Name: microfluidic bioprinting for engineering vascularized tissues and organoids
Uploaded: 2017-08-11T13:00:00
Description: Watch this Scientific Journal Video about Microfluidic Bioprinting for Engineering Vascularized Tissues and Organoids at JoVE.com

The authors acknowledge&#160;the National Cancer Institute of the National Institutes of Health Pathway to Independence Award (K99CA201603).

The neonatal rat cardiomyocytes used in this protocol were isolated from 2-day-old Sprague-Dawley rats following a well-established procedure56 approved by the Institutional Animal Care and Use Committee at the Brigham and Women&#39;s Hospital.
1. Instrumentation of the Bioprinter
<ol>
	<li>Insert a smaller blunt needle (e.g., 27G, 1 inch) as the core into the center of a larger blunt needle (e.g., 18G, &#189; inch) as the sheath to construct the dua...

Construction of the co-axial printhead represents a critical step towards successful microfluidic bioprinting to allow for simultaneous delivery of both the bioink from the core and the crosslinking agent from the sheath. While in this protocol an example printhead was created using a 27G needle as the core and an 18G needle as the shell, it may be readily extended to a variety of combinations using different sizes of needles. However, the alteration in the needle sizes, which results in the change in the amount of flow ...

Tissue engineering targets to generate functional tissue substitutes that can be used to replace, restore, or augment those injured or diseased in the human body1,2,3,4, often through a combination of desired cell types, bioactive molecules5,6, and biomaterials7,8,9,10. More recently, tissue engineering technologies have also been increasingly adopted to generate in vitro tissue and organ models that mimic the important functions of their in vivo counterparts, for applications such as drug development, in replacement of the conventional over-simplified planar cell cultures11,12,13,14,15,16,17,18,19. In both situations, the ability to recapitulate the complex microarchitecture and hierarchical structure of the human tissues is critical in enabling functionality of the engineered tissues10, and in particular, ways to integrate a vascular network into the engineered tissues are of demand since vascularization presents one of the greatest challenges to the field20,21,22,23.
To date, a variety of approaches have been developed in this regard in an attempt to build blood vessel structures into engineered tissue constructs with various degrees of success8. For example, self-assembly of endothelial cells allows for generation of microvascular networks24; delivery of angiogenic growth factors induces sustained neovascularization25,26; use of vascular progenitor cells and pericytes facilitates endothelial cell growth and assembly24,27; designing scaffold properties enables precise modulation of vascularization28,29; and cell sheet technology allows for convenient manipulation of vascular layering30. Nevertheless, these strategies do not endow the capability of controlling the spatial patterning of the vasculature, often leading to random distribution of blood vessels within an engineered tissue construct and thus limited reproducibility. During the past few years bioprinting has emerged as a class of enabling technologies towards the solution of such a challenge, due to their unparalleled versatility of depositing complex tissue patterns at high fidelity and reproducibility in an automated or semi-automated manner31,32,33. Sacrificial bioprinting34,35,36,37,38, embedded bioprinting39,40,41, and hollow structure bioprinting/biofabrication42,43,44,45,46,47,48,49,50,51,52,53 have all demonstrated the feasibility of generating vascular or vascularized tissues.
Alternatively, a microfluidic bioprinting strategy to fabricate microfibrous scaffolds have been recently developed, where a hybrid bioink composed of alginate and gelatin methacryloyl (GelMA) was delivered through the core of a concentric printhead and a calcium chloride (CaCl2) solution was carried through the outer sheath flow of the printhead54,55. The co-extrusion of the two flows allowed for immediate physical crosslinking of the alginate component to enable microfiber formation, while subsequent photocrosslinking ensured permanent stabilization of the multi-layer microfibrous scaffold. Of note, endothelial cells encapsulated within the bioprinted microfibers were found to proliferate and migrate towards the peripheries of the microfibers assuming lumen-like structures that mimicked the vascular bed54,55. These bioprinted, endothelialized vascular beds could be subsequently populated with desired secondary cell types to further construct vascularized tissues55. This protocol thus provides a detailed procedure of such a microfluidic bioprinting strategy enabled by the concentric nozzle design, which ensures convenient fabrication of vascularized tissues for potential applications in both tissue engineering and organoid modeling.

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		<tr height="21">
			<td height="21" style="width:467px;height:21px;">Alginic acid sodium salt from brown algae</td>
			<td style="width:160px;">Sigma-Aldrich</td>
			<td style="width:163px;">A0682</td>
			<td style="width:480px;">BioReagent, plant cell culture tested, low viscosity, powder</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:467px;height:21px;">Gelatin type A from porcine skin</td>
			<td style="width:160px;">Sigma-Aldrich</td>
			<td style="width:163px;">G2500</td>
			<td>Gel strength 300</td>
		</tr>
		<tr height="42">
			<td height="42" style="width:467px;height:42px;">Irgacure 2959 (2-Hydroxy-4&#39;-(2-hydroxyethoxy)-2-methylpropiophenone)</td>
			<td style="width:160px;">Sigma-Aldrich</td>
			<td style="width:163px;">410896</td>
			<td>98%</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:467px;height:21px;">HEPES buffer</td>
			<td style="width:160px;">Sigma-Aldrich</td>
			<td style="width:163px;">H0887</td>
			<td>1 M, pH 7.0-7.6, sterile-filtered, BioReagent, suitable for cell culture</td>
		</tr>
		<tr height="42">
			<td height="42" style="width:467px;height:42px;">Fetal bovine serum&#160;</td>
			<td style="width:160px;">Thermo Fisher Scientific</td>
			<td style="width:163px;">10438026</td>
			<td>Qualified, heat-inactivated, USDA-approved regions</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:467px;height:21px;">Calcium chloride dihydrate</td>
			<td style="width:160px;">Sigma-Aldrich</td>
			<td style="width:163px;">C5080</td>
			<td>BioXtra, &#8805;99.0%</td>
		</tr>
		<tr height="42">
			<td height="42" style="width:467px;height:42px;">Phosphate buffered saline</td>
			<td style="width:160px;">Thermo Fisher Scientific</td>
			<td style="width:163px;">10010023</td>
			<td>pH 7.4</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:467px;height:21px;">Human umbilical vein endothelial cells</td>
			<td style="width:160px;">Angio-Proteomie</td>
			<td style="width:163px;">cAP-0001</td>
			<td>Human Umbilical Vein Endothelial Cells (HUVECs)</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:467px;height:21px;">GFP-expressing human umbilical vein endothelial cells</td>
			<td style="width:160px;">Angio-Proteomie</td>
			<td style="width:163px;">cAP-0001GFP</td>
			<td>GFP-Expressing Human Umbilical Vein Endothelial Cells (GFPHUVECs)</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:467px;height:21px;">Endothelial cell growth medium</td>
			<td style="width:160px;">Lonza</td>
			<td style="width:163px;">CC-3162</td>
			<td>EGM-2 BulletKit</td>
		</tr>
		<tr height="42">
			<td height="42" style="width:467px;height:42px;">Dulbecco&#8217;s Modified Eagle Medium&#160;</td>
			<td style="width:160px;">Thermo Fisher Scientific</td>
			<td style="width:163px;">12430054</td>
			<td>High glucose, HEPES</td>
		</tr>
		<tr height="42">
			<td height="42" style="width:467px;height:42px;">Sylgard 184 silicone elastomer kit</td>
			<td style="width:160px;">Ellsworth Adhesives</td>
			<td style="width:163px;">184 SIL ELAST KIT 0.5KG</td>
			<td>Clear 0.5 kg Kit</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:467px;height:21px;">UV curing lamp system</td>
			<td style="width:160px;">Excelitas Technologies</td>
			<td style="width:163px;">OmniCure S2000</td>
			<td>Spot UV Light Curing System with Intelligent UV Sensor</td>
		</tr>
	</tbody>
</table>

microfluidic bioprinting for engineering vascularized tissues and organoids

Engineering vascularized tissue constructs and organoids has been historically challenging. Here we describe a novel method based on microfluidic bioprinting to generate a scaffold with multilayer interlacing hydrogel microfibers. To achieve smooth bioprinting, a core-sheath microfluidic printhead containing a composite bioink formulation extruded from the core flow and the crosslinking solution carried by the sheath flow, was designed and fitted onto the bioprinter. By blending gelatin methacryloyl (GelMA) with alginate, a polysaccharide that undergoes instantaneous ionic crosslinking in the presence of select divalent ions, followed by a secondary photocrosslinking of the GelMA component to achieve permanent stabilization, a microfibrous scaffold could be obtained using this bioprinting strategy. Importantly, the endothelial cells encapsulated inside the bioprinted microfibers can form the lumen-like structures resembling the vasculature over the course of culture for 16 days. The endothelialized microfibrous scaffold may be further used as a vascular bed to construct a vascularized tissue through subsequent seeding of the secondary cell type into the interstitial space of the microfibers. Microfluidic bioprinting provides a generalized strategy in convenient engineering of vascularized tissues at high fidelity.

The microfluidic bioprinting strategy allows for direct extrusion bioprinting of microfibrous scaffolds using low-viscosity bioinks54,55. As illustrated in Figure 2A, a scaffold with a size of 6 &#215; 6 &#215; 6 mm3 containing &#62;30 layers of microfibers could be bioprinted within 10 min. The immediate ionic crosslinking of the alginate component with CaCl2 al...

Watch this Scientific Journal Video about Microfluidic Bioprinting for Engineering Vascularized Tissues and Organoids at JoVE.com

Microfluidic Bioprinting for Engineering Vascularized Tissues and Organoids

We provide a generalized protocol based on a microfluidic bioprinting strategy for engineering a microfibrous vascular bed, where a secondary cell type could be further seeded into the interstitial space of this microfibrous structure to generate vascularized tissues and organoids.

Engineering vascularized tissue constructs and organoids has been historically challenging. Here we describe a novel method based on microfluidic ...

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