This study is supported by the Dutch Heart Foundation and the Netherlands Institute for Regenerative Medicine.

This protocol follows the LUMC guidelines of the animal research ethics committee.
1. Preparation of Instruments, Culture Medium, and MTCS
Note: Perform all preparations in the laminar flow hood. The MTCS perfusion chamber, bubble trap and stand are described in Lieber et al., 201011.
<ol>
	<li>Disinfect the forceps and micro scissors with 70% ethanol. Prepare a 5 ml syringe with 21G needle with sterile Tyrode&#8217;s Buffer (130 mM NaCl, 5.4 mM KCl, 6.0 mM Hepes, 1.2 mM MgSO4, 1.2 mM KH2PO4, 20 mM Glucose, 1.5 mM CaCl2.2H2O, pH=7.2). Prepare a 5 ml syringe with 21G needle with sterile KCl solution (100 mM).</li>
	<li>Prepare 65 ml of medium per heart: DMEM supplemented with 10% Fetal Calf Serum, antibiotic/antimycotic (A/A; 100 units of penicillin,100 &#956;g of streptomycin, and 0.25 ug of amphotericin B/ml), Insulin-Transferrin-Selenium (ITS; 10 &#956;g/ml insulin, 5.5 &#956;g/ml Transferrin, 6.7 ng/ml sodium selenite) and filter sterilize.</li>
	<li>Sterilize the perfusion chamber and bubble trap by spraying with 70% ethanol and dry with paper towel. Assemble the MTCS (Figure 1D), however, initially without the perfusion chamber. Position the bubble trap on the stand. Use a peristaltic roller pump with easy-load pump heads.
	<ol>
		<li>Using silicon tubing make connections between the reservoir (50 ml tube) and the pump, the pump and the bubble trap, the bubble trap and reservoir (see Figure 1D). Make the tubing inside the incubator long enough to allow medium to reach gas equilibrium with the gas in the incubator through the gas permeable silicon tubing (1 m) and the tubing outside the incubator as short as possible.</li>
	</ol>
	</li>
	<li>Fill the 50 ml tube with 70% ethanol, turn on the pump (flow speed around 1 ml/min to allow proper circulation) and let the ethanol circulate for 30 min&#160;to sterilize all tubing. Remove the ethanol by emptying the reservoir and pumping out the ethanol from the system.</li>
	<li>Fill the 50 ml tube with sterile distilled water, turn on the pump and let the water circulate for 30 min&#160;to get rid of remaining ethanol. Remove the water by emptying the reservoir and pumping out the water from the system.</li>
	<li>Fill the 50 ml tube with 45 ml of medium, put the stand in the incubator. Turn on the pump (flow speed around 1 ml/min) and circulate the medium to fill all tubing, remove all air bubbles and allow the medium to adapt to the gas composition in the incubator for at least 1 hr. Maintain the incubator at standard tissue-culture conditions (5% CO2 and 37 &#176;C). Ensure that no bubbles are present in the tubing.</li>
</ol>
2. Isolation of Mouse Heart
<ol>
	<li>Inject the mouse with 500 units of Heparin. This will prevent the blood from clotting and allows the removal of blood from the heart. After 10 min, anesthetize the mouse in an induction chamber with 4% isoflurane using a precision vaporizer. The anesthesia is sufficient when the mouse is unresponsive to toe pinch.</li>
	<li>Transfer the mouse to a dissection board and maintain anesthesia by means of a facemask connected to a coaxial circuit. Disinfect&#160;the fur of the mouse with&#160;70%&#160;alcohol.&#160;Using scissors open the abdominal cavity to expose the vena cava and diaphragm.</li>
	<li>To expose the heart, make lateral incisions starting from the last to the first ribs and reflect the thoracic cage over mouse&#8217;s head. Stop the anesthesia as mouse is not breathing anymore. Observe the heart beating.</li>
	<li>Insert the 21G needle attached to a 5 ml syringe containing sterile Tyrode&#8217;s Buffer into the inferior vena cava from the abdominal into the thoracic cavity (through diaphragm). Make sure that blood can exit from the vena cava caudal from the needle insertion. Perfuse the Tyrode&#8217;s Buffer gently and with constant pressure into the vena cava until the heart loses partly its red color. Note: The heart remains beating allowing the removal of the blood from the heart.</li>
	<li>Replace the needle with the 21G needle attached to a 5 ml syringe containing sterile KCl solution. Gently perfuse the KCl solution into the vena cava until the heart stops beating and remove the needle. Note: The KCl&#160;solution preserves the heart in the relaxed diastolic phase, which will allow easier insertion of the perfusion needles and perfusion of the coronary system.</li>
	<li>Slightly lift the heart using curved forceps and using scissors dissect the heart free from surrounding tissue but leave arteries and veins proximal to the heart intact and attached to the heart. Transfer the heart to a 15 ml tube containing ice-cold PBS supplemented with antibiotic/antimycotic (A/A). Store the heart in ice-cold PBS for up to 3 hr.</li>
</ol>
3. Cannulation of the Mouse Hearts in the Perfusion Chamber
<ol>
	<li>Perform all procedures in laminar flow hood. Transfer the isolated heart from the 15 ml tube to a 10 cm Petri dish and add PBS supplemented with A/A.</li>
	<li>Under a dissecting microscope, use the micro scissor and forceps to remove all non-cardiac tissue but preserve the ascending aorta to at least the bifurcation with the brachiocephalic artery and the pulmonary veins, 2&#160;mm proximal to the heart. Cut off the tip of the apex of the heart to create access to the left ventricular lumen (typically 2 mm). Place the perfusion chamber in the flow hood under the dissecting microscope.</li>
	<li>Attach a 5 ml syringe with medium to the insert needle using the silicone tubing. Fill the perfusion chamber with 20 ml medium and put the heart on the rotation stage in between the 2 blunted needles in the perfusion chamber (Figure 1). Adjust the height of the rotation stage so the heart is positioned in front of the needles.</li>
</ol>
4. Ligation for Culturing the Mitral Valve (see Figure 1)
<ol>
	<li>Ligate the aorta with suture (silk 7.0). Ligate the left atrial appendage with suture. Insert the needle (nr. 1 in Figure 1) through the pulmonary vein into the left atrium and ligate with suture proximal to its entry in the left atrium. Make sure the needle is not too far into the left atrium as this would damage the mitral valve.</li>
	<li>Insert the needle (nr.2 in Figure&#160;1) with linear motion into the left ventricle. Transfer the medium from the perfusion chamber to a 50 ml tube. Seal the needle to the myocardium with biocompatible glue.</li>
	<li>After the glue has dried, carefully inject medium into heart by connecting a medium-filled syringe to needle nr.1 and check if there is any leakage. Ensure that medium exits from needle nr.2 and the last remaining blood is perfused out of the heart.</li>
</ol>
5. Ligation for Culturing the Aortic Valve (see Figure 1)
<ol>
	<li>Insert the needle (nr.1 in Figure 1) in the aorta and ligate with suture. Make sure the needle is not too far into the aorta as this would damage the aortic valve. Insert the needle (nr.2 in Figure 1) with linear motion into the left ventricle. Transfer the medium from the perfusion chamber to a 50 ml tube. Seal the needle to the myocardium with biocompatible glue.</li>
	<li>After the glue has dried, carefully inject medium into the heart by connecting a medium-filled syringe to needle nr.2 and check if there is any leakage. Ensure that medium exits from needle nr.1 and the last remaining blood is perfused out of the heart.</li>
</ol>
6. Place Perfusion Chamber on Stand
<ol>
	<li>Fill up perfusion chamber with the 20 ml transferred medium. Place gasket and lid on the chamber and tighten with washer and screws.</li>
	<li>Remove the assembled MTCS from the incubator. Attach the perfusion chamber on the stand. Connect the tubing (see Figure 1D). Place the stand in the incubator (5% CO2 and 37 &#176;C). Connect the tubing to the pump. Turn on the pump with flow speed around 600 &#956;l/min.</li>
	<li>Make sure that in the reservoir and/or the bubble trap the level of the medium allows the visualizations of the presence of the flow by the falling of the incoming medium drops. After culture, the heart is removed from the system, fixed and processed for histological examination.</li>
</ol>

<ol>
	<li>Go, A. 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=Heart+Disease+and+Stroke+Statistics--2014+Update:+A+Report+From+the+American+Heart+Association.">Heart Disease and Stroke Statistics--2014 Update: A Report From the American Heart Association.</a> Circulation. 129, e28-e292 (2013).</li><li>Gould, S. T., Srigunapalan, S., Simmons, C. A., Anseth, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hemodynamic+and+Cellular+Response+Feedback+in+Calcific+Aortic+Valve+Disease.">Hemodynamic and Cellular Response Feedback in Calcific Aortic Valve Disease.</a> Circulation Research. 113 (2), 186-197 (2013).</li><li>Kruithof, B. P. T., Krawitz, S. A., Gaussin, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Atrioventricular+valve+development+during+late+embryonic+and+postnatal+stages+involves+condensation+and+extracellular+matrix+remodeling.">Atrioventricular valve development during late embryonic and postnatal stages involves condensation and extracellular matrix remodeling.</a> Developmental biology. 302 (1), 208-217 (2007).</li><li>Schoen, F. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cardiac+valves+and+valvular+pathology:+update+on+function,+disease,+repair,+and+replacement.">Cardiac valves and valvular pathology: update on function, disease, repair, and replacement.</a> Cardiovascular pathology: the official journal of the Society for Cardiovascular Pathology. 14 (4), 189-194 (2005).</li><li>Balachandran, K., Sucosky, P., Yoganathan, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hemodynamics+and+mechanobiology+of+aortic+valve+inflammation+and+calcification.">Hemodynamics and mechanobiology of aortic valve inflammation and calcification.</a> International journal of inflammation. , 263870 (2011).</li><li>Butcher, J. T., Simmons, C. A., Warnock, J. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanobiology+of+the+Aortic+Heart+Valve.">Mechanobiology of the Aortic Heart Valve.</a> The Journal of heart valve disease. 17 (1), 62-73 (2008).</li><li>Balachandran, K., Konduri, S., Sucosky, P., Jo, H., Yoganathan, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+ex+vivo+study+of+the+biological+properties+of+porcine+aortic+valves+in+response+to+circumferential+cyclic+stretch.">An ex vivo study of the biological properties of porcine aortic valves in response to circumferential cyclic stretch.</a> Annals of biomedical engineering. 34 (11), 1655-1665 (2006).</li><li>Weiler, M., Hwai Yap, C., Balachandran, K., Padala, M., Yoganathan, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regional+analysis+of+dynamic+deformation+characteristics+of+native+aortic+valve+leaflets.">Regional analysis of dynamic deformation characteristics of native aortic valve leaflets.</a> Journal of Biomechanics. 44, 1459-1465 (2011).</li><li>Combs, M. D., Yutzey, K. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heart+valve+development:+Regulatory+networks+in+development+and+disease.">Heart valve development: Regulatory networks in development and disease.</a> Circulation Research. 105, 408-421 (2009).</li><li>Kruithof, B. P. T., Duim, S. N., Moerkamp, A. T., Goumans, M. -. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=TGF&#946;+and+BMP+signaling+in+cardiac+cushion+formation:+lessons+from+mice+and+chicken.">TGF&#946; and BMP signaling in cardiac cushion formation: lessons from mice and chicken.</a> Differentiation; research in biological diversity. 84 (1), 89-102 (2012).</li><li>Lieber, S. C., Kruithof, B. P. T., Aubry, N., Vatner, S. F., Gaussin, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+of+a+miniature+tissue+culture+system+to+culture+mouse+heart+valves.">Design of a miniature tissue culture system to culture mouse heart valves.</a> Annals of biomedical engineering. 38 (3), 674-682 (2010).</li></ol>

The authors declare no conflicts of interest.

Critical steps in culturing the cardiac mouse valves include making the time between excision of the heart from the mouse and the ligation in the perfusion chamber as short as possible to ensure viability and ligation of the needles perpendicular to the valves to ensure proper direction of the flow. Additionally, checking the flow after ligation in the perfusion chamber without medium ensures proper insertion and ligation of needles. It is critical to maintain a sterile culture and prevent air bubbles in the tubing, which could potentially get trapped in the heart obstructing the flow.
The total volume of medium used for the perfusion of a heart is 45 ml (note that the medium that is perfused through the heart is not in contact with the 20 ml of medium in the perfusion chamber). For the addition of for example viruses a smaller volume can be preferred. Temporally the reservoir (and part of the tubing) can be removed from the circuit leaving 5-7 ml in the system to allow infection of the valve.
The absence of beating of the heart could be considered a limitation. However, it allows creating an experimental condition in which all stimuli working on the leaflet can be kept constant. This gives the unique opportunity to study the effect of one single modification. When moving valves are required, a pulsatile flow can be created.
To study the valvular biology and the role of molecular, cellular and mechanical stimuli on the valve, modifications can be easily made to the culture system. Molecular modification can be achieved by the addition of growth factors, chemical compounds and viruses mediating gene delivery11 to the perfusion medium. One or multiple cell types can be administered to the perfusion medium to examine the influence of these cells on valvular biology or their contribution to the valve. The influence of oxidative stress or hypoxia can be studied by altering the oxygen-pressure in the culture medium. The hemodynamic stresses on the valve can be varied by changing the flow speed, flow direction, flow pulsatility and the viscosity. The overall morphology can be examined (Figure&#160;2B,C) by H&#38;E, histochemical and immunofluorescent staining. Additionally the organization and composition of the ECM, the phenotype, proliferation, and viability of the valvular cells and the activation of signaling pathways provide insight into the effects of varying these conditions. Genetically modified mice can be used to track the endothelial cells, using endothelial reporter mice (using the Tie2-Cre and floxed reporter mice) indicating the presence of endothelial-to-mesenchymal transformation or mice with loss or gain of function of specific signaling pathways. Overall, the system presented here is a useful tool for studying cardiac valvular biology.

Heart valve disease is a major cause of morbidity and mortality in the Western world; its prevalence increases with age and it affects more than 10% of the population 75 years and older1. The valves of the systemic part of the heart, the aortic and mitral valves, are mostly affected. Heart valve disease is characterized by the loss of the highly organized structure of the valves, which results in the alteration of the mechanical properties2. The structural integrity is therefore critical for the function of the valve.
The leaflets of the valve are comprised of valvular interstitial cells (VIC), valvular endothelial cells (VEC), and extracellular matrix, which is highly organized in an layered pattern3,4. The VICs are responsible for the ECM synthesis, degradation and organization. Factors emanating from the bloodstream, ECs or residing in the ECM act on the VICs orchestrating its function. In addition, mechanical forces act on the leaflet during the cardiac cycle resulting in laminar or oscillatory shear stress, compressive or tensile stresses influencing the behavior of VICs5.
In order to understand how the structure of the valve is regulated, it must first be understood how VICs respond to the diverse set of stimuli experienced during the cardiac cycle. In vitro studies have been very informative about the characteristics and abilities of the valvular cells. The response of these cells in vitro, however, may not always accurately mimic the in vivo response6; for example, the response of VIC to stimuli is dependent on the presence of ECs and the ECM composition5. Furthermore, the response of the valvular cells to stimuli depends on their specific location in the leaflet7. In addition to biochemical stimuli, the behavior of the valvular cells is determined by mechanical forces acting on the valve8. Each region of the valve is subjected to its own specific set of hemodynamic stresses. Although current ex vivo models have shown that mechanical forces are important determinants of valvular structure5, the associated mechanisms are still unclear. While in vivo models have provided insight into the molecular mechanisms underlying valvular development9,10, insights into adult valvular biology is still elusive.
Therefore, an ex vivo flow model was developed in which the cardiac valves can be cultured in their natural position in the heart for an extended period of time11. This has the advantage that the valves remain in their natural configuration and the VICs experience the same environment as in vivo, making the VICs responses to stimuli as natural as possible. In addition, the culture of the valves in their natural position in the heart facilitates subjecting each valvular region to the relevant hemodynamic stresses. In this ex vivo model, i.e., the Miniature Tissue Culture System (MTCS), the valves can be subjected to different biochemical and hemodynamic stimuli allowing the investigation of their role in cardiac valve remodeling.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Dulbecco&#8217;s Modified Eagle Medium</td>
			<td>life technolgies</td>
			<td>10569-010</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>life technolgies</td>
			<td>26140</td>
			<td></td>
		</tr>
		<tr>
			<td>Insulin-Transferrin-Selenium</td>
			<td>life technolgies</td>
			<td>41400-045</td>
			<td></td>
		</tr>
		<tr>
			<td>Antibiotic-Antimycotic</td>
			<td>life technolgies</td>
			<td>15240-06</td>
			<td></td>
		</tr>
		<tr>
			<td>Silk 7-0</td>
			<td>Ethicon</td>
			<td>768G</td>
			<td></td>
		</tr>
		<tr>
			<td>100 mm culture dish</td>
			<td>Greiner bio-one</td>
			<td>664160</td>
			<td></td>
		</tr>
		<tr>
			<td>50 ml tube</td>
			<td>Greiner bio-one</td>
			<td>227261</td>
			<td></td>
		</tr>
		<tr>
			<td>5 ml syringe</td>
			<td>BD</td>
			<td>309649</td>
			<td></td>
		</tr>
		<tr>
			<td>21 G needle</td>
			<td>BD</td>
			<td>304432</td>
			<td></td>
		</tr>
		<tr>
			<td>Heparin</td>
			<td>LEO</td>
			<td>012866-08</td>
			<td></td>
		</tr>
		<tr>
			<td>Forceps</td>
			<td>Fine Science Tools</td>
			<td>11295-00</td>
			<td></td>
		</tr>
		<tr>
			<td>Micro Scissors, Economy, Vannas-type</td>
			<td>Tedpella</td>
			<td>1346</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicon tubing</td>
			<td>Thermo Scientific</td>
			<td>8060-0020</td>
			<td>I.D. x O.D. x Wall: 1.59 x 3.18 x 0.79 mm</td>
		</tr>
		<tr>
			<td>Silicon tubing for pump</td>
			<td>Masterflex</td>
			<td>96400-13</td>
			<td>I.D. x O.D. x Wall: 0,8 x1,59 x 0,40 mm</td>
		</tr>
		<tr>
			<td>Biocompatible glue (Histoacryl)</td>
			<td>B. Braun</td>
			<td>1050071</td>
			<td></td>
		</tr>
		<tr>
			<td>precision vaporizer</td>
			<td>Dr&#228;ger</td>
			<td>Vapor 200</td>
			<td></td>
		</tr>
		<tr>
			<td>peristaltic roller pump</td>
			<td>Masterflex</td>
			<td>7521-35</td>
			<td></td>
		</tr>
		<tr>
			<td>Easy-load pump head</td>
			<td>Masterflex</td>
			<td>7518-00</td>
			<td></td>
		</tr>
		<tr>
			<td>Flow chamber</td>
			<td></td>
			<td></td>
			<td>see Lieber et al., 2010</td>
		</tr>
		<tr>
			<td>Bubble trap</td>
			<td></td>
			<td></td>
			<td>see Lieber et al., 2010</td>
		</tr>
	</tbody>
</table>

culturing mouse cardiac valves in the miniature tissue culture system

Heart valve disease is a major burden in the Western world and no effective treatment is available. This is mainly due to a lack of knowledge of the molecular, cellular and mechanical mechanisms underlying the maintenance and/or loss of the valvular structure. 
Current models used to study valvular biology include in vitro cultures of valvular endothelial and interstitial cells. Although, in vitro culturing models provide both cellular and molecular mechanisms, the mechanisms involved in the 3D-organization of the valve remain unclear. While in vivo models have provided insight into the molecular mechanisms underlying valvular development, insight into adult valvular biology is still elusive. 
In order to be able to study the regulation of the valvular 3D-organization on tissue, cellular and molecular levels, we have developed the Miniature Tissue Culture System. In this ex vivo flow model the mitral or the aortic valve is cultured in its natural position in the heart. The natural configuration and composition of the leaflet are maintained allowing the most natural response of the valvular cells to stimuli. The valves remain viable and are responsive to changing environmental conditions. This MTCS may provide advantages on studying questions including but not limited to, how does the 3D organization affect valvular biology, what factors affect 3D organization of the valve, and which network of signaling pathways regulates the 3D organization of the valve.

The aortic valve (Figure 2) or mitral valve11 can be cultured for at least 3 days. By culturing in the open position (which represents the systolic position for the aortic valve and the diastolic position for the mitral valve), valvular cells remain viable. No cell death is observed as determined by the absence of TUNEL-positive cells (Figure 2H,I) or cleaved caspase-3 expression (not shown and Lieber et al., 201011). The collagen distribution (as visualized by Masson&#8217;s Trichrome staining) is similar to the native condition when cultured in 1% serum (Figure 2D,E). The valves are responsive to changing culture conditions. Increasing the amount of serum to 10% results in thicker leaflets (Figure 2C). Furthermore, a clear collagen-free region is observed at the ventricular side of the leaflet near the attachment to the aortic wall (arrow in Figure 2F). Together these observations show that the cultured valves remain viable, resemble their native counterparts and are responsive to environmental changes.
<img alt="Figure 1" src="/files/ftp_upload/52750/52750fig1.jpg" /> 
Figure 1. The Miniature Tissue Culture system. (A) In the perfusion chamber the heart is laying on the rotation stage and ligated with the blunted needles indicated with nr.1 and nr.2. (B) Perfusion chamber is mounted on the stand. (C) Schematic drawing of the heart when culturing the mitral valve (left) or aortic valve (right). (D) Schematic drawing of the setup of the ex vivo flow system for aortic valve culture. This figure has been partly modified from previous study11. <a href="https://www.jove.com/files/ftp_upload/52750/52750fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/52750/52750fig2.jpg" /> 
Figure 2. Histological analysis of cultured valves from 2 months old mice. (A-C) heamatoxylin and eosin (H&#38;E) (D-F) Masson&#8217;s Trichrome staining and G-I) TUNEL staining of a non-cultured aortic valve (A,D,G), an aortic valve cultured in the presence of 1% serum (B,E,H) or 10% serum (C,F,I) for 3 days in the MTCS. The valve cultured with 1% serum appears similar to the non-cultured valve, whereas the valve cultured with 10% serum is thicker (C) and has an altered ECM pattern (F). No apoptosis is observed in the valves (G-I). Scale bar is 100 um. <a href="https://www.jove.com/files/ftp_upload/52750/52750fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Culturing Mouse Cardiac Valves in the Miniature Tissue Culture System at JoVE.com

Culturing Mouse Cardiac Valves in the Miniature Tissue Culture System

Here, we present an ex vivo flow model in which murine cardiac valves can be cultured allowing the study of the biology of the valve.

Heart valve disease is a major burden in the Western world and no effective treatment is available. This is mainly due to a lack of knowledge of the ...

culturing-mouse-cardiac-valves-in-the-miniature-tissue-culture-system

Nanyang Technological University

Research

JoVE Journal

Bioengineering

8.7K Views.  Leiden University Medical Center. Here, we present an ex vivo flow model in which murine cardiac valves can be cultured allowing the study of the biology of the valve.

Video: Culturing Mouse Cardiac Valves in the Miniature Tissue Culture System

A Method for Ovarian Follicle Encapsulation and Culture in a Proteolytically Degradable 3 Dimensional System

The ovarian follicle is the functional unit of the ovary that secretes sex hormones and supports oocyte maturation. In vitro follicle techniques provide a tool to model follicle development in order to investigate basic biology, and are further being developed as a technique to preserve fertility in the clinic1-4. Our in vitro culture system employs hydrogels in order to mimic the native ovarian environment by maintaining the 3D follicular architecture, cell-cell interactions and paracrine signaling that direct follicle development 5. Previously, follicles were successfully cultured in alginate, an inert algae-derived polysaccharide that undergoes gelation with calcium ions6-8. Alginate hydrogels formed at a concentration of 0.25% w/v were the most permissive for follicle culture, and retained the highest developmental competence 9. Alginate hydrogels are not degradable, thus an increase in the follicle diameter results in a compressive force on the follicle that can impact follicle growth10. We subsequently developed a culture system based on a fibrin-alginate interpenetrating network (FA-IPN), in which a mixture of fibrin and alginate are gelled simultaneously. This combination provides a dynamic mechanical environment because both components contribute to matrix rigidity initially; however, proteases secreted by the growing follicle degrade fibrin in the matrix leaving only alginate to provide support. With the IPN, the alginate content can be reduced below 0.25%, which is not possible with alginate alone 5. Thus, as the follicle expands, it will experience a reduced compressive force due to the reduced solids content. Herein, we describe an encapsulation method and an in vitro culture system for ovarian follicles within a FA-IPN. The dynamic mechanical environment mimics the natural ovarian environment in which small follicles reside in a rigid cortex and move to a more permissive medulla as they increase in size11. The degradable component may be particularly critical for clinical translation in order to support the greater than 106-fold increase in volume that human follicles normally undergo in vivo .

A new method for ovarian follicle encapsulation in a 3D fibrin-alginate interpenetrating network is described. This system combines structural support with proteolytic degradation to support the development of immature follicles to produce mature oocytes. This method may be applied to culture cell aggregates to maintain cell-cell contacts without limiting expansion.

The ovarian follicle is the functional unit of the ovary that secretes sex hormones and supports oocyte maturation. In vitro  follicle techniques provide ...

Encapsulation of Cardiomyocytes in a Fibrin Hydrogel for Cardiac Tissue Engineering

Culturing cells in a three dimensional hydrogel environment is an important technique for developing constructs for tissue engineering as well as studying cellular responses under various culture conditions in vitro. The three dimensional environment more closely mimics what the cells observe in vivo due to the application of mechanical and chemical stimuli in all dimensions 1. Three-dimensional hydrogels can either be made from synthetic polymers such as PEG-DA 2 and PLGA 3 or a number of naturally occurring proteins such as collagen 4, hyaluronic acid 5 or fibrin 6,7. Hydrogels created from fibrin, a naturally occurring blood clotting protein, can polymerize to form a mesh that is part of the body's natural wound healing processes 8. Fibrin is cell-degradable and potentially autologous 9, making it an ideal temporary scaffold for tissue engineering.
Here we describe in detail the isolation of neonatal cardiomyocytes from three day old rat pups and the preparation of the cells for encapsulation in fibrin hydrogel constructs for tissue engineering. Neonatal myocytes are a common cell source used for in vitro studies in cardiac tissue formation and engineering 4. Fibrin gel is created by mixing fibrinogen with the enzyme thrombin. Thrombin cleaves fibrinopeptides FpA and FpB from fibrinogen, revealing binding sites that interact with other monomers 10. These interactions cause the monomers to self-assemble into fibers that form the hydrogel mesh. Because the timing of this enzymatic reaction can be adjusted by altering the ratio of thrombin to fibrinogen, or the ratio of calcium to thrombin, one can injection mold constructs with a number of different geometries 11,12. Further we can generate alignment of the resulting tissue by how we constrain the gel during culture 13.
After culturing the engineered cardiac tissue constructs for two weeks under static conditions, the cardiac cells have begun to remodel the construct and can generate a contraction force under electrical pacing conditions 6. As part of this protocol, we also describe methods for analyzing the tissue engineered myocardium after the culture period including functional analysis of the active force generated by the cardiac muscle construct upon electrical stimulation, as well as methods for determining final cell viability (Live-Dead assay) and immunohistological staining to examine the expression and morphology of typical proteins important for contraction (Myosin Heavy Chain or MHC) and cellular coupling (Connexin 43 or Cx43) between myocytes.

We describe the isolation of neonatal cardiomyocytes and the preparation of the cells for encapsulation in fibrin hydrogel constructs for tissue engineering. We describe methods for analyzing the tissue engineered myocardium after the culture period including active force generated upon electrical stimulation and cell viability and immunohistological staining.

Culturing cells in a three dimensional hydrogel environment is an important technique for developing constructs for tissue engineering as well as studying ...

Capillary Force Lithography for Cardiac Tissue Engineering

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

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

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

Anatomical Reconstructions of the Human Cardiac Venous System using Contrast-computed Tomography of Perfusion-fixed Specimens

A detailed understanding of the complexity and relative variability within the human cardiac venous system is crucial for the development of cardiac devices that require access to these vessels. For example, cardiac venous anatomy is known to be one of the key limitations for the proper delivery of cardiac resynchronization therapy (CRT)1 Therefore, the development of a database of anatomical parameters for human cardiac venous systems can aid in the design of CRT delivery devices to overcome such a limitation. In this research project, the anatomical parameters were obtained from 3D reconstructions of the venous system using contrast-computed tomography (CT) imaging and modeling software (Materialise, Leuven, Belgium). The following parameters were assessed for each vein: arc length, tortuousity, branching angle, distance to the coronary sinus ostium, and vessel diameter.
	CRT is a potential treatment for patients with electromechanical dyssynchrony. Approximately 10-20% of heart failure patients may benefit from CRT2. Electromechanical dyssynchrony implies that parts of the myocardium activate and contract earlier or later than the normal conduction pathway of the heart. In CRT, dyssynchronous areas of the myocardium are treated with electrical stimulation. CRT pacing typically involves pacing leads that stimulate the right atrium (RA), right ventricle (RV), and left ventricle (LV) to produce more resynchronized rhythms. The LV lead is typically implanted within a cardiac vein, with the aim to overlay it within the site of latest myocardial activation. 
	We believe that the models obtained and the analyses thereof will promote the anatomical education for patients, students, clinicians, and medical device designers. The methodologies employed here can also be utilized to study other anatomical features of our human heart specimens, such as the coronary arteries. To further encourage the educational value of this research, we have shared the venous models on our free access website: <a href="http://www.vhlab.umn.edu/atlas" target="_blank">www.vhlab.umn.edu/atlas</a>.

The objective of this research is to recreate and then access the anatomy of the human cardiac venous system using 3D reconstructions generated from contrast-computed tomography scans.

A detailed  understanding of the complexity and relative variability within the human  cardiac venous system is crucial for the development of cardiac ...

Protocol for Relative Hydrodynamic Assessment of Tri-leaflet Polymer Valves

Limitations of currently available prosthetic valves, xenografts, and homografts have prompted a recent resurgence of developments in the area of tri-leaflet polymer valve prostheses. However, identification of a protocol for initial assessment of polymer valve hydrodynamic functionality is paramount during the early stages of the design process. Traditional in vitro pulse duplicator systems are not configured to accommodate flexible tri-leaflet materials; in addition, assessment of polymer valve functionality needs to be made in a relative context to native and prosthetic heart valves under identical test conditions so that variability in measurements from different instruments can be avoided. Accordingly, we conducted hydrodynamic assessment of i) native (n = 4, mean diameter, D = 20 mm), ii) bi-leaflet mechanical (n= 2, D = 23 mm) and iii) polymer valves (n = 5, D = 22 mm) via the use of a commercially available pulse duplicator system (ViVitro Labs Inc, Victoria, BC) that was modified to accommodate tri-leaflet valve geometries. Tri-leaflet silicone valves developed at the University of Florida comprised the polymer valve group. A mixture in the ratio of 35:65 glycerin to water was used to mimic blood physical properties. Instantaneous flow rate was measured at the interface of the left ventricle and aortic units while pressure was recorded at the ventricular and aortic positions. Bi-leaflet and native valve data from the literature was used to validate flow and pressure readings. The following hydrodynamic metrics were reported: forward flow pressure drop, aortic root mean square forward flow rate, aortic closing, leakage&#160;and regurgitant volume, transaortic closing, leakage, and total energy losses. Representative results indicated that hydrodynamic metrics from the three valve groups could be successfully obtained by incorporating a custom-built assembly into a commercially available pulse duplicator system and subsequently, objectively compared to provide insights on functional aspects of polymer valve design.

There has been renewed interest in developing polymer valves. Here, the objectives are to demonstrate the feasibility of modifying a commercial pulse duplicator to accommodate tri-leaflet geometries and to define a protocol to present polymer valve hydrodynamic data in comparison to native and prosthetic valve data collected under near-identical conditions.

Limitations of currently available prosthetic valves, xenografts, and homografts have prompted a recent resurgence of developments in the area of ...

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

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

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

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

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

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

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

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

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

An In Vitro Organ Culture Model of the Murine Intervertebral Disc

Intervertebral disc (IVD) degeneration is a significant contributor to low back pain. The IVD is a fibrocartilaginous joint that serves to transmit and dampen loads in the spine. The IVD consists of a proteoglycan-rich nucleus pulposus (NP) and a collagen-rich annulus fibrosis (AF) sandwiched by cartilaginous end-plates. Together with the adjacent vertebrae, the vertebrae-IVD structure forms a functional spine unit (FSU). These microstructures contain unique cell types as well as unique extracellular matrices. Whole organ culture of the FSU preserves the native extracellular matrix, cell differentiation phenotypes, and cellular-matrix interactions. Thus, organ culture techniques are particularly useful for investigating the complex biological mechanisms of the IVD. Here, we describe a high-throughput approach for culturing whole lumbar mouse FSUs that provides an ideal platform for studying disease mechanisms and therapies for the IVD. Furthermore, we describe several applications that utilize this organ culture method to conduct further studies including contrast-enhanced microCT imaging and three-dimensional high-resolution finite element modeling of the IVD.

An In Vitro Organ Culture Model of the Murine Intervertebral Disc

Whole organ culture of the intervertebral disc (IVD) preserves the native extracellular matrix, cell phenotypes, and cellular-matrix interactions. Here we describe an IVD culture system using mouse lumbar and caudal IVDs in their functional spinal units and several applications utilizing this system.

Intervertebral disc (IVD) degeneration is a significant contributor to low back pain. The IVD is a fibrocartilaginous joint that serves to transmit and ...

Culturing Mammalian Cells in Three-dimensional Peptide Scaffolds

A useful technique for culturing cells in a self-assembling nanofiber three-dimensional (3D) scaffold is described. This culture system recreates an environment that closely mimics the structural features of non-polarized tissue. Furthermore, the particular intrinsic nanofiber structure of the scaffold makes it transparent to visual light, which allows for easy visualization of the sample under microscopy. This advantage was largely used to study cell migration, organization, proliferation, and differentiation and thus any development of their particular cellular function by staining with specific dyes or probes. Furthermore, in this work, we describe the good performance of this system to easily study the redifferentiation of expanded human articular chondrocytes into cartilaginous tissue. Cells were encapsulated into self-assembling peptide scaffolds and cultured under specific conditions to promote chondrogenesis. Three-dimensional cultures showed good viability during the 4 weeks of the experiment. As expected, samples cultured with chondrogenic inducers (compared to non-induced controls) stained strongly positive for toluidine blue (which stains glycosaminoglycans (GAGs) that are highly present in cartilage extracellular matrix) and expressed specific molecular markers, including collagen type I, II and X, according to Western Blot analysis. This protocol is easy to perform and can be used at research laboratories, industries and for educational purposes in laboratory courses.

Here, we present a protocol to obtain 3D-culture systems in self-assembling peptide scaffolds to promote the differentiation of dedifferentiated human articular chondrocytes into cartilage-like tissue.

A useful technique for culturing cells in a self-assembling nanofiber three-dimensional (3D) scaffold is described. This culture system recreates an ...

A Net Mold-based Method of Scaffold-free Three-Dimensional Cardiac Tissue Creation

This protocol describes a novel and easy net mold-based method to create three-dimensional (3-D) cardiac tissues without additional scaffold material. Human-induced pluripotent stem-cell-derived cardiomyocytes (iPSC-CMs), human cardiac fibroblasts (HCFs), and human umbilical vein endothelial cells (HUVECs) are isolated and used to generate a cell suspension with 70% iPSC-CMs, 15% HCFs, and 15% HUVECs. They are co-cultured in an ultra-low attachment "hanging drop" system, which contains micropores for condensing hundreds of spheroids at one time. The cells aggregate and spontaneously form beating spheroids after 3 days of co-culture. The spheroids are harvested, seeded into a novel mold cavity, and cultured on a shaker in the incubator. The spheroids become a mature functional tissue approximately 7 days after seeding. The resultant multilayered tissues consist of fused spheroids with satisfactory structural integrity and synchronous beating behavior. This new method has promising potential as a reproducible and cost-effective method to create engineered tissues for the treatment of heart failure in the future.

This protocol describes a net mold-based method to create three-dimensional scaffold-free cardiac tissues with satisfactory structural integrity and synchronous beating behavior.

This protocol describes a novel and easy net mold-based method to create three-dimensional (3-D) cardiac tissues without additional scaffold material. ...