Hello,
I am fabricating some PDMS microfluidics channel (section length 100um) using SU8 mold but, of course, I am experimenting some backflow when I put my sample there. Is there any way (maybe some particular design trick) to avoid or at least reduce any kind of backflow?
Thank you for your help!
Valerio
The backflow in a 100um channel is due to the air bubbles that are trapped inside it. The best way would be to have two barb connectors and tubings at your inlet and outlet and flow the sample using a syringe pump connected to your inlet tubing.
In case your sample quantity is really low and you cannot use a syringe, then add your sample at the inlet using the appropriate pipette tip that will completely seal your contact while dispensing the sample. Have the barb connector and tubing at the outlet to complete the pathway for sample.
Lastly, make sure you are using enough volume of sample to completely fill your microfluidic channels. This can be determined by trying out a range of sample volume depending on your channel design. The volume at which your channel is completely filled is the volume you need to use. (Eg: your channel may require 100ul of solution and you are introducing only 40ul). This will avoid air bubbles completely.
Hope this helps you.
Two thoughts (1) pull the solution vs push or (2) ensure tight seals. (1) Would pulling the solution through, instead of pushing the solution, make a difference? Plumb your system so there is a material reservoir, water, any solution you want to flow through your channel, then the channel, then a syringe pump, of any pump. (2) Also prevent air from entering system by ensuring tight seals between your ship and any hosing.
first of all you can use isotonic solution to remove the air bubbles (saline)
for the syringe pump it will make the flow not regular.
it is better to used hydro-static pressure by making 2 column of fluid(inlet and outlet) so the flow will pass from the higher column to the lower one as a continuous flow
How do you make PDMS channel? Do you do soft lithography? if yes, do you use vacuum pump to remove bubbles from the pdms mixture and then pour that on the mold? Also it depends on the curing time of the pdms. the heating time and temperature and also ratio of the pdms and curing agent play significant role in the final channel porosity through which may be bubbles and air and supply pressure to the channel.
Thank you all for your useful suggestion. Your suggestion are great but I am actually thinking about some kind of geometry in my channel which could reduce the backflow because I need my solution to stay in the microchannels for a couple of minutes to perform a biological assay. Do you think a bottleneck geometry could help?
By the way:
Dear Sasank Peri and Taymour El-Sherry, thank you for your suggestions: I will try to avoid any trapped bubble.
Dear Jessica Snyder, pulling my solution could actually reduce the backflow: I will give a try! Thank you!
Dear Ali Kalantarifar, I am using a ration of 10:1 between PDMS and curing agent which seems to be a standard in literature and yes, I am using a vacuum chamber to eliminate all the bubbles before curing. However I guess I could spend some time in order to quantify how the recipe affects the backflow. Thank you!
Dear Shuaizhong Zhang, your idea sounds encouraging !! Do you have any reference about circular chns? Thanks !!
First, i think a bottleneck design would definitely help in reducing the local resistance, which probably will reduce the backflow.
Sorry for that i don't have any exact references now. But i have 2 relative papers which could help.
http://www.pnas.org/content/107/36/15670.abstract
https://link.springer.com/article/10.1007/s10404-014-1425-8
in the first one, there is backflows at the two ends of the channel because the the channel is not circulatory or not a loop. In the second one, there is no backflow because the channel network is a closed loop.
Now i am also observing flows in a circular microfluidic channel. Based on the Hagen-Poiseuille equation, when the channel height in increased, the resistance will decrease.
I hope this is helpful for you.
Best regards,
Shuai
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