Name: layered alginate constructs: a platform for co-culture of heterogeneous cell populations
Uploaded: 2016-08-07T15:00:00
Description: Watch this Scientific Journal Video about Layered Alginate Constructs: A Platform for Co-culture of Heterogeneous Cell Populations at JoVE.com

This work was funded by the National Science Foundation (CBET 0845754, AHH).

1. Preparation for Formation of Alginate Discs
<ol>
	<li>Prepare a 4% (w/v) alginate solution in 1x Dulbecco&#39;s Phosphate Buffered Saline without added calcium chloride or magnesium chloride and place in a 37 &#176;C water bath. Concentrations of the alginate solution can vary, but 1 - 4% (w/v) alginate solutions are recommended.</li>
	<li>Mix the alginate solution at a ratio of 1:1 with warm cell culture media base (e.g., Dulbecco&#39;s Modified Eagle Medium) for the desired cell type. The alginate concent...

<ol>
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Here, we describe a protocol for the formation of layered alginate hydrogel discs for studying co-cultures of multiple cell populations, such as those in physiologically layered tissues, e.g., cartilage. Layered structures, such as the described culture platform, can be used to examine the interplay between two distinct cell populations subjected to the same culture environment or under load.
Alginate is an anionic linear polysaccharide that has been found to be biocompatible and has ...

Compressive load bearing tissues such as articular cartilage or intervertebral discs consist of heterogeneous tissue regions that are critical for both biomechanical function and appropriate mechano-transduction in the tissue. Not only is cellular organization and function distinct in different regions, but the extracellular matrices (ECM) are also varied in composition and organization. For example, articular cartilage consists of three primary zones with varying cell morphology, mechanical function, and ECM. Differences in their ECM lead to differential load bearing responsibilities; the superficial layer is primarily involved in tensile response to load, while the middle and deep zones are mainly accountable for response to compression 1. Similarly, in the intervertebral disc, a gel-like nucleus pulposus is surrounded by a lamellar annulus fibrosis and the cells within these two distinct areas experience different types of biophysical stimuli 2. In these types of tissues, cells and the extracellular matrices within the tissue layers interact with each other as the tissue undergoes and responds to mechanical forces.
Recapitulation of such heterogeneous tissue structures remains a challenge in tissue engineering and regenerative medicine, and our understanding of their biological significance is limited. There is a need for culturing platforms for analyzing stratified tissues as well as co-cultures of different populations of cells within one construct. In articular cartilage tissue engineering, scaffold-less layered constructs have been constructed by harnessing the ability of zonal chondrocytes to deposit varied ECM to mimic the different layers of this tissue 3,4. However, layered hydrogel constructs provide an opportunity for investigating the interaction of diverse types of cell populations that lack the ability to form a robust tissue independently. For example, different populations of mesenchymal stem cells can be co-cultured within layered constructs. Such layered scaffolds have been used with both chondrocytes and differentiating mesenchymal stem cells for improved tissue engineering 5. Not only can different cell populations be co-cultured in similar hydrogel layers, but a single cell type can also be cultured within layers that have been manipulated to have varying stiffness or biochemical content to elicit different responses from cells 6,7.
Many different biomaterial hydrogels have been used to layer cell populations for cartilage tissue engineering such as those using polyethylene glycol or poly vinyl alcohol bases 7-9. However, alginate hydrogels are one of the simplest biomaterials from which to create layered scaffolds for studying heterogeneous cell populations in co-culture. While agarose hydrogels are also easily formed, alginate hydrogels have the added benefit of allowing easy isolation of cells from the 3-D construct for analysis of individual cells as has been described previously 10. In previous studies, bi-layered alginate hydrogels have been formed in thin sheets and from these sheets, sections were sliced (e.g., using a biopsy punch) for particular applications such as for analysis of biochemical content or interfacial shear properties 11,12. Another method for forming thin alginate sheets has been described with the potential for stratification into multiple layers, but still would require alteration to the hydrogel for use in mechanical testing 13.
Here, we present a method for reproducibly creating bi-layered alginate hydrogel discs for use in co-culturing different populations of cells. This alginate disc platform possesses several advantages. Primarily, the reproducible shape and small size is conducive for mechanical stimulation of the embedded cells without requiring a biopsy punch or other physical alteration to the hydrogel for many applications. Additionally, cell viability remains high during the layering process,&#160;and after gel formation a clear separation of the two cell populations within the gel is visible with no initial overlapping region.

<table border="0" cellpadding="0" cellspacing="0" width="808">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Alginic Acid sodium salt</td>
			<td style="width:180px;">Sigma Aldrich</td>
			<td style="width:119px;">A1112</td>
			<td style="width:295px;">Solution made in wt% using DPBS (-/-)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">1x Dulbecco&#39;s Phosphate Buffered Saline (-/-)</td>
			<td style="width:180px;">Gibco Life Technologies&#160;</td>
			<td style="width:119px;">14190</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">1x Dulbecco&#39;s Phosphate Buffered Saline (+/+)</td>
			<td style="width:180px;">Gibco Life Technologies&#160;</td>
			<td style="width:119px;">14190</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Dulbecco&#39;s Modified Eagle Medium</td>
			<td style="width:180px;">Gibco Life Technologies&#160;</td>
			<td style="width:119px;">11965</td>
			<td>Example. Use desired medium type</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Syringe Filters (0.02um Nylon)</td>
			<td style="width:180px;">FisherBrand</td>
			<td style="width:119px;">0979C</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Calcium Chloride Dihydrate</td>
			<td style="width:180px;">Fisher Bioreagents</td>
			<td style="width:119px;">BP510</td>
			<td>Prepare solution in sterile water</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Criterion Blotter Filter Paper</td>
			<td style="width:180px;">Biorad</td>
			<td style="width:119px;">1704085</td>
			<td>Cut to size of endplates for mold formation</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Cell Microsieve Membrane (10um pore size)</td>
			<td style="width:180px;">Biodesign Inc of New York</td>
			<td style="width:119px;">N10R</td>
			<td>Cut to size of endplates for mold formation</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">0.25% Trypsin-EDTA (1x), phenol red</td>
			<td style="width:180px;">Gibco Life Technologies&#160;</td>
			<td style="width:119px;">25200</td>
			<td>Thaw in 37&#7506;C water bath</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Sodium citrate dihydrate</td>
			<td style="width:180px;">FisherScience</td>
			<td style="width:119px;">S93364</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:215px;">Ethylenediaminetetraacetic acid tetrasodium salt dihydrate (EDTA)</td>
			<td style="width:180px;">FisherBioreagent</td>
			<td style="width:119px;">BP121</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">Fetal Bovine Serum&#160;</td>
			<td style="width:180px;">Gibco Life Technologies&#160;</td>
			<td style="width:119px;">26140</td>
			<td>Used in example mesenchymal stem cell basal growth media</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Penicilin/Streptomycin (10000 U/ml)</td>
			<td style="width:180px;">Gibco Life Technologies&#160;</td>
			<td style="width:119px;">15140</td>
			<td>Used in example mesenchymal stem cell basal growth media</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:215px;">L-Glutamine (200mM)</td>
			<td style="width:180px;">Gibco Life Technologies&#160;</td>
			<td style="width:119px;">25030081</td>
			<td>Used in example mesenchymal stem cell basal growth media</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:215px;">Non-essential Amino Acids (100x)</td>
			<td style="width:180px;">Gibco Life Technologies&#160;</td>
			<td style="width:119px;">11140050</td>
			<td>Used in example mesenchymal stem cell basal growth media</td>
		</tr>
	</tbody>
</table>

layered alginate constructs: a platform for co-culture of heterogeneous cell populations

Many load bearing tissues possess structurally and functionally distinct regions, typically accompanied by different cell phenotypes with differential mechanosensing characteristics. Engineering and analysis of these tissue types remain a challenge. Layered hydrogel constructs provide an opportunity for investigating the interactions among multiple cell populations within single constructs. Alginate hydrogels are both biocompatible and allow for easy isolation of cells after experimentation. Here, we describe a method for the development of small sized dual layered alginate hydrogel discs. This process maintains high cell viability of human mesenchymal stem cells during the formation process and these layered discs can withstand unconfined cyclic compression, commonly used for stimulation of hMSCs undergoing chondrogenesis. These layered constructs can potentially be scaled up to include additional levels, and also be used to segregate cell populations initially after layering. This dual layer alginate hydrogel culture platform can be used for many different applications including engineering and analysis of cells of load bearing tissues and co-cultures of other cell types.

Figure 1 depicts the formation and layering of the alginate hydrogels. Completed bi-layered gels exhibit a complete initial separation of cell populations as shown in Figure 2. Cell viability of human mesenchymal stem cells) embedded within these hydrogels and layered remains high and comparable to the bulk hydrogels as shown in Figure 3. Viability was assessed after annealing, slicing the gels vertically to access the center and then sta...

Watch this Scientific Journal Video about Layered Alginate Constructs: A Platform for Co-culture of Heterogeneous Cell Populations at JoVE.com

Layered Alginate Constructs: A Platform for Co-culture of Heterogeneous Cell Populations

Engineering and analysis of load bearing tissues with heterogeneous cell populations are still a challenge. Here, we describe a method for creating bi-layered alginate hydrogel discs as a platform for co-culture of diverse cell populations within one construct.

Many load bearing tissues possess structurally and functionally distinct regions, typically accompanied by different cell phenotypes with differential ...

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