturing processes in chemical laboratories and chemical education. Building on the long and successful history of physical modeling of molecular systems, we present select models along with a protocol to facilitate 3D printing of molecular structures that are able to do more than represent shape and connectivity. Models assembled as described incorporate dynamic aspects and degrees of freedom into saturated hydrocarbon structures. As a representative example, cyclohexane was assembled from parts printed and finished using different thermoplastics, and the resulting models retain their functionality at a variety of scales. The resulting structures show configurational space accessibility consistent with calculations and literature, and versions of these structures can be used as aids to illustrate concepts that are difficult to convey in other ways. This exercise enables us to evaluate successful printing protocols, make practical recommendations for assembly, and outline design principles for physical modeling of molecular systems. The provided structures, procedures, and results provide a foundation for individual manufacture and exploration of molecular structure and dynamics with 3D printing.

Physical modeling of microscopic systems helps obtain insights that are difficult to gain by other means. To facilitate the construction of physical molecular models, we demonstrate how 3D printing can be used to assemble functional macroscopic models that capture qualities of molecular systems in a tactile way.

With the growth in accessibility of 3D printing, there has been a growing application of and interest in additive manufacturing processes in chemical ...

3D Printing and In Situ Surface Modification via Type I Photoinitiated Reversible Addition-Fragmentation Chain Transfer Polymerization

3D printing provides facile access to geometrically complex materials. However, these materials have intrinsically linked bulk and interfacial properties dependent on the chemical composition of the resin. In the current work, 3D printed materials are post-functionalized using the 3D printer hardware via a secondary surface-initiated polymerization process, thus providing independent control over the bulk and interfacial material properties. This process begins with preparing liquid resins, which contain a monofunctional monomer, a crosslinking multifunctional monomer, a photochemically labile species that enables initiation of polymerization, and critically, a thiocarbonylthio compound which facilitates reversible addition-fragmentation chain transfer (RAFT) polymerization. The thiocarbonylthio compound, known commonly as a RAFT agent, mediates the chain growth polymerization process and provides polymeric materials with more homogeneous network structures. The liquid resin is cured in a layer-by-layer fashion using a commercially available digital light processing 3D printer to give three-dimensional materials having spatially controlled geometries. The initial resin is removed and replaced with a new mixture containing functional monomers and photoinitiating species. The 3D printed material is then exposed to light from the 3D printer in the presence of the new functional monomer mixture. This allows photoinduced surface-initiated polymerization to occur from the latent RAFT agent groups on the surface of the 3D printed material. Given the chemical flexibility of both resins, this process allows a wide range of 3D printed materials to be produced with tailorable bulk and interfacial properties.

3D Printing and In Situ Surface Modification via Type I Photoinitiated Reversible Addition-Fragmentation Chain Transfer Polymerization

The present protocol describes the digital light processing-based 3D printing of polymeric materials using type I photoinitiated reversible addition-fragmentation chain transfer polymerization and the subsequent in situ material post-functionalization via surface-mediated polymerization. Photoinduced 3D printing provides materials with independently tailored and spatially controlled bulk and interfacial properties.

3D printing provides facile access to geometrically complex materials. However, these materials have intrinsically linked bulk and interfacial properties ...

Novel Process for 3D Printing Decellularized Matrices

3D bioprinting aims to create custom scaffolds that are biologically active and accommodate the desired size and geometry. A thermoplastic backbone can provide mechanical stability similar to native tissue while biologic agents offer compositional cues to progenitor cells, leading to their migration, proliferation, and differentiation to reconstitute the original tissues/organs1,2. Unfortunately, many 3D printing compatible, bioresorbable polymers (such as polylactic acid, PLA) are printed at temperatures of 210 &#176;C or higher - temperatures that are detrimental to biologics. On the other hand, polycaprolactone (PCL), a different type of polyester, is a bioresorbable, 3D printable material that has a gentler printing temperature of 65 &#176;C. Therefore, it was hypothesized that decellularized extracellular matrix (DM) contained within a thermally protective PLA barrier could be printed within PCL filament and remain in its functional conformation. In this work, osteochondral repair was the application for which the hypothesis was tested. As such, porcine cartilage was decellularized and encapsulated in polylactic acid (PLA) microspheres which were then extruded with polycaprolactone (PCL) into filament to produce 3D constructs via fused deposition modeling. The constructs with or without the microspheres (PLA-DM/PCL and PCL(-), respectively) were evaluated for differences in surface features.

This protocol describes the production of polycaprolactone (PCL) filament with embedded polylactic acid (PLA) microspheres which contain decellularized matrices (DM) for 3D printing of structural tissue engineering constructs.

3D bioprinting aims to create custom scaffolds that are biologically active and accommodate the desired size and geometry. A thermoplastic backbone can ...

Phototunable Bioprinted Hydrogels to Probe Cellular Responses to ECM Stiffening

3D Bioprinting Phototunable Hydrogels to Study Fibroblast Activation

Phototunable hydrogels can transform spatially and temporally in response to light exposure. Incorporating these types of biomaterials in cell-culture platforms and dynamically triggering changes, such as increasing microenvironmental stiffness, enables researchers to model changes in the extracellular matrix (ECM) that occur during fibrotic disease progression. Herein, a method is presented for 3D bioprinting a phototunable hydrogel biomaterial capable of two sequential polymerization reactions within a gelatin support bath. The technique of Freeform Reversible Embedding of Suspended Hydrogels (FRESH) bioprinting was adapted by adjusting the pH of the support bath to facilitate a Michael addition reaction. First, the bioink containing poly(ethylene glycol)-alpha methacrylate (PEG&#945;MA) was reacted off-stoichiometry with a cell-degradable crosslinker to form soft hydrogels. These soft hydrogels were later exposed to photoinitator and light to induce the homopolymerization of unreacted groups and stiffen the hydrogel. This protocol covers hydrogel synthesis, 3D bioprinting, photostiffening, and endpoint characterizations to assess fibroblast activation within 3D structures. The method presented here enables researchers to 3D bioprint a variety of materials that undergo pH-catalyzed polymerization reactions and could be implemented to engineer various models of tissue homeostasis, disease, and repair.

Author Spotlight: Understanding Chronic Lung Diseases Using 3D Printed Phototunable Hydrogels 

This article describes how to 3D bioprint phototunable hydrogels to study extracellular matrix stiffening and fibroblast activation.

Phototunable hydrogels can transform spatially and temporally in response to light exposure. Incorporating these types of biomaterials in cell-culture ...

Stereolithographic 3D Printing with Renewable Acrylates

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