THE PUZZLE OF A LIQUID ROPE

1. THE PUZZLEOF A LIQUID ROPE

2. the transformation from a liquid to a solid phase is never trivial; imagine the cooling of a lava stream or the delicate crystal lattice of frozen water, where each crystal is different; solidification processes can be useful or even lethal (e.g. blood coagulation in-or outside veins); however, if done by spiders , the solidification process is simply amazing;

3. most people ignore that spiders, often not greater than a pea, produce up to 2000 feet of thread continuously; where the hell do they store it ???

4. The question involves a solidification process; in general, solidification is due : -- to temperature drop, as in water freezing; -- to solvent evaporation, like sodium chloride in salt works ; nevertheless, none of these models is fit to explain the instantaneous solidification of the thread made up by spiders ; the answer is that spider’s long, silky string comes from the solidification of a liquid;

5. But : --- spiders live at room temperature, thereby excluding all freezing processes; --- the only solvent found inside spiders is water, but water evaporates slowly at room temperature, while spider’s thread solidifies immediately ( it holds the mass of the insect as soon as produced ); --- besides, if the thread was soluble in water, then it would be dissolved by rain or dew; ---

6. so, what remains ? The last chance is a kind of polymerisation process, as for nylon ; unfortunately nylon melts over 250 °C , that is much higher than every survival limit; moreover, polymerisation processes are slow; anyway, a quick look at polymers may help us understand spiders’ work :

7. polymers are buildings with molecular weights of thousand hundreds ; atoms that make up the backbone of a polymer chain come in a regular order; this pattern is reproduced all along the length of the chain. the little recurring structures are called “ monomers “ ;

10. most of polymers are linear, that is joined in a long line to form a huge and flexible chain, often bent in a tangled mess; when molten, these chains will act like elastic cooking “spaghetti” , while cooled in the solid state, they look more like a ball of string; all molecules, the small ones as well as the polymer chains, interact sticking together through forces placed on the backbone;

11. when tangled in a ball, polymers set out a little number of binding forces; when stretched, many more of them appear and work:

12. the yield of spiders has a variable composition based on the amino – acids sequence : …… ala-ala-gly-ala-ala-gly- ala-ala …..

13. finally the enigma is puzzled out; the solution is unbelievably simple, as it often happens in nature: spiders excrete a sticky fluid containing long protein molecules tangled as a thread ball ; each chain, when stressed, shows many chemical structures fit to stick molecules together , the same way polymers do ;

14. this way, stretched molecules can join other ones to form a solid thread; this is the reason why spiders excrete only in conditions of traction; in other words, the protein fluid is drawn out only in presence of an external force, such as wind or gravity ;

15. although hard to agree to, spider’s filament is one of the strongest materials in the world (more than steel) and highly elastic at the same time : tensile strength can withstand a weight of up to 300.000 pounds per square inch ( Nexia Biotechnologies - Montreal ) ;

16. What about copying spider’s silk ??? --- bridge suspension cables could be modelled on its molecular structure; --- car bumpers and bullet-proof vests that absorb impacts as the spider’s web does; --- flexible and resistant material for aircraft ......

17. unfortunately, spider farms are not possible because spiders tend to eat one another; therefore, to get this surprising material (five times stronger than steel and more elastic than kevlar ), only industrial processes can be used;

18. THIS PROVES AGAIN THAT CHEMISTS ARE ABSOLUTELY NECESSARY; spider’s secret being now unveiled, let’s have a little gossip :

19. ..... Arachne, a pretty maid of ancient Greece woved tapestries of such a beauty that goddess Athena, who fancied herself superior to any girl , became furious and turned Arachne into a spider ; now she is living among gods, but is convicted to spin for eternity .......

20. ..... natives from the Pacific, Asia and Australia used spider silk to weave water shedding rain gear, make fishing lines and construct nets; ..... Gengis khan and his soldiers wore a leather garment interwoven with spider silk, to protect them from enemy arrows;

21. o.k., that’s all; by the way, athankful acknowledgement to all members of the team :