PDMS-Membrane Bonding Update
This is just an update on the progress being made towards creating a closed flow cell by bonding PDMS to our membrane chips. For those who were not at the meeting on Tuesday we have successfully bonded PDMS to both glass cover slips as well as out membrane chips using the UV Ozone cleaner.
Yesterday Henry and I decided to try to create a prototype of a closed system. We made a fresh batch of PDMS and once it was cured we found that we can relatively easily insert our capillary tubing into it. We cut out small circular sections of the PDMS and placed two segments of capillary tubing in them (one acting as a possible fluid inlet and the other as a fluid outlet). These PDMS-capillary-tube systems as well as membrane chips were places in the UV ozone cleaner to prepare for bonding. After the UV ozone protocol was complete the PDMS-capillary-tube system was sandwiched against the membrane chips in such a way as to seal the “trench” of the chip with the two segments of capillary tubing directly above the “trench”. We then let these samples sit over night, when we arrived this morning they were all bound.
The problem with this approach is that the membrane side of the chips are facing down and thus every time they are laid on a new surface the possibility of introducing a contaminant increases (increasing the chances of the membrane breaking). I think the next time we try this we are going to use some vacuum grease with the beads to act as a support for the membrane.
This was the best picture I could take of the system. At the bottom is the membrane chip with the membrane side facing down. On top of that is the PDMS with the two inserted capillary tubes.
Originally when we bonded this system we used short pieces of capillary tubing so that we could have the bonding surface of the PDMS facing the UV source within the chamber. When I did this process again I used longer capillary tubing segments and I also UV-ozone bonded small pieces of PDMS onto the bottom (membrane side) of the wafer chips so there was at least some sort of support structure.
I did this test yesterday, when I checked them this morning none of the PDMS had bound to the wafer chips (neither the support PDMS or the top PDMS). I think the reason might be that I did not clean the membranes prior to bonding so there might have been some type of organic layer on the surface preventing bonding from occurring. I am going to try to re-run the bonding today, so on Monday I will be able to report back.