A Clampable Tangential Flow Device for SEM Imaging

Hey all,

So, I’ve been trying to replicate the exosome experiments that I did back during my rotation to varied success. I have had trouble with the plasma that we had frozen with precipitates that would not resuspend upon thawing. We ordered new plasma though so fresh batches of experiments will be coming up very soon.

Another issue that I’ve been having is with recovery of the membrane from the PDMS housing for SEM imaging. As I have previously mentioned, the technique that I use is to carefully cut the housing away until the top surface of the membrane is exposed. However, this is a mildly dangerous technique and I can potentially break the membrane in the process. Additionally, there is a drying issue with these membranes that causes them to break upon extraction, as well as the fact that the chip is still surrounded by the PDMS housing. This actually leads to the major breakage problem, which arises as a result of having to coat these extracted for better conductivity in the SEM. The membrane will survive through the extraction, only to break during the pumping of the gold sputter coater. If the chip did not have the PDMS housing, then there would be no need to coat and I could throw the whole chip with the intact membrane straight in to the SEM. This leads to an interest in designing a clampable system.

Assembling the device without UV/ozone and heat treatment will prevent the layers from bonding to each other and will make the removal of the chip much easier. On Monday, I was just messing around with some of the 300 micron gasket layers and built a device in the old format without any UV/ozone or heat treatment (see video 1). I did this simply for the purpose of seeing how things went together, which was pretty smooth. Then Tuesday, I decided to attempt flow through this device. Using one of Henry’s clamp systems (see video 2), I was able to clamp the device and flow PBS through at 10 microliters/min without any leakage. This was very promising and the membrane remained intact throughout the process. After flowing approximately 200 microliters through the device, I stopped the flow and removed the device from the clamp. Because there was no UV/ozone treatment and no heat treatment of the device, I was able to remove the PDMS block and top channel layer to easily access the chip layer. The membrane was still intact so I carefully removed it (it did not stick at all and came out quite easily) and set it in a rack to dry. After letting it sit for a couple of hours, the membrane was still intact, which was very promising. The ability to get flow through this device without any bonding steps means that it has the potential to provide rapid assembly and operation, while enabling me to be able to remove the chips for SEM processing.

I have yet to run plasma through the system, which is the next step. I plan to do this tomorrow and hopefully I’ll get some promising results, especially on the drying aspect of the chip. Additionally, I should note that care has to be taken to not over tighten the clamp so as to not warp the device, which will unseal the layers and allow flow through the bottom channel. I’m working on a redesigned clamp (since the one Henry gave me is breaking) that will either be CNCed or printed. Below, I have a video of the device assembly for this system as well as a video of the clamping. I will update this post with a video of flow through the device, and hopefully some results from the SEM.

Video 1: Device assembly at 8x speed.

Video 2: Clamping of the device in the polycarbonate clamp.