Name: Non-plasma Bonding of PDMS for Inexpensive Fabrication of Microfluidic Devices (Video) | JoVE Journal
Uploaded: 2007-11-01T00:41:54.000+00:00
Duration: 4 min 45 s
Description: Learn non-plasma bonding of PDMS microfluidic devices to glass for neuroscience cell culture applications. This reversible, watertight method uses electrostatic forces and poly-L-lysine coating without expensive equipment.

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5 minutes

Preparing Microfluidic Devices For Neuron Cell Culture
1) Clean Corning No.1 24 mm X 40 mm glass slides
<ul>
<li>Sonicate the glass slides in a water bath sonicator for 30 minutes</li>
<li>Rinse the glass slides with 70% EtOH</li>
<li>Wash slides three times with dH2O</li>
<li>Dry slides in a tissue culture hood for several hours, preferably overnight</li>
</ul>
Note: We have special metal trays that we load with the slides. The slides are separated individually and placed in slots in this metal rack. We can then place these metal loading trays in a glass dish that we fill with water, place in the water bath sonicator, and sonicate for 30 minutes. Subsequent washes are carried out in this dish.
2) Preparing the PDMS devices
<ul>
<li>Cut out the PDMS mold from the silicon wafer, punch holes in the PDSM cast and quarter it</li>
<li>Clean the PDMS devices by first blowing inert gas (Argon or Nitrogen) across them. Then use 3M Scotch Brand 471 tape to lift off any remaining debris</li>
</ul>
Note: It is important to keep the devices face up. Initially, when we cut the PDMS away from the silicon wafer, the side in contact with the wafer is the clean side: it contains the microfluidic channels. We try to be as careful as we can as to not damage the device, and keep the clean side face up until we are ready for plasma bonding.
<ul>
<li>Autoclave devices in plastic containers</li>
<li>After autoclaving, clean No. 1 Corning glass slides and plasma-treat devices using a Harrick brand plasma cleaner, <a href="http://www.harrickplasma.com/" target="_blank">www.harrickplasma.com</a> </li>
<li>Place the devices clean side down on the glass slide.</li>
</ul>
The device is now plasma bonded to the glass slide.
3) Coating The Devices With Poly L-Lysine (PLL)
<ul>
<li>PLL is added to a well on each side of the device and allowed to flow through into the next well</li>
</ul>
=&gt; 150 µl of PLL for the large wells and 30 µl PLL for the smaller wells. It does not have to be exact as long as the wells are full.
Note: If you look at a device you will see 4 wells: each two are connected. You want to put the PLL in one well so that it will flow through the device into the next well.
<ul>
<li>Allow the PLL to flow through the device for about 10 minutes and then add more PLL to the wells to fill them up</li>
<li>Place the devices containing PLL in an incubator at 37°C for a minimum of 4 hours (overnight is preferable)</li>
<li>Vacuum out the excess PLL after treatment, but be careful not to suck all the liquid out of the device</li>
</ul>
Note: You do not want to introduce air bubbles to the channels or chamber. Just vacuum out the excess PLL in the wells.
<ul>
<li>Add autoclaved dH2O to each well on either side of the device, and allow to flow to the other well by capillary action</li>
</ul>
Figure 1 is a diagram of a microfluidic device. Notice how the Blue (Soma side) is connected and the Red (Axonal side) are connected. When we say put the PLL, or water or media, on one well on each side of the device, what we mean, for example, is: Place 150 ul of autoclaved dH2O in one Blue Well then place 150 µl of autoclaved dH20 into one Red Well. The water (or PLL, or Media, or Cells) will flow through the device to the other corresponding well.
<img src="/files/ftp_upload/old/410_2008_8_27_3/410_Figure-01.png" alt="Static equilibrium diagram, labeled soma and axon sides, 450 um, for neuroscience studies." width="362" height="216" data-altupdatedat="1787630408000" data-alt="Figure 1">
  Figure 1

Note: Please note that, from now on, when I say "place media, cells, water or PLL in the TOP wells", I am referring to the diagram above where the Soma would be on the left and the Axons will grow to the right.
<ul>
<li>Aspirate off the water (again being careful not to fully remove all the liquid from the device), then add another 150 µl of autoclaved dH2O to one of each connected well and allow it to flow through to the corresponding well.</li>
<li>Place the device containing dH2O in an incubator at 37°C for 1 hour, then repeat the wash step again. Wash the devices three times with dH2O for one hour each, which is the total.</li>
</ul>
Note: Due to the possibility that borate from the PLL can absorb into the PDMS, some in the Jeon Lab recommend incubating the devices overnight with autoclaved dH2O after a couple of initial quick rinses. This will ensure that all free borate will leach out of the PDMS prior to the loading of cells. If this is not done, there may be a release of borate into the media over time, which could lead to cytotoxicity.
<ul>
<li>Add Neural Basal Media (NBM) with the necessary factors (glutamax, B27, PenStrep) to the top wells </li>
</ul>
Note: The devices can be incubated overnight and plated with cells the next day, or incubated a minimum of 3 hours with NMB + factors before plating the cells.
Preparing The Neurons For Loading Into The Devices
We use 18 day old fetal rat cortex that we either buy from a company called Brain Bits or that is prepared here on campus for us. We prefer to get the tissue fresh.
<ol>
<li>Obtain 1 fetal brain cortex (2 pieces of tissue) stored in Hibernate E</li>
<li>Take 3 long glass pipettes and fire them each into successively smaller sizes using an alcohol lamp</li>
<li>remove tissues from Hibernate E with a glass pipette and place in 2 ml of NMB + Factors in a sterile 15 ml tube.</li>
<li>Trituration: Using a bulb and glass pipette the cortex is passed up and down about 5 to 10 times. Then, the next smaller pipette is used to pipette up and down the tissue. Finally, the smallest pipette is used to pipette up and down the tissue. We like to make sure that there are no visible chunks. Note: Recently, the Jeon Lab began comparing cells from tissue stored in Hibernate E to cells that were prepared from Tissue initially treated with 0.125% Trypsin in 50% Ca++ free and Mg++ free dissection buffer. The consensus is that tissue prepared using trypsin yield more viable cells than tissue placed initially in Hibernate E. If you are NOT going to use the tissue right away, then you need to store the tissue in Hibernate E. If you are going to use the tissue right away and would like increased viability, then treat the tissue with Trypsin prior to mechanical trituration as following: 1) dilute 1 ml 0.25% Trypsin (Gibco, Invitrogen) with 1 ml of Ca++ free Mg++ free dissection buffer (final Trypsin = 0.125%) into a 15 ml tube (keep ice cold); 2) place tissue in buffer and incubate immediately at 37°C for 8 minutes; 3) add 10 ml DMEM/10% FBS to stop the Trypsin reaction and continue protocol below. </li>
<li>Centrifuge cells at 1100 rpm for 1 minute</li>
<li>Aspirated media carefully off the cell pellet</li>
<li>Add 1 ml of NMB + factors to the pellet and re-suspended it by pipetting up and down</li>
<li>Pass the re-suspended cells by gravity flow through a filter to remove any clumps (BD Falcon cell strainer 40 um nylon)</li>
<li>Count and plate cells: 
<ul>
<li>Into a microfuge tube, add 60 µl NMB + factors, 20 µl of cell suspension, and 20 µl of trypan blue then mix</li>
<li>Add about 10 µl of this solution to a hemocytometer and count the live cells (not blue)</li>
<li>Adjust concentration to 2.5 - 4.5 x106 cells/ml Note: We generally obtain a concentration of about 2.5 - 4.5 x 106 cells/ml. depending on the volume the cells are resuspended in (normally 1 ml NBM + B27/Glutamax/PenStrep percortex). If the tissue was prepared with trypsin, the yield will likely be increased.</li>
</ul>
</li>
</ol>
Plating The Devices
<ol>
<li>Load cells (primary neurons) into one well of the device </li>
<li>Plate 5 µl per small device and 20 µl per big device Note: You can load 10 µl of cells on the top of the device and 10 µl on the bottom of the device (half total volume), or directly all 20 µl of cells in the top somal well (5 µl in the top somal well for the small devices). </li>
<li>Incubate for 10 minutes in a 37°C incubator so cells can start to attach</li>
<li>Add approximately 150/30 µl of NMB + factors to each well depending on device size Note: Volumes may vary depending on the thickness of the PDMS. All that matters is that the wells are full.</li>
</ol>
Supplemental On Using The Devices Without Plasma Bonding
Without plasma treating, Christina Tu, a technician, who does it successfully every week without plasma, says to just load the cells right away.
Remember to remove the media from both wells on the soma side (axon side won't matter if you leave the media in). It's the fluid flow that allows the cells to enter the main channel. If you have media in the wells, you won't get fluid flow.

<ol><li>Park, J. W., Vahidi, B., Taylor, A. M., Rhee, S. W., Jeon, N. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Microfluidic+culture+platform+for+neuroscience+research%5BTitle%5D)+AND+%22Nat+Protoc%22%5BJournal%5D)">Microfluidic culture platform for neuroscience research.</a> Nat Protoc. 1 (4), 2128-2136 (2006).</li>
<li>Taylor, A. M., Blurton-Jones, M., Rhee, S. W., Cribbs, D. H., Cotman, C. W., Jeon, N. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+microfluidic+culture+platform+for+CNS+axonal+injury%2C+regeneration+and+transport%5BTitle%5D)+AND+%22Nat+Methods%22%5BJournal%5D)">A microfluidic culture platform for CNS axonal injury, regeneration and transport.</a> Nat Methods. 2 (8), 599-605 (2005).</li>
</ol>

The authors have nothing to disclose.

Here we demonstrated how to use the neuron microfluidic device without needing a plasma cleaner. We refer to this as non-plasma bonding.

<table><tbody><tr><td>PDMS</td><td>Reagent</td><td>Dow Corning</td><td></td><td>Sylgard 184 with curing agent Please consult Dow Corning to find a vendor near you</td></tr><tr><td>Cornig No. 1 Cover Glass</td><td>Cover Glass</td><td>Corning</td><td>Corning No. X2935 244</td><td>Available through Fisher Scientific, Fish Catalog number 12-531D</td></tr><tr><td>B27</td><td>Reagent</td><td>Invitrogen</td><td>17504-044</td><td>B27 is a proprietary supplement available through Invitrogen under their Gibco line of cell culture reagents.</td></tr><tr><td>Glutamax</td><td>Reagent</td><td>Invitrogen</td><td>35050-061</td><td>Glutamax is available through Invitrogen under their Gibco line of celll culture reagents.</td></tr><tr><td>60 mm Petri Dish</td><td>Tool</td><td>Fisher Scientific</td><td>08-757-13A</td><td>60 mm polystyrene sterile petri dishes are used to house the device bound to glass.</td></tr><tr><td>Poly-L-Lysine</td><td>Reagent</td><td>Sigma-Aldrich</td><td>P-1274</td><td></td></tr><tr><td>BD Falcon 50 ml Tube</td><td>Tool</td><td>BD Biosciences</td><td>Falcon No. 352098</td><td>Available through Fisher Scientific catalog number 14-959-49A</td></tr><tr><td>BD Falcon 15 ml tube</td><td>Tool</td><td>BD Biosciences</td><td>Falcon No. 352097</td><td>Available through Fisher Scientific catalog number 14-959-70C</td></tr></tbody></table>

non-plasma bonding of pdms for inexpensive fabrication of microfluidic devices

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 ...

Labs that routinely do photolithography and soft lithography typically have what is called a plasma cleaner. A plasma cleaner has an electric coil, which creates a partially ionized gas consisting of electrons, ions, neutral atoms and molecules. The plasma creates reactive species on the surface of the glass and the device, which when placed together will form a permanent bond.The plasma also makes the surface of the device hydrophilic, which facilitates the addition of liquids. In some cases, however, a permanent irreversible bond is not desirable. Also, many labs do not have access to a plasma cleaner.To address this concern today will demonstrate reversible non plasma bonding of the neuron device to cover glass electrostatic forces between the PDMS and the glass forms a bond that is watertight and suitable for cell culture. I'd like to introduce you to Kiana Lee. She'll be doing the demonstrations Today.Corning number 1 24 millimeter by 40 millimeter cover slips are cleaned using a water bath sonicate. The glasses are placed in a stainless steel rack that is then placed in a glass container filled with deionized water. The glass container is then placed into the water bath sonicate.The glass slides are then sonicated for 30 minutes. After sonic deionized water is dumped out of the glass container. 70%ethanol is placed in the glass container with the glass slides, which is then brought inside a standard biosafety cabinet in order to keep them sterile.After rinsing with 70%ethanol, the stainless steel rack is removed from the glass container and the glass slides allow it to dry completely for several hours or overnight. Next, while in the bowel safety cabinet, the glass slides are coated with PLL by soaking them in a container filled with PLL solution. The glass slides are allowed to soak in the PLL solution for a minimum of three hours or overnight.After PLL coating, the PLL liquid is removed from the dish and then the glass slides are thoroughly rinsed with deionized water. After rinsing the PLL coated glass with water several times, water is then filled in the dish and the glass slides are allowed to soak in water for several hours. After soaking for several hours in deionized water, the water is aspirated from the dish.The glass slides will be rinsed quickly and then the glass slides will be removed from the dish placed in a stainless steel rack and allowed to dry overnight In a biosafety cabinet, Neuron devices are brought into the biosafety cabinet and rinse thoroughly with 70%ethanol to sterilize them. The excess ethanol is then aspirated away from the device. The devices are then allowed to dry overnight in the biosafety cabinet the next day.This sterile neuron device is simply placed on top of the clean, sterile and PLL treated glass. The PDMS forms a reversible bomb with the glass that is liquid tight. A device is bonded to the glass with gentle pressure cells, or media are then added immediately to the device.Waiting too long to add media or cells to the device after the assembly can make it more difficult for the liquid to enter the device. It is important to note that the liquid does not readily enter the non plasma treated devices as fast as a plasma treated device. Plasma treated devices are initially hydrophilic just after plasma treated liquids readily flow into the hydrophilic device, whereas the flow through the non plasma bonded devices is much slower.In some cases, it may be necessary to use a pipette to force liquid into the device. In this video, We have shown you how to non plasma bond the neuron device to cover glass. This is an efficient and inexpensive method to reversibly BLO, PDMS to glass surfaces.We hope you have found this video informative and helpful. So that's it from the John Lab. Thanks for watching.

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Learn non-plasma bonding of PDMS microfluidic devices to glass for neuroscience cell culture applications. This reversible, watertight method uses electrostatic forces and poly-L-lysine coating without expensive equipment.

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

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