20211106 microfluidics

Preparing the chip & plasma cleaning

- Cut out Vilde and Dag's chip designs.

- Made 1.6mm holes in the inlets&outlets

- Plasma cleaned as described in the plasma cleaning test from before.

- the 25um high wafer is broken. We will need to create a new 25um mold.

Adding new PDMS to wafer

- Used 43.70g PDMS and 3.68 g curing agent.

- We should consider using less PDMS when creating new chips on an already used mold, since they have been too thick.

Troubles with microfluidic chips

We had a few problem with punching the chips: starting with Vilde's, after some time after plasma it seemed that the chip closed itself (the part facing the air, approx half way in height). Also, we observed that the PDMS seemed to slide which compressed the holes. The "sliding" was in different directions in the different holes. We then tried to re-punch holes out *from the top* which seemed to work. To be sure, we cut out another chip (Thomas') but after plasma it turned out to be the same problem. We still managed to get tubes in, watertight.

Next time: perhaps insert the tubes into the holes right after plasma cleaning so we don't have this problem again.

Why?

- these PDMS chip were coming from the same wafer (broken BTW), which was covered which a very thick layer of PDMS

Preparing collagen

- Did a 1:1000 dilution of asedic acid (17.5 M) - used 10 mikroliters (acid) and 10 mL(sterilized water).

- Did a 2:3 dilution of collagen - 300 uL of the diluted acid and 200 uL of collagen.

- Put the collagen in the chip with a flow of around 50 uL/min, stopped the flow and waited an hour. Rinsed with PBS, aspirated and put the cells in (specified below). Noticed that the collagen had attached in a 'patchy' manner. The cells stuck to these patches and not to the rest of the surface.

Microfluidics

- We used the tubes labled "For Elveflow Material".

- For collagen we used a 1 mL syringe with a 0.6mm tip. For flow see above.

- Inserted cells with a 2.5 mL syringe and 0.6mm tip. Flow: 20 uL/min.

- Co2 independent medium: 5 mL syringe and 0.6mm tip. Going to keep flow over the weekend - 0.9 uL/min.

- Lots of small and medium sized bubbles! After injecting cells, there were very few bubbles which dissolved after a while. After the media was added we got many more and bigger bubbles.

Note

We put the flow of CO2 independent medium briefly at 0.9 mL/min and, when noticing, put it back at .9 ul/min. This is when the bubbles appeared. It is very likely that this crazy flow has led to a tremendous amount of pressure in the chip for a while leading to a dissolution of part of the gas contained in the PDMS into the medium. Upon decreasing the pressure, the gas was less solvable in the medium and cavitation events occurred, leading to the observed bubbles.

- Started a timelapse showing the cell culture inside the chip. Taking pictures every 30 min for 4 days.

- Tried using Elveflow Flow Switch to control flow, but unfortunately could not make it work. BTW, we need to download and install the newest Elveflow software.