Name: preparation of 3d collagen gels and microchannels for the study of 3d interactions in vivo
Uploaded: 2016-05-09T14:00:00
Description: Watch this Scientific Journal Video about Preparation of 3D Collagen Gels and Microchannels for the Study of 3D Interactions In Vivo at JoVE.com

The authors would like to acknowledge grant numbers UO1CA143069, R01CA142833, R01CA114462, RO1CA179556, T32-AG000213-24, and T32-GM008692-18 for funding this work. We also acknowledge Jeremy Bredfelt and Yuming Liu of LOCI for the development of and assistance with the CT-FIRE analysis.

1. Neutralization, Dilution and Polymerization of Collagen Solutions for 3D Investigation and Cellular Contraction Assays
<ol>
	<li>On ice in sterile tissue culture hood, neutralize collagen (1:1) with sterile, ice-cold 100 mM HEPES in 2x PBS, pH 7.4, in a 15 ml conical tube. Mix thoroughly with plastic pipette until solution is homogenous and mixing swirls are no longer visible. Be careful not to introduce air bubbles during the mixing process. Store briefly on ice.</li>
	<li>Dilute neutralized collagen to the appropr...

<ol>
	<li>Conklin, M. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aligned+collagen+is+a+prognostic+signature+for+survival+in+human+breast+carcinoma.">Aligned collagen is a prognostic signature for survival in human breast carcinoma.</a> Am J Pathol. 178, 1221-1232 (2011).</li><li>Provenzano, P. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Collagen+reorganization+at+the+tumor-stromal+interface+facilitates+local+invasion.">Collagen reorganization at the tumor-stromal interface facilitates local invasion.</a> BMC Med. 4, 38 (2006).</li><li>Riching, K. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=3D+collagen+alignment+limits+protrusions+to+enhance+breast+cancer+cell+persistence.">3D collagen alignment limits protrusions to enhance breast cancer cell persistence.</a> Biophys J. 107, 2546-2558 (2014).</li><li>Even-Ram, S., Yamada, K. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+migration+in+3D+matrix.">Cell migration in 3D matrix.</a> Curr Opin Cell Biol. 17, 524-532 (2005).</li><li>Friedl, P., Wolf, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plasticity+of+cell+migration:+a+multiscale+tuning+model.">Plasticity of cell migration: a multiscale tuning model.</a> J Cell Biol. 188, 11-19 (2010).</li><li>Petrie, R. J., Gavara, N., Chadwick, R. S., Yamada, K. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nonpolarized+signaling+reveals+two+distinct+modes+of+3D+cell+migration.">Nonpolarized signaling reveals two distinct modes of 3D cell migration.</a> J Cell Biol. 197, 439-455 (2012).</li><li>Cukierman, E., Pankov, R., Yamada, K. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+interactions+with+three-dimensional+matrices.">Cell interactions with three-dimensional matrices.</a> Curr Opin Cell Biol. 14, 633-639 (2002).</li><li>Wozniak, M. A., Desai, R., Solski, P. A., Der, C. J., Keely, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ROCK-generated+contractility+regulates+breast+epithelial+cell+differentiation+in+response+to+the+physical+properties+of+a+three-dimensional+collagen+matrix.">ROCK-generated contractility regulates breast epithelial cell differentiation in response to the physical properties of a three-dimensional collagen matrix.</a> J Cell Biol. 163, 583-595 (2003).</li><li>Paszek, M. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tensional+homeostasis+and+the+malignant+phenotype.">Tensional homeostasis and the malignant phenotype.</a> Cancer Cell. 8, 241-254 (2005).</li><li>Provenzano, P. P., Inman, D. R., Eliceiri, K. W., Keely, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Matrix+density-induced+mechanoregulation+of+breast+cell+phenotype,+signaling+and+gene+expression+through+a+FAK-ERK+linkage.">Matrix density-induced mechanoregulation of breast cell phenotype, signaling and gene expression through a FAK-ERK linkage.</a> Oncogene. 28, 4326-4343 (2009).</li><li>Tlsty, T. D., Coussens, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tumor+stroma+and+regulation+of+cancer+development.">Tumor stroma and regulation of cancer development.</a> Annu Rev Pathol. 1, 119-150 (2006).</li><li>Provenzano, P. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Collagen+density+promotes+mammary+tumor+initiation+and+progression.">Collagen density promotes mammary tumor initiation and progression.</a> BMC Med. 6, 11 (2008).</li><li>Provenzano, P. P., Inman, D. R., Eliceiri, K. W., Trier, S. M., Keely, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Contact+guidance+mediated+three-dimensional+cell+migration+is+regulated+by+Rho/ROCK-dependent+matrix+reorganization.">Contact guidance mediated three-dimensional cell migration is regulated by Rho/ROCK-dependent matrix reorganization.</a> Biophys J. 95, 5374-5384 (2008).</li><li>Guo, C., Kaufman, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Flow+and+magnetic+field+induced+collagen+alignment.">Flow and magnetic field induced collagen alignment.</a> Biomaterials. 28, 1105-1114 (2007).</li><li>Sung, K. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Control+of+3-dimensional+collagen+matrix+polymerization+for+reproducible+human+mammary+fibroblast+cell+culture+in+microfluidic+devices.">Control of 3-dimensional collagen matrix polymerization for reproducible human mammary fibroblast cell culture in microfluidic devices.</a> Biomaterials. 30, 4833-4841 (2009).</li><li>Lee, P., Lin, R., Moon, J., Lee, L. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+alignment+of+collagen+fibers+for+in+vitro+cell+culture.">Microfluidic alignment of collagen fibers for in vitro cell culture.</a> Biomed Microdevices. 8, 35-41 (2006).</li><li>Wozniak, M. A., Keely, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+three-dimensional+collagen+gels+to+study+mechanotransduction+in+T47D+breast+epithelial+cells.">Use of three-dimensional collagen gels to study mechanotransduction in T47D breast epithelial cells.</a> Biol Proced Online. 7, 144-161 (2005).</li><li>Gallagher, S., Winston, S. E., Fuller, S. A., Hurrell, J. G., Ausubel, F. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immunoblotting+and+immunodetection.">Immunoblotting and immunodetection.</a> Current protocols in molecular biology. , 18 (2008).</li><li>Liu, X., Harada, S., Ausubel, F. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DNA+isolation+from+mammalian+samples.">DNA isolation from mammalian samples.</a> Current protocols in molecular biology. , 14 (2013).</li><li>Roeder, B. A., Kokini, K., Sturgis, J. E., Robinson, J. P., Voytik-Harbin, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tensile+mechanical+properties+of+three-dimensional+type+I+collagen+extracellular+matrices+with+varied+microstructure.">Tensile mechanical properties of three-dimensional type I collagen extracellular matrices with varied microstructure.</a> J Biomech Eng. 124, 214-222 (2002).</li><li>Bredfeldt, J. 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=Computational+segmentation+of+collagen+fibers+from+second-harmonic+generation+images+of+breast+cancer.">Computational segmentation of collagen fibers from second-harmonic generation images of breast cancer.</a> J Biomed Opt. 19, 16007 (2014).</li><li>Bischel, L. L., Beebe, D. J., Sung, 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=Microfluidic+model+of+ductal+carcinoma+in+situ+with+3D,+organotypic+structure.">Microfluidic model of ductal carcinoma in situ with 3D, organotypic structure.</a> BMC Cancer. 15, 12 (2015).</li></ol>

3D collagen gels are a valuable addition to our toolbox to understand how cells interpret and respond to their local microenvironment. This manuscript has provided a very basic protocol for embedding cells within a 3D collagen matrix, and to reproducibly generate matrices with random or aligned collagen fibers. Both protocols work as adaptable platforms where different collagen isoforms, crosslinkers, or other matrix proteins could potentially be added at the time of polymerization. It is also easy to modify the platform...

Many cellular processes have been extensively studied in 2 dimensions, thereby forming a collective knowledge of basic cell signaling mechanisms. These studies, however, neglect important cellular cues received from the structural and mechanical properties of the local cellular microenvironment and extracellular matrix (ECM). To better understand how cells interact within a physiological context, it is important to study them in 3-dimensional (3D) assays. The ECM for these 3D assays can either be cell-derived or reconstituted from purified proteins. Regardless of the source of the ECM, 3D matrix assays have proven to be invaluable for understanding how cells navigate and interact within the physiological world. For example, cells grown in 3D matrices display distinct modes of locomotion that depend on the mechanical nature of their surrounding ECM which are not observed in 2D experiments4-6. Moreover, cells cultured in 3D also have fewer and less pronounced stress fibers and focal adhesions than their counterparts grown on hard surfaces such as glass or plastic7. 
The importance of contextual 3D assays is not limited to cell migration, however. Some other cell signaling events can only be investigated through the use of 3D assays. During tissue and cell differentiation, the stiffness of the extracellular environment and ECM provides signals that can influence morphogenic events. For example, mammary epithelial tubulogenesis only occurs in low stiffness 3D matrices, but not in stiff matrices nor on 2D substrata8,9. When cultured within stiff 3D matrices, these same epithelial cells take on an aberrant phenotype with increased proliferation and cell membrane protrusions driven through altered FAK and ERK signaling10. Many other signaling pathways and cellular processes are known to be similarly affected by the stiffness of the local cellular environment, and these signaling cascades highlight the importance of investigating signaling events and cellular phenotype in the context of appropriate local mechanical properties of a 3D ECM. 
Collagen I is a particularly relevant protein to use for in vitro studies as it is the most abundant component of the ECM and is responsible for many of the mechanical properties of the cellular microenvironment. While it was originally thought of as merely a structural protein, its role is now known to be much more complex. Collagen fiber composition, architecture, orientation, density, and stiffness all provide a concentrated milieu of signaling information5. During the progression of certain diseases, such as chronic inflammation and tumorigenesis, the collagen network is dramatically remodeled2,11. More specifically in breast cancers, increased collagen deposition and tissue stiffness accompany and likely contribute to tumor progression. In these early tumors, the stiffened collagen network appears strained and more aligned, such that most of the fibers encapsulate the growing tumor2. As the tumor progresses, the collagen continues to reorganize, and regions of the fibrillar network become orientated perpendicular to the tumor boundary2,12. Perpendicular alignment serves as a prognostic biomarker where these patients have a poorer disease free progression and overall survival1. One explanation for this correlation is that the poor outcomes are a consequence of increased dissemination of tumor cells via persistent cell migration in aligned collagen networks3. 
To understand how cells specifically respond to alignment and organization that is observed in tumor progression, it is necessary to generate both random and aligned 3D collagen matrices for experimentation. There are three basic methodologies to induce alignment within fibrillar networks. The first technique utilizes a strain-inducing device where the collagen between two points is contracted or stretched to generate alignment. Fibers parallel to the axis of force are pulled taut while fibers perpendicular to the axis are compressed and buckled. While strain-induced techniques typically offer superb alignment, this approach requires bulky equipment that is not easily adaptable to many platforms3,13. Alternatively, cell-induced strain can be created by placing localized plugs of cells that subsequently contract and align the collagen13. This method has the problem of being variable, as many parameters may be subject to change. The second method utilizes magnetic beads and a magnetic field during polymerization to induce collagen alignment13,14. Good results can be obtained from this method with unsophisticated equipment, but it does require the use of antibodies or some other method to magnetize the polymer. Therefore, it can be somewhat expensive to use, and the stiffness of the collagen gel is potentially modified by the increased connections in the network. Moreover, the magnetic beads used in this process are often autofluorescent, which is problematic for imaging experiments. Lastly, alignment can be generated by PDMS microfluidic channels3,15,16. In this method, collagen alignment is achieved by flowing polymerizing collagen through small microfluidic channels. These microfluidic channels can be made in a multitude of designs, and are easily adaptable to many platforms. Moreover, they are very economical as very small quantities of collagen and other reagents are used due to their diminutive sizes.
Provided here is a simple protocol for embedding cells within a 3-dimensional, fibrillar collagen hydrogel. In addition, a more advanced technique, wherein PDMS microfluidic channels are used to control the organization and alignment of the collagen matrix is also provided. This protocol is readily adaptable to many platforms, and can reproducibly generate both aligned and random collagen matrices for investigation of cell migration, cell division, and other cellular processes in a 3-dimensional, physiological microenvironment.

<table border="0" cellpadding="0" cellspacing="0" width="687">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">High Concentration Rat tail Collagen</td>
			<td style="width:155px;">Corning</td>
			<td style="width:119px;">354249</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">SylGard184 elastomer kit</td>
			<td style="width:155px;">Corning</td>
			<td style="width:119px;">NC9285739</td>
			<td>Elastomer for PDMS channels</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">HEPES</td>
			<td style="width:155px;">Fisher</td>
			<td style="width:119px;">BP310</td>
			<td>For HEPES neutralization buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">KCl&#160;</td>
			<td style="width:155px;">Fisher</td>
			<td style="width:119px;">BP366</td>
			<td>For HEPES neutralization buffer</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:247px;">KH2PO4</td>
			<td style="width:155px;">Fisher</td>
			<td style="width:119px;">BP362</td>
			<td>For HEPES neutralization buffer</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:247px;">Na2HPO4</td>
			<td style="width:155px;">Fisher</td>
			<td style="width:119px;">S374</td>
			<td>For HEPES neutralization buffer</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">NaCl</td>
			<td style="width:155px;">Fisher</td>
			<td style="width:119px;">BP358</td>
			<td>For HEPES neutralization buffer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">Levy Improved Neubauer Hemacytometer</td>
			<td style="width:155px;">Fisher</td>
			<td style="width:119px;">15170-208</td>
			<td>cell counting</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">6-well non-tissue culture plate&#160;</td>
			<td style="width:155px;">Corning</td>
			<td style="width:119px;">351146</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">50 mm glass bottom dish</td>
			<td style="width:155px;">MatTek</td>
			<td style="width:119px;">P50g-1.5-30-f</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">Bel-Art Plastic Vacuum Desiccator</td>
			<td style="width:155px;">Bel-Art</td>
			<td style="width:119px;">F4200-2021</td>
			<td>Degassing chamber for PDMS</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">transparency film&#160;</td>
			<td style="width:155px;">3M</td>
			<td style="width:119px;">pp2950</td>
			<td>Plastic film for pouring pdms channels</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:247px;">ThermoScientific CimaRec</td>
			<td style="width:155px;">ThermoScientific&#160;</td>
			<td style="width:119px;">HP141925</td>
			<td>Hot plate for curing PDMS microchannels</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:247px;">Vacuum regulator</td>
			<td style="width:155px;">Precision Medical</td>
			<td style="width:119px;">PM3100</td>
			<td>Vacuum regulator for collagen microchannels</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:247px;">8&#34; X 8&#34; rubber sheet&#160;</td>
			<td style="width:155px;">Amazon - Rubber-Cal</td>
			<td style="width:119px;">Silicone - 60A&#160;</td>
			<td>rubber sheet for pouring PDMS microchannel</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:247px;">8&#34; X 8&#34; X .125&#34; acrylic sheet</td>
			<td style="width:155px;">Amazon&#160;</td>
			<td style="width:119px;">Plexiglass sheets</td>
			<td>for pouring PDMS microchannels</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">10 lb weights</td>
			<td style="width:155px;">Amazon</td>
			<td style="width:119px;">CAP Barbell</td>
			<td>for pouring PDMS microchannels</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">15 ml Conical tubes</td>
			<td style="width:155px;">Fisher&#160;</td>
			<td align="right" style="width:119px;">352097</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">50 ml Conical tubes</td>
			<td style="width:155px;">Fisher&#160;</td>
			<td align="right" style="width:119px;">352098</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:247px;">Plastic pipets</td>
			<td style="width:155px;">Dot Scientific</td>
			<td style="width:119px;">229202B, 229206B, and 667225B</td>
			<td>2ml, 5ml, and 25ml</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:247px;">70%EtOH</td>
			<td style="width:155px;">Fisher</td>
			<td style="width:119px;">NC9663244</td>
			<td></td>
		</tr>
	</tbody>
</table>

preparation of 3d collagen gels and microchannels for the study of 3d interactions in vivo

Historically, most cellular processes have been studied in only 2 dimensions. While these studies have been informative about general cell signaling mechanisms, they neglect important cellular cues received from the structural and mechanical properties of the local microenvironment and extracellular matrix (ECM). To understand how cells interact within a physiological ECM, it is important to study them in the context of 3 dimensional assays. Cell migration, cell differentiation, and cell proliferation are only a few processes that have been shown to be impacted by local changes in the mechanical properties of a 3-dimensional ECM. Collagen I, a core fibrillar component of the ECM, is more than a simple structural element of a tissue. Under normal conditions, mechanical cues from the collagen network direct morphogenesis and maintain cellular structures. In diseased microenvironments, such as the tumor microenvironment, the collagen network is often dramatically remodeled, demonstrating altered composition, enhanced deposition and altered fiber organization. In breast cancer, the degree of fiber alignment is important, as an increase in aligned fibers perpendicular to the tumor boundary has been correlated to poorer patient prognosis1. Aligned collagen matrices result in increased dissemination of tumor cells via persistent migration2,3. The following is a simple protocol for embedding cells within a 3-dimensional, fibrillar collagen hydrogel. This protocol is readily adaptable to many platforms, and can reproducibly generate both aligned and random collagen matrices for investigation of cell migration, cell division, and other cellular processes in a tunable, 3-dimensional, physiological microenvironment.

While 3D assays can be done within the same stiffness of collagen gel, varying the gel stiffness can be used to determine how the cells will respond to mechanical changes in their cellular microenvironment. A stiff collagen hydrogel is defined as a gel where the embedded cells are unable to locally contract the surrounding collagen. The intrinsic contractility of different cell types is unique, and thus it is best to begin with a simple contractility curve to establish the collagen concen...

Watch this Scientific Journal Video about Preparation of 3D Collagen Gels and Microchannels for the Study of 3D Interactions In Vivo at JoVE.com

Preparation of 3D Collagen Gels and Microchannels for the Study of 3D Interactions In Vivo

Collagen is a core component of the ECM, and provides essential cues for several cellular processes ranging from migration to differentiation and proliferation. Provided here is a protocol for embedding cells within 3D collagen hydrogels, and a more advanced technique for generating randomized or aligned collagen matrices using PDMS microchannels.

Preparation of 3D Collagen Gels and Microchannels for the Study of 3D Interactions In Vivo

Historically, most cellular processes have been studied in only 2 dimensions.  While these studies have been informative about general cell signaling ...

The overall goal of this procedure is to generate aligned and random 3D collagen matrices, for the purpose of observing cell migration or other cellular processes in the context of a 3D environment. This method is designed to capture collagen features that we find in real tissues, which can help answer the key questions such as the mechanisms that cells use to recognize an aligned or random extracellular matrix. The main advantage of this technique is that you can manipulate the organization of the 3D environment, image cells within and you can do this cost effectively with equipment that is commonly available.Generally, individuals new to this method will struggle because they don't mix the collagen solution and the neutralization buffer well enough and they draw the collagen through the channels inconsistently. Demonstrating this procedure will be Brian Burkel, who is a senior scientist in my laboratory. To begin, thoroughly mix the collagen and HEPES buffer prior to adding cells and media to ensure proper neutralization of the collagen.Then, add the cells and media to the neutralized collagen mixture and place it on ice as described in the accompanying text protocol. Pipette the ice cold mixture into a sterile non-tissue culture treated surface to minimize the attachment and growth of cells outside of the collagen gel. Use a pipette to evenly spread out the solution.Allow the gel to polymerize at room temperature for approximately 10 to 15 minutes. Next, cover the gels, and move them to a 37 degree Celsius incubator for an additional 45 to 60 minutes to finish polymerization. Upon polymerization, the gel will turn opaque.Once polymerized, add two to three milliliters of media. Then, release the gels from the sides of the well by running a 200 pipette around the perimeter of the well. Swirl the dish gently to release the gel from the bottom surface.In order to create PDMS Microchannels for aligning collagen matrices. First prepare an SuA silicon master, using standard soft lithography techniques described elsewhere. Next, use a craft stick to thoroughly mix 20 grams of elastomer base with 2 grams of curing agent in a disposable cup.Once well-mixed, degas the PDMS mixture by placing the disposable cup in a vacuum chamber under a vacuum pressure of 550 millimeters of mercury. Degas the mixture for approximately one to one and a half hours. While degassing the PDMS, prepare the silicon master by placing a clean sheet of transparency film onto a hot plate followed by the silicon master.Ensure that the micro channel mold faces up. After one to one and a half hours, remove the degassed PDMS from the vacuum chamber. Slowly pour the PDMS into the center of the master and allow gravity to spread it evenly.Next, carefully roll a second sheet of transparency film on top of the silicon master and PDMS to avoid air bubbles. Gently place a rubber sheet on top of the transparency, followed by a 1/8 inch sheet of acrylic, then, add the first of three ten pound weights on top of the acrylic sheet. Initially, the first weight will float, allow it to settle and stabilize before proceeding with the two remaining weight plates.When ready to continue, set a hot plate to 70 degrees Celsius and cure the PDMS for four hours. Once cured, allow the PDMS to cool for a minimum of one additional hour and then, carefully peel the top transparency film for the wafer. Finally, remove the channels with the forceps.Place the channels upside down on a new clean transparency film and clean all of the ports with using a circular motion with sharp forceps. Remove any fragments of PDMS that come loose. Next, place a piece of packing tape to the bench, sticky side up and set the PDMS channel side-down on top of the tape.Press down on the channels with the round end of a pair of forceps to ensure good contact. Remove the channels and repeat this process on both sides until all of the visible debris has been removed. Then, transfer the clean, prepped PDMS channels into a 50 milliliter conical tube filled with 70%ethanol.Vortex the channels at maximum speed for 30 seconds, and then replace the solution with fresh, 70%ethanol. Using aseptic techniques, transfer the PDMS channel side up, to a clean and sterile dish. Then, UV treat the channels until the ethanol has evaporated.Once dry, flip the channels over onto a cover slip or glass bottom dish and press them down onto the glass to make a good seal. Add a patch of sterile PDMS to cover and close the center part of the channels and allow the setup to dry thoroughly before proceeding. Next, place a 100 microliter droplet of a 10 micro grams per milliliter collagen solution on the top of a channel and draw it through the channel using a vacuum.Incubate the channels at 37 degrees Celsius for one hour and then transfer the channels, still filled with collagen coating solution into a refrigerator. Chill the set up for approximately for 15 to 30 minutes and then use an aspirator or pipette to remove the collagen coating solution from the channels. Begin by neutralizing the collagen solution, diluting it with cell media and incubating it on ice for 15 minutes.Then, place 120 to 150 microliters of the collagen solution into port A of a pre chilled channel. Next, attach a 25 milliliter pipette to a vacuum line and place it over port C.Use it to draw in the mixture through a single uniform motion, stopping once the collagen reaches the end. The single most important step to generating random matrices is to slowly draw the collagen through the channel.If it is drawn through too rapidly, it will result in increased alignment in the portion of the channel or throughout the entirety of the channel. Carefully remove any excess solution from the port regions and then place sterile PDMS patches over both ports, A and C.After two to three minutes, remove the center PDMS patch covering port B and add two to three micro litters of cells at a concentration of one to three million cells per milliliter into the center port. Allow the gel time to partially polymerize at room temperature for another 10 to 15 minutes and then transfer the constract to a 37 degree celsius incubator for an additional 15 to 30 minutes.Once polymerized, remove the PDMS port covers and add media to completely cover the channel. Here 50, 000 four T one cells were enbedded in either a 2 mg/ml or a 3.5 mg/ml collagen gel for 5 days. The four T cell one line is a highly contractile Med Aesthetic cancer line but it's only able to contract the high density gel by approximately 10%Comporable low density gels are contracted 57%during the same time frame.The degree of collagen alignment is modulated by the rate of collagen flow such that higher collagen flow rate yield better alignment. The use of narrower channels coupled with higher vacuum pressures enhances the alignment of the collagen network, while a wider channel used in conjunction with low vacuum pressures generates random matrices. Once mastered, pouring collagen gels or channels can be done in two and a half hours if performed properly.While attempting this procedure, it's important to remember to set up the components prior to starting. Once you begin working with the collagen, you need to work quickly. After it's development, this technique paved the way for researchers in the field of 3D cell biology, to explore cell adhesion, migration and invasion into three dimensional extracellular environments.After watching this video, you should have a good understanding of how to pour collagen gels of varying densities and how to generate, both random and aligned collagen matrices.

preparation-3d-collagen-gels-microchannels-for-study-3d-interactions

Research

JoVE Journal

Bioengineering

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, ...

Imaging Denatured Collagen Strands In vivo and Ex vivo via Photo-triggered Hybridization of Caged Collagen Mimetic Peptides

Collagen is a major structural component of the extracellular matrix that supports tissue formation and maintenance. Although collagen remodeling is an integral part of normal tissue renewal, excessive amount of remodeling activity is involved in tumors, arthritis, and many other pathological conditions. During collagen remodeling, the triple helical structure of collagen molecules is disrupted by proteases in the extracellular environment. In addition, collagens present in many histological tissue samples are partially denatured by the fixation and preservation processes. Therefore, these denatured collagen strands can serve as effective targets for biological imaging. We previously developed a caged collagen mimetic peptide (CMP) that can be photo-triggered to hybridize with denatured collagen strands by forming triple helical structure, which is unique to collagens. The overall goals of this procedure are i)&#160;to image denatured collagen strands resulting from normal remodeling activities in vivo, and ii) to visualize collagens in ex vivo tissue sections using the photo-triggered caged CMPs. To achieve effective hybridization and successful in vivo and ex vivo imaging, fluorescently labeled caged CMPs are either photo-activated immediately before intravenous injection, or are directly activated on tissue sections. Normal skeletal collagen remolding in nude mice and collagens in prefixed mouse cornea tissue sections are imaged in this procedure. The imaging method based on the CMP-collagen hybridization technology presented here could lead to deeper understanding of the tissue remodeling process, as well as allow development of new diagnostics for diseases associated with high collagen remodeling activity.

Imaging Denatured Collagen Strands In vivo and Ex vivo via Photo-triggered Hybridization of Caged Collagen Mimetic Peptides

This procedure demonstrates in vivo near IR fluorescence imaging of collagen remodeling activities in mice as well as ex vivo staining of collagens in tissue sections using caged collagen mimetic peptides that can be photo-triggered to hybridize with denatured collagen strands.

Collagen is a major structural component of the extracellular matrix that supports tissue formation and maintenance. Although collagen remodeling is an ...

Engineering 3D Cellularized Collagen Gels for Vascular Tissue Regeneration

Synthetic materials are known to initiate clinical complications such as inflammation, stenosis, and infections when implanted as vascular substitutes. Collagen has been extensively used for a wide range of biomedical applications and is considered a valid alternative to synthetic materials due to its inherent biocompatibility (i.e., low antigenicity, inflammation, and cytotoxic responses). However, the limited mechanical properties and the related low hand-ability of collagen gels have hampered their use as scaffold materials for vascular tissue engineering. Therefore, the rationale behind this work was first to engineer cellularized collagen gels into a tubular-shaped geometry and second to enhance smooth muscle cells driven reorganization of collagen matrix to obtain tissues stiff enough to be handled.
The strategy described here is based on the direct assembling of collagen and smooth muscle cells (construct) in a 3D cylindrical geometry with the use of a molding technique. This process requires a maturation period, during which the constructs are cultured in a bioreactor under static conditions (without applied external dynamic mechanical constraints) for 1 or 2 weeks. The &#8220;static bioreactor&#8221; provides a monitored and controlled sterile environment (pH, temperature, gas exchange, nutrient supply and waste removal) to the constructs. During culture period, thickness measurements were performed to evaluate the cells-driven remodeling of the collagen matrix, and glucose consumption and lactate production rates were measured to monitor the cells metabolic activity. Finally, mechanical and viscoelastic properties were assessed for the resulting tubular constructs. To this end, specific protocols and a focused know-how (manipulation, gripping, working in hydrated environment, and so on) were developed to characterize the engineered tissues.

In this work, we present a technique for the rapid fabrication of living vascular tissues by direct culturing of collagen, smooth muscle cells and endothelial cells. In addition, a new protocol for the mechanical characterization of engineered vascular tissues is described.

Synthetic materials are known to initiate clinical complications such as inflammation, stenosis, and infections when implanted as vascular substitutes. ...

Planar Gradient Diffusion System to Investigate Chemotaxis in a 3D Collagen Matrix

The importance of cell migration can be seen through the development of human life. When cells migrate, they generate forces and transfer these forces to their surrounding area, leading to cell movement and migration. In order to understand the mechanisms that can alter and/or affect cell migration, one can study these forces. In theory, understanding the fundamental mechanisms and forces underlying cell migration holds the promise of effective approaches for treating diseases and promoting cellular transplantation. Unfortunately, modern chemotaxis chambers that have been developed are usually restricted to two dimensions (2D) and have complex diffusion gradients that make the experiment difficult to interpret. To this end, we have developed, and describe in this paper, a direct-viewing chamber for chemotaxis studies, which allows one to overcome modern chemotaxis chamber obstacles able to measure cell forces and specific concentration within the chamber in a 3D environment to study cell 3D migration. More compelling, this approach allows one to successfully model diffusion through 3D collagen matrices and calculate the coefficient of diffusion of a chemoattractant through multiple different concentrations of collagen, while keeping the system simple and user friendly for traction force microscopy (TFM) and digital volume correlation (DVC) analysis.

Cell migration is an important part of human development and life. In order to understand the mechanisms that can alter cell migration, we present a planar gradient diffusion system to investigate chemotaxis in a 3D collagen matrix, which allows one to overcome modern diffusion chamber limitations of existing assays.

The importance of cell migration can be seen through the development of human life. When cells migrate, they generate forces and transfer these forces to ...

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

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

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

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

Bioprinting of Cartilage and Skin Tissue Analogs Utilizing a Novel Passive Mixing Unit Technique for Bioink Precellularization

Bioprinting is a powerful technique for the rapid and reproducible fabrication of constructs for tissue engineering applications. In this study, both cartilage and skin analogs were fabricated after bioink pre-cellularization utilizing a novel passive mixing unit technique. This technique was developed with the aim to simplify the steps involved in the mixing of a cell suspension into a highly viscous bioink. The resolution of filaments deposited through bioprinting necessitates the assurance of uniformity in cell distribution prior to printing to avoid the deposition of regions without cells or retention of large cell clumps that can clog the needle. We demonstrate the ability to rapidly blend a cell suspension with a bioink prior to bioprinting of both cartilage and skin analogs. Both tissue analogs could be cultured for up to 4 weeks. Histological analysis demonstrated both cell viability and deposition of tissue specific extracellular matrix (ECM) markers such as glycosaminoglycans (GAGs) and collagen I respectively.

Cartilage and skin analogs were bioprinted using a nanocellulose-alginate based bioink. The bioinks were cellularized prior to printing via a single step passive mixing unit. The constructs were demonstrated to be uniformly cellularized, have high viability, and exhibit favorable markers of differentiation.

Bioprinting is a powerful technique for the rapid and reproducible fabrication of constructs for tissue engineering applications. In this study, both ...

Rigid Embedding of Fixed and Stained, Whole, Millimeter-Scale Specimens for Section-free 3D Histology by Micro-Computed Tomography

For over a hundred years, the histological study of tissues has been the gold standard for medical diagnosis because histology allows all cell types in every tissue to be identified and characterized. Our laboratory is actively working to make technological advances in X-ray micro-computed tomography (micro-CT) that will bring the diagnostic power of histology to the study of full tissue volumes at cellular resolution (i.e., an X-ray Histo-tomography modality). Toward this end, we have made targeted improvements to the sample preparation pipeline. One key optimization, and the focus of the present work, is a straightforward method for rigid embedding of fixed and stained millimeter-scale samples. Many of the published methods for sample immobilization and correlative micro-CT imaging rely on placing the samples in paraffin wax, agarose, or liquids such as alcohol. Our approach extends this work with custom procedures and the design of a 3-dimensional printable apparatus to embed the samples in an acrylic resin directly into polyimide tubing, which is relatively transparent to X-rays. Herein, sample preparation procedures are described for the samples from 0.5 to 10 mm in diameter, which would be suitable for whole zebrafish larvae and juveniles, or other animals and tissue samples of similar dimensions. As proof of concept, we have embedded the specimens from Danio, Drosophila, Daphnia, and a mouse embryo; representative images from 3-dimensional scans for three of these samples are shown. Importantly, our methodology leads to multiple benefits including rigid immobilization, long-term preservation of laboriously-created resources, and the ability to re-interrogate samples.

We developed protocols and designed a custom apparatus to enable embedding of millimeter-scale specimens. We present sample preparation procedures with an emphasis on embedding in acrylic resin and polyimide tubing to achieve rigid immobilization and long-term storage of specimens for the interrogation of tissue architecture and cell morphology by micro-CT.

For over a hundred years, the histological study of tissues has been the gold standard for medical diagnosis because histology allows all cell types in ...

Preparation and Characterization of Graphene-Based 3D Biohybrid Hydrogel Bioink for Peripheral Neuroengineering

Peripheral neuropathies can occur as a result of axonal damage, and occasionally due to demyelinating diseases. Peripheral nerve damage is a global problem that occurs in 1.5%-5% of emergency patients and may lead to significant job losses. Today, tissue engineering-based approaches, consisting of scaffolds, appropriate cell lines, and biosignals, have become more applicable with the development of three-dimensional (3D) bioprinting technologies. The combination of various hydrogel biomaterials with stem cells, exosomes, or bio-signaling molecules is frequently studied to overcome the existing problems in peripheral nerve regeneration. Accordingly, the production of injectable systems, such as hydrogels, or implantable conduit structures formed by various bioprinting methods has gained importance in peripheral neuro-engineering. Under normal conditions, stem cells are the regenerative cells of the body, and their number and functions do not decrease with time to protect their populations; these are not specialized cells but can differentiate upon appropriate stimulation in response to injury. The stem cell system is under the influence of its microenvironment, called the stem cell niche. In peripheral nerve injuries, especially in neurotmesis, this microenvironment cannot be fully rescued even after surgically binding severed nerve endings together. The composite biomaterials and combined cellular therapies approach increases the functionality and applicability of materials in terms of various properties such as biodegradability, biocompatibility, and processability. Accordingly, this study aims to demonstrate the preparation and use of graphene-based biohybrid hydrogel patterning and to examine the differentiation efficiency of stem cells into nerve cells, which can be an effective solution in nerve regeneration.

In this manuscript, we demonstrate the preparation of a biohybrid hydrogel bioink containing graphene for use in peripheral tissue engineering. Using this 3D biohybrid material, the neural differentiation protocol of stem cells is performed. This can be an important step in bringing similar biomaterials to the clinic.

Peripheral neuropathies can occur as a result of axonal damage, and occasionally due to demyelinating diseases. Peripheral nerve damage is a global ...

Microengineering 3D Collagen Hydrogels with Long-Range Fiber Alignment

Aligned collagen I (COL1) fibers guide tumor cell motility, influence endothelial cell morphology, control stem cell differentiation, and are a hallmark of cardiac and musculoskeletal tissues. To study cell response to aligned microenvironments in vitro, several protocols have been developed to generate COL1 matrices with defined fiber alignment, including magnetic, mechanical, cell-based, and microfluidic methods. Of these, microfluidic approaches offer advanced capabilities such as accurate control over fluid flows and the cellular microenvironment. However, the microfluidic approaches to generate aligned COL1 matrices for advanced in vitro culture platforms have been limited to thin "mats" (&lt;40 &#181;m in thickness) of COL1 fibers that extend over distances less than 500 &#181;m and are not conducive to 3D cell culture applications. Here, we present a protocol to fabricate 3D COL1 matrices (130-250 &#181;m in thickness) with millimeter-scale regions of defined fiber alignment in a microfluidic device. This platform provides advanced cell culture capabilities to model structured tissue microenvironments by providing direct access to the micro-engineered matrix for cell culture.

This protocol demonstrates the use of a microfluidic channel with changing geometry along the fluid flow direction to generate extensional strain (stretching) to align fibers in a 3D collagen hydrogel (&lt;250 &#181;m in thickness). The resulting alignment extends across several millimeters and is influenced by the extensional strain rate.

Aligned collagen I (COL1) fibers guide tumor cell motility, influence endothelial cell morphology, control stem cell differentiation, and are a hallmark ...

Agarose Fluid Gels Formed by Shear Processing During Gelation for Suspended 3D Bioprinting

The use of granular matrices to support parts during the bioprinting process was first reported by Bhattacharjee et al. in 2015, and since then, several approaches have been developed for the preparation and use of supporting gel beds in 3D bioprinting. This paper describes a process to manufacture microgel suspensions using agarose (known as fluid gels), wherein particle formation is governed by the application of shear during gelation. Such processing produces carefully defined microstructures, with subsequent material properties that impart distinct advantages as embedding print media, both chemically and mechanically. These include behaving as viscoelastic solid-like materials at zero shear, limiting long-range diffusion, and demonstrating the characteristic shear-thinning behavior of flocculated systems. 
On the removal of shear stress, however, fluid gels have the capacity to rapidly recover their elastic properties. This lack of hysteresis is directly linked to the defined microstructures previously alluded to; because of the processing, reactive, non-gelled polymer chains at the particle interface facilitate interparticle interactions-similar to a Velcro effect. This rapid recovery of elastic properties enables bioprinting high-resolution parts from low-viscosity biomaterials, as rapid reformation of the support bed traps the bioink in situ, maintaining its shape. Furthermore, an advantage of agarose fluid gels is the asymmetric gelling/melting transitions (gelation temperature of ~30 &#176;C and melting temperature of ~90 &#176;C). This thermal hysteresis of agarose makes it possible to print and culture the bioprinted part in situ without the supporting fluid gel melting. This protocol shows how to manufacture agarose fluid gels and demonstrates their use to support the production of a range of complex hydrogel parts within suspended-layer additive manufacture (SLAM).

Shear processing during hydrogel formation results in the production of microgel suspensions that shear-thin but rapidly restructure following the removal of shear forces. Such materials have been used as a supporting matrix for bioprinting complex, cell-laden structures. Here, methods used to manufacture the supporting bed and compatible bioinks are described.

The use of granular matrices to support parts during the bioprinting process was first reported by Bhattacharjee et al. in 2015, and since then, several ...