Though our understanding of the silk-making process is not yet complete, scientists do know that the key to making silk lies in the animal’s careful managing of the water content in its silk glands.
Silk gets its strength from its proteins. Parts of the proteins are hydrophilic, or water-loving; and parts are hydrophobic, or water-fearing. For some time it was a mystery how silkworms managed to convert these proteins into silk threads without the proteins crystallizing before the animal is ready to spin them. Premature crystallization would clog up their silk glands, which would likely prove fatal to the little creatures.
The answer lies in the silkworm’s slowly decreasing the water content in its silk glands and in the proteins’ ability to retain water, keeping the solution soluble up until it is spun. As the water decreases, the water-loving parts of the proteins fold together in chains, forcing the water-fearing parts together.
As the water level continues to drop, the folded chains of silk push together more and more to form larger and larger gel-like structures. All the while the water-loving parts retain enough water so that the solution does not crystallize prematurely, before there is enough of the material to begin spinning.
spin ： (蚕)吐丝;过去式spun或 span 过去分词spun 现在分词spinning