|Photo by Fir0002/flagstaffotos (GFDL license)|
I’ve never worked on spider silk myself, but my work on synthetic polymers and biological physics took me to conferences where spider silk work was presented and it always struck me as a very interesting. Spider silk has a rather impressive set of material properties, yet it is produced rapidly at the back end of a spider under everyday conditions. This is a pretty electron micrograph of spider spinnarets from where the silk comes (warning: page includes creepy crawlies).
I introduced molecules, and proteins back in this post. Proteins are the key molecules used to make organisms, an organism’s DNA are the instructions to make a set of proteins. Spider silk is made from protein. A spider is able to produce a whole range of silks with different physical properties: dragline silk is used to make the outer-rim and spokes of a web and is strong and tough; capture-spiral silk is sticky, stretchy and tough; tubiliform silk is used for egg cases and is the stiffest; aciniform silk used for wrapping prey is the toughest; minor-ampullate silk used to make temporary scaffolding for building a web (it’s not as strong but very stretchy). From a technical point of view “strong” refers to how hard it is to stretch something, and “tough” refers to how hard it is to break something. Spider silk is similar to silkworm silk but it is stronger and more extensible.
The closest synthetic material to spider silk in terms of it’s strength per weight is Kevlar. Kevlar is processed using hot sulphuric acid under high pressure which as you might imagine is not very nice. Spider silk, on the other hand is made at room temperature and pressure from an aqueous solution of benign materials. Not only this, a spider can eat the silk it’s already made and use it to make more silk. As scientists, this makes us more than a little bit jealous.
Not only is spider silk interesting of itself, but from a material scientist point of view, it really isn’t fun to make and use new polymers (you need to build expensive plant to make them, you need to work out your ingredient supply chain, you need to check for safety and environmental problems). If, on the other hand, you can get the properties you want from one of your pre-existing polymers by changing the microstructure then life is much easier. Spider silk may provide hints as to how this might be done.
Scientists have done research on the effect of different drugs on web spinning, filmmakers have made some fun of this experiment* (warning: contains spiders). Other interesting biomaterials include, mollusc adhesive and slug slime and I’ve already written about why butterflies are blue.
Update: Curtesy of @happymouffetard, the evolutionary origin of spider-silk spinnarets appears to be hair follicles, according to this article.
*Thanks to Stephen Curry for pointing me to the “spiders on drugs” video.