This work was supported by grants from the Ministry of Education Innovation Team Development Program of China (No. IRT1279).

The protocol was carried out in accordance with the Guidelines for the Care and Use of Laboratory Animals and was approved by the Committee on the Ethics of Animal Experiments of Xi&#39;an Jiaotong University, Xi&#39;an, Shaanxi Province, China.
1. Preparation prior to the training
NOTE: The vascular reconstruction training machine is shown in Figure 1. It consists of a control panel and an operating floor.
<ol>
	<li>Click the Clean button on the control panel to clean and drain the residual liquid from the operating floor.</li>
	<li>Click the Add Liquid button on the control panel and add 0.9% saline into the machine from the operating floor until the prompt &#34;The testing liquid is adequate&#34; appears on the control panel.</li>
	<li>Prepare the magnetic tractor, which consists of a circular permanent magnet with a diameter of 20 mm and a thickness of 1 mm, an acrylonitrile butadiene styrene (ABS) plastic casing, a spiral spring, a 30 cm nylon traction wire, and a stainless-steel clamp with plastic sleeves or a vascular clamp.
	<ol>
		<li>Glue the circular magnet and the plastic casing together using an acrylate adhesive. The traction force will increase with the lengthening of the traction wire. Use a universal testing machine to test the association between the length of the traction wire and the traction force (Figure 2).</li>
		<li>Fix the clamp and the plastic casing on the upper holder and the lower holder of the universal testing machine, respectively. Gradually elevate the upper holder to stretch the traction wire between the two holders. Test the strength of the traction wire while it is being stretched. 
		NOTE: The magnetic suture tractor and magnetic vascular tractor are shown in Figure 3.</li>
	</ol>
	</li>
	<li>Prepare a magnetic suture puller.
	<ol>
		<li>Use a quasi-oval polylactic acid board with a thickness of 2 mm, a major axis diameter of 10 cm, a minor axis diameter of 2 cm, three magnetic balls with a diameter of 5 mm, and three magnetic cylinders with a diameter of 5 mm and a height of 5 mm.</li>
		<li>Punch three holes with a diameter of 3 mm and a depth of 0.5 mm on the polylactic acid board, so that the magnetic balls can cling to the board by magnetic attraction force from the magnetic cylinders under the board. 
		NOTE: The magnetic suture puller is shown in Figure 4.</li>
	</ol>
	</li>
	<li>Fix the suture under the magnetic ball after one stitch. This plays the role of a suture puller, preventing the previous suture from loosening. Extract the end with the suture needle with a force of about 0.3 N, closely in parallel to the polylactic acid board, and continue the next stitch.</li>
	<li>Ligate all the vein branches using 3-0 silk sutures to avoid leakage after anastomosis. Use tissue scissors to trim the ends of the veins and clear the excess tissue on the wall of the veins to make the veins smooth. 
	NOTE: The vasculature used in this study included the right and left iliac veins (diameter ~10 mm) harvested from Bama pigs weighing 50&#8211;60 kg. To simplify the reconstruction, only a few branches of the iliac veins were picked, and the two veins were similar in size. The vasculature was kept at -20 &#176;C. Before training, it was immersed in 0.9% saline at room temperature.</li>
</ol>
2. Fix the veins on the operating floor
<ol>
	<li>Tie the two veins on the water inlet and water outlet of the training machine with 2-0 silk sutures. 
	NOTE: This study uses the two-point vascular anastomosis5.</li>
	<li>Adjust the length of the water outlet of the training machine and ensure that the ends of the two veins are tension-free in a parallel direction.</li>
	<li>Straighten the veins and lay two 4-0 polypropylene traction sutures at the 6 o&#8217;clock and 12 o&#8217;clock positions.</li>
	<li>Insert the needle of the traction sutures from the outside of the vein and then insert from the inside of the other vein.</li>
	<li>Wet the surgical glove and sutures to avoid damaging the sutures. Gently tie at least five knots to avoid tearing the walls of the veins.</li>
	<li>Use the two stainless-steel clamps of the magnetic suture tractor to grasp the traction sutures and attract the circular magnets of the magnetic suture tractors to the ferromagnetic stainless-steel operating floor. Adjust the position of magnetic attraction and ensure that the ends of the two veins are stretched in a vertical direction.</li>
	<li>Use the two vascular clamps of the magnetic vascular tractor to clamp the anterior wall of the veins and attract the circular magnets of the magnetic vascular tractors on the operating floor. Adjust the position of attraction and ensure that the anterior walls of the veins are retracted, and the posterior walls of the veins are clearly exposed.</li>
</ol>
3. Anastomosis of posterior walls
<ol>
	<li>Use the two stainless-steel clamps of the magnetic suture tractor to grasp the traction sutures and attract the circular magnets of the magnetic suture tractors on the ferromagnetic stainless-steel operating floor. Leave the tail segment of the polypropylene suture at the 12 o&#8217;clock position for the traction suture and use the segment with the needle for continuous suture.</li>
	<li>Ensure intima-to-intima contact between the two veins.</li>
	<li>Insert the first suture from the outside of the vein to the inside.</li>
	<li>In subsequent sutures, insert the needle from the inside of the vein and then insert from the outside of the other vein.</li>
	<li>Check that the sutures are not loose.</li>
	<li>After one suture, ensure that the polypropylene suture is hung on the magnetic suture puller and pull the polypropylene gently until the magnetic ball presses the polypropylene.</li>
	<li>Extract the end with the needle of the suture with a force of about 0.3 N, closely in parallel to the polylactic acid board, and continue the next stitch. 
	NOTE: By using this technique, the tail of the polypropylene suture will be sufficiently tight. As the sutures continue, the polypropylene suture will become shorter. According to the length of the suture, select the most suitable of the three magnetic balls, and then manually press the suture under it.</li>
	<li>Insert the last suture from the inside of the vein to the outside to ensure intima-to-intima contact between the two veins.</li>
	<li>Avoid stenosis after anastomosis by two means: Keep same, proper margin and needle spacing when stitching, and keep the &#34;growth factor&#34;15 when knotting. 
	NOTE: The &#34;growth factor&#34; is the reserved space away from the vessel wall when tying the first knot after the anastomosis so that vessels can remain flexible rather than stenose.
	<ol>
		<li>Maintain the same suture margin and needle spacing. 
		NOTE: In this study, iliac veins with a diameter of approximately 10 mm were used, so the suture margin and needle spacing was about 1 mm.</li>
		<li>Keep the &#34;growth factor&#34;15 when tying the knots. After anastomosis of the posterior walls, tie the end of the suture and the tail segment of the suture at the 6 o&#8217;clock position together away from the vein wall in order to prevent suture stenosis. Use the standard method for tying knots.</li>
	</ol>
	</li>
</ol>
4. Anastomosis of anterior walls
<ol>
	<li>After anastomosis of the posterior walls, remove the magnetic vascular tractor, leave the tail as a traction suture, and use the segment with the needle at the 6 o&#8217;clock position for the anastomosis of the anterior walls.</li>
	<li>Insert the needle from the outside of the vein and then insert from the inside of the other vein. 
	NOTE: The methods used in the anastomosis of the posterior walls to ensure the intima-to-intima contact between the two veins (the suture not being loose and avoiding stenosis after anastomosis) were followed in the anastomosis of the anterior walls5,15.</li>
	<li>After anastomosis of the anterior walls, cut off two traction sutures using suture scissors.</li>
</ol>
5. Test the effect of anastomosis
<ol>
	<li>Set the test parameters.
	<ol>
		<li>Set the perfusion pressure as 2.0 kPa on the control panel. 
		NOTE: The normal vein pressure will not exceed 2.0 kPa.</li>
		<li>Set the duration of peak pressure as 5 s on the control panel.</li>
		<li>Set the temperature as 25 &#176;C on the control panel.</li>
		<li>Set the pressure deviation as 0.1 kPa on the control panel.</li>
	</ol>
	</li>
	<li>Click the Test button and observe the time and pressure on the control panel and whether the reconstructed vein leaks. 
	NOTE: If the vein does not leak during the peak pressure, the anastomosis is successful. If leaks are found, the leakage position should be located and sutured, and then the test should be performed again. The results of the test in this video are shown in Figure 5.</li>
</ol>
6. Checking the safety of the magnetic suture puller
NOTE: To test whether the magnetic suture puller damaged the polypropylene suture, perform the breaking strength and light microscopy tests. In this experiment, three groups with six segments of 4-0 polypropylene suture in each were tested: a control group with no intervention on the polypropylene suture, a manual group in which the polypropylene suture was manually pulled with sterile gloves 20x, and a magnetic puller group in which the magnetic puller pulled the polypropylene suture 20x.
<ol>
	<li>Test the breaking strength of the polypropylene suture on the universal testing machine. Fix the two ends of the polypropylene suture on the upper holder and the lower holder of the universal testing machine. Gradually elevate the upper holder. Test the strength of the polypropylene suture while it is being stretched. Set the breaking strength as the tension force when the suture snaps. Compare the breaking strength among the three groups and perform pairwise comparisons.</li>
	<li>Observe the damage of the polypropylene suture under a light microscope. Define the number of damage points as the number of fibrous or coarse fracture points visible at 200x magnification. Compare the number of damage points among the three groups and perform pairwise comparisons.</li>
</ol>

<ol><li>Obora, Y., Tamaki, N., Matsumoto, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Nonsuture+microvascular+anastomosis+using+magnet+rings%3A+preliminary+report%5BTitle%5D)+AND+%22Surgical+Neurology%22%5BJournal%5D)">Nonsuture microvascular anastomosis using magnet rings: preliminary report.</a> Surgical Neurology. 9 (2), 117-120 (1978).</li>
<li>Holt, G. P., Lewis, F. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+new+technique+for+end-to-end+anastomosis+of+small+arteries%5BTitle%5D)+AND+%22Surgical+Forum%22%5BJournal%5D)">A new technique for end-to-end anastomosis of small arteries.</a> Surgical Forum. 11, 242-243 (1960).</li>
<li>Enzmann, F. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Trans-Iliac+Bypass+Grafting+for+Vascular+Groin+Complications%5BTitle%5D)+AND+%22European+Journal+of+Vascular+and+Endovascular%22%5BJournal%5D)">Trans-Iliac Bypass Grafting for Vascular Groin Complications.</a> European Journal of Vascular and Endovascular. , 1-6 (2019).</li>
<li>Bala, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Acute+mesenteric+ischemia%3A+Guidelines+of+the+World+Society+of+Emergency+Surgery%5BTitle%5D)+AND+%22World+Journal+of+Emergency+Surgery%22%5BJournal%5D)">Acute mesenteric ischemia: Guidelines of the World Society of Emergency Surgery.</a> World Journal of Emergency Surgery. 12 (1), 1-11 (2017).</li>
<li>Makowka, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Surgical+Technique+of+Orthotopic+Liver+Transplantation%5BTitle%5D)+AND+%22Gastroenterology+Clinics+of+North+America%22%5BJournal%5D)">Surgical Technique of Orthotopic Liver Transplantation.</a> Gastroenterology Clinics of North America. 17 (1), 33-51 (1998).</li>
<li>Tang, A. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+elimination+of+anastomosis+in+open+trauma+vascular+reconstruction%3A+A+novel+technique+using+an+animal+model%5BTitle%5D)+AND+%22Journal+of+Trauma+and+Acute+Care+Surgery%22%5BJournal%5D)">The elimination of anastomosis in open trauma vascular reconstruction: A novel technique using an animal model.</a> Journal of Trauma and Acute Care Surgery. 79 (6), 937-942 (2015).</li>
<li>Rivas, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Magnetic+Surgery%3A+Results+from+First+Prospective+Clinical+Trial+in+50+Patients%5BTitle%5D)+AND+%22Annals+of+Surgery%22%5BJournal%5D)">Magnetic Surgery: Results from First Prospective Clinical Trial in 50 Patients.</a> Annals of Surgery. 267 (1), 88-93 (2018).</li>
<li>Arain, N. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Magnetically+Anchored+Cautery+Dissector+Improves+Triangulation%2C+Depth+Perception%2C+and+Workload+During+Single-Site+Laparoscopic+Cholecystectomy%5BTitle%5D)+AND+%22Journal+of+Gastrointestinal+Surgery%22%5BJournal%5D)">Magnetically Anchored Cautery Dissector Improves Triangulation, Depth Perception, and Workload During Single-Site Laparoscopic Cholecystectomy.</a> Journal of Gastrointestinal Surgery. 16 (9), 1807-1813 (2012).</li>
<li>Mortagy, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Magnetic+anchor+guidance+for+endoscopic+submucosal+dissection+and+other+endoscopic+procedures%5BTitle%5D)+AND+%22World+Journal+of+Gastroenterology%22%5BJournal%5D)">Magnetic anchor guidance for endoscopic submucosal dissection and other endoscopic procedures.</a> World Journal of Gastroenterology. 23 (16), 2883-2890 (2017).</li>
<li>Cho, Y. B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Transvaginal+endoscopic+cholecystectomy+using+a+simple+magnetic+traction+system%5BTitle%5D)+AND+%22Minimally+Invasive+Therapy+and+Allied+Technologies%22%5BJournal%5D)">Transvaginal endoscopic cholecystectomy using a simple magnetic traction system.</a> Minimally Invasive Therapy and Allied Technologies. 20 (3), 174-178 (2011).</li>
<li>Dong, D. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Miniature+magnetically+anchored+and+controlled+camera+system+for+trocar-less+laparoscopy%5BTitle%5D)+AND+%22World+Journal+of+Gastroenterology%22%5BJournal%5D)">Miniature magnetically anchored and controlled camera system for trocar-less laparoscopy.</a> World Journal of Gastroenterology. 23 (12), 2168-2174 (2017).</li>
<li>Shimizu, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Moist-condition+training+for+cerebrovascular+anastomosis%3A+A+practical+step+after+mastering+basic+manipulations%5BTitle%5D)+AND+%22Neurologia+Medico-Chirurgica%22%5BJournal%5D)">Moist-condition training for cerebrovascular anastomosis: A practical step after mastering basic manipulations.</a> Neurologia Medico-Chirurgica. 55 (8), 689-692 (2015).</li>
<li>Maluf, M. A., Massarico, A., Nova, T. V., Lupp, A., Cardoso, C., Gomes, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Cardiovascular+Surgery+Residency+Program%3A+Training+Coronary+Anastomosis+Using+the+Arroyo+Simulator+and+UNIFESP+Models%5BTitle%5D)+AND+%22Revista+Brasileira+de+Cirurgia+Cardiovascular%22%5BJournal%5D)">Cardiovascular Surgery Residency Program: Training Coronary Anastomosis Using the Arroyo Simulator and UNIFESP Models.</a> Revista Brasileira de Cirurgia Cardiovascular. 30 (5), 562-570 (2015).</li>
<li>Bismuth, J., Duran, C., Donovan, M., Davies, M. G., Lumsden, A. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+Cardiovascular+Fellows+Bootcamp%5BTitle%5D)+AND+%22Journal+of+vascular+surgery%22%5BJournal%5D)">The Cardiovascular Fellows Bootcamp.</a> Journal of vascular surgery. 56 (4), 1155-1161 (2012).</li>
<li>Starzl, T. E., Iwatsuki, S., Shaw, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+Growth+Factor+in+Fine+Vascular+Anastomoses%5BTitle%5D)+AND+%22Surgery+Gynecology+And+Obstetrics%22%5BJournal%5D)">A Growth Factor in Fine Vascular Anastomoses.</a> Surgery Gynecology And Obstetrics. 159 (2), 164-165 (1984).</li>
</ol>

The authors have nothing to disclose.

With the help of magnetic tractors and a magnetic suture puller, a trainee can complete vein anastomosis individually and precisely. Magnetic tractors pull the tissue that blocks the anastomosis field and provide suitable strength for stretching the veins in a vertical direction, thus achieving clear exposure for vein anastomosis. In traditional manual anastomosis, at least one assistant is required for surgical exposure. The use of magnetic tractors could achieve the required exposure and substitute for assistants. In a...

Vascular reconstruction is a basic skill required for surgeons. Although Obora1 and Holt2 invented several mechanical reconstruction methods to simplify the reconstruction of small vessels (diameters &#60;10 mm), these methods are not commonly applied in macrovascular anastomosis. Manual vascular anastomosis is still performed in many operations, including vascular surgery3, emergency surgery4, and solid organ transplantation5. Thus, it is essential for surgeons to practice manual vascular anastomosis. However, an optimal training system for vascular reconstruction in vitro is uncommon, and inexperienced surgeons must undergo considerable training in vivo on large animals6 before they can master the technique. Because failure is inevitable during initial training, many animals are likely to die of vascular complications, which is concerning regarding animal welfare. Further, during the procedure of end-to-end vascular reconstruction, to avoid mistakes in stitch positions or loose sutures, the surgeon needs at least one assistant to expose the posterior vascular wall and pull the suture. Thus, vascular reconstruction usually cannot be performed by the surgeon individually, and the efficiency of preparation is usually limited by the proficiency of the assistant.
Magnetic anchoring surgery has become a topic of interest in recent years7,8,9,10,11. The clinical trial by Rivas et al.7 showed that with his magnetic surgical instrument and following the principle of magnetic anchoring, surgeons can perform reduced-port laparoscopic cholecystectomy. The use of this instrument also allows for a reduced role for the assistant during open surgery. Through the magnetic field, the magnetic device is adsorbed onto an anchoring point. This magnetic anchoring device can act as a mechanical arm, grasping and retracting the tissue or organ, exposing the surgical field, and simplifying the operation. Based on this rationale, we invented magnetic tractors to retract the vascular wall and suture, and a magnetic suture puller to pull the polypropylene sutures.
The use of a vascular reconstruction training machine was another milestone in this study. It consists of an operating floor and a control panel: the vasculature is fixed on the operating floor, and the trainee can practice on it. After anastomosis, the trainee can set the perfusion parameters on the control panel in order to test the quality of anastomosis. Compared to previous vascular anastomosis training systems6,12,13,14, the use of this system provides two main advantages: First, magnetic devices can be used to expose the surgical field, so that the trainees can practice on it individually. Second, the trainee can check the effect of anastomosis using a perfusion test.
In the present study, we introduce a training and testing system where the trainee can complete manual vascular reconstruction in vitro individually using a magnetic anchoring technique and the quality of reconstruction can also be tested. Limited by the design and size of the water inlet and water outlet on the operating floor, the training system can only perform end-to-end reconstruction on vessels with a &#62;5 mm diameter.

<table><tbody><tr><td>Circular permanent magnet</td><td>Hangzhou Permanent Magnet Group Co.LTD</td><td>20*1mm</td><td>Magnetic tractor</td></tr><tr><td>Magnetic balls</td><td>Hangzhou Permanent Magnet Group Co.LTD</td><td>5mm</td><td>Magnetic suture puller</td></tr><tr><td>Magnetic cylinders</td><td>Hangzhou Permanent Magnet Group Co.LTD</td><td>5*5mm</td><td>Magnetic suture puller</td></tr><tr><td>Polypropylene suture</td><td>Johnson and Johnson</td><td>PROLENE 4-0</td><td>Used for anastomosis</td></tr><tr><td>Silk suture</td><td>SILK</td><td>2-0?3-0</td><td>Used for fixing vascular and ligation</td></tr><tr><td>Surgical insturments</td><td>Jinzhong Shanghai</td><td>JZ-2018</td><td>Suture scissors, tissue scissors? forceps, needle and needle holder</td></tr><tr><td>Universal testing machine</td><td>Zwick GmbH&amp;amp;Co</td><td>Z010</td><td>Used for testing the association between the length of traction wire and the traction force</td></tr></tbody></table>

a training and testing system for performing vascular reconstruction in vitro

Manual vascular reconstruction training is essential for a beginner surgeon. However, an optimal training system for vascular reconstruction in vitro has yet to be developed. In this study, we introduce an in vitro training and testing system using a magnetic anchoring technique with which a trainee can practice manual vascular reconstruction individually. Additionally, this system can also be used to test the quality of the reconstruction. The described system includes a vascular reconstruction training machine, magnetic tractors, and a magnetic suture puller. In this manuscript, we detail an end-to-end vein anastomosis using porcine right and left iliac veins. To identify the potential damage caused by a magnetic suture puller on the suture, we created three groups with six segments of 4-0 polypropylene sutures each: a control group with no intervention on the polypropylene suture, a group in which the polypropylene suture is manually pulled with sterile gloves 20x, and a magnetic puller group in which the magnetic puller pulled the polypropylene suture 20x. These groups were tested by light microscopy and breaking strength tests, and the effect of reconstruction was assessed. In the light microscopy test, the control group was less likely to be damaged (p &#60; 0.05) and the number of damaged points of the manual group and magnetic puller group were similar (p &#62; 0.05). The results of the breaking strength test were compared across groups and no significant difference was observed (p &#62; 0.05). The end-to-end anastomosis of the porcine iliac veins was successfully performed using this training system, and the reconstructed veins could undergo 2.0 kPa perfusion pressure. Using this training and testing system the trainee can practice manual vascular reconstruction in vitro individually with the aid of magnetic tractors and a magnetic suture puller, and the quality of the reconstruction can be tested.

The vascular reconstruction training machine is shown in Figure 1 and includes two main parts: the operating floor and the control panel. The operating floor consists of a water inlet, a water outlet, and a water storage basin. The two ends of the vasculature are tied to the water inlet and water outlet to test the effect of anastomosis. The length of the water outlet is adjustable, and we set the parameters (e.g., the perfusion pressure, duration of peak pressure, temperature, and pressure ...

Watch this Scientific Journal Video about A Training and Testing System for Performing Vascular Reconstruction In Vitro at JoVE.com

A Training and Testing System for Performing Vascular Reconstruction In Vitro

Here we present a training and testing system where a trainee can complete manual vascular reconstruction in vitro individually using a magnetic anchoring technique. The system can also be used to test the quality of reconstruction.

Manual vascular reconstruction training is essential for a beginner surgeon. However, an optimal training system for vascular reconstruction in vitro has ...

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JoVE Journal

Medicine

7.9K Views.  First Affiliated Hospital of Xi'an Jiaotong University. Here we present a training and testing system where a trainee can complete manual vascular reconstruction in vitro individually using a magnetic anchoring technique. The system can also be used to test the quality of reconstruction.

Video: A Training and Testing System for Performing Vascular Reconstruction In Vitro

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 ...

Bioengineering

Tissue Engineering of a Human 3D in vitro Tumor Test System

Cancer is one of the leading causes of death worldwide. Current therapeutic strategies are predominantly developed in 2D culture systems, which inadequately reflect physiological conditions in vivo. Biological 3D matrices provide cells an environment in which cells can self-organize, allowing the study of tissue organization and cell differentiation. Such scaffolds can be seeded with a mixture of different cell types to study direct 3D cell-cell-interactions. To mimic the 3D complexity of cancer tumors, our group has developed a 3D in vitro tumor test system.	
	Our 3D tissue test system models the in vivo situation of malignant peripheral nerve sheath tumors (MPNSTs), which we established with our decellularized porcine jejunal segment derived biological vascularized scaffold (BioVaSc). In our model, we reseeded a modified BioVaSc matrix with primary fibroblasts, microvascular endothelial cells (mvECs) and the S462 tumor cell line. For static culture, the vascular structure of the BioVaSc is removed and the remaining scaffold is cut open on one side (Small Intestinal Submucosa SIS-Muc). The resulting matrix is then fixed between two metal rings (cell crowns).	
	Another option is to culture the cell-seeded SIS-Muc in a flow bioreactor system that exposes the cells to shear stress. Here, the bioreactor is connected to a peristaltic pump in a self-constructed incubator. A computer regulates the arterial oxygen and nutrient supply via parameters such as blood pressure, temperature, and flow rate. This setup allows for a dynamic culture with either pressure-regulated pulsatile or constant flow.	
	In this study, we could successfully establish both a static and dynamic 3D culture system for MPNSTs. The ability to model cancer tumors in a more natural 3D environment will enable the discovery, testing, and validation of future pharmaceuticals in a human-like model.

Tissue Engineering of a Human 3D in vitro Tumor Test System

Methods to create human 3D tumor tissues as test systems are described. These technologies are based on a decellularized Biological Vascularized Scaffold (BioVaSc), primary human cells and a tumor cell line, which can be cultured under static as well as under dynamic conditions in a flow bioreactor.

Cancer is one of the leading causes of death worldwide.  Current therapeutic strategies are predominantly developed in 2D culture  systems, which ...

A Full Skin Defect Model to Evaluate Vascularization of Biomaterials In Vivo

Insufficient vascularization is considered to be one of the main factors limiting the clinical success of tissue-engineered constructs. In order to evaluate new strategies that aim at improving vascularization, reliable methods are required to make the in-growth of new blood vessels into bio-artificial scaffolds visible and quantify the results. Over the past couple of years, our group has introduced a full skin defect model that enables the direct visualization of blood vessels by transillumination and provides the possibility of quantification through digital segmentation. In this model, one surgically creates full skin defects in the back of mice and replaces them with the material tested. Molecules or cells of interest can also be incorporated in such materials to study their potential effect. After an observation time of one&#8217;s own choice, materials are explanted for evaluation. Bilateral wounds provide the possibility of making internal comparisons that minimize artifacts among individuals as well as of decreasing the number of animals needed for the study. In comparison to other approaches, our method offers a simple, reliable and cost effective analysis. We have implemented this model as a routine tool to perform high-resolution screening when testing vascularization of different biomaterials and bio-activation approaches.

A Full Skin Defect Model to Evaluate Vascularization of Biomaterials In Vivo

Vascularization is key to approaches in successful tissue engineering. Therefore, reliable technologies are required to evaluate the development of vascular networks in tissue-constructs. Here we present a simple and cost-effective method to visualize and quantify vascularization in vivo.

Insufficient vascularization is considered to be one of the main factors limiting the clinical success of tissue-engineered constructs. In order to ...

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 ...

Generation and Grafting of Tissue-engineered Vessels in a Mouse Model

The construction of vascular conduits is a fundamental strategy for surgical repair of damaged and injured vessels resulting from cardiovascular diseases. The current protocol presents an efficient and reproducible strategy in which functional tissue engineered vessel grafts can be generated using partially induced pluripotent stem cell (PiPSC) from human fibroblasts. We designed a decellularized vessel scaffold bioreactor, which closely mimics the matrix protein structure and blood flow that exists within a native vessel, for seeding of PiPSC-endothelial cells or smooth muscle cells prior to grafting into mice. This approach was demonstrated to be advantageous because immune-deficient mice engrafted with the PiPSC-derived grafts presented with markedly increased survival rate 3 weeks after surgery. This protocol represents a valuable tool for regenerative medicine, tissue engineering and potentially patient-specific cell-therapy in the near future.

Here, we present a protocol to generate tissue engineered vessel grafts that are functional for grafting into mice by double seeding partially induced pluripotent stem cell (PiPSC) - derived smooth muscle cells and PiPSC - derived endothelial cells on a decellularized vessel scaffold bioreactor.

The construction of vascular conduits is a fundamental strategy for surgical repair of damaged and injured vessels resulting from cardiovascular diseases. ...

Tissue Engineering by Intrinsic Vascularization in an In Vivo Tissue Engineering Chamber

In reconstructive surgery, there is a clinical need for an alternative to the current methods of autologous reconstruction which are complex, costly and trade one defect for another. Tissue engineering holds the promise to address this increasing demand. However, most tissue engineering strategies fail to generate stable and functional tissue substitutes because of poor vascularization. This paper focuses on an in vivo tissue engineering chamber model of intrinsic vascularization where a perfused artery and a vein either as an arteriovenous loop or a flow-through pedicle configuration is directed inside a protected hollow chamber. In this chamber-based system angiogenic sprouting occurs from the arteriovenous vessels and this system attracts ischemic and inflammatory driven endogenous cell migration which gradually fills the chamber space with fibro-vascular tissue. Exogenous cell/matrix implantation at the time of chamber construction enhances cell survival and determines specificity of the engineered tissues which develop. Our studies have shown that this chamber model can successfully generate different tissues such as fat, cardiac muscle, liver and others. However, modifications and refinements are required to ensure target tissue formation is consistent and reproducible. This article describes a standardized protocol for the fabrication of two different vascularized tissue engineering chamber models in vivo.

Tissue Engineering by Intrinsic Vascularization in an In Vivo Tissue Engineering Chamber

This is a guideline for constructing in vivo vascularized tissue using a microsurgical arteriovenous loop or a flow-through pedicle configuration inside a tissue engineering chamber. The vascularized tissues generated can be employed for organ regeneration and replacement of tissue defects, as well as for drug testing and disease modeling.

In reconstructive surgery, there is a clinical need for an alternative to the current methods of autologous reconstruction which are complex, costly and ...

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.

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 Arteriovenous (AV) Loop in a Small Animal Model to Study Angiogenesis and Vascularized Tissue Engineering

A functional blood vessel network is a prerequisite for the survival and growth of almost all tissues and organs in the human body. Moreover, in pathological situations such as cancer, vascularization plays a leading role in disease progression. Consequently, there is a strong need for a standardized and well-characterized in vivo model in order to elucidate the mechanisms of neovascularization and develop different vascularization approaches for tissue engineering and regenerative medicine.
We describe a microsurgical approach for a small animal model for induction of a vascular axis consisting of a vein and artery that are anastomosed to an arteriovenous (AV) loop. The AV loop is transferred to an enclosed implantation chamber to create an isolated microenvironment in vivo, which is connected to the living organism only by means of the vascular axis. Using 3D imaging (MRI, micro-CT) and immunohistology, the growing vasculature can be visualized over time. By implanting different cells, growth factors and matrices, their function in blood vessel network formation can be analyzed without any disturbing influences from the surroundings in a well controllable environment. 
In addition to angiogenesis and antiangiogenesis studies, the AV loop model is also perfectly suited for engineering vascularized tissues. After a certain prevascularization time, the generated tissues can be transplanted into the defect site and microsurgically connected to the local vessels, thereby ensuring immediate blood supply and integration of the engineered tissue. By varying the matrices, cells, growth factors and chamber architecture, it is possible to generate various tissues, which can then be tailored to the individual patient's needs.

The Arteriovenous AV Loop in a Small Animal Model to Study Angiogenesis and Vascularized Tissue Engineering

We describe a microsurgical approach for the generation of an arteriovenous (AV) loop as a model for analyzing vascularization in vivo in an isolated and well-characterized environment. This model is not only useful for the investigation of angiogenesis, but is also optimally suited for engineering axially vascularized and transplantable tissues.

A functional blood vessel network is a prerequisite for the survival and growth of almost all tissues and organs in the human body. Moreover, in ...

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.

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, ...

Stepwise Cell Seeding on Tessellated Scaffolds to Study Sprouting Blood Vessels

The cardiovascular system is a key player in human physiology, providing nourishment to most tissues in the body; vessels are present in different sizes, structures, phenotypes, and performance depending on each specific perfused tissue. The field of tissue engineering, which aims to repair or replace damaged or missing body tissues, relies on controlled angiogenesis to create a proper vascularization within the engineered tissues. Without a vascular system, thick engineered constructs cannot be sufficiently nourished, which may result in cell death, poor engraftment, and ultimately failure. Thus, understanding and controlling the behavior of engineered blood vessels is an outstanding challenge in the field. This work presents a high-throughput system that allows for the creation of organized and repeatable vessel networks for studying vessel behavior in a 3D scaffold environment. This two-step seeding protocol shows that vessels within the system react to the scaffold topography, presenting distinctive sprouting behaviors depending on the compartment geometry in which the vessels reside. The obtained results and understanding from this high throughput system can be applied in order to inform better 3D bioprinted scaffold construct designs, wherein fabrication of various 3D geometries cannot be rapidly assessed when using 3D printing as the basis for cellularized biological environments. Furthermore, the understanding from this high throughput system may be utilized for the improvement of rapid drug screening, the rapid development of co-cultures models, and the investigation of mechanical stimuli on blood vessel formation to deepen the knowledge of the vascular system.

Engineered tissues heavily rely on proper vascular networks to provide vital nutrients and gases and remove metabolic waste. In this work, a stepwise seeding protocol of endothelial cells and support cells creates highly organized vascular networks in a high-throughput platform for studying developing vessel behavior in a controlled 3D environment.

The cardiovascular system is a key player in human physiology, providing nourishment to most tissues in the body; vessels are present in different sizes, ...

A Training and Testing System for Performing Vascular Reconstruction In Vitro

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