The authors would like to acknowledge Drs. Jonathan Reichner and Angle Byrd for cell experiment insight. The National Science Foundation Graduate Research Fellowship Program (GRFP) supported this work.

1. 3D Mold Design and Parts
<ol>
	<li>Mold
	<ol>
		<li>Before working, obtain a silicone elastomer kit, a live cell imaging chamber, a 22 mm glass coverslip, and a machined aluminum metal cube with dimensions 10.07 mm x 3.95 mm x 5.99 mm. Prepare the live cell imaging chamber for molding by placing the coverslip in the bottom holder and assembling the rest of the chamber as directed by the vendor.</li>
		<li>Next, using forceps, place the machined aluminum metal cube in the middle of the live cell imaging chamber housing and on top of the coverslip, and then set aside.</li>
		<li>Mix silicone elastomer solutions according to manufacturer&#8217;s protocol to make 5 ml of elastomer.</li>
		<li>Using a disposable lab spatula, pour silicone elastomer solution into live cell imaging chamber setup and ensure not to move placed machined aluminum metal cube. Place the system on the lab bench, in a safe location O/N for curing.</li>
		<li>The next morning, deconstruct the live cell imaging chamber, as recommended by the manufacturer and pull out mold using forceps. Using forceps, carefully extract the machined aluminum metal cube from mold. Go to the sink and rinse the mold with deionized water. Place the mold on a paper towel to dry.</li>
		<li>Once dry, using a hobby utility knife, cut slits through the mold, spaced 2.34 mm apart from each longitudinal end, inside the silicone mold. Ensure the mold stays in a safe and dry place until you are ready to construct the system for an experiment.</li>
	</ol>
	</li>
	<li>Hydrophilic and Hydrophobic Glass Coverslips Preparation
	<ol>
		<li>To allow the collagen matrix to adhere to a surface, create hydrophilic coverslips:
		<ol>
			<li>Using a disposable pipette, measure out 150 &#181;l of 3-aminopropyl-trimethoxysilane and pour solution in a 50 ml tube. Add 30 ml of 100% ethanol to the 50 ml tube with a second disposable pipette and close the lid. Vortex the solution for 2 min, ensuring complete mixing. Pour solution in a glass Petri dish and set aside.</li>
			<li>Pour 15 ml of 100% ethyl alcohol in a second Petri dish and set aside (make sure to label dishes).</li>
			<li>Using a new disposable pipette, measure out 30 ml of deionized water and pour solution into a 50 ml tube. Next, using a new disposable pipette measure out 1,875 &#181;l of glutaraldehyde and pour solution into the same 50 ml tube and close the lid. Vortex the solution for 2 min, ensuring complete mixing. Pour mixture into third Petri dish, and set aside.</li>
			<li>Using forceps, take out one 22 mm round glass coverslip and rinse both sides with 100% ethanol mixture using a disposable pipette.</li>
			<li>Place rinsed glass coverslip into 3-aminopropyl-trimethoxysilane with 30 ml of 100% ethanol solution dish and allow to sit in solution for 5 min.</li>
			<li>With forceps, take out glass coverslip and rinse again with 100% ethanol solution with disposable pipette.</li>
			<li>Drop rinsed glass coverslip into 1,875 &#181;l of glutaraldehyde and 30 ml of deionized water mixture and set aside for 30 min.</li>
			<li>After 30 min, remove glass coverslip with forceps and rinse with deionized water and place onto dry tissue O/N to dry at RT.</li>
			<li>Repeat coverslip dipping and moving for as many coverslips as needed with the same generated solutions.</li>
		</ol>
		</li>
		<li>Make hydrophobic coverslips by the given protocol.
		<ol>
			<li>Add 500 &#181;l of tridecafluoro-1,1,2,2-tetrahydrooctyl, 100 &#181;l of acetic acid and 19.4 ml of hexane in a 50 ml tube and vortex for 2 min. Pour solution in glass Petri dish and set aside.</li>
			<li>Using clean forceps, take out one glass coverslip and drop into prepared mixed solution for 2 min. After 2 min have passed, take out glass coverslip with forceps and rinse with deionized water using a disposable pipette and place coverslip onto dry tissue O/N to dry at RT. Store coverslip in plastic Petri dishes until used.</li>
			<li>Repeat coverslip dipping and moving for as many coverslips as needed with the same generated solutions.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
2. Mold Assembly
<ol>
	<li>Before using molds, using a disposable pipette rinse the mold with 90% ethyl alcohol over a chemical waste container. Next, place the mold in a Petri dish filled with deionized water and allow to sit O/N.</li>
	<li>Take mold out of solution using forceps and place on a towel to air dry before starting the mold assembly.</li>
	<li>While the mold is air-drying, cut the square hydrophilic coverslips into two rectangles slightly larger than 3.95 mm x 5.99 mm using a high-precision diamond-scribing tool. Slide each cut rectangle coverslip into the slots cut into the silicone mold.</li>
	<li>Flip the mold upside down and apply vacuum grease along the bottom of the silicone mold using a disposable pipette. Next, flip the mold back right-side up and press the bottom of the mold onto the circular hydrophilic glass coverslip to create a seal.</li>
	<li>With disposable gloves, pick up the assembled mold and place into a disposable Petri dish and then into a bio-hood. Turn on UV Bio-hood lamp for 1 hr to sterilize the mold before experimentation occurs.</li>
</ol>
3. Collagen Mixture and 3D Matrix
<ol>
	<li>Before preparing the collagen mixture, stain and prepare cells for imaging according to standard protocols28.</li>
	<li>Using standard laboratory techniques and protocols29,30, in a bio-hood, mix cell media and chemoattractant in a 15 ml tube to desired chemoattractant concentration. Pipette 5 ml of specific cell media-chemoattractant concentration solution into a 15 ml tube and move the solution into a heated water bath.</li>
	<li>Using a pipette, extract 5 ml of just cell media into a second 15 ml tube and place in a heated water bath to heat up the solution for microscopy experiments.</li>
	<li>In a bio-hood, pipette 30 &#181;l of 10x phosphate buffered solution (PBS) into micro centrifuge tube. Add 6 &#181;l of 1 N sodium hydroxide (NaOH) into same micro centrifuge tube and vortex for 15 sec.</li>
	<li>Obtain collagen I rat tail solution from the fridge and move to the bio-hood using standard laboratory techniques and protocols29. Ensure the collagen is still cold. Pipette 168.3 &#181;l of collagen into same micro centrifuge tube.</li>
	<li>Next, add 18 &#181;l of yellow-green fluorescent carboxylate-modified microspheres using a pipette to the same micro centrifuge tube. Vortex the micro centrifuge tube with all the solutions for 30 sec.</li>
	<li>Add 77.7 &#181;l of desired cell media-cell mixture (approximately 2 x 106 cells/ml concentration) into micro centrifuge tube and mix using pipette tip for 20 sec. As necessary, alter the matrix density by following the custom collagen mixture adapted for the addition of fluorescent beads and cell viability table (Table 1).</li>
	<li>Pipette 300 &#181;l of collagen-cell mixture into the center well (well #2) of the prepared mold assembly. Place the mold onto a disposable Petri dish and move it into a standard incubator for 20 min at 37 &#176;C with 5% CO2.</li>
	<li>Remove system from incubator and place back into bio-hood. Using forceps, remove both hydrophobic cover slips by clamping onto the top of each coverslip and pulling up and away from the mold.</li>
	<li>Move the whole system to the desired microscopy and image to ensure collagen mold sides are still straight to allow for a planar diffusion gradient.</li>
	<li>With the system still under the microscope, using a 100 &#181;l single-channel pipette, add 100 &#181;l of cell media into well #1. Next, using a 100 &#181;l single-channel pipette add 100 &#181;l of cell media with desired chemoattractant concentration into well #3.</li>
	<li>Immediately after adding solutions into both wells, commence imaging.</li>
</ol>
4. Imaging and Diffusion Modeling
<ol>
	<li>If one wants to find the diffusion coefficient for the specific collagen density to calculate the specific concentration, follow the protocol below:
	<ol>
		<li>Follow the given protocol above titled &#8220;Collagen Mixture and 3D Matrix,&#8221; instead of generating cell media with desired chemoattractant concentration, make 5 &#181;M rhodamine in a 15 ml tube using standard calculations and protocols30.</li>
		<li>Image the 3D collagen matrices with a confocal system mounted on an inverted microscope using an argon laser (488 nm) to capture the fluorescence. Image every 2 or 3 sec for up to 7 hr.</li>
	</ol>
	</li>
	<li>For Diffusion Modeling: Using the mathematical model shown below, write a computational software code for processing and analysis with these general steps. 
	<img alt="Equation 1" src="/files/ftp_upload/52948/52948eq1.jpg" />
	<ol>
		<li>Import images into computational software for rescaling and normalizing by the maximum intensity. Convert images to a gray color-map of the image to select the edge. Pick an axis along the center of the image, to the right of the center and to the left of the center.</li>
		<li>Using the computational software code, plot the normalized intensity, along with the true intensity and the difference between the two.</li>
		<li>Next, input the parameters necessary for fitting (concentration, time, and length).</li>
		<li>Plot the normalized concentration versus time and the concentration profile across the x-axis with a polynomial fit to the data.</li>
		<li>Calculate the coefficient of diffusion using the computational software code.</li>
	</ol>
	</li>
</ol>
5. Experimental Measurements
<ol>
	<li>Referring back to the diffusion equation, rewrite the equation to find the specific concentration at any location within the system as shown in below. 
	<img alt="Equation 2" src="/files/ftp_upload/52948/52948eq2.jpg" /> 
	Where: 
	L = Length of the collagen matrix 
	x = location under investigation 
	D = coefficient of diffusion 
	t = elapsed time</li>
	<li>During chemotaxis experiments, ensure to record the specific time that the moment chemokine was added to system. Once cell migration movement is found, ensure to record confocal time-lapse recording, and note the specific time and location from edge where imaging occurred.</li>
	<li>During data analysis, plug the noted elapsed time, location and coefficient of diffusion for the specific cell into the equation to find the normalized specific concentration at any point within the collagen for both diffusion and cell experiments.</li>
</ol>
6. Tracking Cell Migration Utilizing TFM
<ol>
	<li>To track cell migration using TFM/DVC techniques follow the protocol below:
	<ol>
		<li>After the addition of desired chemoattractant concentration into well #3, start imaging the 3D collagen matrices with a confocal system mounted on an inverted microscope to find a cell to investigate.</li>
		<li>Once a moving cell is found, place the cell in the middle of the field of view and utilize a piezoelectric motor (to image in the z-axis), image every 1 or 2 min.</li>
		<li>For calculating cell force generation and deformation, generate a computational code to find the displacements of the fluorescence beads following the TFM/DVC protocols31.</li>
	</ol>
	</li>
</ol>

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The authors declare that they have no competing financial interests.

The most critical steps for successful diffusion experiments with or without cells are: correctly setting up the mold assembly; developing the necessary manual dexterity to prevent damage during extraction of hydrophobic coverslips; ensuring to find a very good linear starting line to correctly calculate the diffusion coefficient; correct experimental calculations of both collagen and chemoattractant; correctly use of live cell imaging system to ensure matrix does not dry out; and maintaining a sterile, healthy culture.<...

The preferred movement of cells towards a concentration gradient, known as chemotaxis, plays an important role in pathological and physiological processes in the body. Such examples are skin and mucosa wound healing1, morphogenesis2, inflammation3, and tumor growth4,5. It has also been shown that cancer cells can migrate through both individual and collective cell-migration strategies6. Moreover, diffusional instability mechanisms can induce the separation of single or clustered cells from a tumorous body/object and then can immigrate towards a source of nutrients and thus invade wider areas and tissues7.
Furthermore, it has been shown that diverse migration mechanisms can be active in 2D and in 3D, due to different roles of adhesion molecules8. Therefore, a move to physiologically relevant in vitro assays to investigate cell motility in a measureable and simple way is of significance in understanding cell movement phenomena9. Unfortunately, the difficulty in analyzing cell migration, a comprehensive quantifiable chemotaxis assay usually requires a long laborious method, founded on the measurement of impartial cell motility and transport phenomena models.
Past experimental approaches to investigate cell chemotaxis include the Boyden chamber10 and the under agarose assay11. However, within these early assays, cell migration experiments did not monitor the movement in respect to time. More, importantly, the concentration gradients used for the experiments were not well defined or completely understood while only sustaining the signaling for no more than a few hr. Furthermore, early chemotaxis chamber attempts restricted cell migration to two dimensions and did not allow one to monitor the kinetics of migration12. Looking at the Boyden chamber, an endpoint assay would not allow the researcher to observe migration visually and could not directly differentiate chemotaxis (directional movement) from chemokinesis (random movement). Additionally, several variables&#8212;differences in the pore size and thickness of membranes&#8212;made the chamber very difficult to easily reproduce and concealed the migrant reaction of cells to chemokines13,14.
With the new understanding of microfluidics, new chambers and micro-devices have been investigated as an instrument to investigate cell locomotion under interstitial flow conditions or chemotaxis15,16. Under these new devices, new cell metrics were introduced and investigated, like the effect of shear stress on a cell17,18. Unfortunately, past and current microfluidic chemotaxis chambers limited studies of cell migration to 2D substrates&#8212;an important setback since many biological processes, including tumor cell invasion and metastasis, and immune cell migration, involve 3D migration.
Direct observation chambers&#8212;where a chemoattractant solution is in contact with a 3D gel containing cells have also been also reported19,20. These chambers have two compartments, one containing a chemoattractant and one containing cells, are joined beside one another horizontally21 or as concentric rings22. These systems are pointed in the right direction, but do not keep a chemotaxis system for an extended period of time.
Furthermore, researchers have also examined diffusivity through collagen membranes in dialysis cells, as well as the diffusion of tracer molecules through collagen samples subjected to hydrostatic pressure23-25. Some diffusion experiments in collagen gels rely on physical and chemical modifications of the gel using magnetic fields and chemical incorporation26. A popular method for modeling diffusivity in collagenous tissues relies on the fluorescence imaging of continuous point photobleaching. This method has revealed anisotropy in the diffusion coefficients of macromolecules in oriented collagenous tissues. Yet, photobleaching has been used in articular cartilage and not collagen matrices. While similar, the necessary modeling experiments must be carried through specifically understanding the diffusion coefficient of collagen gels. More importantly, the systems do not utilize a method for measuring cell force generation.
Unfortunately, most systems seem to be missing one or two key elements for an ideal system: the allowing of cell tracking, a diffusion gradient understanding with a chemotactic factor through the matrix, a relatively simple set up with an ease of reproducibility, the minimization of cell-cell interactions, and the ability to measure dimensional units for quantification (i.e., velocity, force, specific concentration). Moghe et al.27 proposed a system that fulfilled most of these requirements in which cells were initially dispersed throughout the gel rather than concentrated on the filter surface, but was difficult to measure forces that the cell generates.
To this purpose, 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, which is based on time-lapse microscopy, coupled with image analysis techniques to measure cell forces in a 3D environment. This protocol provides a simple, yet innovative way of creating a simple 3D diffusion chamber that can be used to investigate 3D chemotaxis in different cells.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Silicone elastomer kit</td>
			<td>Dow Corning Corp</td>
			<td>182 SIL ELAST KIT .5KG</td>
			<td>a two-part misture with a 10:1 mix</td>
		</tr>
		<tr>
			<td>Live cell imaging chamber</td>
			<td>Live Cell Instrument</td>
			<td>CM-B18-1</td>
			<td>CMB for 18mm round coverslips</td>
		</tr>
		<tr>
			<td>22mm Glass Coverslip</td>
			<td>Fisher Scientific</td>
			<td>NC0180281</td>
			<td>Neuvitro Corp. cover slip 22mm 1.5</td>
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			<td>Machined aluminum metal cube</td>
			<td></td>
			<td></td>
			<td></td>
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			<td>Hobby utility knife</td>
			<td>X-Acto</td>
			<td>X3201</td>
			<td></td>
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			<td>3-(aminopropyl) trimethoxysilane</td>
			<td>Sigma-Aldrich</td>
			<td>281778-5ML</td>
			<td></td>
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			<td>Glutaraldehyde</td>
			<td>Polysciences, Inc</td>
			<td>00216A-10</td>
			<td>Glutaraldehyde, EM Grade, 8%</td>
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			<td>50 ml tube</td>
			<td>Fisher Scientific</td>
			<td>14-432-22</td>
			<td>Standard floor model and tabletop centrifuges</td>
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			<td>Glass petri dish</td>
			<td>Fisher Scientific</td>
			<td>08-747A</td>
			<td>Reusable Petri Dishes: Complete (60 x 15mm)</td>
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		<tr>
			<td>Forceps</td>
			<td>Fisher Scientific</td>
			<td>22-327-379</td>
			<td>Fine Point Forceps</td>
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			<td>Cover glasses</td>
			<td>Fisher Scientific</td>
			<td>12-518-105A</td>
			<td>Rectangle; 30 x 22mm; Thickness No. 1</td>
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			<td>Tridecafluoro-1,1,2,2-tetrahydrooctyl</td>
			<td>Gelest</td>
			<td>SIT8174.0</td>
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			<td>Acetic acid</td>
			<td>Sigma-Aldrich</td>
			<td>320099</td>
			<td>Acetic acid ACS reagent, &#8805;99.7%</td>
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			<td>Hexane</td>
			<td>Sigma-Aldrich</td>
			<td>296090</td>
			<td>Hexane</td>
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		<tr>
			<td></td>
			<td></td>
			<td></td>
			<td>anhydrous, 95%</td>
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		<tr>
			<td>Ethyl alcohol</td>
			<td>Sigma-Aldrich</td>
			<td>E7023</td>
			<td>200 proof, for molecular biology</td>
		</tr>
		<tr>
			<td>High-precision diamond scribing tool</td>
			<td>Lunzer</td>
			<td>PV-081-3</td>
			<td>Straight extended tip scribe, .020&#34; (.50mm) diameter by .200&#34; (5.0mm) tip length</td>
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			<td>Vacuum grease</td>
			<td>Dow Corning</td>
			<td>14-635-5C</td>
			<td>High-Vacuum Grease</td>
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			<td>15 ml tube</td>
			<td>Fisher Scientific</td>
			<td>14-959-49D</td>
			<td>15 ml conical centrifuge tubes with hydrophobic, biologically inert surface</td>
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		<tr>
			<td>10X phosphate buffered solution</td>
			<td>Fisher Scientific</td>
			<td>BP399-500</td>
			<td>1.37 M Sodium Chloride, 0.027 M Potassium Chloride, and 0.119 M Phosphate Buffer</td>
		</tr>
		<tr>
			<td>1N sodium hydroxide</td>
			<td>Sigma-Aldrich</td>
			<td>38215</td>
			<td>Sodium hydroxide concentrate</td>
		</tr>
		<tr>
			<td>Collagen I, rat tail</td>
			<td>BD Biosciences</td>
			<td>354236</td>
			<td>Rat tail&#160;</td>
		</tr>
		<tr>
			<td>Micro centrifuge tube</td>
			<td>Fisher Scientific</td>
			<td>02-681-332</td>
			<td>Volume: 2.0 ml; O.D. x L: 13 x 40 mm; sterile; single-wrapped</td>
		</tr>
		<tr>
			<td>Carboxylate-modified microspheres</td>
			<td>Invitrogen</td>
			<td>&#160;F-8813</td>
			<td>Carboxylate-modified microspheres, 0.5 &#181;m, yellow-green fluorescent (505/515), 2% solids</td>
		</tr>
		<tr>
			<td>Rhodamine</td>
			<td>Sigma-Aldrich</td>
			<td>83689</td>
			<td>Rhodamine B for fluorescence</td>
		</tr>
	</tbody>
</table>

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.

The ability of this assay to accurately assess the migration of the cell relies upon a good setup of the system. Therefore, it is critical for make sure to design the diffusion system mold accurately and take great care in placing both hydrophobic and hydrophilic coverslips, as illustrated in Figure 1. If the system is properly designed and during the diffusion modeling stage ensuring to find a very good linear starting line, one is able to achieve nice fluoresces images, as depicted in Figure 2<...

Watch this Scientific Journal Video about Planar Gradient Diffusion System to Investigate Chemotaxis in a 3D Collagen Matrix at JoVE.com

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

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 ...

planar-gradient-diffusion-system-to-investigate-chemotaxis-3d

Research

JoVE Journal

Bioengineering

8.4K Views.  California State University, Long Beach. 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.

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

Analysis of Cell Migration within a Three-dimensional Collagen Matrix

The ability to migrate is a hallmark of various cell types and plays a crucial role in several physiological processes, including&#160;embryonic development, wound healing, and immune responses. However, cell migration is also a key mechanism in cancer enabling these cancer cells to detach from the primary tumor to start metastatic spreading. Within the past years various cell migration assays have been developed to analyze the migratory behavior of different cell types. Because the locomotory behavior of cells markedly differs between a two-dimensional (2D) and three-dimensional (3D) environment it can be assumed that the analysis of the migration of cells that are embedded within a 3D environment would yield in more significant cell migration data. The advantage of the described 3D collagen matrix migration assay is that cells are embedded within a physiological 3D network of collagen fibers representing the major component of the extracellular matrix. Due to time-lapse video microscopy real cell migration is measured allowing the determination of several migration parameters as well as their alterations in response to pro-migratory factors or inhibitors. Various cell types could be analyzed using this technique, including lymphocytes/leukocytes, stem cells, and tumor cells. Likewise, also cell clusters or spheroids could be embedded within the collagen matrix concomitant with analysis of the emigration of single cells from the cell cluster/ spheroid into the collagen lattice. We conclude that the 3D collagen matrix migration assay is a versatile method to analyze the migration of cells within a physiological-like 3D environment.

Cell migration is a biological phenomenon that is involved in a plethora of physiological, such as wound healing and immune responses, and pathophysiological processes, like cancer. The 3D-collagen matrix migration assay is a versatile tool to analyze the migratory properties of different cell types within in a 3D physiological-like environment.

The ability to migrate is a hallmark of various cell types and plays a crucial role in several physiological processes, including&#160;embryonic ...

Concentric Gel System to Study the Biophysical Role of Matrix Microenvironment on 3D Cell Migration

The ability of cells to migrate is crucial in a wide variety of cell functions throughout life&#160;from embryonic development and wound healing&#160;to tumor and cancer metastasis. Despite intense research efforts, the basic biochemical and biophysical principles of cell migration are still not fully understood, especially in the physiologically relevant three-dimensional (3D) microenvironments. Here, we describe an in vitro assay designed to allow quantitative examination of 3D cell migration behaviors. The method exploits the cell&#8217;s mechanosensing ability and propensity to migrate into previously unoccupied extracellular matrix (ECM). We use the invasion of highly invasive breast cancer cells, MDA-MB-231, in collagen gels as a model system. The spread of cell population and the migration dynamics of individual cells over weeks of culture can be monitored using live-cell imaging and analyzed to extract spatiotemporally-resolved data. Furthermore, the method is easily adaptable for diverse extracellular matrices, thus offering a simple yet powerful way to investigate the role of biophysical factors in the microenvironment on cell migration.

The mechanical properties and microstructure of the extracellular matrix strongly affect 3D migration of cells. An in vitro method to study the spatiotemporal cell migration behavior in biophysically variable environments, at both population and individual cell levels, is described.

The ability of cells to migrate is crucial in a wide variety of cell functions throughout life&#160;from embryonic development and wound healing&#160;to ...

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. ...

Gradient Strain Chip for Stimulating Cellular Behaviors in Cell-laden Hydrogel

Artificial guidance for cellular alignment is a hot topic in the field of tissue engineering. Most of the previous research has investigated single strain-induced cellular alignment on a cell-laden hydrogel by using complex experimental processes and mass controlling systems, which are usually associated with contamination issues. Thus, in this article, we propose a simple approach to building a gradient static strain using a fluidic chip with a plastic PDMS cover and a UV transparent glass substrate for the stimulation of cellular behavior in a 3D hydrogel. Overloading photo-patternable cell prepolymer in the fluidic chamber can generate a convex curved PDMS membrane on the cover. After UV crosslinking, through a concentric circular micropattern under the curved PDMS membrane, and buffer washing, a microenvironment for investigating cell behaviors under a variety of gradient strains is self-established in a single fluidic chip, without external instruments. NIH3T3 cells were demonstrated after observing the change in the cellular alignment trend under geometry guidance, in cooperation with strain stimulation, which varied from 15 - 65% on hydrogels. After a 3-day incubation, the hydrogel geometry dominated the cell alignment under low compressive strain, where cells aligned along the hydrogel elongation direction under high compressive strain. Between these, the cells showed random alignment due to the dissipation of the radical guidance of hydrogel elongation and the geometry guidance of the patterned hydrogel.

This article introduces a simple approach to providing non-continuous gradient static strains on a concentric cell-laden hydrogel to regulate cell alignment for tissue engineering.

Artificial guidance for cellular alignment is a hot topic in the field of tissue engineering. Most of the previous research has investigated single ...

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.

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.

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

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 ...

A Method for Determination and Simulation of Permeability and Diffusion in a 3D Tissue Model in a Membrane Insert System for Multi-well Plates

In vitro cultivated skin models have become increasingly relevant for pharmaceutical and cosmetic applications, and are also used in drug development as well as substance testing. These models are mostly cultivated in membrane-insert systems, their permeability toward different substances being an essential factor. Typically, applied methods for determination of these parameters usually require large sample sizes (e.g., Franz diffusion cell) or laborious equipment (e.g., fluorescence recovery after photobleaching (FRAP)). This study presents a method for determining permeability coefficients directly in membrane-insert systems with diameter sizes of 4.26 mm and 12.2 mm (cultivation area). The method was validated with agarose and collagen gels as well as a collagen cell model representing skin models. The permeation processes of substances with different molecular sizes and permeation through different cell models (consisting of collagen gel, fibroblast, and HaCaT) were accurately described.
Moreover, to support the above experimental method, a simulation was established. The simulation fits the experimental data well for substances with small molecular size, up to 14 x 10-10 m Stokes radius (4,000 MW), and is therefore a promising tool to describe the system. Furthermore, the simulation can considerably reduce experimental efforts and is robust enough to be extended or adapted to more complex setups.

A method for determination of permeability in a membrane insert system for multi-well plates and in silico parameter optimization for the calculation of diffusion coefficients using simulation are presented.

In vitro cultivated skin models have become increasingly relevant for pharmaceutical and cosmetic applications, and are also used in drug development as ...

A Novel Tenorrhaphy Suture Technique with Tissue Engineered Collagen Graft to Repair Large Tendon Defects

Surgical management of large tendon defects with tendon grafts is challenging, as there are a finite number of sites where donors can be readily identified and used. Currently, this gap is filled with tendon auto-, allo-, xeno-, or artificial grafts, but clinical methods to secure them are not necessarily translatable to animals because of the scale. In order to evaluate new biomaterials or study a tendon graft made up of collagen type 1, we have developed a modified suture technique to help maintain the engineered tendon in alignment with the tendon ends. Mechanical properties of these grafts are inferior to the native tendon. To incorporate engineered tendon into clinically relevant models of loaded repair, a strategy was adopted to offload the tissue engineered tendon graft and allow for the maturation and integration of the engineered tendon in vivo until a mechanically sound neo-tendon was formed. We describe this technique using incorporation of the collagen type 1 tissue engineered tendon construct.

In this paper, we present an in vitro and in situ protocol to repair a tendon gap of up to 1.5 cm by filling it with engineered collagen graft. This was performed by developing a modified suture technique to take the mechanical load until the graft matures into the host tissue.

Surgical management of large tendon defects with tendon grafts is challenging, as there are a finite number of sites where donors can be readily ...

Calorespirometry: A Powerful, Noninvasive Approach to Investigate Cellular Energy Metabolism

Many cell lines used in basic biological and biomedical research maintain energy homeostasis through a combination of both aerobic and anaerobic respiration. However, the extent to which both pathways contribute to the landscape of cellular energy production is consistently overlooked. Transformed cells cultured in saturating levels of glucose often show a decreased dependency on oxidative phosphorylation for ATP production, which is compensated by an increase in substrate-level phosphorylation. This shift in metabolic poise allows cells to proliferate despite the presence of mitochondrial toxins. In neglecting the altered metabolic poise of transformed cells, results from a pharmaceutical screening may be misinterpreted since the potentially mitotoxic effects may not be detected using model cell lines cultured in the presence of high glucose concentrations. This protocol describes the pairing of two powerful techniques, respirometry and calorimetry, which allows for the quantitative and noninvasive assessment of both aerobic and anaerobic contributions to cellular ATP production. Both aerobic and anaerobic respirations generate heat, which can be monitored via calorimetry. Meanwhile, measuring the rate of oxygen consumption can assess the extent of aerobic respiration. When both heat dissipation and oxygen consumption are measured simultaneously, the calorespirometric ratio can be determined. The experimentally obtained value can then be compared to the theoretical oxycaloric equivalent and the extent of the anaerobic respiration can be judged. Thus, calorespirometry provides a unique method to analyze a wide range of biological questions, including drug development, microbial growth, and fundamental bioenergetics under both normoxic and hypoxic conditions.

This protocol describes calorespirometry, the direct and simultaneous measurement of both heat dissipation and respiration, which provides a noninvasive approach to assess energy metabolism. This technique is used to assess the contribution of both aerobic and anaerobic pathways to energy utilization by monitoring the total cellular energy flow.

Many cell lines used in basic biological and biomedical research maintain energy homeostasis through a combination of both aerobic and anaerobic ...

A Human 3D Extracellular Matrix-Adipocyte Culture Model for Studying Matrix-Cell Metabolic Crosstalk

The extracellular matrix (ECM) plays a central role in regulating tissue homeostasis, engaging in crosstalk with cells and regulating multiple aspects of cellular function. The ECM plays a particularly important role in adipose tissue function in obesity, and alterations in adipose tissue ECM deposition and composition are associated with metabolic disease in mice and humans. Tractable in vitro models that permit dissection of the roles of the ECM and cells in contributing to global tissue phenotype are sparse. We describe a novel 3D in vitro model of human ECM-adipocyte culture that permits study of the specific roles of the ECM and adipocytes in regulating adipose tissue metabolic phenotype. Human adipose tissue is decellularized to isolate ECM, which is subsequently repopulated with preadipocytes that are then differentiated within the ECM into mature adipocytes. This method creates ECM-adipocyte constructs that are metabolically active and retain characteristics of the tissues and patients from which they are derived. We have used this system to demonstrate disease-specific ECM-adipocyte crosstalk in human adipose tissue. This culture model provides a tool for dissecting the roles of the ECM and adipocytes in contributing to global adipose tissue metabolic phenotype and permits study of the role of the ECM in regulating adipose tissue homeostasis.

We describe a 3D human extracellular matrix-adipocyte in vitro culture system that permits dissection of the roles of the matrix and adipocytes in contributing to adipose tissue metabolic phenotype.

The extracellular matrix (ECM) plays a central role in regulating tissue homeostasis, engaging in crosstalk with cells and regulating multiple aspects of ...