Name: microgel-extracellular matrix composite support for the embedded 3d printing of human neural constructs
Uploaded: 2023-05-05T15:00:00
Description: Watch this Scientific Journal Video about Microgel-Extracellular Matrix Composite Support for the Embedded 3D Printing of Human Neural Constructs at JoVE.com

&#65279;The research was primarily funded by the BrainMatTrain European Union Horizon 2020 Programme (No. H2020-MSCA-ITN-2015) under the Marie Sk&#322;odowska- Curie Initial Training Network and Grant Agreement No. 676408. C.R. and J.U.L. would like to gratefully acknowledge the Lundbeck Foundation (R250-2017-1425) and the Independent Research Fund Denmark (8048-00050) for their support.&#160;We gratefully acknowledge funding for the HORIZON-EIC-2021-PATHFINDEROPEN-01 Project 101047177 OpenMIND.

1. Preparation of the buffers and reagents
<ol>
	<li>Prepare cell growth medium by adding the following supplements to DMEM/F12 with L-alanyl-L-glutamine dipeptide: 30 mM glucose, 5 &#181;M HEPES, 0.5% w/v lipid-rich bovine serum albumine, 40 &#181;M L-alanine, 40 &#181;M L-asparagine monohydrate, 40 &#181;M L-aspartic acid, 40 &#181;M L-glutamic acid, 40 &#181;M L-proline, 1% N2 supplement, 1% penicillin-streptomycin, and 20 ng/L each of epidermal growth factor (EGF) and fibroblast growth factor (FGF)...

<ol>
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The SHAPE composite material approach provides a versatile route for the formulation of annealable and biofunctional support baths for the embedded 3D printing of cellular inks. While this protocol provides an example of the 3D printing of neural constructs, the SHAPE toolbox could easily be adapted to biofabrication with other cell sources for the precise engineering of a range of target tissue types. The printing approach would also allow for the precise patterning of multiple cell types to study their interaction or t...

The precise and programmable 3D printing of cell-laden hydrogel constructs that mimic soft tissues in vitro presents a major challenge. For instance, attempts based on the direct extrusion of soft hydrogels are inherently problematic, as the poor mechanical properties required to recapitulate the in vivo microenvironment lead to a lack of structural integrity, deformations of the predefined features, or the complete collapse of the fabricated structures. A conventional workaround for this issue is to print a supporting scaffold from a stiffer biocompatible material that allows the final construct to maintain its shape. However, this approach greatly limits the design possibilities and requires careful rheological fine-tuning of the adjacent inks.
To overcome the limitations of the traditional layer-by-layer extrusion-based 3D printing, embedded 3D printing has emerged in recent years as a powerful alternative for soft material and tissue fabrication1,2,3,4,5,6. Instead of extruding the ink in ambient air on top of a surface, the ink is directly deposited through a syringe needle inside a support bath that is solid-like at rest but reversibly fluidizes around the moving needle tip to allow the precise deposition of soft cell-laden material. The deposited material is kept in place as the support resolidifies in the wake of the needle. As such, embedded 3D printing allows for the high-resolution freeform fabrication of intricate structures from soft biomaterials with expanded design possibilities7,8.
Granular gels have been extensively explored as support bath materials for embedded 3D printing, since they can be formulated to exhibit smooth, localized, and reversible solid-to-liquid transitions at low yield stresses9,10,11. While they show excellent rheological properties for high-resolution printing, granular gels have been restricted to a handful of biomaterials12. The lack of diversity in granular gel formulations, which is particularly evident if one considers the wide range of biomaterials available for bulk hydrogel formulations, is caused by the need for the cost-effective generation of a large number of microgels using simple chemistries. Due to the limited biomaterial landscape of granular gel supports, the tuning of the extracellular microenvironment provided by the printing support presents a challenge in the field.
Recently, a modular approach has been developed for the generation of embedded 3D printing supports, termed self-healing annealable particle-extracellular matrix (SHAPE) composites13. This approach combines the distinct rheological properties of granular gels with the biofunctional versatility of bulk hydrogel formulations. The presented SHAPE composite support consists of packed alginate microparticles (granular phase, ~70% volume fraction) with an increased interstitial space filled with a viscous collagen-based ECM pregel solution (continuous phase, ~30% volume fraction). It has further been shown that the SHAPE support facilitates the high-resolution deposition of human neural stem cells (hNSCs) that, after the annealing of the support bath, can be differentiated into neurons and maintained for weeks to reach functional maturation. Embedded 3D printing inside the SHAPE support bath overcomes some of the major limitations related to conventional techniques for neural tissue biofabrication while providing a versatile platform.
This work details the steps for the embedded 3D printing of hNSCs inside the SHAPE support and their subsequent differentiation into functional neurons (Figure 1). First, alginate microparticles are generated via shearing during internal gelation. This approach allows the easy generation of large volumes of microparticles without the need for specialized equipment and cytotoxic reagents. Furthermore, alginate is a widely available and economical material source for the formation of biocompatible hydrogel substrates for a diverse range of cell types. The generated alginate microparticles are combined with a collagen solution to form the SHAPE composite support material. Then, the hNSCs are harvested and loaded into a syringe as a cellular bioink for 3D printing. A 3D bioprinter is used for the extrusion-based embedded printing of hNSCs inside the SHAPE composite. The 3D-printed cells are differentiated into neurons to give rise to spatially defined and functional human neural constructs. Finally, the protocol describes how the generated tissue constructs can be characterized using live-cell imaging and immunocytochemistry. Additionally, tips for optimization and troubleshooting are provided. Notably, both the components of the granular and continuous phases could be exchanged with other hydrogel formulations to accommodate different biofunctional moieties, mechanical properties, and crosslinking mechanisms, as required by other cell and tissue types beyond neural applications.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1 mL Gastight Syringe 1001 TLL</td>
			<td>Hamilton</td>
			<td>81320</td>
			<td></td>
		</tr>
		<tr>
			<td>3DDiscovery 3D bioprinter</td>
			<td>RegenHU</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Acetic acid</td>
			<td>Sigma-Aldrich</td>
			<td>A6283</td>
			<td></td>
		</tr>
		<tr>
			<td>AlbuMAX</td>
			<td>ThermoFisher</td>
			<td>11020021</td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa Fluor 488 secondary antibody</td>
			<td>ThermoFisher</td>
			<td>A-11001</td>
			<td>Goat anti-Mouse</td>
		</tr>
		<tr>
			<td>Blunt Needle, Sterican (21 G)</td>
			<td>Braun</td>
			<td>9180109</td>
			<td></td>
		</tr>
		<tr>
			<td>Blunt Needle (27 G)</td>
			<td>Cellink</td>
			<td>NZ5270505001</td>
			<td></td>
		</tr>
		<tr>
			<td>BioCAD software</td>
			<td>SolidWorks</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Calcein AM</td>
			<td>ThermoFisher</td>
			<td>65-0853-39</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium carbonate</td>
			<td>Sigma-Aldrich</td>
			<td>C5929</td>
			<td></td>
		</tr>
		<tr>
			<td>Dibutyryl-cAMP sodium salt</td>
			<td>Sigma-Aldrich</td>
			<td>D0627</td>
			<td></td>
		</tr>
		<tr>
			<td>Cultrex Rat Collagen I (5 mg/mL)</td>
			<td>R&#38;D Systems</td>
			<td>3440-100-01</td>
			<td></td>
		</tr>
		<tr>
			<td>DAPI</td>
			<td>ThermoFisher</td>
			<td>62248</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM/F-12, GlutaMAX</td>
			<td>ThermoFisher</td>
			<td>10565018</td>
			<td></td>
		</tr>
		<tr>
			<td>Donkey serum</td>
			<td>Sigma-Aldrich</td>
			<td>D9663</td>
			<td></td>
		</tr>
		<tr>
			<td>DPBS</td>
			<td>ThermoFisher</td>
			<td>14190094</td>
			<td></td>
		</tr>
		<tr>
			<td>EGF</td>
			<td>R&#38;D Systems</td>
			<td>236-EG</td>
			<td></td>
		</tr>
		<tr>
			<td>FGF</td>
			<td>R&#38;D Systems</td>
			<td>3718-FB</td>
			<td></td>
		</tr>
		<tr>
			<td>Formaldehyde solution 4%, buffered, pH 6.9</td>
			<td>Sigma-Aldrich</td>
			<td>100496</td>
			<td></td>
		</tr>
		<tr>
			<td>GDNF</td>
			<td>R&#38;D Systems</td>
			<td>212-GD</td>
			<td></td>
		</tr>
		<tr>
			<td>Geltrex</td>
			<td>ThermoFisher</td>
			<td>A1569601</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td>Sigma-Aldrich</td>
			<td>G7021</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES Buffer (1 M)</td>
			<td>ThermoFisher</td>
			<td>15630080</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Alanine</td>
			<td>Sigma-Aldrich</td>
			<td>5129</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Asparagine monohydrate</td>
			<td>Sigma-Aldrich</td>
			<td>A4284</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Aspartic acid</td>
			<td>Sigma-Aldrich</td>
			<td>A9256</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Glutamic acid</td>
			<td>Sigma-Aldrich</td>
			<td>G1251</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Proline</td>
			<td>Sigma-Aldrich</td>
			<td>P0380</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnetic stirrer RET basic</td>
			<td>IKA</td>
			<td>3622000</td>
			<td></td>
		</tr>
		<tr>
			<td>N-2 Supplement</td>
			<td>ThermoFisher</td>
			<td>17502048</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin</td>
			<td>ThermoFisher</td>
			<td>15140122</td>
			<td></td>
		</tr>
		<tr>
			<td>S25N-10G dispersing tool</td>
			<td>IKA</td>
			<td>4447100</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Alginate (80-120 cP)</td>
			<td>FUJIFILM Wako</td>
			<td>194-13321</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium azide</td>
			<td>Sigma-Aldrich</td>
			<td>S2002</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium bicarbonate</td>
			<td>Sigma-Aldrich</td>
			<td>S5761</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium hydroxide</td>
			<td>Sigma-Aldrich</td>
			<td>S5881</td>
			<td></td>
		</tr>
		<tr>
			<td>T18 Digital ULTRA-TURAX homogenizer</td>
			<td>IKA</td>
			<td>3720000</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Sigma-Aldrich</td>
			<td>X100</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin/EDTA Solution</td>
			<td>ThermoFisher</td>
			<td>R001100</td>
			<td></td>
		</tr>
		<tr>
			<td>TUBB3 antibody</td>
			<td>BioLegend</td>
			<td>801213</td>
			<td>Mouse</td>
		</tr>
		<tr>
			<td>Xanthan gum&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>G1253</td>
			<td></td>
		</tr>
	</tbody>
</table>

microgel-extracellular matrix composite support for the embedded 3d printing of human neural constructs

The embedded 3D printing of cells inside a granular support medium has emerged in the past decade as a powerful approach for the freeform biofabrication of soft tissue constructs. However, granular gel formulations have been restricted to a limited number of biomaterials that allow for the cost-effective generation of large amounts of hydrogel microparticles. Therefore, granular gel support media have generally lacked the cell-adhesive and cell-instructive functions found in the native extracellular matrix (ECM).
To address this, a methodology has been developed for the generation of self-healing annealable particle-extracellular matrix (SHAPE) composites. SHAPE composites consist of a granular phase (microgels) and a continuous phase (viscous ECM solution) that, together, allow for both programmable high-fidelity printing and an adjustable biofunctional extracellular environment. This work describes how the developed methodology can be utilized for the precise biofabrication of human neural constructs.
First, alginate microparticles, which serve as the granular component in the SHAPE composites, are fabricated and combined with a collagen-based continuous component. Then, human neural stem cells are printed inside the support material, followed by the annealing of the support. The printed constructs can be maintained for weeks to allow the differentiation of the printed cells into neurons. Simultaneously, the collagen continuous phase allows for axonal outgrowth and the interconnection of regions. Finally, this works provides information on how to perform live-cell fluorescence imaging and immunocytochemistry to characterize the 3D-printed human neural constructs.

Alginate microgel preparation via shear thinning during internal gelation followed by mechanical fragmentation yields alginate microgels that are polydispersed in size and flake-like in shape as seen in Figure 2G. The size of these irregular particles ranges from less than 1 &#181;m to approximately 40 &#181;m in diameter. When tightly packed, the microparticles form a transparent bulk material that is only slightly more opaque than the corresponding cell culture medium (<strong cla...

Watch this Scientific Journal Video about Microgel-Extracellular Matrix Composite Support for the Embedded 3D Printing of Human Neural Constructs at JoVE.com

Microgel-Extracellular Matrix Composite Support for the Embedded 3D Printing of Human Neural Constructs

This work describes a protocol for the freeform embedded 3D printing of neural stem cells inside self-healing annealable particle-extracellular matrix composites. The protocol enables the programmable patterning of interconnected human neural tissue constructs with high fidelity.

The embedded 3D printing of cells inside a granular support medium has emerged in the past decade as a powerful approach for the freeform biofabrication ...

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