Name: micropatterning and assembly of 3d microvessels
Uploaded: 2016-09-09T15:00:00
Description: Watch this Scientific Journal Video about Micropatterning and Assembly of 3D Microvessels at JoVE.com

The authors would like to acknowledge the Lynn and Mike Garvey Imaging Laboratory at the Institute for Stem Cell and Regenerative Medicine as well as the Washington Nanofabrication Facility at the University of Washington. They also acknowledge the financial support of National Institute of Health grants DP2DK102258 (to YZ), and training grants T32EB001650 (to SSK and MAR) and T32HL007312 (to MAR).

1. Microfabrication of Patterned Polydimethylsiloxane (PDMS) with Network Design
<ol>
	<li>Wafer Fabrication to Create a Negative Template of the Network Design
	<ol>
		<li>Create a network pattern using any computer-aided design (CAD) software. Ensure that the diagonal dimension between the inlet and outlet match the distance between the inlet and outlet reservoirs on the housing devices in future steps (see 2.1.1). 
		Note: The design of the pattern itself is custom depending on the specific res...

<ol>
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Engineered microvessels are an in vitro model where physiological characteristics such as luminal geometry, hydrodynamic forces, and multi-cellular interactions are present and tunable. This type of platform is powerful in that it offers the ability to model and study endothelial behavior in a variety of contexts where the in vitro culture conditions can be matched to that of the microenvironment in question. For example, the mechanisms driving endothelial processes, such as angiogenesis, are known to o...

The microvasculature in each organ helps define the tissue microenvironment, maintain tissue homeostasis and regulate inflammation, permeability, thrombosis, and fibrinolysis 1,2. Microvascular endothelium, in particular, is the interface between blood flow and the surrounding tissue and therefore plays a critical role in modulating vascular and organ function in response to stimuli such as hydrodynamic forces and circulating cytokines and hormones 3-5. Understanding the detailed interactions between the endothelium, blood, and the surrounding tissue microenvironment is important for the study of vascular biology and disease progression. However, progress in studying these interactions has been hindered by limited in vitro tools that do not recapitulate in vivo microvascular structure and function 6,7. As a result, the field and therapeutic advancement has relied heavily on costly and time-consuming animal models that often fail to translate to success in humans 8-10. While in vivo models are invaluable in the study of disease mechanisms and vascular functions, they are complex and often lack precise control of individual cellular, biochemical, and biophysical cues.
Vasculature throughout the body possesses a mature hierarchical structure in conjunction with expansive capillary beds, providing optimized perfusion and nutrient transport simultaneously 11. Initially, vasculature forms as a primitive plexus which reorganizes to a hierarchically branched network during early development 12,13. Although many of the signals involved in these processes are well understood 14-16, it remains elusive how such vascular patterning is determined 15. In turn, recapitulating this process in vitro to engineer organized vascular networks has been difficult. Many existing in vitro platforms to model vasculature, such as two dimensional endothelial cell cultures, lack important characteristics such as multi-cellular proximity, three dimensional luminal geometry, flow, and extracellular matrix. Tube formation assays in 3D hydrogels (collagen or fibrin) 17-19 or invasion assays 20,21 have been used to study endothelial function in 3D and their interactions with other vascular 17,22 or tissue cell types 23. However, assembled lumens in these assays lack interconnectivity, hemodynamic flow, and appropriate perfusion. Furthermore, the propensity for vascular regression in these tube formation assays 24 prevents long term culture and maturation which limits the degree of functional studies that can be performed. Thus, there is a burgeoning need to engineer in vitro platforms of microvascular networks that can appropriately model endothelial characteristics and are capable of long term culture.
A variety of vascular engineering techniques have emerged over the years for medical applications to replace or bypass affected vessels in patients with vascular disease. Large diameter vessels made from synthetic materials such as polyethylene terephthalate (PET), and polytetrafluoroethylene (ePTFE) have had considerable therapeutic success with long term patency (average 95% patency over 5 years) 25. Although small diameter synthetic grafts (&#60; 6 mm) typically face complications such as intimal hyperplasia and thrombopoiesis 26-28, tissue engineered small diameter grafts made with biological material have made significant progress 29,30. Despite advancements of this kind, engineered vessels on the microscale have remained a challenge. To adequately model the microvasculature, it is necessary to generate complex network patterns with sufficient mechanical strength to maintain patency and with a matrix composition that allows for both nutrient permeation for parenchymal cells and cellular remodeling.
This protocol presents a novel artificial perfusable vessel network that mimics a native in vivo setting with a tunable and controllable microenvironment 31-34. The described method generates engineered microvessels with diameters on the order of 100 &#181;m. Engineered microvessels are fabricated by perfusing endothelial cells through a microfluidic channel that is embedded within soft type I collagen hydrogel. This system has the capacity to generate patterned networks with open luminal structure, replicate multi-cellular interactions, modulate extracellular matrix composition, and apply physiologically relevant hemodynamic forces.

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			<td height="21" style="height:21px;width:459px;">Wafer Fabrication</td>
			<td style="width:225px;"></td>
			<td style="width:140px;"></td>
			<td style="width:540px;"></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">AutoGlow Plasma System</td>
			<td>AutoGlow</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Headway Spin Coater</td>
			<td>Headway Research, Inc&#160;</td>
			<td colspan="2">PWM32 Spin Coater&#160;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">ABM Contact Aligner</td>
			<td>AB-M</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Alpha Step Profilometer</td>
			<td>Tencor</td>
			<td>Alpha Step 200</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">SU-8 Developer</td>
			<td>Microchem</td>
			<td>Y020100</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">SU-8 Resist</td>
			<td>Microchem</td>
			<td>SU-8 2000</td>
			<td></td>
		</tr>
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			<td height="20" style="height:20px;">8&#34; silicon wafer</td>
			<td>Wafer World Inc.</td>
			<td></td>
			<td></td>
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		<tr height="20">
			<td height="20" style="height:20px;">Tabletop Micro Pattern Generator</td>
			<td>Heidelberg Instruments</td>
			<td>&#956;PG 101</td>
			<td>For generation of photomask</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Hot plate</td>
			<td>VWR</td>
			<td>97042-646</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Ispropyl alcohol</td>
			<td>Avantor Performance Materials</td>
			<td>9088</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Petri dishes (120 x 120 mm, square)</td>
			<td>Sigma-Aldrich</td>
			<td>Z617679</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Trichloro(3,3,3-trifluoropropyl)silane</td>
			<td>Sigma-Aldrich</td>
			<td>MKBG3805V</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">Polydimethylsiloxane (PDMS) elastomer base and curing agent</td>
			<td>Dow Corning</td>
			<td>Sylgard 184</td>
			<td>Mixed at 10:1 (w/w)</td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">Vacuum desiccator</td>
			<td>Sigma-Aldrich</td>
			<td>Z119024-1EA</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">Oven</td>
			<td>VWR</td>
			<td>9120976</td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">Device Fabrication and Culture</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="17">
			<td height="17" style="height:17px;">poly(methyl methacrylate) (PMMA)</td>
			<td>Plexiglas</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Corona Treater</td>
			<td>Electro-Technic Products, Inc.</td>
			<td>BD-20</td>
			<td>Handheld device for plasma treatment of PMMA devices and PDMS molds</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Soldering Iron</td>
			<td>Weller&#160;</td>
			<td>WTCPS</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Stainless Steel Truss Head Slotted Machine Screw</td>
			<td>McMaster-Carr&#160;</td>
			<td>91785A096</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Stainless steel dowel pins</td>
			<td>McMaster-Carr&#160;</td>
			<td>93600A060</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Tweezers&#160;</td>
			<td>Miltex</td>
			<td>24-572</td>
			<td>Any similar tweezers may be used</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Spatula (Micro Spoon)</td>
			<td>Electron Microscopy Services</td>
			<td>62410-01</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Screw driver</td>
			<td></td>
			<td></td>
			<td>Any flat head screwdriver may be used, autoclaved</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Glass coverslips (22 x 22 mm)</td>
			<td>Fisher Scientific</td>
			<td>12-542B</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Bleach</td>
			<td>Clorox</td>
			<td>4460030966</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Petri dishes (150 X 25mm)</td>
			<td>Corning</td>
			<td>430599</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Petri dishes (100 X 20 mm)</td>
			<td>Corning</td>
			<td>2909</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Cotton, cut into 1 cm x 3 cm pieces</td>
			<td></td>
			<td></td>
			<td>Autoclaved</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Polyethyleneimine (PEI)</td>
			<td>Sigma-Aldrich</td>
			<td>P3143</td>
			<td>Dilute to 1% in cell culture grade water</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Glutaraldehyde</td>
			<td>Sigma-Aldrich</td>
			<td>G6257</td>
			<td>Dilute to 0.1% in cell culture grade water</td>
		</tr>
		<tr height="26">
			<td height="26" style="height:26px;">Sterile H2O</td>
			<td></td>
			<td></td>
			<td>Autoclaved DI H2O</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Type I collagen, dissolved in 0.1% acetic acid</td>
			<td></td>
			<td></td>
			<td>Isolated from rat tails as described in Rajan et. al. 2006 (ref #37)</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1 mL syringe</td>
			<td>BD</td>
			<td>309659</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">10 mL syringe</td>
			<td>BD</td>
			<td>309604</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">15 mL conical tubes</td>
			<td>Corning</td>
			<td>352097</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">30 mL conical tubes</td>
			<td>Corning</td>
			<td>352098</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">M199 10X Media&#160;</td>
			<td>Life Technologies</td>
			<td>11825-015</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1N NaOH (sterile)</td>
			<td>Sigma-Aldrich</td>
			<td>415413</td>
			<td>Dilute to 1N in cell culture grade water</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HUVECs&#160;</td>
			<td>Lonza</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Endothelial growth media</td>
			<td>Lonza</td>
			<td>CC-3124</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Trypsin</td>
			<td>Corning</td>
			<td>25-052-CI</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Fetal bovine serum (FBS)</td>
			<td>Thermofisher Scientific</td>
			<td>10082147</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Dextran from Leuconostoc spp. (70kDa)</td>
			<td>Sigma-Aldrich</td>
			<td>31390</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Phosphate Buffered Saline (PBS)</td>
			<td>Corning</td>
			<td>21-031-CV</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Hemocytometer</td>
			<td>Hausser Scientific Co.</td>
			<td>3200</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Gel loading tips</td>
			<td>VWR</td>
			<td>37001-152</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">18G Blunt Fill Needle</td>
			<td>BD&#160;</td>
			<td>305180</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">20G Stainless Steel Dispensing Needle</td>
			<td>McMaster-Carr</td>
			<td>75165A123</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Tygon 1/32&#8221; ID, 3/32&#34; OD Silicon Tubing</td>
			<td>Cole-Parmer</td>
			<td>EW-95702-00</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1/16&#34; Tube-to-tube Coupling</td>
			<td>McMaster-Carr</td>
			<td>5116K165</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">90&#176; Elbow Connectors, Tube-to-Tube</td>
			<td>McMaster-Carr</td>
			<td>5121K901</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Luer Lock Coupling (Female, 1/16&#34; ID)</td>
			<td>McMaster-Carr</td>
			<td>51525K211</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Plastic Forceps, with Jaw Grips</td>
			<td>Electron Microscopy Services</td>
			<td>72971</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Dual Syringe Pump</td>
			<td>Harvard Apparatus</td>
			<td>70-4505</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">5 mL Polystyrene Round-bottom tube</td>
			<td>Fisher Scientific</td>
			<td>14-959-2A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Device Analysis</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Formaldehyde</td>
			<td>Sigma-Aldrich</td>
			<td>F8775</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Bovine Serum Albumin</td>
			<td>Sigma-Aldrich</td>
			<td>A8806-5G</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Triton X-100</td>
			<td>Sigma-Aldrich</td>
			<td>T-9284</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Rabbit anti-hCD31</td>
			<td>Abcam</td>
			<td>ab32457</td>
			<td>1:25 working dilution</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">FITC conjugated anti-von Willebrand Factor antibody</td>
			<td>Abcam</td>
			<td>ab8822</td>
			<td>1:100 working dilution</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Goat anti-rabbit 568 secondary antibody</td>
			<td>Thermofisher Scientific</td>
			<td>A-11011</td>
			<td>1:100 working dilution</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Hoescht</td>
			<td>Thermofisher Scientific</td>
			<td>H1399</td>
			<td>Resuspended in DMSO</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Sodium cacodylate&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>C0250</td>
			<td>To make 0.2M cacodylate buffer</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Ethanol</td>
			<td>VWR International</td>
			<td>BDH1164-4LP</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">40kDa FITC-conjugated Dextran</td>
			<td>Sigma-Aldrich</td>
			<td>FD40S&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Additional Culture Reagents&#160;</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">CHIR-99021</td>
			<td>Selleck Chem</td>
			<td>S2924</td>
			<td>Small molecule GSK-3 inhibitor</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Human recombinant VEGF</td>
			<td>Peprotech</td>
			<td>100-20</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Human recombinant bFGF</td>
			<td>Peprotech</td>
			<td>AF-100-18B</td>
			<td></td>
		</tr>
	</tbody>
</table>

micropatterning and assembly of 3d microvessels

In vitro platforms to study endothelial cells and vascular biology are largely limited to 2D endothelial cell culture, flow chambers with polymer or glass based substrates, and hydrogel-based tube formation assays. These assays, while informative, do not recapitulate lumen geometry, proper extracellular matrix, and multi-cellular proximity, which play key roles in modulating vascular function. This manuscript describes an injection molding method to generate engineered vessels with diameters on the order of 100 &#181;m. Microvessels are fabricated by seeding endothelial cells in a microfluidic channel embedded within a native type I collagen hydrogel. By incorporating parenchymal cells within the collagen matrix prior to channel formation, specific tissue microenvironments can be modeled and studied. Additional modulations of hydrodynamic properties and media composition allow for control of complex vascular function within the desired microenvironment. This platform allows for the study of perivascular cell recruitment, blood-endothelium interactions, flow response, and tissue-microvascular interactions. Engineered microvessels offer the ability to isolate the influence from individual components of a vascular niche and precisely control its chemical, mechanical, and biological properties to study vascular biology in both health and disease.

The engineered vessel platform creates functional microvasculature embedded within a natural collagen type I matrix and allows for tight control of the cellular, biophysical and biochemical environment in vitro. To fabricate engineered microvessels, human umbilical vein endothelial cells (HUVECs) are perfused through the collagen-embedded microfluidic network where they attach to form a patent lumen and confluent endothelium. As illustrated in Figure 1A-C, the ve...

Watch this Scientific Journal Video about Micropatterning and Assembly of 3D Microvessels at JoVE.com

Micropatterning and Assembly of 3D Microvessels

This manuscript presents an injection molding method to engineer microvessels that recapitulate physiological properties of endothelium. The microfluidic-based process creates patent 3D vascular networks with tailorable conditions, such as flow, cellular composition, geometry, and biochemical gradients. The fabrication process and examples of potential applications are described.

In vitro platforms to study endothelial cells and vascular biology are largely limited to 2D endothelial cell culture, flow chambers with polymer or glass ...

The overall goal of using engineered micro-vessels is to replicate the structure and function of vessels in the body to study vascular physiology in normal and diseased states. This method can help answer key questions in the field of vascular biology such as how different anathema cells respond to flow, how they influence tissue function, and how vascular diseases initiate and progress over time. The main advantage of this technique is it can be easily modified to mimic different organ systems and disease states.This can be done by changing the cell types, the matrix and media composition, and other variables. Generally individuals new to this method could struggle before they become aware of common mistakes that can lead to poor vessel quality. Visual demonstration of this method is critical because there are several tricks to successful fabrication during the injection molding and assembly steps.For this procedure, have the flat and micro-patterned PDMS molds and the PMMA housing pieces prepared in advance. A description of how to make these parts is provided in the text protocol. Autoclave the PDMS molds along with the screws, pins, forceps, and a spatula.Do not autoclave the PMMA pieces. They must be sterilized in bleach under a hood. After allowing the PMMA pieces to soak in bleach for at least an hour, rinse off the bleach with autoclaved water two times.Then, place the pieces in sterile dishes. Aspirate excess water and let them air dry. With everything cleaned, start the protocol by treating the inner wells of both the top and bottom PMMA pieces using a handheld plasma treater for approximately one minute.Turn the light off to help visualize the coverage of the plasma treatment. Next, add 1%PEI onto the inner wells. If the PEI doesn't spread easily, increase the plasma treatment time.After letting the PEI react for 10 minutes, remove the solution and then rinse the devices off with sterile water and let them air dry. Once dried, apply 0.1%glutaraldehyde onto the treated surfaces and allow the glutaraldehyde to react for half an hour. Then, rinse the pieces with sterile water twice and allow them to air dry.Now, prepare fresh 0.75%neutralized collagen for vessel fabrication by combining the pre allocated stock collagen volume with the neutralization solution of medium and sodium hydroxide. Stir slowly and carefully with a spatula until the solution is homogeneous and is orange in color. Then, if needed, add cells at the desired concentration and continue to stir the solution until the cells are uniformly distributed.In preparation for the assembly process, place the micropatterned PDMS mold into a 100 by 20 millimeter dish and treat the mold with plasma for one minute. Next, align the top PMMA piece onto the PDMS so the square reservoirs line up with the inlet and outlet reservoirs. Then, put stainless steel dowel pins into the inlet and outlet reservoir holes so they will remain open after collagen injection.Now, load the collagen cell mixture into a one milliliter syringe without introducing air bubbles. Then using forceps, gently press down on the top PMMA piece to secure it to the PDMS mold and slowly inject about one half milliliter of collagen cell mixture into the injection port. The collagen must fill the 20 by 20 millimeter area over the pattern and not leak out.Then, carefully close the dish without jostling the dowel pins. Next, into the bottom PMMA piece place a 22 square millimeter glass coverslip in the inner well. Then, dispense about 0.25 milliliters of collagen evenly onto the glass.Complete the bottom half by gently lowering the flat PDMS into the collagen so it is flat against the PMMA with no air bubbles in between. Now, carefully place both halves of the device into a 37 degree Celsius incubator and allow the collagen solution to gel for 30 minutes before proceeding. After gelation, add enough PBS to surround the PDMS on the bottom piece.Then, use forceps to remove any excess collagen around the edges and slowly peel the flat PDMS piece off while keeping the collagen hydrated with PBS. To prepare the top piece, use forceps to lift the PMMA and PDMS assembly and flip it over. Then add a few drops of PBS to the inner face and remove the PDMS mold from the top PMMA piece, peeling quickly and firmly.Next, with a second pair of forceps, gently remove the pins from the other side of the PMMA housing. Ensure the inlet and outlet are clear of excess collagen by moving the pins up and down before their removal. If the pins fall out on their own, simply use another sterile dowel pin to ensure that the inlet and outlet are clear.Then, drop more PBS onto the micro patterned collagen, flip the piece over, and place screws into the four corner holes. Now, gently lay the top piece on the bottom piece aligning the screws into their holes. Do not let the two pieces slide against each other.Then, gently screw the pieces together using a spatula and a gentle touch so they are not overtightened. It is critical to be gentle and precise during assembly. By applying an ample amount of PBS, the friction between the inner face is reduced.While securing the screws, proceed slowly and stop as soon as any resistance is met. Next, aspirate the PBS surrounding the PMMA surfaces and place a small piece of cotton under one edge of the device. Then, aspirate any PBS from the reservoirs.Now, refill the reservoirs with cell culture medium and incubate the device for at least an hour for gelation. Once the device is assembled, use an endothelial cell suspension at 10 million cells per milliliter to seed the device. Remove the medium in the inlet and outlet reservoirs and using a 20 microleter pipette with gel loading tips, add 10 microliters of the cell suspension into the center of the inlet reservoir.The cells will immediately flow into and coat the network. Once the cells have filled the network and the flow has equilibrated, add 150 microliters of medium into both reservoirs. Then incubate the device for an hour or more so the cells can spread and attach.For long term culture, remove the medium every 12 hours and add back 150 microliters of fresh medium to the inlet reservoir and 50 microliters to the outlet reservoir. After 24 hours of culturing, a syringe pump can be used to establish continuous flow conditions. After bringing the materials to the bio hood, remove the tubing from the autoclave bags and place it in a dish.Then, prepare a sterile flow dish by melting side holes and then threading the tubing through. Prepare a 10 milliliter syringe with culture medium containing 3.5%Dextran. Next, attach the filled syringe to the lure lock at the end of the inlet tubing.Then, secure the syringe to the pump and profuse medium until any trapped air bubbles have exited the tubing. Once the tubing is filled with medium and is clear of bubbles, transfer the device to a new dish and insert the inlet connector joint into the housing inlet. Then, set the syringe pump to the desired flow rate and begin profusion.Prepare the outlet by filling the tubing with cell culture media using an 18 gauge needle and a one milliliter syringe. Clamping it and removing the needle. Then, melt a hole in the cap of the outlet collection tube using a soldering iron.Afterwards, add media to the collection tube, insert the tubing, and attach the connector joint into the housing outlet. Throughout this process, a clamp is used to retain the medium in the tubing. Once completed, transfer the entire setup into an incubator.Depending on the experimental conditions, the syringe may need to be refilled after 24 to 36 hours. During syringe replacement, ensure bubbles are not introduced into the tubing. Human umbilical vein and ethelial cells were profused through the collagen embedded micro fluidic network to form a patent lumen and confluent endothelium.Several vessel geometries were used to establish different flow conditions. Continuous flow culture conditions were used to apply constant shear stress on the endothelium. Devices cultured under gravity driven flow conditions also maintained long term viability and patency.A critical feature of these micro-vessels is their ability to respond to inflammatory stimuli. This was investigated by profusing the micro-vessels with whole blood. Non-stimulated micro-vessels contained non-activated endothelium and remained quiescent.Stimulated micro-vessels became activated and their response initiated thrombus formation. Another interesting application for the system is to study phenotypic changes in vasculature formed from different endothelial cell populations. For example, micro-vessels formed from unique populations of stem cells exhibited different angiogenic sprouting capabilities.After watching this video you should have a good understanding of how to fabricate micro-vessels and use them to study vascular biology and to build complex model organ systems. While attempting this procedure it is important to remember that practice will improve with the rate of successful vessel formation and allow for more consistent results. Once mastered, several devices can be made in three to four hours.Following this procedure, other methods like the profusion of whole blood, Dextran, or pharmaceutical treatments can be performed to assess endothelial quiescence, permeability, drug response, and the general morphology of cells and vessels.

micropatterning-and-assembly-of-3d-microvessels

Research

JoVE Journal

Bioengineering

Preparation of 3D Collagen Gels and Microchannels for the Study of 3D Interactions In Vivo

Historically, most cellular processes have been studied in only 2 dimensions. While these studies have been informative about general cell signaling mechanisms, they neglect important cellular cues received from the structural and mechanical properties of the local microenvironment and extracellular matrix (ECM). To understand how cells interact within a physiological ECM, it is important to study them in the context of 3 dimensional assays. Cell migration, cell differentiation, and cell proliferation are only a few processes that have been shown to be impacted by local changes in the mechanical properties of a 3-dimensional ECM. Collagen I, a core fibrillar component of the ECM, is more than a simple structural element of a tissue. Under normal conditions, mechanical cues from the collagen network direct morphogenesis and maintain cellular structures. In diseased microenvironments, such as the tumor microenvironment, the collagen network is often dramatically remodeled, demonstrating altered composition, enhanced deposition and altered fiber organization. In breast cancer, the degree of fiber alignment is important, as an increase in aligned fibers perpendicular to the tumor boundary has been correlated to poorer patient prognosis1. Aligned collagen matrices result in increased dissemination of tumor cells via persistent migration2,3. The following is a simple protocol for embedding cells within a 3-dimensional, fibrillar collagen hydrogel. This protocol is readily adaptable to many platforms, and can reproducibly generate both aligned and random collagen matrices for investigation of cell migration, cell division, and other cellular processes in a tunable, 3-dimensional, physiological microenvironment.

Preparation of 3D Collagen Gels and Microchannels for the Study of 3D Interactions In Vivo

Collagen is a core component of the ECM, and provides essential cues for several cellular processes ranging from migration to differentiation and proliferation. Provided here is a protocol for embedding cells within 3D collagen hydrogels, and a more advanced technique for generating randomized or aligned collagen matrices using PDMS microchannels.

Historically, most cellular processes have been studied in only 2 dimensions.  While these studies have been informative about general cell signaling ...

Automated Robotic Liquid Handling Assembly of Modular DNA Devices

Recent advances in modular DNA assembly techniques have enabled synthetic biologists to test significantly more of the available &#34;design space&#34; represented by &#34;devices&#34; created as combinations of individual genetic components. However, manual assembly of such large numbers of devices is time-intensive, error-prone, and costly. The increasing sophistication and scale of synthetic biology research necessitates an efficient, reproducible way to accommodate large-scale, complex, and high throughput device construction.
Here, a DNA assembly protocol using the Type-IIS restriction endonuclease based Modular Cloning (MoClo) technique is automated on two liquid-handling robotic platforms. Automated liquid-handling robots require careful, often times tedious optimization of pipetting parameters for liquids of different viscosities (e.g. enzymes, DNA, water, buffers), as well as explicit programming to ensure correct aspiration and dispensing of DNA parts and reagents. This makes manual script writing for complex assemblies just as problematic as manual DNA assembly, and necessitates a software tool that can automate script generation. To this end, we have developed a web-based software tool, http://mocloassembly.com, for generating combinatorial DNA device libraries from basic DNA parts uploaded as Genbank files. We provide access to the tool, and an export file from our liquid handler software which includes optimized liquid classes, labware parameters, and deck layout. All DNA parts used are available through Addgene, and their digital maps can be accessed via the Boston University BDC ICE Registry. Together, these elements provide a foundation for other organizations to automate modular cloning experiments and similar protocols.
The automated DNA assembly workflow presented here enables the repeatable, automated, high-throughput production of DNA devices, and reduces the risk of human error arising from repetitive manual pipetting. Sequencing data show the automated DNA assembly reactions generated from this workflow are ~95% correct and require as little as 4% as much hands-on time, compared to manual reaction preparation.

Here, an automated workflow to perform modular DNA &#34;device&#34; assembly using a modular cloning DNA assembly method on liquid-handling robots is presented. The protocol uses an intuitive software tool for generating liquid handler picklists for combinatorial DNA device library generation, which we demonstrate using two liquid handling platforms.

Recent advances in modular DNA assembly techniques have enabled synthetic biologists to test significantly more of the available &#34;design space&#34; ...

Synthesis of Cationized Magnetoferritin for Ultra-fast Magnetization of Cells

Many important biomedical applications, such as cell imaging and remote manipulation, can be achieved by labeling cells with superparamagnetic iron oxide nanoparticles (SPIONs). Achieving sufficient cellular uptake of SPIONs is a challenge that has traditionally been met by exposing cells to elevated concentrations of SPIONs or by prolonging exposure times (up to 72 hr). However, these strategies are likely to mediate toxicity. Here, we present the synthesis of the protein-based SPION magnetoferritin as well as a facile surface functionalization protocol that enables rapid cell magnetization using low exposure concentrations. The SPION core of magnetoferritin consists of cobalt-doped iron oxide with an average particle diameter of 8.2 nm mineralized inside the cavity of horse spleen apo-ferritin. Chemical cationization of magnetoferritin produced a novel, highly membrane-active SPION that magnetized human mesenchymal stem cells (hMSCs) using incubation times as short as one minute and iron concentrations as lows as 0.2 mM.

A protocol for the synthesis and cationization of cobalt-doped magnetoferritin is presented, as well as a method to rapidly magnetize stem cells with cationized magnetoferritin.

Many important biomedical applications, such as cell imaging and remote manipulation, can be achieved by labeling cells with superparamagnetic iron oxide ...

Bioprinting of Cartilage and Skin Tissue Analogs Utilizing a Novel Passive Mixing Unit Technique for Bioink Precellularization

Bioprinting is a powerful technique for the rapid and reproducible fabrication of constructs for tissue engineering applications. In this study, both cartilage and skin analogs were fabricated after bioink pre-cellularization utilizing a novel passive mixing unit technique. This technique was developed with the aim to simplify the steps involved in the mixing of a cell suspension into a highly viscous bioink. The resolution of filaments deposited through bioprinting necessitates the assurance of uniformity in cell distribution prior to printing to avoid the deposition of regions without cells or retention of large cell clumps that can clog the needle. We demonstrate the ability to rapidly blend a cell suspension with a bioink prior to bioprinting of both cartilage and skin analogs. Both tissue analogs could be cultured for up to 4 weeks. Histological analysis demonstrated both cell viability and deposition of tissue specific extracellular matrix (ECM) markers such as glycosaminoglycans (GAGs) and collagen I respectively.

Cartilage and skin analogs were bioprinted using a nanocellulose-alginate based bioink. The bioinks were cellularized prior to printing via a single step passive mixing unit. The constructs were demonstrated to be uniformly cellularized, have high viability, and exhibit favorable markers of differentiation.

Bioprinting is a powerful technique for the rapid and reproducible fabrication of constructs for tissue engineering applications. In this study, both ...

Fabrication of Custom Agarose Wells for Cell Seeding and Tissue Ring Self-assembly Using 3D-Printed Molds

Engineered tissues are being used clinically for tissue repair and replacement, and are being developed as tools for drug screening and human disease modeling. Self-assembled tissues offer advantages over scaffold-based tissue engineering, such as enhanced matrix deposition, strength, and function. However, there are few available methods for fabricating 3D tissues without seeding cells on or within a supporting scaffold. Previously, we developed a system for fabricating self-assembled tissue rings by seeding cells into non-adhesive agarose wells. A polydimethylsiloxane (PDMS) negative was first cast in a machined polycarbonate mold, and then agarose was gelled in the PDMS negative to create ring-shaped cell seeding wells. However, the versatility of this approach was limited by the resolution of the tools available for machining the polycarbonate mold. Here, we demonstrate that 3D-printed plastic can be used as an alternative to machined polycarbonate for fabricating PDMS negatives. The 3D-printed mold and revised mold design is simpler to use, inexpensive to produce, and requires significantly less agarose and PDMS per cell seeding well. We have demonstrated that the resulting agarose wells can be used to create self-assembled tissue rings with customized diameters from a variety of different cell types. Rings can then be used for mechanical, functional, and histological analysis, or for fabricating larger and more complex tubular tissues.

This protocol describes a platform for fabricating self-assembled tissue rings in variable sizes using a customized 3D-printed plastic mold. PDMS negatives are cured in the 3D-printed mold; then agarose is cast in the cured PDMS negatives. Cells are seeded into the resulting agarose wells where they aggregate into tissue rings.

Engineered tissues are being used clinically for tissue repair and replacement, and are being developed as tools for drug screening and human disease ...

Protocols of 3D Bioprinting of Gelatin Methacryloyl Hydrogel Based Bioinks

Gelatin methacryloyl (GelMA) has become a popular biomaterial in the field of bioprinting. The derivation of this material is gelatin, which is hydrolyzed from mammal collagen. Thus, the arginine-glycine-aspartic acid (RGD) sequences and target motifs of matrix metalloproteinase (MMP) remain on the molecular chains, which help achieve cell attachment and degradation. Furthermore, formation properties of GelMA are versatile. The methacrylamide groups allow a material to become rapidly crosslinked under light irradiation in the presence of a photoinitiator. Therefore, it makes great sense to establish suitable methods for synthesizing three-dimensional (3D) structures with this promising material. However, its low viscosity restricts GelMA's printability. Presented here are methods to carry out 3D bioprinting of GelMA hydrogels, namely the fabrication of GelMA microspheres, GelMA fibers, GelMA complex structures, and GelMA-based microfluidic chips. The resulting structures and biocompatibility of the materials as well as the printing methods are discussed. It is believed that this protocol may serve as a bridge between previously applied biomaterials and GelMA as well as contribute to the establishment of GelMA-based 3D architectures for biomedical applications.

Presented here is a method for the 3D bioprinting of gelatin methacryloyl.

Gelatin methacryloyl (GelMA) has become a popular biomaterial in the field of bioprinting. The derivation of this material is gelatin, which is hydrolyzed ...

Temperature-Controlled Assembly and Characterization of a Droplet Interface Bilayer

The droplet interface bilayer (DIB) method for assembling lipid bilayers (i.e., DIBs) between lipid-coated aqueous droplets in oil offers key benefits versus other methods: DIBs are stable and often long-lasting, bilayer area can be reversibly tuned, leaflet asymmetry is readily controlled via droplet compositions, and tissue-like networks of bilayers can be obtained by adjoining many droplets. Forming DIBs requires spontaneous assembly of lipids into high density lipid monolayers at the surfaces of the droplets. While this occurs readily at room temperature for common synthetic lipids, a sufficient monolayer or stable bilayer fails to form at similar conditions for lipids with melting points above room temperature, including some cellular lipid extracts. This behavior has likely limited the compositions&#8212;and perhaps the biological relevance&#8212;of DIBs in model membrane studies. To address this problem, an experimental protocol is presented to carefully heat the oil reservoir hosting DIB droplets and characterize the effects of temperature on the lipid membrane. Specifically, this protocol shows how to use a thermally conductive aluminum fixture and resistive heating elements controlled by a feedback loop to prescribe elevated temperatures, which improves monolayer assembly and bilayer formation for a wider set of lipid types. Structural characteristics of the membrane, as well as the thermotropic phase transitions of the lipids comprising the bilayer, are quantified by measuring the changes in electrical capacitance of the DIB. Together, this procedure can aid in evaluating biophysical phenomena in model membranes over various temperatures, including determining an effective melting temperature (TM) for multi-component lipid mixtures. This capability will thus allow for closer replication of natural phase transitions in model membranes and encourage the formation and use of model membranes from a wider swath of membrane constituents, including those that better capture the heterogeneity of their cellular counterparts.

This protocol details the use of a feedback temperature-controlled heating system to promote lipid monolayer assembly and droplet interface bilayer formation for lipids with elevated melting temperatures, and capacitance measurements to characterize temperature-driven changes in the membrane.

The droplet interface bilayer (DIB) method for assembling lipid bilayers (i.e., DIBs) between lipid-coated aqueous droplets in oil offers key benefits ...

Control of Cell Geometry through Infrared Laser Assisted Micropatterning

Micropatterning is an established technique in the cell biology community used to study connections between the morphology and function of cellular compartments while circumventing complications arising from natural cell-to-cell variations. To standardize cell shape, cells are either confined in 3D molds or controlled for adhesive geometry through adhesive islands. However, traditional micropatterning techniques based on photolithography and deep UV etching heavily depend on clean rooms or specialized equipment. Here we present an infrared laser assisted micropatterning technique (microphotopatterning) modified from Doyle et al. that can be conveniently set up with commercially available imaging systems. In this protocol, we use a Nikon A1R MP+ imaging system to generate micropatterns with micron precision through an infrared (IR) laser that ablates preset regions on poly-vinyl alcohol coated coverslips. We employ a custom script to enable automated pattern fabrication with high efficiency and accuracy in systems not equipped with a hardware autofocus. We show that this IR laser assisted micropatterning (microphotopatterning) protocol results in defined patterns to which cells attach exclusively and take on the desired shape. Furthermore, data from a large number of cells can be averaged due to the standardization of cell shape. Patterns generated with this protocol, combined with high resolution imaging and quantitative analysis, can be used for relatively high throughput screens to identify molecular players mediating the link between form and function.

The protocol presented here enables automated fabrication of micropatterns that standardizes cell shape to study cytoskeletal structures within mammalian cells. This user-friendly technique can be set up with commercially available imaging systems and does not require specialized equipment inaccessible to standard cell biology laboratories.

Micropatterning is an established technique in the cell biology community used to study connections between the morphology and function of cellular ...

A Micropatterning Assay for Measuring Cell Chirality

Chirality is an intrinsic cellular property, which depicts the asymmetry in terms of polarization along the left-right axis of the cell. As this unique property attracts increasing attention due to its important roles in both development and disease, a standardized quantification method for characterizing cell chirality would advance research and potential applications. In this protocol, we describe a multicellular chirality characterization assay that utilizes micropatterned arrays of cells. Cellular micropatterns are fabricated on titanium/gold-coated glass slides via microcontact printing. After seeding on the geometrically defined (e.g., ring-shaped), protein-coated islands, cells directionally migrate and form a biased alignment toward either the clockwise or the counterclockwise direction, which can be automatically analyzed and quantified by a custom-written MATLAB program. Here we describe in detail the fabrication of micropatterned substrates, cell seeding, image collection, and data analysis and show representative results obtained using the NIH/3T3 cells. This protocol has previously been validated in multiple published studies and is an efficient and reliable tool for studying cell chirality in vitro.

We present a protocol for determining multicellular chirality in vitro, using the micropatterning technique. This assay allows for automatic quantification of the left-right biases of various types of cells and can be used for screening purposes.

Chirality is an intrinsic cellular property, which depicts the asymmetry in terms of polarization along the left-right axis of the cell. As this unique ...

Gelatin Methacryloyl Granular Hydrogel Scaffolds: High-throughput Microgel Fabrication, Lyophilization, Chemical Assembly, and 3D Bioprinting

The emergence of granular hydrogel scaffolds (GHS), fabricated via assembling hydrogel microparticles (HMPs), has enabled microporous scaffold formation in situ. Unlike conventional bulk hydrogels, interconnected microscale pores in GHS facilitate degradation-independent cell infiltration as well as oxygen, nutrient, and cellular byproduct transfer. Methacryloyl-modified gelatin (GelMA), a (photo)chemically crosslinkable, protein-based biopolymer containing cell adhesive and biodegradable moieties, has widely been used as a cell-responsive/instructive biomaterial. Converting bulk GelMA to GHS&#160;may open a plethora of opportunities for tissue engineering and regeneration. In this article, we demonstrate the procedures of high-throughput GelMA microgel fabrication, conversion to resuspendable dry microgels (micro-aerogels), GHS formation via the chemical assembly of microgels, and granular bioink fabrication for extrusion bioprinting. We show how a sequential physicochemical treatment via cooling and photocrosslinking enables the formation of mechanically robust GHS.&#160;When light is inaccessible (e.g., during deep tissue injection), individually crosslinked GelMA HMPs may be bioorthogonally assembled via enzymatic crosslinking using transglutaminases. Finally, three-dimensional (3D) bioprinting of microporous GHS&#160;at low HMP packing density is demonstrated via the interfacial self-assembly of heterogeneously charged nanoparticles.

This article describes protocols for high-throughput gelatin methacryloyl microgel fabrication using microfluidic devices, converting microgels to resuspendable powder (micro-aerogels), the chemical assembly of microgels to form granular hydrogel scaffolds, and developing granular hydrogel bioinks with preserved microporosity for 3D bioprinting.

The emergence of granular hydrogel scaffolds (GHS), fabricated via assembling hydrogel microparticles (HMPs), has enabled microporous scaffold formation ...