This work was supported by the National Natural Science Foundation of China (grant number 31771064); the Science and Technology Planning Project of Guangdong Province (grant numbers 2013B010404030, 2014A010105029, and 2016A020214012); the Science and Technology Planning Project of Guangzhou (grant number 201607010063); and the Undergraduate Innovation and Entrepreneurship Training Program (grant number 201610559028); the National Science Foundation for Young Scientists of China (grant number 31800819).

All stem cell and animal experiment procedures were conducted according to the ethical guidelines of the National Guide for the Care and Use of Laboratory Animals and approved by the Jinan University Animal Care and Use Committee (Guangzhou, China).
1. Preparation of the DPP Scaffold with the PLA2 Decellularization Method14
Note: See Figure 1A for a schematic of the PLA2 decellularization method.
<ol>
	<li>Prepare 100 mL of 200 U/mL PLA2 solution. Add 0.5 g of sodium deoxycholate and 2 mL of PLA2 in 198 mL of carbonate buffer solution.This solution should be used within 24 h after its preparation.</li>
	<li>Obtain the fresh porcine pericardium (FPP) from the slaughterhouse and return to the laboratory within 1 h. 
	NOTE: The FPP should be stored at 4 &#176;C during the transportation. Steps 1.2 - 1.10 should be conducted with continuous shaking in a thermostat-controlled water bath.</li>
	<li>Thoroughly wash the FPP with 200 mL of phosphate buffer solution (PBS) containing 1% penicillin-streptomycin in a 500 mL beaker at 10 &#176;Cfor 10 min. Repeat this step 2x.</li>
	<li>Split the FPP into two layers and remove the adipose tissue with forceps and scissors. 
	NOTE: Keep the FPP wet by adding 50 mL of PBS every 20 min during the removal of adipose tissue.</li>
	<li>Shape the FPP into 10 x 10 cm2 pieces with scissors. Wash the FPP with 200 mL of carbonate buffer solution (CBS) containing 1% penicillin-streptomycin in a 500 mL beaker at 10 &#176;C for 10 min. Repeat this step 2x.</li>
	<li>Transfer the FPP to pure water and soak it at 10&#176;C for 12 h.</li>
	<li>Soak the 10 x 10 cm2 samples in 50 mL of CBS containing 200 U/mL PLA2 and 0.5% (w/v) sodium deoxycholate solution at 37 &#176;C for 6 h.</li>
	<li>Wash the samples with CBS containing 1% penicillin-streptomycin at 10 &#176;C for 10 min. Repeat this step 2x.</li>
	<li>Soak each sample in 50 mL of CBS containing 200 U/mL PLA2 and 0.5% (w/v) sodium deoxycholate solution at 37 &#176;C for 2 h.</li>
	<li>Wash the samples with CBS containing 1% penicillin-streptomycin at 10 &#176;C for 2 h. Repeat this step for 10x at least. Place the samples on flat plates and dry them to constant weight in a constant temperature oven at 55 &#176;C. 
	NOTE: The sample needs to be completely dried. Weigh the DPP sample every 10 min and repeat that 3x or until the weight no longer changes.</li>
	<li>Shape each DPP sample into a 10.5 mm-diameter circle with a trephine. Pack each DPP in a sterile sealed bag.</li>
	<li>Sterilize the DPP samples by gamma irradiation (25 kGy). Stored the DPP samples at 4 &#176;C before use. 
	NOTE: All samples can be stored for up to six months at 4 &#176;C.</li>
</ol>
2. Preparations for the Cell Sheet Construction
<ol>
	<li>Autoclave all instruments and tissue carrier components at 121 &#176;C for 30 min, including 1.5 mL centrifugal tubes, forceps, toothed forceps, scissors, black bases (tissue carrier component), and white tension rings (tissue carrier component).</li>
	<li>Prepare 20 mL of germ-free 10% sucrose solution. Weight 2 g of sucrose and dissolve the sucrose in 18 mL of ultrapure water. Autoclave the 10% sucrose solution at 121 &#176;C for 30 min or filter the solution with a 0.22 &#181;m filter.</li>
	<li>Autoclave the dynamic perfusion system devices at 121 &#176;C for 30 min, including a gas exchange equipment, a 500 mL glass bottle, a perfusion culture container, and the connective tubes.</li>
	<li>Prepare the autoclaved instruments and tissue carrier components.Put the black base part of the tissue carrier in a culture dish.</li>
	<li>Pick up a dried DPP scaffold and put it in the center of the black base.Put a white tension ring on the DPP scaffold and fix it in the tissue carrier. 
	NOTE: Ensure the scaffold is totally fixed in the tissue carrier and there is no gap between the black base and the white tension ring. If not, separate the tissue carrier and fix the scaffold again.</li>
	<li>Add 100 &#181;L of culture medium on the DPP scaffold for rehydration. 
	NOTE: If the scaffold is not fixed well in the tissue carrier, the culture medium will infiltrate the culture dish.</li>
	<li>Put the scaffold into a 37 &#176;C incubator and allow it to soak for 15 min.</li>
</ol>
3. Preparation of the Cells for Cell Sheet Construction
Note: This protocol is for cell culture using a 100 mm dish. See Figure 1B for a schematic of the construction of the multilayered cell structure.
<ol>
	<li>Isolate BMSCs13. 
	NOTE: This method is designed for constructing a multilayered MSC cell sheet. Rat BMSCs are used in this protocol. The BMSCs are isolated using the whole bone marrow adherent method, and the BMSCs are expanded in vitro to obtain enough cell amount.
	<ol>
		<li>Autoclave the instruments at 121 &#176;C for 30 min, including forceps, toothed forceps, and scissors. Prepare a 2 mL injection syringe and BMSC culture medium (Dulbecco&#39;s modified Eagle&#39;s medium [DMEM], 10% fetal bovine serum, 1% glutamine, and 1% penicillin-streptomycin).</li>
		<li>Euthanize the three-week-old male Sprague-Dawley (SD) rats by cervical vertebra dislocation. Soak the animal in 100 mL of 75% alcohol solution in a beaker for 5 min.</li>
		<li>Take the animal out of the beaker and place it prone on the operation table. Incise the skin on the back of the animal with scissors and forceps. Isolate the skin and muscle tissues to expose the thigh femurs.</li>
		<li>Isolate the thigh femurs and put it in 30 mL of PBS in a 50 mL centrifuge tube. Place two thigh femurs into one tube. Vortex the centrifuge tube to wash the tissue thoroughly. Repeat this step 2x.</li>
		<li>Cut both ends of the femurs with scissors and expose the marrow cavity.</li>
		<li>Aspirate 2 mL of BMSC culture medium with an injection syringe. Insert the needle into the marrow cavity and flush out the bone marrow with culture medium. Flush out every two thigh femurs into one 100 mm culture dish.</li>
		<li>For each 100 mm culture dish, add 2 mL of culture medium in the culture dish. Put the culture dish into the 37 &#176;C incubator and static culture for 72 h.</li>
		<li>Take out the culture dish from the incubator. Replace the supernatant with 6 mL of fresh culture medium.</li>
		<li>Observe primary BMSCs under a microscope. Following this, passage the BMSCs every 5 - 7 d.</li>
	</ol>
	</li>
	<li>Take the cells out of the incubator. Observe the cells under a microscope and choose suitable cells for cell sheet construction. When the BMSCs reach 80% - 90% confluence, the cells can be chosen as the seeded cells.</li>
	<li>Remove the culture medium from the culture dish. Gently wash the cells with 2 mL of warm PBS. Remove all PBS from the culture dish and make sure no liquid remains. Add 2 mL of 0.25% trypsin (or another dissociating solution) to the dish and incubate at 37 &#176;C for 3 min.</li>
	<li>Stop the trypsin effect by adding 2 mL of the culture medium, and gently wash the cells from the dish. Transfer the cell suspension into a new 15 mL centrifuge tube. Centrifugate the cells at 225 x&#160;g for 5 min.</li>
	<li>Remove the supernatant. Resuspend the cells with 3 mL of 10% (w/v) sucrose solution. 
	NOTE: 10% (w/v) sucrose solution is used to wash the cells in order to obtain a uniform cell-hydrogel mixture in the following steps.</li>
	<li>Aspirate 10 &#181;L of the cell suspension and count the cell number with a hemocytometer. Calculate the volume needed for the next step. For one cell sheet, three million BMSCs are used.</li>
	<li>Extract three million cells and transfer them into a new 15 mL centrifuge tube. Centrifuge the cells at 225 x&#160;g for 5 min.</li>
	<li>Remove the supernatant. Resuspend the cells with 1 mL of 10% (w/v) sucrose solution. Transfer the cell suspension into a 1.5 mL centrifuge tube. 
	NOTE: Using a 1.5 mL centrifugal tube is beneficial for preparing the cell-hydrogel mixture.</li>
	<li>Centrifuge the cells at 260 xg for 5 min. Completely remove the supernatant and obtain the cell sediment.</li>
</ol>
4. Preparation of the BMSCs and the RAD16-I Peptide Hydrogel Mixture
Note: See Figure 1B for a schematic of the construction of the multilayered cell structure.
<ol>
	<li>Add 20 &#181;L of 10% (w/v) sucrose solution to the 1.5 mL centrifugal tube. Gently resuspend the BMSCs and obtain a uniform suspension. 
	NOTE: Do not generate any bubbles during the resuspension.</li>
	<li>Add 20 &#181;L of RAD16-I peptide hydrogel at the top of the suspension. Gently stir the RAD16-I peptide and cell suspension with the pipette tip. When the cell suspension and hydrogel are mixed together, gently pipette the mixture a couple of times.</li>
	<li>Take out the DPP scaffold from the tissue carrier and gently aspirate the culture medium with a pipette tip. 
	NOTE: Ensure the DPP scaffold is fully rehydrated before adding the cell-hydrogel mixture.</li>
	<li>Aspirate the mixture and evenly add it to the DPP scaffold. 
	NOTE: The total volume of the mixture would be about 40 - 50 &#181;L. It is recommended to add the mixture 10 &#181;L at a time from the center to the outside of the scaffold.</li>
	<li>Add 1 mL of culture medium to the bottom of the tissue carrier. Put the cell sheet in the 37 &#176;C incubator for 5 min.</li>
	<li>Take out the cell sheet from the incubator. Gently add 4 mL of culture medium in the culture dish and immerse the cell sheet. Put the cell sheet in the 37 &#176;C incubator for 2 h of static culture.</li>
</ol>
5. In Vitro Culture of a 3D Multilayered Cell Sheet Using a Dynamic Culture System
NOTE: See Figure 1C for a schematic of the 3D dynamic system.
<ol>
	<li>Prepare the dynamic perfusion system, including a peristaltic pump, gas exchange equipment, a 500 mL glass bottle, a perfusion culture container, and the connective tubes. Assemble the dynamic perfusion system as shown in Figure 2.</li>
	<li>Add 200 mL of culture medium to the sterile glass bottle. Insert the cell sheet into the chamber of the culture container. 
	NOTE: Pay attention to the direction of the upper surface of the cell sheet.</li>
	<li>Add 3 mL of culture medium in the tissue container and close the container. Put the dynamic perfusion system in the incubator and start the pump. Set the flow rate of the peristaltic pump at 8 mL/min. Culture the cell sheet in the dynamic perfusion system for 48 h.</li>
</ol>
6. Obtaining the Multilayered MSC Cell Sheet
<ol>
	<li>Autoclave the instruments and tissue carrier components at 121 &#176;C for 30 min, including 1.5 mL centrifugal tubes, forceps, and toothed forceps.</li>
	<li>Pull out the input duct from the glass bottle to stop the supply of culture medium to the container. 
	NOTE: Stop the peristaltic pump when the culture container is empty.</li>
	<li>Take out the cell sheet from the culture container and put it in a culture dish.</li>
	<li>Use one forceps to immobilize the tissue carrier and use another toothed forceps to separate the white tension ring from the black base. Finally, obtain the multilayered BMSCs cell sheet.</li>
	<li>For short preservation, each cell sheet can be transferred to a 1.5 mL centrifugal tube with the forceps. The DPP scaffold should be attached to the inner wall of the centrifugal tube, and the cell sheet should spread out as much as possible in the centrifuge tube.</li>
	<li>Gently add 1 mL of culture medium in the centrifugal tube to immerse the cell sheet. Close the cap of the centrifugal tube and store the cell sheet at 4 &#176;C. 
	NOTE: The cell sheet should be transplanted or analyzed as soon as possible. It is recommended to use the cell sheet within 4 h.</li>
</ol>

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The authors have nothing to disclose.

The present protocol reports an efficient method for constructing a multilayered MSC sheet. This cell sheet exhibits optimal mechanical strength, high cell seeding density, and favorable stem cell bioactivity. Using BMSCs as an example, the 3D cell structure is quickly constructed with RAD16-I peptide hydrogel. After being cultured in the dynamic perfusion system, the multilayered BMSC sheet is successfully obtained and the BMSCs maintain a high expression of stem cell markers.
Constructing th...

Stem cell therapy has been reported as an effective treatment for many diseases; however, low cell retention and poor survival within the target zone remain critical issues following traditional stem cell injection. To solve this problem, tissue engineering scientists developed the cell sheet technique. A monolayered cell sheet with intact extracellular matrix was firstly prepared by using the temperature-response culture dish1, and its follow-up studies reported the significant improvements of stem cell retention and survival within the infarcted area2,3. Among the methods, constructing the multilayered cell sheet has been reported as an effective strategy for improving the cell survival and the cell sheet therapeutic effect3,4. Since then, scientists have worked on developing different cell sheet construction methods in order to increase the cell amount, stem cell property, and mechanical property of the cell sheets. So far, certain types of cell sheet have been constructed and studied in the treatment of myocardial infarction5, cartilage injury6, and skin wound7.
The bioactivity of stem cells before transplantation showed an emerging influence on injured tissue regeneration, and different cell sheet construction strategies have different effects on the stem cells. On one hand, confluent cell sheets only consisted of high-density stem cells, and natural extracellular matrices could be acquired by stacking monolayered cell sheets8 or by using magnetic tissue engineering techniques9. On the other hand, researchers developed different scaffolds to provide adequate mechanical strength and support cell growth10,11,12, which allowed a low stem cell seeding density to ensure the nutrition supply. However, despite these approaches, the low efficient nutrition supply within the multilayered cell sheet structure remains a major concern during the in vitro construction. Therefore, an efficient and feasible cell sheet construction system is urgently required.
This protocol describes the steps to prepare a multilayeredmesenchymal stem cell (MSC) cell sheet. In this construction system, the cell sheet mechanical strength is provided by a DPP. Based on this scaffold, the 3D cell structure can be quickly constructed with RAD16-I peptide hydrogel, and a dynamic perfusion system is used to culture the multilayered cell sheet, in order to stabilize the 3D cell sheet structure and provide sufficient nutrition supply for the cells. Using this system, a multilayered BMSC sheet was successfully prepared and exhibited an optimal therapeutic effect on the rat myocardial infarction model13.

<table border="0" cellpadding="0" cellspacing="0" style="width:657px;" width="658">
	<tbody>
		<tr height="25">
			<td height="25" style="height:25px;width:216px;">Phospholipase A2</td>
			<td style="width:108px;">Sigma-Aldrich</td>
			<td style="width:167px;">P6534</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Sodium deoxycholate</td>
			<td style="width:108px;">Sigma-Aldrich</td>
			<td style="width:167px;">D6750-100G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Phosphate buffer</td>
			<td style="width:108px;">Gibco BRL</td>
			<td style="width:167px;">89033</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Penicillin streptomycin / amphotericin&#160;</td>
			<td style="width:108px;">Gibco BRL</td>
			<td style="width:167px;">15640055</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Buffer bicarbonate</td>
			<td style="width:108px;">Sigma-Aldrich</td>
			<td style="width:167px;">C3041</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Table concentrator</td>
			<td style="width:108px;">Changzhou Aohua Instrument Co.</td>
			<td style="width:167px;">KT20183</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Dulbecco&#39;s Modified Eagle Medium(DMEM)</td>
			<td style="width:108px;">Corning Cellgro</td>
			<td style="width:167px;">10-014-CVR</td>
			<td></td>
		</tr>
		<tr height="38">
			<td height="38" style="height:38px;width:216px;">South American fetal bovine serum&#160;</td>
			<td style="width:108px;">Gibco BRL</td>
			<td style="width:167px;">10270-106/P30-3302</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">L-Glutamine</td>
			<td style="width:108px;">Corning Cellgro</td>
			<td style="width:167px;">25-005-CI</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">0.25% Trypsin/2.21 mM EDTA</td>
			<td style="width:108px;">Corning Cellgro</td>
			<td style="width:167px;">25-053-CI</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Biosafety cabinet</td>
			<td style="width:108px;">Esco,Singapore</td>
			<td style="width:167px;">AC2-2S1</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Constant temperature incubator&#160;</td>
			<td style="width:108px;">Esco,Singapore</td>
			<td style="width:167px;">CLS-170B-8</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Centrifuge tube&#160;</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Pump tubing</td>
			<td style="width:108px;">Ismatec</td>
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			<td>tissue carrier components&#160;</td>
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			<td height="21" style="height:21px;">MINUSHEET</td>
			<td style="width:108px;">Regensburg</td>
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			<td height="21" style="height:21px;">MINUSHEET 0006</td>
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			<td>gas exchange equipment&#160;</td>
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			<td height="21" style="height:21px;">MINUSHEET 0002</td>
			<td style="width:108px;">Regensburg</td>
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			<td>500 mL glass bottle&#160;</td>
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		<tr height="21">
			<td height="21" style="height:21px;">MINUSHEET 1301</td>
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			<td style="width:167px;"></td>
			<td>perfusion culture container&#160;</td>
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construction of a multilayered mesenchymal stem cell sheet with a 3d dynamic culture system

Stem cell therapy shows a promising future in regenerating injured organ and tissues, and the cell sheet technique has been developed to improve the low cell retention and poor survival within the target zone. However, during the in vitro construction process, a solution for maintaining stem cell bioactivity and increasing the cell amount within the cell sheet is urgently needed. Here, this protocol presents a method for constructing a multilayered cell sheet with favorable stem cell bioactivity and optimal operability. Decellularized porcine pericardium (DPP) is prepared by phospholipase A2 (PLA2) decellularization method as the cell sheet scaffold, and rat bone marrow mesenchymal stem cells (BMSCs) are isolated and expanded as the seeded cells. The temporary multilayered cell sheet structure is constructed by using RAD16-I peptide hydrogel. Finally, the cell sheet is cultured with a dynamic perfusion system to stabilize the three-dimensional (3D) structure, and the cell sheet could be obtained following a 48-hour culture in vitro. This protocol provides an efficient and feasible method for constructing a multilayered stem cell sheet, and the cell sheet could be developed as a favorable stem cell therapy product in the future.

The schematic of the multilayered stem cell sheet construction is shown in Figure 1. Preparing the cell sheet scaffold by the PLA2 decellularization method is the first step. Based on the scaffold, a temporary 3D cell structure is constructed by mixing the stem cells with the RAD16-1 peptide hydrogel. In order to obtain a multilayered cell sheet with favorable stem cell bioactivity and optimal mechanical strength, the cell sheet is cultured in a dy...

Watch this Scientific Journal Video about Construction of a Multilayered Mesenchymal Stem Cell Sheet with a 3D Dynamic Culture System at JoVE.com

Construction of a Multilayered Mesenchymal Stem Cell Sheet with a 3D Dynamic Culture System

This article provides an efficient and feasible method for constructing multilayered stem cell sheets with favorable stem cell property.

Stem cell therapy shows a promising future in regenerating injured organ and tissues, and the cell sheet technique has been developed to improve the low ...

construction-multilayered-mesenchymal-stem-cell-sheet-with-3d-dynamic

Research

JoVE Journal

Bioengineering

7.4K Views.  Jinan University. This article provides an efficient and feasible method for constructing multilayered stem cell sheets with favorable stem cell property. 

Video: Construction of a Multilayered Mesenchymal Stem Cell Sheet with a 3D Dynamic Culture System

Microfabricated Platforms for Mechanically Dynamic Cell Culture

The ability to systematically probe in vitro cellular response to combinations of mechanobiological stimuli for tissue engineering, drug discovery or fundamental cell biology studies is limited by current bioreactor technologies, which cannot simultaneously apply a variety of mechanical stimuli to cultured cells. In order to address this issue, we have developed a series of microfabricated platforms designed to screen for the effects of mechanical stimuli in a high-throughput format. In this protocol, we demonstrate the fabrication of a microactuator array of vertically displaced posts on which the technology is based, and further demonstrate how this base technology can be modified to conduct high-throughput mechanically dynamic cell culture in both two-dimensional and three-dimensional culture paradigms.

In this protocol, we demonstrate the fabrication of a microactuator array of vertically displaced posts on which the technology is based, and how this base technology can be modified to conduct high-throughput mechanically dynamic cell culture in both two-dimensional and three-dimensional culture paradigms.

The ability to systematically probe in vitro cellular response to combinations of mechanobiological stimuli for tissue engineering, drug discovery or ...

Alginate Microcapsule as a 3D Platform for Propagation and Differentiation of Human Embryonic Stem Cells (hESC) to Different Lineages

Human embryonic stem cells (hESC) are emerging as an attractive alternative source for cell replacement therapy since they can be expanded in culture indefinitely and differentiated to any cell types in the body. Various types of biomaterials have also been used in stem cell cultures to provide a microenvironment mimicking the stem cell niche1-3. The latter is important for promoting cell-to-cell interaction, cell proliferation, and differentiation into specific lineages as well as tissue organization by providing a three-dimensional (3D) environment4 such as encapsulation. The principle of cell encapsulation involves entrapment of living cells within the confines of semi-permeable membranes in 3D cultures2. These membranes allow for the exchange of nutrients, oxygen and stimuli across the membranes, whereas antibodies and immune cells from the host that are larger than the capsule pore size are excluded5. Here, we present an approach to culture and differentiate hESC DA neurons in a 3D microenvironment using alginate microcapsules. We have modified the culture conditions2 to enhance the viability of encapsulated hESC. We have previously shown that the addition of p160-Rho-associated coiled-coil kinase (ROCK) inhibitor, Y-27632 and human fetal fibroblast-conditioned serum replacement medium (hFF-CM) to the 3D platform significantly enhanced the viability of encapsulated hESC in which the cells expressed definitive endoderm marker genes1. We have now used this 3D platform for the propagation of hESC and efficient differentiation to DA neurons. Protein and gene expression analyses after the final stage of DA neuronal differentiation showed an increased expression of tyrosine hydroxylase (TH), a marker for DA neurons, &gt;100 folds after 2 weeks. We hypothesized that our 3D platform using alginate microcapsules may be useful to study the proliferation and directed differentiation of hESC to various lineages. This 3D system also allows the separation of feeder cells from hESC during the process of differentiation and also has potential for immune-isolation during transplantation in the future.

Alginate Microcapsule as a 3D Platform for Propagation and Differentiation of Human Embryonic Stem Cells hESC to Different Lineages

We have optimized a microencapsulation technique as an effective 3D platform for propagation and differentiation of embryonic stem cells to endoderm and dopaminergic (DA) neurons. It also provides an opportunity for immune-isolation of cells from the host during transplantation. This platform can be adapted for other cell types.

Human embryonic stem cells (hESC) are emerging as an attractive alternative source for cell replacement therapy since they can be expanded in culture ...

Preparation of 3D Fibrin Scaffolds for Stem Cell Culture Applications

Stem cells are found in naturally occurring 3D microenvironments in vivo, which are often referred to as the stem cell niche 1. Culturing stem cells inside of 3D biomaterial scaffolds provides a way to accurately mimic these microenvironments, providing an advantage over traditional 2D culture methods using polystyrene as well as a method for engineering replacement tissues 2. While 2D tissue culture polystrene has been used for the majority of cell culture experiments, 3D biomaterial scaffolds can more closely replicate the microenvironments found in vivo by enabling more accurate establishment of cell polarity in the environment and possessing biochemical and mechanical properties similar to soft tissue.3 A variety of naturally derived and synthetic biomaterial scaffolds have been investigated as 3D environments for supporting stem cell growth. While synthetic scaffolds can be synthesized to have a greater range of mechanical and chemical properties and often have greater reproducibility, natural biomaterials are often composed of proteins and polysaccharides found in the extracelluar matrix and as a result contain binding sites for cell adhesion and readily support cell culture. Fibrin scaffolds, produced by polymerizing the protein fibrinogen obtained from plasma, have been widely investigated for a variety of tissue engineering applications both in vitro and in vivo 4. Such scaffolds can be modified using a variety of methods to incorporate controlled release systems for delivering therapeutic factors 5. Previous work has shown that such scaffolds can be used to successfully culture embryonic stem cells and this scaffold-based culture system can be used to screen the effects of various growth factors on the differentiation of the stem cells seeded inside 6,7.
 This protocol details the process of polymerizing fibrin scaffolds from fibrinogen solutions using the enzymatic activity of thrombin. The process takes 2 days to complete, including an overnight dialysis step for the fibrinogen solution to remove citrates that inhibit polymerization. These detailed methods rely on fibrinogen concentrations determined to be optimal for embryonic and induced pluripotent stem cell culture. Other groups have further investigated fibrin scaffolds for a wide range of cell types and applications - demonstrating the versatility of this approach 8-12.

This work details the preparation of 3D fibrin scaffolds for culturing and differentiating plutipotent stem cells. Such scaffolds can be used to screen the effects of various biological compounds on stem cell behavior as well as modified to contain drug delivery systems.

Stem cells are found in naturally occurring 3D microenvironments in vivo, which are often referred to as the stem cell niche 1. Culturing stem cells ...

Correlative Microscopy for 3D Structural Analysis of Dynamic Interactions

Cryo-electron tomography (cryoET) allows 3D visualization of cellular structures at molecular resolution in a close-to-physiological state1. However, direct visualization of individual viral complexes in their host cellular environment with cryoET is challenging2, due to the infrequent and dynamic nature of viral entry, particularly in the case of HIV-1. While time-lapse live-cell imaging has yielded a great deal of information about many aspects of the life cycle of HIV-13-7, the resolution afforded by live-cell microscopy is limited (~ 200 nm). Our work was aimed at developing a correlation method that permits direct visualization of early events of HIV-1 infection by combining live-cell fluorescent light microscopy, cryo-fluorescent microscopy, and cryoET. In this manner, live-cell and cryo-fluorescent signals can be used to accurately guide the sampling in cryoET. Furthermore, structural information obtained from cryoET can be complemented with the dynamic functional data gained through live-cell imaging of fluorescent labeled target.
In this video article, we provide detailed methods and protocols for structural investigation of HIV-1 and host-cell interactions using 3D correlative high-speed live-cell imaging and high-resolution cryoET structural analysis. HeLa cells infected with HIV-1 particles were characterized first by confocal live-cell microscopy, and the region containing the same viral particle was then analyzed by cryo-electron tomography for 3D structural details. The correlation between two sets of imaging data, optical imaging and electron imaging, was achieved using a home-built cryo-fluorescence light microscopy stage. The approach detailed here will be valuable, not only for study of virus-host cell interactions, but also for broader applications in cell biology, such as cell signaling, membrane receptor trafficking, and many other dynamic cellular processes.

We describe a correlative microscopy method that combines high-speed 3D live-cell fluorescent light microscopy and high-resolution cryo-electron tomography. We demonstrate the capability of the correlative method by imaging dynamic, small HIV-1 particles interacting with host HeLa cells.

Cryo-electron tomography (cryoET) allows 3D visualization of cellular structures at molecular resolution in a close-to-physiological state1. However, ...

Tissue Engineering: Construction of a Multicellular 3D Scaffold for the Delivery of Layered Cell Sheets

Many tissues, such as the adult human hearts, are unable to adequately regenerate after damage.2,3 Strategies in tissue engineering propose innovations to assist the body in recovery and repair. For example, TE approaches may be able to attenuate heart remodeling after myocardial infarction (MI) and possibly increase total heart function to a near normal pre-MI level.4 As with any functional tissue, successful regeneration of cardiac tissue involves the proper delivery of multiple cell types with environmental cues favoring integration and survival of the implanted cell/tissue graft. Engineered tissues should address multiple parameters including: soluble signals, cell-to-cell interactions, and matrix materials evaluated as delivery vehicles, their effects on cell survival, material strength, and facilitation of cell-to-tissue organization. Studies employing the direct injection of graft cells only ignore these essential elements.2,5,6 A tissue design combining these ingredients has yet to be developed. Here, we present an example of integrated designs using layering of patterned cell sheets with two distinct types of biological-derived materials containing the target organ cell type and endothelial cells for enhancing new vessels formation in the &#8220;tissue&#8221;. Although these studies focus on the generation of heart-like tissue, this tissue design can be applied to many organs other than heart with minimal design and material changes, and is meant to be an off-the-shelf product for regenerative therapies. The protocol contains five detailed steps. A temperature sensitive Poly(N-isopropylacrylamide) (pNIPAAM) is used to coat tissue culture dishes. Then, tissue specific cells are cultured on the surface of the coated plates/micropattern surfaces to form cell sheets with strong lateral adhesions. Thirdly, a base matrix is created for the tissue by combining porous matrix with neovascular permissive hydrogels and endothelial cells. Finally, the cell sheets are lifted from the pNIPAAM coated dishes and transferred to the base element, making the complete construct.

For creation of highly organized structures of complex tissue, one must assemble multiple material and cell types into an integrated composite. This combinatorial design incorporates organ-specific layered cell sheets with two distinct biologically-derived materials containing a strong fibrous matrix base, and endothelial cells for enhancing new vessels formation.

Many tissues, such as the adult human hearts, are unable to adequately regenerate after damage.2,3 Strategies in tissue engineering propose innovations to ...

Optimizing Attachment of Human Mesenchymal Stem Cells on Poly(&#949;-caprolactone) Electrospun Yarns

Research into biomaterials and tissue engineering often includes cell-based in vitro investigations, which require initial knowledge of the starting cell number. While researchers commonly reference their seeding density this does not necessarily indicate the actual number of cells that have adhered to the material in question. This is particularly the case for materials, or scaffolds, that do not cover the base of standard cell culture well plates. This study investigates the initial attachment of human mesenchymal stem cells seeded at a known number onto electrospun poly(&#949;-caprolactone) yarn after 4 hr in culture. Electrospun yarns were held within several different set-ups, including bioreactor vessels rotating at 9 rpm, cell culture inserts positioned in low binding well plates and polytetrafluoroethylene (PTFE) troughs placed within petri dishes. The latter two were subjected to either static conditions or positioned on a shaker plate (30 rpm). After 4 hr incubation at 37&#160;oC, 5% CO2, the location of seeded cells was determined by cell DNA assay. Scaffolds were removed from their containers and placed in lysis buffer. The media fraction was similarly removed and centrifuged &#8211; the supernatant discarded and pellet broken up with lysis buffer. Lysis buffer was added to each receptacle, or well, and scraped to free any cells that may be present. The cell DNA assay determined the percentage of cells present within the scaffold, media and well fractions. Cell attachment was low for all experimental set-ups, with greatest attachment (30%) for yarns held within cell culture inserts and subjected to shaking motion. This study raises awareness to the actual number of cells attaching to scaffolds irrespective of the stated cell seeding density.

This article describes a range of set-ups for seeding human mesenchymal stem cells onto materials, in this case electrospun yarns, that do not cover the base of standard culture well plates in order to maximize and quantify the number of cells that initially attach compared to the known seeding density.

Research into biomaterials and tissue engineering often includes cell-based in vitro investigations, which require initial knowledge of the starting cell ...

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 ...

Micropatterning and Assembly of 3D Microvessels

In vitro platforms to study endothelial cells and vascular biology are largely limited to 2D endothelial cell culture, flow chambers with polymer or glass based substrates, and hydrogel-based tube formation assays. These assays, while informative, do not recapitulate lumen geometry, proper extracellular matrix, and multi-cellular proximity, which play key roles in modulating vascular function. This manuscript describes an injection molding method to generate engineered vessels with diameters on the order of 100 &#181;m. Microvessels are fabricated by seeding endothelial cells in a microfluidic channel embedded within a native type I collagen hydrogel. By incorporating parenchymal cells within the collagen matrix prior to channel formation, specific tissue microenvironments can be modeled and studied. Additional modulations of hydrodynamic properties and media composition allow for control of complex vascular function within the desired microenvironment. This platform allows for the study of perivascular cell recruitment, blood-endothelium interactions, flow response, and tissue-microvascular interactions. Engineered microvessels offer the ability to isolate the influence from individual components of a vascular niche and precisely control its chemical, mechanical, and biological properties to study vascular biology in both health and disease.

This manuscript presents an injection molding method to engineer microvessels that recapitulate physiological properties of endothelium. The microfluidic-based process creates patent 3D vascular networks with tailorable conditions, such as flow, cellular composition, geometry, and biochemical gradients. The fabrication process and examples of potential applications are described.

In vitro platforms to study endothelial cells and vascular biology are largely limited to 2D endothelial cell culture, flow chambers with polymer or glass ...

Tunable Hydrogels from Pulmonary Extracellular Matrix for 3D Cell Culture

Here we present a method for establishing multiple component cell culture hydrogels for in vitro lung cell culture. Beginning with healthy en bloc lung tissue from porcine, rat, or mouse, the tissue is perfused and submerged in subsequent chemical detergents to remove the cellular debris. Histological comparison of the tissue before and after processing confirms removal of over 95% of double stranded DNA and alpha galactosidase staining suggests the majority of cellular debris is removed. After decellularization, the tissue is lyophilized and then cryomilled into a powder. The matrix powder is digested for 48 hr in an acidic pepsin digestion solution and then neutralized to form the pregel solution. Gelation of the pregel solution can be induced by incubation at 37 &#176;C and can be used immediately following neutralization or stored at 4 &#176;C for up to two weeks. Coatings can be formed using the pregel solution on a non-treated plate for cell attachment. Cells can be suspended in the pregel prior to self-assembly to achieve a 3D culture, plated on the surface of a formed gel from which the cells can migrate through the scaffold, or plated on the coatings. Alterations to the strategy presented can impact gelation temperature, strength, or protein fragment sizes. Beyond hydrogel formation, the hydrogel stiffness may be increased using genipin.

This is a method to create a 3-dimensional cell culture scaffold from pulmonary extracellular matrix. Intact lung is processed into hydrogels that can support the growth of cells in three-dimensions.

Here we present a method for establishing multiple component cell culture hydrogels for in vitro lung cell culture. Beginning with healthy en bloc lung ...

Exploring the Potential of Mesenchymal Stem Cell Sheet on The Development of Hepatocellular Carcinoma In Vivo

An in vivo animal model that mimics human cancer could have various applications that deliver significant clinical information. The currently used techniques for the development of in vivo cancer models have considerable limitations. Therefore, in this study, we aim to implement cell sheet technology to develop an in vivo cancer model. Hepatocellular carcinoma (HCC) is successfully developed in nude rats using cell sheets created from HCC cell line cells. The cancer cell sheets are generated through intracellular adhesion and the formation of a stratified structure, controlled by the extracellular matrix. This allows for the HCC sheet transplantation into the liver and the creation of a tumor-bearing animal model within a month. In addition, the role of mesenchymal stem cells (MSC) in the development of this cancer model is investigated. In addition to the HCC cell line sheet, another two cell sheets are created: a sheet of HCC cells and bone marrow MSCs (BMMSCs) and a sheet of HCC cells and umbilical cord MSCs (UCMSCs). Sheets that have a combination of both HCC cells and MSCs are also capable of producing a tumor-bearing animal. However, the addition of MSCs reduces the size of the formed tumor, and this adverse effect on tumor development varies depending on the used MSCs' source. This indicates that a cell sheet made of certain MSC subtypes could be utilized in tumor management and control.

Exploring the Potential of Mesenchymal Stem Cell Sheet on The Development of Hepatocellular Carcinoma In Vivo

Here, we present a protocol to develop an in vivo cancer model using cell sheet technology. Such a model could be very useful for the evaluation of anticancer therapeutics.