A. Microfabrication of the gradient-generating microfluidic device
<ol>
<li>The Si wafer is treated with reactive oxygen plasma (5 min at 30W, Harrick Scientific, NY).</li>
<li>Negative photoresist (SU-8 50, Microchem, MA) is spin-coated at 1000 rpm for 1 min on a Si wafer.</li>
<li>The wafer is soft baked at 65&deg;C for 10 min and subsequently at 95&deg;C for 30 min on a hotplate.</li>
<li>The wafer is exposed to UV light (200W) for 3 min through a transparency mask with a minimum feature size of 30 &micro;m.</li>
<li>The wafer is post baked at 65&deg;C for 1 min and at 95&deg;C for 10 min.</li>
<li>Si master mold with 100 &micro;m thick channels is developed using SU-8 photoresist developer.</li>
<li>The wafer containing microchannels is placed in a Petri-dish.</li>
<li>Poly(dimethylsiloxane) (PDMS) (Sylgard 184) molds are fabricated by mixing silicone elastomer and curing agent (10:1 ratio).</li>
<li>The PDMS mixture is poured onto the Si master mold.</li>
<li>The Si master mold is placed on a vacuum desiccator to remove bubbles for 10 min.</li>
<li>PDMS is cured at 70&deg;C for 1~2 hours.</li>
<li>PDMS molds are peeled off from the Si master mold.</li>
</ol>
B. Experimental setup
<ol>
<li>Cell inlet, outlet, and infusing inlets of the PDMS-based microfluidic device are punched by using sharp punchers.</li>
<li>A device and a glass slide (2&times;3 inch) are irreversibly bonded by the reactive oxygen plasma (5 min at 30W, Harrick Scientific, NY).</li>
<li>Polyethylene tubing (PE 20, Becton Dickinon, MD) is inserted into the infusing inlets of the microfluidic device and subsequently connected to a syringe pump.</li>
<li>Fluorescein isothiocyanate (FITC)-dextran (MW=10kD, 10 &micro;M, Sigma) and buffer (PBS, Invitrogen, CA) are infused into the microfluidic device to confirm stable gradients inside the fluidic device.</li>
<li>Extracellular matrix (ECM) (i.e., fibronectin) is coated inside the microfluidic device for 1 hour in incubator (37&deg;C).</li>
<li>NIH 3T3 fibroblast cells are trypsinized and dissociated.</li>
<li>Dissociated cells are loaded into the microfluidic device (800 &micro;m wide) at the cell density of 2&times;106 cells/ml.</li>
<li>2 ml media and 50 ng/ml epidermal growth factor (EGF) is infused into a microfluidic device for generating soluble gradients using a syringe pump (0.05 &micro;l/min).</li>
<li>Cells are real-time monitored every 5 min by using an inverted microscope (Nikon TE 2000).</li>
</ol>
&nbsp;

<ol>
	<li>Jeon, N. L., Baskaran, H., Dertinger, S. K. W., Whitesides, G. M., Van de Water, L., 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=Neutrophil+chemotaxis+in+linear+and+complex+gradients+of+interleukin-8+formed+in+a+microfabricated+device.">Neutrophil chemotaxis in linear and complex gradients of interleukin-8 formed in a microfabricated device.</a> Nat. Biotechnol. 20, 826-830 (2002).</li><li>Lin, F., Nguyen, C. M., Wang, S. J., Saadi, W., Gross, S. P., Jeon, N. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effective+neutrophil+chemotaxis+is+strongly+influenced+by+mean+IL-8+concentration.">Effective neutrophil chemotaxis is strongly influenced by mean IL-8 concentration.</a> Biochem. Biophys. Res. Commun. 319, 576-581 (2004).</li><li>Chung, B. G., Flanagan, L. A., Rhee, S. W., Schwartz, P. H., Lee, A. P., Monuki, E. S., Jeon, N. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+neural+stem+cell+growth+and+differentiation+in+a+gradient-generating+microfluidic+device.">Human neural stem cell growth and differentiation in a gradient-generating microfluidic device.</a> Lab Chip. 5, 401-406 (2005).</li><li>Saadi, W., Wang, S. J., Lin, F., Jeon, N. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+parallel-gradient+microfluidic+chamber+for+quantitative+analysis+of+breast+cancer+cell+chemotaxis.">A parallel-gradient microfluidic chamber for quantitative analysis of breast cancer cell chemotaxis.</a> Biomed. Microdevices. 8, 109-118 (2007).</li><li>Chung, B. G., Park, J. W., Hu, J. S., Huang, C., Monuki, E. S., Jeon, N. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+hybrid+microfluidic-vacuum+device+for+interfacing+with+conventional+cell+culture+platform.">A hybrid microfluidic-vacuum device for interfacing with conventional cell culture platform.</a> BMC Biotechnol. 7, (2007).</li></ol>

Cells exposed to stable concentration gradients of EGF in a microfluidic device migrated toward higher concentrations. The directional orientation of cell migration, chemotactic index, motility of migrating cells were investigated by cell tracking analysis. Therefore, this gradient-generating microfluidic platform could be useful for studying cancer metastasis, embryogenesis, and axon guidance.

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		<div>
		<table border="1">
		<thead>
		<tr>
		<th>Material Name</th>
		<th>Type</th>
		<th>Company</th>
		<th>Catalogue Number</th>
		<th>Comment</th>
		</tr>
		</thead>
		<tbody>
		
<tr>
<td>Dextran-FITC</td>
<td>Reagent</td>
<td>Sigma Aldrich</td>
<td>FD10S </td>
<td>Fluorescein isothiocyanate (FITC) conjugated-dextran (10kD)</td>
</tr>
<tr>
<td>hr-EGF</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>13247-051 </td>
<td>human recombinant Epidermal growth factor </td>
</tr>
<tr>
<td>PDMS</td>
<td>&nbsp;</td>
<td>K.R. Anderson Co. Inc.</td>
<td>2065622 </td>
<td>Poly(dimethylsiloxane) (PDMS), Dow Corning Sylgard 184 (8.6 lb)</td>
</tr>
<tr>
<td>Negative photoresist </td>
<td>&nbsp;</td>
<td>Microchem</td>
<td>SU-8 50</td>
<td>&nbsp;</td>
<tr>
<td>Si wafer</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>silicone wafer, 4 inch</td>
</tr>
<tr>
<td>Petri dishes</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Polyethylene tubing </td>
<td>&nbsp;</td>
<td>Becton Dickinon</td>
<td>PE 20</td>
<td>&nbsp;</td>
<tr>
<td>PBS</td>
<td>&nbsp;</td>
<td>Invitrogen</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Fibronectin</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>NIH 3T3 </td>
<td>cell-line</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>fibroblast cells</td>
</tr>
<tr>
<td>Inverted microscope</td>
<td>&nbsp;</td>
<td>Nikon </td>
<td>TE 2000</td>
<td>&nbsp;</td>		</tbody>
		</table>
		</div>
			<div>
					</div>

a gradient-generating microfluidic device for cell biology

 The fabrication and operation of a gradient-generating microfluidic device for studying cellular behavior is described.  A microfluidic platform is an enabling experimental tool, because it can precisely manipulate fluid flows, enable high-throughput experiments, and generate stable soluble concentration gradients.  Compared to conventional gradient generators, poly(dimethylsiloxane) (PDMS)-based  microfluidic devices can generate stable concentration gradients of growth factors with well-defined profiles.  Here, we developed simple gradient-generating microfluidic devices with three separate inlets.  Three microchannels combined into one microchannel to generate concentration gradients.  The stability and shape of growth factor gradients were confirmed by fluorescein isothyiocyanate (FITC)-dextran with a molecular weight similar to epidermal growth factor (EGF).  Using this microfluidic device, we demonstrated that fibroblasts exposed to concentration gradients of EGF migrated toward higher concentrations.  The directional orientation of cell migration and motility of migrating cells were quantitatively assessed by cell tracking analysis.  Thus, this gradient-generating microfluidic device might be useful for studying and analyzing the behavior of migrating cells.

Watch this Scientific Journal Video about A Gradient-generating Microfluidic Device for Cell Biology at JoVE.com

A Gradient-generating Microfluidic Device for Cell Biology

We describe a protocol for the microfabrication of the gradient-generating microfluidic device that can generate spatial and temporal gradients in well-defined microenvironment. In this approach, the gradient-generating microfluidic device can be used to study directed cell migration, embryogenesis, wound healing, and cancer metastasis.

 The fabrication and operation of a gradient-generating microfluidic device for studying cellular behavior is described.  A microfluidic platform is an ...

a-gradient-generating-microfluidic-device-for-cell-biology

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Biology

15.2K Views.  Brigham and Women's Hospital. We describe a protocol for the microfabrication of the gradient-generating microfluidic device that can generate spatial and temporal gradients in well-defined microenvironment. In this approach, the gradient-generating microfluidic device can be used to study directed cell migration, embryogenesis, wound healing, and cancer metastasis.

Video: A Gradient-generating Microfluidic Device for Cell Biology

Fabrication of a Microfluidic Device for the Compartmentalization of Neuron Soma and Axons

In this video, we demonstrate the technique of soft lithography with polydimethyl siloxane (PDMS) which we use to fabricate a microfluidic device for culturing neurons. Previously, a silicon wafer was patterned with the design for the neuron microfluidic device using SU-8 and photolithography to create a master mold, or what we simply refer to as a "master". Next, we pour the silicon polymer PDMS on top of the master which is then cured by heating the PDMS to 80&deg;C for 1 hour. The PDMS forms a negative mold of the device. The PDMS is then carefully cut and lifted away from the master. Holes are punched where the reservoirs will be and the excess PDMS trimmed away from the device. Nitrogen is used to blow away any excess debris from the device. At this point the devices are now ready for use and can either bonded to corning No. 1 cover glass with a plasma sterilizer/cleaner or can be reversibly bound to the cover glass by simply placing the device on top of the cover glass. The reversible bonding of the device to glass is covered in a separate video and requires first that the device be sterilized either with 70% ethanol or by autoclaving. Plasma treating sterilizes the devices so no further treatment is necessary. It is, however, important, when plasma-treating the devices, to add liquid to the devices within 10 minutes of the plasma treatment while the surfaces are still hydrophilic. Waiting longer than 10 minutes to add liquid to the device makes it difficult for the liquid to enter the device. The neuron devices are typically plasma-bound to cover glass and 0.5 mg/ml poly-L-lysine (PLL) in pH 8.5 borate buffer is immediately added to the device. After a minimum of 3 hours incubating with PLL, the devices are washed with dH2O water a minimum of 3 times with at least 15 minutes between each wash. Next, the water is removed and fresh media is added to the device. At this point the device is ready for use. It is important to remember at this point to never remove all the media from the device. Always leave media in the main channel.

In this video we demonstrate the technique of soft lithography with polydimethyl siloxane (PDMS) which we use to farbricate a microfluidic device for culturing neurons.

In this video, we demonstrate the technique of soft lithography with polydimethyl siloxane (PDMS) which we use to fabricate a microfluidic device for ...

A Microfluidic Device with Groove Patterns for Studying Cellular Behavior

We describe a microfluidic device with microgrooved patterns for studying cellular behavior. This microfluidic platform consists of a top fluidic channel and a bottom microgrooved substrate. To fabricate the microgrooved channels, a top poly(dimethylsiloxane) (PDMS) mold containing the impression of the microfluidic channels was aligned and bonded to a microgrooved substrate. Using this device, mouse fibroblast cells were immobilized and patterned within microgrooved substrates (25, 50, 75, and 100 &mu;m wide). To study apoptosis in a microfluidic device, media containing hydrogen peroxide, Annexin V, and propidium iodide was perfused into the fluidic channel for 2 hours. We found that cells exposed to the oxidative stress became apoptotic. These apoptotic cells were confirmed by Annexin V that bound to phosphatidylserine at the outer leaflet of the plasma membrane during the apoptosis process. Using this microfluidic device with microgrooved patterns, the apoptosis process was observed in real-time and analyzed by using an inverted microscope containing an incubation chamber (37&deg;C, 5% CO2). Therefore, this microfluidic device incorporated with microgrooved substrates could be useful for studying the cellular behavior and performing high-throughput drug screening.

We describe a protocol for the fabrication of microfluidic devices that can enable cell capture and culture. In this approach patterned microstructures such as grooves within microfluidic channels are used to create low shear stress regions within which cell can dock.

We describe a microfluidic device with microgrooved patterns for studying cellular behavior.  This microfluidic platform consists of a top fluidic channel ...

Brain Slice Stimulation Using a Microfluidic Network and Standard Perfusion Chamber

We have demonstrated the fabrication of a two-level microfluidic device that can be easily integrated with existing electrophysiology setups. The two-level microfluidic device is fabricated using a two-step standard negative resist lithography process 1. The first level contains microchannels with inlet and outlet ports at each end. The second level contains microscale circular holes located midway of the channel length and centered along with channel width. Passive pumping method is used to pump fluids from the inlet port to the outlet port 2. The microfluidic device is integrated with off-the-shelf perfusion chambers and allows seamless integration with the electrophysiology setup. The fluids introduced at the inlet ports flow through the microchannels towards the outlet ports and also escape through the circular openings located on top of the microchannels into the bath of the perfusion. Thus the bottom surface of the brain slice placed in the perfusion chamber bath and above the microfluidic device can be exposed with different neurotransmitters. The microscale thickness of the microfluidic device and the transparent nature of the materials [glass coverslip and PDMS (polydimethylsiloxane)] used to make the microfluidic device allow microscopy of the brain slice. The microfluidic device allows modulation (both spatial and temporal) of the chemical stimuli introduced to the brain slice microenvironments.

We demonstrate fabrication of a simple microfluidic device that can be integrated with standard electrophysiology setups to expose microscale surfaces of a brain slice in a well controlled manner to different neurotransmitters.

We have demonstrated the fabrication of a two-level microfluidic device that can be easily integrated with existing electrophysiology setups. The ...

Preparing E18 Cortical Rat Neurons for Compartmentalization in a Microfluidic Device

In this video, we demonstrate the preparation of E18 cortical rat neurons. E18 cortical rat neurons are obtained from E18 fetal rat cortex previously dissected and prepared. The E18 cortex is, upon dissection, immediately dissociated into individual neurons. It is possible to store E18 cortex in Hibernate E buffer containing B27 at 4&deg;C for up to a week before the dissociation is performed. However, there will be a drop in cell viability. Typically we obtain our E18 Cortex fresh. It is transported to the lab in ice cold Calcium free Magnesium free dissection buffer (CMFM). Upon arrival, trypsin is added to the cortex to a final concentration of 0.125%. The cortex is then incubated at 37&deg;C for 8 minutes. DMEM containing 10% FBS is added to the cortex to stop the reaction. The cortex is then centrifuged at 2500 rpm for 2 minutes. The supernatant is removed and 2 ml of Neural Basal Media (NBM) containing 2% B27 (vol/vol) and 0.25% Glutamax (vol/vol) is added to the cortex which is then re-suspended by pipetting up and down. Next, the cortex is triturated with previously fire polished glass pipettes, each with a successive smaller opening. After triturating, the cortex is once again centrifuged at 2500 rpm for 2 minutes. The supernatant is then removed and the cortex pellet re-suspended with 2 ml of NBM containing B27 and Glutamax. The cell suspension is then passed through a 40 um nylon cell strainer. Next the cells are counted. The neurons are now ready for loading into the neuron microfluidic device.

In this video we demonstrate the preparation of E18 Cortical Rat Neurons.

In this video, we demonstrate the preparation of E18 cortical rat neurons. E18 cortical rat neurons are obtained from E18 fetal rat cortex previously ...

Micro-scale Engineering for Cell Biology

Cell Capture Using a Microfluidic Device

Non-plasma Bonding of PDMS for Inexpensive Fabrication of Microfluidic Devices

In this video, we demonstrate how to use the neuron microfluidic device without plasma bonding.  In some cases it may be desirable to reversibly bond devices to the Corning No. 1 cover glass.  This could be due, perhaps, to a plasma cleaner not being available.  In other instances, it may be desirable to remove the device from the glass after the culturing of neurons for certain types of microscopy or for immunostaining, though it is not necessary to remove the device for immunostaining since the neurons can be stained in the device.  Some researchers, however, still prefer to remove the device.  In this case, reversible bonding of the device to the cover glass makes that possible.  There are some disadvantages to non-plasma bonding of the devices in that not as tight of a seal is formed.  In some cases axons may grow under the grooves rather than through them.  Also, because the glass and PDMS are hydrophobic, liquids do not readily enter the device making it necessary at times to force media and other reagents into the device.  Liquids will enter the device via capillary action, but it takes significantly longer as compared to devices that have been plasma bonded.  The plasma cleaner creates temporary hydrophilic charges on the glass and device that facilitate the flow of liquids through the device after bonding within seconds.  For non-plasma bound devices, liquid flow through the devices takes several minutes.  It is also important to note that the devices to be used with non-plasma bonding need to be sterilized first, whereas plasma treated devices do not need to be sterilized prior to use because the plasma cleaner will sterilize them.

In this video we demonstrate how to use the neuron microfluidic device without plasma bonding.

In this video, we demonstrate how to use the neuron microfluidic device without plasma bonding.  In some cases it may be desirable to reversibly bond ...

Assessing Neural Stem Cell Motility Using an Agarose Gel-based Microfluidic Device

While microfluidic technology is reaching a new level of maturity for macromolecular assays, cell-based assays are still at an infant stage1. This is largely due to the difficulty with which one can create a cell-compatible and steady microenvironment using conventional microfabrication techniques and materials. We address this problem via the introduction of a novel microfabrication material, agarose gel, as the base material for the microfluidic device. Agarose gel is highly malleable, and permeable to gas and nutrients necessary for cell survival, and thus an ideal material for cell-based assays. We have shown previously that agarose gel based devices have been successful in studying bacterial and neutrophil cell migration2. In this report, three parallel microfluidic channels are patterned in an agarose gel membrane of about 1mm thickness. Constant flows with media/buffer are maintained in the two side channels using a peristaltic pump. Cells are maintained in the center channel for observation. Since the nutrients and chemicals in the side channels are constantly diffusing from the side to center channel, the chemical environment of the center channel is easily controlled via the flow along the side channels. Using this device, we demonstrate that the movement of neural stem cells can be monitored optically with ease under various chemical conditions, and the experimental results show that the over expression of epidermal growth factor receptors (EGFR) enhances the motility of neural stem cells. Motility of neural stem cells is an important biomarker for assessing cells aggressiveness, thus tumorigenic factor3. Deciphering the mechanism underlying NSC motility will yield insight into both disorders of neural development and into brain cancer stem cell invasion.

We demonstrate that the over expression of epidermal growth factor receptors (EGFR) enhances the motility of neural stem cells(NSCs) using a novel agarose gel based microfluidic device. This technology can be readily adaptable to other mammalian cell systems where cell sources are scarce, such as human neural stem cells, and the turn around time is critical.

While microfluidic technology is reaching a new level of maturity for macromolecular assays, cell-based assays are still at an infant stage1. This is ...

Microcontact Printing of Proteins for Cell Biology

The ability to pattern proteins and other biomolecules onto substrates is important for capturing the spatial complexity of the extracellular environment. Development of microcontact printing by the Whitesides group (<a href="http://gmwgroup.harvard.edu/">http://gmwgroup.harvard.edu/</a>) in the mid-1990s revolutionalized this field by making microelectronics/microfabrication techniques accessible to laboratories focused on the life sciences. Initial implementations of this method used polydimethylsiloxane (PDMS) stamps to create patterns of functionalized chemicals on material surfaces1. Since then, a range of innovative approaches have been developed to pattern other molecules, including proteins2. This video demonstrates the basic process of creating PDMS stamps and uses them to pattern proteins, as these steps are difficult to accurately express in words. We focus on patterning the extracellular matrix protein fibronectin onto glass coverslips as a specific example of patterning.
An important component of the microcontact printing process is a topological master, from which the stamps are cast; the raised and lowered regions of the master are mirrored into the stamp and define the final pattern. Typically, a master consists of a silicon wafer coated with photoresist and then patterned by photolithography, as is done here. Creation of masters containing a specific pattern requires specialized equipment, and is best approached in consultation with a fabrication center or facility. However, almost any substrate with topology can be used as a master, such as plastic diffraction gratings (see Reagents for one example), and such serendipitous masters provide readily available, simple patterns. This protocol begins at the point of having a master in hand.

Microcontact printing is used extensively to pattern proteins and other molecules on material surfaces. We demonstrate the basic steps of this process, stamping patterns of fibronectin onto glass.

The ability to pattern proteins and other biomolecules onto substrates is important for capturing the spatial complexity of the extracellular environment. ...

The Microfluidic Probe: Operation and Use for Localized Surface Processing

Microfluidic devices allow assays to be performed using minute amounts of sample and have recently been used to control the microenvironment of cells. Microfluidics is commonly associated with closed microchannels which limit their use to samples that can be introduced, and cultured in the case of cells, within a confined volume. On the other hand, micropipetting system have been used to locally perfuse cells and surfaces, notably using push-pull setups where one pipette acts as source and the other one as sink, but the confinement of the flow is difficult in three dimensions. Furthermore, pipettes are fragile and difficult to position and hence are used in static configuration only. 
The microfluidic probe (MFP) circumvents the constraints imposed by the construction of closed microfluidic channels and instead of enclosing the sample into the microfluidic system, the microfluidic flow can be directly delivered onto the sample, and scanned across the sample, using the MFP. . The injection and aspiration openings are located within a few tens of micrometers of one another so that a microjet injected into the gap is confined by the hydrodynamic forces of the surrounding liquid and entirely aspirated back into the other opening. The microjet can be flushed across the substrate surface and provides a precise tool for localized deposition/delivery of reagents which can be used over large areas by scanning the probe across the surface. 
In this video we present the microfluidic probe1 (MFP). We explain in detail how to assemble the MFP, mount it atop an inverted microscope, and align it relative to the substrate surface, and finally show how to use it to process a substrate surface immersed in a buffer.

In this video we present the microfluidic probe1 (MFP). We explain in detail how to assemble the MFP, mount it atop an inverted microscope, and align it relative to the substrate surface, and finally show how to use it to process a substrate surface immersed in a buffer solution.

Microfluidic devices allow assays to be performed using minute amounts of sample and have recently been used to control the microenvironment of cells. ...