Hi Deval,

You are using PDMS microchannel I assume?

Before the loading, a 1~5 min plasma treatment can pretty much guarantee bubble-free loading for the PDMS channel. As long as your chip didn't dry-out, it should be OK to retrieve fluid without bubble issue (if you push in more solution from the inlet and collect the liquid from the outlet).

If you don't have plasma handy, it is inevitable to get bubble trapped at the sharp corner/bifurcation part, as PDMS is a hydrophobic material. You can try to close the outlet, and push some more liquid from the inlet. If your chip can hold the pressure (without leakage at the tubing connection, or the bonding is good), the bubbles should be able to be pushed out through the PDMS (as PDMS is a air permeable material). My suggestion will be pre-load the chip with DI water/PBS depends on your application, get rid of the bubble with the pressure trick, then load the solution for your experiment.

Just remember wet-loading is the bubble-free method as long as you are careful. If your experiment requires a dry phase within the channel, you better have some nice bubble trap design, and be ready to spend sometime flipping your device around!

Hi Deval, 

I experienced the same problem with chips (PDMS) having channels with area of 9 cm2 and height 400 microns. These chips were used for cell culture. The only way which worked is to make the surface of the channel hydrophillic. Plasma is the best way in terms of reproducibility and throughput (as suggested by Xiang). Alternativelly you can use piranha solution (mix of concentrated sulfuric acid + hydrogen peroxide) to oxidize the surface of PDMS. It works but it is a clumsy approach and needs to be optimized for your case. Further ionic polymers like polystyrene sulfonate (anionic) or Poly(diallyldimethylammonium chloride) can help as well, but you need to be sure that they do not interfere with your application..

Thanks for your answers Mr. Xiang Le and Mr. Jan Vitecek.

Sorry I forgot to mention the material. I am working with low cost concept so mostly polymers like PMMA.

The surfaces are hydrophobic. I haven't really tried using hydrophilic surface as I am not very sure about hydrophilic surfaces.

My my application involves using dyes. Even if I am some how able to make the polymer surface hydrophilic and am able to fill that hydrophilic channel without bubbles, will I be able to retrieve the dye completely without leaving any traces or stains of the dye behind in the hydrophilic channel?

My reason for using hydrophobic surface was to retrieve the dye solution completely without leaving any traces or stains behind in the channel.

Channel height is around 100 to 200 microns and area around 10 cm x 10 cms.

Hi Deval,

Have you tried putting your dyes into a surfactant solution (e.g. 0.05% Tween-20)? That will increase the wettability of your PMMA. It should also help prevent the dye from adsorbing to the surface.

Best,

Allan

Haven't tried that Allan... Will surely do. Thanks.

Hi,

If you cannot add a surfactant solution or cannot modify the wettability of your channel, you can try to fill your channel with CO2 before priming (take care to potential pH change) or simply  pressurize the fluid and wait for residual air evacuation through the pdms itself

Thanks Eric. As I am using acrylic, and not PDMS, the second option is not feasible.

Will try the first option.

You could look into phaseguides  http://pubs.rsc.org/en/Content/ArticleLanding/2011/LC/c0lc00643b#!divAbstract

especially easy to realise if you work with PMMA, although this might add 50-100 microns to your channel (height)

http://pubs.rsc.org/en/Content/ArticleLanding/2011/LC/c0lc00643b#!divAbstract

Thanks Maiwenn...Phase guides is one of my options.