For a microfluidic device of mine, cells are sticking to a PDMS surface (not oxidized). Are there any surface treatments that can be used to reduce this effect? It may also be that the surface of the PDMS is not perfectly smooth. In that case how can I ensure the PDMS being spin coated is smoother?
Hi Sachin,
Thanks for your reply. Currently the cells are suspended in Hank's Buffered Saline Solution (HBSS) + 2% BSA. But I see that many times there is a BSA treatment BEFORE cells are introduced to the device.
Another question I have is the effect of an oxygen plasma treatment. Some literature suggests it reduces cell adhesion:
Article A microengraving method for rapid selection of single cells ...
Where as others suggest it increases cell adhesion:
Bodas et al. Hydrophilization and hydrophobic recovery of PDMS by oxygen
plasma and chemical treatment—An SEM investigation, Sensors and Actuators B 123 (2007) 368–373
Maybe someone could clarify the effects of an oxygen plasma treatment?
David,
Some comments that may help:
1. Large part of cell adhesion is due to sedimentation. So, you can reduce it if the density of your liquid is similar to the cells. You can increase liquid density by adding a salt. Other solution is to increse the liquid viscosity, which reduces the sedimentation velocity.
2. Relation between adhesion and surface properties is complicated. Oxygen plasma treatment renders PDMS surface hydrophilic.
Our group has a paper on surface properties andadhesion of E. Coli:
Article Micro and macro flow systems to study Escherichia coli adhes...
It seems that hydrophobicity is not a factor in our case. Maybe because sedimentation is more important. We use E. coli and the result will also depend on the surface properties of the cells.
3. PDMS is very smooth and I don't think that that is the problem.
4. Adhesion also decreases with flow rate, but you will need wall shear stresses of about 1 Pa (very high) to reduce it significantly.
Hi David,
My first comment somehow got deleted. Nevertheless, I don't think roughness is an issue here. If Joao feels its because of sedimentation, and if it applies to your case too, then the problem should be solved. Like I said before, I think wettability will be more important in my case where there are oil droplets getting stuck to the pdms walls. Good luck!
Haven't tried myself, but you could try to plasma-coat the PDMS with a teflon-like polymer. This is a second half of the Bosch etching process for passivation: C4F8 gas, flow 50-100 sccm, RF 0-10W, ICP RF ~2000W, pressure some tens of mtorrs, or any conditions that give low bias voltage. A couple of seconds should grow a teflon-like substance on the surface to which nothing really sticks well.
Hi,
Some time passed since you posted the question but maybe it can help some other people.
Coating the PDMS with PEG, pluronic (0.2% wt/vol, ref doi:10.1038/nprot.2014.120), or BSA (0.1mg/mL), in water of PBS for an hour or more, helps to reduce the adhesion of the cells to the surface.
Good luck.
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