Spinneret Day 2

So I finished a primary design for the spinneret yesterday evening and tried to print it, but the printer I have access to couldn't print all that well-it kept coming off the platform because the supports weren't strong enough.

Today I worked on a new design that would be more printer-friendly.

The small cylinder to the left was the first edition. It was about a centimeter in diameter, but couldn't print well. The new one I did today is to the right of it.

This has a wider base and is a bit larger, so hopefully the printer will be able to handle it.







For scale, the top cylindrical part is about 2cm in diameter. (I also fixed the aperture, it's now about 30 μm in diameter.)











I did something a little different with the internal structure...

This is more like what I had envisioned for the spinneret. The fluid (dope) comes from the right through a cone that compresses it until it reaches the tube which will do most of the work. Keep in mind, that tube is about 30 millionths a meter in diameter. After passing through the tube, the dope should polymerize and be silk as it exits the spinneret to the left. 

I found that such a small structure doesn't even register on the path code for the printer. My final product should be an assembly of the parts I made. As mentioned before, it will not be functional or even tested. I will also include 3D  (STL) files of each part in the project, with images such as the one above to illustrate my intentional design.

In the next few days (since we won't be at school friday!) I should work on integrating a method for creating a pH/ion gradient within the spinneret. (I have some ideas.) Hmmm...

- Noah

Beginning the Design Process

I was out last thursday because I was getting my wisdom teeth out (all 4). So please don't murder my grade for missing the thursday blog


Anyways, today I worked on the 3d design of what will be a prototype for a "biomimetic silk spinner." I used a 3d designing app to create a basic form of what the "spinneret" end would look like.

I had to spend a lot of today learning how to use the program, and this is only the beginning. I still need to modify the interior and shape.  Here's what I managed to get done today:

You can see in the top screenshot the entire thing. It's about 4cm in diameter. The aperture of the spinneret is however, much smaller. In the second image, you can see a tiny blue dot that is actually a tube that runs the length of the cylinder. It's about 60X10⁻⁶ m in diameter - twice as large as I need it to be. (I just realized I made the radius 30μm instead of the diameter. Crap) 

I'll be working on this every so often so that I can have a printed prototype to present in May. 

What I need to make sure is that I can construct each piece in a way that I can assemble them. This is the fun part of my project!

- Noah

Synthesis

Today, I focused on the physical process of silk synthesis in a laboratory.

The process used in SLU's biomimetic spinning process is as follows:

"Highly concentrated NT2RepCT spinning dope in a syringe is pumped through a pulled-glass capillary with a tip size of 10-30 μm, with the tip submerged into a low-pH aqueous collection bath. Fibers can be taken up from the collection bath and rolled up onto frames."

This method yields fibers 40 μm in diameter (wet; 30 μm capillary). SLU has reported that it has been able to produce strands up to a km in length.

The dope used by SLU (NT2RepCT) is of course a chemical I won't be able to replicate- it is a chimeric protein created by genetically modifying e coli bacteria. However, like in real spiders, they used the dope in a highly concentrated solution, with the concentration interval being 100-500 mg/ml. The low-pH solution that the dope is pumped into should have a pH from 5.5 to 3. That interval supposedly produced the strongest, continuous fibers. pH's lower than 2.5 yielded no fibers, and any pH higher than 6 yielded discontinuous fibers. SLU also varied the diameter of their syringe (which was a custom, pulled-glass capillary), from 10 μm in diameter to 30 μm.

The silk fibers produced in this process are extraordinary, but still not as impressive as nature. "The mechanical characteristics of the fibers were highly reproducible, although the toughness and ultimate tensile strength were lower than native silk. One possible way to increase the toughness could be to spin NT2RepCT fibers with diameters closer to that of native dragline silk, as this apparently has an impact on the mechanical properties of silk fibers."

The SLU report also encouraged that their method can be further developed. It said some examples could be a pH gradient, and an ion composition gradient. This would make their current set-up more like an actual spider, and may result in stronger fibers. I aim to implement such developments in a biomimetic spinning device, along with other things that I may encounter in the future.

The ultimate goal of refining this method is to make artificial spider silk fibers that perform at or above the level of natural spider silk in terms of mechanical properties. And with that, have the process be economically feasible enough that it can be used in an industrial level for mass production of synthetic silk to be used in whatever product/industry necessary.

- Noah

Last Wednesday (Junior SAT Day)

I missed last Wednesday, not because I didn't want to write (I had a draft in progress), but because I simply forgot.

I've been out of town this entire spring break, so that's why I'm just now rectifying my mistake.

Anyways, here's what I did:

Because silk has low birefrigence, I may not be able to apply it to as much as I thought I could. I suppose there are still uses with optical materials with low birefrigence, I'll just have to keep looking.

My study on the structure of spider silk should only be a small portion of my final paper, but it'll be an important component nonwithstanding. It'll give me a better understanding of how the silk functions structurally, and how those unique structural properties could be applied in developing new materials, whether they are made to duplicate spider silk or not.

My main focus in my paper will be the applications of spider silk. I figure that here forward, as I begin writing, I should concentrate my research on all potential or possible applications. My looking in to birefrigence, for example, shows that even spider silk has its limits, and it's important that I thoroughly investigate every potential before making any conclusions about it being even feasible.

Now that I've wrapped up structure and some resulting properties, I'll look at deconstructing SLU's process step-by-step, so that I can first write about it, but then also apply that to the designing of my "biomimetic silk spinner." I may not even have a physical model finished/prepared, but it'll be an interesting synthesis of what I've learned.

I start my paper...

Today, I really wasn't able to do much research, we just reviewed the guidelines for our final thesis paper and presentation.

I began my final paper. I formatted the title page, made a table of contents, and have all of the topics/subjects I will cover planned out. Hopefully, each week I can finish (mostly) each section, so that I'll be finished in plenty of time to get it reviewed, corrected, etc. Plus, it'll be nice to be done with.

I should also probably start looking for judges.

- Noah

Today, I looked at the primary and secondary structure of spider silk.

Side note, apparently spider silk has low birefrigence. Now this actually is okay, because you don't want the index of refraction to change much if used in fiber optics. And, because it's already been used/planned to be used in molecule detection, it's been proven to be applicable there.

Okay, now, structure. Primary structure is fairly simple and I discussed it some in my presentation. Primary structure of spider silk is mainly (90%) repetitive amino acid sequences. Most of these amino acids are glycine and alanine. This chart I made shows the molar %. --->

"Structural analysis revealed that oligopeptides with the sequence (GA)n/(A)n tend to form α-helices in solution and β-sheet structures in assembled fibers." This allows for the elasticity of spider silk. ( A β-sheet looks like a piece of paper that's been creased along the length so it looks like... nevermind, here's a picture: --->) So when stress is applied, the protein will stretch ("straighten out"...?) instead of breaking. The repetitive protein sequences is also crucial to its tensile strength. 

However, at the terminals (ends) of the protein, there are nonrepetitive proteins. These are crucial for protein assembly because they form intermolecular bonds that stabilize dimers (2+ monomers), etc. during the "assembly." 

At a more macroscopic level, spider silk looks more like a rope that's coated in a protective "skin."  In this diagram, you can see the macroscopic view with a diameter of 1-50𝜇m (1𝜇m = 1x10⁻⁶m). Then there are subunits (diameter of 2nm and average length of 7nm. 1nm = 1x10⁻⁹ m) which are comprised of the repetitive amino acid sequences which form the β-sheet structures (in blue). 

We still don't fully understand the entire structure and functions within the spider silk. It's probably one of the most complicated structures we know of. But it's also fascinating, so I will do all that I can to learn as much as I can about the structure, at least enough to present my thesis, which I think I've surpassed already. (At least I'll have plenty to write about.)

So what I know right now isn't even scratching the surface of the current understanding, and there's no way I will know as much as we know, that would take years. Really, as long as I have a fundamental understanding of how the structure works, how it changes during fiber formation, and how the structure gives silk its properties, I'll be set. Next week, I'll focus on tertiary and quarternary structure, and begin looking at making a step by step journey through silk synthesis in nature, so that I can compare it to laboratory methods later. 

- Noah