This work was supported by grant funding from NHMRC and Stafford Fox Medical Foundation. The authors acknowledge the surgical assistance of Sue McKay, Liliana Pepe, Anna Deftereos and Amanda Rixon of the Experimental Medical and Surgical Unit, St. Vincent&#39;s Hospital, Melbourne. Support is also provided by the Victorian State Government&#39;s Department of Innovation, Industry and Regional Development&#39;s Operational Infrastructure Support Program.

The protocols described here have been approved by the Animal Ethics Committee of St. Vincent&#39;s Hospital Melbourne, Australia, and were conducted under strict adherence to the Australian National Health and Medical Research Council Guidelines.
NOTE: Two chamber protocols are described below. The two different models and their specific chamber designs are illustrated in Figure 1. Chamber (1) is made of polycarbonate (for rat arteriovenous loop chamber model). It is cylindrical with an internal diameter 13 mm and height 4 mm. A window at one point in the wall allows unimpeded access for the pedicle. In the second model (for rat flow-through pedicle chamber model), the chamber is made of polyacrylic and is rectangular (10 x 8 x 4 mm3 internal dimensions). It has two 1.5 mm openings on opposite sides to accommodate the femoral artery and vein as they transgress the chamber.
1. Rat Arteriovenous Loop Chamber Model (One Chamber Per Animal)
NOTE: Prior to starting surgery, make sure all the instruments have been properly sterilized. Likewise, ensure the instruments rest on sterile towels and are at a reasonable distance from the surgical field to avoid contamination during the procedure.
<ol>
	<li>Preparation of the Animal for Surgery
	<ol>
		<li>Use rats weighing at least 250 g for their large size of vessels for creation of the arteriovenous loop.</li>
		<li>Anaesthetize the animal with 4% isoflurane inhalation. Corroborate adequate depth of anesthesia by assessing unresponsiveness to toe-pinch. After anesthesia, keep the animal adequately anesthetized&#160;throughout the procedure with 2% isoflurane.</li>
		<li>Place the animal in a supine position on a warming pad and apply sterile lubricant to the eyes to prevent desiccation during surgery.</li>
		<li>Using an electric razor, shave both groins and remove hair with a piece of moist gauze.</li>
		<li>Prep the surgical sites with chlorhexidine/70% ethanol solution and drape the animal with sterile towels.&#160;Administer a single dose of Carprofen (5 mg/kg, subcutaneously) as analgesic.</li>
	</ol>
	</li>
	<li>Harvest of Femoral Vein Graft
	<ol>
		<li>Using a #15 blade, make a 4 cm long skin incision on the left groin parallel to the inguinal ligament. This exposes the inguinal fat pad.</li>
		<li>Cut through the fat pad circumferentially with scissors leaving it attached to its vascular pedicle based on the epigastric vessels.</li>
		<li>Using micro scissors, free the filmy connective tissue adhesions between the abdominal wall and underlying femoral vessels.</li>
		<li>Place a retractor on the abdominal wall and pull medially. This exposes the inguinal ligament and the whole length of the femoral vessels.</li>
		<li>Using micro forceps and curved scissors dissect the epigastric vein and isolate it from its surrounding fat by gently pulling and cutting. This vein acts as a tether when constructing the loop.</li>
		<li>Using micro forceps and curved micro scissors open the perivascular sheath containing the femoral vessels and nerve all the way from the inguinal ligament to its bifurcation distal to the epigastric branch.</li>
		<li>Using micro forceps, pick up the femoral vein by its adventitia and gently separate it from the surrounding tissues and accompanying artery. Do this with micro forceps and curved round-pointed micro scissors by pulling the tissue apart and cutting through it. 
		NOTE: Never grab the whole thickness of the vein wall as this might cause trauma to the intima making it prone to thrombosis.</li>
		<li>Ligate side branches found during the dissection with 10/0 nylon suture or coagulate them with a bipolar coagulator.</li>
		<li>With the femoral vein completely free, ligate its proximal and distal ends with 4/0 silk sutures. Make sure to obtain a vein graft of at least 10 mm length and include approximately 0.5 cm length of the epigastric branch to be used as a guy rope tether to hold the loop open in the chamber.</li>
		<li>Using micro forceps and straight micro scissors, trim the adventitia from the graft&#39;s ends by gently pulling and cutting. This can also be done later, before microsurgical anastomoses.</li>
		<li>Flush the vein graft with heparinized saline solution (10 U/ml of heparin) and leave it to rest in the solution. Close the wound using continuous running 4/0 silk suture plus two or three additional simple interrupted stitches.</li>
	</ol>
	</li>
	<li>Creation of Arteriovenous Loop and Implantation of Chamber
	<ol>
		<li>Repeat steps 1.2.1 to 1.2.4 in the exact same way on the contralateral limb.</li>
		<li>Using micro forceps, dissect and isolate both the epigastric artery and vein form the surrounding fat pad. Do this by gently pulling the tissue away from the vessels</li>
		<li>Using micro forceps, pick up the femoral artery by its adventitia and free it from the surrounding tissues. Do this with micro forceps and curved round-pointed micro scissors by pulling the tissue apart and cutting through it. Ligate or coagulate its side branches.</li>
		<li>Ligate the femoral artery and vein distal to the emergence of the epigastric vessels using 4/0 silk suture.</li>
		<li>Place a single clamp proximally on each of the femoral artery and vein. Using a sharp straight micro scissor, make a clean transverse cut in each vessel distal to the emergence of the epigastric branches. Place a sterile plastic contrast background under the vessels.</li>
		<li>Flush the vessels vigorously with generous amounts of heparinized saline until all the blood is removed from the lumen.</li>
		<li>Bring the vein graft into the operative field and remove any redundant adventitia from the vessels&#39; ends as per step 1.2.10, if needed.</li>
		<li>Perform both microsurgical anastomoses with 10/0 nylon suture. Anastomose the proximal end of the vein graft to the femoral vein and the distal end to the femoral artery. This will allow the blood to flow from the arterial to the venous side without resistance from valves inside the vein graft. 
		NOTE: Make sure the femoral vessels and the vein graft rest in their natural position without any twists.</li>
		<li>Check for leaks at both anastomotic sites. Resolve small leaks, which look like non-pulsating blood coming out of the anastomotic site, by placing a small piece of fat on top and gently compressing for 5-10 min. Larger pulsating leaks that rapidly flood the entire field will need additional stitches.</li>
		<li>Check patency of the arteriovenous loop. Gentle occlusion of the femoral artery should make it shrink while the same in the femoral vein should engorge it.</li>
		<li>Place the base of the tissue engineering chamber under the arteriovenous loop with the latter resting in its natural position without twists or kinks.</li>
		<li>Secure the base of the chamber to the inguinal ligament and underlying muscle fascia with 6/0 nylon sutures.</li>
		<li>Place the lid over the base so that the femoral vessels enter the chamber through a notch (window in the side of the chamber). When closing the lid, make sure it catches the epigastric branches, between the chamber base and lid, which act as tethers to hold the arteriovenous loop into position.</li>
		<li>Close the wound using continuous running 4/0 silk suture plus two or three additional simple interrupted stitches.</li>
		<li>Allow the animal to recover from anesthesia on a warming pad.&#160;</li>
		<li>Do not leave the animal unattended until it has regained sufficient consciousness to maintain sternal recumbency. Likewise, do not return an animal that has undergone surgery to the company of other animals until fully recovered. 24 hr&#160;later, administer another single dose of Carprofen (5 mg/kg, subcutaneously) as analgesic.</li>
		<li>Treat the wound with topical antibiotic ointment for 5 days. If the wound is opened, anesthetize the animal as in step 1.1.2 through 1.1.5 and close the wound as in 1.3.14. Monitor the health of animal daily. Euthanize the animal using a lethal dose of intraperitoneal lethabarb injection (163 mg/kg in 0.25 ml by 23 G needle) if the animal shows more than one moderate signs of inacitivity, poor appetite, weight loss and loss of color.</li>
	</ol>
	</li>
</ol>
2. Flow-through Pedicle Chamber (Two Chambers per Animal)
<ol>
	<li>Preparation of the Animal for Surgery
	<ol>
		<li>Repeat steps 1.1.1 through 1.1.4. Two chambers can be implanted into both groin regions of a single rat.</li>
	</ol>
	</li>
	<li>Isolation of Femoral Vessels and Insertion of the Chamber
	<ol>
		<li>Repeat steps 1.2.1 through 1.2.8.</li>
		<li>With both artery and vein completely freed of surrounding tissues and their branches ligated, bring the chamber into the operative field.</li>
		<li>Place each of the intact femoral vessels on the corresponding slit of the chamber base making sure there are no twists or kinks.</li>
		<li>Close the chamber by attaching the lid to the base. Close the wound using continuous running 4/0 silk suture plus two or three additional simple interrupted stitches and allow the animal to recover as previously described.</li>
	</ol>
	</li>
</ol>
3. Harvest of Chambers and Tissue Processing
<ol>
	<li>Once the experiment&#39;s time points (4-6 weeks post-implantation) are reached, anesthetize the animal as in step 1.1.2 and repeat steps 1.1.3 through 1.1.5.</li>
	<li>Open the wound using a #15 blade and cut through the tissues with scissors until the chamber is completely exposed.</li>
	<li>Expose the femoral vessels proximal to the construct and test for vascular patency: gently occlude the vessel with two microforceps, then milk the blood in a distal direction and finally release the proximal forceps. If the vessel fills with blood again, this confirms patency. Ligate the femoral vessels proximally in the case of the arteriovenous loop and both proximally and distally in the case of the flow-through configuration, and remove the chambers with the containing tissue en bloc.</li>
	<li>At the end of the experiment, euthanize the animal using a lethal dose of intraperitoneal lethobarb injection (163 mg/kg in 0.25 ml by 23 G needle).</li>
	<li>Fix tissues in 4% paraformaldehyde at room temperature for 24 hr. Divide tissues into multiple transverse sections (1-2 mm thick) and embed in paraffin wax or optimal cutting temperature compound for paraffin sections (5 &#181;m) or frozen sections (10 &#181;m), respectively.3,4,8,17,22,24</li>
	<li>Perform routine histological staining such as hematoxylin and eosin to examine the general morphology of tissues. Perform immunohistochemical staining with specific antibody to identify cell type of interest,3,4,8,17,22,24,29 for example cardiac troponin T immunostaining for cardiomyocytes.</li>
</ol>

<ol>
	<li>Spiliopoulos, K., 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=Current+status+of+mechanical+circulatory+support:+A+systematic+review.">Current status of mechanical circulatory support: A systematic review.</a> Cardiol Res Pract. , 574198 (2012).</li><li>Hsu, P. L., Parker, J., Egger, C., Autschbach, R., Schmitz-Rode, T., Steinseifer, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+circulatory+support+for+right+heart+failure:+Current+technology+and+future+outlook.">Mechanical circulatory support for right heart failure: Current technology and future outlook.</a> Artif Organs. 36 (4), 332-347 (2012).</li><li>Lokmic, Z., Stillaert, F., Morrison, W. A., Thompson, E. W., Mitchell, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+arteriovenous+loop+in+a+protected+space+generates+a+permanent,+highly+vascular,+tissue-engineered+construct.">An arteriovenous loop in a protected space generates a permanent, highly vascular, tissue-engineered construct.</a> FASEB J. 21 (2), 511-522 (2007).</li><li>Morritt, A. 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=Cardiac+tissue+engineering+in+an+in+vivo+vascularized+chamber.">Cardiac tissue engineering in an in vivo vascularized chamber.</a> Circulation. 115 (3), 353-360 (2007).</li><li>Tanaka, Y., Tsutsumi, A., Crowe, D. M., Tajima, S., Morrison, W. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Generation+of+an+autologous+tissue+(matrix)+flap+by+combining+an+arteriovenous+shunt+loop+with+artificial+skin+in+rats:+preliminary+report.">Generation of an autologous tissue (matrix) flap by combining an arteriovenous shunt loop with artificial skin in rats: preliminary report.</a> B J Plast Surg. 53 (1), 51-57 (2000).</li><li>Cronin, K. 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=New+murine+model+of+spontaneous+autologous+tissue+engineering,+combining+an+arteriovenous+pedicle+with+matrix+materials.">New murine model of spontaneous autologous tissue engineering, combining an arteriovenous pedicle with matrix materials.</a> Plast Reconstr Surg. 113 (1), 260-269 (2004).</li><li>Forster, N. 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=A+prevascularized+tissue+engineering+chamber+supports+growth+and+function+of+islets+and+progenitor+cells+in+diabetic+mice.">A prevascularized tissue engineering chamber supports growth and function of islets and progenitor cells in diabetic mice.</a> Islets. 3 (5), 271-283 (2011).</li><li>Choi, Y. S., Matsuda, K., Dusting, G. J., Morrison, W. A., Dilley, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineering+cardiac+tissue+in+vivo+from+human+adipose-derived+stem+cells.">Engineering cardiac tissue in vivo from human adipose-derived stem cells.</a> Biomaterials. 31 (8), 2236-2242 (2010).</li><li>Jeyaraj, R., G, N., Kirby, G., Rajadas, J., Mosahebi, A., Seifalian, A. M., Tan, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vascularisation+in+regenerative+therapeutics+and+surgery.">Vascularisation in regenerative therapeutics and surgery.</a> Mater Sci Eng C Mater Biol Appl. 54, 225-238 (2015).</li><li>Dew, L., Macneil, S., Chong, C. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vascularization+strategies+for+tissue+engineers.">Vascularization strategies for tissue engineers.</a> Regen Med. 10 (2), 211-224 (2015).</li><li>Weigand, 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=Acceleration+of+vascularized+bone+tissue-engineered+constructs+in+a+large+animal+model+combining+intrinsic+and+extrinsic+vascularization.">Acceleration of vascularized bone tissue-engineered constructs in a large animal model combining intrinsic and extrinsic vascularization.</a> Tissue Eng Part A. 21 (9-10), 1680-1694 (2015).</li><li>Vacanti, J. P., Langer, R., Upton, J., Marler, J. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transplantation+of+cells+in+matrices+for+tissue+regeneration.">Transplantation of cells in matrices for tissue regeneration.</a> Adv Drug Deliv Rev. 33 (1-2), 165-182 (1998).</li><li>Beahm, E. K., Walton, R. L., Patrick, C. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Progress+in+adipose+tissue+construct+development.">Progress in adipose tissue construct development.</a> Clin Plast Surg. 30 (4), 547-558 (2003).</li><li>Vunjak-Novakovic, 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=Challenges+in+cardiac+tissue+engineering.">Challenges in cardiac tissue engineering.</a> Tissue Eng Part B Rev. 16 (2), 169-187 (2010).</li><li>Garcia, J. R., Garcia, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biomaterial-mediated+strategies+targeting+vascularization+for+bone+repair.">Biomaterial-mediated strategies targeting vascularization for bone repair.</a> Drug Deliv Transl Res. , (2015).</li><li>Forster, 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=Expansion+and+hepatocytic+differentiation+of+liver+progenitor+cells+in+vivo+using+a+vascularized+tissue+engineering+chamber+in+mice.">Expansion and hepatocytic differentiation of liver progenitor cells in vivo using a vascularized tissue engineering chamber in mice.</a> Tissue Eng Part C Methods. 17 (3), 359-366 (2011).</li><li>Tilkorn, D. 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=Implanted+myoblast+survival+is+dependent+on+the+degree+of+vascularization+in+a+novel+delayed+implantation/prevascularization+tissue+engineering+model.">Implanted myoblast survival is dependent on the degree of vascularization in a novel delayed implantation/prevascularization tissue engineering model.</a> Tissue Eng Part A. 16 (1), 165-178 (2010).</li><li>Chang, Q., Lu, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+strategy+for+creating+a+large+amount+of+engineered+fat+tissue+with+an+axial+vascular+pedicle+and+a+prefabricated+scaffold.">A novel strategy for creating a large amount of engineered fat tissue with an axial vascular pedicle and a prefabricated scaffold.</a> Med hypotheses. 79 (2), 267-270 (2012).</li><li>Walton, R. L., Beahm, E. K., Wu, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=De+novo+adipose+formation+in+a+vascularized+engineered+construct.">De novo adipose formation in a vascularized engineered construct.</a> Microsurg. 24 (5), 378-384 (2004).</li><li>Debels, H., Gerrand, Y. W., Poon, C. J., Abberton, K. M., Morrison, W. A., Mitchell, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+adipogenic+gel+for+surgical+reconstruction+of+the+subcutaneous+fat+layer+in+a+rat+model.">An adipogenic gel for surgical reconstruction of the subcutaneous fat layer in a rat model.</a> J Tissue Eng Regen Med. , (2015).</li><li>Lokmic, Z., Mitchell, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineering+the+microcirculation.">Engineering the microcirculation.</a> Tissue Eng Part B Rev. 14 (1), 87-103 (2008).</li><li>Yap, K. K., 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=Enhanced+liver+progenitor+cell+survival+and+differentiation+in+vivo+by+spheroid+implantation+in+a+vascularized+tissue+engineering+chamber.">Enhanced liver progenitor cell survival and differentiation in vivo by spheroid implantation in a vascularized tissue engineering chamber.</a> Biomaterials. 34 (16), 3992-4001 (2013).</li><li>Findlay, M. 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=Tissue-engineered+breast+reconstruction:+Bridging+the+gap+toward+large-volume+tissue+engineering+in+humans.">Tissue-engineered breast reconstruction: Bridging the gap toward large-volume tissue engineering in humans.</a> Plast Reconstr Surg. 128 (6), 1206-1215 (2011).</li><li>Tee, R., Morrison, W. A., Dusting, G. J., Liu, G. S., Choi, Y. S., Hsiao, S. T., Dilley, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transplantation+of+engineered+cardiac+muscle+flaps+in+syngeneic+rats.">Transplantation of engineered cardiac muscle flaps in syngeneic rats.</a> Tissue Eng Part A. 18 (19-20), 1992-1999 (2012).</li><li>Dolderer, 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=Long-term+stability+of+adipose+tissue+generated+from+a+vascularized+pedicled+fat+flap+inside+a+chamber.">Long-term stability of adipose tissue generated from a vascularized pedicled fat flap inside a chamber.</a> Plast Reconstr Surg. 127 (6), 2283-2292 (2011).</li><li>Sekine, 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=Endothelial+cell+coculture+within+tissue-engineered+cardiomyocyte+sheets+enhances+neovascularization+and+improves+cardiac+function+of+ischemic+hearts.">Endothelial cell coculture within tissue-engineered cardiomyocyte sheets enhances neovascularization and improves cardiac function of ischemic hearts.</a> Circulation. 118, 145-152 (2008).</li><li>Ting, A. 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=The+adipogenic+potential+of+various+extracellular+matrices+under+the+influence+of+an+angiogenic+growth+factor+combination+in+a+mouse+tissue+engineering+chamber.">The adipogenic potential of various extracellular matrices under the influence of an angiogenic growth factor combination in a mouse tissue engineering chamber.</a> Acta Biomater. 10 (5), 1907-1918 (2014).</li><li>Zhan, 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=Self-synthesized+extracellular+matrix+contributes+to+mature+adipose+tissue+regeneration+in+a+tissue+engineering+chamber.">Self-synthesized extracellular matrix contributes to mature adipose tissue regeneration in a tissue engineering chamber.</a> Wound Repair Regen. 23 (3), 443-452 (2015).</li><li>Messina, A., Bortolotto, S. K., Cassell, O. C., Kelly, J., Abberton, K. M., Morrison, W. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Generation+of+a+vascularized+organoid+using+skeletal+muscle+as+the+inductive+source.">Generation of a vascularized organoid using skeletal muscle as the inductive source.</a> FASEB J. 19 (11), 1570-1572 (2005).</li><li>Lim, S. Y., Hern&#225;ndez, D., Dusting, G. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Growing+vascularized+heart+tissue+from+stem+cells.">Growing vascularized heart tissue from stem cells.</a> J Cardiovasc Pharmacol. 62 (2), 122-129 (2013).</li><li>Poon, C. 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=Preparation+of+an+adipogenic+hydrogel+from+subcutaneous+adipose+tissue.">Preparation of an adipogenic hydrogel from subcutaneous adipose tissue.</a> Acta Biomater. 9 (3), 5609-5620 (2013).</li><li>Dilley, R. J., Morrison, W. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vascularisation+to+improve+translational+potential+of+tissue+engineering+systems+for+cardiac+repair.">Vascularisation to improve translational potential of tissue engineering systems for cardiac repair.</a> Int J Biochem Cell Biol. 56, 38-46 (2014).</li><li>Lesman, A., Koffler, J., Atlas, R., Blinder, Y. J., Kam, Z., Levenberg, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineering+vessel-like+networks+within+multicellular+fibrin-based+constructs.">Engineering vessel-like networks within multicellular fibrin-based constructs.</a> Biomaterials. 32 (31), 7856-7869 (2011).</li><li>Hussey, A. 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=Seeding+of+pancreatic+islets+into+prevascularized+tissue+engineering+chambers.">Seeding of pancreatic islets into prevascularized tissue engineering chambers.</a> Tissue Eng Part A. 15 (12), 3823-3833 (2009).</li><li>Chen, X., Aledia, A. S., Popson, S. A., Him, L., Hughes, C. C., George, S. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+anastomosis+of+endothelial+progenitor+cell-derived+vessels+with+host+vasculature+is+promoted+by+a+high+density+of+cotransplanted+fibroblasts.">Rapid anastomosis of endothelial progenitor cell-derived vessels with host vasculature is promoted by a high density of cotransplanted fibroblasts.</a> Tissue Eng Part A. 16 (2), 585-594 (2010).</li><li>Lin, R. Z., Melero-Martin, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fibroblast+growth+factor-2+facilitates+rapid+anastomosis+formation+between+bioengineered+human+vascular+networks+and+living+vasculature.">Fibroblast growth factor-2 facilitates rapid anastomosis formation between bioengineered human vascular networks and living vasculature.</a> Methods. 56 (3), 440-451 (2012).</li><li>Dolderer, 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=Spontaneous+large+volume+adipose+tissue+generation+from+a+vascularized+pedicled+fat+flap+inside+a+chamber+space.">Spontaneous large volume adipose tissue generation from a vascularized pedicled fat flap inside a chamber space.</a> Tissue Eng. 13 (4), 673-681 (2007).</li><li>Wei, F. C., Lin Tay, S. K., Neligan, P. C., Gurtner, G. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Principles+and+techniques+of+microvascular+surgery.">Principles and techniques of microvascular surgery.</a> Plastic Surgery. Volume 1. , 587-620 (2013).</li><li>Sekine, 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=In+vitro+fabrication+of+functional+three-dimensional+tissues+with+perfusable+blood+vessels.">In vitro fabrication of functional three-dimensional tissues with perfusable blood vessels.</a> Nat.Comm. 4 (1399), 1-10 (2013).</li><li>Lim, S. Y., Sivakumaran, P., Crombie, D. E., Dusting, G. J., P&#233;bay, A., Dilley, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Trichostatin+A+enhances+differentiation+of+human+induced+pluripotent+stem+cells+to+cardiogenic+cells+for+cardiac+tissue+engineering.">Trichostatin A enhances differentiation of human induced pluripotent stem cells to cardiogenic cells for cardiac tissue engineering.</a> Stem Cells Transl Med. 2 (9), 715-725 (2013).</li><li>Lim, S. Y., 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=In+vivo+tissue+engineering+chamber+supports+human+induced+pluripotent+stem+cell+survival+and+rapid+differentiation.">In vivo tissue engineering chamber supports human induced pluripotent stem cell survival and rapid differentiation.</a> Biochem Biophys Res Commun. 422 (1), 75-79 (2012).</li><li>Piao, Y., Hung, S. S., Lim, S. Y., Wong, R. C., Ko, M. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficient+generation+of+integration-free+human+induced+pluripotent+stem+cells+from+keratinocytes+by+simple+transfection+of+episomal+vectors.">Efficient generation of integration-free human induced pluripotent stem cells from keratinocytes by simple transfection of episomal vectors.</a> Stem Cells Transl Med. 3 (7), 787-791 (2014).</li></ol>

The authors declare no competing interests.

Engineering of the microcirculation is currently being investigated essentially through two approaches. The first involves developing a highly interconnected vascular network within the construct in vitro so that when implanted, capillaries from the host vascular bed connect with those of the transplanted construct through a process called inosculation, thus ensuring the delivery of nutrients not only to the periphery but also to the core.21,32,33 This is called pre-vascularization. The second approac...

Fabricating functional vascularized tissue using a tissue engineering approach is an emerging paradigm in regenerative medicine.1,2 Many approaches to engineer new and healthy tissue for the replacement of injured tissue or defective organs have been developed,3-6 experimentally in small animal models with promising clinical potential.7,8 However, vascularization remains one of the great challenges for tissue engineering limiting its potential to grow tissues of clinically relevant size.9
Current approaches to vascularize tissue follow either an extrinsic pathway where new vessels grow from the recipient vascular bed and invade throughout the implanted tissue constructs10 or an intrinsic vascularization pathway where the vasculature grows and expands in unison with the newly developing tissue.11 The extrinsic approach traditionally involves seeding cells onto a scaffold in vitro and implanting the complete construct into the living animal with the expectation that nutrients, previously supplied by culture media, will be sourced from the circulation.12,13 The concept is simplistic as vascular ingrowth is too slow and only very thin implants (&#60;1-2 mm thick) will remain viable. Providing nutrients and oxygen by means of a sufficient and rapid vascularization is at the heart of any successful attempts to grow more complex and larger tissue-engineered substitutes such as bone, muscle, fat and solid organs.14,15 Intrinsic vascularization offers the potential for larger constructs to develop by progressive tissue growth commensurate with its expanding blood supply. One design is the in vivo implantation into a chamber of a vascular pedicle with or without a cell seeded scaffold.5,6 This has paved the way to new procedures for the generation of thicker intrinsically vascularized tissues.16,17
More recently, strategies have been developed to pre-vascularize tissue grafts, prior to implantation. These incorporated blood vessel networks are aimed to inosculate with host vessels at implantation allowing for the rapid provision of a complete blood supply to improve the survival of all parts of a transplanted thick tissue graft.18
We pioneered an in vivo vascularized tissue engineering model in small animals that involves a subcutaneously implanted semi-rigid enclosed chamber containing a perfused vascular pedicle and cell-containing biomaterials. The chamber creates an ischemic environment that stimulates angiogenic sprouting from the implanted vessels.3 The vascular pedicle can either be a reconstructed arteriovenous loop or an intact flow-through artery and vein.3-6,19 This vascular pedicle sprouts a functioning and extensive arterio-capillary-venous network that links at both arteriole and venous ends with the vascular pedicle.3,20 Furthermore, the surrounding hollow support chamber protects the developing tissue from potentially deforming mechanical forces and prolongs the ischaemic drive to enhance vascularization.3,21,22 If the vessel pedicle is simply implanted into normal tissue and not inside the protected space of the chamber, angiogenic sprouting ceases along the same timeline as a normal wound and no new tissue will accumulate around the pedicle. Investigators have used this in vivo configuration to produce three-dimensional functional vascularized tissue constructs with supportive vasculature and of clinically relevant size.4,23 Furthermore, the engineered vascularized tissue constructs with its intact vascular pedicle can be harvested for subsequent transplantation at the injury site.24,25 A more clinically feasible scenario would be creating the chamber at the definitive site for reconstruction such as the breast. Thus, this de novo tissue engineering approach could have clinical potential to provide a new source of functional target tissue for reconstructive surgery.26-28 
The following protocol will provide a general guide to construct an in vivo vascularized tissue engineering chamber in the rat, which could be adapted in different animal models and employed to examine the intricate processes of angiogenesis, matrix production, and cellular migration and differentiation.

<table border="0" cellpadding="0" cellspacing="0" width="649">
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			<td height="20" style="height:20px;width:123px;">1 15 Blade Scalpel</td>
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			<td style="width:163px;">BB515</td>
			<td style="width:176px;"></td>
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			<td height="20" style="height:20px;">1 Toothed Adson Forceps</td>
			<td>Braun</td>
			<td>BD527R</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1 Needle Holder</td>
			<td>Braun</td>
			<td>BM201R</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1 Bipolar Coagulator&#160;</td>
			<td>Braun</td>
			<td>US335</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1 Micro Needle Holder B-15-8.3</td>
			<td>S &#38; T</td>
			<td>00763</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1 Micro Dilator Forceps D-5a.2</td>
			<td>S &#38; T</td>
			<td>00125</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1 Micro Jeweler&#39;s Forceps JF-5</td>
			<td>S &#38; T</td>
			<td>00108</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1 Micro Scissors - Straight SAS-11</td>
			<td>S &#38; T</td>
			<td>00098</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1 Micro Scissors - Curved SDC-11</td>
			<td>S &#38; T</td>
			<td>00090</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">2 Single Clamps B-3</td>
			<td>S &#38; T</td>
			<td>00400</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">2 10/0 nylon suture</td>
			<td>S &#38; T</td>
			<td>03199</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1 6/0 nylon suture</td>
			<td>Braun</td>
			<td>G2095469</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">2 4/0 Silk Sutures</td>
			<td>Braun</td>
			<td>C0760145</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Xilocaine 1%</td>
			<td>Dealmed</td>
			<td>150733</td>
			<td>10 mg/ml</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Heparin Sodium</td>
			<td>Dealmed</td>
			<td>272301</td>
			<td>5000 UI / ml</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Ringer Lactate</td>
			<td>Baxter</td>
			<td>JB2323</td>
			<td>500 ml</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">1 dome-shaped tissue engineering chamber</td>
			<td>custom made</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">1 flow-through chamber</td>
			<td>custom made</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Lectin I, Griffonia Simplicifolia&#160;</td>
			<td>Vector Laboratories</td>
			<td>B-1105</td>
			<td>1.67 &#956;g/mL</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Troponin T antibody</td>
			<td>Abcam</td>
			<td>Ab8295</td>
			<td>4 &#956;g/mL</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Human-specific Ku80 antibody</td>
			<td>Abcam</td>
			<td>Ab80592</td>
			<td style="width:176px;">0.06 &#956;g/mL</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Desmin antibody</td>
			<td>Dako</td>
			<td>M0760</td>
			<td style="width:176px;">2.55 &#956;g/mL</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Cell Tracker CM-DiI dye</td>
			<td>Thermo Fisher Scientific</td>
			<td>C-7000</td>
			<td>3 mg/106 cells</td>
		</tr>
	</tbody>
</table>

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.

The microsurgical creation of tissue engineering chambers was performed as described in the protocol above. Tissues generated inside the chambers can be examined histologically as describe in protocol step 3. Various tissue types have been successfully engineered using the in vivo vascularized chamber (Figure 2). These include cardiac tissue with neonatal rat cardiomyocytes (Figure 2A), muscle tissue with rat skeletal myoblasts (Figure 2B...

Watch this Scientific Journal Video about Tissue Engineering by Intrinsic Vascularization in an In Vivo Tissue Engineering Chamber at JoVE.com

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.

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 ...

tissue-engineering-intrinsic-vascularization-an-vivo-tissue

Research

JoVE Journal

Bioengineering

8.8K Views.  St Vincent's Institute of Medical Research. 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. 

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

Fabrication of Biologically Derived Injectable Materials for Myocardial Tissue Engineering

This protocol provides methods for the preparation of an injectable extracellular matrix (ECM) gel for myocardial tissue engineering applications. Briefly, decellularized tissue is lyophilized, milled, enzymatically digested, and then brought to physiological pH. The lyophilization removes all water content from the tissue, resulting in dry ECM that can be ground into a fine powder with a small mill. After milling, the ECM powder is digested with pepsin to form an injectable matrix. After adjustment to pH 7.4, the liquid matrix material can be injected into the myocardium. Results of previous characterization assays have shown that matrix gels produced from decellularized pericardial and myocardial tissue retain native ECM components, including diverse proteins, peptides and glycosaminoglycans. Given the use of this material for tissue engineering, in vivo characterization is especially useful; here, a method for performing an intramural injection into the left ventricular (LV) free wall is presented as a means of analyzing the host response to the matrix gel in a small animal model. Access to the chest cavity is gained through the diaphragm and the injection is made slightly above the apex in the LV free wall. The biologically derived scaffold can be visualized by biotin-labeling before injection and then staining tissue sections with a horse radish peroxidase-conjugated neutravidin and visualizing via diaminobenzidine (DAB) staining. Analysis of the injection region can also be done with histological and immunohistochemical staining. In this way, the previously examined pericardial and myocardial matrix gels were shown to form fibrous, porous networks and promote vessel formation within the injection region.

Methods for preparing an injectable matrix gel from decellularized tissue and injecting it into rat myocardium in vivo are described.

This protocol provides methods for the preparation of an injectable extracellular matrix (ECM) gel for myocardial tissue engineering applications.  ...

Elastomeric PGS Scaffolds in Arterial Tissue Engineering

Cardiovascular disease is one of the leading cause of mortality in the US and especially, coronary artery disease increases with an aging population and increasing obesity1. Currently, bypass surgery using autologous vessels, allografts, and synthetic grafts are known as a commonly used for arterial substitutes2. However, these grafts have limited applications when an inner diameter of arteries is less than 6 mm due to low availability, thrombotic complications, compliance mismatch, and late intimal hyperplasia3,4. To overcome these limitations, tissue engineering has been successfully applied as a promising alternative to develop small-diameter arterial constructs that are nonthrombogenic, robust, and compliant. Several previous studies have developed small-diameter arterial constructs with tri-lamellar structure, excellent mechanical properties and burst pressure comparable to native arteries5,6. While high tensile strength and burst pressure by increasing collagen production from a rigid material or cell sheet scaffold, these constructs still had low elastin production and compliance, which is a major problem to cause graft failure after implantation. Considering these issues, we hypothesized that an elastometric biomaterial combined with mechanical conditioning would provide elasticity and conduct mechanical signals more efficiently to vascular cells, which increase extracellular matrix production and support cellular orientation.
The objective of this report is to introduce a fabrication technique of porous tubular scaffolds and a dynamic mechanical conditioning for applying them to arterial tissue engineering. We used a biodegradable elastomer, poly (glycerol sebacate) (PGS)7 for fabricating porous tubular scaffolds from the salt fusion method. Adult primary baboon smooth muscle cells (SMCs) were seeded on the lumen of scaffolds, which cultured in our designed pulsatile flow bioreactor for 3 weeks. PGS scaffolds had consistent thickness and randomly distributed macro- and micro-pores. Mechanical conditioning from pulsatile flow bioreactor supported SMC orientation and enhanced ECM production in scaffolds. These results suggest that elastomeric scaffolds and mechanical conditioning of bioreactor culture may be a promising method for arterial tissue engineering.

Elastomeric PGS scaffolds with vascular smooth muscle cells cultured in a pulsatile flow bioreactor may lead to promising small-diameter arterial constructs with native ECM production in a relatively short culture period.

Cardiovascular disease is one of the leading cause of mortality in the US and especially, coronary artery disease increases with an aging population and ...

Tissue Engineering of the Intestine in a Murine Model

Tissue-engineered small intestine (TESI) has successfully been used to rescue Lewis rats after massive small bowel resection, resulting in return to preoperative weights within 40 days.1 In humans, massive small bowel resection can result in short bowel syndrome, a functional malabsorptive state that confers significant morbidity, mortality, and healthcare costs including parenteral nutrition dependence, liver failure and cirrhosis, and the need for multivisceral organ transplantation.2 In this paper, we describe and document our protocol for creating tissue-engineered intestine in a mouse model with a multicellular organoid units-on-scaffold approach. Organoid units are multicellular aggregates derived from the intestine that contain both mucosal and mesenchymal elements,3 the relationship between which preserves the intestinal stem cell niche.4 In ongoing and future research, the transition of our technique into the mouse will allow for investigation of the processes involved during TESI formation by utilizing the transgenic tools available in this species.5The availability of immunocompromised mouse strains will also permit us to apply the technique to human intestinal tissue and optimize the formation of human TESI as a mouse xenograft before its transition into humans. Our method employs good manufacturing practice (GMP) reagents and materials that have already been approved for use in human patients, and therefore offers a significant advantage over approaches that rely upon decellularized animal tissues. The ultimate goal of this method is its translation to humans as a regenerative medicine therapeutic strategy for short bowel syndrome.

This article and the accompanying video present our protocol for generating tissue-engineered intestine in the mouse, using an organoid units-on-scaffold approach.

Tissue-engineered small intestine (TESI) has successfully been used to rescue Lewis rats after massive small bowel resection, resulting in return to ...

Capillary Force Lithography for Cardiac Tissue Engineering

Cardiovascular disease remains the leading cause of death worldwide1. Cardiac tissue engineering holds much promise to deliver groundbreaking medical discoveries with the aims of developing functional tissues for cardiac regeneration as well as in vitro screening assays. However, the ability to create high-fidelity models of heart tissue has proven difficult. The heart&#8217;s extracellular matrix (ECM) is a complex structure consisting of both biochemical and biomechanical signals ranging from the micro- to the nanometer scale2. Local mechanical loading conditions and cell-ECM interactions have recently been recognized as vital components in cardiac tissue engineering3-5.
A large portion of the cardiac ECM is composed of aligned collagen fibers with nano-scale diameters that significantly influences tissue architecture and electromechanical coupling2. Unfortunately, few methods have been able to mimic the organization of ECM fibers down to the nanometer scale. Recent advancements in nanofabrication techniques, however, have enabled the design and fabrication of scalable scaffolds that mimic the in vivo structural and substrate stiffness cues of the ECM in the heart6-9.
Here we present the development of two reproducible, cost-effective, and scalable nanopatterning processes for the functional alignment of cardiac cells using the biocompatible polymer poly(lactide-co-glycolide) (PLGA)8 and a polyurethane (PU) based polymer. These anisotropically nanofabricated substrata (ANFS) mimic the underlying ECM of well-organized, aligned tissues and can be used to investigate the role of nanotopography on cell morphology and function10-14.
Using a nanopatterned (NP) silicon master as a template, a polyurethane acrylate (PUA) mold is fabricated. This PUA mold is then used to pattern the PU or PLGA hydrogel via UV-assisted or solvent-mediated capillary force lithography (CFL), respectively15,16. Briefly, PU or PLGA pre-polymer is drop dispensed onto a glass coverslip and the PUA mold is placed on top. For UV-assisted CFL, the PU is then exposed to UV radiation (&#955; = 250-400 nm) for curing. For solvent-mediated CFL, the PLGA is embossed using heat (120 &#176;C) and pressure (100 kPa). After curing, the PUA mold is peeled off, leaving behind an ANFS for cell culture. Primary cells, such as neonatal rat ventricular myocytes, as well as human pluripotent stem cell-derived cardiomyocytes, can be maintained on the ANFS2.

In this protocol, we demonstrate the fabrication of biomimetic cardiac cell culture substrata made from two distinct polymeric materials using capillary force lithography. The described methods provide a scalable, cost-effective technique to engineer the structure and function of macroscopic cardiac tissues for in vitro and in vivo applications.

Cardiovascular disease remains the leading cause of death worldwide1. Cardiac tissue engineering holds much promise to deliver groundbreaking medical ...

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 ...

Generation of a Three-dimensional Full Thickness Skin Equivalent and Automated Wounding

In vitro models are a cost effective and ethical alternative to study cutaneous wound healing processes. Moreover, by using human cells, these models reflect the human wound situation better than animal models. Although two-dimensional models are widely used to investigate processes such as cellular migration and proliferation, models that are more complex are required to gain a deeper knowledge about wound healing. Besides a suitable model system, the generation of precise and reproducible wounds is crucial to ensure comparable results between different test runs. In this study, the generation of a three-dimensional full thickness skin equivalent to study wound healing is shown. The dermal part of the models is comprised of human dermal fibroblast embedded in a rat-tail collagen type I hydrogel. Following the inoculation with human epidermal keratinocytes and consequent culture at the air-liquid interface, a multilayered epidermis is formed on top of the models. To study the wound healing process, we additionally developed an automated wounding device, which generates standardized wounds in a sterile atmosphere.

The goal of this protocol is to build up a three-dimensional full thickness skin equivalent, which resembles natural skin. With a specifically constructed automated wounding device, precise and reproducible wounds can be generated under maintenance of sterility.

In vitro models are a cost effective and ethical alternative to study cutaneous wound healing processes. Moreover, by using human cells, these models ...

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. ...

Sandwich-like Microenvironments to Harness Cell/Material Interactions

Cell culture has been traditionally carried out on bi-dimensional (2D) substrates where cells adhere using ventral receptors to the biomaterial surface. However in vivo, most of the cells are completely surrounded by the extracellular matrix (ECM), resulting in a three-dimensional (3D) distribution of receptors. This may trigger differences in the outside-in signaling pathways and thus in cell behavior.
This article shows that stimulating the dorsal receptors of cells already adhered to a 2D substrate by overlaying a film of a new material (a sandwich-like culture) triggers important changes with respect to standard 2D cultures. Furthermore, the simultaneous excitation of ventral and dorsal receptors shifts cell behavior closer to that found in 3D environments. Additionally, due to the nature of the system, a sandwich-like culture is a versatile tool that allows the study of different parameters in cell/material interactions, e.g., topography, stiffness and different protein coatings at both the ventral and dorsal sides. Finally, since sandwich-like cultures are based on 2D substrates, several analysis procedures already developed for standard 2D cultures can be used normally, overcoming more complex procedures needed for 3D systems.

The following protocol describes the procedure to assemble sandwich-like cultures to be used as an intermediate stage between bi-dimensional (2D) and three-dimensional (3D) cellular environments. The engineered systems can have applications in microscopy, biomechanics, biochemistry and cell biology assays.

Cell culture has been traditionally carried out on bi-dimensional (2D) substrates where cells adhere using ventral receptors to the biomaterial surface. ...

Preparation of Thermoresponsive Nanostructured Surfaces for Tissue Engineering

Thermoresponsive poly(N-isopropylacrylamide) (PIPAAm)-immobilized surfaces for controlling cell adhesion and detachment were fabricated by the Langmuir-Schaefer method. Amphiphilic block copolymers composed of polystyrene and PIPAAm (St-IPAAms) were synthesized by reversible addition-fragmentation chain transfer (RAFT) radical polymerization. A chloroform solution of St-IPAAm molecules was gently dropped into a Langmuir-trough apparatus, and both barriers of the apparatus were moved horizontally to compress the film to regulate its density. Then, the St-IPAAm Langmuir film was horizontally transferred onto a hydrophobically modified glass substrate by a surface-fixed device. Atomic force microscopy images clearly revealed nanoscale sea-island structures on the surface. The strength, rate, and quality of cell adhesion and detachment on the prepared surface were modulated by changes in temperature across the lower critical solution temperature range of PIPAAm molecules. In addition, a two-dimensional cell structure (cell sheet) was successfully recovered on the optimized surfaces. These unique PIPAAm surfaces may be useful for controlling the strength of cell adhesion and detachment.

Nanoscaled sea-island surfaces composed of thermoresponsive block copolymers were fabricated by the Langmuir-Schaefer method for controlling spontaneous cell adhesion and detachment. Both the preparation of the surface and the adhesion and detachment of cells on the surface were visualized.

Thermoresponsive poly(N-isopropylacrylamide) (PIPAAm)-immobilized surfaces for controlling cell adhesion and detachment were fabricated by the ...

Isolation of Murine Adipose Tissue-derived Microvascular Fragments as Vascularization Units for Tissue Engineering

A functional microvascular network is of pivotal importance for the survival and integration of engineered tissue constructs. For this purpose, several angiogenic and prevascularization strategies have been established. However, most cell-based approaches include time-consuming in vitro steps for the formation of a microvascular network. Hence, they are not suitable for intraoperative one-step procedures. Adipose tissue-derived microvascular fragments (ad-MVF) represent promising vascularization units. They can be easily isolated from fat tissue and exhibit a functional microvessel morphology. Moreover, they rapidly reassemble into new microvascular networks after in vivo implantation. In addition, ad-MVF have been shown to induce lymphangiogenesis. Finally, they are a rich source of mesenchymal stem cells, which may further contribute to their high vascularization potential. In previous studies we have demonstrated the remarkable vascularization capacity of ad-MVF in engineered bone and skin substitutes. In the present study, we report on a standardized protocol for the enzymatic isolation of ad-MVF from murine fat tissue.

We present a protocol to isolate adipose tissue-derived microvascular fragments that represent promising vascularization units. They can be rapidly isolated, do not require in vitro processing and, thus, may be used for one-step prevascularization in different fields of tissue engineering.

A functional microvascular network is of pivotal importance for the survival and integration of engineered tissue constructs. For this purpose, several ...