Link to the video lecture
Following the Nature protocol, we started the experiment by adding 4.2g of sodium carbonate (this quantity is for 5g of cocoon silk) to 2 liters of deionized water (the protocol indicates ultrapure water -often referred as milli-q water-), mixing it gently and heating the mix until boiling point.
We then weighted about 5g of coccoon silk, cut them in pieces with stainless steel scissors (the protocol indicates titatium scissors) and put the silk inside the boiling water for 25 minutes. The more time you leave it the more the fibers will break apart, but because for a later step we had a dialisis membrane with bigger holes than the specified in the protocol, we though to leave the silk for less time.
For washing out the salt we submerged the silk in one liter of deionized water for 1 hour. Then we changed the water and repeated for 4 hours.
Finally we squeezed the excess of water, pressed against drying paper to absorb water and let the silk to dry overnight under the chemical hood (without fan or extraction).
Here it comes the nasty part. We got 100g of Lithium Bromide (LiBr) at Quimics Dalmau (63 EUR, they don't sell it in smaller quantities). First Warning: Lithium salts are pychoactive (a chemical substance that changes brain function and results in alterations in perception, mood, or consciousness). The following steps involving LiBr MUST be executed under a chemical hood. We didn't, but don't tell anyone.
First we have to create a 9.3 M solution of LiBr. In our case, for 3.35g of silk we dissolved 16.11g LiBr. Second Warning: This reaction is VERY exotermic, do it inside a recipient filled with crushed ice. Also stir with a steel bar because the salt does not dissolve very well forming 'stones' -I think the correct word is precipitation-.
Then we tightly pressed the silk fibers inside a glass recipient and added 13 ml of LiBr solution and put in a 60ºC for 6 hours.
The result you should obtain is an amber viscous liquid, no silk fibers at all and probably some black spots (from the insect).
We got a piece of dialisis membrane from Cellu Sep, the only problem is the membrane should be 3.5 kDa and ours is 12 kDa. Nuria said that a pork intestine had porus of about 3.5 kDa but we did not get a piece of intestine to try.
We made a knot at the bottom of the membrane, but we had problems trying to open the other end because we didn't know at that time, but you must hydrate the membrane (submerge into water) before trying to open it. Finally we hidrated the membrane, introduced the amber liquid and submerged into water to find that it was leaking quite a lot. We broke it while forcing it to open. In the end we could fix the leaking but only 3 ml of silk suspension were obtained.
We did the experiment with the CD and we found a very strong iridiscent surface.
Then we wanted to obtain a negative control so we used the part of the CD that does not has the iridiscent surface. But the problem was that the silk was still iridiscent. Not that strong as before but still noticeable. Then we found that if you bend the plastic, it also was a bit iridiscent, and because the sild becomes curvy when its removed from the plastic it also acquired some of these properties.
So we repeated the experiment once more usinc a petri plate, see below!
We couldn't manage to adapt the jeringe to the 3D printer but the we though about the 3Doodler project and we thought we could do the bio-doodler. So we manually did it with a micropippet, we generated the words FABLAB SB for Fab Lab Sitges Barcelona. Here is the result. The problem you have when you try to remove them is that they are not flat anymore. We could also see that the silk in the petri board was not iridiscent.
On Wednesdays we always have a review session of last week's assignment. Here is the link to this week assignments review.