This work was financially supported by the Kosair Charities Pediatric Heart Research Program at the University of Louisville and the Organoid Project at the RIKEN Center for Biosystems Dynamics Research. HiPSCs used in our published protocols were provided by the Center for iPS Cell Research and Application, Kyoto University, Kyoto, Japan.

1. Maintenance of hiPSCs and cardiovascular differentiation
<ol>
	<li>Expand and maintain hiPSCs on thin-coat basement membrane matrix (growth factor reduced, 1:60 dilution) in conditioned medium extracted from mouse embryonic fibroblasts (MEF-CM) with human basic fibroblast growth factor (hbFGF)4. 
	NOTE: We used a hiPSCs (4-factor (Oct3/4, Sox2, Klf4 and c-Myc) line: 201B6). Add hbFGF at the appropriate concentration for each cell line. Laminin-511 fragment can also be used for the coating of culture dish instead of basement membrane matrix. Commercially available medium designed for feeder-free culture of hiPSCs can be used as a substitute for MEF-CM.</li>
	<li>Use Versene (0.48 mM ethylenediaminetetraacetic acid (EDTA) solution) to detach and dissociate cells when cell confluency reaches 90&#8210;100%. 
	NOTE: Other commercially available products for cell dissociation can also be used.</li>
	<li>Plate cells at a density of 10,000 cells/mm2 on matrix-coated cell culture plates in MEF-CM with hbFGF and culture for two to three days.</li>
	<li>When the culture becomes fully confluent, cover the cells with matrix (1:60 dilution with MEF-CM) for one day.</li>
	<li>Replace the MEF-CM with RPMI 1640 + B27 medium. Add 100 ng/mL of Activin A and 100 ng/mL of Wnt3A to the medium for one day. 
	NOTE: This is day 0 of differentiation. To upregulate canonical Wnt signaling, GSK3&#946; inhibitors can also be used instead of Wnt3A.</li>
	<li>On day 1 of differentiation, change the medium to new RPMI 1640 + B27 with 10 ng/mL of BMP4 and 10 ng/mL of hbFGF. Culture cells for two (MC protocol) or four (CM+EC protocol) days without medium change5. 
	NOTE: CM+EC protocol is optimized to simultaneously induce cardiomyocytes (CMs) and vascular endothelial cells (ECs). MC protocol is optimized to preferentially induce vascular mural cells (MCs).</li>
	<li>CM+EC protocol for the induction of CMs and ECs (Figure 1A).
	<ol>
		<li>Replace the medium on day 5 of differentiation with RPMI 1640 + B27 supplemented with 50 ng/mL of VEGF165.</li>
		<li>Change the culture medium every 48 h until day 13&#8210;15 of differentiation.</li>
	</ol>
	</li>
	<li>MC protocol for the induction of vascular mural cells (Figure 1B)
	<ol>
		<li>Replace the medium with RPMI1640 + 10% fetal bovine serum (FBS) at day 3 of differentiation.</li>
		<li>Change the culture medium every 48 h until day 13&#8210;15 of differentiation.</li>
	</ol>
	</li>
</ol>
2. Cell harvest and lineage analysis on differentiation day 13&#8210;15
<ol>
	<li>Wash the cells with Ca2+ and Mg2+ free phosphate-buffered saline (PBS).</li>
	<li>Add cell dissociation solution (containing proteases, collagenases and DNAses) in the cell culture dish to cover the plate. Incubate the plate for 5 min at 37 &#176;C.</li>
	<li>Collect and dissociate the cells with culture medium using a pipette after incubation.</li>
	<li>Allocate 1 x 106 cells for lineage analysis with flow cytometry. To eliminate dead cells, stain the cells with fixable viability dye.</li>
	<li>Stain the cells with membrane surface markers in PBS with 5% FBS. Use the following dilutions of antibody in fluorescence activated cell sorting (FACS) staining buffer: anti-PDGFR&#946; (1:100), anti-VE cadherin (1:100), anti-TRA-1-60 (1:20).</li>
	<li>For intracellular proteins, resuspend and fix the cells with 4% paraformaldehyde (PFA) in PBS.</li>
	<li>Stain the cells with anti-cardiac isoform of Troponin T (cTnT) in PBS with 5% FBS and 0.75% Saponin, then label the cTnT antibody with 488 mouse IgG1 (dilution 1:50).</li>
	<li>Resuspend the stained cells in PBS with 5% FBS and put them in FACS tubes with cell strainer.</li>
	<li>Analyze the cell composition of the stained cells from each differentiation protocol with flow cytometry to facilitate the generation of cell suspensions with defined lineage distributions. 
	NOTE: While performing this procedure, the remaining cell suspension for ECTs is preserved in a 4 &#176;C refrigerator.</li>
</ol>
3. Fabrication of PDMS tissue mold
<ol>
	<li>Cast a 0.5 mm thick and over 30 mm x 30 mm layer of polydimethylsiloxane (PDMS) by mixing the prepolymer and cross-linking solution at a ratio of 10:1 and then cure at 80 &#176;C for 3 h.</li>
	<li>Cut the PDMS sheet and bond it with silicone adhesive to fabricate a 21 mm x 20.5 mm rectangular tray with 7 mm long, 0.5 mm wide, and 2.5 mm high rectangular posts at a staggered position. Horizontal post spacing between two lines of posts is 2.5 mm (Figure 2B).</li>
	<li>Autoclave the tray at 120 &#176;C for 20 min.</li>
	<li>Coat the tray with 1% poloxamer 407 in PBS for 1 h. Rinse the poloxamer 407 and rinse the mold with PBS sufficiently prior to use.</li>
</ol>
4. ECT construction
<ol>
	<li>After the cell lineage analysis, combine the cells from CM+EC and MC protocols so that the final concentration of MCs is 10 to 20% in a total cell number of six million cells per construct5.</li>
	<li>Suspend mixed six million cells in ECT culture medium (alpha minimum essential medium supplemented with 10% FBS, 50 &#181;M 2-mercaptoethanol and 100 U/mL Penicillin-Streptomycin).</li>
	<li>Preparation of matrix solution
	<ol>
		<li>Mix 133 &#181;L of acid-soluble rat tail collagen type I solution (2 mg/mL, pH 3) with 17 &#181;L of 10x minimum essential medium (MEM). Then mix the solution with 17 &#181;L of alkali buffer (0.2 M NaHCO3, 0.2 M HEPES, and 0.1 M NaOH). 
		NOTE: Collagen must be kept on ice (4 &#176;C). Check buffer color and if the medium does not become pinkish when all solutions are mixed, add additional alkali buffer to the medium. The mixing steps must be mix collagen I + 10x MEM, and then add alkali buffer. DO NOT change this order. Do NOT generate bubbles in the mix.</li>
		<li>Add 67 &#181;L of basement membrane matrix to the neutralized collagen solution. 
		NOTE: The mixed solution must be kept on ice (4 &#176;C).</li>
	</ol>
	</li>
	<li>Centrifuge the prepared cell suspension containing six million cells at 1,100 rpm (240 x g) for 5 min and resuspend the cells with 167 &#181;L of high-glucose DMEM + 20% FBS + 1% penicillin-streptomycin (100x).</li>
	<li>Mix the cell suspension and the matrix solution. The total volume of cell/matrix mixture for one construct is 400 &#956;L. 
	NOTE: The cell/matrix mixture should be non-viscous and a pinkish color at this step. Keep it on ice as the gel will solidify at room temperature. The final concentration of collagen type I is 0.67 mg/mL.</li>
	<li>Pour the cell/matrix mixture evenly over the poloxamer 407 coated PDMS tissue mold, which is placed in a six-well culture plate12. 
	NOTE: Pour the mixture carefully to avoid generating bubbles in order to prevent filling defects in the poured gel.</li>
	<li>Incubate the cell/matrix mixture in a standard CO2 incubator (37C, 5 % CO2) for 60 min.</li>
	<li>After the tissue is formed, soak the tissue mold with 4 mL of ECT culture medium. 
	NOTE: Although the cell/matrix is crosslinked in 60 min, the construct is still very fragile. Add medium gently to avoid damaging it.</li>
	<li>Culture the tissue for 14 days with medium change every day.</li>
	<li>Prior to ECT implantation, remove the ECT from the loading posts gently using sterilized fine forceps. 
	NOTE: The final ECT dimensions after removal from the mold are less than the original mold. A 2.1 cm x 2.05 cm mold generates a released ECT of approximately 1.5 cm x 1.5 cm. A larger 3.9 cm x 4.05 cm mold generates an ECT of approximately 3 cm x 3 cm. Unloaded ECT shows intrinsic spontaneous beating in warm culture medium. Although it initially maintains a mesh structure, an unloaded ECT shrinks and condenses over time. It is possible to hold the tissue softly with fine forceps and then use 7-0 silk suture to attach the ECT to the epicardium.</li>
</ol>

<ol>
	<li>Sanganalmath, S. K., Bolli, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+therapy+for+heart+failure:+A+comprehensive+overview+of+experimental+and+clinical+studies,+current+challenges,+and+future+directions.">Cell therapy for heart failure: A comprehensive overview of experimental and clinical studies, current challenges, and future directions.</a> Circulation Research. 113, 810-834 (2013).</li><li>Fisher, S. A., Doree, C., Mathur, A., Martin-Rendon, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Meta-Analysis+of+Cell+Therapy+Trials+for+Patients+With+Heart+Failure.">Meta-Analysis of Cell Therapy Trials for Patients With Heart Failure.</a> Circulation Research. 116, 1361-1377 (2015).</li><li>Menasch&#233;, P., 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=Human+embryonic+stem+cell-derived+cardiac+progenitors+for+severe+heart+failure+treatment:+first+clinical+case+report:+Figure+1.">Human embryonic stem cell-derived cardiac progenitors for severe heart failure treatment: first clinical case report: Figure 1.</a> European Heart Journal. 36, 2011-2017 (2015).</li><li>Masumoto, 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=Human+iPS+cell-engineered+cardiac+tissue+sheets+with+cardiomyocytes+and+vascular+cells+for+cardiac+regeneration.">Human iPS cell-engineered cardiac tissue sheets with cardiomyocytes and vascular cells for cardiac regeneration.</a> Scientific Reports. 4, 6716 (2014).</li><li>Masumoto, 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=The+myocardial+regenerative+potential+of+three-dimensional+engineered+cardiac+tissues+composed+of+multiple+human+iPS+cell-derived+cardiovascular+cell+lineages.">The myocardial regenerative potential of three-dimensional engineered cardiac tissues composed of multiple human iPS cell-derived cardiovascular cell lineages.</a> Scientific Reports. 6, 29933 (2016).</li><li>Zimmermann, W. 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=Engineered+heart+tissue+grafts+improve+systolic+and+diastolic+function+in+infarcted+rat+hearts.">Engineered heart tissue grafts improve systolic and diastolic function in infarcted rat hearts.</a> Nature Medicine. 12, 452-458 (2006).</li><li>Fujimoto, K. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Engineered+fetal+cardiac+graft+preserves+its+cardiomyocyte+proliferation+within+postinfarcted+myocardium+and+sustains+cardiac+function.">Engineered fetal cardiac graft preserves its cardiomyocyte proliferation within postinfarcted myocardium and sustains cardiac function.</a> Tissue engineering. Part A. 17, 585-596 (2011).</li><li>Lancaster, J. 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=Surgical+treatment+for+heart+failure:+cell-based+therapy+with+engineered+tissue.">Surgical treatment for heart failure: cell-based therapy with engineered tissue.</a> Vessel Plus. 2019, (2019).</li><li>Bian, W., Liau, B., Badie, N., Bursac, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mesoscopic+hydrogel+molding+to+control+the+3D+geometry+of+bioartificial+muscle+tissues.">Mesoscopic hydrogel molding to control the 3D geometry of bioartificial muscle tissues.</a> Nature protocols. 4, 1522-1534 (2009).</li><li>Zhang, D., 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+cardiac+patch+for+advanced+functional+maturation+of+human+ESC-derived+cardiomyocytes.">Tissue-engineered cardiac patch for advanced functional maturation of human ESC-derived cardiomyocytes.</a> Biomaterials. 34, 5813-5820 (2013).</li><li>Christoforou, 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=Induced+pluripotent+stem+cell-derived+cardiac+progenitors+differentiate+to+cardiomyocytes+and+form+biosynthetic+tissues.">Induced pluripotent stem cell-derived cardiac progenitors differentiate to cardiomyocytes and form biosynthetic tissues.</a> PloS one. 8, 65963 (2013).</li><li>Nakane, T., 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=Impact+of+Cell+Composition+and+Geometry+on+Human+Induced+Pluripotent+Stem+Cells-Derived+Engineered+Cardiac+Tissue.">Impact of Cell Composition and Geometry on Human Induced Pluripotent Stem Cells-Derived Engineered Cardiac Tissue.</a> Scientific Reports. 7, 45641 (2017).</li><li>Kowalski, W. 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=Quantification+of+Cardiomyocyte+Alignment+from+Three-Dimensional+(3D)+Confocal+Microscopy+of+Engineered+Tissue.">Quantification of Cardiomyocyte Alignment from Three-Dimensional (3D) Confocal Microscopy of Engineered Tissue.</a> Microscopy and Microanalysis. 1, (2017).</li></ol>

The authors have no financial or scientific conflicts to disclose.

Following the completion of our investigation of a linear format, hiPSC derived ECT5, we adapted the protocol to mix hiPSC-derived CMs, ECs, and MCs to facilitate the in vitro expansion of vascular cells within ECTs and subsequent in vivo vascular coupling between ECTs and recipient myocardium.
To facilitate the generation of larger, implantable mesh ECT geometries we used thin PDMS sheets to design the 3D molds with loading posts arrayed at staggered positions. During ...

Numerous preclinical studies and clinical trials have confirmed the efficiency of cell-based cardiac regenerative therapies for failing hearts1,2,3. Among various cell types, human induced pluripotent stem cells (hiPSCs) are promising cell sources by virtue of their proliferative ability, potential to generate various cardiovascular lineages4,5, and allogenicity. In addition, tissue engineering technologies have made it possible to transfer millions of cells onto a damaged heart5,6,7,8.
Previously, we reported the generation of three-dimensional (3D) linear engineered cardiac tissues (ECTs) from hiPSC-derived cardiovascular lineages using a commercially available culture system for 3D bioartificial tissues5,7. We found that the coexistence of vascular endothelial cells and mural cells with cardiomyocytes within the ECT facilitated structural and electrophysiological tissue maturation. Furthermore, we validated the therapeutic potential of implanted hiPSC-ECTs in an immune tolerant rat myocardial infarction model to improve cardiac function, regenerate myocardium, and enhance angiogenesis5. However, the linear ECTs constructed by this method were 1 mm by 10 mm cylinders and therefore not suitable for the implantation in preclinical studies with larger animals or clinical use.
Based on the successful use of tissue molds to generate porous engineered tissue formation using rat skeletal myoblasts and cardiomyocytes9, human ESC-derived cardiomyocytes10 and mouse iPSCs11, we developed a protocol to generate scalable hiPSC-derived larger implantable tissue using polydimethylsiloxane (PDMS) molds. We evaluated a range of mold geometries to determine the most effective mold characteristics. Mesh-shaped ECTs with multiple bundles and junctions exhibited excellent characteristics in cell viability, tissue function and scalability compared to plain-sheet or linear formats that lacked pores or junctions. We implanted the mesh-shaped ECT in a rat myocardial infarction model and confirmed its therapeutic effects similar to implanted cylindrical ECTs12. Here we describe the protocol to generate a hiPSC-derived mesh-shaped ECT.

<table>
	<tbody>
		<tr>
			<td>Materials</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Cell Culture Dishes 100x20 mm style</td>
			<td>Falcon/ Thomas scientific</td>
			<td>9380C51</td>
			<td></td>
		</tr>
		<tr>
			<td>Multiwell Plates For Cell Culture 6well 50/CS</td>
			<td>Falcon / Thomas scientific</td>
			<td>6902A01</td>
			<td></td>
		</tr>
		<tr>
			<td>Sylgard 184 Silicone Elastomer Kit</td>
			<td>Dow Corning</td>
			<td>761036</td>
			<td></td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Reagents</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Accumax</td>
			<td>Innovative Cell Technologies</td>
			<td>AM-105</td>
			<td></td>
		</tr>
		<tr>
			<td>BMP4, recombinant (10&#181;g)</td>
			<td>R&#38;D</td>
			<td>RSD-314-BP-010</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagen, Type I solution from rat tail</td>
			<td>Sigma</td>
			<td>C3867</td>
			<td></td>
		</tr>
		<tr>
			<td>Growth factor-reduced Matrigel</td>
			<td>Corning</td>
			<td>356231</td>
			<td></td>
		</tr>
		<tr>
			<td>Human VEGF (165) IS, premium grade</td>
			<td>Miltenyi</td>
			<td>130-109-385</td>
			<td></td>
		</tr>
		<tr>
			<td>Pluronic F-127, 0.2 &#181;m filtered (10% Solution in Water)</td>
			<td>Molecular Probes</td>
			<td>P-6866</td>
			<td></td>
		</tr>
		<tr>
			<td>Recombinant human bFGF</td>
			<td>WAKO</td>
			<td>060-04543</td>
			<td></td>
		</tr>
		<tr>
			<td>Recombinant Human/Mouse/Rat ActivinA (50&#181;g)</td>
			<td>R&#38;D</td>
			<td>338-AC-050</td>
			<td></td>
		</tr>
		<tr>
			<td>rh Wnt-3a (10&#181;g)</td>
			<td>R&#38;D</td>
			<td>5036-WN</td>
			<td></td>
		</tr>
		<tr>
			<td>Versene solution</td>
			<td>Gibco</td>
			<td>15040066</td>
			<td></td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Culture medium and supplements</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>10x MEM</td>
			<td>Invitrogen</td>
			<td>11430</td>
			<td></td>
		</tr>
		<tr>
			<td>2 Mercaptro Ethanol</td>
			<td>SIGMA</td>
			<td>M6250</td>
			<td></td>
		</tr>
		<tr>
			<td>B27 supplement minus insulin</td>
			<td>Gibco</td>
			<td>A1895601</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM, high glucose</td>
			<td>Gibco</td>
			<td>11965084</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum (500ml)</td>
			<td>Any</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum (500ml)</td>
			<td>Any</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>L-Glutamine</td>
			<td>Gibco</td>
			<td>25030081</td>
			<td></td>
		</tr>
		<tr>
			<td>NaHCO3</td>
			<td>Any</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>PBS 1x</td>
			<td>Gibco</td>
			<td>10010-031</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin (5000 U/mL)</td>
			<td>Gibco</td>
			<td>15070-063</td>
			<td></td>
		</tr>
		<tr>
			<td>RPMI1640 medium</td>
			<td>Gibco</td>
			<td>21870092</td>
			<td></td>
		</tr>
		<tr>
			<td>&#945;MEM</td>
			<td>Invitrogen</td>
			<td>11900024</td>
			<td></td>
		</tr>
		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Flowcytometry</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>anti-TRA-1-60, FITC, Clone: TRA-1-60, BD Biosciences</td>
			<td>BD / Fisher</td>
			<td>560380</td>
			<td></td>
		</tr>
		<tr>
			<td>anti-Troponin T, Cardiac Isoform Ab-1, Clone: 13-11, Thermo Scientific Lab Vision</td>
			<td>Fisher</td>
			<td>MS-295-P0</td>
			<td></td>
		</tr>
		<tr>
			<td>BD FACS Clean Solution</td>
			<td>BD</td>
			<td>340345</td>
			<td></td>
		</tr>
		<tr>
			<td>BD FACSFlow Sheath Fluid</td>
			<td>BD</td>
			<td>342003</td>
			<td></td>
		</tr>
		<tr>
			<td>BD FACSRinse Solution</td>
			<td>BD</td>
			<td>340346</td>
			<td></td>
		</tr>
		<tr>
			<td>EDTA</td>
			<td>Any</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Falcon Tube with Cell Strainer Cap (Case of 500)</td>
			<td>Corning</td>
			<td>352235</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum (500ml)</td>
			<td>Any</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>LIVE/DEAD Fixable Aqua Dead Cell Stain Kit, for 405 nm excitation</td>
			<td>Molecular Probes</td>
			<td>L34957</td>
			<td></td>
		</tr>
		<tr>
			<td>PDGFRb; anti-CD140b, R-PE, Clone: 28D4, BD Biosciences</td>
			<td>BD / Fisher</td>
			<td>558821</td>
			<td></td>
		</tr>
		<tr>
			<td>Saponin</td>
			<td>Sigma-Aldrich</td>
			<td>47306-50G-F</td>
			<td></td>
		</tr>
		<tr>
			<td>VEcad-FITC; anti-CD144, FITC, Clone: 55-7H1, BD Biosciences</td>
			<td>BD / Fisher</td>
			<td>560411</td>
			<td></td>
		</tr>
		<tr>
			<td>Zenon Alexa Fluor 488 Mouse IgG1 Labeling Kit</td>
			<td>Molecular Probes</td>
			<td>Z25002</td>
			<td></td>
		</tr>
	</tbody>
</table>

preparation of mesh-shaped engineered cardiac tissues derived from human ips cells for in vivo myocardial repair

The current protocol describes methods to generate scalable, mesh-shaped engineered cardiac tissues (ECTs) composed of cardiovascular cells derived from human induced pluripotent stem cells (hiPSCs), which are developed towards the goal of clinical use. HiPSC-derived cardiomyocytes, endothelial cells, and vascular mural cells are mixed with gel matrix and then poured into a polydimethylsiloxane (PDMS) tissue mold with rectangular internal staggered posts. By culture day 14 ECTs mature into a 1.5 cm x 1.5 cm mesh structure with 0.5 mm diameter myofiber bundles. Cardiomyocytes align to the long-axis of each bundle and spontaneously beat synchronously. This approach can be scaled up to a larger (3.0 cm x 3.0 cm) mesh ECT while preserving construct maturation and function. Thus, mesh-shaped ECTs generated from hiPSC-derived cardiac cells may be feasible for cardiac regeneration paradigms.

Figure 1A,B shows the schematics of CM+EC and MC protocol. After inducing CMs and ECs from CM+EC protocol and MCs from MC protocol, the cells are mixed adjusting final MC concentrations to represent 10 to 20% of total cells. The 2 cm&#160;wide tissue mold is fabricated according to the design drawing from 0.5 mm thick PDMS sheet (Figure 2A,B). Six million of CM+EC+MC cells are combined with collagen I, and matrix and poured onto...

Watch this Scientific Journal Video about Preparation of Mesh-Shaped Engineered Cardiac Tissues Derived from Human iPS Cells for In Vivo Myocardial Repair at JoVE.com

Preparation of Mesh-Shaped Engineered Cardiac Tissues Derived from Human iPS Cells for In Vivo Myocardial Repair

The present protocol generates mesh-shaped engineered cardiac tissues containing cardiovascular cells derived from human induced pluripotent stem cells to allow the investigation of cell implantation therapy for heart diseases.

The current protocol describes methods to generate scalable, mesh-shaped engineered cardiac tissues (ECTs) composed of cardiovascular cells derived from ...

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Research

JoVE Journal

Bioengineering

5.3K Views.  RIKEN Center for Biosystems Dynamics Research. The present protocol generates mesh-shaped engineered cardiac tissues containing cardiovascular cells derived from human induced pluripotent stem cells to allow the investigation of cell implantation therapy for heart diseases.

Video: Preparation of Mesh-Shaped Engineered Cardiac Tissues Derived from Human iPS Cells for In Vivo Myocardial Repair

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.  ...

Construction of Defined Human Engineered Cardiac Tissues to Study Mechanisms of Cardiac Cell Therapy

Human cardiac tissue engineering can fundamentally impact therapeutic discovery through the development of new species-specific screening systems that replicate the biofidelity of three-dimensional native human myocardium, while also enabling a controlled level of biological complexity, and allowing non-destructive longitudinal monitoring of tissue contractile function. Initially, human engineered cardiac tissues (hECT) were created using the entire cell population obtained from directed differentiation of human pluripotent stem cells, which typically yielded less than 50% cardiomyocytes. However, to create reliable predictive models of human myocardium, and to elucidate mechanisms of heterocellular interaction, it is essential to accurately control the biological composition in engineered tissues. 
To address this limitation, we utilize live cell sorting for the cardiac surface marker SIRP&#945; and the fibroblast marker CD90 to create tissues containing a 3:1 ratio of these cell types, respectively, that are then mixed together and added to a collagen-based matrix solution. Resulting hECTs are, thus, completely defined in both their cellular and extracellular matrix composition.
Here we describe the construction of defined hECTs as a model system to understand mechanisms of cell-cell interactions in cell therapies, using an example of human bone marrow-derived mesenchymal stem cells (hMSC) that are currently being used in human clinical trials. The defined tissue composition is imperative to understand how the hMSCs may be interacting with the endogenous cardiac cell types to enhance tissue function. A bioreactor system is also described that simultaneously cultures six hECTs in parallel, permitting more efficient use of the cells after sorting.

This manuscript describes the creation of defined engineered cardiac tissues using surface marker expression and cell sorting. The defined tissues can then be used in a multi-tissue bioreactor to investigate mechanisms of cardiac cell therapy in order to provide a functional, yet controlled, model system of the human heart.

Human cardiac tissue engineering can fundamentally impact therapeutic discovery through the development of new species-specific screening systems that ...

In Vivo Quantitative Assessment of Myocardial Structure, Function, Perfusion and Viability Using Cardiac Micro-computed Tomography

The use of Micro-Computed Tomography (MicroCT) for in vivo studies of small animals as models of human disease has risen tremendously due to the fact that MicroCT provides quantitative high-resolution three-dimensional (3D) anatomical data non-destructively and longitudinally. Most importantly, with the development of a novel preclinical iodinated contrast agent called eXIA160, functional and metabolic assessment of the heart became possible. However, prior to the advent of commercial MicroCT scanners equipped with X-ray flat-panel detector technology and easy-to-use cardio-respiratory gating, preclinical studies of cardiovascular disease (CVD) in small animals required a MicroCT technologist with advanced skills, and thus were impractical for widespread implementation. The goal of this work is to provide a practical guide to the use of the high-speed Quantum FX MicroCT system for comprehensive determination of myocardial global and regional function along with assessment of myocardial perfusion, metabolism and viability in healthy mice and in a cardiac ischemia mouse model induced by permanent occlusion of the left anterior descending coronary artery (LAD).

In Vivo Quantitative Assessment of Myocardial Structure, Function, Perfusion and Viability Using Cardiac Micro-computed Tomography

This method outlines the use of Quantum Micro-Computed Tomography (MicroCT) to assess cardiac morphology, function, perfusion, metabolism and viability with iodinated contrast agent in mice with experimentally-induced myocardial ischemia. The technique can be applied for non-destructive high-throughput longitudinal in vivo imaging of various animal models of human heart disease.

The use of Micro-Computed Tomography (MicroCT) for in vivo studies of small animals as models of human disease has risen tremendously due to the fact that ...

Applications of In Vivo Functional Testing of the Rat Tibialis Anterior for Evaluating Tissue Engineered Skeletal Muscle Repair

Despite the regenerative capacity of skeletal muscle, permanent functional and/or cosmetic deficits (e.g., volumetric muscle loss (VML) resulting from traumatic injury, disease and various congenital, genetic and acquired conditions are quite common. Tissue engineering and regenerative medicine technologies have enormous potential to provide a therapeutic solution. However, utilization of biologically relevant animal models in combination with longitudinal assessments of pertinent functional measures are critical to the development of improved regenerative therapeutics for treatment of VML-like injuries. In that regard, a commercial muscle lever system can be used to measure length, tension, force and velocity parameters in skeletal muscle. We used this system, in conjunction with a high power, bi-phase stimulator, to measure in vivo force production in response to activation of the anterior crural compartment of the rat hindlimb. We have previously used this equipment to assess the functional impact of VML injury on the tibialis anterior (TA) muscle, as well as the extent of functional recovery following treatment of the injured TA muscle with our tissue engineered muscle repair (TEMR) technology. For such studies, the left foot of an anaesthetized rat is securely anchored to a footplate linked to a servomotor, and the common peroneal nerve is stimulated by two percutaneous needle electrodes to elicit muscle contraction and dorsiflexion of the foot. The peroneal nerve stimulation-induced muscle contraction is measured over a range of stimulation frequencies (1-200 Hz), to ensure an eventual plateau in force production that allows for an accurate determination of peak tetanic force. In addition to evaluation of the extent of VML injury as well as the degree of functional recovery following treatment, this methodology can be easily applied to study diverse aspects of muscle physiology and pathophysiology. Such an approach should assist with the more rational development of improved therapeutics for muscle repair and regeneration.

Applications of In Vivo Functional Testing of the Rat Tibialis Anterior for Evaluating Tissue Engineered Skeletal Muscle Repair

We describe an in vivo protocol to measure dorsiflexion of the foot following stimulation of the peroneal nerve and contraction of the anterior crural compartment of the rat hindlimb. Such measurements are an indispensable translational tool for evaluating skeletal muscle pathology and tissue engineering approaches to muscle repair and regeneration.

Despite the regenerative capacity of skeletal muscle, permanent functional and/or cosmetic deficits (e.g., volumetric muscle loss (VML) resulting from ...

Automated Contraction Analysis of Human Engineered Heart Tissue for Cardiac Drug Safety Screening

Cardiac tissue engineering describes techniques to constitute three dimensional force-generating engineered tissues. For the implementation of these procedures in basic research and preclinical drug development, it is important to develop protocols for automated generation and analysis under standardized conditions. Here, we present a technique to generate engineered heart tissue (EHT) from cardiomyocytes of different species (rat, mouse, human). The technique relies on the assembly of a fibrin-gel containing dissociated cardiomyocytes between elastic polydimethylsiloxane (PDMS) posts in a 24-well format. Three-dimensional, force-generating EHTs constitute within two weeks after casting. This procedure allows for the generation of several hundred EHTs per week and is technically limited only by the availability of cardiomyocytes (0.4-1.0 x 106/EHT). Evaluation of auxotonic muscle contractions is performed in a modified incubation chamber with a mechanical interlock for 24-well plates and a camera placed on top of this chamber. A software controls a camera moved on an XYZ axis system to each EHT. EHT contractions are detected by an automated figure recognition algorithm, and force is calculated based on shortening of the EHT and the elastic propensity and geometry of the PDMS posts. This procedure allows for automated analysis of high numbers of EHT under standardized and sterile conditions. The reliable detection of drug effects on cardiomyocyte contraction is crucial for cardiac drug development and safety pharmacology. We demonstrate, with the example of the hERG channel inhibitor E-4031, that the human EHT system replicates drug responses on contraction kinetics of the human heart, indicating it to be a promising tool for cardiac drug safety screening.

Here, we show the generation of human engineered heart tissue from induced pluripotent stem cells (hiPSC)-derived cardiomyocytes. We present a method to analyze contraction force and exemplary alteration of contraction pattern by the hERG channel inhibitor E-4031. This method shows high level of robustness and suitability for cardiac drug screening.

Cardiac tissue engineering describes techniques to constitute three dimensional force-generating engineered tissues. For the implementation of these ...

Protocol for MicroRNA Transfer into Adult Bone Marrow-derived Hematopoietic Stem Cells to Enable Cell Engineering Combined with Magnetic Targeting

While CD133+ hematopoietic stem cells (SCs) have been proven to provide high potential in the field of regenerative medicine, their low retention rates after injection into injured tissues as well as the observed massive cell death rates lead to very restricted therapeutic effects. To overcome these limitations, we sought to establish a non-viral based protocol for suitable cell engineering prior to their administration. The modification of human CD133+ expressing SCs using microRNA (miR) loaded magnetic polyplexes was addressed with respect to uptake efficiency and safety as well as the targeting potential of the cells. Relying on our protocol, we can achieve high miR uptake rates of 80&#8211;90% while the CD133+ stem cell properties remain unaffected. Moreover, these modified cells offer the option of magnetic targeting. We describe here a safe and highly efficient procedure for the modification of CD133+ SCs. We expect this approach to provide a standard technology for optimization of therapeutic stem cell effects and for monitoring of the administered cell product via magnetic resonance imaging (MRI).

This protocol illustrates a safe and efficient procedure to modify CD133+ hematopoietic stem cells. The presented non-viral, magnetic polyplex-based approach may provide a basis for the optimization of therapeutic stem cell effects as well as for monitoring the administered cell product via magnetic resonance imaging.

While CD133+ hematopoietic stem cells (SCs) have been proven to provide high potential in the field of regenerative medicine, their low retention rates ...

Fabrication of 3D Cardiac Microtissue Arrays using Human iPSC-Derived Cardiomyocytes, Cardiac Fibroblasts, and Endothelial Cells

Generation of human cardiomyocytes (CMs), cardiac fibroblasts (CFs), and endothelial cells (ECs) from induced pluripotent stem cells (iPSCs) has provided a unique opportunity to study the complex interplay among different cardiovascular cell types that drives tissue development and disease. In the area of cardiac tissue models, several sophisticated three-dimensional (3D) approaches use induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) to mimic physiological relevance and native tissue environment with a combination of extracellular matrices and crosslinkers. However, these systems are complex to fabricate without microfabrication expertise and require several weeks to self-assemble. Most importantly, many of these systems lack vascular cells and cardiac fibroblasts that make up over 60% of the nonmyocytes in the human heart. Here we describe the derivation of all three cardiac cell types from iPSCs to fabricate cardiac microtissues. This facile replica molding technique allows cardiac microtissue culture in standard multi-well cell culture plates for several weeks. The platform allows user-defined control over microtissue sizes based on initial seeding density and requires less than 3 days for self-assembly to achieve observable cardiac microtissue contractions. Furthermore, the cardiac microtissues can be easily digested while maintaining high cell viability for single-cell interrogation with the use of flow cytometry and single-cell RNA sequencing (scRNA-seq). We envision that this in vitro model of cardiac microtissues will help accelerate validation studies in drug discovery and disease modeling.

Here, we describe an easy-to-use methodology to generate 3D self-assembled cardiac microtissue arrays composed of pre-differentiated human-induced pluripotent stem cell-derived cardiomyocytes, cardiac fibroblasts, and endothelial cells. This user-friendly and low cell requiring technique to generate cardiac microtissues can be implemented for disease modeling and early stages of drug development.

Generation of human cardiomyocytes (CMs), cardiac fibroblasts (CFs), and endothelial cells (ECs) from induced pluripotent stem cells (iPSCs) has provided ...

Single-Cell Optical Action Potential Measurement in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Conventional intracellular microelectrode techniques to quantify cardiomyocyte electrophysiology are extremely complex, labor intensive, and typically carried out in low throughput. Rapid and ongoing expansion of induced pluripotent stem cell (iPSC) technology presents a new standard in cardiovascular research and alternate methods are now necessary to increase throughput of electrophysiological data at a single cell level. VF2.1Cl is a recently derived voltage sensitive dye which provides a rapid single channel, high magnitude response to fluctuations in membrane potential. It possesses kinetics superior to those of other existing voltage indicators and makes available functional data equivalent to that of traditional microelectrode techniques. Here, we demonstrate simplified, non-invasive action potential characterization in externally paced human iPSC derived cardiomyocytes using a modular and highly affordable photometry system.

Here we describe optical acquisition and characterization of action potentials from induced pluripotent stem cell derived cardiomyocytes using a high-speed modular photometry system.

Conventional intracellular microelectrode techniques to quantify cardiomyocyte electrophysiology are extremely complex, labor intensive, and typically ...

Cardiac Spheroids as in vitro Bioengineered Heart Tissues to Study Human Heart Pathophysiology

Despite several advances in cardiac tissue engineering, one of the major challenges to overcome remains the generation of a fully functional vascular network comprising several levels of complexity to provide oxygen and nutrients within bioengineered heart tissues. Our laboratory has developed a three-dimensional in vitro model of the human heart, known as the "cardiac spheroid" or "CS". This presents biochemical, physiological, and pharmacological features typical of the human heart and is generated by co-culturing its three major cell types, such as cardiac myocytes, endothelial cells, and fibroblasts. Human induced pluripotent stem cells-derived cardiomyocytes (hiPSC-CMs or iCMs) are co-cultured at ratios approximating the ones found in vivo with human cardiac fibroblasts (HCFs) and human coronary artery endothelial cells (HCAECs) in hanging drop culture plates for three to four days. The confocal analysis of CSs stained with antibodies against cardiac Troponin T, CD31 and vimentin (markers for cardiac myocytes, endothelial cells and fibroblasts, respectively) shows that CSs present a complex endothelial cell network, resembling the native one found in the human heart. This is confirmed by the 3D rendering analysis of these confocal images. CSs also present extracellular matrix (ECM) proteins typical of the human heart, such as collagen type IV, laminin and fibronectin. Finally, CSs present a contractile activity measured as syncytial contractility closer to the one typical of the human heart compared to CSs that contain iCMs only. When treated with a cardiotoxic anti-cancer agent, such as doxorubicin (DOX, used to treat leukemia, lymphoma and breast cancer), the viability of DOX-treated CSs is significantly reduced at 10 &#181;M genetic and chemical inhibition of endothelial nitric oxide synthase, a downstream target of DOX in HCFs and HCAECs, reduced its toxicity in CSs. Given these unique features, CSs are currently used as in vitro models to study heart biochemistry, pathophysiology, and pharmacology.

This protocol aims to fabricate 3D cardiac spheroids (CSs) by co-culturing cells in hanging drops.&#160;Collagen-embedded CSs are treated with doxorubicin (DOX, a cardiotoxic agent) at physiological concentrations to model heart failure. In vitro testing using DOX-treated CSs may be used to identify novel therapies for heart failure patients.

Despite several advances in cardiac tissue engineering, one of the major challenges to overcome remains the generation of a fully functional vascular ...

Fibroblast Derived Human Engineered Connective Tissue for Screening Applications

Fibroblasts are phenotypically highly dynamic cells, which quickly transdifferentiate into myofibroblasts in response to biochemical and biomechanical stimuli. The current understanding of fibrotic processes, including cardiac fibrosis, remains poor, which hampers the development of new anti-fibrotic therapies. Controllable and reliable human model systems are crucial for a better understanding of fibrosis pathology. This is a highly reproducible and scalable protocol to generate engineered connective tissues (ECT) in a 48-well casting plate to facilitate studies of fibroblasts and the pathophysiology of fibrotic tissue in a 3-dimensional (3D) environment. ECT are generated around the poles with tunable stiffness, allowing for studies under a defined biomechanical load. Under the defined loading conditions, phenotypic adaptations controlled by cell-matrix interactions can be studied. Parallel testing is feasible in the 48-well format with the opportunity for the time-course analysis of multiple parameters, such as tissue compaction and contraction against the load. From these parameters, biomechanical properties such as tissue stiffness and elasticity can be studied.

Presented here is a protocol to generate engineered connective tissues for a parallel culture of 48 tissues in a multi-well plate with double poles, suitable for mechanistic studies, disease modeling, and screening applications. The protocol is compatible with fibroblasts from different organs and species and is exemplified here with human primary cardiac fibroblasts.

Fibroblasts are phenotypically highly dynamic cells, which quickly transdifferentiate into myofibroblasts in response to biochemical and biomechanical ...