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><tbody><tr><td>GelPak</td><td>GelPak</td><td>PF-60-X4</td><td>Different thickness/stickiness are available. One alternative could be to cast your PDMS&amp;nbsp;yourself.</td></tr><tr><td>Silicon grease</td><td>GE Bayer Silicones</td><td>Baysilone-Paste</td><td>This one is biocompatible</td></tr><tr><td>Stretching device</td><td>GREM m&amp;eacute;canique</td><td>Stretcher 2011</td><td>&amp;nbsp;</td></tr><tr><td>EDC (N-(3-Dimethylaminopropyl)-N&amp;prime;-ethylcarbodiimide hydrochloride)</td><td>Sigma</td><td>3450</td><td>Stable 6 months at -20 &amp;deg;C</td></tr><tr><td>NHS (N-Hydroxysulfosuccinimide sodium salt)</td><td>Sigma</td><td>56485</td><td>Protect from humidity</td></tr><tr><td>Pll-g-peg (PLL(20)-g[3.5]-PEG(2) 20 mg)</td><td>SurfaceSolutions (Zurich)</td><td></td><td>&amp;nbsp;</td></tr><tr><td>Synthetic Quartz photomask</td><td>Toppan</td><td></td><td>Take standard binary photomask in Quartz</td></tr><tr><td>Fibronectin from bovine plasma</td><td>Sigma</td><td>F1141</td><td>&amp;nbsp;</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. This manuscript presents a technique to apply or release forces on adherent cells or tissues using unidirectional stretching.

Video: Stretching Micropatterned Cells on a PDMS Membrane

Creating Two-Dimensional Patterned Substrates for Protein and Cell Confinement

Microcontact printing provides a rapid, highly reproducible method for the creation of well-defined patterned substrates.1 While microcontact printing can be employed to directly print a large number of molecules, including proteins,2 DNA,3 and silanes,4 the formation of self-assembled monolayers (SAMs) from long chain alkane thiols on gold provides a simple way to confine proteins and cells to specific patterns containing adhesive and resistant regions. This confinement can be used to control cell morphology and is useful for examining a variety of questions in protein and cell biology. Here, we describe a general method for the creation of well-defined protein patterns for cellular studies.5 This process involves three steps: the production of a patterned master using photolithography, the creation of a PDMS stamp, and microcontact printing of a gold-coated substrate. Once patterned, these cell culture substrates are capable of confining proteins and/or cells (primary cells or cell lines) to the pattern.
The use of self-assembled monolayer chemistry allows for precise control over the patterned protein/cell adhesive regions and non-adhesive regions; this cannot be achieved using direct protein stamping. Hexadecanethiol, the long chain alkane thiol used in the microcontact printing step, produces a hydrophobic surface that readily adsorbs protein from solution. The glycol-terminated thiol, used for backfilling the non-printed regions of the substrate, creates a monolayer that is resistant to protein adsorption and therefore cell growth.6 These thiol monomers produce highly structured monolayers that precisely define regions of the substrate that can support protein adsorption and cell growth. As a result, these substrates are useful for a wide variety of applications from the study of intercellular behavior7 to the creation of microelectronics.8
While other types of monolayer chemistry have been used for cell culture studies, including work from our group using trichlorosilanes to create patterns directly on glass substrates,9 patterned monolayers formed from alkane thiols on gold are straight-forward to prepare. Moreover, the monomers used for monolayer preparation are commercially available, stable, and do not require storage or handling under inert atmosphere. Patterned substrates prepared from alkane thiols can also be recycled and reused several times, maintaining cell confinement.10

Self-assembled monolayers (SAMs) formed from long chain alkane thiols on gold provide well-defined substrates for the formation of protein patterns and cell confinement. Microcontact printing of hexadecanethiol using a polydimethylsiloxane (PDMS) stamp followed by backfilling with a glycol-terminated alkane thiol monomer produces a pattern where protein and cells adsorb only to the stamped hexadecanethiol region.

Microcontact printing provides a rapid, highly reproducible method for the creation of well-defined patterned substrates.1  While microcontact printing ...

Stencil Micropatterning of Human Pluripotent Stem Cells for Probing Spatial Organization of Differentiation Fates

Human pluripotent stem cells (hPSCs), including embryonic stem cells and induced pluripotent stem cells, have the intrinsic ability to differentiate into all three germ layers. This makes them an attractive cell source for regenerative medicine and experimental modeling of normal and diseased organogenesis. However, the differentiation of hPSCs in vitro is heterogeneous and spatially disordered. Cell micropatterning technologies potentially offer the means to spatially control stem cell microenvironments and organize the resultant differentiation fates. Micropatterning hPSCs needs to take into account the stringent requirements for hPSC survival and maintenance. Here, we describe stencil micropatterning as a method that is highly compatible with hPSCs. hPSC micropatterns are specified by the geometries of the cell stencil through-holes, which physically confine the locations where hPSCs can access and attach to the underlying extracellular matrix-coated substrate. Due to this mode of operation, there is greater flexibility to use substrates that can adequately support hPSCs as compared to other cell micropatterning methods. We also highlight critical steps for the successful generation of hPSC micropatterns. As an example, we demonstrate that stencil micropatterning of hPSCs can be used to modulate spatial polarization of cell-cell and cell-matrix adhesions, which in turn determines mesoendoderm differentiation patterns. This simple and robust method to micropattern hPSCs widens the prospects of establishing experimental models to investigate tissue organization and patterning during early embryonic development.

Human pluripotent stem cells (hPSCs) have the intrinsic ability to differentiate and self-organize into distinct tissue patterns; although this requires the presentation of spatial environmental gradients. We present stencil micropatterning as a simple and robust method to generate biochemical and mechanical gradients for controlling hPSC differentiation patterns.

Human pluripotent stem cells (hPSCs), including embryonic stem cells and induced pluripotent stem cells, have the intrinsic ability to differentiate into ...

Developmental Biology

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 ...

Patterning of Microorganisms and Microparticles through Sequential Capillarity-assisted Assembly

Controlled patterning of microorganisms into defined spatial arrangements offers unique possibilities for a broad range of biological applications, including studies of microbial physiology and interactions. At the simplest level, accurate spatial patterning of microorganisms would enable reliable, long-term imaging of large numbers of individual cells and transform the ability to quantitatively study distance-dependent microbe-microbe interactions. More uniquely, coupling accurate spatial patterning and full control over environmental conditions, as offered by microfluidic technology, would provide a powerful and versatile platform for single-cell studies in microbial ecology. 
This paper presents a microfluidic platform to produce versatile and user-defined patterns of microorganisms within a microfluidic channel, allowing complete optical access for long-term, high-throughput monitoring. This new microfluidic technology is based on capillarity-assisted particle assembly and exploits the capillary forces arising from the controlled motion of an evaporating suspension inside a microfluidic channel to deposit individual microsized objects in an array of traps microfabricated onto a polydimethylsiloxane (PDMS) substrate. Sequential depositions generate the desired spatial layout of single or multiple types of micro-sized objects, dictated solely by the geometry of the traps and the filling sequence. 
The platform has been calibrated using colloidal particles of different dimensions and materials: it has proven to be a powerful tool to generate diverse colloidal patterns and perform surface functionalization of trapped particles. Furthermore, the platform was tested on microbial cells, using Escherichia coli cells as a model bacterium. Thousands of individual cells were patterned on the surface, and their growth was monitored over time. In this platform, the coupling of single-cell deposition and microfluidic technology allows both geometric patterning of microorganisms and precise control of environmental conditions. It thus opens a window into the physiology of single microbes and the ecology of microbe-microbe interactions, as shown by preliminary experiments.

We present a technology that uses capillarity-assisted assembly in a microfluidic platform to pattern micro-sized objects suspended in a liquid, such as bacteria and colloids, into prescribed arrays on a polydimethylsiloxane substrate.

Controlled patterning of microorganisms into defined spatial arrangements offers unique possibilities for a broad range of biological applications, ...

Engineering

A Versatile Method of Patterning Proteins and Cells

Substrate and cell patterning techniques are widely used in cell biology to study cell-to-cell and cell-to-substrate interactions. Conventional patterning techniques work well only with simple shapes, small areas and selected bio-materials. This article describes a method to distribute cell suspensions as well as substrate solutions into complex, long, closed (dead-end) polydimethylsiloxane (PDMS) microchannels using negative pressure. This method enables researchers to pattern multiple substrates including fibronectin, collagen, antibodies (Sal-1), poly-D-lysine (PDL), and laminin. Patterning of substrates allows one to indirectly pattern a variety of cells. We have tested C2C12 myoblasts, the PC12 neuronal cell line, embryonic rat cortical neurons, and amphibian retinal neurons. In addition, we demonstrate that this technique can directly pattern fibroblasts in microfluidic channels via brief application of a low vacuum on cell suspensions. The low vacuum does not significantly decrease cell viability as shown by cell viability assays. Modifications are discussed for application of the method to different cell and substrate types. This technique allows researchers to pattern cells and proteins in specific patterns without the need for exotic materials or equipment and can be done in any laboratory with a vacuum.

This report describes a simple, easy to perform technique, using low pressure vacuum, to fill microfluidic channels with cells and substrates for biological research.

Substrate and cell patterning techniques are widely used in cell biology to study cell-to-cell and cell-to-substrate interactions. Conventional patterning ...

Simple, Affordable, and Modular Patterning of Cells using DNA

The relative positioning of cells is a key feature of the microenvironment that organizes cell-cell interactions. To study the interactions between cells of the same or different type, micropatterning techniques have proved useful. DNA Programmed Assembly of Cells (DPAC) is a micropatterning technique that targets the adhesion of cells to a substrate or other cells using DNA hybridization. The most basic operations in DPAC begin with decorating cell membranes with lipid-modified oligonucleotides, then flowing them over a substrate that has been patterned with complementary DNA sequences. Cells adhere selectively to the substrate only where they find a complementary DNA sequence. Non-adherent cells are washed away, revealing a pattern of adherent cells. Additional operations include further rounds of cell-substrate or cell-cell adhesion, as well as transferring the patterns formed by DPAC to an embedding hydrogel for long-term culture. Previously, methods for patterning oligonucleotides on surfaces and decorating cells with DNA sequences required specialized equipment and custom DNA synthesis, respectively. We report an updated version of the protocol, utilizing an inexpensive benchtop photolithography setup and commercially available cholesterol modified oligonucleotides (CMOs) deployed using a modular format. CMO-labeled cells adhere with high efficiency to DNA-patterned substrates. This approach can be used to pattern multiple cell types at once with high precision and to create arrays of microtissues embedded within an extracellular matrix. Advantages of this method include its high resolution, ability to embed cells into a three-dimensional microenvironment without disrupting the micropattern, and flexibility in patterning any cell type.

Here we present a protocol to micropattern cells at single-cell resolution using DNA-programmed adhesion. This protocol uses a benchtop photolithography platform to create patterns of DNA oligonucleotides on a glass slide and then labels cell membranes with commercially available complementary oligonucleotides. Hybridization of the oligos results in programmed cell adhesion.

The relative positioning of cells is a key feature of the microenvironment that organizes cell-cell interactions. To study the interactions between cells ...

Pattern Generation for Micropattern Traction Microscopy

Micropattern traction microscopy allows control of the shape of single cells and cell clusters. Furthermore, the ability to pattern at the micrometer length scale allows the use of these patterned contact zones for the measurement of traction forces, as each micropatterned dot allows for the formation of a single focal adhesion that then deforms the soft, underlying hydrogel. This approach has been used for a wide range of cell types, including endothelial cells, smooth muscle cells, fibroblasts, platelets, and epithelial cells. 
This review describes the evolution of techniques that allow the printing of extracellular matrix proteins onto polyacrylamide hydrogels in a regular array of dots of prespecified size and spacing. As micrometer-scale patterns are difficult to directly print onto soft substrates, patterns are first generated on rigid glass coverslips that are then used to transfer the pattern to the hydrogel during gelation. First, the original microcontact printing approach to generate arrays of small dots on the coverslip is described. A second step that removes most of the pattern to leave islands of small dots is required to control the shapes of cells and cell clusters on such arrays of patterned dots. 
Next, an evolution of this approach that allows for the generation of islands of dots using a single subtractive patterning step is described. This approach is greatly simplified for the user but has the disadvantage of a decreased lifetime for the master mold needed to make the patterns. Finally, the computational approaches that have been developed for the analysis of images of displaced dots and subsequent cell-generated traction fields are described, and updated versions of these analysis packages are provided.

We describe improvements to a standard method for measuring cellular traction forces, based on microcontact printing with a single subtractive patterning step of dot arrays of extracellular matrix proteins on soft hydrogels. This method allows for simpler and more consistent fabrication of island patterns, essential for controlling cell cluster shape.

Micropattern traction microscopy allows control of the shape of single cells and cell clusters. Furthermore, the ability to pattern at the micrometer ...

Generation of Multicue Cellular Microenvironments by UV-Photopatterning of Three-Dimensional Cell Culture Substrates

The extracellular matrix is an important regulator of cell function. Environmental cues existing in the cellular microenvironment, such as ligand distribution and tissue geometry, have been increasingly shown to play critical roles in governing cell phenotype and behavior. However, these environmental cues and their effects on cells are often studied separately using in vitro platforms that isolate individual cues, a strategy that heavily oversimplifies the complex in vivo situation of multiple cues. Engineering approaches can be particularly useful to bridge this gap, by developing experimental setups that capture the complexity of the in vivo microenvironment, yet retain the degree of precision and manipulability of in vitro systems.
This study highlights an approach combining ultraviolet (UV)-based protein patterning and lithography-based substrate microfabrication, which together enable high-throughput investigation into cell behaviors in multicue environments. By means of maskless UV-photopatterning, it is possible to create complex, adhesive protein distributions on three-dimensional (3D) cell culture substrates on chips that contain a variety of well-defined geometrical cues. The proposed technique can be employed for culture substrates made from different polymeric materials and combined with adhesive patterned areas of a broad range of proteins. With this approach, single cells, as well as monolayers, can be subjected to combinations of geometrical cues and contact guidance cues presented by the patterned substrates. Systematic research using combinations of chip materials, protein patterns, and cell types can thus provide fundamental insights into cellular responses to multicue environments.

Traditionally, cell culture is performed on planar substrates that poorly mimic the natural environment of cells in vivo. Here we describe a method to produce cell culture substrates with physiologically relevant curved geometries and micropatterned extracellular proteins, allowing systematic investigations into cellular sensing of these extracellular cues.

The extracellular matrix is an important regulator of cell function. Environmental cues existing in the cellular microenvironment, such as ligand ...

A Novel Ink-Free, Label-Free Magnetic-Archimedes Cell Patterning Method

Cell Patterning Using Magnetic-Archimedes Strategy

Cell patterning, allowing precise control of cell positioning, presents a unique advantage in the study of cell behavior. In this protocol, a cell patterning strategy based on the Magnetic-Archimedes (Mag-Arch) effect is introduced. This approach enables precise control of cell distribution without the use of ink materials or labeling particles. By introducing a paramagnetic reagent to enhance the magnetic susceptibility of the cell culture medium, cells are repelled by magnets and arrange themselves into a pattern complementary to the magnet sets positioned beneath the microfluidic substrate.
In this article, detailed procedures for cell patterning using the Mag-Arch-based strategy are provided. Methods for patterning single-cell types as well as multiple cell types for co-culture experiments are offered. Additionally, comprehensive instructions for fabricating microfluidic devices containing channels for cell patterning are provided. Achieving this feature using parallel methods is challenging but can be done in a simplified and cost-effective manner. Employing Mag-Arch-based cell patterning equips researchers with a powerful tool for in vitro research.

Author Spotlight: Magnetic-Based Cell Patterning Method for High-Throughput Biomedical Applications 

This protocol describes an ink-free, label-free, substrate-independent, high-throughput cell patterning method based on the Magnetic Archimedes effect.

Cell patterning, allowing precise control of cell positioning, presents a unique advantage in the study of cell behavior. In this protocol, a cell ...

A Reconfigurable Barrier Tissue Platform with Open-Well and Microfluidic Modes

Transforming Static Barrier Tissue Models into Dynamic Microphysiological Systems

Microphysiological systems are miniaturized cell culture platforms used to mimic the structure and function of human tissues in a laboratory setting. However, these platforms have not gained widespread adoption in bioscience laboratories where open-well, membrane-based approaches serve as the gold standard for mimicking tissue barriers, despite lacking fluid flow capabilities. This issue can be primarily attributed to the incompatibility of existing microphysiological systems with standard protocols and tools developed for open-well systems.
Here, we present a protocol for creating a reconfigurable membrane-based platform with an open-well structure, flow enhancement capability, and compatibility with conventional protocols. This system utilizes a magnetic assembly approach that enables reversible switching between open-well and microfluidic modes. With this approach, users have the flexibility to begin an experiment in the open-well format using standard protocols and add or remove flow capabilities as needed. To demonstrate the practical usage of this system and its compatibility with standard techniques, an endothelial cell monolayer was established in an open-well format. The system was reconfigured to introduce fluid flow and then switched to the open-well format to conduct immunostaining and RNA extraction. Due to its compatibility with conventional open-well protocols and flow enhancement capability, this reconfigurable design is expected to be adopted by both engineering and bioscience laboratories.

Author Spotlight: Developing a Unique Modular Microphysiological System to Mimic Human Barrier Tissue

This protocol describes a reconfigurable membrane-based cell culture platform that integrates the open-well format with fluid flow capabilities. This platform is compatible with standard protocols and allows for reversible transitions between open-well and microfluidic culture modes, accommodating the needs of both engineering and bioscience laboratories.

Microphysiological systems are miniaturized cell culture platforms used to mimic the structure and function of human tissues in a laboratory setting. ...