I face this problem while pumping bead solutions through a "hydrophilic" PDMS microfluidic device. Now since the surface was made hydrophilic and PDMS is hydrophobic, I'm thinking adhesion shouldn't be a problem.
Worth mentioning also is that the flow rates I'm running the chip at are relatively high (2-3 ml/min) and the bead concentration is 1 million per ml.
Any suggestions would be greatly appreciated.
You can pre-incubate your pdms chip with 1-3% PVP, which may block the hydrophobic chip walls and prevent adherence. PVA should also work, if you can it dissolved.
It is not clear if, in your case, particle adhesion only becomes a problem when PDMS is hydrophilic. Please clarify.
Adhesion is more problematic when the particles sedimentate. To eliminate sedimentation one solution is tune the liquid density (by adding a salt or glycerol) so that it matches the particles density.
Adding surfactants and changing the ionic strength of the fluid may also influence adhesion.
First, it is good to use the PDMS based microfluidic chip as soon as possible (or store it under right conditions) to preserve its hydrophilicity. Second, using PVP as Peter suggested is a very good option. Incubating the chip first with a PVP (Polyvinylpyrrolidone) solution and/or using beads in buffer to which PVP is added helps a lot. PVP comes as a powder ( https://www.sigmaaldrich.com/catalog/product/sial/81420?lang=en®ion=SE&gclid=Cj0KCQjwoqDtBRD-ARIsAL4pviBQfHyyYswqqsZn-UGuWOB64IbnpkAd29jV97lXNQp0hCrjDwHNWkIaAhq_EALw_wcB) and I have used the one from Sigma Aldrich and it works really well for these applications.
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