This work was founded by Institut Curie, Paris, France. The mechanical stretcher was designed by Damien Cuvelier (Institut Curie) and is manufactured by GREM (mecanique-grem.com). The patterning on PDMS was developed by Ammar Azioune (Bordeaux II University).

1. Passivation of the PDMS
<ol>
	<li>Cut a piece of PDMS approximately 35 mm x 20 mm from a pre&#160;made sheet (for instance, GelPak, as listed in the table of materials).</li>
	<li>Remove the top and the bottom protective layers of plastic (if necessary) and use tweezers to place the PDMS in a plastic (not cell culture treated) Petri dish.</li>
	<li>Wash the PDMS with 70% ethanol for 5 min on a rotator at 30 oscillations/min.</li>
	<li>Dry the surface by flowing air on it.</li>
	<li>Illuminate with deep UV (&#955; = 180 nm) for 5 min at a distance from the UV bulbs of about 5 cm (see Materials sheet for lamp reference; parameters will vary for different lamps).</li>
	<li>Prepare 200 &#181;l&#160;of EDC/NHS solution for each PDMS piece (this must be prepared just before use because the reactivity of the solution decays in a matter of hr). For 1 ml of 0.05 M MES + 0.5 M NaCl buffer at pH 6.0, add 11.5 mg of Sulfo-NHS and 19.2 mg of EDC.</li>
	<li>Transfer the PDMS sheets from the Petri dish to the lid of the Petri dish, which has not been illuminated. This will ensure that the surroundings of the PDMS are very hydrophobic and facilitate the next step.</li>
	<li>Add EDC/NHS solution and incubate for 15 min at room temperature.</li>
	<li>Rinse EDC/NHS with water.</li>
	<li>Add PLL-g-PEG solution (0.5 mg/ml in HEPES 10 mM pH 8.6) and incubate from 3 hr to overnight at room temperature.</li>
	<li>Rinse the PLL-g-PEG with water. Passivated PDMS (functionalized with PLL-g-PEG) can be stored for several days at 4&#160;&#176;C.</li>
</ol>
2. Patterning of the PDMS
<ol>
	<li>Take a PDMS sheet and place it on a synthetic quartz photomask bearing the microfeatures for patterning (see Figure 1). Place the PDMS side bearing the PLL-g-PEG facing the chrome side of the photomask.</li>
	<li>Illuminate for 7 min through the photomask at a distance from the UV bulbs of about 5 cm.</li>
	<li>Add water onto the mask + PDMS and peel the PDMS slowly off the mask.</li>
	<li>Incubate with fibronectin solution at 50 mg/ml in HEPES buffer at pH 8.6 for 1 hr at room temperature. It is possible to use others ECM proteins, but these have not been tested with this protocol.</li>
	<li>Rinse with PBS.</li>
</ol>
3. Mounting the Device
<ol>
	<li>Mount the previously passivated PDMS onto the stretching device (see Discussion for troubleshooting).
	<ol>
		<li>Attach one side of the PDMS to the fixed part of the stretcher.</li>
		<li>Fix the other side to the mobile part of the stretcher without clamping too much of the PDMS sheet.</li>
	</ol>
	</li>
	<li>Cut a rectangle of PDMS (22 mm x 19 mm) in a thick PDMS stab and cut another rectangle inside in order to have a pool (or frame) that will retain the cells and media (see Figure 2).</li>
	<li>Add silicone grease under this PDMS pool and place it on top of the PDMS sheet to create a medium&#160;retaining pool. The grease will allow the gliding of the pool over the PDMS sheet during stretching.</li>
</ol>
4. Patterning the Cells
<ol>
	<li>Detach the cells from a 50% confluency culture flask with Versene.</li>
	<li>Count the cells and resuspend them at a concentration of 200,000 cells/ml.</li>
	<li>Add 1 ml of cell suspension in the pool (see Discussion for additional details).</li>
	<li>Let the cells bind to the patterns for 10-30 min (depending on the cell type, RPE-1 cells will take 10 min and HeLa cells 20 min).</li>
	<li>Gently flush the floating cells with equilibrated medium (equilibrate medium in incubator).</li>
	<li>Let the cells spread for a few hr on the patterns (RPE-1 will need at least 2 hr; HeLa cells will need 3 hr).</li>
	<li>Add a coverslip on top of the pool to avoid evaporation and medium leakage in case the PDMS breaks.</li>
	<li>Put the device on an inverted microscope and start imaging. Avoid the use of oil immersion objectives as it will not work due to focusing problems.</li>
</ol>
5. Stretching
<ol>
	<li>Turn the micrometric screw while correcting the stage position in the x-, y-,&#160;and z-axis (mainly x). The stage position needs to be corrected to counteract the widening of the PDMS and the loss of focus. (See &#34;During the stretch&#34; paragraph in the DISCUSSION).</li>
</ol>

<ol>
	<li>Vogel, V., Sheetz, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Local+force+and+geometry+sensing+regulate+cell+functions.">Local force and geometry sensing regulate cell functions.</a> Nat. Rev. Mol. Cell Biol. 7, 265-275 (2006).</li><li>Terenna, C. R., 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=Physical+mechanisms+redirecting+cell+polarity+and+cell+shape+in+fission+yeast.">Physical mechanisms redirecting cell polarity and cell shape in fission yeast.</a> Curr. Biol. 18 (22), 1748-1753 (2008).</li><li>Guillot, C., Lecuit, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanics+of+epithelial+tissue+homeostasis+and+morphogenesis.">Mechanics of epithelial tissue homeostasis and morphogenesis.</a> Science. 340 (6137), 1185-1189 (2013).</li><li>Bosveld, F., 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=Mechanical+control+of+morphogenesis+by+Fat/Dachsous/Four-jointed+planar+cell+polarity+pathway.">Mechanical control of morphogenesis by Fat/Dachsous/Four-jointed planar cell polarity pathway.</a> Science. 336 (6082), 724-727 (2012).</li><li>Farhadifar, R., Roper, J. C., Aigouy, B., Eaton, S., Julicher, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+influence+of+cell+mechanics,+cell-cell+interactions,+and+proliferation+on+epithelial+packing.">The influence of cell mechanics, cell-cell interactions, and proliferation on epithelial packing.</a> Curr. Biol. 17, 2095-2104 (2007).</li><li>Rauzi, M., Verant, P., Lecuit, T., Lenne, P. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nature+and+anisotropy+of+cortical+forces+orienting+Drosophila+tissue+morphogenesis.">Nature and anisotropy of cortical forces orienting Drosophila tissue morphogenesis.</a> Nat. Cell Biol. 10, 1401-1410 (2008).</li><li>Mitrossilis, D., 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=Real-time+single-cell+response+to+stiffness.">Real-time single-cell response to stiffness.</a> Proc. Natl. Acad. Sci. U.S.A. 107 (38), 16518-16523 (2010).</li><li>Irimia, D., Charras, G., Agrawal, N., Mitchison, T., Toner, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polar+stimulation+and+constrained+cell+migration+in+microfluidic+channels.">Polar stimulation and constrained cell migration in microfluidic channels.</a> Lab Chip. 12, 1783-1790 (2007).</li><li>Fink, 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=External+forces+control+mitotic+spindle+positioning.">External forces control mitotic spindle positioning.</a> Nat. Cell. Biol. 13 (7), 771-778 (2011).</li><li>Azioune, A., Storch, M., Bornens, M., Th&#233;ry, M., Piel, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simple+and+rapid+process+for+single+cell+micro-patterning.">Simple and rapid process for single cell micro-patterning.</a> Lab Chip. 9 (11), 1640-1642 (2009).</li><li>Azioune, A., Carpi, N., Tseng, Q., Th&#233;ry, M., Piel, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protein+micropatterns:+A+direct+printing+protocol+using+deep+Uvs.">Protein micropatterns: A direct printing protocol using deep Uvs.</a> Methods Cell Biol. 97, 133-146 (2010).</li><li>Azioune, A., 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=Robust+method+for+high-throughput+surface+patterning+of+deformable+substrates.">Robust method for high-throughput surface patterning of deformable substrates.</a> Langmuir. 27 (12), 7349-7352 (2011).</li><li>Carpi, N., Piel, M., Azioun, A., Cuvelier, D., Fink, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Micropatterning+on+silicon+elastomer+(PDMS)+with+deep+UVs.">Micropatterning on silicon elastomer (PDMS) with deep UVs.</a> Protoc. Exch. , (2011).</li><li>Sinha, B., 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=Cells+respond+to+mechanical+stress+by+rapid+disassembly+of+caveolae.">Cells respond to mechanical stress by rapid disassembly of caveolae.</a> Cell. 144 (3), 402-413 (2011).</li></ol>

The authors declare no competing financial interests.

Although this technique has been used numerous times and is thoroughly tested, there are several critical steps that can lead to a failed experiment.
About the PDMS:
For this work, GelPak, a commercially available thin PDMS sheet, was used. Alternatively PDMS sheets can be cast directly from PDMS mix. We recommend using GelPak because it is more reproducible, and is less likely to break compared to custom made PDMS.
About the device:
<p cla...

The cells composing a tissue in higher organisms are subject to mechanical tensions and stretching forces coming either from the external environment or from surrounding cells1,2. Cells must adapt to and resist these forces in order to maintain tissue integrity. Such forces are also important for tissues morphogenesis during development3,4. Applying mechanical forces on cultured cells is a way to mimic what might happen in a tissue, but with a quantitative and independent control of cell shape and cell deformation5,6. For this, several techniques might be used. One can press on the cells (the whole cell or part of it), for example using AFM or derivatives7,8&#160;or stretch the substrate the cells are growing on.
The method described in this paper demonstrates how to stretch a plane substrate plated with cells. This technique was originally developed to assess the role of forces exerted on mitotic mammalian cells9. Mitotic cells stay connected to the substrate through retraction fibers and stretching the membrane exerted a force on those fibers, which in turn provoked the rotation of the mitotic spindle. The interest of combining adhesive micropatterns and stretching is to achieve independent control of forces and shape of individual cells. It is for example possible to stretch an ovoid cell into a perfectly isotropic round shape, while uniaxial stretch is applied. If the cells are not platted on micropatterns, uniaxial stretching results in cell elongation, with most cells having a long axis aligned with the stretch axis. It is then difficult to separate the effect of the long axis alignment and the effect of the stretch applied to the cells.
The device is suitable for any live cell imaging, including long time lapse fluorescent microscopy, and drugs can be added during the experiment. The deep UVs&#160;micropatterning method10&#160;was described in details in Azioune et al.11&#160;Patterning on PDMS was described in Azioune et al.12&#160;The present stretching protocol is a video version of Carpi et al.13

<table border="0" cellpadding="0" cellspacing="0" width="573">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">GelPak</td>
			<td style="width:71px;">GelPak</td>
			<td style="width:119px;">PF-60-X4</td>
			<td style="width:167px;">Different thickness/stickiness are available. One alternative could be to cast your PDMS yourself.</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Silicon grease</td>
			<td style="width:71px;">GE Bayer Silicones</td>
			<td style="width:119px;">Baysilone-Paste</td>
			<td>This one is biocompatible</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Stretching device</td>
			<td style="width:71px;">GREM m&#233;canique</td>
			<td style="width:119px;">Stretcher 2011</td>
			<td></td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:216px;">EDC (N-(3-Dimethylaminopropyl)-N&#8242;-ethylcarbodiimide hydrochloride)</td>
			<td style="width:71px;">Sigma</td>
			<td align="right" style="width:119px;">3450</td>
			<td>Stable 6 months at -20 &#176;C</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">NHS (N-Hydroxysulfosuccinimide sodium salt)</td>
			<td style="width:71px;">Sigma</td>
			<td align="right" style="width:119px;">56485</td>
			<td>Protect from humidity</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Pll-g-peg (PLL(20)-g[3.5]-PEG(2) 20 mg)</td>
			<td style="width:71px;">SurfaceSolutions (Zurich)</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Synthetic Quartz photomask</td>
			<td style="width:71px;">Toppan</td>
			<td style="width:119px;"></td>
			<td>Take standard binary photomask in Quartz</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Fibronectin from bovine plasma</td>
			<td style="width:71px;">Sigma</td>
			<td style="width:119px;">F1141</td>
			<td></td>
		</tr>
	</tbody>
</table>

stretching micropatterned cells on a pdms membrane

Mechanical forces exerted on cells and/or tissues play a major role in numerous processes. We have developed a device to stretch cells plated on a PolyDiMethylSiloxane (PDMS) membrane, compatible with imaging. This technique is reproducible and versatile. The PDMS membrane can be micropatterned in order to confine cells or tissues to a specific geometry. The first step is to print micropatterns onto the PDMS membrane with a deep UV technique. The PDMS membrane is then mounted on a mechanical stretcher. A chamber is bound on top of the membrane with biocompatible grease to allow gliding during the stretch. The cells are seeded and allowed to spread for several hours on the micropatterns. The sample can be stretched and unstretched multiple times with the use of a micrometric screw. It takes less than a minute to apply the stretch to its full extent (around 30%). The technique presented here does not include a motorized device, which is necessary for applying repeated stretch cycles quickly and/or computer controlled stretching, but this can be implemented. Stretching of cells or tissue can be of interest for questions related to cell forces, cell response to mechanical stress or tissue morphogenesis. This video presentation will show how to avoid typical problems that might arise when doing this type of seemingly simple experiment.

The technique presented in this video protocol allowed the application of forces on the retraction fibers of mitotic mammalian cells. Indeed, during cell division, at the mitotic stage, mammalian cells retract to take the shape of a sphere and leave behind thin actin cables surrounded by membrane which are attached to the substrate. These cables (retraction fibers), are the memory of the cell&#160;geometry before going into division. Making micropatterns with deep UV through a photomask on PDMS thin film (Figure ...

Watch this Scientific Journal Video about Stretching Micropatterned Cells on a PDMS Membrane at JoVE.com

Stretching Micropatterned Cells on a PDMS Membrane

This manuscript presents a technique to apply or release forces on adherent cells or tissues using unidirectional stretching.

Mechanical forces exerted on cells and/or tissues  play a major role in numerous processes. We have developed a device to stretch  cells plated on a ...

stretching-micropatterned-cells-on-a-pdms-membrane

Research

JoVE Journal

Bioengineering

15.2K Views.  Institut Curie.  Эта рукопись представляет технику применять или освободить силы на прикрепленных клеток или тканей с использованием однонаправленной растяжения. 

Video: Stretching Micropatterned Cells on a PDMS Membrane

Micropatterned Surfaces to Study Hyaluronic Acid Interactions with Cancer Cells

Cancer invasion and progression involves a motile cell phenotype, which is under complex regulation by growth factors/cytokines and extracellular matrix (ECM) components within the tumor microenvironment. Hyaluronic acid (HA) is one stromal ECM component that is known to facilitate tumor progression by enhancing invasion, growth, and angiogenesis1. Interaction of HA with its cell surface receptor CD44 induces signaling events that promote tumor cell growth, survival, and migration, thereby increasing metastatic spread2-3. HA is an anionic, nonsulfated glycosaminoglycan composed of repeating units of D-glucuronic acid and D-N-acetylglucosamine. Due to the presence of carboxyl and hydroxyl groups on repeating disaccharide units, native HA is largely hydrophilic and amenable to chemical modifications that introduce sulfate groups for photoreative immobilization 4-5. Previous studies involving the immobilizations of HA onto surfaces utilize the bioresistant behavior of HA and its sulfated derivative to control cell adhesion onto surfaces6-7. In these studies cell adhesion preferentially occurs on non-HA patterned regions.
To analyze cellular interactions with exogenous HA, we have developed patterned functionalized surfaces that enable a controllable study and high-resolution visualization of cancer cell interactions with HA. We utilized microcontact printing (uCP) to define discrete patterned regions of HA on glass surfaces. A "tethering" approach that applies carbodiimide linking chemistry to immobilize HA was used 8. Glass surfaces were microcontact printed with an aminosilane and reacted with a HA solution of optimized ratios of EDC and NHS to enable HA immobilization in patterned arrays. Incorporating carbodiimide chemistry with mCP enabled the immobilization of HA to defined regions, creating surfaces suitable for in vitro applications. Both colon cancer cells and breast cancer cells implicitly interacted with the HA micropatterned surfaces. Cancer cell adhesion occurred within 24 hours with proliferation by 48 hours. Using HA micropatterned surfaces, we demonstrated that cancer cell adhesion occurs through the HA receptor CD44. Furthermore, HA patterned surfaces were compatible with scanning electron microscopy (SEM) and allowed high resolution imaging of cancer cell adhesive protrusions and spreading on HA patterns to analyze cancer cell motility on exogenous HA.

A novel approach that allows the high-resolution analysis of cancer cell interactions with exogenous hyaluronic acid (HA) is described. Patterned surfaces are fabricated by combining carbodiimide chemistry and microcontact printing.

Cancer invasion and progression involves a motile cell phenotype, which is under complex regulation by growth factors/cytokines and extracellular matrix ...

Improved Visualization and Quantitative Analysis of Drug Effects Using Micropatterned Cells

To date, most HCA (High Content Analysis) studies are carried out with adherent cell lines grown on a homogenous substrate in tissue-culture treated micro-plates. Under these conditions, cells spread and divide in all directions resulting in an inherent variability in cell shape, morphology and behavior. The high cell-to-cell variance of the overall population impedes the success of HCA, especially for drug development. The ability of micropatterns to normalize the shape and internal polarity of every individual cell provides a tremendous opportunity for solving this critical bottleneck 1-2.
To facilitate access and use of the micropatterning technology, CYTOO has developed a range of ready to use micropatterns, available in coverslip and microwell formats. In this video article, we provide detailed protocols of all the procedures from cell seeding on CYTOOchip micropatterns, drug treatment, fixation and staining to automated acquisition, automated image processing and final data analysis. With this example, we illustrate how micropatterns can facilitate cell-based assays. Alterations of the cell cytoskeleton are difficult to quantify in cells cultured on homogenous substrates, but culturing cells on micropatterns results in a reproducible organization of the actin meshwork due to systematic positioning of the cell adhesion contacts in every cell. Such normalization of the intracellular architecture allows quantification of even small effects on the actin cytoskeleton as demonstrated in these set of protocols using blebbistatin, an inhibitor of the actin-myosin interaction.

Adhesive micropatterns that normalize cellular architecture can be used to increase sensitivity in the detection of drug effects, improve reproducibility and simplify automated image acquisition and analysis. Such technology will benefit drug/siRNA screening assays, performed on conventional cell culture supports and consequently suffering from excessive cell-to-cell variability.

To date, most HCA (High Content Analysis) studies are carried out with adherent cell lines grown on a homogenous substrate in tissue-culture treated ...

Stretching Short Sequences of DNA with Constant Force Axial Optical Tweezers

Single-molecule techniques for stretching DNA of contour lengths less than a kilobase are fraught with experimental difficulties. However, many interesting biological events such as histone binding and protein-mediated looping of DNA1,2, occur on this length scale. In recent years, the mechanical properties of DNA have been shown to play a significant role in fundamental cellular processes like the packaging of DNA into compact nucleosomes and chromatin fibers3,4. Clearly, it is then important to understand the mechanical properties of short stretches of DNA. In this paper, we provide a practical guide to a single-molecule optical tweezing technique that we have developed to study the mechanical behavior of DNA with contour lengths as short as a few hundred basepairs.
The major hurdle in stretching short segments of DNA is that conventional optical tweezers are generally designed to apply force in a direction lateral to the stage5,6, (see Fig. 1). In this geometry, the angle between the bead and the coverslip, to which the DNA is tethered, becomes very steep for submicron length DNA. The axial position must now be accounted for, which can be a challenge, and, since the extension drags the microsphere closer to the coverslip, steric effects are enhanced. Furthermore, as a result of the asymmetry of the microspheres, lateral extensions will generate varying levels of torque due to rotation of the microsphere within the optical trap since the direction of the reactive force changes during the extension.
Alternate methods for stretching submicron DNA run up against their own unique hurdles. For instance, a dual-beam optical trap is limited to stretching DNA of around a wavelength, at which point interference effects between the two traps and from light scattering between the microspheres begin to pose a significant problem. Replacing one of the traps with a micropipette would most likely suffer from similar challenges. While one could directly use the axial potential to stretch the DNA, an active feedback scheme would be needed to apply a constant force and the bandwidth of this will be quite limited, especially at low forces.
We circumvent these fundamental problems by directly pulling the DNA away from the coverslip by using a constant force axial optical tweezers7,8. This is achieved by trapping the bead in a linear region of the optical potential, where the optical force is constant-the strength of which can be tuned by adjusting the laser power. Trapping within the linear region also serves as an all optical force-clamp on the DNA that extends for nearly 350 nm in the axial direction. We simultaneously compensate for thermal and mechanical drift by finely adjusting the position of the stage so that a reference microsphere stuck to the coverslip remains at the same position and focus, allowing for a virtually limitless observation period.

We illustrate the use of a constant force axial optical tweezers to explore the mechanical properties of short DNA molecules. By stretching DNA axially, we minimize steric hindrances and artifacts arising in conventional lateral manipulation, allowing us to study DNA molecules as short as ~100 nm.

Single-molecule techniques for stretching DNA of contour lengths  less than a kilobase are fraught with experimental difficulties. However, many ...

A Novel Stretching Platform for Applications in Cell and Tissue Mechanobiology

Tools that allow the application of mechanical forces to cells and tissues or that can quantify the mechanical properties of biological tissues have contributed dramatically to the understanding of basic mechanobiology. These techniques have been extensively used to demonstrate how the onset and progression of various diseases are heavily influenced by mechanical cues. This article presents a multi-functional biaxial stretching (BAXS) platform that can either mechanically stimulate single cells or quantify the mechanical stiffness of tissues. The BAXS platform consists of four voice coil motors that can be controlled independently. Single cells can be cultured on a flexible substrate that can be attached to the motors allowing one to expose the cells to complex, dynamic, and spatially varying strain fields. Conversely, by incorporating a force load cell, one can also quantify the mechanical properties of primary tissues as they are exposed to deformation cycles. In both cases, a proper set of clamps must be designed and mounted to the BAXS platform motors in order to firmly hold the flexible substrate or the tissue of interest. The BAXS platform can be mounted on an inverted microscope to perform simultaneous transmitted light and/or fluorescence imaging to examine the structural or biochemical response of the sample during stretching experiments. This article provides experimental details of the design and usage of the BAXS platform and presents results for single cell and whole tissue studies. The BAXS platform was used to measure the deformation of nuclei in single mouse myoblast cells in response to substrate strain and to measure the stiffness of isolated mouse aortas. The BAXS platform is a versatile tool that can be combined with various optical microscopies in order to provide novel mechanobiological insights at the sub-cellular, cellular and whole tissue levels.

We present in this article a novel stretching platform that can be used to investigate single cell responses to complex anisotropic biaxial mechanical deformation and quantify the mechanical properties of biological tissues.

Tools that allow the application of mechanical forces to cells and tissues or that can quantify the mechanical properties of biological tissues have ...

Luminescence Resonance Energy Transfer to Study Conformational Changes in Membrane Proteins Expressed in Mammalian Cells

Luminescence Resonance Energy Transfer, or LRET, is a powerful technique used to measure distances between two sites in proteins within the distance range of 10-100 &#197;. By measuring the distances under various ligated conditions, conformational changes of the protein can be easily assessed. With LRET, a lanthanide, most often chelated terbium, is used as the donor fluorophore, affording advantages such as a longer donor-only emission lifetime, the flexibility to use multiple acceptor fluorophores, and the opportunity to detect sensitized acceptor emission as an easy way to measure energy transfer without the risk of also detecting donor-only signal. Here, we describe a method to use LRET on membrane proteins expressed and assayed on the surface of intact mammalian cells. We introduce a protease cleavage site between the LRET fluorophore pair. After obtaining the original LRET signal, cleavage at that site removes the specific LRET signal from the protein of interest allowing us to quantitatively subtract the background signal that remains after cleavage. This method allows for more physiologically relevant measurements to be made without the need for purification of protein.

We describe here an improved Luminescence Resonance Energy Transfer (LRET) method where we introduce a protease cleavage site between the donor and acceptor fluorophore sites. This modification allows us to obtain specific LRET signals arising from membrane proteins of interest, allowing for the study of membrane proteins without protein purification.

Luminescence Resonance Energy Transfer, or LRET, is a powerful technique used to measure distances between two sites in proteins within the distance range ...

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

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

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

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

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

Gene Transfection toward Spheroid Cells on Micropatterned Culture Plates for Genetically-modified Cell Transplantation

To improve the therapeutic effectiveness of cell transplantation, a transplantation system of genetically modified, injectable spheroids was developed. The cell spheroids are prepared in a culture system on micropatterned plates coated with a thermosensitive polymer. A number of spheroids are formed on the plates, corresponding to the cell adhesion areas of 100 &#181;m diameter that are regularly arrayed in a two-dimensional manner, surrounded by non-adhesive areas that are coated by a polyethylene glycol (PEG) matrix. The spheroids can be easily recovered as a liquid suspension by lowering the temperature of the plates, and their structure is well maintained by passing them through injection needles with a sufficiently large caliber (over 27 G). Genetic modification is achieved by gene transfection using the original non-viral gene carrier, polyplex nanomicelle, which is capable of introducing genes into cells without disrupting the spheroid structure. For primary hepatocyte spheroids transfected with a luciferase-expressing gene, the luciferase is sustainably obtained in transplanted animals, along with preserved hepatocyte function, as indicated by albumin expression. This system can be applied to a variety of cell types including mesenchymal stem cells.

This protocol describes a cell transplantation system using genetically modified, injectable spheroids. Cell spheroids are cultured on micropatterned culture plates and recovered after gene introduction using polyplex nanomicelles. This system facilitates prolonged transgene expression from the transplanted cells in host animals while maintaining the innate function of the cells.

To improve the therapeutic effectiveness of cell transplantation, a transplantation system of genetically modified, injectable spheroids was developed. ...

Microfluidic Genipin Deposition Technique for Extended Culture of Micropatterned Vascular Muscular Thin Films

The chronic nature of vascular disease progression requires the development of experimental techniques that simulate physiologic and pathologic vascular behaviors on disease-relevant time scales. Previously, microcontact printing has been used to fabricate two-dimensional functional arterial mimics through patterning of extracellular matrix protein as guidance cues for tissue organization. Vascular muscular thin films utilized these mimics to assess functional contractility. However, the microcontact printing fabrication technique used typically incorporates hydrophobic PDMS substrates. As the tissue turns over the underlying extracellular matrix, new proteins must undergo a conformational change or denaturing in order to expose hydrophobic amino acid residues to the hydrophobic PDMS surfaces for attachment, resulting in altered matrix protein bioactivity, delamination, and death of the tissues.
Here, we present a microfluidic deposition technique for patterning of the crosslinker compound genipin. Genipin serves as an intermediary between patterned tissues and PDMS substrates, allowing cells to deposit newly-synthesized extracellular matrix protein onto a more hydrophilic surface and remain attached to the PDMS substrates. We also show that extracellular matrix proteins can be patterned directly onto deposited genipin, allowing dictation of engineered tissue structure. Tissues fabricated with this technique show high fidelity in both structural alignment and contractile function of vascular smooth muscle tissue in a vascular muscular thin film model. This technique can be extended using other cell types and provides the framework for future study of chronic tissue- and organ-level functionality.

We present a method for microfluidic deposition of patterned genipin and fibronectin on PDMS substrates, allowing extended viability of vascular smooth muscle cell-dense tissues. This tissue fabrication method is combined with previous vascular muscular thin film technology to measure vascular contractility over disease-relevant time courses.

The chronic nature of vascular disease progression requires the development of experimental techniques that simulate physiologic and pathologic vascular ...

Double Emulsion Generation Using a Polydimethylsiloxane (PDMS) Co-axial Flow Focus Device

Double emulsions are useful in a number of biological and industrial applications in which it is important to have an aqueous carrier fluid. This paper presents a polydimethylsiloxane (PDMS) microfluidic device capable of generating water/oil/water double emulsions using a coaxial flow focusing geometry that can be fabricated entirely using soft lithography. Similar to emulsion devices using glass capillaries, double emulsions can be formed in channels with uniform wettability and with dimensions much smaller than the channel sizes. Three dimensional flow focusing geometry is achieved by casting a pair of PDMS slabs using two layer soft lithography, then mating the slabs together in a clamshell configuration. Complementary locking features molded into the PDMS slabs enable the accurate registration of features on each of the slab surfaces. Device testing demonstrates formation of double emulsions from 14 &#181;m to 50 &#181;m in diameter while using large channels that are robust against fouling and clogging.

Double Emulsion Generation Using a Polydimethylsiloxane PDMS Co-axial Flow Focus Device

Microfluidic double emulsions generation typically involves devices with patterned wettability or custom-fabricated glass components. Here we describe the fabrication and testing of an all polydimethylsiloxane (PDMS) double emulsion generator that does not require surface treatment or complicated fabrication processes, and is capable of producing double emulsions down to 14 &#181;m.

Double emulsions are useful in a number of biological and industrial applications in which it is important to have an aqueous carrier fluid. This paper ...

Treatment of Ligament Constructs with Exercise-conditioned Serum: A Translational Tissue Engineering Model

In vitro experiments are essential to understand biological mechanisms; however, the gap between monolayer tissue culture and human physiology is large, and translation of findings is often poor. Thus, there is ample opportunity for alternative experimental approaches. Here we present an approach in which human cells are isolated from human anterior cruciate ligament tissue remnants, expanded in culture, and used to form engineered ligaments. Exercise alters the biochemical milieu in the blood such that the function of many tissues, organs and bodily processes are improved. In this experiment, ligament construct culture media was supplemented with experimental human serum that has been &#39;conditioned&#39; by exercise. Thus the intervention is more biologically relevant since an experimental tissue is exposed to the full endogenous biochemical milieu, including binding proteins and adjunct compounds that may be altered in tandem with the activity of an unknown agent of interest. After treatment, engineered ligaments can be analyzed for mechanical function, collagen content, morphology, and cellular biochemistry. Overall, there are four major advantages versus traditional monolayer culture and animal models, of the physiological model of ligament tissue that is presented here. First, ligament constructs are three-dimensional, allowing for mechanical properties (i.e., function) such as ultimate tensile stress, maximal tensile load, and modulus, to be quantified. Second, the enthesis, the interface between boney and sinew elements, can be examined in detail and within functional context. Third, preparing media with post-exercise serum allows for the effects of the exercise-induced biochemical milieu, which is responsible for the wide range of health benefits of exercise, to be investigated in an unbiased manner. Finally, this experimental model advances scientific research in a humane and ethical manner by replacing the use of animals, a core mandate of the National Institutes of Health, the Center for Disease Control, and the Food and Drug Administration.

We present a model of ligament tissue in which three-dimensional constructs are treated with the human exercise-conditioned serum and analyzed for collagen content, function, and cellular biochemistry.

In vitro experiments are essential to understand biological mechanisms; however, the gap between monolayer tissue culture and human physiology is large, ...