Team:UCLA/Notebook/Materials/12 May 2015

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• Tried extrusion, this time with PEEK tubing (0.005 inch inner diameter) cut with the tubing cutter
  • tube length was 10 mm
  • dope was 20% w/v cellulose acetate with a few drops of blue food coloring
  • extrusion rate of 6 uL/min
  • fibers still don't form. Rather, the dope blobs up upon coming into contact with the water
  • some observations:
    • the syringe pump inevitably reaches a point where it stops pushing. The motor is still working, but the drive screw is clearly not moving at all (and hence, the drive block isn't moving). Curiously, dope still comes out of the tubing when the motor is stalled
    • periodically, an air bubble comes out from the tube -- is this an indication that there is air in the tubing? Air is something that might be providing huge back pressure against the motor's force
      • speaking of air bubbles, I'm not able to load a syringe with dope without there being air bubbles in the dope.
        • I tried removing the plunger and pipetting dope in. But when inserting the plunger back in, bubbles are formed at the plunger/dope interface.
        • I tried using a large diameter needle to draw dope up. But there is inevitably dead space in the needle that is introduced into the syringe as bubbles.
    • a thin stream can be observed rising from the tip of the tube to the surface of the water. I think that this is acetone leaving the dope. The question is, is acetone leaving the dope that's already in the coagulation bath, or leaving the dope that's inside of the tube? If it's the latter, then that may explain why the motor stops being able to push out the dope.
  • At the end of the day, I just removed the water bath and wiped down the tip of the tubing with acetone. I'll try again tomorrow and see what happens.

• played around with the new dialysis clips. Loaded a dialysis bag with red food coloring solution to visualize leaks.
  • some things we learned:
    • apply the clips so that they clamp down on the flat part of the fold
    • have ample length of tubing folded over for the clips
    • going up to 3 folds for the tubing is ok. The fold will still be held by the clips.

• started a new dialysis, using the Snakeskin dialysis tubing and dialysis clips.
  • we cut 15 mm of tubing for 10 mL of silk solution. This was waaaaay too big. The dialysis clips allow us to be a bit more conservative on how much tubing we use per mL solution.
  • start time: 5:15 pm
  • 1st change: 6:25 pm
  • 2nd change: 1:00 pm, May 13
  • 3rd change: 7:00 pm, May 13
  • 4th change: 2:00 pm, May 14
    • Note: no leakage observed. Good sign so far.

• centrifuged the previously dialyzed silk
  • note to self: just use a more powerful centrifuge. It isn't worth it to split up the sample into microtubes to spin in our table top centrifuge.
  • ended up with 25 mL of silk
  • pipetted out 500 uL to dry to see our silk concentration
    • I am expecting a very low concentration, due to the way that our dialysis was leaking.