Name: scaling of engineered vascular grafts using 3d printed guides and the ring stacking method
Uploaded: 2017-03-27T11:30:00
Description: Watch this Scientific Journal Video about Scaling of Engineered Vascular Grafts Using 3D Printed Guides and the Ring Stacking Method at JoVE.com

The authors would like to thank our fellow Lam lab colleagues Ammar Chishti and Bijal Patel for their kind assistance with some of the histology and cell culture. Funding was provided by the Wayne State University Nanomedicine Fellowship (CBP), Start-Up Funds and Cardiovascular Research Institute Seed Grant (MTL).

1. Cell Culture Preparation
<ol>
	<li>Utilize human aortic smooth muscle cells purchased commercially.</li>
	<li>Maintain cells in smooth muscle cell growth media composed of 88.6% 231 media, 0.1% each of recombinant human insulin (rH-insulin), recombinant human fibroblast growth factor (rH-FGF), recombinant human epidermal growth factor (rH-FGF), and ascorbic acid; and 5% each of fetal bovine serum (FBS) and L-glutamine; and 1% antibiotic/antimycotic. 
	NOTE: Each growth factor, FBS and L-glutamine are purchased ...

<ol>
	<li>Luciani, G. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Operative+risk+and+outcome+of+surgery+in+adults+with+congenital+valve+disease.">Operative risk and outcome of surgery in adults with congenital valve disease.</a> ASAIO J. 54 (5), 458-462 (2008).</li><li>Lawson, J. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bioengineered+human+acellular+vessels+for+dialysis+access+in+patients+with+end-stage+renal+disease:+two+phase+2+single-arm+trials.">Bioengineered human acellular vessels for dialysis access in patients with end-stage renal disease: two phase 2 single-arm trials.</a> Lancet. 14 (387), 2026-2034 (2016).</li><li>McAllister, T. N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effectiveness+of+haemodialysis+access+with+an+autologous+tissue-engineered+vascular+graft:+a+multicentre+cohort+study.">Effectiveness of haemodialysis access with an autologous tissue-engineered vascular graft: a multicentre cohort study.</a> Lancet. 373 (9673), 1440-1446 (2009).</li><li>Wystrychowski, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=First+human+use+of+an+allogeneic+tissue-engineered+vascular+graft+for+hemodialysis+access.">First human use of an allogeneic tissue-engineered vascular graft for hemodialysis access.</a> J Vasc Surg. 60 (5), 1353-1357 (2014).</li><li>Konig, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+properties+of+completely+autologous+human+tissue+engineered+blood+vessels+compared+to+human+saphenous+vein+and+mammary+artery.">Mechanical properties of completely autologous human tissue engineered blood vessels compared to human saphenous vein and mammary artery.</a> Biomaterials. 30 (8), 1542-1550 (2009).</li><li>Gui, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Construction+of+tissue-engineered+small-diameter+vascular+grafts+in+fibrin+scaffolds+in+30+days.">Construction of tissue-engineered small-diameter vascular grafts in fibrin scaffolds in 30 days.</a> Tissue Eng Part A. 20 (9-10), 1499-1507 (2014).</li><li>Sundaram, S., Echter, A., Sivarapatna, A., Qiu, C., Niklason, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Small-diameter+vascular+graft+engineered+using+human+embryonic+stem+cell-derived+mesenchymal+cells.">Small-diameter vascular graft engineered using human embryonic stem cell-derived mesenchymal cells.</a> Tissue Eng Part A. 20 (3-4), 740-750 (2014).</li><li>Quint, C., Arief, M., Muto, A., Dardik, A., Niklason, L. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Allogeneic+human+tissue-engineered+blood+vessel.">Allogeneic human tissue-engineered blood vessel.</a> J Vasc Surg. 55 (3), 790-798 (2012).</li><li>Quint, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Decellularized+tissue-engineered+blood+vessel+as+an+arterial+conduit.">Decellularized tissue-engineered blood vessel as an arterial conduit.</a> Proc Natl Acad Sci U S A. 31 (108), 9214-9219 (2011).</li><li>Dahl, S. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Readily+available+tissue-engineered+vascular+grafts.">Readily available tissue-engineered vascular grafts.</a> Sci Transl Med. 2 (68), (2011).</li><li>Syedain, Z. H., Meier, L. A., Lahti, M. T., Johnson, S. L., Tranquillo, R. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Implantation+of+completely+biological+engineered+grafts+following+decellularization+into+the+sheep+femoral+artery.">Implantation of completely biological engineered grafts following decellularization into the sheep femoral artery.</a> Tissue Eng Part A. 20 (11-12), 1726-1734 (2014).</li><li>Syedain, Z. H., Meier, L. A., Bjork, J. W., Lee, A., Tranquillo, R. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Implantable+arterial+grafts+from+human+fibroblasts+and+fibrin+using+a+multi-graft+pulsed+flow-stretch+bioreactor+with+noninvasive+strength+monitoring.">Implantable arterial grafts from human fibroblasts and fibrin using a multi-graft pulsed flow-stretch bioreactor with noninvasive strength monitoring.</a> Biomaterials. 32 (3), 714-722 (2011).</li><li>Meier, L. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Blood+outgrowth+endothelial+cells+alter+remodeling+of+completely+biological+engineered+grafts+implanted+into+the+sheep+femoral+artery.">Blood outgrowth endothelial cells alter remodeling of completely biological engineered grafts implanted into the sheep femoral artery.</a> J Cardiovasc Transl Res. 7 (2), 242-249 (2014).</li><li>Pinnock, C. B., Meier, E. M., Joshi, N. N., Wu, B., Lam, M. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Customizable+engineered+blood+vessels+using+3D+printed+inserts.">Customizable engineered blood vessels using 3D printed inserts.</a> Methods. S1046-2023 (15), 30184-30185 (2015).</li><li>Blakely, A. M., Manning, K. L., Tripathi, A., Morgan, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bio-Pick,+Place,and+Perfuse:+A+New+Instrument+for+Three-Dimensional+Tissue+Engineering.">Bio-Pick, Place,and Perfuse: A New Instrument for Three-Dimensional Tissue Engineering.</a> Tissue Eng Part C Methods. 21 (7), 737-746 (2015).</li><li>Gwyther, T. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineered+vascular+tissue+fabricated+from+aggregated+smooth+muscle+cells.">Engineered vascular tissue fabricated from aggregated smooth muscle cells.</a> Cells Tissues Organs. 194 (1), 13-24 (2011).</li><li>Fearon, W. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Changes+in+coronary+arterial+dimensions+early+after+cardiac+transplantation.">Changes in coronary arterial dimensions early after cardiac transplantation.</a> Transplantation. 27 (6), 700-705 (2007).</li><li>Erbel, R., Eggebrecht, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aortic+dimensions+and+the+risk+of+dissection.">Aortic dimensions and the risk of dissection.</a> Heart. 92 (1), 137-142 (2006).</li><li>Ha, D. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transforming+growth+factor-beta+1+produced+by+vascular+smooth+muscle+cells+predicts+fibrosis+in+the+gastrocnemius+of+patients+with+peripheral+artery+disease.">Transforming growth factor-beta 1 produced by vascular smooth muscle cells predicts fibrosis in the gastrocnemius of patients with peripheral artery disease.</a> J Transl Med. 14, 39 (2016).</li><li>Skalli, O., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Alpha-smooth+muscle+actin,+a+differentiation+marker+of+smooth+muscle+cells,+is+present+in+microfilamentous+bundles+of+pericytes.">Alpha-smooth muscle actin, a differentiation marker of smooth muscle cells, is present in microfilamentous bundles of pericytes.</a> J Histochem Cytochem. 37 (3), 315-321 (1989).</li><li>von der Ecken, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure+of+the+F-actin-tropomyosin+complex.">Structure of the F-actin-tropomyosin complex.</a> Nature. 519 (7541), 114-117 (2015).</li></ol>

The Ring Stacking Method presents multiple advantages over current vascular tissue engineered construct techniques. The RSM can be adapted to create human vessels of any size by simply customizing the post and outer shell dimensions. Our method allows for development of polymer-free engineered vessels composed solely of human cells and rapidly degrading support material found in the body&#39;s natural wound healing process. Polymer grafts are known to cause restenosis in the clinic and could become problematic if contain...

In treatment of coronary artery disease (CAD), a patient&#39;s own blood vessels are harvested as graft material for bypass surgery. However, oftentimes, ill patients do not have viable vessels to donate to themselves, and in cases where they do, the donor site causes considerable additional harm and has a serious risk for infection.1 Engineered vascular grafts could fill this need. Scalability is of utmost importance for engineering vessels in order to meet the wide range of patient vessel size requirements. However, present methods for engineering vessels are not easily scalable, and typically require remanufacture of complex molds or polymer scaffolds. Most engineered grafts either utilize a polymer tubular scaffold that is seeded with vascular fibroblasts, smooth muscle, or endothelial cells; or rolling a cell sheet around a mandrel to create a tissue tube. Two engineered vascular grafts in clinical trials are based on a decellularized polymer-ECM platform.2,3,4 Polymer grafts available for use in vascular repair are already known to have issues with patency, which could arise as a major issue with long-term application of a graft with a sustained polymer presence. Tubular molds have been used to fabricate completely cellular vessels,5,6,7,8,9,10,11,12,13 which procedures would require additional design and tool manufacturing for custom molds in order to produce vessels in a variety of sizes.
The method described herein encompasses a novel technique for creating easily scalable engineered vascular grafts using customizable 3D printed inserts and traditional culture plates.14 Cells are seeded into plates with inserts of a central post and outer shell. The post controls lumen diameter and allows the cell monolayer to self-assemble into a ring of tissue. The outer shell controls thickness of the ring, and thus wall thickness of the final vessel. Completed tissue rings are then stacked to form a tubular, vascular graft. The advantage to this method, termed the &#34;Ring Stacking Method,&#34; is that any adherent cell type can be seeded into the plate setup and tissue rings or tubes of any size needed for the desired application can be generated by simply modifying guide inserts. Comparative techniques in tissue engineering creating rings of tissue remain difficult to scale,15,16 requiring remanufacture of molds for each desired size. Additionally, vascular grafts made using this method can be produced in 2-3 weeks, several weeks faster compared to other engineered vessels.6 For the clinic, this time discrepancy can make a significant difference in the treatment of a deteriorating patient.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Human Aortic Smooth Muscle Cells&#160;</td>
			<td>ATCC</td>
			<td>PCS-100-012</td>
			<td>vascular smooth muscle cells</td>
		</tr>
		<tr>
			<td>Medium 231</td>
			<td>Gibco (Life Technologies&#160;</td>
			<td>M-231-500</td>
			<td>media specific to vascular smooth muscle cells</td>
		</tr>
		<tr>
			<td>Human Aortic Smooth Muscle Cell Growth Kit&#160;</td>
			<td>ATCC</td>
			<td>PSC-100-042</td>
			<td>growth factors for maintaining vascular smooth muscle cell viability</td>
		</tr>
		<tr>
			<td>Replicator Mini 3D printer&#160;</td>
			<td>MakerBot&#160;</td>
			<td>N/A</td>
			<td>3D printer</td>
		</tr>
		<tr>
			<td>Poly(lactic acid) 3D ink (PLA)</td>
			<td>MakerBot&#160;</td>
			<td>N/A</td>
			<td>3D printer filament</td>
		</tr>
		<tr>
			<td>Poly(dimethlysiloxane) (PDMS)</td>
			<td>Ellworth Adhesives&#160;</td>
			<td>3097358-1004</td>
			<td>polymer for gluing plate parts</td>
		</tr>
		<tr>
			<td>Fibrinogen</td>
			<td>Hyclone Labratories, Inc.</td>
			<td>SH30256.01</td>
			<td>fibrin gel component</td>
		</tr>
		<tr>
			<td>Thrombin&#160;</td>
			<td>Sigma Life Sciences</td>
			<td>F3879-5G</td>
			<td>fibrin gel component</td>
		</tr>
		<tr>
			<td>Tranforming Growth Factor-Beta 1&#160;</td>
			<td>PeproTech</td>
			<td>100-21</td>
			<td>growth factor for stimulating collagen production</td>
		</tr>
		<tr>
			<td>Hemocytometer&#160;</td>
			<td>Hausser Scientific Co.</td>
			<td>3200</td>
			<td>for cell counting</td>
		</tr>
		<tr>
			<td>Polycarbonate tubing&#160;</td>
			<td>US Plastics&#160;</td>
			<td>PCTUB1.750X1.625</td>
			<td>material for making tall, ring stacking plates</td>
		</tr>
		<tr>
			<td>Polycarbonate sheet&#160;</td>
			<td>Home Depot</td>
			<td>409497</td>
			<td>material for making tall, ring stacking plates</td>
		</tr>
		<tr>
			<td>Adhesive polymer solvent&#160;</td>
			<td>SCIGRIP</td>
			<td>10799</td>
			<td>material for making tall, ring stacking plates</td>
		</tr>
		<tr>
			<td>Instron&#160; 5940</td>
			<td>Instron</td>
			<td>N/A</td>
			<td>tensile testing machine</td>
		</tr>
		<tr>
			<td>U-Stretch</td>
			<td>Cell Scale</td>
			<td>N/A</td>
			<td>tensile testing machine</td>
		</tr>
		<tr>
			<td>Smooth Muscle Actin&#160;</td>
			<td>MA5-11547</td>
			<td>Thermo Fisher</td>
			<td>antibody</td>
		</tr>
		<tr>
			<td>Tropomyosin</td>
			<td>MA5-11783</td>
			<td>Thermo Fisher</td>
			<td>antibody</td>
		</tr>
	</tbody>
</table>

scaling of engineered vascular grafts using 3d printed guides and the ring stacking method

Coronary artery disease remains a leading cause of death, affecting millions of Americans. With the lack of autologous vascular grafts available, engineered grafts offer great potential for patient treatment. However, engineered vascular grafts are generally not easily scalable, requiring manufacture of custom molds or polymer tubes in order to customize to different sizes, constituting a time-consuming and costly practice. Human arteries range in lumen diameter from about 2.0-38 mm and in wall thickness from about 0.5-2.5 mm. We have created a method, termed the "Ring Stacking Method," in which variable size rings of tissue of the desired cell type, demonstrated here with vascular smooth muscle cells (SMCs), can be created using guides of center posts to control lumen diameter and outer shells to dictate vessel wall thickness. These tissue rings are then stacked to create a tubular construct, mimicking the natural form of a blood vessel. The vessel length can be tailored by simply stacking the number of rings required to constitute the length needed. With our technique, tissues of tubular forms, similar to a blood vessel, can be readily manufactured in a variety of dimensions and lengths to meet the needs of the clinic and patient.

Demonstrated here is fabrication of 3 different engineered vascular graft sizes (Figure 1), showing that the Ring Stacking Method (RSM) is scalable. To prove applicability, the 3 different vessel sizes chosen correlate to actual human vessel size for the left anterior descending artery (small; lumen diameter = 4 mm)17, descending aorta (intermediate; lumen diameter = 10 mm) and ascending aorta (large; lumen diameter = 20 mm)18</su...

Watch this Scientific Journal Video about Scaling of Engineered Vascular Grafts Using 3D Printed Guides and the Ring Stacking Method at JoVE.com

Scaling of Engineered Vascular Grafts Using 3D Printed Guides and the Ring Stacking Method

Scalable engineered blood vessels would improve clinical applicability. Using easily sizable 3D-printed guides, rings of vascular smooth muscle were created and stacked into a tubular form, forming a vascular graft. Grafts can be sized to meet the range of human coronary artery dimensions by simply changing the 3D-printed guide size.

Coronary artery disease remains a leading cause of death, affecting millions of Americans. With the lack of autologous vascular grafts available, ...

The overall goal of this method is to robustly and consistently generate engineered blood vessels of any size. This technique allows the reliable and effective engineering of blood vessels. The main advantage of this technique is that vessels of any size can be easily and reliably fabricated.We first had the idea for this method when we were discussing how to engineer a tube of tissue and likened our method to constructing roadway tunnels, one segment at a time. To prepare the 3D printed inserts first add a thin layer of two, four, or six mL of uncured silicone to the bottoms of a 35, 60, or 100 millimeter Petri dish, respectively. To create posts for the 35 mm plates, pour PDMS into a different 100 mm plate to a seven mm height, and heat the PDMS on a hotplate at 60 degrees Celsius for two to three hours.When the PDMS is cured, use a five mm biopsy punch to create cylindrical posts. Using a small amount of uncured PDMS to secure the cylinders to the center of each 35 mm plate. Place a 3D printed outer shell about 66.7 mm in diameter equidistant from the post in the 100 mm plates.Before the PDMS at the bottom of the 60 and 100 mm plates is cured, place 10 and 20 mm diameter 3D printed posts centrally into each 60 and 100 mm plates respectively. Allow the dishes to cure in the open air on the 60 degree Celsius hotplate for two to three hours, followed by eighteen hours of polymer degassing. At the end of the degassing, sterilize the insides of all of the plates with 70%ethanol and cover each plate for 30 minutes.Then carefully aspirate the ethanol from each plate to allow air drying. When the plates are dry transfer them to a biological safety cabinet next to their corresponding face up lids. and expose the materials to UV light for 30 minutes to complete the sterilization.To prepare the Fibrin Hydrogel first add 0.5, 1.1 and 1.81 mL of growth medium supplemented with Fibrin gel and TGF Beta 1 to 35, 60 and 100 mm culture dishes respectively. Next, add 40 88.4, and 145 microliters of Thrombin to the 35, 60, and 100 mm plates respectively, and gently swirl each plate by hand. When the Thrombin is evenly distributed add 160, 354, and 580 microliters of Fibrinogen with a drop-wise circular motion to the Thrombin medium mixture in the 35, 60, and 100 mm plates, respectively, and gently swirl the plates to evenly distribute the Hydrogel.Allow the Hydrogel to cure for 10 to 15 minutes at room temperature. Then trypsinize the smooth muscles cells of interest, expanded in 150 mm cell culture plates, and collect the detached cells by centrifugalization. Re-suspend the pellets in three ml of differentiation medium and use a two mL pipette to vigorously triturate the cells to break up any cell clumps.After counting, split the cells into 2/10 10 to the 6th, 1/10 10 to the 7th, and 1.4 x 10 to the 7th cells per mL aliquots in 50 ml conical tubes, labeled according to their corresponding culture plates. Add differentiation medium to each tube to obtain final seeding volumes of two, four, and five mL for each 35, 60 and 100 mm plate respectively Then, carefully add the cell solutions drop-wise onto the prepared Hydrogel in each corresponding plate for expansion in the cell culture incubator. After two to four days the rings will have completely contracted in towards their posts.So add 10, 20, or 35 mL of TGF Beta 1 to each 35, 60 and 100 mm ring, respectively. To assemble the vascular construct for the 35 mm vessel cut a two inch section from the top of a 50 mL of a polycarbonate conical tube And PDMS glue the top edge into a 35 mm plate to create a tall plate for ring stacking. For the 60 and 100 mm vessel tall ring stacking plates cut a 1.75 inch diameter polycarbonate tube into 2.5 inch sections length-wise to serve as the tall plate walls.For the tall plate bottoms, cut a 0.125 inch thick polycarbonate sheet into two inch diameter circle pieces. Using acrylic solvent cement bind the polycarbonate tube sections to the circular cut pieces. 3D print five, ten, and 20 mm diameter posts with a 50 mm length.Then add 10 mL of uncured silicone to each container, centrally placing each 3D printed post into each 35, 60 and 100 mm container before the PDMS is completely cured. And place the dishes on a 60 degree Celsius hotplate for two to three hours. When the PDMS is cured, sterilize the plates with 70%ethanol as just demonstrated, followed by exposure of the dried ethanol sterilized containers to UV light for 30 minutes.Now, use two pairs of very fine forceps to carefully lift first one side, and then the other, of a tightly rolled smooth muscle Hydrogel ring from its post. Then carefully slide one side of the ring and then the other onto the tall post of the corresponding next sized larger container. Working circumferentially, with gentle gradual movements, slowly push the ring down the post, subsequently stacking additional tissue rings until the desired vessel length has been obtained.When all of the rings have been stacked turn the plates so that the posts are parallel with the working surface, and gently add 40, 80, and 160 microliters of Thrombin to the outer surface of each 35, 60, and 100 mm vessel respectively while slowly rotating the plates. Next, add 40, 80, and 160 microliters of Fibrinogen to each 35, 60, and 100 mm construct respectively, as quickly and evenly as possible while briskly rotating the construct. The Thrombin and Fibrinogen will quickly set into a firm gel upon mixing.Then add 20 mL of differentiation medium to each construct container and place the vessels into a 37 degree Celsius incubator until needed. Histological analysis reveals a high cellularity in all ringed sizes, with a small amount of residual Fibrin gel observed on the outer edges of the small rings. In the larger rings some Fibrin gel is interspersed with the cellular content, with indications of collagen production apparent in both the intermediate and large rings.Tissue ring analysis for Alpha smooth muscle Actin and Tropomyosin expression reveals that all of the ring sizes are positive for both antibodies verifying that the smooth muscle phenotype was maintained. Tensile testing indicates a consistent trend of increasing strength correlating with an increasing ring and vessel size in all three sizes of rings. Cell seeding numbers for creating the various ring sizes also correlates with the seeding surface area.These vessel constructs are also able to withstand flow for up to five minutes at flow rates from 100 to 417 ml per minute with only minor leaking observed where the vessels connect to the profusion system. Once mastered, the rings can be engineered in one hour if the technique is properly performed. While attempting this procedure it's important to remember to mix the Hydrogel components thoroughly to ensure setting of the gel and proper ring formation.Following this procedure, other methods, like creating rings of other cell types, can be performed for engineering other types of tissues. After watching this video you should have a good understanding of how to use the ring stacking method to engineer vascular tissues of various sizes.

scaling-engineered-vascular-grafts-using-3d-printed-guides-ring

Research

JoVE Journal

Bioengineering

Engineering Biological-Based Vascular Grafts Using a Pulsatile Bioreactor

Much effort has been devoted to develop and advance the methodology to regenerate functional small-diameter arterial bypasses. In the physiological environment, both mechanical and chemical stimulation are required to maintain the proper development and functionality of arterial vessels1,2.
Bioreactor culture systems developed by our group are designed to support vessel regeneration within a precisely controlled chemo-mechanical environment mimicking that of native vessels. Our bioreactor assembly and maintenance procedures are fairly simple and highly repeatable3,4. Smooth muscle cells (SMCs) are seeded onto a tubular polyglycolic acid (PGA) mesh that is threaded over compliant silicone tubing and cultured in the bioreactor with or without pulsatile stimulation for up to 12 weeks. There are four main attributes that distinguish our bioreactor from some predecessors. 1) Unlike other culture systems that simulate only the biochemical surrounding of native blood vessels, our bioreactor also creates a physiological pulsatile environment by applying cyclic radial strain to the vessels in culture. 2) Multiple engineered vessels can be cultured simultaneously under different mechanical conditions within a controlled chemical environment. 3) The bioreactor allows a mono layer of endothelial cells (EC) to be easily coated onto the luminal side of engineered vessels for animal implantation models. 4) Our bioreactor can also culture engineered vessels with different diameter size ranged from 1 mm to 3 mm, saving the effort to tailor each individual bioreactor to fit a specific diameter size. 
The engineered vessels cultured in our bioreactor resemble native blood vessels histologically to some degree. Cells in the vessel walls express mature SMC contractile markers such as smooth muscle myosin heavy chain (SMMHC)3. A substantial amount of collagen is deposited within the extracellular matrix, which is responsible for ultimate mechanical strength of the engineered vessels5. Biochemical analysis also indicates that collagen content of engineered vessels is comparable to that of native arteries6. Importantly, the pulsatile bioreactor has consistently regenerated vessels that exhibit mechanical properties that permit successful implantation experiments in animal models3,7. Additionally, this bioreactor can be further modified to allow real-time assessment and tracking of collagen remodeling over time, non-invasively, using a non-linear optical microscopy (NLOM)8. To conclude, this bioreactor should serve as an excellent platform to study the fundamental mechanisms that regulate the regeneration of functional small-diameter vascular grafts.

Our group has developed a bioreactor culture system that mimics the physiological pulsatile stresses of the cardiovascular system to regenerate implantable small-diameter vascular grafts.

Much effort has been devoted to develop and advance the methodology to regenerate functional small-diameter arterial bypasses. In the physiological ...

Rapid and Low-cost Prototyping of Medical Devices Using 3D Printed Molds for Liquid Injection Molding

Biologically inert elastomers such as silicone are favorable materials for medical device fabrication, but forming and curing these elastomers using traditional liquid injection molding processes can be an expensive process due to tooling and equipment costs. As a result, it has traditionally been impractical to use liquid injection molding for low-cost, rapid prototyping applications. We have devised a method for rapid and low-cost production of liquid elastomer injection molded devices that utilizes fused deposition modeling 3D printers for mold design and a modified desiccator as an injection system. Low costs and rapid turnaround time in this technique lower the barrier to iteratively designing and prototyping complex elastomer devices. Furthermore, CAD models developed in this process can be later adapted for metal mold tooling design, enabling an easy transition to a traditional injection molding process. We have used this technique to manufacture intravaginal probes involving complex geometries, as well as overmolding over metal parts, using tools commonly available within an academic research laboratory. However, this technique can be easily adapted to create liquid injection molded devices for many other applications.

We have devised a method for low-cost and rapid prototyping of liquid elastomer rubber injection molded devices by using fused deposition modeling 3D printers for mold design and a modified desiccator as a liquid injection system.

Biologically inert elastomers such as silicone are favorable materials for medical device fabrication, but forming and curing these elastomers using ...

Surgical Technique for the Implantation of Tissue Engineered Vascular Grafts and Subsequent In Vivo Monitoring

The development of Tissue Engineered Vessels (TEVs) is advanced by the ability to routinely and effectively implant TEVs (4-5 mm in diameter) into a large animal model. A step by-step protocol for inter-positional placement of the TEV and real-time digital assessment of the TEV and native carotid arteries is described here. In vivo monitoring is made possible by the implantation of flow probes, catheters and ultrasonic crystals (capable of recording dynamic diameter changes of implanted TEVs and native carotid arteries) at the time of surgery. Once implanted, researchers can calculate arterial blood flow patterns, invasive blood pressure and artery diameter yielding parameters such as pulse wave velocity, augmentation index, pulse pressures and compliance. Data acquisition is accomplished using a single computer program for analysis throughout the duration of the experiment. Such invaluable data provides insight into TEV matrix remodeling, its resemblance to native/sham controls and overall TEV performance in vivo.

Surgical Technique for the Implantation of Tissue Engineered Vascular Grafts and Subsequent In Vivo Monitoring

A step-by-step protocol for the inter-positional placement of Tissue Engineered Vessels (TEVs) into the carotid artery of a sheep using end-to-end anastomosis and real-time digital assessment in vivo until animal sacrifice.

The development of Tissue Engineered Vessels (TEVs) is advanced by the ability to routinely and effectively implant TEVs (4-5 mm in diameter) into a large ...

Athymic Rat Model for Evaluation of Engineered Anterior Cruciate Ligament Grafts

Anterior cruciate ligament (ACL) rupture is a common ligamentous injury that often requires surgery because the ACL does not heal well without intervention. Current treatment strategies include ligament reconstruction with either autograft or allograft, which each have their associated limitations. Thus, there is interest in designing a tissue-engineered graft for use in ACL reconstruction. We describe the fabrication of an electrospun polymer graft for use in ACL tissue engineering. This polycaprolactone graft is biocompatible, biodegradable, porous, and is comprised of aligned fibers. Because an animal model is necessary to evaluate such a graft, this paper describes an intra-articular athymic rat model of ACL reconstruction that can be used to evaluate engineered grafts, including those seeded with xenogeneic cells. Representative histology and biomechanical testing results at 16 weeks postoperatively are presented, with grafts tested immediately post-implantation and contralateral native ACLs serving as controls. The present study provides a reproducible animal model with which to evaluate tissue engineered ACL grafts, and demonstrates the potential of a regenerative medicine approach to treatment of ACL rupture.

Animal models are important tools for the evaluation of tissue-engineered grafts. This paper presents the protocol for preparing an electrospun biodegradable polymer graft for use in anterior cruciate ligament tissue engineering, as well as a surgical protocol for implantation in a rat model.

Anterior cruciate ligament (ACL) rupture is a common ligamentous injury that often requires surgery because the ACL does not heal well without ...

Engineering 3D Cellularized Collagen Gels for Vascular Tissue Regeneration

Synthetic materials are known to initiate clinical complications such as inflammation, stenosis, and infections when implanted as vascular substitutes. Collagen has been extensively used for a wide range of biomedical applications and is considered a valid alternative to synthetic materials due to its inherent biocompatibility (i.e., low antigenicity, inflammation, and cytotoxic responses). However, the limited mechanical properties and the related low hand-ability of collagen gels have hampered their use as scaffold materials for vascular tissue engineering. Therefore, the rationale behind this work was first to engineer cellularized collagen gels into a tubular-shaped geometry and second to enhance smooth muscle cells driven reorganization of collagen matrix to obtain tissues stiff enough to be handled.
The strategy described here is based on the direct assembling of collagen and smooth muscle cells (construct) in a 3D cylindrical geometry with the use of a molding technique. This process requires a maturation period, during which the constructs are cultured in a bioreactor under static conditions (without applied external dynamic mechanical constraints) for 1 or 2 weeks. The &#8220;static bioreactor&#8221; provides a monitored and controlled sterile environment (pH, temperature, gas exchange, nutrient supply and waste removal) to the constructs. During culture period, thickness measurements were performed to evaluate the cells-driven remodeling of the collagen matrix, and glucose consumption and lactate production rates were measured to monitor the cells metabolic activity. Finally, mechanical and viscoelastic properties were assessed for the resulting tubular constructs. To this end, specific protocols and a focused know-how (manipulation, gripping, working in hydrated environment, and so on) were developed to characterize the engineered tissues.

In this work, we present a technique for the rapid fabrication of living vascular tissues by direct culturing of collagen, smooth muscle cells and endothelial cells. In addition, a new protocol for the mechanical characterization of engineered vascular tissues is described.

Synthetic materials are known to initiate clinical complications such as inflammation, stenosis, and infections when implanted as vascular substitutes. ...

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 ...

3D Printed Porous Cellulose Nanocomposite Hydrogel Scaffolds

This work demonstrates the use of three-dimensional (3D) printing to produce porous cubic scaffolds using cellulose nanocomposite hydrogel ink, with controlled pore structure and mechanical properties. Cellulose nanocrystals (CNCs, 69.62 wt%) based hydrogel ink with matrix (sodium alginate and gelatin) was developed and 3D printed into scaffolds with uniform and gradient pore structure (110-1,100 &#181;m). The scaffolds showed compression modulus in the range of 0.20-0.45 MPa when tested in simulated in vivo conditions (in distilled water at 37 &#176;C). The pore sizes and the compression modulus of the 3D scaffolds matched with the requirements needed for cartilage regeneration applications. This work demonstrates that the consistency of the ink can be controlled by the concentration of the precursors and porosity can be controlled by the 3D printing process and both of these factors in return defines the mechanical properties of the 3D printed porous hydrogel scaffold. This process method can therefore be used to fabricate structurally and compositionally customized scaffolds according to the specific needs of patients.&#160;

The three critical steps of this protocol are i) developing the right composition and consistency of the cellulose hydrogel ink, ii) 3D printing of scaffolds into various pore structures with good shape fidelity and dimensions and iii) demonstration of the mechanical properties in simulated body conditions for cartilage regeneration.

This work demonstrates the use of three-dimensional (3D) printing to produce porous cubic scaffolds using cellulose nanocomposite hydrogel ink, with ...

Simultaneous Quantification of Selected Kynurenines Analyzed by Liquid Chromatography-Mass Spectrometry in Medium Collected from Cancer Cell Cultures

The kynurenine pathway and the tryptophan catabolites called kynurenines have received increased attention for their involvement in immune regulation and cancer biology. An in vitro cell culture assay is often used to learn about the contribution of different tryptophan catabolites in a disease mechanism and for testing therapeutic strategies. Cell culture medium that is rich in secreted metabolites and signaling molecules reflects the status of tryptophan metabolism and other cellular events. New protocols for the reliable quantification of multiple kynurenines in the complex cell culture medium are desired to allow for a reliable and quick analysis of multiple samples. This can be accomplished with liquid chromatography coupled with mass spectrometry. This powerful technique is employed in many clinical and research laboratories for the quantification of metabolites and can be used for measuring kynurenines.
Presented here is the use of liquid chromatography coupled with single quadrupole mass spectrometry (LC-SQ) for the simultaneous determination of four kynurenines, i.e., kynurenine, 3-hydroxykynurenine, 3-hydroxyanthranilic, and xanthurenic acid in the medium collected from in vitro cultured cancer cells. SQ detector is simple to use and less expensive compared to other mass spectrometers. In the SQ-MS analysis, multiple ions from the sample are generated and separated according to their specific mass-to-charge ratio (m/z), followed by the detection using a Single Ion Monitoring (SIM) mode.
This paper draws the attention on the advantages of the reported method and indicates some weak points. It is focused on critical elements of LC-SQ analysis including sample preparation along with chromatography and mass spectrometry analysis. The quality control, method calibration conditions and matrix effect issues are also discussed. We described a simple application of 3-nitrotyrosine as one analog standard for all target analytes. As confirmed by experiments with human ovary and breast cancer cells, the proposed LC-SQ method&#160;generates reliable results and can be further applied to other in vitro cellular models.

Described here is a protocol for the determination of four different tryptophan metabolites generated in the kynurenine pathway (kynurenine, 3-hydroxykynurenine, xanthurenic acid, 3-hydroxyanthranilic acid) in the medium collected from cancer cell cultures analyzed by liquid chromatography coupled with a single quadrupole mass spectrometry.

The kynurenine pathway and the tryptophan catabolites called kynurenines have received increased attention for their involvement in immune regulation and ...

Evaluation of Left Ventricular Structure and Function using 3D Echocardiography

Three-dimensional (3D) quantification of the left ventricle (LV) provides significant added value in terms of diagnostic accuracy and precise risk stratification in various cardiac disorders. Recently, 3D echocardiography became available in routine cardiology practice; however, high-quality image acquisition and subsequent analysis have a steep learning curve. The present article aims to guide the reader through a detailed 3D protocol by presenting tips and tricks and also by highlighting the potential pitfalls to facilitate the widespread but technically sound use of this important technique concerning the LV. First and foremost, we show the acquisition of a high-quality 3D dataset with optimal spatial and temporal resolution. Then, we present the analytical steps toward a detailed quantification of the LV by using one of the most widely applied built-in software. We will quantify LV volumes, sphericity, mass and also systolic function by measuring ejection fraction and myocardial deformation (longitudinal and circumferential strain). We will discuss and provide clinical examples about the essential scenarios where the transition from a conventional echocardiographic approach to a 3D-based quantification is highly recommended.

In this article, we provide a step-by-step acquisition and analysis protocol for the volumetric assessment and speckle-tracking analysis of the left ventricle by 3D echocardiography, particularly focusing on practical aspects that maximize the feasibility of this technique.

Three-dimensional (3D) quantification of the left ventricle (LV) provides significant added value in terms of diagnostic accuracy and precise risk ...

Evaluating Regional Pulmonary Deposition using Patient-Specific 3D Printed Lung Models

Development of targeted therapies for pulmonary diseases is limited by the availability of preclinical testing methods with the ability to predict regional aerosol delivery. Leveraging 3D printing to generate patient-specific lung models, we outline the design of a high-throughput, in vitro experimental setup for quantifying lobular pulmonary deposition. This system is made with a combination of commercially available and 3D printed components and allows the flow rate through each lobe of the lung to be independently controlled. Delivery of fluorescent aerosols to each lobe is measured using fluorescence microscopy. This protocol has the potential to promote the growth of personalized medicine for respiratory diseases through its ability to model a wide range of patient demographics and disease states. Both the geometry of the 3D printed lung model and the air flow profile setting can be easily modulated to reflect clinical data for patients with varying age, race, and gender. Clinically relevant drug delivery devices, such as the endotracheal tube shown here, can be incorporated into the testing setup to more accurately predict a device&#8217;s capacity to target therapeutic delivery to a diseased region of the lung. The versatility of this experimental setup allows it to be customized to reflect a multitude of inhalation conditions, enhancing the rigor of preclinical therapeutic testing.

We present a high-throughput, in vitro method for quantifying regional pulmonary deposition at the lobe level using CT scan-derived, 3D printed lung models with tunable air flow profiles.