Finishing Off the Spider’s Web

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Figure 1. Representation of silk devices to repair bones

Hello, once again! Where did we leave off last time? Oh, right. We talked about the applications of spider silk and spider venom in real life! Where could we really go from this point, you may ask. Well, since we didn’t want to cut off this great trend of information relating to spiders so abruptly, we figured we would end this series with a closing blog post with some cool new information that you have not heard before, and some interesting links for those even more involved in the learning experience.

First off, we would like to detail some information that we received from an expert in this field! David Kaplan, a Professor and Chair in the Department of Biomedical Engineering at Tufts University, gave us a lot of information about spider silk specifically. He did research on spider silkalong with other scientists, and they found out that spider silk could be used to replace damaged tissue, like discussed in our previous blog post. Let’s get down to some of the information that he sent us in this experiment (“The use of silk-based devices for fracture fixation”).

David Kaplan and his colleagues gave a detailed description of the use of spider silk for health and medicine. “The silk-based devices compare favorably with current poly-lactic-co-glycolic acid fixation systems, however, silk-based devices offer numerous advantages including ease of implantation, conformal fit to the repair site, sterilization by autoclaving and minimal inflammatory response.” Woah. That is a lot of information to take in, so let’s break it down. No pun intended (breaking bones joke).

Figure 1 (top right) shows some uses for silk to repair damaged bones, through the use of binding to the areas that need attention, and fitting to that mold. Like David Kaplan and the other scientists said in their introduction to the experiments, silk-based devices are great because they have a “conformal fit to the repair site.” This is interesting because it opens up a wide range of opportunities with spiders. To think that all of this silk that spiders produce could be used to actually aid people with their recovery processes is truly a miracle in science and chemistry. Wait, there’s that word again, chemistry. Don’t think we forgot about sticking to the chemistry behind this!

Though we’re going to be repeating most of the ideas that we have already mentioned before here, we want to solidify the ideas of why spider silk has these properties of strength and possibility to fit into a bone structure. Spider silk contains the great property of having many polar molecules within it, along with strong covalent bonds between the chains of amino acids. All of these terms should be coming together now, since they have been mentioned in all of the other blog posts. These intermolecular and intramolecular forces all combine with the helical curvature of spider silk to form this extremely strong material. This ability to conform to the space that the spider silk is in also has a chemistry background to it. Spider silk actually has a crystalline, yet amorphous structure. The proteins found in spider silk have both crystalline and amorphous regions, and these amorphous regions are what gives spider elasticity and the ability to conform to space. Several people have went as far as to classify spider silk as a very viscous liquid, but this amorphous portion of spider silk can not be confused as being a liquid. It’s almost like the spider silk is similar to glass, in the way that glass had long been thought of as a liquid, but just takes a very long time to flow.

Figure 2. Demonstrates molecules in amorphous solids vs crystalline

Figure 3. A tropical wandering spider biting on its prey

Wait what? Okay, maybe we’re getting a little carried away here, but it’s true! Many chemists regard glass as a very viscous liquid because the molecules within are still flowing and many would notice that glass in church buildings, being there for a long time, has a thickness at the bottom because many of the molecules have sunken down to that level! However, this myth was altered quite recently when glass was classified officially as an amorphous solid, which are noncrystalline solids which lack a definite lattice pattern (note: a lattice pattern deals with the actual arrangement of the molecules in a substance at a molecular level). Moral of the story: do not confuse amorphousness as being a liquid.

Anyway, let’s get back on track here. Yes, spider silk has this sort of ability to mold to materials, and its due to this idea that components of it that resemble liquids. In fact, most of David Kaplan’s article details the viscosity, or the state of being thick or a semifluid, of silk and silk solutions. Now, we think that’s enough about spider silk, we’ve pretty much told everything that’s new and interesting about it without freaking you guys out with too much chemistry! It’s probably best to talk about spider venom for a short period of time now just to close off all of this discussion.

Many people might think that spider fangs are just teeth that are no more complex than human teeth. However, spider fangs are actually complex systems in order to optimize the process of injecting venom into the victim. Spider fangs are actually composed of extremely fine layers of chitin fibres. Chitin fibres are actually the same materials used in shells of arthropods, such as arachnids, insects, and crustaceans. Although flies, grasshoppers, and other insects that spiders prey on are shielded by chitin, this same material can be used to paralyze or even kill them by spider fangs.

Figure 3 (top right) actually shows a tropical wandering spider biting an insect shielded by chitin with its chitin layered fangs. How ironic! In fact, these layers of chitin fibres are actually crucial influences of the mechanical properties of spider fangs.

Figure 4. Metal ions found in spider fangs

So you may be wondering how these layers of chitin fibre add functionality to spider fangs, so we will delve right into that. The layers of chitin fibre are actually parallel to the surface of the fang because the parallelism offers a lot of mechanical resistance, causing the fang to be more stiff and more forceful when biting its victim. The chitin fibres are actually what allows the spiders to bite into its victims without breaking its fangs and giving it enough time to inject its venom into the prey to paralyze it. There are also other components to the stiffness of spider fangs. Scientists have actually discovered metal ions of calcium and zinc (figure 4) in the protein matrix of the spider fang. These metal ions are found most concentrated on the tip of the fang, making the tip stiff and sharper. The metals also serve another useful purpose of stabilizing the protein matrix of the fang, and this stable protein matrix effectively sense the stress that arises during the penetration of the victim’s shell. Hm, so that’s why venomous spiders manage to keep a healthy pair of fangs for a long time!

Well, it looks like this wraps up our series on spider silk and venom. All of you have learned about polarity, intermolecular forces, intramolecular forces, covalent bonds, amino acid chains, basic nomenclature, viscosity, solubility, and even some organic chemistryWe hope you guys haven’t gotten lost in the midst of all of this learning. A great thing about knowing the details of spider silk and venom is that it seems like an up-and-coming idea in science to use this spider silk for health and medicine, as aforementioned. Who knows, these blogs may have even sparked an interest in spiders for you! At any rate, now all of you reading these blogs should definitely be able to impress your friends at a party with your knowledge of the inner workings of a spider’s web. This is of course before they find the information too tedious…er, overwhelming with knowledge!  Thanks for following this series on the chemistry of spiders.

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