This work was partially supported by funding from the Food and Drug Administration (U01 FD006676-01 awarded to the Health and Environmental Sciences Institute) and by funding from the National Institutes of Health (HL151094 to Dr. Geisse). We thank Dr. Alec S. T. Smith for his assistance with the preparation of this manuscript.

<ol>
	<li>Sharma, A., Wu, J. C., Wu, S. M. <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+cardiomyocytes+for+cardiovascular+disease+modeling+and+drug+screening.">Induced pluripotent stem cell-derived cardiomyocytes for cardiovascular disease modeling and drug screening.</a> Stem Cell Research &amp; Therapy. 4, 150 (2013).</li><li>Mudera, V., Smith, A. S. T., Brady, M. A., Lewis, M. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effect+of+cell+density+on+the+maturation+and+contractile+ability+of+muscle+derived+cells+in+a+3D+tissue-engineered+skeletal+muscle+model+and+determination+of+the+cellular+and+mechanical+stimuli+required+for+the+synthesis+of+a+postural+phenotype.">The effect of cell density on the maturation and contractile ability of muscle derived cells in a 3D tissue-engineered skeletal muscle model and determination of the cellular and mechanical stimuli required for the synthesis of a postural phenotype.</a> Journal of Cellular Physiology. 225 (3), 646-653 (2010).</li><li>Vandenburgh, 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=Tissue-engineered+skeletal+muscle+organoids+for+reversible+gene+therapy.">Tissue-engineered skeletal muscle organoids for reversible gene therapy.</a> Human Gene Therapy. 7 (17), 2195-2200 (1996).</li><li>Rao, L., Qian, Y., Khodabukus, A., Ribar, T., 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=Engineering+human+pluripotent+stem+cells+into+a+functional+skeletal+muscle+tissue.">Engineering human pluripotent stem cells into a functional skeletal muscle tissue.</a> Nature Communications. 9 (1), 126 (2018).</li><li>Fleming, J. 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=Bioengineered+human+skeletal+muscle+capable+of+functional+regeneration.">Bioengineered human skeletal muscle capable of functional regeneration.</a> BMC Biology. 18 (1), 145 (2020).</li><li>Madden, L., Juhas, M., Kraus, W. E., Truskey, G. A., 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=Bioengineered+human+myobundles+mimic+clinical+responses+of+skeletal+muscle+to+drugs.">Bioengineered human myobundles mimic clinical responses of skeletal muscle to drugs.</a> eLife. 4, 04885 (2015).</li><li>Urciuolo, 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=Engineering+a+3D+in+vitro+model+of+human+skeletal+muscle+at+the+single+fiber+scale.">Engineering a 3D in vitro model of human skeletal muscle at the single fiber scale.</a> PLOS One. 15 (5), 0232081 (2020).</li><li>Afshar, M. E., 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+96-well+culture+platform+enables+longitudinal+analyses+of+engineered+human+skeletal+muscle+microtissue+strength.">A 96-well culture platform enables longitudinal analyses of engineered human skeletal muscle microtissue strength.</a> Scientific Reports. 10, 6918 (2020).</li><li>Sakar, M. S., 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=Formation+and+optogenetic+control+of+engineered+3D+skeletal+muscle+bioactuators.">Formation and optogenetic control of engineered 3D skeletal muscle bioactuators.</a> Lab on a Chip. 12 (23), 4976-4985 (2012).</li><li>Vila, O. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantification+of+human+neuromuscular+function+through+optogenetics.">Quantification of human neuromuscular function through optogenetics.</a> Theranostics. 9 (5), 1232-1246 (2019).</li><li>Khodabukus, A., Baar, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Defined+electrical+stimulation+emphasizing+excitability+for+the+development+and+testing+of+engineered+skeletal+muscle.">Defined electrical stimulation emphasizing excitability for the development and testing of engineered skeletal muscle.</a> Tissue Engineering Part C: Methods. 18 (5), 349-357 (2011).</li><li>Vandenburgh, 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=Drug-screening+platform+based+on+the+contractility+of+tissue-engineered+muscle.">Drug-screening platform based on the contractility of tissue-engineered muscle.</a> Muscle &amp; Nerve. 37 (4), 438-447 (2008).</li><li>Bielawski, K. S., Leonard, A., Bhandari, S., Murry, C. E., Sniadecki, N. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Real-time+force+and+frequency+analysis+of+engineered+human+heart+tissue+derived+from+induced+pluripotent+stem+cells+using+magnetic+sensing.">Real-time force and frequency analysis of engineered human heart tissue derived from induced pluripotent stem cells using magnetic sensing.</a> Tissue Enineering Part C Methods. 22 (10), 932-940 (2016).</li><li>Smith, A. S. 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=High-throughput,+real-time+monitoring+of+engineered+skeletal+muscle+function+using+magnetic+sensing.">High-throughput, real-time monitoring of engineered skeletal muscle function using magnetic sensing.</a> bioRxiv. , 492879 (2022).</li><li>Scheraga, H. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+thrombin-fibrinogen+interaction.">The thrombin-fibrinogen interaction.</a> Biophysical Chemistry. 112 (2-3), 117-130 (2004).</li><li>Hinds, S., Bian, W., Dennis, R. G., 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=The+role+of+extracellular+matrix+composition+in+structure+and+function+of+bioengineered+skeletal+muscle.">The role of extracellular matrix composition in structure and function of bioengineered skeletal muscle.</a> Biomaterials. 32 (14), 3575-3583 (2011).</li><li>Carvalho, 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=Doxorubicin:+the+good,+the+bad+and+the+ugly+effect.">Doxorubicin: the good, the bad and the ugly effect.</a> Current Medicinal Chemistry. 16 (25), 3267-3285 (2009).</li><li>Ahmad, 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=Cardiac+dysfunction+associated+with+a+nucleotide+polymerase+inhibitor+for+treatment+of+hepatitis+C.">Cardiac dysfunction associated with a nucleotide polymerase inhibitor for treatment of hepatitis C.</a> Hepatology. 62 (2), 409-416 (2015).</li><li>Gill, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=From+the+cover:+Investigative+nonclinical+cardiovascular+safety+and+toxicology+studies+with+BMS-986094,+an+NS5b+RNA-dependent+RNA+polymerase+inhibitor.">From the cover: Investigative nonclinical cardiovascular safety and toxicology studies with BMS-986094, an NS5b RNA-dependent RNA polymerase inhibitor.</a> Toxicological Sciences. 155 (2), 348-362 (2017).</li><li>Ostap, E. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=2,3-Butanedione+monoxime+(BDM)+as+a+myosin+inhibitor.">2,3-Butanedione monoxime (BDM) as a myosin inhibitor.</a> Journal of Muscle Research and Cell Motility. 23 (4), 305-308 (2002).</li><li>Fryer, M. W., Gage, P. W., Neering, I. R., Dulhunty, A. F., Lamb, G. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Paralysis+of+skeletal+muscle+by+butanedione+monoxime,+a+chemical+phosphatase.">Paralysis of skeletal muscle by butanedione monoxime, a chemical phosphatase.</a> Pfl&#252;gers Archiv: European Journal of Physiology. 411 (1), 76-79 (1988).</li><li>Fleming, J. 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=Functional+regeneration+of+tissue+engineered+skeletal+muscle+in+vitro+is+dependent+on+the+inclusion+of+basement+membrane+proteins.">Functional regeneration of tissue engineered skeletal muscle in vitro is dependent on the inclusion of basement membrane proteins.</a> Cytoskeleton. 76 (6), 371-382 (2019).</li><li>Capel, 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=Scalable+3D+printed+molds+for+human+tissue+engineered+skeletal+muscle.">Scalable 3D printed molds for human tissue engineered skeletal muscle.</a> Frontiers in Bioengineering and Biotechnology. 7, 20 (2019).</li><li>Tsui, 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=Tunable+electroconductive+decellularized+extracellular+matrix+hydrogels+for+engineering+human+cardiac+microphysiological+systems.">Tunable electroconductive decellularized extracellular matrix hydrogels for engineering human cardiac microphysiological systems.</a> Biomaterials. 272, 120764 (2021).</li><li>Tsui, 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=Conductive+silk-polypyrrole+composite+scaffolds+with+bioinspired+nanotopographic+cues+for+cardiac+tissue+engineering.">Conductive silk-polypyrrole composite scaffolds with bioinspired nanotopographic cues for cardiac tissue engineering.</a> Journal of Materials Chemistry B. 6 (44), 7185-7196 (2018).</li><li>Gabella, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Muscle+cells,+nerves,+fibroblasts+and+vessels+in+the+detrusor+of+the+rat+urinary+bladder.">Muscle cells, nerves, fibroblasts and vessels in the detrusor of the rat urinary bladder.</a> Journal of Smooth Muscle Research. 55, 34-67 (2019).</li><li>Christov, 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=Muscle+satellite+cells+and+endothelial+cells:+close+neighbors+and+privileged+partners.">Muscle satellite cells and endothelial cells: close neighbors and privileged partners.</a> Molecular Biology of the Cell. 18 (4), 1397-1409 (2007).</li><li>Bersini, S., 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=Engineering+an+environment+for+the+study+of+fibrosis:+A+3D+human+muscle+model+with+endothelium+specificity+and+endomysium.">Engineering an environment for the study of fibrosis: A 3D human muscle model with endothelium specificity and endomysium.</a> Cell Reports. 25 (13), 3858-3868 (2018).</li><li>Gilbert-Honick, 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=Engineering+functional+and+histological+regeneration+of+vascularized+skeletal+muscle.">Engineering functional and histological regeneration of vascularized skeletal muscle.</a> Biomaterials. 164, 70-79 (2018).</li><li>Maffioletti, S. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+human+iPSC-derived+artificial+skeletal+muscles+model+muscular+dystrophies+and+enable+multilineage+tissue+engineering.">Three-dimensional human iPSC-derived artificial skeletal muscles model muscular dystrophies and enable multilineage tissue engineering.</a> Cell Reports. 23 (3), 899-908 (2018).</li></ol>

All authors are employees and equity holders in Curi Bio Inc., the company that commercializes the Mantarray hardware and associated software.

This study describes methods for generating 3D engineered cardiac and skeletal muscle tissues within a 24-well consumable casting kit. By following these methods, it is possible to consistently achieve a complete array of 24 tissues with no casting failures for subsequent drug screening. Critical considerations for achieving such an outcome are ensuring that during casting all the steps are performed on ice to prevent premature polymerization of the hydrogels, removal of cell dissociation reagent prior to tissue casting, thorough mixing of the cell and hydrogel suspension for each tissue, replacement of pipette tips between tissues, and the use of heat-inactivated FBS (if used at all). Also, it is important to ensure that the post lattice is not moved once casting starts and is transferred gently once hydrogels have formed.
Major modifications include the use of different cell types to achieve cardiac versus skeletal EMTs and the doping of hydrogels with variable concentrations of basement membrane proteins to promote cellular maturation and tissue stability. The beneficial effects of such doping must be tested on a case-by-case basis, but has been shown to improve functional outcomes and tissue longevity under certain circumstances14,16,22. It is also noteworthy that the cell densities listed are a guide and may need to be optimized for different cell lines. Alternative hydrogel compositions could also be considered as a means to modify the structural and functional properties of the achieved EMTs23,24,25. The native muscle microenvironment also contains supporting cell types to promote vascularization, innervation, and matrix deposition to support myocytes in form and function26,27. While the system described here currently incorporates fibroblasts into 3D cardiac tissues, additional cell types may create a more physiological relevant model to study the safety and efficacy of therapeutic compounds in vitro. Previously, a range of supporting cell types have successfully been integrated into 3D-engineered tissues presenting an exciting template for future study using the magnetic sensing contractility platform28,29,30.
Troubleshooting for this protocol centers on the formation of unreliable or inconsistent tissues during the casting process. Care must be taken to avoid bubble formation in the hydrogels as they are cast while still facilitating even distribution of the cells during mixing. Optimization experiments will likely be needed for each new cell type to identify ideal cell densities, cell ratios, and matrix composition.
A major limitation for this technique is the significant number of cells required to establish a full plate of 24 EMTs. For the data presented here, 15 million cardiomyocytes and 18 million skeletal myoblasts were used per plate. Certain researchers may not have access to such large pools of cellular material, which may inhibit their ability to use this platform to its fullest extent. If end-users do not have access to magnetic sensing hardware, measurements of post deflections need to be performed optically, which significantly reduces throughput and prevents the simultaneous recording of muscle contractions across multiple wells. However, the Mantarray hardware overcomes these limitations to offer the first commercial system capable of continuous, non-invasive analysis of EMT contraction simultaneously across multiple constructs.
Magnetic sensing across 24 wells facilitates longitudinal studies of EMT functional development in real-time and allows accurate measurement of acute responses to chemical, environmental, or genetic manipulation. While magnetic sensing has several advantages such as simultaneous measurement across multiple tissues, and does not require complicated data analysis, optical detection methods do enable simultaneous measurement of physiological metrics such as calcium flux or voltage mapping. However, data sets such as those illustrated in the results section demonstrate the breadth of applications this technology has in the drug development space. Given that few assays on the market offer the means to perform a direct assessment of contractile output in engineered muscle, these methods hold the potential to revolutionize the preclinical development pipeline.

Induced pluripotent stem cell (iPSC) models are increasingly becoming key players in the preclinical pipeline for therapeutic discovery and development, as well as basic biological research and disease modeling1,2,3,4,5. Contractile tissues, such as cardiac and skeletal muscle derived from iPSCs hold great potential for improving the predictive power of human in vitro studies as direct assessment of muscle contractile force and kinetics are quantitative metrics to study overall tissue function4,6,7,8. Typically, measurements of contractile force have been obtained either indirectly by optical tracking of substrate deflection9,10 or directly by attachment of cells/tissues to a force transducer4,11,12. These methods, while accurate, are inherently low-throughput and typically require highly skilled operators to collect and analyze data.
Previous work has shown that magnetic field sensing circumvents these obstacles and provides an alternate method to assess engineered muscle function simultaneously across multiple tissue constructs13. The Mantarray (Magnetometric Analyzer for eNgineered Tissue ARRAY) 3D Contractility Platform builds on this technology using a device capable of measuring the contractility of engineered muscle tissues in a highly-parallel manner that leverages the complexity of 3D cellular models with higher-throughput screening14. The platform enables label-free, quantitative, real-time monitoring of contractile function in cardiac and skeletal muscle tissues in or outside of a standard cell-culture incubator, eliminating the need for optical-based contractile imaging and analysis. This technology facilitates direct comparison of healthy and diseased cell lines and enables measurement of a drug&#39;s effect on contractile tissues, establishing quantifiable, in vitro, safety, and efficacy data for new and existing therapeutic compounds.
Engineered 3D muscle tissues can be fabricated between two posts in a highly reproducible manner using the Mantarray consumable, 24-well casting plate (Figure 1). One post is rigid, while the other post is flexible and contains a small magnet. When the tissue construct contracts, it displaces the flexible post and the embedded magnet. The EMT plate is positioned within the instrument, and post displacement is measured via an array of magnetic sensors on a circuit board below the plate holder. The measured changes in the magnetic field are converted into absolute contractile force using a mathematical algorithm. The instrument employs rapid data sampling rates to enable the collection of detailed information about the functional capacity and maturity of the cell type(s) being assayed, including contraction frequency, velocity, and decay time. These functional measurements can be obtained across all 24 wells simultaneously with the magnetic sensing platform or individually and sequentially using traditional optical methods.
This study describes a highly reproducible method for engineering 3D skeletal muscle and cardiac microtissues in a fibrin-based hydrogel. During a brief, 80-min reaction, thrombin catalyzes the conversion of fibrinogen into fibrin, providing a scaffold for muscle cells to develop in suspended culture15. Stromal cells help remodel the matrix and tissues become contractile as muscle cells form a syncytium within the hydrogel. The contractility of these tissues was analyzed using the magnetic sensing approach, both before and after compound exposure, validating this modality for use in dose-response drug studies. Primary human myoblasts from a healthy donor biopsy were obtained commercially and cultured in 2D according to the vendor&#39;s protocols. Cells were expanded using a skeletal muscle growth medium through three passages to generate sufficient cell numbers to fabricate 3D tissues. Stromal cells and hiPSC-derived cardiomyocytes were cultured according to the vendor&#39;s protocol for 3 days to allow recovery from cryopreservation before casting cells into tissues. Representative results are provided illustrating the types of data sets that can be collected using the magnetic sensing platform. Common pitfalls associated with the generation of engineered tissues using these methods are also addressed.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>100 &#181;m cell strainer&#160;</td>
			<td>CELLTREAT</td>
			<td>229485</td>
			<td></td>
		</tr>
		<tr>
			<td>100 mm cell culture dish</td>
			<td>ThermoFisher</td>
			<td>150466</td>
			<td></td>
		</tr>
		<tr>
			<td>50 mL Steriflip filter</td>
			<td>MilliporeSigma&#160;</td>
			<td>SCGP00525</td>
			<td></td>
		</tr>
		<tr>
			<td>500 mL filter flask</td>
			<td>MilliporeSigma&#160;</td>
			<td>S2GVU05RE</td>
			<td></td>
		</tr>
		<tr>
			<td>6-aminocaproic acid</td>
			<td>Sigma</td>
			<td>A2504</td>
			<td></td>
		</tr>
		<tr>
			<td>B27</td>
			<td>Gibco</td>
			<td>17504044</td>
			<td></td>
		</tr>
		<tr>
			<td>Cardiosight Maintenance Medium</td>
			<td>NEXEL</td>
			<td>CM-002A</td>
			<td></td>
		</tr>
		<tr>
			<td>Cardiosight Plating Medium</td>
			<td>NEXEL</td>
			<td>CM-020A</td>
			<td></td>
		</tr>
		<tr>
			<td>C-Pace EM stimulator&#160;</td>
			<td>IonOptix&#160;</td>
			<td>EM</td>
			<td></td>
		</tr>
		<tr>
			<td>Curi Bio Muscle Differentiation Media Kit</td>
			<td></td>
			<td>Primary - DIFF</td>
			<td></td>
		</tr>
		<tr>
			<td>Curi Bio Muscle Maintenance Media Kit</td>
			<td>Curi Bio</td>
			<td>Primary - MAINT</td>
			<td></td>
		</tr>
		<tr>
			<td>DAPI</td>
			<td>Invitrogen</td>
			<td>D1306</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM, high glucose, GlutaMAX</td>
			<td>Gibco</td>
			<td>10566-016</td>
			<td></td>
		</tr>
		<tr>
			<td>Dnase</td>
			<td>Sigma</td>
			<td>11284932001</td>
			<td></td>
		</tr>
		<tr>
			<td>DPBS</td>
			<td>Gibco</td>
			<td>14190-250</td>
			<td></td>
		</tr>
		<tr>
			<td>Dystrophin antibody&#160;</td>
			<td>Abcam</td>
			<td>ab154168</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal bovine serum (FBS)</td>
			<td>Thermo Scientific</td>
			<td>10082147</td>
			<td>Must be heat-inactivated</td>
		</tr>
		<tr>
			<td>Fibrinogen (Bovine)</td>
			<td>Sigma</td>
			<td>E8630</td>
			<td></td>
		</tr>
		<tr>
			<td>Glutaraldehyde</td>
			<td>Sigma</td>
			<td>354400</td>
			<td></td>
		</tr>
		<tr>
			<td>Ham&#39;s F10</td>
			<td>Gibco</td>
			<td>11550043</td>
			<td></td>
		</tr>
		<tr>
			<td>Hemacytometer&#160;</td>
			<td>Sigma&#160;</td>
			<td>Z359629</td>
			<td></td>
		</tr>
		<tr>
			<td>HS-27A Fibroblasts</td>
			<td>ATCC</td>
			<td>CRL-2496</td>
			<td></td>
		</tr>
		<tr>
			<td>Human Skeletal Muscle Myoblasts&#160;</td>
			<td>Lonza&#160;</td>
			<td>CC-2580</td>
			<td></td>
		</tr>
		<tr>
			<td>Luer Lock 0.2 &#181;m syringe filter</td>
			<td>Corning</td>
			<td>431219</td>
			<td></td>
		</tr>
		<tr>
			<td>Luer Lock 10 mL syringe</td>
			<td>BH Supplies</td>
			<td>BH10LL</td>
			<td></td>
		</tr>
		<tr>
			<td>Mantarray Instrument</td>
			<td>Curi Bio</td>
			<td>MANTA-24-B1</td>
			<td>System</td>
		</tr>
		<tr>
			<td>Mantarray Plate Kits</td>
			<td>Curi Bio</td>
			<td>MA-24-SKM-5</td>
			<td>Pack of 5 kits</td>
		</tr>
		<tr>
			<td>Mantarray stimulation lid&#160;</td>
			<td>Curi Bio</td>
			<td>EM</td>
			<td></td>
		</tr>
		<tr>
			<td>Matrigel (ECM)</td>
			<td>Corning</td>
			<td>356231</td>
			<td></td>
		</tr>
		<tr>
			<td>Nexel Cardiosight-S, Cardiomyocytes</td>
			<td>NEXEL</td>
			<td>C-002</td>
			<td></td>
		</tr>
		<tr>
			<td>Optical Microscope</td>
			<td>Nikon Ti2E</td>
			<td>MEA54000</td>
			<td></td>
		</tr>
		<tr>
			<td>Pan Myosin Heavy Chain antibody&#160;</td>
			<td>DSHB</td>
			<td>MF-20</td>
			<td></td>
		</tr>
		<tr>
			<td>Poly(ethyleneimine)</td>
			<td>Sigma</td>
			<td>P3143</td>
			<td></td>
		</tr>
		<tr>
			<td>ROCK inhibitor</td>
			<td>StemCell Technologies</td>
			<td>Y-27632</td>
			<td></td>
		</tr>
		<tr>
			<td>RPMI</td>
			<td>Gibco</td>
			<td>11875-093</td>
			<td></td>
		</tr>
		<tr>
			<td>Skeletal Muscle Growth Medium (SkGM-2)</td>
			<td>Lonza</td>
			<td>CC-3245</td>
			<td></td>
		</tr>
		<tr>
			<td>Standard 24-well plates</td>
			<td>Greiner</td>
			<td>M8812&#160;</td>
			<td>Other manufacturer&#39;s plates will not fit</td>
		</tr>
		<tr>
			<td>Standard 6-well plates</td>
			<td>ThermoFisher</td>
			<td>140675</td>
			<td></td>
		</tr>
		<tr>
			<td>Stromal medium (DMEM + 20% FBS)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>T175 Filter Flask</td>
			<td>ThermoFisher</td>
			<td>159910</td>
			<td></td>
		</tr>
		<tr>
			<td>T225 Filter Flask</td>
			<td>ThermoFisher</td>
			<td>159934</td>
			<td></td>
		</tr>
		<tr>
			<td>Thrombin</td>
			<td>Sigma</td>
			<td>T4648</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypan Blue solution, 0.4%</td>
			<td>ThermoFisher</td>
			<td>15250061</td>
			<td></td>
		</tr>
		<tr>
			<td>TrypLE Select Enzyme (10x)</td>
			<td>Thermo Scientific</td>
			<td>A1217702</td>
			<td></td>
		</tr>
		<tr>
			<td>TrypLE Select Enzyme (1x)</td>
			<td>Thermo Scientific</td>
			<td>12563011</td>
			<td></td>
		</tr>
	</tbody>
</table>

preclinical drug testing in scalable 3d engineered muscle tissues

Accurately modeling healthy and disease conditions in vitro is vital for the development of new treatment strategies and therapeutics. For cardiac and skeletal muscle diseases, contractile force and kinetics constitute key metrics for assessing muscle function. New and improved methods for generating engineered muscle tissues (EMTs) from induced pluripotent stem cells have made in vitro disease modeling more reliable for contractile tissues; however, reproducibly fabricating tissues from suspended cell cultures and measuring their contractility is challenging. Such techniques are often plagued with high failure rates and require complex instrumentation and customized data analysis routines. A new platform and device that utilizes 3D EMTs in conjunction with a label-free, highly-parallel, and automation-friendly contractility assay circumvent many of these obstacles. The platform enables facile and reproducible fabrication of 3D EMTs using virtually any cell source. Tissue contractility is then measured via an instrument that simultaneously measures 24 tissues without the need for complex software analysis routines. The instrument can reliably measure micronewton changes in force, allowing for dose-dependent compound screening to measure the effect of a drug or therapeutic on contractile output. Engineered tissues made with this device are fully functional, generating twitch and tetanic contractions upon electrical stimulation, and can be analyzed longitudinally in culture over weeks or months. Here, we show data from cardiac muscle EMTs under acute and chronic dosing with known toxicants, including a drug (BMS-986094) that was pulled from clinical trials after patient fatalities due to unanticipated cardiotoxicity. Altered skeletal muscle function in engineered tissues in response to treatment with a myosin inhibitor is also presented. This platform enables the researcher to integrate complex, information-rich bioengineered model systems into their drug discovery workflow with minimal additional training or skills required.

Cells were cast into engineered muscle tissues in the 2-post consumable plate (Figure 1). Successful EMTs will appear uniform, and the matrix will be evenly distributed between the posts (Figure 2A). The matrix should also wrap around both posts, producing equivalent anchor points for the tissue. Failures in casting are rare with this method and are usually obvious with a visual inspection. Unsuccessful EMT production can range from catastrophic failures, such as tissue detachment from the posts (Figure 2B) to more subtle structural flaws, such as air bubbles and loose attachment to the posts (Figure 2C,D). Tissues with minor flaws may still be viable, but the data from these tissues should be examined carefully to ensure it is comparable to uncompromised EMTs. For example, air bubbles within an EMT may be squeezed out as the tissue compacts over time, rendering a fully functional construct without contractile deficiencies. These tissues must be evaluated on a case-by-case basis, however, as the location of the air bubbles may affect functional recovery. Air bubbles generated at the posts, for instance, may affect tissue attachment, which could impede long-term adherence to the post.
Tissues begin to compact within the first 24 h as cells remodel the matrix within the hydrogel (Figure 3). Compaction is a gradual process and usually proceeds over the first 2-4 weeks of culture. Overall, tissue compaction is consistent between technical and biological replicates (Figure 4). It is normal for some cell lines to compact the matrix more than others as tissues mature over time. The percentage of myogenic cells within a construct influences the rate and overall degree of EMT compaction. Total myogenic content for both cardiac and skeletal muscle cell lines should be above 80% to minimize variation between engineered tissues. This is particularly important when comparing contractile forces and kinetics across cell lines.
Within the first few days after casting, cardiomyocytes begin to spontaneously beat in culture, rhythmically bending the flexible post with each muscle contraction. Skeletal muscle constructs contract in response to electrical stimulation by day 7 after starting differentiation. Field stimulation was applied to skeletal muscle tissues via an external stimulator attached to a custom 24-well electrode lid. The lid, fabricated with a pair of carbon electrodes for each well, sits on top of the 24-well plate of tissues, simultaneously stimulating each EMT to induce muscle contractions. Tissues were paced using a 10 V stimulus for 10 ms pulse durations at 1 Hz during functional measurements. Contractile tissues indicate skeletal myoblasts that have fused, forming myotubes complete with functional sarcomeres and contractile machinery. Skeletal EMTs stain positive for myosin heavy chain (MyHC) and dystrophin is localized to the myotube membrane revealing a classic ring shape in cross-sectional immunohistochemical analysis (Figure 5). Once EMTs are functional, contractility can be measured daily in the magnetic sensing instrument, tracking force and kinetics as the constructs develop and mature over time. Both cardiac and skeletal muscle tissues remain contractile for weeks to months in 3D culture (Figure 6), and they can be used for a wide range of contractility studies.
The magnetic detection approach can be used to simultaneously measure acute and chronic effects of structural cardiotoxicants, such as doxorubicin (Figure 7) and BMS-986094 (Figure 8), as well as other drugs that affect muscle contractility. Optical tracking methods of contraction detection can also be used, but care must be taken when studying acute drug effects as measurements must be taken sequentially. The extended longevity of cardiac and skeletal EMTs in 3D culture enables long-term drug studies in these tissues. This permits users to explore the effects of repeat dosing, as well as continued, long-term exposure to compounds that may show cardiotoxic effects over time as occurs with doxorubicin. Doxorubicin (dox) is an anti-cancer chemotherapy drug17. The amount of drug administered to patients varies, depending on the type of cancer, age of the patient, height and weight of the patient, as well as other factors. For this reason, it is important to test the effect of dox across a wide range of concentrations and delivery schedules. Here, cardiac EMTs were treated over the course of 27 days with three separate concentrations (0.1 &#181;M, 1 &#181;M, and 10 &#181;M) of dox (Figure 7). The groups were stratified further by treating EMTs at each concentration with either a bolus treatment or continuous administration with a medium change every 72 h. Wells given bolus treatments of dox were exposed to the drug at three separate time points, allowing for recovery between dosing. The two highest doses of bolus and continuous exposure showed an immediate and prolonged cessation of contractile force generation throughout the study. The middle and lowest concentrations had varying effects on the tissues, depending on the administration method. In the lowest concentration of the drug, the bolus group showed no difference from the controls. However, contractile force diminished after 2 weeks of continuous exposure. The mid-range concentration of the drug had an interesting effect. While continuous dosing reduced force over the first couple of days of treatment and lasted throughout the experiment, the bolus group showed a recovery of contractile force back to control levels when the drug was washed out after 3 days. However, the second bolus of the drug caused a full cessation of force, followed by no recovery (Figure 7), indicating that repeatedly dosing at this concentration may have a cardiotoxic effect in patients treated with this drug. The broad scope of this study, in both time and experimental conditions, highlights the utility of 3D engineered tissues in toxicity screening, as they remain contractile and responsive to chemical exposure over extended periods of time, allowing for long-term drug studies within a single set of muscle tissues. This facilitates not only identifying compounds that may have a cardiotoxic effect with chronic exposure but also detecting potential cardiotoxic timing of administration.
In vitro toxicity testing in engineered human muscle tissues is one way to help keep human patients safe in clinical trials. BMS-986094 is a nucleotide polymerase (NS5B) inhibitor used to treat hepatitis C. The drug was in Phase II clinical development when Bristol-Myers Squibb discontinued development due to several cases of unexpected heart failure in patients18,19. Here, BMS-986094 was applied to cardiac EMTs to test whether 3D engineered muscle tissues would develop a cardiotoxic reaction to the drug (Figure 8). Three different concentrations of the drug were applied, and tissues were monitored over 13 days. Contractile force dropped with the addition of the drug in a dose-dependent manner (Figure 8A). Twitch frequency was also significantly affected as the beat rate slowed and eventually stopped as expected with continued exposure to the cardiotoxic compound (p &#60; 0.05, Figure 8B). These results demonstrate how 3D-engineered human muscle tissues can be used to facilitate bringing new drugs to the market and flag compounds that eventually fail due to cardiotoxicity. Moreover, this technology could potentially save lives by exposing dangerous drugs before they are put into patients in clinical trials.
The ability to measure the effect of acute and chronically applied drugs on human contractile tissue is a vital first step when investigating therapeutics for safety and efficacy. It is important to know, however, that the concentration of drugs applied are physiologically relevant and appropriate for in vitro testing. Skeletal muscle tissues were used to establish an IC50 value for 2,3-Butanedione monoxime (BDM) in a full dose-response curve. This drug is a well-characterized ATPase inhibitor of skeletal muscle myosin-II20. BDM inhibits muscle contractions by preventing myosin cross-bridge formation with the actin filament in sarcomeres21. Results shown here reveal a dose-dependent decrease in absolute force when the drug is applied and complete recovery of contractile force when the drug is washed out, indicating the transient effect is preventing muscle contractions and not merely killing cells within the tissue (Figure 9A). Furthermore, a full dose-response curve was measured across the seven concentrations examined, establishing an IC50 of 3.2 mM in these human microtissues (Figure 9B).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/64399/64399fig01.jpg" /> 
Figure 1: EMT casting in the 2-post Mantarray consumable 24-well plate. (A) Myogenic and stromal cells were cultured on 2D surfaces prior to tissue casting. (B) Cells are lifted from 2D surfaces and mixed together with extracellular matrix proteins to form hydrogels in the individual plate casting wells shown in the inset. (C) 24-well plate containing engineered tissues in every well. (D) Representative tissues showing relaxed and contracted engineered muscle, comparing displacement of the magnetic post (green bars). <a href="https://www.jove.com/files/ftp_upload/64399/64399fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/64399/64399fig02.jpg" /> 
Figure 2: Successful and unsuccessful EMT casting. (A) Ideal engineered muscle tissue 24 h post-casting uniformly compacted around the posts with homogenous cell/matrix composition throughout the tissue. (B) Failed EMT showing detachment of the hydrogel from the flexible post. (C) EMT containing air bubbles throughout the tissue. (D) Unequal tissue deposition around both posts. Tissue is loosely anchored to the flexible post on one side. Scale bars are 1 mm. <a href="https://www.jove.com/files/ftp_upload/64399/64399fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/64399/64399fig03.jpg" /> 
Figure 3: Compaction in engineered muscle tissue over time. (A) EMT construct shown 1 day after casting. Tissues are transferred into differentiation medium, beginning day 0 of cell fusion and hydrogel compaction. (B-E) The same EMT at day 7 through day 21 showing a slightly shorter overall length between the two posts over time and smaller width when measured through the middle section of the EMT. Scale bars are 1 mm. <a href="https://www.jove.com/files/ftp_upload/64399/64399fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/64399/64399fig04.jpg" /> 
Figure 4: EMT diameter over time. Four plates of tissues were tracked over 21 days, comparing EMT diameter throughout compaction. Each tissue was measured through the mid-section every week using optical microscopy. Time points show consistent EMT size between plates. Maximal compaction is reached at day 21 as matrix remodeling is stabilized. The table shows the standard deviation (% of total) of compaction within each plate of tissues and the average deviation for all plates. Colored bars are individual plates. Error bars are SD of EMTs within plates. <a href="https://www.jove.com/files/ftp_upload/64399/64399fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/64399/64399fig05.jpg" /> 
Figure 5: Immunohistochemistry of the engineered skeletal muscle tissues. EMTs were fixed on day 10 of culture and embedded in paraffin. Thin cross-sections (7 &#956;m) were stained with antibodies against myosin heavy chain and dystrophin prior to imaging. Green = MyHC, red = Dystrophin, blue = DAPI. Objective magnification is 40X; scale bar is 50 &#181;m. <a href="https://www.jove.com/files/ftp_upload/64399/64399fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/64399/64399fig06.jpg" /> 
Figure 6: Contractile force in engineered muscle tissues over time. (A) Average absolute twitch force measured from cardiac EMTs from day 7 through day 63 in culture; n = 3 per group. (B) Average absolute twitch force in skeletal EMTs derived from a primary cell line on day 7 through day 53 in culture; n = 3. Error bars are SD for both graphs. <a href="https://www.jove.com/files/ftp_upload/64399/64399fig06large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/64399/64399fig07.jpg" /> 
Figure 7: Acute and chronic doxorubicin treatment in the engineered muscle tissue. Three separate dose concentrations of dox, 0.1 &#181;M, 1 &#181;M, and 10 &#181;M, were delivered either in bolus or administered continuously to engineered muscle tissues over the course of 27 days. Bolus doses of the drug were added at media changes on days 0, 12, and 24, noted by the green arrows on the X-axis. The drug was added to the media at every media change for continuous dosing, noted by the black and green arrows on the X-axis. The percent change in force from baseline values (pre-drug treatment) is on the Y-axis, and the time in days of treatment is on the X-axis. Light orange = DMSO continuous control, dark orange = DMSO bolus control, light green = 0.1 &#181;M dox continuous, dark green = 0.1 &#181;M dox bolus, light blue = 1 &#181;M dox continuous, dark blue = 1 &#181;M Dox bolus, light yellow = 10 &#181;M dox continuous, dark yellow = 10 &#181;M dox bolus. Error bars are SD; n = 3 per condition. <a href="https://www.jove.com/files/ftp_upload/64399/64399fig07large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/64399/64399fig08.jpg" /> 
Figure 8: Chronic treatment with BMS-986094 in engineered muscle tissue. EMTs were treated with 0.4 &#181;M (green), 2 &#181;M (dark blue), and 10 &#181;M (light blue) BMS-986094 over 13 days. (A) Contractile twitch force (Y-axis) decreases at all drug concentrations in the first 2 days, whereas the control tissues in DMSO continue to get stronger over time (X-axis). (B) The cardiac beat rate, or twitch frequency, ceases in a dose-dependent like manner in tandem with a cessation of contractile force shown in graph A. Control tissues in DMSO (gray) maintain a regular beat rate throughout the experiment. Error bars are SD; n = 3 per condition. <a href="https://www.jove.com/files/ftp_upload/64399/64399fig08large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/64399/64399fig09.jpg" /> 
Figure 9: Dose-response to BDM in engineered skeletal muscle tissues. (A) Absolute twitch force decreases in a dose-dependent manner when primary cell-derived EMTs are exposed to 2,3-Butanedione monoxime (BDM) on day 16 in 3D culture. Absolute twitch force returns to near baseline values when the drug is washed out. (B) Absolute twitch force normalized to baseline values decreases in a dose-dependent manner when exposed to BDM yielding a full dose-response curve and IC50 value; n = 4 per dose. Error bars are SD. <a href="https://www.jove.com/files/ftp_upload/64399/64399fig09large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Preclinical Drug Testing in Scalable 3D Engineered Muscle Tissues at JoVE.com

Preclinical Drug Testing in Scalable 3D Engineered Muscle Tissues

This protocol provides methods for generating 3D engineered cardiac and skeletal muscle tissues and describes their use in preclinical drug screening modalities. The described methods utilize a magnetic sensing system to facilitate the simultaneous assessment of 24 tissues in parallel.

Accurately modeling healthy and disease conditions in vitro is vital for the development of new treatment strategies and therapeutics. For cardiac and ...

preclinical-drug-testing-in-scalable-3d-engineered-muscle-tissues

Research

JoVE Journal

Bioengineering

3.1K Views.  Curi Bio Inc.. This protocol provides methods for generating 3D engineered cardiac and skeletal muscle tissues and describes their use in preclinical drug screening modalities. The described methods utilize a magnetic sensing system to facilitate the simultaneous assessment of 24 tissues in parallel.

Video: Preclinical Drug Testing in Scalable 3D Engineered Muscle Tissues

Production, Characterization and Potential Uses of a 3D Tissue-engineered Human Esophageal Mucosal Model

The incidence of both esophageal adenocarcinoma and its precursor, Barrett&#8217;s Metaplasia, are rising rapidly in the western world. Furthermore esophageal adenocarcinoma generally has a poor prognosis, with little improvement in survival rates in recent years. These are difficult conditions to study and there has been a lack of suitable experimental platforms to investigate disorders of the esophageal mucosa.
A model of the human esophageal mucosa has been developed in the MacNeil laboratory which, unlike conventional 2D cell culture systems, recapitulates the cell-cell and cell-matrix interactions present in vivo and produces a mature, stratified epithelium similar to that of the normal human esophagus. Briefly, the model utilizes non-transformed normal primary human esophageal fibroblasts and epithelial cells grown within a porcine-derived acellular esophageal scaffold. Immunohistochemical characterization of this model by CK4, CK14, Ki67 and involucrin staining demonstrates appropriate recapitulation of the histology of the normal human esophageal mucosa.
This model provides a robust, biologically relevant experimental model of the human esophageal mucosa. It can easily be manipulated to investigate a number of research questions including the effectiveness of pharmacological agents and the impact of exposure to environmental factors such as alcohol, toxins, high temperature or gastro-esophageal refluxate components. The model also facilitates extended culture periods not achievable with conventional 2D cell culture, enabling, inter alia, the study of the impact of repeated exposure of a mature epithelium to the agent of interest for up to 20 days. Furthermore, a variety of cell lines, such as those derived from esophageal tumors or Barrett&#8217;s Metaplasia, can be incorporated into the model to investigate processes such as tumor invasion and drug responsiveness in a more biologically relevant environment.

This manuscript describes the production, characterization and potential uses of a tissue engineered 3D esophageal construct prepared from normal primary human esophageal fibroblast and squamous epithelial cells seeded within a de-cellularized porcine scaffold. The results demonstrate the formation of a mature stratified epithelium similar to the normal human esophagus.

The incidence of both esophageal adenocarcinoma and its precursor, Barrett&#8217;s Metaplasia, are rising rapidly in the western world. Furthermore ...

Engineered 3D Silk-collagen-based Model of Polarized Neural Tissue

Despite huge efforts to decipher the anatomy, composition and function of the brain, it remains the least understood organ of the human body. To gain a deeper comprehension of the neural system scientists aim to simplistically reconstruct the tissue by assembling it in vitro from basic building blocks using a tissue engineering approach. Our group developed a tissue-engineered silk and collagen-based 3D brain-like model resembling the white and gray matter of the cortex. The model consists of silk porous sponge, which is pre-seeded with rat brain-derived neurons, immersed in soft collagen matrix. Polarized neuronal outgrowth and network formation is observed with separate axonal and cell body localization. This compartmental architecture allows for the unique development of niches mimicking native neural tissue, thus enabling research on neuronal network assembly, axonal guidance, cell-cell and cell-matrix interactions and electrical functions.

Insight into the complex actions of the brain requires advanced research tools. Here we demonstrate a novel silk-collagen-based 3D engineered model of neural tissue resembling brain-like architecture. The model can be used to study neuronal network assembly, axonal guidance, cell-cell interactions and electrical activity.

Despite huge efforts to decipher the anatomy, composition and function of the brain, it remains the least understood organ of the human body. To gain a ...

Engineered Vascularized Muscle Flap

One of the main factors limiting the thickness of a tissue construct and its consequential viability and applicability in vivo, is the control of oxygen supply to the cell microenvironment, as passive diffusion is limited to a very thin layer. Although various materials have been described to restore the integrity of full-thickness defects of the abdominal wall, no material has yet proved to be optimal, due to low graft vascularization, tissue rejection, infection, or inadequate mechanical properties. This protocol describes a means of engineering a fully vascularized flap, with a thickness relevant for muscle tissue reconstruction. Cell-embedded poly L-lactic acid/poly lactic-co-glycolic acid constructs are implanted around the mouse femoral artery and vein and maintained in vivo for a period of one or two weeks. The vascularized graft is then transferred as a flap towards a full thickness defect made in the abdomen. This technique replaces the need for autologous tissue sacrifications and may enable the use of in vitro engineered vascularized flaps in many surgical applications.

To date, thick tissue defects are typically reconstructed by applying autologous tissue flaps or engineered tissues. In this protocol, we present a new method for engineering vascularized tissue flap bearing an autologous pedicle, to serve as a substitute to autologous flaps.

One of the main factors limiting the thickness of a tissue construct and its consequential viability and applicability in vivo, is the control of oxygen ...

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 ...

A Combined 3D Tissue Engineered In Vitro/In Silico Lung Tumor Model for Predicting Drug Effectiveness in Specific Mutational Backgrounds

In the present study, we combined an in vitro 3D lung tumor model with an in silico model to optimize predictions of drug response based on a specific mutational background. The model is generated on a decellularized porcine scaffold that reproduces tissue-specific characteristics regarding extracellular matrix composition and architecture including the basement membrane. We standardized a protocol that allows artificial tumor tissue generation within 14 days including three days of drug treatment. Our article provides several detailed descriptions of 3D read-out screening techniques like the determination of the proliferation index Ki67 staining&#39;s, apoptosis from supernatants by M30-ELISA and assessment of epithelial to mesenchymal transition (EMT), which are helpful tools for evaluating the effectiveness of therapeutic compounds. We could show compared to 2D culture a reduction of proliferation in our 3D tumor model that is related to the clinical situation. Despite of this lower proliferation, the model predicted EGFR-targeted drug responses correctly according to the biomarker status as shown by comparison of the lung carcinoma cell lines HCC827 (EGFR -mutated, KRAS wild-type) and A549 (EGFR wild-type, KRAS-mutated) treated with the tyrosine-kinase inhibitor (TKI) gefitinib. To investigate drug responses of more advanced tumor cells, we induced EMT by long-term treatment with TGF-beta-1 as assessed by vimentin/pan-cytokeratin immunofluorescence staining. A flow-bioreactor was employed to adjust culture to physiological conditions, which improved tissue generation. Furthermore, we show the integration of drug responses upon gefitinib treatment or TGF-beta-1 stimulation - apoptosis, proliferation index and EMT - into a Boolean in silico model. Additionally, we explain how drug responses of tumor cells with a specific mutational background and counterstrategies against resistance can be predicted. We are confident that our 3D in vitro approach especially with its in silico expansion provides an additional value for preclinical drug testing in more realistic conditions than in 2D cell culture.

A Combined 3D Tissue Engineered In Vitro/In Silico Lung Tumor Model for Predicting Drug Effectiveness in Specific Mutational Backgrounds

We present a three-dimensional (3D) lung cancer model based on a biological collagen scaffold to study sensitivity towards non-small-cell-lung-cancer-(NSCLC)-targeted therapies. We demonstrate different read-out techniques to determine the proliferation index, apoptosis and epithelial-mesenchymal transition (EMT) status. Collected data are integrated into an in silico model for prediction of drug sensitivity.

In the present study, we combined an in vitro 3D lung tumor model with an in silico model to optimize predictions of drug response based on a specific ...

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 ...

Biomechanical Characterization of Human Soft Tissues Using Indentation and Tensile Testing

Regenerative medicine aims to engineer materials to replace or restore damaged or diseased organs. The mechanical properties of such materials should mimic the human tissues they are aiming to replace; to provide the required anatomical shape, the materials must be able to sustain the mechanical forces they will experience when implanted at the defect site. Although the mechanical properties of tissue-engineered scaffolds are of great importance, many human tissues that undergo restoration with engineered materials have not been fully biomechanically characterized. Several compressive and tensile protocols are reported for evaluating materials, but with large variability it is difficult to compare results between studies. Further complicating the studies is the often destructive nature of mechanical testing. Whilst an understanding of tissue failure is important, it is also important to have knowledge of the elastic and viscoelastic properties under more physiological loading conditions.
This report aims to provide a minimally destructive protocol to evaluate the compressive and tensile properties of human soft tissues. As examples of this technique, the tensile testing of skin and the compressive testing of cartilage are described. These protocols can also be directly applied to synthetic materials to ensure that the mechanical properties are similar to the native tissue. Protocols to assess the mechanical properties of human native tissue will allow a benchmark by which to create suitable tissue-engineered substitutes.

Tissue biomechanics is important for maintaining cell shape and function and for determining phenotype. This report demonstrates non-destructive mechanical protocols for characterizing elastic and viscoelastic properties of human soft tissues, which can be directly applied to tissue-engineered substrates to allow a close matching of engineered materials to native tissue.

Regenerative medicine aims to engineer materials to replace or restore damaged or diseased organs. The mechanical properties of such materials should ...

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 ...

Standardized and Scalable Assay to Study Perfused 3D Angiogenic Sprouting of iPSC-derived Endothelial Cells In Vitro

Pre-clinical drug research of vascular diseases requires in vitro models of vasculature that are amendable to high-throughput screening. However, current in vitro screening models that have sufficient throughput only have limited physiological relevance, which hinders the translation of findings from in vitro to in vivo. On the other hand, microfluidic cell culture platforms have shown unparalleled physiological relevancy in vitro, but often lack the required throughput, scalability and standardization. We demonstrate a robust platform to study angiogenesis of endothelial cells derived from human induced pluripotent stem cells (iPSC-ECs) in a physiological relevant cellular microenvironment, including perfusion and gradients. The iPSC-ECs are cultured as 40 perfused 3D microvessels against a patterned collagen-1 scaffold. Upon the application of a gradient of angiogenic factors, important hallmarks of angiogenesis can be studied, including the differentiation into tip- and stalk cell and the formation of perfusable lumen. Perfusion with fluorescent tracer dyes enables the study of permeability during and after anastomosis of the angiogenic sprouts. In conclusion, this method shows the feasibility of iPSC-derived ECs in a standardized and scalable 3D angiogenic assay that combines physiological relevant culture conditions in a platform that has the required robustness and scalability to be integrated within the drug screening infrastructure.

This method describes the culture of iPSC-derived endothelial cells as 40 perfused 3D microvessels in a standardized microfluidic platform. This platform enables the study of gradient-driven angiogenic sprouting in 3D, including anastomosis and stabilization of the angiogenic sprouts in a scalable and high-throughput manner.

Pre-clinical drug research of vascular diseases requires in vitro models of vasculature that are amendable to high-throughput screening. However, current ...

Advanced 3D Liver Models for In vitro Genotoxicity Testing Following Long-Term Nanomaterial Exposure

Due to the rapid development and implementation of a diverse array of engineered nanomaterials (ENM), exposure to ENM is inevitable and the development of robust, predictive in vitro test systems is essential. Hepatic toxicology is key when considering ENM exposure, as the liver serves a vital role in metabolic homeostasis and detoxification as well as being a major site of ENM accumulation post exposure. Based upon this and the accepted understanding that 2D hepatocyte models do not accurately mimic the complexities of intricate multi-cellular interactions and metabolic activity observed in vivo, there is a greater focus on the development of physiologically relevant 3D liver models tailored for ENM hazard assessment purposes in vitro. In line with the principles of the 3Rs to replace, reduce and refine animal experimentation, a 3D HepG2 cell-line based liver model has been developed, which is a user friendly, cost effective system that can support both extended and repeated ENM exposure regimes (&#8804;14 days). These spheroid models (&#8805;500 &#181;m in diameter) retain their proliferative capacity (i.e., dividing cell models) allowing them to be coupled with the &#8216;gold standard&#8217; micronucleus assay to effectively assess genotoxicity in vitro. Their ability to report on a range of toxicological endpoints (e.g., liver function, (pro-)inflammatory response, cytotoxicity and genotoxicity) has been characterized using several ENMs across both acute (24 h) and long-term (120 h) exposure regimes. This 3D in vitro hepatic model has the capacity to be utilized for evaluating more realistic ENM exposures, thereby providing a future in vitro approach to better support ENM hazard assessment in a routine and easily accessible manner.

This procedure was established to be used for developing advanced 3D hepatic cultures in vitro, which can provide a more physiologically relevant assessment of the genotoxic hazards associated with nanomaterial exposures over both an acute or long-term, repeated dose regimes.

Due to the rapid development and implementation of a diverse array of engineered nanomaterials (ENM), exposure to ENM is inevitable and the development of ...